Chapter 7

Mixed-ligands complexes of In(III) with Succinic acid and

Amino acids

The investigations on mixed-ligands complexes have been

stimulated due to their analytical applications. Mixed-ligands

complexes are formed in solutions containing metal ions with two or

more different ligands. Their formation as intermediates in ligand

displacement reactions as well as in metal ion and enzyme catalysed

reactions and their possible significance for various biological

processes1-10.

A number of reviews have appeared on the stability of mixed-

ligands complexes. The kinetics of ligand interactions, structures,

isomerism and analytical use of certain types of reactions11.

Sankar and Cruck12-13 isolated the mixed [Cu(II)-(Histidine)-

(Threonine)] complexes14 from human serium and they prepared

similar mixed complexes of Cu(II) ion with amino acid at the

Chapter-7 211

physiological pH. The mixed halide complex of Cd(II) and Pb(II) have

been reported by M. Zarigen15, Fridman16, et al. and S.C. Shrivastav17

et al.

Most of the earlier studies on mixed-ligands complexes are of

spectrophotometric measurements18-19. Some have involved

potentiometric measurements using metal ion or oxidation - reduction

electrodes20-28 while the other have made use of data obtained from pH

- titration curves29-39 and solubility measurements.

The mixed-ligands complexes of pyridine and ammonia with

Cd(II) ion have been studied by Nazarora at a glass electrode while

spectrophotometric measurements have been carried out of the Co(II)

complexes with pyridine and anions like chloride, cynate and

thiocynate etc. was done by J. Carbral40 et al. They also studied the

mixed-ligand-complexes of Co(II) with - picoline and anions like

chloride, cynate and thiocynate anions. The hydroxyhalide complexes

of Cd(II) have been reported by K.H.Gayer41 and R.M Hass, M.

Quintin42 and coworkers.

Schaap and McMaster extended the method of DeFord and

Hume for simple complexes to study mixed ligands complexes by

polarography. They applied their method to various mixed-ligands

system successfully and verified the versatility of the method.

Chapter-7 212

The mixed ligands-complex formation by Cd(II) ion with

oxalate ions and ethylenediamine has been studied from solubility

measurements by Fridman43 and coworkers while potentiometric

studies on some complexes are reported by Water44 et al. The Cd(II)-

oxalate-ethylenediamine system has been investigated by other

workers too.

Renu Kulshrestha, Nirupana Sengar and Mukhtar Singh45

studied the mixed-ligands complexes of In(III) with pyridine-

carboxylate ions and thiocycolate, formate ions polarographically. S.L.

Jain46 studied the mixed-ligand complaxes of In(III) with L-Glutamate-

Methionate and L-Glutamate-valinate/L-prolinate systems

Polarographically.

Schaap and McMaster's method has been used by many other

workers47-56 to calculate the formation constants of mixed-ligands

complexes. An attempt has been made to interpert the results on the

basis of statistical probabilities57, steric and electrostatic factors.

Mixed-ligands complexes of Rb and Cs metal salts of same

organic acids with quinaldinic acid N-oxide have been studied by D.

Prakash, A.K. Gupta, S. Kumar and A.K. Yadav58. The mixed-ligands

complexes of Rb and Cs metal salts of some organic acids with 1,10-

Chapter-7 213

phenonthroline have been studied by D. Prakash59, Y.K.P. Yadav.

Birendra Kumar and A.K. Gupta60.

Sudesh Kumar Singh, C.P. Singh Chandel61 studied the stability

constants of Cd(II) complexes with amino acids and pthalate system.

Mahendra Kumar Verma and C.P. Singh Chandel62 studied the mixed

complexes of Cd(II) with citruline and some bicarboxylic acids. S.K.

Singh and C.P.S. Chandel63 studied on mixed-ligands complexes of

lead ion with some amino acids and phthalate at DME. The stability

constants of Cd(II) complexes with pyridine and some amino acids

(glycine and alanine) have been reported by Amit Verma. P.K.S.

Chauhan and R.K. Paliwal64 studied the mixed-ligands complexes of

alkali metal 5-hydroxy-1,4-nepthaquinone with oxygen donor ligands.

R. Chandra65 studied the mixed-ligand complexes of 2-hydroxy-1,4-

nepthaquinone with oxygen donor ligands. The mixed-ligands

complexes of alkaline earth metal, salts of some organic acids with

isonitroso-P-methylacetophenone have been investigated by S.R.

Prasad66. The mixed-ligands complexes of Terbium(III) and

Dyprosium(III) with aminopolycarboxylic acid and amino acids at

different ionic strength have been reported by A. Asthana and

K.Divedi67. D.K. Sharma and Arun Kumar Sinha68 studied the mixed-

ligands complexes of Pb(II) chelates of organic acids with Picolinic

Chapter-7 214

acid and quinaldinic acid. The stability constants of ternary complexes

of uranyl with pyridoxine (vitamine B6) and bicarboxylic acids (malic,

malonic, tartaric and oxalic) have been determined by G. Sharma and

C.P.S. Chandel69. Mixed-ligands complexes of Rb and Cs metal salts

of some organic acids with picolinic acid have been reported by D.

Prakash, A.K. Gupta, R.N. Shukla and A.K. Yadav70 and mixed-

ligands complexes of some transition metal chelates of O-nitrophenol

acid and 8-hydroxy quinoline with quinalidinic acid have been

investigated by D. Prakash, N. Amir, B. Kumar and Eqbal71. Mixed-

ligands complexes of Cd(II) with -Citrulline and bicarboxlic acids

have been carried out polarographically at d.m.e. by M. Kumar and

C.P.S. Chandel72.

Many researchers73-81 have studied mixed-ligands complexes of

alkali metal. Salts of glycine, -alanine, alkaline earth metal chelates of

organic acid, Cu(II) with -picoline, glycolate and lactate and mixed-

ligands complexes of transition metals.

The literature survey reveals that there is insufficient study and

lack of data on the succinic acid, amino acids mixed complexes of

In(III). Moreover mixed-ligands complex of In(III) have not been take

upto a study at large. It has been considered worth while to undertake

the detailed study under constant temperature at 308K. To evaluate

Chapter-7 215

their formation constants by the method developed by W.B. Schaap

and D.L. McMasters has been made to interpret the results on the basis

of statistical probabilities.

Experimental Set-up

The test solutions were prepared in standard measuring flasks of

pyrex glass using conductivity water. The solutions contain 1.0 mM of

In(III) with varying concentration of strong ligands (serine, glycine,

leucine, isoleucine) and fixed concentration of weak ligand (succinic

acid). KNO3 of concentration 0.1M was used as supporting electrolyte

to maintain constant the ionic strength of the solution at 0.1M and

0.002% TritonX-100 was used as maxima suppressor.

A CL-362 polarographic analyser was used. Purified nitrogen

was streamed through the test solution for 10-15 minutes to remove the

dissolved oxygen. The current variation as a function of applied

potential was then plotted to obtain the polarogram. All reagents were

of A.R. grade. A.R. grade KNO3 was used as supporting electrolyte in

all systems of In(III) ion to maintain ionic strength 1.0 at constant

temperature 308K. The capillary of the polarograph is having the

following characteristics.

m = 4.62 mg/sec

t = 3 sec.

Chapter-7 216

RESULTS

The ligands choosen for study were serine, glycine, leucine,

isoleucine, succinic acid. The simple commplexes of In(III) with

serine, glycine, leucine, isoleucine, succinic acid were first investigated

and their overall formation constants were evaluated by DeFord and

Hume's method and verified by Mihailov's method from the cathodic

shift in half-wave potential as a function of ligand concentration.

The following combinations for mixed-ligands complexes of

In(III) were studied.

In(III) with

(a) (i) Serine

(ii) Succinic acid

(b) (i) glycine

(ii) succinic acid

(c) (i) Isoleucine

(ii) Succinic acid

(d) (i) Leucine

(ii) Succinic acid

Chapter-7 217

Overall formation constant values of simple complexes of In(III)

with succinic acid, serine, glycine, leucine, isoleucine are summarised

in Table 7.1.

TABLE 7.1

Formation constants values of In(III) complexes

Complex species 308K

[In(Succinate)]+1 2.046

[In(Succinate)2]-1 2.9634

[In(Succinate)3]-3 3.363

[In(Serinate)]+2 5.218

[In(Serinate)2]+1 5.544

[In(Serinate)3] 7.544

[In(Glycinate)]+2 3.669

[In(Glycinate)2]+1 4.124

[In(Glycinate)3] 5.612

[In(Isoleucine)]+2 2.626

[In(Isoleucine)2]+1 3.511

[In(Isoleucine)3] 5.079

[In(leucine)]+2 2.240

[In(leucine)2]+1 3.351

[In(leucine)3] 4.431

Chapter-7 218

In the case of each ligand, In(III) forms 1:3 highest complex

species. In all the case, the reduction of simple complexes was

diffusion controlled as revealed by straight line plots id vs h1/2eff and

indicates the reduction is quasi-reversible.

(a) The mixed-ligands complexes

In(III)-Succinic acid-serine system

The weaker ligand in this system is succinic acid and two

concentrations of the weaker ligand were kept constant. So as to get the

values of mixed stability constant11 and 12 using the relation.

B = 10 + 11[Y] + 12 [Y]2

The experiments were carried out at two fixed concentration of

succinic acid 0.04M and 0.2M. The displacing ligand was stronger

chelating serine whose concentration was varied to a wide range.

The In(III) ion with succinic acid and serine mixed complexes

reduced quasi-reversible at the dropping mercury electrode with the

involvement of three electrons. The ions reaching the d.m.e. were

solely due to diffusion. The above conclusions were drawn from the

slopes of the log plots of Ed.e. vs [log i/[id-i]] and constancy of id vs

h1/2eff.

Chapter-7 219

The first set of solutions containing 1.0 mM of In(III), 0.04M

fixed succinic acid and sufficient amount of KNO3 to maintain constant

ionic strength with maximum suppressor 0.002%. Triton X-100 were

polarographed at varying concentration of serine at 308K. The

polarogrpahic measurements and derived Fi0(X,Y) function are

recorded in Table 7.2.

In the second set of observations, all other conditions except the

concentration of succinic acid which was now 0.2M fixed, were the

same. The polarograms were again recorded at the same temperature

(308K). Polarographic measurements and derived Fi0 function values at

0.2 M concentration of succinic acid are recorded, Table 7.3.

A cathodic shift in half-wave potential is observed as a function

of serine concentration. The magnitude of the shift in half-wave

potential is greater in presence of succinic acid than obtained for the

simple of In(III)-Serine system. It indicates the formation of mixed-

ligands complex by serine and succinic acid with In(III).

The Schaap and McMaster's method was applied and Fi0

functions as described earlier were calculated from which the values of

A.B.C. and D were obtained by Leden's graphical extrapolation

method.

Chapter-7 220

The values of A,B,C and D at two fixed concentration of

succinic acid were obtained as shown Figs. 7.1 and 7.2 and are


TABLE 7.4

Values of constants of the ternary In(III) complex of (Serine)(Succinic acid) at 308K

Temp. Succinic acid log A log B log C log D

308K0.04M 1.1812 5.246 6.392 7.556

0.2M 2.041 5.440 6.945 7.568According to theory discussed in chapter two, the following

equation are available to determine the formation constants of mixed

ligands complex.

B = 10 + 11[Y] + 12 [Y]2 (i)

C = 20 + 21[Y] (ii)

Equation (i) contains two unknowns. Since two sets of data are

available in Table 7.2 and 7.3 at 308K. Two equations with two

unknowns were simutaneously solved to give log 11 and log 12 for

1:1:1 and 1:1:2 mixed-ligands complexes, respectively. The formation

constant for the 1:2:1 mixed-ligands complex was computed from

equation (ii) and both in experimental values of 'C' give same values

for 21. These 11, 12 and 21 values are given in Table 7.5.

Chapter-7 221

As expected the value of D are found to concede, with that of

30, the observed value of log D and log 30 are in good agreement.

The overall formation constants of mixed [In(III)(ser)succinic

acid] complex at 308K temperature recorded in Table 7.5

TABLE 7.5

The overall formation constants of mixed In(III)-(Serine)(Succinic

acid) complex at 308K.

Metal complex species

[In(Serine)(Succinic acid)] log 11 6.6378

[In(Serine)(Succinic acid)2]-2 log 12 6.7564

[In(Serine)2(Succinic acid)]-1 log 21 7.5985

The stability constant of mixed-ligand complex as calculated on

the basis of statistical probabilities of the formation of [In(X)(Y)],

[In(X)(Y)2]-2 and [In(X)2(Y)]-1 gave the values of log 11, log 12 and

log 21 to be equal to 6.6378, 6.7564 and 7.5985, respectively.

Calculate values of log 12 and log 21 are in close agreement with

those observed but the value of log 11 calculated and observed are not

in well agreement.

The numerical values are log K values for the step indicated in

the scheme-1 where K is the equilibrium constant for that step. The

equilibrium between various species formed in the ternary system have

Chapter-7 222

been shown in the scheme-I. The values of log K for binary system

have been taken from chapter II at 308K. It can be seen from scheme-I

that [In(suc.)]+1 can add to (Ser) more easily than [In(succ)2]+2 to add

(succ) and also that tendency of [In(succ)2]-1 to add (ser) is more than

to ad (succ.). In the same way [In(ser.)2]+1 has greater tendency to add

(succ) than to add (serine).likewise [In(ser)(succ)] can add (ser) more

easily than (succinic) as indicated by the values of equilibrium

constants. From these results it can be concluded that In(III) forms

stable mixed-ligands complexes as compared to single ligand in binary

system.

The schematic representation of all the complex species present

in the system and equilibria amongst them are shown in scheme-1.

Scheme-1 : In(III)-Succinic acid-Serine system at 308K

Chapter-7 223

The tentative structures of these complexes are as follows:

(b) In(III)-Succinic acid-glycine system

The weaker ligand in this system is succinic acid and the two

fixed concentrations were 0.04M and 0.2M. The In(III) ion with

succinic acid and glycine mixed complexes reduce quasi-reversibly at

the dropping mercury electrode with the involvement of 3 electrons.

The ions reaching to the d.m.e. were solely due to diffusion. The above

conclusions were drawn from the slopes of the log plots of Ed.e. vs log

i/[id-i] and constancy of id vs h1/2eff.

Chapter-7 224

All the solutions containing fixed concentrations of In(III) and

0.04M of succinic acid and sufficient KNO3 to maintain constant the

ionic strength and varying concentration of glycine at 308K.

A cathodic shift in half-wave potential is observed as a function

of glycine concentration. The magnitude of the shift in half-wave

potential is greater in presence of glycine than obtained for simple

In(III)-succinc acid system. It indicates the formation of mixed-ligands

complex formation by glycine and succinic acid with In(III) ion. The

Schaap and McMaster Fi0 function as described earlier were calculated

from which the values of A, B, C and D were obtained by Leden's

graphical extrapolation method and are recorded in Table 7.6 and Fig.

7.3.

The experiment was carried out under identical conditions to

obtain the another set of polarographic measurements except the

concentration of succinic acid which was now kept constant at 0.2M.

The values of A, B, C and D at 0.2M fixed concentration of succinic

acid were obtained as shown in Fig. 7.4 and are recorded in Table 7.7.

The values of A, B, C, D at two fixed concentrations of succinic

acid are recorded in Table 7.8.

Chapter-7 225

TABLE 7.8

Values of A, B, C and D for mixed complex of In(III)-Succinic

acid-Glycine system at 308K

Succinic acid

(moles.litre-1)

log A log B log C log D

0.04M 0.146 3.246 4.146 5.59

0.2M 0.531 3.959 4.491 5.602

From the expression of B and C, the overall formation constants

of mixed In(III)-(Succinic acid)(glycine) complex at different

temperatures recorded in Table 7.9

TABLE 7.9

Overall formation constants of mixed In(III)-(Succinic acid)

(glycine) complex at 308K


[In(Succinic acid)(Glycine)] log 11 5.004

[In(Succinic acid)2(Glycine)]-2 log 12 5.5569

[In(Succinic acid)(Glycine)2]-1 log 21 6.2376

Chapter-7 226


in the system and equilibria amongst them are as shown in scheme-2.

The numerical values are logK values where K is equilibrium constant

of the step indicated in the scheme-2.

Scheme-2 : In(III)-Succinic acid-glycine system 308K.


Chapter-7 227

(c) In(III)-Succinic acid-Isoleucine system

The weaker ligand in this system is succinic acid and two fixed

concentration were 0.04M and 0.2M. The slopes of the plots Ed.e. vs log

i/(id-i) are indicating the quasi-reversible nature of reduction. The

direct proportionality of the diffusion current to square root of effective

height of mercury column clearly showed that the reduction involved

three electrons and entirely diffusion controlled. The half-wave

potential values shifted towards more negative direction with the

increases in concentration of isoleucine. It was also observed that the

cathodic shift in half-wave potential was greater in presence of

succinic acid than in their absence. This observation clearly establishes

for mixed-ligands complex formation by succinic acid and isoleucine

with In(III).

Chapter-7 228

All the solutions containing 1 mM In(III). 0.1M KNO3 as

supporting electrolyte, 0.04M fixed succinic acid and 0.002%. Triton

X-100 were polarographed at varying concentrations of isoleucine at

308K in first set of observation.

In the second set of observation, all conditions were the same

except the concentration of succinic acid which was now 0.2M fixed

the polarograms were again recorded at the same temperature 308K.

Polarographic measurements and derived Fi0 functions values at

two concentrations of succinic acid at 308K temperature are recorded

in Tables 7.10 and 7.11. The method of Schaap and McMaster yielded

the values of A, B, C and D which were obtained by graphical

extrapolation Fi0 function as shown in Figs. 7.5 and 7.6 at 308K.

The values of A, B, C and D are recorded at two fixed

concentrations of succinic acid and recorded in Table 7.12 at 308K.

TABLE 7.12

Succinic acid log A log B log C log D

0.04M 0.079 2.906 3.543 5.167

0.2M 0.544 3.839 3.958 5.170

Chapter-7 229

From the expression of B and C the values of 11, 12 and 21

were-calculated by Schaap and McMaster's method. These values

obtained are given in Table 7.13.

TABLE 7.13


(Isoleucine) complex at 308K


[In(Succ.)(Isoleu.)] log 11 3.7924

[In(Succ.)2(Isoleu.)]-2 log 12 4.9802

[In(Succ.)(Isoleu.)2]-1 log 21 5.0840

The numerical values in each step are log K values where K is

the equilibrium constant for each step indicated in the scheme-3. The

equilibria between various formed complex species in the ternary

system have been shown in scheme-3. The values of log K for binary

system have been taken from chapter II. It can be seen from the

scheme [In(succ)]+1 can add to (Isoleu) more easily than [In(isoleu)]+2

to add (succ) and also that tendency of [Ind(Succ)2]-1 to add (isoleu) is

more than to add (succ)-2. In the same way [In(Isoleucine)2]+1 has

Chapter-7 230

greater tendency to add (succ)-2 than to add (isoleu). Like wise

[In(Succ)(isoleu)] and (isoleu)-1 more easily than to add (succ)-2 as

indicated by the values of equilibrium constants. In the same way

[In(Isoleu)2(succ)]-1 add (isoleu)-1 more easily than to add (succ)-2.

From these results it can be concluded that In(III) forms more stable

complexes with mixed ligands as compared to single ligand binary

system.


in the system and the equilibria amongst them are shown in Scheme-3.

Scheme-3 : Succinic acid-isoleucine system at 308K

Chapter-7 231


(d) In(III)-Succinic acid Leucine system

The reduction of In(III) in the presence of leucine and succinic

acid was found to be quasi-reversible involving three electrons and

diffusion controlled at 308K. The above conclusions were drawn from

the slope of the conventional log plots and straight line plots of id vs

h1/2eff.

Chapter-7 232

All the solutions contained In(III) ion concentration equal 1 mM,

0.04M succinic acid ion (fixed) and requisite amount of KNO3 to keep

the ionic strength constant at 1.0 and varying amount of leucine were

polarogrpahed. The polarographic measurements are recorded in Table 7.14.

In other set of measurements, all other conditions were same

except the fixed concentration of succinic acid was changed and a

fixed at 0.2M. The polarographic measurements of second set are


When leucine was added to the complexed (with succinic acid),

In(III) ion, a negative shift Er1/2 which was greater in presence of

succinic acid than in absence of it shows mixed-ligand complex

formation.

The Fi0 function were calculated and by the graphical

extrapolation method as derived by Laden (Figs. 7.7 and 7.8). The

values of A, B, C and D are recorded in Table 7.16.

TABLE 7.16

Values of A, B, C and D, for mixed-lingands complex of In(III)-Succinic acid at 308K

Succinic acid

log A log B log C log D

0.04M 0.0410 2.4860 3.5532 4.4142

0.2M 0.1760 3.227 3.5470 4.4310

Chapter-7 233

The stability constants of mixed-ligand complexes are recorded

in Table 7.17.

TABLE 7.17


(leucine) complex at 308K


[In(Leu)(Succi.)] log 11 1.64018

[In(Leu)(Succi)2]-2 log 12 4.42463

[In(Leu)2(Succi)]-1 log 21 4.5214

The numerical values of log K, where K is equilibrium constant

of the steps indicated in the scheme-4.

On comparison of the tendencies of [(In(leu))]+2 and [In(suc)]+1

to add leucine, one finds that leucine has greater tendency to add to

[In(succ)]+1 than to [In(leu)]+2 showing thereby that mixed-ligand

complex formation is favoured. The tendency of [In(succ)(leu)] to add

leucine is more than to add succinic acid, which shows that leucine is

stronger ligand than succinic acid which is seen from other

observations and from the electronic structures of the two ligands.

Chapter-7 234

The stronger complexing tendency of [Leu] than of (suc) may

also be concluded from the equilibrium constants of several steps in the

Scheme-4.


in the system and equilibria amongst these are shown in scheme-4.

Scheme-4 : In(III)-Succinic acid-leucine system at 308K


Chapter-7 235

DISCUSSION

The values of stability constants for mixed-ligands complex are

greater than the stability constants for simple metal ligand system.

Values of stability constant for mixed-ligand complexes of

In(III)-succinic acid-amino acids are compiled in table 7.18.

TABLE 7.18

Stability constants of mixed-ligands complexes of In(III)

Ligands log11 log12 log21

Succinic acid-Serine 6.6378 6.7564 7.564

Succinic acid-Glycine 5.004 5.5969 6.2376

Succinic acid-Isoleucine 3.7924 4.9802 5.0840

Succinic acid-Leucine 1.64018 4.42468 4.5214

Chapter-7 236

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Chapter 7

Documents

mixed ligands complexes

mixedligands complexes

coii complexes

complexes of coii

simple complexes

various mixedligands

formation constants

different ligands