Part A: Stability Constants of Metal Complexes CRITICAL SURVEY …publications.iupac.org/pac-2007/1983/pdf/5509x1477.pdf · stability constants of indium complexes by ion exchange

Pure & Appi. Chem., Vol.55, No.9, pp.1477—1528, 1983. 0033—4545/83 $3.00+0.00Printed in Great Britain. Pergamon Press Ltd.

©1983 IUPAC

INTERNATIONAL UNION OF PUREAND APPLIED CHEMISTRY

ANALYTICAL CHEMISTRY DIVISION

COMMISSION ON EQUILIBRIUM DATA*

Critical Evaluation of Equilibrium Constants in SolutionPart A: Stability Constants of Metal Complexes

CRITICAL SURVEY OF STABILITYCONSTANTS OF COMPLEXES OF

INDIUM

Prepared for publication byD. G. TUCK

University of Windsor, Ontario, Canada

*Membershjp of the Commission for 1981—83 is as follows:

Chairman: S. AHRLAND (Sweden); Secretary: H. OHTAKI (Japan); Titular Members:E. D. GOLDBERG (USA); I. GRENTHE (Sweden); L. D. PETTIT (UK); P. VALENTA(FRG); Associate Members: G. ANDEREGG (Switzerland); A. C. M. BOURG (France);D. S. GAMBLE (Canada); E. HOGFELDT (Sweden); A. S. KERTES (Israel); W. A. E.McBRYDE (Canada); I. NAGYPAL (Hungary); G. H. NANCOLLAS (USA); D. D.PERRIN (Australia); J. STARY (Czechoslovakia); 0. YAMAUCHI (Japan); NationalRepresentatives: A. F. M. BARTON (Australia); M. T. BECK (Hungary); A. BYLICKI(Poland); C. LUCA (Romania); I. N. MAROV (USSR); A. E. MARTELL (USA).

CRITICAL SURVEY OF STABILITY CONSTANTS OF COMPLEXES OF INDIUM

I, Introduction VI. Indium(I) complexesII. Neutral cationic species VII. Carboxylato complexesIII. Hydrolysis of Ifl3(aq) and related VIII. Monobasic bidentate chelating

topics agentsIV. Halide and pseudohalide complexes IX. Miscellaneous organic ligandsV. Oxyanion complexes References

I. INTRODUCTION

In the introduction to this series of IUPAC review articles, Beck (75B) has

identified some of the problems involved in the measurement and critical

evaluation of stability constants. Many of the difficulties which Beck

discusses clearly apply in the case of complexes of indium, and in partic-

ular, the failure of 'constants' which nominally describe a given system to

agree within reasonable limits is readily apparent on examination of the

standard compilations of such data (64S, 7lSa). A critical review of this

information, and that which has been published since the appearance of these

standard references, is therefore appropriate.

It may well be that the easy availability of a useful radioactive tracer

[ll4m1 t½ 50d, from (n, i) on indium meta]j provoked many of the studies of

stability constants of indium complexes by ion exchange and solvent extrac-

tion methods. Equally, the use of the metal as a working electrode has led

to a number of electrochemical investigations of complex formation. Whatever

the reasons, a large number of stability constants of indium complexes h.s been

reported, especially in the period 1950-1975, but unfortunately these

results did not lead to any clear understanding of the solution chemistry of

the element, even in such apparently uncomplicated systems as In/Cl (see

(77J)). It therefore seems reasonable to discuss the reported stability

constants in terms of the structural information which is available on those

species which exist, or have been postulated to exist, in aqueous solution,

and to examine the measure of agreement between these differing approaches to

the chemistry of the element. A general comment which can be made at the

outset is that despite the implicit chemical information contained in a given

stability constant, few authors have discussed their results in the context

of the overall chemistry of the element, and it is equally true that stabil-

ity constant measurements have contributed little to our knowledge of the

coordination chemistry of indium in solution.

The material in this review is organised into a series of discussions by

ligand, or groups of ligands, and individual or collective results are eval-

uated in terms of the criteria laid down by the I.U.P.A.C. Commission on

Equilibrium Data. Wherever possible, a brief structural introduction serves

to establish a point of departure. Thus a survey of studies of cationic3+ .In

(aq)leads to a discussion of the crucial matter of hydrolysis:

inorganic ligands (halide, pseudohalide, oxyanion) are then considered: and1478

Stability constants of complexes of indium 1479

carboxylic acids, rnonobasic chelating agents, and various polydentate organic

ligands, complete the review. The information is essentially restricted to

complexes of indium(III), since only sparse information is available on the

aqueous solution chemistry of indium(I) and (II) , despite the increased

interest in these oxidation states in recent years (75C)

The general chemistry of indium is dealt with in various standard texts, and

a number of reviews have appeared in recent years (73W, 75C, 75P, 75T). The

electrochemistry of the element has been discussed by Losev and Molodov (76L).

II. NEUTRAL CATIONIC SPECIES

II. 1. The 1n3+ cation(aq)

There is now an overwhelming accumulation of evidence that the indium species

in non-complexing aqueous solutions (e.g. aqueous perchloric acid) is3+ .

[In(H20)6] . Firstly, there is extensive preparative evidence on the exis-

tence of InL63+ cations, where L is some monodentate oxygen donor ligand

(64C, 75C). Secondly, n.m.r. studies (both and 1151n) of indium(III).

perchlorate in aqueous solution (66C, 68Fa) have identified the predominant

species as {In(H20)6]3+, and this conclusion has been confirmed independently

by dilatometric measurements of ionic volumes (74Ca) , and more recently byX-ray diffraction methods (77M). Rapid exchange between bound water and the

bulk phase has also been demonstrated (68Gb). Finally, with acetone/water

(7lF), and with trimethyl phosphate (fliP), TMP/water, TMP/acetone, and TMP/

water/acetone (72C), one finds [In(H20)613+, {In(TMP)6]3, or mixed hexa-

coordinate cationic species. A similar conclusion has been reported for

solutions in N,N'-dimethylformamide and DMF/H20, and confirmed preparatively

(65Ga)

The formation of complexes of indium(III). under conditions in which

hydrolysis has been completely suppressed (see below) must therefore be via

equilibria of the general form

[In(H 0) + nLx [In(H 0) L (3-nx)+ + nH 0 (1)2 6 — — 2 6—nn —2implying that the substituted products also involve six-coordinate indium.

While accepting that this statement is indeed valid for the great majority of

systems, it must also be emphasised that four- and five-coordination is well

established in the chemistry of indium (III), especially with ligands which

are 'soft' and/or stereochemically demanding (75C), so that there may well be

ligands for which specific values of n in eq. (1) will involve changes in

coordination number, in particular by the elimination of water molecules. We

return to this matter below in the context of indium (111)-halide complexes.

II. 2. Cationic complexes with ligands

The cation [In(NH3)6J3 which has been identified in liquid ammonia solution

(76G), is clearly analogous to [In(H2O)3+, and a large number of related

cationic complexes is known (75C). Few stability constant measurements have

been reported. McBryde (78M) has critically reviewed the results for the

pAAC5S: 9-C

1480 COMMISSION ON EQUILIBRIUM DATA

2,2'-bipyridine (bipy) and 1,10-phenanthroline complexes of a large number of

elements. For indium, the values given are:

1, 10-phenanthroline

log K1 log K2 log K3 Ref.

1M NaNO3, 25°C 5.51 4.59 4.40 (7lKa)

1M K2S04 5.70 4.34 3.96 (72K)

2 ,2-bipyridine1M

NaNO3 3.45 4.61 — (7lKa)

1M K2S04 4.75 3.25 (72K)

For the bipy experiments, agreement between the two series of measurements

is lacking, and in one case K2 > K1. McBryde also quotes results for

In(III)/bipy in 50% aqueous ethanol (25°C,1.OM electrolyte), for which

log K1 = 4.18. All of these results are rated as doubtful. A similar rating

is given by the present author to values for 2,3-dihydroxypyridine, 2-amino-

and 2-thiol-3-hydroxy-pyridine, for which l and 2 have been determined

polarographically (77S). A related polarographic study (78T) of thiourea

complexation yielded a tentative value of log K1 = 1.97+ 0.07

(I = O.5(NaC1O4), T = 25°C), said to be in agreement with unpublished

measurements (75Kc) based on distribution experiments. These few results

emphasise the need for reliable values for simple cationic indium (III)

complexes, and for some thermochemical information.

III. HYDROLYSIS OF In3+ AND RELATED TOPICS(aq)

III. 1. Introduction

The pH range in which the solution chemistry of indium (III) can be studied

is defined in practice by the onset of hydrolysis, since it is common experi-

ence that increasing alkalinity results in the formation of hydroxy complexes.

Precipitation eventually occurs, unless the formation of soluble complexes

with other ligands predominates, and here one immediately encounters an

important experimental fact established by early work (41Mb), namely that

precipitation takes place well before the [OH] : [1n3+] ratio reaches 3.0. It

has also been reported that the kinetics of the redissolution of metastable

precipitates and polynuclear complexes are complex (67P). In general then it

is crucial in quantitative studies of indium (III) solution chemistry to

ensure that all polymeric species have been completely destroyed before pro-

ceeding to other work.

The present section attempts to establish reliable thermodynamic results for3+ -

the range of possible In /OH species, recognising that a proper accounting

of the formation of such complexes is a sine qua non in the measurement of

other stability constants, as has been demonstrated in the case of

In3/ha1ide complexes (67L). The whole field of cation hydrolysis of indium

(and other elements) has been extensively reviewed by Baes and Mesmer (76B),

who have recalculated certain of the literature results.


III. 2. Hydrolysis constants for 1n3+(aq)

The hydrolysis of the 1n3+(aq) ion can be represented by one of the related

equations:

In3 + OH In(QH)2 (2a)(aq)

In3 + H 0 —s In(OH)2 + H (2b)(aq) 2

[In(H2O)6J3 + H20 —s [In(H2O)5OH]2 + H3O (2c)

where all species are aquated. Electrode kinetics have demonstrated that

dissociation, not substitution, is involved in the hydrolysis (67L), so that

we shall discuss the processes in terms of equations

{In(OH)3'] [Hsuch as (2b) with *13 = . In view of the

l,n 3+— [In I

relationship l n l nwa, the assumed value of Kw5 noted in Table 1.

The earliest measurements of*

1refer to uncertain standard states

(36H, 4lMa, 42M), and take no account of competing equilibria (but see (52H)).

The careful emf work of Biedermann (56B, 56Ba) gave a value subsequently

confirmed in the same laboratory by solvent extraction studies (72Fa),

despite detailed differences in the relevant aqueous phases. The series of

measurements by Kul'ba and co-workers (74Kb, 75Ka, 75Kb) refer to 3M LiC1O4

solution, and therefore do not provide confirmation of the type necessary in

recommending a value for K11. The tentative values are:

—log K11 (3M NaC1O4) = 4.42 ± 0.05

-log 1 (3M LiC1O4)= 4.25 ± 0.04

Later work employing electrochemical cells similar to those used by Kul'ba et

al. gave results for log K1 1 over the range 0 - l.OM LiC1O4 in good agree-ment with the earlier results, and the values (81Y; Table 1) are also

tentatively accepted. The hydroxide stability constants log K1 1 corre-

sponding to the above values are 9.80 and 9.97 (log Kw = -14.22).

Of the other results recorded in Table 1, the value derived from Biedermann's

results by an unspecified least squares treatment (76B) is in good agreement

with the tentative values above, but the results of the extraction studies of

Aziz and Lyle (69A) differ by an amount which exceeds the sum of the reported

errors. The results in 65H appear to contain a serious error. It is

unfortunate that the studies of the effect of variation of ionic strength

(69B) agree so poorly with other similar results (e.g. 81Y),not only because

of the intrinsic interest of such work, but also because only these papers

and ref. 65H quote values for the constants beyond *K1 l It may be that the

formation of In(OH)n species was not the only set of acid dependent equi-

libria in the experimental solutions used in this work (69B); for example,

deprotonation of the competing alizarin-3-sulphonic acid beyond the assumed

HL anion may also have been significant (cf. section IX).

1482 CONNISSION ON EQUILIBRIUM DATA

The range of values reported for K 2 such as to raise doubts about the

correct identification of the processess being studied. The two sets of

solvent extraction experiments agree closely in this respect, but differ from*

other work, and the agreement for K between NaC1O and LiClO solutions

breaks down completely for K1 2 The two sets of studies with LiC1O4

solution are again in good agreement, but further work is required; at

present, -log K12 2.9 ± 0.1 can be used for 3M LiC1O4, but must be regar-

ded as doubtful (but see ref. 76B). A value of log l 3 = -12.4 has been

derived by Baes and Mesmer (76B) from the low solubilitv of In(OH)3 in nearly

neutral solution (4.8 x lO mol l at pH 7.22). The results in Table 1

suggest that K1 1 K1 2 K1 which therefore implies that log l 3_12lin reasonable agreement with the derived result, but such arguments do not

lead to any reliable numerical value for K1 3 at the present time.

Finally we note that Schlyter (615) has measured tH° and AS0 for the form-

ation of 1n3+/OH complexes in 3M NaC1O4 at 25°C, relying upon Biedermann's

values for K1 1 etc. in interpreting his results. The enthalpy values are of

poor accuracy because of the low concentrations of the species involved:

2+ * —1In(OH) MT°1011 = 20.3 ± 3.8 kJ mol

—lLS l,0l,l = -17 ± 13 J K mol

+ * 1In (OH)2: LH°1 2

= 58 + 38 kJ mol

SOlOl2 = 38 125 J K1 Mol1

The nature of the experimental method renders these results of inherently

doubtful value.

III. 3. Hydrolysis in mixed aqueous — non-aqueous media*

Russian workers have reported some interesting measurements of K1 1

and K1 2 in the systems water/dimethylsuiphoxide (74Kb, 8lY), water!

dimethylformamide (74Kb), water/acetone (75Kb) water/acetonitrile (75Ka) and

water/ 1,4 -dioxane (8lY). With acetone and acetonitrile, hydrolysis

increases with increasing mole fraction of organic solvent, whereas with

dimethylsulphoxide the reverse is observed. These results have been qual-

itatively explained in terms of changing dielectric constant, increasing

proton affinity of the bulk phase, and the formation of fIn(H20)6LJ3+

species. A detailed analysis of the results would be valuable, eseially

since these effects may be important in aqueous systems in terms of ionic

strength changes and the like.

III. 4. The solubility product of In(OH)3

The hydrolysis of Ifl3(aq) leads eventually to the precipitation of In(OH)3

(but see III. 6. below), and the existence of this compound, rather than a

hydrated oxide, has been confirmed (37N). Measurements of the solubility

product of In(OH)3 have been reviewed by Feitknecht and Schindler (63F), who

emphasise the difficulty of establishing reliable values for such constants.


TABLE 1. Hydrolysis constants for the 1n3+(aq) O1•

T * * *(flc) K11 K12 K13 Comments Ref.

23 3.7 No allowance for 36H

In/S042 complexing

25 3.85 Recalcn. allows for In - 4lMa, 42Mcomplexing with Cl Br, I. recalc.log *K is unweighted by 52Haverage (52H).

25 4.42+0.05 3.9+0.2 pH range 1.91 — 3.86 56B, 56BaLower values for K (4.25)recalc. by (76B). Resultslater confirmed (72Fa).

25 4.4+0.1 4.4+0.3 pH range 2.7 — 4.5 56R—(log Kw = —14.22)

25 6.95+0.1 pH range 4.20 — 5.40 61B

20 2.11 2.45 2.68 pH range 2 — 3.5 65H

MediumMethod (concn. N)

pH titration Various concns.of 1n2(S04)3

pH titration Various concns.of mCi , InBror mm3

pH titration, 3.0 MaC1O4In by emf

pH titration, 3.0 MaClO inIn by extraction equil. with

TTA in benzene

emf 3 NaC1

In by extraction I = 1?in equil. withBHPA in C6H6or toluene

by emf, 3.0 MaClO4 25In by extraction in equil. with

DEHP in toluene

In by MaClO4:I = 0 25

spectroscopy 0.10.30.51.0

pH titration

pH titration,In by emf

pH titration

emf

3.0 LiC1O4

3.0 LiC1O4

3.0 LiC1O4

LiC1O4:I

4.63±0.05 4.38+0.05 pH range 3.25 — 4.75 69A(log Kw = —14.22)

3.543.483.403.333.11

4.284.194.013.923.54

5.165.084.964.854.48

pH range 4.6 — 5.6(log K = —14.0)no errr limits quoted.Values at I = 0 byextrapolation by authors

69B

25 4.22+0.04 2.92+0.05 pH range 0.5 — 4.0K not quotedw

74Kb

25 4.22+0.044.260.04

2.92±0.052.84±0.05

—results from [HJ expts.—results from In expts.K not quoted.w

75Ka

25 4.26+0.02 pH range 0.6 — 2.2K not quoted.w

75b

0

0.10.31.0

25252525

3.66+0.064.00+0.044.040.044.l50.04

2.40+0.082.790.052.77+0.052.83±0.05

K not quotedVlues at I = 0 byextrapolation by authors

81Y


The early workers reported values for log K5 at 25°C of -33.2 (380) and

—33.1 (41Mb) based on pH measurements alone. Moeller (41Mb) also demon-

strated that is temperature dependent, but the relevant numerical values

cannot be regarded as reliable, at least in part because no account was taken

of complex formation with the balancing anion (chloride, sulphate). The

importance of establishing that equilibrium has actually been reached was

demonstrated by Aksel'rud and Spivakovskii (59A), who showed that the value

of obtained after 76 days aging is significantly different from that

after only 1 day. Their value for K5 is log K5 = -36.92 ± 0.1 (tentative),

but independent confirmation of this result would be welcome. The value

reported by Kovalenko (6lKa), log K5 = -32.85, obviously suffers from the

fact that only 1 h was allowed for equilibration, and should be rejected.

III. 5. Anionic hydroxo complexes of indium(III)

A small number of papers bear upon the existence in aqueous solution on mono-(n-3) -nuclear complexes of the type [Ifl(OH)ni — (n > 3), which should be struc-

(n-3)- . -7-turally related to InFn — and similar anions. The lack of even qual-

itative agreement is the first point to strike the reviewer. Both Lacroix

(49L) and Deichman (58D) claim that In(OH)3 does not undergo further reaction

with aqueous caustic soda to yield either soluble or insoluble indates,

whereas Thompson and Dacer (63T) reported a measurable solubility in the

range 0.76 - 6.03 M NaOH, and derived constants f or an equilibrium which they

write as

In(OH) +OH — HInO+HO (3)3(c) ç—— 2 3 2

but which could equally well involve [In(OH)4] , [In(OH)4(H20)2] etc., as

the solution species. From their experimental result, log { {H21n0 i/a } =

—3.0 ± 0.5 at 25°C, it has been estimated that log l 4 = -22.07OH

(log Kw = -14.0). Aksel'rud (60A) has concluded from mass-action arguments,

that [In(OH)41 is indeed formed in such solutions, and has used earlierexperimental results (56A, 58A) to derive log = 35.23, orlog 14 -20.8 (log K = -14.0).

Unfortunately even this measure of agreement is called into question by the

work of Ivanov-Emin et al. (601a), who find that the solubility of In(OH)3 in

aqueous NaOH (1-17 M) goes through a sharp maximum at 11.33 M, a concen-

tration higher than that reached in any of the experiments just discussed.

It is further claimed that the solid in equilibrium with these solutions is

In(OH)3 below this maximum, but hydrated Na3[In(OH)61 above it. None of the

papers quoted apparently takes account of the aging of precipitates

(cf. (59A) or of possible peptisation (cf. (41Mb)).

In the circumstances, no value can be recommended for This whole

topic of anionic hydroxo complexes of indium (III) could benefit from

combined thermodynamic, preparative and structural studies.


III. 6. Mixed hydroxo-halogeno compounds

The formation of mixed In/OH/L complexes is always a potential problem in

both quantitative and preparative work. A number of mixed hydroxo/anion

complexes have been identified in the solid state (41Mb, 49L, 60A, 67P, 68Db).

In particular, basic chlorides are said to be formed during the addition of

NaOH to aqueous InCl3 solution, including In(OH)28Cl02 (57D, 59A),

In(OH)15Cl15 and In(OH)175C1175 (59A); log K5 for In(OH)1 5Cl15 =-22.38 at I - 0 (doubtful, since no error limits given).

Some quantitative results are available on the information of In/OH/Cl

solution species. Biedermann, Li and Yu (61B) concluded that in chloride

media, the formula hInOH2+ actually represents mixed In/C1OH species, al-

though the difference in their K1 1 for 3M NaC1 and that for 3M NaC1O4 hardly

seems explicable in such terms, or in changes in the medium. On the evidence

from higher species, [In(OH)Cl] is the more convincing (see (76B)). Fern

(72Fa) gave results (25 C) for

2+ + + *InCl + H,,O —s InCl(OH) + H ; log K = -3.9 + 0.1

or

3+ - + + *In +H2O

+ Cl —s InCl(OH) + H ; log K1 1 1 = -1.3 + 0.1

(tentative), using K11for InCl+ = 2.8 (see. below): 'The agreement between

K, , and K, implies that the dissociation of XIn(OH) —) XInOH is, , ,

independent of the nature of X, within the limits of the data. This is notsurprising, given that K (i.e., AG) for any system involves an important

common term for the formation of H3O+, but nevertheless further results on

this matter would be welcome.

III. 7. Polymeric indium(III)-hydroxo complexes

The detailed nature of the processes which intervene between the formation of

[In(H2O)5OHJ2 and the precipitation of In(OH)3 is largely unestablished.

Eyring and Owen (7OEa) have studied the fast forward reaction in

2InOH2 —s [In2(OH)2]4 (4)

identifying the rate—determining step as the loss of a water molecule from

the coordination shell of one InOH2+ ion. Biedermann (56B, 56Ba) explained

his thermodynamic results in terms of further core-linked species

[In2(OH)2]4, [In3(OH)4]5, [Inn+1(OH)2n] with *log n+l,2n = -0.52 -

4•6a ±°•°4a (doubtful) (but see 76B)). A later result (6lB), log =

-10.1 ± 0.1, is in reasonable agreement with the more generalized formula.

Questions as to the number of polymeric species which exist in significant

concentrations and their relative importance find no satisfactory answer at

present, and a similar comment applies to the matter of mixed polynuclear

complexes. A tentative constant (72Fa) applies to the formation of

[In2 (OH)Cl]4;2+ 3+ 4+ + *

InCl + H 0 + In — In,C1(OH) + H ; log K,, , , = 2.3+0.l,. ,

The existence of such species is strongly supported by the crystal structure

1486 CONNISSION ON EQUILIBRIUM DATA

identification of a gallium hydrolysis product containing the

GaN/ Ga

unit (72D). Any discussion of formation constants for higher species is

clearly not justified given our present knowledge.

III. 8. Sulphide species

The solubility product of In2S3 (I = 1M NaClO4, T = 20°C) is

log K = —77.4 + 2.4

and the formation constants for the complexes In(SH)2+ and [In(SH)2] are

log .1<11 = 10.5 ± 1.3

log K12 = 6.6 + 0.1

(all doubtful) (7OTb). An earlier report (log = -73.24, I — 0, T = 25°C)(62T) has been criticized (7OTb). Further work in this area is required.

IV. HALIDE AND PSEUDOHALIDE COMPLEXES

IV. 1. Structural information

The matter of the species which can exist in aqueous solutions containing

indium(III) and halide anion has provoked such debate that a review of the

species known to be stable in the solid state seems an appropriate starting

point for our discussion. In adopting this approach, one must emphasize that

the existence of a specific complex in the crystalline state is in itself no

proof of the stability of that same species in aqueous solution, given the

very different nature of the energy factors involved in the two phases. On

the other hand, an understanding of those species which can exist is at least

a reasonable basis from which to examine the evidence as to those which are

claimed to do so.

There appear to be no X-ray structural determinations on monosubstituted

cations [In(H20)5X]2+, nor of [In(H20)4X2]+, but complexes related to the

latter, namely [InCl2(bipy)2 (and other bidentate ligands) (48S, 69W, 78C)

and 11n12(dmso)4]+ (70E) have been identified. A large number of InX3L3

complexes have been reported (75C) , and in particular the crystal structure

of InCl3(H20)3 has been elucidated (75W), as has that of InF3(H20)3 (66Ha);

both are six-coordinate monomers. Thus far no difficulties arise, but for

anionic complexes the information is less complete, and in particular the

question of the coordination number at indium remains difficult. Fluoride

complexes are known to include InF63 (70S), in which indium is six-coordin-

ate, and the hydrated salts MInF4.2H2O and MInF5.H20 may well contain aquo-

fluoro anionic complexes. For chloride, six-coordination has been unambig-

uously characterized in the anions [InCl4(H20)2](75Z), [InCl5(H2O)]2 (48K),

and InCl63 (72 Sd, 760, 77C), thus confirming earlier preparative and

spectroscopic studies (64T, 71G). At the same time, anhydrous InCl4

(tetrahedral) and InCl52 (square-based pyramidal) (69Ba) are also known,

both in the solid state (69Ba, 69T) and in non-aqueous solution (6OWa, 68Wa).

With bromide as ligand, only InBr4 and InBr63 have been identified both


spectroscopically (55W, 7lG) and crystallographically (81K, 82K) but neither

InBr52 nor substituted species are known at present. The only anionic iodo-

complex unambiguously identified in either solid state or non-aqueous

solution is mI4 (58W, 70E,. 75C). Mixed halogeno complexes InXnY4 n are

also known (BUD, BUM, 82K).

No information appears to be available on cationic or neutral aquo-pseudo-

halide complexes, although InX3L3 adducts are known for -NCS and -NCO with

organic donors. The anions [In(NCS)5]2 and {In(NCS)6]3 have been prep-ared,

and X-ray crystallography has confirmed that the latter involves six-coordin-

ate indium(III) and N-bonded ligands (75C). The species [In(NCSe)6]3,

[In(NCO)4 and [In(CN)4J have also been reported, but structural infor-

mation on these is lacking. In general, chemical evidence suggest that

pseudohalide systems are qualitatively very similar to the chloride analogues.

The solution equilibria which must be postulated if all species are to be

included are

(1) (2)() (4) (s)[in.(HO)6r

'LX(Hp)3 [Lx4(k1o)2] ==

[L..x5 (H1o)]

11. ()

1L'

1I,SCHEME 1

There can be little doubt as to the reality of equilibria (l)-(3) (77J), but

the relative concentration of the two tetrahalogeno InX4- and [InX4(H2O)2

species in solution appears to depend on the halide involved. The Raman

studies of Hanson and Plane (69H) confirmed the conclusion reached by

Woodward et al. (55W, 6UWa) that neither InCl4 nor InBr4 exist in aqueous

solution, even at high halide concentrations, even though the species

extracted from such solutions into basic organic solvents (55W, 6UWa, 73Hb),

and sorbed on anion exchange resins (7UDb) is InX4. In contrast, mI4 has

been identified spectroscopically in aqueous hydriodic acid (58W). In all

cases, the addition of hydrophilic solvents (e.g., methanol) to these aqueous

solutions increases the concentration of InX4, in the order I > Br > Cl (69H,

7ODa). The recent detailed Raman studies of Irish et al. (77J) confirm that

aquo-complexes up to [InCl4(H20)4] exist in aqueous solution (chloride only).

In summary, it is clear that complexes up to n = 4 must be considered for all

four halides, and possibly for pseudohalides. A detailed understanding of

the inter-relationships between the possible anions is at present lacking,

and further quantitative and spectroscopic studies are required. Such

results will surely reveal more about these interesting systems than recent

conductance results (e.g., 73C) which are capable of a variety of qualitative

explanations. Equally importantly, a discussion of stability constant

measurements based on anion exchange or solvent extraction should recognize


that these processes may involve species (e.g., InX4) which are present inaqueous solution only in extremely low concentrations, and that partition mayinvolve a major change in the aqueous phase equilibria, including changes in

the coordination number of indium. It is not always clear that such consid-

erations have been given proper weight in the discussion of experimental

results.

IV. 2. Fluoro complexes

The literature values for the stability constants for indium(III)-fluoride

complexes are given in Table 2, and the corresponding thermochemical results

in Table 3. For lM NaC1O4 at 25°C three sets of results (68A, 69R, 71W) are

in satisfactory agreement, extending to K and the values for 20°C 2M NaC1O4

(54Sa) support these results. The (unweighted) means of the three sets of

data for these complexes are

log K1 3.70 + 0.03 recommended

log K2 2.66 ± 0.15 tentative



It is worth noting that the uncertainty in log K1 is close to the variation

in the values of pK1(HF) adopted in different calculations.

The early cation exchange results (54Sd) are almost certainly in error

because of the high pH (3.8) of the solutions, for although the authors state

that no precipitation occurred, hydrolysis must be a significant competing

process under such conditions (cf. Section II). A study of the temperature

dependence (55H) unfortunately lacks any independent confirmation, but the

results at 25°C are in reasonable agreement with those given, allowing for

the different media involved, and for the fact that not only the values of

pK1(HF), but also K1, K2, K3 and Kh for iron(III)—fluoride complexes, are

involved in the calculation.

The agreement amongst the thermochemical results (Table 3) is not so satis-

factory. Of the three LH° values, that of Walker, Twine and Choppin (71W)

exceeds the other two by an amount which is higher than the stated experi-

mental error. From the work of Phyl (69R) and Vasilev (74V) with 1M NaC1O4,

one finds

9.1 ± 0.2 kJ mol1, AS°1 101 ± 1 J K1 mol1 (recommended)

8.0 ± 0.4 81 + 4 (tentative)H°3 10 ± 3 tS°3 75 + 10 (doubtful)

AH°4 10 ± 2 AS°4 56 + 7 (doubtful)

One may note in passing that although the percentage error in S° cannot be

less than that in AG° and/or AH°, the published errors do not always obey

this restriction.

The changes in H° with n are only slight, implying that the replacement of

In—OH2 by In—F involves essentially constant changes in bonding and solvation

factors at each stage. Vasilev and Kozlovskii (74Va) have extended their

1

2

Table 2. Stability constants for indium(III)/fluoride species.

Medium

T

Log K

(concn. H)

(CC)

a

TABLE 3. Thermochemical parameters for InF(3F complexes (all at 298K)

—tiG

±11'

Con

men

ts

kJ rr

011

kJ m

l J

K1

n1l1

(S

ee also Table 2)

Method

4

Comments

Ref.

cation exchange,

resin

(In)

1 NaClO4

25

3.00

2.8

2.8

- log Kj(HF) 2.85 (assumed)

pH 3.8

545d

No errors quoted; K2 & K3

"only orders of magnitude"

emf: In e

lectrode

2 MaCb4

20

3.70+0.03

2.56±0.09

2.36±0.15

1.09±0.40

log K1(HF) 2.91; K2 0.70

pH 1.7

Values confirmed by ligand

displacement m

etho

d.

Na3

InF6

ppts. at [F] > 0.

lM

54Sa

emf (In)

0.5 MaCb4

15

25

35

3.70

3.75

3.83

2.55

2.61

2.78

—

—

—

—

log K1)HF) 2.85

"

" 2.

91

"

" 3.

00

No errors quoted.

pH 1.3

55H

cation exchange

resin

1.0 NaClO4

in e

quil. with

25

3.67±0.03

2.58±0.06

2.36±0.10

—

log K1(HF) 2.93

pH 2.5 -

3.

8 68A

+ ex

trac

tion

DEHP in t

oluene

(In)

emf (F)

1.0 NaClO4

25

3.69±0.03

2.83±0.04

2.11±0.10

1.27+0.10

log K (HF) 2.95, log K2(HF)

pH l.5 — 2.

0 0.58

69R

H by emf.

1.0 NaClO4

25

3.72+0.03

log K (HF) 2.94, pH 0.7 —1.30

71W

K2 no c

alc'd b

ecau

se errors too large

Medium

Ref

.

n=1

NaCl0&4

21.1

10.3

105

Recalc'n (55H) assumes

±H

(}IF

) =

12.

4,

±S(HF) =

96;

N

o er

rors

quo

ted.

55H, 55P

1.0 NaC1O,,

21.0±0.1

9.20±0.17

101.20.8

Assumes A

H(H

F) =

11.

7, tH(HF)

= 3

.4

69R

1.0 NaClO,,

21.3±0.2

12.5±0.6

114±7

71W

1.0 NaCl0

8.9±0.2

100.7±0.8

Stability consts. of (69R) assumed

thro

ugho

ut

Hydrolysis (1—2%) allowed for; K1 = 1

0'

74V

n= 2

"

16.2±0.2

7.7±0.4

80±2

69R

—

8.3±0.6

82±2

74V

n= 3

m

12.0±0.4

13.8±1.3

87±2

69R

—

6.9±1.0

63±4

74V

0=4

7.3±0.5 (69R)

10±2

56±

7 74V

Go


calorimetric measurements to the temperature range 15-35°C at ionic strengths0 - 2M NaClO4, and report that the monotonic increase in ACp (from 105 J K1

—1 —1 —1 . .mol , for n = l,to 293 J K mol for n = 4) is in agreement with a series

of consecutive replacements of H20 by F in the indium coordination sphere.(3-ntIt follows that all the complexes are of the type {In(H2O)6nFn] — , in

agreement with the proposal that the stability constants do indeed refer to

equilibria (1)-(4) in Scheme 1.

IV. 3. Chloro complexes

In contrast to the fluoride systems, the indium-chloride stability constants

show a surprising range of values. For example, the reported log K1 results

vary from 4.3 to 0.05, and even when the more obviously inconsistent results

are eliminated, no single value predominates. The situation is also compli-

cated by an almost perverse refusal to use a standard medium, even in studies

from the sane laboratory. That this is no trivial matter is shown by the

work of Mikhailova et al. (69M), who found K1 varying by almost a power of

ten when different alkali metal nitrates were used as background electrolyte

(see Table 4), and in addition claimed that no complexes higher than n = 1

exist in lithium nitrate media. No allowance for the possible formation of

indium-nitrate species appears to have been made in this work.

Of the experimental methods used, the polarographic technique seems to be theleast satisfactory in this particular system. Doubts have been expressed asto the polarographic reversibility of the reduction processes (62M), with theimplication that all constants derived from such experiments are unreliable.

Other authors (601, 67L) claim that the three-electron reduction is revers-

ible, but opine that Cozzi and Vivarelli (53C, 54C) used an incorrect value

for E°½, and that recalculation with the correct value would lower the

derived log K1 by 1.3 units. Given these problems, and the failure of other

workers to report stepwise stability constants (51S, 58Z), it seems appropri-

ate to remove all the polarographic data from further consideration. The

most recent polarographic results (75K) must also be subject to considerable

doubt, for although K1 is close to that from other methods, the fact that K2

shows no such agreement, and that K3 > K2, does not inspire confidence. One

can, for other reasons, eliminate from consideration the values reported by

Schufle and Eiland (545d) (suspect because of probable hydrolysis (see IV. 2.

above)), and those involving anion exchange (63M), which are based on the

surely invalid assumption that = 0.

What then remain are values which unfortunately show no constancy as to

experimental conditions. In perchioric acid media, one finds

acid strength (M) log K1 log K2 log K3 Ref

0.5 2.47 0.64 0.83 64V

0.69 2.36 1.27 0.32 54C

1.0 2.52 — 61W

2.0 2.51 — 61W

and confidence in the last two sets is reduced by the failure to identify any

higher complexes. Accordingly, over the range 0.5 - O.69M perchloric acid,


one has

2.41 + 0.05 recommended

0.95 + 0.4 doubtful

0.5 + 0.3 doubtful

justified by

of detailed

stability

For sodium perchlorate solutions with pH < 3.0, the reported values are:

log K2 log K3 Ref.

— — 54Sb

1.35 — 54Sc

1.0 0.2 54S, 72F

1.26 0.4 72F

1.57 70H

and again it seems justifiable to state average values valid for the concen-

tration range 1 - 4M sodium perchlorate.

log K12.40 ± 0.2 tentative

log K21.30 + 0.3 doubtful

log K30.30 ± 0.3 doubtful

The cation exchange results for various concentrations of alkali metal

nitrates (69M) are regarded as doubtful for lithium nitrate, and tentative

for the other two salts.

In concluding this part of the discussion, one can only lament the lack of

reliable recommended values for these stability constants, given the amount

of effort and the range of experimental methods which have been applied to

the problem.

log K1

log K2

log K3

with the use of the rather broadly defined standard state being

the agreement within the limits stated and by the present lack

knowledge as to the effect of changes of ionic strength on the

constants.

NaC1O4 concn. (M) log K11 2.18

2.20

2 2.43

3 2.58

4 2.61

The only thermochemical work is

values, based on values of K1 -

AG°

AS°

n=2 AG°

AH°

AS°

AG°

AS°

—12.0 ± 0.25.1 + 0.257.3 + 1.2—8.6 ± 0.23.3 + 0.339.7 + 1.71.4 + 0.5

33 ± 8

108 + 17

that of Rhyl (69R), who finds the following

K3 refined from Sunden (54S)

kJ mo11—1kJ mol tentative

—1 —1JK mol

tentative

doubtful

(2M NaC1O4, at 25°C, pH 2.0). These results do not lend themselves to any

thermochemical analysis of the type performed for the fluoride system.

TABLE 4.

Stability constants for indium(III)/chloride species.

0.01 —

11.6

HC1

corr.

I =

0

1')

polarography

cation exchange

resin

extraction into

naphthalene-l-

carboxylic acid in

di-iso-propyl ether

varying; aq. soln

of InCl3

2 NaClO4

0.69 HC104

1 NaClO4

in equil. with

org. phase

pH 2.7 —

3.8

recalcn. of results

of Moeller (4lMa)

53C,

54 Ca

54C

- pH

3.8

54Sd

No errors reported.

Higher consts. not

calculable from results

pH 1.7

Values confirmed by

ligand displacement

method.

pH2.5

Higher consts. not

calculable. No consts.

from anion exchange

resin expts.

—

pH2.

7—3.

0

54Sb,

54 Sc

polarography

corr to 1= 0

25

—

(2)6

.28

- (4

)7.4

4 Only InC12 and

InCl4 assumed.

58Z

Method

Medium

(concn. M)

T

(°C)

1

log Kn

2

3

4

Comments

Ref.

polarography

25

—

—

(134)%—l

cf 62M

5lS

cation exchange

1 NaC1O4

resin

emf, In electrode

2 NaClO4

cation exchange

1 NaClO4

52H

- pH

l.0

cf (67L)

cf (59Ba)

0. 32±0. 12

1.00

25

2.35

25

4.3+0.1

1.8±0.2

20

2.36±0.02 1.27±0.08

25

1.42

0.81

20

2.15±0.03 1.44±0.03

20

2.18±0.03

20

2.20±0.03 1.35±0.05

5 4S

54Sc

TABLE 4. (continued)

extraction into

DNNS in heptane and

TNOA in benzene

cation exchange

resin

catio

n exchange

resin

extraction (In) by

TTA in CHC13

1 HC1O4

in equil. with

org. phase

2 HC1O4

in equil. with

org. phase

corr. to I =

0

25

1.75

25

2.49

25

2.66

4 N

aC1O

4 25

2.

61

in e

quil. with

org. phase

potentiometric

3 NaC1O4

(In, Cl)

- N

o er

rors

qu

oted

. 62

F

-

? acid added

Mixed B

r/C

l sp

ecie

s id

entif

ied.

—

1.6

assu

med

0

in m

echa

nism

. [H

C1]

0.08

— 9.

0 No er

rors

quo

ted.

-

Als

o va

lues

in

mix

ed

64V

H20

/EtO

H

—

pH 1

.75

69M

—

No

erro

rs q

uote

d.

- N

o co

mpl

exes

hi

gher

th

an n

= 1

in

LiN

O3

—

pH 2.

0 —

4.0

70H

N

o er

rors

quo

ted.

- pH

l 72

F

0.2±

0.2

-

Rec

alc.

by

(72F

) as

sum

ing

n =

3 co

mpl

ex present

Med

ium

M

etho

d (c

oncn

. M

) T

(°

C)

1 2

log

K

4 C

omm

ents

R

ef.

25

2.52

-

- -

No

erro

rs q

uote

d 61

W

Cl,

by AgC1 electrode

polarography

po te

n tio

me t

ric

anio

n ex

chan

ge

resi

n,

solv

ent

extr

actio

n in

to T

IOA

in

xyl

ene

4 N

aNO

3 4

NaN

O3

corr

. to

0

0.5

HC1O4

1.5 LiNO3

1.5 NaNO3

1.5

KN

O3

—

No

erro

rs q

uote

d.

? acid added.

62A

2.51

25

1.72

0.92

25

2.26

0.24

—

25

—

—

1.05

25

0.05

0.45

0

?

2.47

0.64

0.83

1.54

—0.50

1.74

0.51

1.59

—

25

2.58

±0.

02

1.26

±0.

04

0.4±

0.1

20

2.43

±0.

05

1.0±

0.1

63M

2 N

aC1O

4

pola

rogr

aphy

2.

70

0.50

1.

00

-0.9

0 75

K

54S,

72

F


IV. 4. Bromo complexes

Using the criteria established in IV. 3., we can reject values based on

polarography (54Ca, 54Cb, 62F, 75K), and the cation exchange studies at high

pH (54Sd), and are then left with a set of results (Table 5) for O.69M

perchioric acid (54C)

log K12.01 + 0.02 tentative


log K3 0.18 ± 0.12 doubtful

Concn. (M)

1log K1 log K2 log K31.93 0.67 —

1.90

log K4 Ref.

— 54Sc

The thermochemical results reported by Rhyl (69R) yield

IV. 5. lodo complexes

From the results in Table

for 0.69M perchloric acid

log

log K2

log K3

log K1

log K2

log K3

1.64 ± 0.05

0.91 + 0.22

—0.08 + 0.25

1.5 ± 0.5

0.6 + 0.5

0 +0.5

tentative

doubtful

doubtful

doubtful

doubtful

doubtful

and values which apply to various concentrations of sodium perchlorate

2 1.98 0.58 — — 54S

4 2.08 1.28 0.60 0.85 57B

2.36 0.80 — — 70H

It is then possible to derive

this whole concentration range

constants which can be taken as valid over



log K30.3 ± 0.3 doubtful

log K4 0 ± 1 rejected

n = 1 AG° -11.3 0.1 kJ mol1LH° 1.95 + 0.05 kJ mol1AS° 44.3 + 0.8 J K1 mol1

n = 2 AG°

AH°

AS°

-3.4

5.65

30.5

+

+

+

0.2

0.2

1.2

kJ

kJ

J

molmol1K1 mol1

Itentative

doubtful

6, and following the previous argument, one finds

The results for sodium perchlorate media are few in number, and rendered

unreliable by the fact that Sunden (54Sa) reports K2 > K1; while such a

result is not impossible, there is no other evidence to support such a finding

for indium-halide systems. The values for 2 - 4M NaC1O4 solutions are

there fore

Given these findings, the thermochemical results (69R) must also be treated


with reservation:

n = 1 AG° -• ± 0.8 kJ mol1AH° -3.05 + 0.08 kJ mol1 doubtful

AS° 10 + 3 J K1 mol1—ln = 2 AG -7.1 + 1.3 kJ mol

AH° 3.4 ± 0.1 kJ mol1 doubtful

AS° 35 ± 4 J K1 mol1

Despite the reported experimental accuracy, these values must bear the doubts

expressed about the stability constants (54Sa), on which AG°, and hence AH°

and AS°, are based.

IV. 6. Pseudohalide complexes

A number of the constants reported for thiocyanate complexes (see Table 7)

can be rejected immediately. Three series of spectrophotometric measurements

either make assumptions, or reach conclusions, about the absence of complexes

beyond In(NCS)2+ or In(NCS)2+ which are at variance with work on the known

chemistry of indium-thiocyanate systems, and of the analogous halides (64K,

68D, 62S). The polarographic results again suffer from uncertainties as to

the reversibility of the reduction processes (63R, 65Na, 73R) said to be

'quasi-reversible' (65Na), and are rejected, despite the fact that one

analysis produces values for K5 and K6 (but note K5 > K4). One is then left

with two emf (54Sa, 63G) and one solvent extraction (70H) results, from which

for 1.6 - 4M sodium perchlorate, 20 - 25°C



log K3 0.92 + 0.3 doubtful

The reservations about K1 apply because the three results involved are based

on different standard states and temperatures. The effects of pressure

(3000 atm) on the formation of indium—thiocyanate complexes have been reported

(77P, 78P).

The thermochemical results yield

n = 1 AG° —14.6 ± 0.2 kJ mol1 )AH° —6.9 + 0.2 kJ mol1 tentativeAS° 25.5 + 0.8 J K1 mol1

n = 2 AG° -5.60 + 0.25 kJ mol1)

AH° -15.9 ± 0.9 kJ mo11 doubtfulAS° 35 + 3 J K mo11 )

n = 3 AG° -6.0 ± 0.4 kJ mo11 )AU° 10 ± 1 kJ mol1 doubtful

AS° 53 + 4 J K1 mol1 J

The doubts expressed as to the n = 2 and 3 results arise from the values of

AG° (i.e., K), since K3 > K2, following Sunden (54Sa).

No stability constant results have been reported for other pseudohalides.

Indeed it may be that certain of these systems are not experimentally access-

ible since it has been reported (73R) that at the acidity required to prevent

PAAC55 :9—H

TABLE 5.

Stability constants for indium(III)/bromicle species.

1 NaC1O4

in equil. with

org. phase

1 NaC1O4

(i) polarography

4 NaNO3

(ii) enf, In/Hg

electrode

extraction (In) into

TTA in CHC13


"

25 %l.9

TBP in hexane

p01 arography

- pH

l.0

See (67L)

-

pH3.

8 No errors reported

-

Hig

her consts. not

calculable.

pH 1.7

—

pH 2.7 —

3.0

pH 2.5.

Higher consts.

not calculable

pH 1.0.

Na2SO3 added.

No errors reported.

No higher complexes.

-

Aci

d added?

No errors reported

Mixed Cl/Br complexes

also identified

1.3

0.59+0.08 —0.52±0.07 log K5 — 1.

6;

log K6

-2.2

not deterninable

Resin species assumed

to be R3InBr6. pH 1.7

—

No

erro

rs

repo

rted

. pH

2.0

-1.06

Assume InBr3(solv). in

organic phase

54Ca,

54 Cb

54C

5 45d

54S

2.10

0.30

0.10

—0.90

75K

Medium

Method

(concn. M)

T

(°C)

1

log

2

K a

Comments

Ref.

varying; aq.

25 2.20

- —

-

Recalcn. of results

52H

soin. of InBr3

of Moeller (42M)

pH 2.6 —

3.4

polarography

cation exchange resin

cation exchange

resin

2 NaC1O4

0.69 HC1O4

1 NaClO4

emf. In electrode

2 NaC1O4

extraction

(see Table 4)

cation exchange resin

25 3.8+0.1

1.0±0.2

20 2.01±0.02 1.09±0.09 0.18±0.12

25

1.20

0.58

0.70

20

1.98±0.03 0.58+0.04

20

1.93+0.03 0.67±0.05

20

1.90±0.03

1.36(i)

1.52(i)

1.72(u)

spectrophotometric

4 NaClO

21.7 2.08

1.28

anion exchange

resin

0.60

0.85

C

0.1 —

9.3

LiBr

4 NaClO

in equil. with

org. phase

'room

temp'

25 2.36

5 4Sc

5 4Sc

57B

62F

6 2Aa

70H

0.80

1.42

—0.08

TABLE 6.

Stability constants for indium(IIfl/iodide

species.

Medium

T

Method

(concn. M)

(SC)

1

2

3

Comments

Ref.

varying: aq.

25

1.98

-

- so

lns.

of mI3

pH 3.4 -

2.6

52H

No errors reported.

polarography

2 NaC1O4

25 3.1

0.7

-

No errors reported.

54Ca, 53C

See (67L). pH?

cation exchange

0.69 HC104

20

1.64+0.05

0.91+0.23 —0.08+0.25

resin

54C

cation exchange

1 NaC1O4

25

0.30

-

- re

sin

pH 3.8

54Sd

emf, In electrode

2 NaC1O4

20

1.00+0.20

1.26+0.30

—

pH 1.7

54Sa


4 NaC1O4

25

1.97

0.31

-0.39

TTA in CHC13

in equil with

org. phase

pH 2.0

70H

No errors reported.

extraction into

"

2.0

0.18

0.02

TBP in hexane

Assume 1n13(solv) extracted

log K4 = -1

.06

polarography

1.35

0.05

-0.10

log K4 -

0.80

75K

TABLE 7

.

Stability constants for indium(III)/thiocyanate

species.

Mediuni

T

log Kn

Method

(concn. M)

(SC)

1

2

—

3 4

Comments

Ref.

emf: In electrode

2 NaC1O4

20

2.58+0.02

1.02+0.03

1.03+0.05

—

spec

trop

hoto

met

ric

1 NaC1O4

25

—

-

- pH 1.7

54Sa

Job's plot shows only In(NCS)2

62S

present.

pH 1.60

emf: In/Hg electrode

1.6 NaC1O4

20 2.58

1.42

0.74

0.06

63G

polarography

2 NaClO4

30

2.08

1.13

1.04

—0.01

log K5 0.58

63R

log K

0.03

Error? pH = 1

spectrophotometric

0.6 HC1O4

20

2.34+0.02

-

- -

(com

p. formation

of F

eNCS2+)

Assume no complexes beyond

64K

InNCS2+.

Assume log K

for FeNCS2+ = 2.

15

1

polarography

2 NaC1O4

25 1.7

0.6

-0.22

1.14

Assume no complexes beyond n = 4 64Na

pH 3.0.

No errors quoted.

spectrophotometric

0, corr.

30-32

3.15+0.01

-

- -

emf: Ag/AgSCN

"

" 35

3.

26±

0.04

-

- -

pH 2.3 (Analysis said to show

68D

kabsence of higher

pH 2.0 complexes.

extraction(In)

into

4 NaClO4

25 2.44

1.67

0.99

-

TT

A in CHC13

in e

quil. with

org. phase

pH 3.0

70H

extraction(In)

into

"

" 2.

4 1.71

0.99

-0.63

TB? in hexane

log K5 = 0.

88

Assume In(NCS)3 in org. phase.

polarography

2 NaNO3

27

0.78

1.71

1.42

-

? added acid

73R

No complexes beyond n =

3


precepitation of indium hydroxide, decomposition of SeCN occurs, with pre-

cipitation of red selenium; the abstract of this paper has a misprint which

leads the reader to expect results for In/SeCN complexes.

IV. 7. General discussion

In view of the efforts which have been expended on the experiments reviewed

in this section, the yield of 'recommended' stability constants is very dis-

appointing. There are no firm results for complexes higher than n = 1 in any

system, and the results for n > 3 are all extremely tenuous. Equally regret-

tably, the data cast no light on the problem of the species in solution be-

yond n = 3, discussed in sub-section IV. 1. All in all, the indium(III)-

halide systems clearly lack definitive stability constants, and one final

irony is that the results for K1 for InC12, InBr2+ and InI2+ derived in 1952

(52H) from the early results of Moeller (4lMa, 42M) are remarkably close to

the values recommended.

Given the problems of establishing recommended values for K3 etc., any com-

parison of the stability constants for the different halides must be re-

stricted to K1, K2, AH°1, and AS°1. The results for 1 - 4M sodium perchorate

give

log K1 log K2 AH°1 AS°1F 3.70 2.66 9.1 101

Cl 2.40 1.30 5.1 57

Br 2.10 0.95 1.95 44

I 1.5 0.6 —3 10

NCS 2.53 1.35 —7 25

It is immediately obvious that the order F > Cl > Br > I holds for both K1

and K2, this being the classical order for a hard cation such as 1n3+. The

same order also holds for AH°, and AS°, and a detailed analysis of these

results might lead to some insight into the bonding terms. The order for

(n 1 - 4) in methanol is Cl > Br > NCS > I (80S). Finally we should

note that K1 and K2 for thiocyante would imply strong similarity to chloride,

but that this cannot be extended to the thermochemical results.

V. OXYANION COMPLEXES

Compared with the number of publications dealing with halide complexes, the

study of the ligation of indium(III) by oxyanion ligands have been almost

neglected. Equally, there is no firm base of preparative chemistry from

which to discuss those results which are available. The present review is

ordered in terms of Group V—VI-VII ligands, there being no results on indium-

carbonate, silicate, etc.

V. 1. Oxyanions of Group V

Indium(III)-nitrite complexes have been identified in anhydrous methanol

solutions of In(NO3)3 and NaNO2; conductimetric and potentiometric studies

gave log K(at 25°C)=5.20, 3.50, 3.38, 2.32, 2.00 and 0.64, for n 1 — 6

(all tentative). Crystalline In(NO2)3.1MeOH was obtained from solution (74G).


Both cationic and anionic indium nitrate complexes have been prepared; the

latter are salts of the IIn(N03)41 anion (65S, 66T, 731), while the cationic

species are of the type [InL(NO3)2] (L = bipy or phen) (66T). The form-

ation of indium—nitrate complexes in solution has been demonstrated by Raman

spectroscopy (63H, 64H). Two quantitative studies of complex formation gave

0.69M HC1O4, 20°C, cation exchange resin (68F)

log K1 = 0.18 + 0.08')

(tentative)log K2 = —0.48 + 0.10 J

4M Na(C104), 25°C, pH = 2.0, extraction into TTA in CHC13 (70H)

log K1 = -0.43 (doubtful)

Indium orthophosphate precipitates quantitatively from solution (pH 3.25) as

InPO4.2H20, for which the solubility product (68Da)

log K = -21.63 (doubtful)sp

(25°C, I = 1 NaClO4). Aging of the precipitate is said to be important, but

no information is given on the relevance, if any, of this factor in the mea-

surement of (cf. Section III. 4.). Mixed hydroxo-phosphate complexes

were also detected. No stability constants have been reported for higher

complexes of PO43, although salts containing [In(P04)213 and [1n2(P04)4]6anions have been characterized (65D). A 1:1 complex with the H2P04 anion is

reported, with log K1 = 1.43 (ion exchange, I = 0.9, 20°C, [H] 0.1 - 0.51M)

(doubtful) (74F).

Two insoluble indium pyrophosphates have been prepared and their solubility

products measured at 20°C, pH 0.6 —1.5 (64G).

In (P 0 ) log K —64.47 + 0.154 273 sp — tentativeInHP 0 log K -12.44 + 0.1627 sp —

Other pyrophosphates have also been prepared and examined (67D). A study of

competitive complex formation (In/Xylenol Orange/pyrophosphate) has led to

values for the equilibrium.

InH2XO + H2P2072 —s InHP2O7 + H3X03 (5)

for which log (InHP2O7) = 10.23 ± 0.18 at I = 0.1 NaC1O4, 20°C, pH 3.65—5.53,

and = 12.31 ± 0.18 at I ÷ 0. For the process

InH2XO + 2H2P2072 —s InH3(P307)22 + H3XO (6)

log (InH3(P2O7)2) = 15.77 ± 0.15 at I -- 0 (69S). It is assumed that H2P2072

is the predominant (> 90%) pyrophosphate species present under the conditions

used. These results should be regarded as doubtful, since the complex pre-

sumed to be formed in (5) is reportedly insoluble (see above). The stability

constants of the pyrophosphate complexes I In(HP207)2]4 (log l = 21.99 ±

0.02) and [In(P2O7)2] (log 2 = 23.80 ± 0.02) (tentative) have been deter-

mined by a partition method (I = 0.l(NaC1O4),pH 6.9 - 8.3) (78Mb). The

xylenol orange competitive method (67A) has been used in studying the

triphosphate complex [In(H2P3010)2]3 , for which log K = 12.18 ± 0.22 at

I = 0.1 (NaClO4), T = 20°C, pH 3.65-5.53 (doubtful). No complexes of

indium(III) with arsenate, antimonate, etc. have been reported, but it is


relevant to include here the organophosphorus complexing agent I

Me CH P(O) (OH)/2 2

0 CH2P(O) (OH)2

which forms soluble 1:1 and 1:2 complexes with indium: log K1 = 15.4,log K2 = 3.3 (potentiometric titration, 0.1 KC1) (68K) (doubtful)

V. 2. Oxyanions of Group VI

Detailed studies of indium-sulphato complexes constitute the most important

entry in this section. Infrared (64L) and Raman (63H, 64H) work has shown

that such complexes exist in aqueous solution, whilst other physical measure-

ments have been interpreted in terms of [In(S04)212 and [In(S04)3]3 anions

(61D); phase rule studies have identified the crystalline solids

NaIn(S04)2.2H20 and Na2In(OH) (S04)2.3H20 (66D). Table 8 shows that the

measured stability constants lead to the unweighted mean for 1M NaC1O4,

20—25°C.

log K1 1.78 ± 0.02 recommended

log K2 0.75 ± 0.05 recommended


The single value for K1 in 2.OM NaC1O4 (54Sc) is essentially indistinguish-

able from the value recommended above, given the reported experimental errors.

Thermochemical results (691) corrected to zero ionic strength give

n = 1 log K1 3.04 ± 0.09AG° -17.3 ± 0.5 kJ mo11

= 29.0 ± 0.4 kJ mol1AS° = 155.5 ± 1.3 J K1 mol

n = 2 log K2 1.96 + 0.08AG° = -11.2 + 0.5 kJ molAH° = -7.32 ± 0.25 kJ mo11AS° = 13.0 ± 1.3 J K1 mol1

The reported stability constants are in poor agreement with those recommended

above, and while any errors in K may be reduced in their effect on AH and AS,

as the authors claim, the differences are such that all of these results must

be rated doubtful.

A series of sulphonic acid derivatives have also been studied (71E) and may

be included here

HSCH2CH (SH) CH2SO3Na

HSCH2CH(SH)CH2ECH2CH2SO3Na(E = 0, 5, 502)

All are said to form 2:3 complexes with indium, with log K2 3 in each caseZ55 (doubtful).


TABLE 8. Stability constants for indium(III)/sulphate species.

Method

.Medium(concn. M)

m

( C) 1

logKn2 — 3 Corffrnts Ref.

cation exchange 1 NaCl0 20 1.74±0.09 — - pH 2.5 54Sbresin

extraction into 1 NaCl0 20 1.85±0.07 0.77±0.06 0.4±0.1 pH 2.7 — 3.0 54Sc

ct-oxynaphthoic in equil.acid in di-iso- with org.propyl ether phase

cation exchange 2 NaCl0 20 1.74±0.09 — - 54Sc

solubility I = 2 1.78 — — 66D

extraction into 1 NaClO4 25 1.79±0.01 0.72±0.02 — pH 3.2 68ADEHP in toluene in equil.

with org.phase

thernDchem. I ÷ 0 25 3.04±0.09 1.96±0.08 — "enough acid 691

titration (corr) to suppresshydrolysis".

V. 3. Oxyanions of Group VII

The following values have been reported by Hasegawa (70H), using extraction

into TTA in chloroform, 25°C, 4M NaC1O4, pH 2.0 (dO3, Br03) or 3.0 (103).

log K1 log K2

dO3- -0.37 doubtful

Br03--0.12 doubtful

1031.02 1.62 rejected

The order of K1 is the order of the anion basicities, but for iodate the con-

clusion that K2 > K1must reduce confidence in these results.

Finally we should note that perchlorate shows no evidence of complexing with

indium(III) in solution (Raman spectroscopy) (63H, 64H)), which is a welcome

conclusion in view of the number of authors who have used aqueous perchlorate

media in the study of complexing by other ligands.

VI. INDIUM(I) COMPLEXES

The halides of indium(I) are insoluble in aqueous solution, and indium(I)

species generated in situ (e.g. electrochemically) undergo oxidation and/or

disproportionation. Despite these difficulties,a small number of stability

constants have been determined by studying the disappearance of In' in various

media, using polarographic methods to follow such reactions (82R). The re-

sults (25°C, pH 2.80, I = 0.7 (various Group I nitrates)) are as follows:

F log 2 = 2.46•

Cl log K1 = 2.37 doubtful

Br log K1 = 1.56, log K2 = 0.55 J

These experiments give some hope of further studies of the solution chemistry

of indium(I).


VII. CARBOXYLATO COMPLEXES

VII. 1. Introduction

A thorough analysis of the stability constants of complexes of indium(III)

with carboxylate anions is rendered difficult both by the general absence of

duplicate results, and by the lack of a firm base of preparative and/or

structural information. Thus although a number of neutral indium-

tricarboxylato compounds are known in the solid state (75C), there are no

reports on the preparation of either cationic or anionic complexes apart from

oxalate (see below) and one negative result in respect of acetate species

(73Ha), and in consequence, the reality of the anionic complexes implied by

K4, K5 and K6, (c.f. Table 9) is not as yet supported by other work.

Table 9 presents the published results in the order of increasing ligand

molecular weight, grouping the parent acids in the sequence monobasic >

substituted monobasic, (including aromatic compounds) > dibasic > tribasic.The very considerable problem of the unambiguous identification of the

structure of the ligand actually bound to the metal, i.e •, of the number of

ionized protons and the sites of ionization, becomes increasingly important.

VII. 2. Monobasic acids

Sunden's results for the series HCOOH -CH3COOH

-C2H5COOH

are regarded as

tentative, since the reported experimental errors are all less than + 0.2 and

the results are confirmed by other workers within the limits of available

evidence. Thus for acetic acid, the polarographic values (53C, 54Ca, 57C)

give log = 9.8 ± 0.8, but since the work of these authors give high results

for halide complexes (see Section IV. 3.), a corrected value of log 8.5

would be more reasonable; Sunden finds log = 7.9, which gives some con-

fidence in his other values for constants up to K3. The most recent results

(73T) appear to be too low, and are rejected, as are those for chloroacetic

acid, both because of a lack of correlation with pKa and because of the order

K2 > K3>

K1. For di- and trichloroacetic acids, the K1 values are doubtful,

in part because K2 > K1in each case, but the K1 values appear to have a rea-

sonable dependence upon pKa (see Fig. 1, and below).

For glycolic acid, Sunden's value for K1 is supported by three separate

measurements, from which one finds

log K1 = 2.99 ± 0.05 (recommended)

for the range 0.3 - 2.0 perchlorate (H or Na). The values for K2 and K3 in

such media are also in good agreement

log K2 = 2.49 ± 0.1 tentative

log K3 = 1.70 ± 0.1 )

and the K4 and K5 values in Table 9 (entry 6a) must also be treated as better

than ddubtful. The polaographic value for again appears to be too high

and is rejected.

For lactic acid, the two series of measurements are in good agreement, but

since the temperature and pH range of one study (72Sd) are not stated by the


authors, the earlier set of results are tentatively accepted. Asimilaraqree-

ment exists in the case of the isomer 3-hydroxypropionic acid, where the

solvent extraction work (68T) supports the extensive potentiometric titration

studies (72Sa), so that the latter values for K1 and K2 are tentatively

accepted, as are the measurements by the same workers on other 3—substituted

propionic acids.

There is little to be said concerning the results for the remaining monobasic

acid systems. All (i.e. entries (2-23) are doubtful or rejected either be-

cause the experimental accuracies are not known, or because the conditions

are not specified, or both. The two sets of measurements on amino acids

(76K, 77K) unfortunately show little agreement in those cases for which dupli-

cate values are available (Entries 24 and 27), and neither paper quotes

experimental errors.

Fig. 1 shows a graph of log K1 versus PKa for those cases where K1 values are

tentative or recommended; the PI<a values are either from measurements asso-

ciated with the determination of K1, or from refs 64S and 72Sa. The points

generally lie within 0.25 log units of a straight line drawn through the

6

origin, except for 3-hydroxy and 3-mercaptopropionic acid (latter point not

shown on the graph). It is obviously tempting to discuss such deviations in

terms of differing degrees of ligand chelation (see, e.g. (72Sa)), but such

speculation seems profitless in the absence of structural information on the

mode of ligation in such systems. The value for K1 for chloroacetic acid

does not lie on the line drawn, which must call this determination into

question.

VII. 3. Dibasic acids3— —

Preparative studies have shown that [Inox3] and [Inox2(H20)2] anions are

stable in the crystalline state (75C), but the stability constants for

oxalate complexes of indium lack any certainty. The values of log K1 = 5.30,log K2 = 5.22 (66H) are of unstated accuracy, but are in keeping with

log = 14.7 (63S), which js tentatively accepted. The earlier value for

(49L) is rejected; the remaining results are doubtful. Re-investigation

of this system is obviously needed.

to K1

12

I0

8

0 ///,///////

2

2 4 é 8 10 12

1

2b

2c

2d

2e

Formic acid

CH202

HL

53S

emf (ligand, In)

2 NaClO4

8OSa

polarography

0.5 Cl04-

emf (ligand, In)

2 NaClO4

53C,54Ca polarography

2 NaClO4

polarography

0.5 C104

extraction

0.2-2 NaC1O4

into BEHP

80Sa

polarography

0.5 C104-

20

?

K1 2.74+0.03

K2 1.98+0.02

K3 0.98+0.05

K4 1.0 +0.1

20

?

K

3.50+0.02

K 2.450.05

K

1.95+0.05

K3 l.l80.08

K4 0.15+0.15

K 1

.11+0.2

25

4.64

9.0 ±0.2

25

3—4

10.6

25

?

K

2.91

2.11

?

?

K1 3.26

Hydrolysis not

signi ficant

Polynuclear

complexes

negligible

See (1)

See text

H

cri

H 0 z C

Sol

n. buffered

by HL + NaL

InL3 prepared

Values for I =

0 by

ex

trap

olat

ion

3

Chloroacetic acids

Cl CH

COOH

n

3-n

3a

C1CH2COOH

3b

C12CHCOOH

3c

C13CCOOH

25

?

K1 0.71

K2 1.61

K3 1.07

25

K

1.03

K 1

.27

K

0.80

K 0

.81

Rejected

Doubtful

Rejected

Doubtful

Rejected

TABLE 9.

Stability constants for indium(III) carboxylate species.

V

—

Method

-- V.V

V

__V

T

V•V

.•

V

-_.V

.V—

_

Entry

Parent Acid

Ref.

(concn. N)

Medium

(°C)

pH

log Kn

Comments

Rating

2a

-

Ace

tic a

cid

C2H402

HL

53S

C

?

?

K1 2.60

Tentative

K1-K4

Re jected

57C

73T

Rejected

73L

as (2d)

as (2d)

74La

as (2d)

1.0

74La

C

H

H

H

C


4

5b

Glyoxylic acid

HC0. COOH

C2 H2 03

6a

Glycolic acid

53S

C2H403

HOCH2 COOH

6b

57C

7.30

0.40

1.00

0.70

2.50

K1

6.00

K

2 1.

30

K

1.60

K 1

.75

K5 0.90

20

?

K

3.57+0.02

K1 2.790.04

K2 1.79±0.10

K 0

.93T0.15

K5 1.03+0.2

?

?

3.61

20

?

K1 2.93+0.03

K

2.59±0.04

K2 1.69±0.09

K3 0.67±0.06

K 0

.73+0.15

25

3.0—

9.5

5.0

extraction

0.3 HC1O4

into DNNS

in heptane

pH titration,

corr. to

p=O. 14

6e

76S

TTA extraction

1 NaC1O4

30

?

?

pK(HL) 3.64

No higher

complexes proposed

Method

T

Entry

Parent Acid

Ref.

(concn. N)

Medium

(°C)

pH

log Kn

Comments

Rating

76C

polarography

1

30

?

I

5a

Propionic acid 53S

40

as (1)

2 NaC1O4

8OSa

polarography

0.5 Cl04

emf, ligand

2 NaClO4

polarography

0.5 Cl04

Rejected

C/D

rP

Rej

ecte

d .

All

tentative

S

S 0

Rej

ecte

d 2

0 S

ee

text

(D 0 S

6c

60W

6d

60W

See

(1)

See

(1)

InL3 p

repa

red

25

—

K1

3.15

25

1.5— K

2.95

12.0

1

9a

3-hydroxy-

propionic acid

C3H603

9b

7 OKa

conductimetric,

various non—aq.

solvents

72Sd

extraction into

TTA in CHC13

68T

See (6f)

0.1—0.4

NaC1O4

K

2.94

K 2

.40

K 1

.61

25

-

K1

give

n fo

r so

lven

t sy

stem

s st

udie

d.

25

2.10 K1 3.52

K 2.66

2.06

p=0.l, 25C

K

3.75+0.03

K 3.040.05

AH

+36+6

AS2 25013

pK(HL) 3.61

See text

evidence of

Doubtful

complex

formation

pK(HL) 3.92

alternative

value K2 2.81

pK(HL) measured

over range of T

and p. Values

given for 3 temps

and 4 ionic

strengths; data

extrapolated to

p= 0

Values also at

p =

0. AH derived

from temp.

dependence of


Entry

Parent Acid

Ref.

Method

(concn. M)

Medium

T

(°C)

pH

log Kn

Comments

Rating

6f

68T

extraction

BEHP in

into

toluene

0.5 Cl04

25

2.04

6g

7

Thioglycolic

acid HSCH2COOH

8a

Lactic acid,

2-hydroxy-

propionic acid

C3H603

8b

I'

U,

76S

68T

TTA extraction

see (6f)

1 NaC1O4

0.5 NaC1O4

1 NaC1O4

0.5 NaC1O4

30

25

2.00

K1

K2

K3

?

?

K1

K2

K3

7 2.96

2.60

1.64

3 . 1

7 3.

10

1.98

pK(H

L)

3.68

"pH

low enough

to suppress

hydrolysis

9c

725a

pH titration

72 Sa

25,

35,

45

0

See

text

0 0

Ten

ta tLve

0.1 NaC1O4

TA

BLE

9.

(continued)

10

3—mercaptopropionic

72Sa

acid

C3H602S

13

DL-pencillamine,

2-amino-3-methyl

—3 -mercaptobutyric

acid

C5H11N02 S HL

14

Methionine

C5H1102NS

CH3SCH2CH2CH (NH2) COOH

15

Gluconic acid

C6H1207

16

Quinic acid

1,3,4,5 tetra—

hydroxycyc lohexane -

1-ca

rbox

ylic

acid

C7H1206

p=0.l, 25°C

K1 11.87+0.03

K2

7.66±0.05

K3

6.250.05

AH

2

-70+8

AS2 26020

25,

i=0.l, 25°C

35,

K1 2.72+0.03

45

K2 2.54+0.05

AH

2 +31+6

AS11112

2001

3

K1 3.0

K2 1.6

K

1.0

K 0

.5

21

K

15.33

14.46

K(InLH) 18.86

K(InL(LH) 33.39

K(In (L) OH) 11. 25

30

K

8.23

K 5

.69

?

?

?

?

?

K

2.56

2.83

as above

All

tentative

complex formation

reported

All

)

tent

ativ

e

Doubtful

pK(HL) 3.3

K2>K1

}Reected

Method

T

Entry Parent Acid

Ref.

(concn. M)

Medium

(°C)

pH

log Kn

Comments

Rating

25,

35,

45

11

3-aminopropionic

acid

C3H702N

12

Levulinic acid

C5H803

CH3COCH2 CH2 COOH

as above

pK(HL) 3.58

as above

0.1 NaClO4

72Sa

as above

7lP

polarography

?

76Ka

potentiometric 0.1 KNO3

77R

polarography

I =

1

70P

?

?

70T

solvent

?

extraction

BEHP

rt

0 0 rr

S rt

0 frh

C) 0 S

(D 0 (I) 0

} Dou

btfu

l

Doubtful

3

0


Q

cx

17

Salicylic acid

C7H603

18

Anthranilic acid

C7H702N

19

5—nitrosalicylic

acid

C7H505N

HL

20

Phenylacetic acid

C8H802

HL

21

Mandelic acid

2 -phenyl-2 -hydroxy-

acetic acid

C8H803

HL

21b

21c

ii

22

Acetylsalicylic

acid

CQHOOA

HL

23

1-hydroxy-1-

(dibutyiphosphinyl) -

prop

ioni

c acid

C11H2304P HL

735

?

70K,

potentiometric

71K

57C

polarography

0.2 NaC1O

75% EtOH

70T

solvent

?

extraction

See (16)

7OTa

spectrophoto-

0.1 NaClO

metric

30

?

K1 7.5

1<2 6.3

K3 5.9

?

?

1<1 2.58

K2 2.82

pK[HL] 2.

94

Met

al hydroxides

ppts. at pH at

which complex

formation should

be studied.

Dou

btfu

l

Dou

btfu

l

Dou

btfu

l 0

Dou

btfu

l C

Rej

ecte

d

24a

DL

-o-

Ala

nine

76

K

pH

titra

tion

0.01

HL,

3.3mM

InC

l3

24

?

K

8.40

8.25

No errors quoted

Dou

btfu

l

Method

T

Entry

Parent Acid

Ref.

(concn.

M)

Medium

(°C)

pH

log Kn

Comments

Rating

K1 2.59

K K

K3

8.90

5.96

0.5 dO4

25

3.0—

10.2

20% EtOH

3.75

57C

polarography

0.5 C104

76S

TTA extraction

?

68Ga

polarography

1 NaClO4

25

3.0—

9.3

JR study of

complexes

InL3 prepared

K2 >K1!

InL3

prep

ared

2

Red

uctio

n "q

uasi

—

reve

rsib

le"

Order of K n

30

?

Dou

btfu

l t1

C

Rej

ecte

d C

?

4.48

0.

22

1.78

0.33

1.32

25

5 K

1 8.

8 Rejected

TA

BLE

9.

(continued)

rt

H rt

C) 0 0 (I) 0 C') 0 C)

(C'

(C'

Cl) 0 H

0 Ui 0

Entry

Parent Acid

Ref.

Method

(concn. M)

Medium

T

(°C)

pH

24b

DL-ct- Alanine

77K

polarography

0.2 NaClO4

30

5

log K n

Comments

Rating

K1

K2

10.25

5.96

(10.67)

(5.55)

Two different methods

of calculation.

No errors quoted.

Doubtful

24c

8lM

polarography

0.5(KNO3)

30

?

K K 9

.18

7.31

No errors quoted.

Doubtful

25

26

— A

lani

ne

L- Asparagine

76K

76K

pH titration

"

as(24a)

IV

24

?

K K

K1

K2

8.30

8.22

7.17

7.21

as(24a)

Doubtful

Doubtful

27a

Glycine

76K

K1

K2

8.22

8.02

Doubtful

27b

28

'

DL—

Leucine

77K

76K

polarography

pH titration

0.2 NaC1O4

asC24a)

30

24

5

?

K K

K K 9

.85

6.08

7.76

7.65

(10.10)

(5.82)

as(24b)

as(24a

Doubtful

Doubtful

29

L— Leucine

76K

It K

K 8.

26

7.48

Doubtful

30

31

DL- Methionine

DL- Phenylalanine

76K

76K

"

pH

titra

tion

as(2

4a)

24

?

K 4

K 4 7

.75

7.42

7.36

7.22

H

as(2

4a)

Doubtful

Doubtful

32

L— Proline

76K

" '

" K 4 9

.04

8.64

" D

oubt

ful

33

DL—Serine

76K

K 4 7

.53

7.05

Doubtful

34

DL- Taurine

76K

It K 4 7

.44

7.13

II Doubtful

36d

37

Maleic acid, H2L

(cis) HOOC. C2H2 .

CO

OH

C4H404

38

Succinic acid, H2L

C4H604

39a

Malic acid, H2L

C4H605

39b

49L

pH titration

60W

extraction into

0.3 HC1O4

DNNS in

heptane

63S

extraction into

0.1 KC1O4

8-quinolol in

CHC13

66H

extraction into

1 NaC1O4

TTA in CHC13

67Na polarography

0.2 NaC1O4

polarography

0.5 C104

polarography

0.5 dO4

72Sb pH titration,

temp.

dependence

Corr. to

1=0

K1 8.28

K2 7.52

18(?)

2 8

.6

8

25

-

1n3+

+

HLE

? InHL2+

K 3.08

20

3—5

14.7±0.1

25

3—

K

5.30

3.4

K 5

.22

25

3—

K1 5.0

4.5

K2 2.1

K3 3.8

25

3.3

K1 6.8±0.32

{In(OH)L2]

18. 5±0. 3

25

2.7—

K1 6.8+0.22

3.4

[In(OH)L2J

18. 9±0.1

as(24a)

Doubtful

dl H2L

Rejected

used

Values for Ki, K2

and pK1, pK2 at 3

temps and 4 ionic

strengths; also

corr. to 1=0

pK1[H2L] 4.59,

pK2 3.05

No ionization of

OH group

Errors?


Method

T

Entry

Parent Acid

Ref.

(concn. M)

Medium

(°C)

pH

log K

Comments

Rating

35

DL- Valine

76K

pH titration

as(24a)

24

?

36a

Oxalic acid

H2L

C2H204

36b

36 c

pptn. of InL2

complexes noted

pK1[H2L] 3.18

See text

Rejected

pK1{H2LJ 1.28

Doubtful

53C,

54Ca

53C,

54 Ca

3—

No need to

postulate InL3

K3 >K2

In (OH)L

prepared

0 T

enta

tive

0 0

Dou

btfu

l tj

Rej

ecte

d

Rejected

0.1—0.4

NaClO4

25,

I 0.1, 25°C

35,

K1 4.60

45

K2 3.61

35

—50.4

+43,. 5

+304

Doubtful

40

Aspartic acid, H2L

H2N—çH-CO0H

H2C-COOH

C4 H704 N

72Sb as above

42a

Tartaric acid, H2L

53C,

2, 3-dihydroxybutane 54Ca

-dioic acid, C4H606

43

Iminodiacetic acid,

H2 L

HN (CH2COOH) 2

C4H7N04

44

HIMDA, H2L

63Ra ion exchange

C6H1105N

0.1—0.4

NaC1O4

Corr. to

1=0

0.1—0.4

25,

NaC1O

35,

4

45

Corr. to

35

1=0

I 0.1, 25°C

K1 3.26

K2 2.84

AHJ2 +41.8

+304

I 0.1, 25°C

K

14.47

K 1

1.29

—158

AH2 —51

AS2 +346

1.75

In(dHL)

6.8+0.1

2

In(mesoHL)2 7.5±0.1

In(OH) (dL)2 18.5±0.1

In(OH) (mesoL)2

18.9±0.1

K1 4.48±0.04

?

3—9

K1 [In(HL)]°3 12.37

K2 [In(HL)2]6 10.80

K3 [In(HL)3}

7.15

25

3—

K

9.54

11

8.87

as above

pK1[H2L] 3.70,

pK2 1.84

Errors?

Doubtful

Reversibility of Rejected

electrode pro-

cess?

K2 may

refer to2InL2 or

[InL2OH]

Doubtful


Method

T

Entry

Parent Acid

Ref.

(concn. M)

Medium

(°C)

pH

log Kn

Comments

Rating

25,

35,

45

35

41

Thiomalic acid, H2L

72Sb as above

HS-H-COOH

H2á-COOH

C4H604S

polarography

0.5 C104

25

42b

42c

63C

extraction into

8-quinolol in

CHC13

,

but treated

7lB

pH titration

as H4L

0.1 KC1O

20

4.5—

12

Crystalline

In(OH) (L)H20

identified.

pK1[H2L] 3.77,

pK2 2.60

(ID

Dou

btfu

l

Rejected

rD 0 C

D

CD

(I

D

0

Dou

btfu

l 0-

Rej

ecte

d

66M

potentiometric

titration

1 NaNO3

0.3 KC1

0.5

?

?

K1 11.0±0.1

45

Phthalic acid, H2L

C8H604

46a

Citric acid, H3L

2-hydroxypropane,

1, 2, 3.-carboxylic

acid

C6H807

46b

47a

Nitrilotriacetic

acid! H3L

N(CH2COOH)

47b

47c

47d

63Rb potentiometric

titration, anion

exchange resin

cation exhange

resin

77L

extraction into

1 NaC1O

BEHP

63S

extraction (see

0.1 KC1O4

entry 33)

63Rb cation exchange

0.5 NH4C104

resin

65Za spectrophotometric

(FeL complex)

67B

redox emf.

(Fe/FeUI)

1.25—

K

5.00

4.5

K 2.81

K3 1.22

?

1—

11

0.6

—l

7.1

25

1.5—

2.5

?

20—

2.5—

22

3.4

0.1 NaClO4

0.1 KNO3

0.1 NaC1O4

K1 15.88

20

2

K1 16.9

Na[InL(H20)2] and

H[InL(H20) 2

prepared.

charge on com-

plexes identified

by ion exchange

Critical review

of refs 54Se,

56S, 63Ra, 63S,

65B, 65Z, 67B

by 78A

N)


Method

T

Entry

Parent Acid

Ref.

(concn. N)

Medium

(°C)

pH

log Kn

Comments

Rating

78S

polarography

?

30

0.1 KNO3

0.5 NaC1O4

46c

",

H4L

1n3+

± H3L

InLH+ +

211+

K 1.05+0.04

K1 6.18

K(ML) 10.58+

0.03

K(MHL) 6.17+

0.09

78Ta polarography

3.2 NaC1O4

25

0.01 In3+HL

-0.5

In(H2L4+ 2H

20

?

2 2

4.4

0.3

K

14.88+0.09

—l

1

—

Evi9ence for

H2L -

as p

redom-

inant ion

pK123 13.53

48

HEDTA, H3L

C10H1807N2

49

EDTA, H4L

C10H1608N2

} Dou

btfu

l

Rejected

Re j ec

ted

Rejected

Rejected

(see text)

t.i

See

te

xt

Dou

btfu

l

All tent

ativ

e

63R

a io

n ex

chan

ge

78A

See Comments

0.5

?

?

K1 17.16+0.03

20

K1 24.95

20

—

K1 24.37

pK[InHL] 1.5

pK[InL]

8.63


Entry

50

Ref.

Method

(concn. M)

Medium

T

(°C)

pH

log Kn

Comments

Rating

67B

redox

Fe") (Fe"!

0.1 NaC1O '

20

?

K1 21.15

pK[HInL] 1.64

Doubtful

Parent Acid

(trimethylene-

dinitro) —tetra

acetic acid, H4L

C1 1H1808 N2

51a

EEDTA, H4L

C12H2009N2

65Z

spectroscopic

?

Sib

"

65B

redox (Fe"/

Fe")

0.1 NaC1O L

52a

[(2,2—thiodi-

ethylene)dinitrilol

tetra—acetic acid,

H4L

C12H2008N2S

66Z

spectroscopic

I

0

52b

67B

redox (Fe"!

Fe)

0.1 NaC1O4

53a

CDTA, H4L

C14H2208N2

63Ra

ion exchange

0.5

?

53b

" 67B

redox (Fe'/

Fe')

0.1 NaC1O4

20

54

HDTA, H4L

C14H2408N2

65Z

spectroscopic

?

18-

20

55a

DTPA, H5L

C14 H2 301 0N3

63Ra

ion exchange

0.5

?

55b

65Z

spectroscopic

?

18—

20

55c

67B

redox (Fe"/

Fe")

20

55d

DTPA, H5L

C14H23010N3

74Lb

extraction

1.0 NaC1O4

?

18—

20

?

K1 22.67

Doubtful

20

? K

1 25

.5

Dou

btfu

l

18-

20

? K

24

.1

1 D

oubt

ful

20

? K1 20.26

pK(InHL) 1.88

InL +

OH

In

OH

L2 -

K 4

.2

Doubtful

?

K1 25.05±0.09

Doubtful

?

K1 28.74

Doubtful

?

In3 + H

L3

InH

L

K

9.03

Dou

btfu

l

?

K1 27.65±0.04

?

K

28.42

1

mean

28.4±0.8

(Mean)

Doubtful

K1 29.0

?

K[InL] 27.25+0.02

K[InHL] 18.45+0.02

K[InH2L] 11.68±0.02

K[In(H3L)2} 14.17±0.02

Rejected

0 0

(I) 0 rt

Cl) 0 r)

0 H

(Cl

(Cl

(ll 0 0 0 H

H


The polarographic results on maleic, succinic acid and malic acids are all

rejected, in line with the previous discussion. The measurements on malic,

aspartic and thiomalic acids (72Sb) are all tentatively accepted, despite the

absence of stated errors, aiven the confirmation by others of the work by the

same authors on substituted propionic acids (72Sa) (see VI. 2. above).

The results for tartaric acid raise a point noted earlier and to which we

shall return later, namely the problem of identifying the ligand(s) involved

in the equilibria being studied. The three sets of values are all predicated

on different species, and even on differing numbers of ionizable protons

(i.e., H2L or H4L) (cf. entries 42a, 42c). Here surely is a case, as else-

where, in which the use of thermodynamics and the law of mass action has

little point unless coupled with (say) spectroscopic identification of the

species present in solution. For the present, the results on tartaric acid

are all regarded as doubtful or rejected. Similarly, for iminodiacetic acid,

doubts have been registered by the authors (66M) as to the reversibility of

the electrode process, leading to uncertainty as to the equilibria actually

being studied, and here again the results are therefore rejected.

VII. 4. Tribasic and higher acids

The problems noted in the last paragraph are the more important with tribasic

acids, as illustrated by citric acid, where the results are all rejected be-

cause of the failure to identify the equilibria unambiguously. There is even

disagreement as to whether citric acid is to be regarded as tn- or tetrabasic

(63Rb, 78Ta). Other authors (78Sa) have commented on the complications of

the polarographic reduction processes in 1n3+/citrate media.

The parent acids in this section include many of the derivatives or analogues

of ethylenediaminotetraacetic acid, which itself has been the subject of a

critical review by Anderegg (78A), and results for this ligand are therefore

not discussed in the present work. Complexes of this and similar ligands

with 1111n have been used for in vivo investigations (79G). For

acetic acid (entry 47), three reports yield a mean of log K1 = 15.9 (doubtful)

for differing media. In other cases (eg. EEDTA, CDTA), the agreement between

different authors is poor, and one can only suggest that the results of 67B

can be treated as being reliable because the values derived in this paper for

the In/EDTA system find some independent confirmation. For DTPA, the mean of

28.4 for log K1 again confirms the work in 64B.

In general, one can only repeat the opinion that physical methods must be

coupled to thermodynamic studies if the equilibria involved in such compli-

cated systems are to be properly understood.

VII. 5. Mixed ligand systems

Despite the problems of arriving at a satisfactory series of results for such

ligands as NTA, EDTA, etc., a number of investigations have been made of

systems in which more than one ligand is involved. Results have been pub-

lished on In/EDTA/halide (78F), In/EDTA/NCS (78E) and In/NTA/NCS (79E)


systems. Other authors have reported stability constants for In/NTA with

various polybasic acids (78A), and for In/NCS with complexones (79Ea). The

comments made above as to thermodynamic significance must also apply to these

mixed ligand systems.

VIII. MONOBASIC BIDENTATE CHELATING AGENTS

Because of the importance of bidentate chelating agents such as acetylacetone

(Hacac, 2,4-pentanedione) in the development of coordination chemistry, it

seems appropriate to give separate consideration to the stability constants

for complexes of these ligands. The appropriate neutral InL3 complexes are

structurally well established, and the solution chemistry (e.g., ligand ex-

change) has been the subject of spectroscopic and other investigations (75C).

The three sets of results for indium/acac (Table 10) are not in particularly

good agreement, and the unweighted means of the values (0-0.5 NaC1O4, 25-30°C)

give



log K3 6.2 doubtful

The value for In/benzoylacetone is doubtful; the results of extraction into

different organic solvents are accepted as giving different stability constantresults (cf. Beck (75B)). For thenoyltrifluoroacetone (TTA) the apparent

agreement between two sets of experiments would be more encouraging if one set

of cOnditions were clearly defined (72Sc). The values of Schweitzer and

Anderson (68S) are tentatively accepted, being confirmed both by other K1 - K3results, and by a previously reported value for 2 (56R). The results for a

series of substituted diketonates)including TTA (72B),apply to mixed aqueous-

organic solutions, and so cannot be compared with the results just noted.

For 8-hydroxyquinoline (Hoxine) the agreement between the similar but inde-

pendent measurements in such that one can recommend the results (0.1 NaC1O4,

25°C)

log K1 12.00 ± 0.05

log K2 11.95 ± 0.05

log K3 11.45 ± 0.05

The situation with the solubility product of In(oxine)3 is less satisfactory,

and in view of the disagreement between the two results, both should be re-

jected. A recent study by Thompson (78Tb) refers to 50% (w/w) aqueous

dioxane; constants for In/oxine are tentatively accepted, as are the con-

clusions for the apparently more complicated system involving 2-methyl-8-

hydroxyquinoline in the same medium.

There are a number of papers, not available to the present reviewer, dealing

with various derivatives of 8-hydroxyquinoline. In particular, the effect of

halogen substitution at the C5-position of 8-mercaptoquinoline has been

studied, with the order of stability (133) being 5-HL > 5-FL > 5-C1L > 5-BrL >

5-iL (68C, 69C); similarly 8-mercapto > 8—hydroxyquinoline (66B). Mixed

TABLE 10.

Stability constants for indium(III) complexes with monobasic biclentate chelating agents.

Medium

T

Entry

Ligand

Pef.

Method

(concn. M)

(°C)

pH

log K

Comments

Rating

la

2,4—pentanedione

551

potentiometric

corr. to

30

K1 8.0±0.2

pptn. prevents

See text

EL

I =

0 K2 7.1+0.2

detn. of K

C5H802

No interfeence

from hydrolysis

lb

'a

58R

ex

trac

tion

into

I = 0.

1 var-

var-

K1 8.06

Quoted in (60S)

CHC13, C6H6,

ied

ied

K2 6.20

CC14

lc

66Ca polarography

0.5 NaC1O4

25

0.7- K1 8.8

3.5

K2 7.3

K3 6.2

2

Benzoylacetone, HL 59R

extraction into

?

?

CC14:

20.7

Quoted in (60S)

Doubtful

C6H5COCH2COCH3

CHC13, C6H6 or

C6H6, or CHC13:

CC14

20.85

3a

Thenoyltrifluoro-

56R

extraction into

3 NaC1O4

25

2.7-

12.4

pptn. occurs at

See text

acetone, EL

benzene

4.3

pH >5

C4H3 SCOCH2 COCF3

3b

68S

extraction into

0.1 NaC1O

25

1-7

K1 6.0±0.2

Tentative

CHC1

K2 6.0±0.2

K1 - K3

K3 5.6±0.2

1n3++ i

:-+ 0H

InL(OH)+

K 1.6.8

1n3± + L

+20

H

InL(OIJ)2

K 26.0 + 2L +

0H

InL2

OH

K 22.0

3c

72Sc extraction into

1 NaC1O4

?

?

K1 6.51

"pH low enough

See text

CC14

K2 5.46

to suppress

K3 5.20

hydrolysis"

TA

BLE

10.

continued

Substituted

1,1,1 trifluoro—

methy1-—di-

ketonates

CF3 COCH2 COR

(HL)

8-hydroxy-

quinoline, HL

C9 H7 ON

8 —mercapto—

quinoline

C9H7NS

HL

5-bromo-8-

mercaptoquinol me

72B

pH titration

68S

extraction

0.1 NaC1O4

into

CHC13

65Zb extraction

0.1 C1O4

into

CHC13,

C6H6,

iAmOH

78Tb potentio-

50%(W/W)

met

ric

aq. dioxane

I = 0.

1

49L

pH titration

66B

extraction

into CHC13

50% (W/W)

aq. dioxane

I = 0.

1

67C

extraction

I =

0.1

into CHC13

25

25

1—

K1 12.0+0.2

6

K2 11.9+0.2

K3 11.4+0.2

25

?

K1 13.30+0.01

K2 12.16±0.01

K3 10.97+0.02

20 9

43.6

83

Estimated error

0.05 throughout

pKa values also

reported in

same solvent.

K2 for phenyl

probably too

high

values for

InpHqLn

complexes

InL3 ppts.

Doubtful

at pH > 3.

5 (685a)

Doubtful

4

Medium

T

Entry

Ligand

Ref.

Method

(concn. M)

(°C) pH

log K

Comments

Rating

0.1 Et NC1O

46% dixan

5a

5b

5c

Sd

5e

6

7

8

25

?

K1

K2

R

2—furyl

2—thienyl

phenyl

2-naphthyl

i—Bu

t—Bu

K1

K2

5.93 5.45

5.97 5.76

5.85 5.95

6.93 6.65

6.78 6.40

6.85 6.56

?

18?

2.65 K

—36.7

sp

' K

—3134

sp

25

?

1,2,2

32.00±0.08

1,0,2

l,—1,2

25.97±0.05

20.74±0.01

12.00

11.99

11.48

2-methyl-8-

hydroxyquinoline

HL

K1

Tentative

K2

Doubtful

S rt

See

te

xt

2

S

Cl) S

S

Cl) 0 0

Rej

ecte

d

Rejected

Tentative

'Hydrolysis only

affects values

at high pH'

57P

78Tb potentio-

metric

20?

41.3

3


cmplexes of oxine and acetate (68Sa) and of oxine and 8-mercaptoquino1ine

(66A) have also been reported. The whole field of oxine complexes has been

reviewed by Stary, Zolotov and Petrukhin (79Sc).

IX. MISCELLANEOUS ORGANIC LIGANDS

In this section are collected together the stability constants for a number

of ligands which do not conveniently fit into any of the previous sections.

(Table 11) In many cases the parent compounds, and/or the complexes are

coloured, and these systems therefore readily lend themselves to spectrophoto-

metric investigation. Many of the compounds studied are in fact indicators,

and have been used as such in complexometric titrations, so that knowledge ofthe extent of their interaction with a metal ion is therefore of considerableuse to the analytical chemist, and the results in Table 11 represent valuable

source material in this context. A quantitative understanding of the com-III

plexation of In by biochemically active molecules may also become important

as the use of this radioactive tracer increases, and an interesting study

(79K) reports values for complexes with transferrin (log K1 = 30.5,log K2 = 25.5; doubtful) . As reliable stability constants however, most of

the values in Table 11 are at best doubtful, since in only very few cases is

the ligand which actually complexes unambiguously identified, so that the re—

ported constant may apply to an ill-defined equilibrium, and in many cases to

undefined temperature. The few cases in which two sets of results are re-

ported for the same ligand do not give concordant values. As noted earlier,

the precise structural identification of the structure of the anion(s) derived

from the parent acids under different pH conditions is itself a major problem

which cannot be solved by mass action studies alone. One paper (7lD) claims

to offer a theoretical approach to this problem. Until such questions are

capable of solution, it is inevitable that stability constants derived as in

most of the work reported in Table 11 must be of little value. The only

system for which tentative values are available is in the case of

N-phenylbenzohydroxamic acid, where the work of Schweitzer and Anderson (68S)

is preferred over that of the Russian workers (65H) because the latter gives

no experimental errors.

A small number of studies have reported stability constants for such systems

as In(OH)L2Y2 (80G) and InL2Br4 (79Ga), where L = bromopyrogallol red andY = 2,2'-bipyridine or l,lO-phenanthroline (cf. Table 11, entry 14). The

comments made earlier about such measurements (Section VII. 5.) must also

apply here.

Acknowledgement - This review was prepared during a period ofsabbatical leave. I should like to acknowledge the award of

leave by the University of Windsor, and the hospitality extended

to me by the members of the School of flblecular Sciences,

University of Sussex.

TABLE 11.

Stability constants for complexes of indium(III) with miscellaneous organic ligands.

2

pyrogallol

C6H603

3a

Tiron

C6H608S2

3b

4

purpuric acid,

H5L CSHSO6N5

(murexide =

H4L

.NH

3)

5

TAR H2L

C9H702N3S

6

4-COOH-TAR

C10H704N3S

H3L

7a

pyridylazo-

resorcinol

(PAR)

H2L

C11H9 02 N3

67N

potentiometric

titration, &

spec tropho tome tric

7lD

spectrophotometric

0.1 NaclO4, 25

50% HeOH

Ethanol soln

of ligand

1.5

K

18.64

—7

34.44

1n3+ +

HL

In

H2L

*K 10.8±0.2

Refs to prep.

studies of InL,

InL2, InL3

Correcion made

for In + h

ydro

lysi

s

Both consts.

conditional

ML

in

pH

ran

ge I

- 3

M

L2

at p

H 5

.5

Cal

cns.

on

st

ruct

ure

of H3L

at diff. pH

K no

t id

entif

ied.

C

ompl

ex said to

be anionic (ML2?)

1

pyrocatechol

C6H602

Medium

T

Entry

Ligand

Ref.

Method

(concn. M)

(°C) pH

log K

Comments

Rating

?

1.5— K

18.71

10.5

34.63

74Ka spectrophotometric 0.1 NaClO4

74Ka

74Ka

"

65N

sp

ectr

opho

tom

etric

va

ryin

g I

65G

spectrophotometric 0.1 KNO3

?

1.5—

K

18.12

10.5

33.66

29

3.5

I=0(extrap) .

4.46

1=0.05 3.91+0.03

1=0.1

3.79T0.05

1=0.2

3.72±0.04

20—

"

AH

6.0+0.5 —

45

AS93+l

12

3.0

In3 + H

L

In

H4L

2 K 4.61±0.2

7

pptn. of In(as

hydroxide?) at

pH > 4

K by Job's plot

kinetics investi-

gated by temp.

jump

Dou

btfu

l

Dou

btfu

l H

Rej

ecte

d

Rejected

I T

enta

tive

CD

CD

cn

0

Dou

btfu

l

Rej

ecte

d ?

1—

K

4.36+0.4

10

4 7

.40

66Da Spectrophotometric

25

4.0

9.3

7b

pyridylazo-

resorcinol

(PAR)

H2L

C11H902N3

8

2,2dihydroxyazo- 62K

benzene

H2L

C12H1002N2

50% (v/v) aq.

dioxan

I =

0.2

(NaC1O4)

Spectrophotometric

0.1 KC1

35% EtOH

>5 . 0

K 12.54

K 11.46

25

5.5— In3 + H

L

6.5

InL2+

2H K =

5.

2 InL + H

2L

InL +

2H K = 8

.0

NQ errors quoted

Rejected

no chelation

Doubtful

below pH 4

lOa

N-phenylbenzo-

hydroxamic acid

C13H1102N HL

lOb

12

Kaempferol

H4L

C15H1006

13

Thoron

C16H13O10N2S2As

68S

extraction

0.1 NaC1O4

into CHC13

65H

extraction into

I = 1

CHC1 or

ben zne

7lN

spectrophotometric

1 NaC1O4

25

2—

K1 11.8

5

InL2 + A

p In

AL

K 3.03

InL + +

A

2InA

L2

K 1

.92

InL3

+

A A

InAL3

K 1.25

(HA = C

H3C

OO

H)

25

1—

K1 9.2+0.2

7

K2 9.2±0.2

K3 7.9±0.2

20

2—

K1 9.40

3.5

K2 8.94

K3 8.58

?

1—

In(H4L)2

6

K7.0

(pH 1.6)

In (H3L) +

K 8.4

(pH 6.0)

?

5.9—

K1 10.51

6.3

InL3 shown to

Tentative

org. phase

species

See text

deoxygenated

Rejected

soins, under

argon

[In(OH) (H3L)21

Rejected

site of complex—

ing speculative

Complex anionic,

stable in pH range

3.5 — 6

.5

14

Bromopyrogallol

red

C19H10O8Br2S

15

Chrome Azurol S

C23H1609C12S

69Pa spectrophotometric

6 4N

spectrophotometric

25

3.0

K1 10.97

25

4.0

4.4±0.1

equil. not

identified.

Complex stable at

pH 3.5 — 5.

5

Re jected

Re jec ted


78Sb Spectrophotometric

Medium

T

Entry

Ligand

Ref. Method

(concn. M)

(°C) pH

log K

Comments

Rating

4-methyl-2—

68W

spectrophotometric

(2 -pyridy1azo)

phenol HL

C12H110N3

2.0 (IlOAc +

OA

c)

3.4% dioxan

Doubtful

UI

0 H

CJi

H

0 0

11

Leucoalizarin-S

C14H907S

H4L

74M

spectrophotometric

?

34—40% EtOH

68G

spectrophotometric

?

25

3.0

K 9.9±0.4

Rejected

16b

17

5-(5—bromo-2—

pyridylazo) -2—

(methylamino) -p-

cresol

18

5—(3,5—dibromo—2—

pyridylazo) —2-

(ethylamino) -p-

cresol

l9a

1—(2-pyridylazo)

-2 -naphthol

(PAN)

19b

1- (2—pyridylazo)

—2—naphthol

(PAN)

20

3,4-dihydroxy-

ben zene—a zo

1'-naphthalene-

suiphonic acid

HL

21

Calgamite

22

Socochrome

Dark Blue

23

4-sulphonaphthol-

(l—azo—l' )

—

2,4—

dioxyben zene

spectrometric,

pH titration

spec tropho tometric

spectropho tone tric

polarography

I 0.06

50% EtOH

spectrophotometric 50%(v/v)

aq.

dioxan

I =

0.2

(NaC1O4)

spectrophotometric 50%(v/v) aq.

dioxan

I =

0.2

(NaC1O4)

spectrophotometric 50%(v/v) aq.

dioxan

I =

0.2

(NaC1O4)

spectrophotoinetric

I =

0.1

T

(°C) pH

log Kn

25

4.0

5.0±0.1

20

K(In(H2L)) 14.31

K(In(H2L)25) 24.63

?

3—

6.62

5

?

2—

6.22

5

?

5.0

K1 17.09

K2 14.87

?

5.0

K

16.48

14.66

20

? K

1 13

.60

K2

32.3

9

Comments

Complex a

nion

ic

Electrolytes cause

pptn. of coloured

complex

Complex stable at

pH 3.0 — 6.

5

TABLE

Entry

l6a

11

continued

Ligand

Xylenol orange

C31H32013N2S

H6L

Ref.

Method

66Db spectrophotometric

Medium

(concn. N)

9

0.l N

aC1O4

9

77Ka

66Gb

66Gb

73T

78 Sb

76D

78 Sb

78 Sb

77P

?

?

?

5.0

5

K 13.05±0.06

K1 12

.19

K2

10.5

7

K[I

nL2]

8.21

Rating

Rejected

Rej

ecte

d

Re j e

c ted

Re j e

c ted

Re j

ec te

d

Rej

ecte

d

Rejected

Re j e

c ted

Rej

ecte

d

Rej

ecte

d

rt

a C) 0 S C

l) rt

a S Cl)

0 0 B

CD

CD

Cl)

0

No errors quoted

No errors quoted

No errors quoted 2+

Form

atio

n of InOH,

In (OH) 2 corrected

TTA

BEHPBPHATNOAT IOADNNSTBP

32.35.

36.38.40.41.42.

Entry3

4

HLMDAHEDTA

EDTAEEDTACDTAHDTADTPA

TironPurpuricacid

5 TAR6 4-COOH-TAR7 PAR

11 Leuco-alizarin-S

12 Kaempferol13 Thoron

15 ChromeAzurol S

16 XylenolOrange

21 Calganite

22 SocochromeDark Blue

4,5-Dihydroxybenzene-l, 3-disulphonic acidN- (4'-Hydroxy-2',6'-dioxo-l',3'-diazin-5'-yl)-5_imino(perhydro-l, 3-diazine-2, 4, 6-trione)4- (2'-Thiazolylazo)-l, 3-hydroxybenzene4- (2-4-Carboxythiazolyazo) -resorcinol1, 3-Dihydroxy-4- (2'-pyridylazo)benzene-(pyridylazoresorcinol)1,2,9, l0-Tetrahydroxyanthracene—3-sulphonate anion

3,5 , 7', 4 '-Tetrahydroxyflavone1- (2'-Arsonophenylazo) -2-hydroxy-naphthalene-3,6-disulphonic acid2",6" — Dichloro - 4'—hydroxy —3,3'—dimethyl — 3" —

sulphofuchsone - 5,5'- dicarboxylic acid5,5 '-Bis -N ,N-bis (carboxymetiiyl) aminomethyl-4'-hydroxy - 3,3'-dimethylfuchsone - 2" -

sulphonic acid3-Uydroxy-4- { (6-hvdroxy-m-tolyl)azo]-l-naphthalenesulphonic acid

—

3-Hydroxy-4-{ (2-hydroxynaphthyl)azoj-l-naphthalenesulphonic acid

36H.3714.

380.4 lMa.

411th.42:4.48K.

48S.49L.5lS.

52H.5 3C.

53S.54C.54Ca.54S.54Sa.54 Sb.

54Sc.

REFERENCES


Abbreviations Used Throughout Tables.

l-(2'-Thienyl)-4,4,4-trifluorobutane-l, 3-dione(thenoyltrifluoroacetone)Bis— (2-ethylhexyl) phosphoric acidN-Benzoy lphenylhydroxylamineTri-n-octylamineTriisooctylamineDinonylnaphthalenesulphonic acidTri-n-butyl phosphate

Names of Polycarboxylic Acids in Table 9.

N-2-Hydroxyethyliminodiace tic acidN'- (2-hydroxyethyl)ethylenediamine-N,N,N'triacetic acidEthylenediarnine-N,N,N' ,N'-tetraacetic acid{(2,2'—Oxydiethylene)dinitrilo]tetraacetic acid(trans—l,2-Cyclohexylenedinitrilo) tetraacetic acid(Hexamethylenedinitrilo) tetraace tic acid{(N-Carboxymethyl-2,2-iminodiethylene)dinitrilo_tetraacetic acid

Proper Names of Ligands in Table 11.

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(1963)

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Part A: Stability Constants of Metal Complexes CRITICAL SURVEY …publications.iupac.org/pac-2007/1983/pdf/5509x1477.pdf · stability constants of indium complexes by ion exchange

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