Indian Journal of ChemistryVol. 14A, August 1976, pp.
592-595
Mixed Metal & Polynuclear Complexes in Ti
(IV)-Cu(lI)-Tartrate Systems. P. BISWAS. T. S. KRISHNAMOORTHY &
CH. VENKATESWARLU
Analytical Chemistry Division. Bhabha Atomic Research Centre.
Bombay 400085
Received 13 November 1975; accepted 15 December 1975
A systematic study of Ti-Cu-Tart system with complementary
tristimulus colorimetry, Job'sand molar ratio methods reveals the
formation of Ti2CuTart, TiCuTart, TiCu2 Tart, Ti2Tart andCu.Tart
complexes. The maximum pH up to which the mixed metal complexes
remain in solutionincreases with decrease of Ti(IV) and increase of
Cu(I1) in the complex. TiCu2Tart and Cu.Tart
exhibit a tendency to add on hydroxyl groups with increase of pH
above 7.
MIXED metal complexes (mmc) are relativelyless investigated than
the mixed ligand ones.Amongst the ligands favouring the formationof
rnrnc, hydroxy carboxylic acids>" are receivinggreater attention
in the last decade and a half. Themetal i ons studied are mostly
di- and trivalent,except for a mention of tetravalent thorium",
Thispaper describes the spectrophotometric study ofmixed metal
tartrates (mmt) and polynuclear tar-trates involving Ti(IV), Cu(II)
and tartrate (Tart).
Materials and MethodsCopper solution (0,2211) was prepared by
dissolving
CuS04.5HzO (BDH, Analar) in acidified water.Titanium solution,
other reagents and instrumentsused were the same as described
earlier".
As complex formation is slow, the PH of the mixedsolutions were
initially adjusted to the.desired valueand readjusted after leaving
the solutions overnight.(During complexation a decrease of pH of
about aunit was observed.) The volumes were made upand the
absorbance values measured with 5 ern cells.
Complementary tristimulus colorimetric (CTSC)analysis- of
systems was carried out, dividing thespectra into three regions,
viz. 600-750 nm (u = ~Amm), 775-925 nm (v) and 950-1100 nm (w).
Varia-
tion of Q••(= u ), as a function of PH is pre-l-£+V+W
sented, as the other two are indicating the
sametransformations.
Results and DiscussionMixed metal tartrates - Cu(U)Tart system
has
been studied in the PH range of 4·0-9·0 by severalworkers--".
Formation of 1: 1 and 1: 2 as well aspolynuclear complexes, with
and without associatedhydroxyls are reported. In the present
studies,mixtures of equimolar Ti and Cu (4'Ox 10-3M) withTart (2·0
X 10-2211) at PH 8·0 indicated the formationof mmt on keeping them
warm for 6 hr. The bluecolour of cupric tartrate complexes changes
to green.As the molarity of Tart was reduced to that of Ti,mmt
formation was observed at a lower pH (6·0)and temperature (28°).
However, it takes a fewhours to come to equilibrium as mentioned
earlier.Then spectra of mixtures of equimolar solutions
592
(Cu-Tart and Ti-Cu-Tart) at PH values of 3·0 to10·0 were scanned
against corresponding Tart blanks.Those at pH 9·0 are gi"en in Fig.
1 (curves 1 and 2).
UJUZ
BISWAS et al.: MIXED l\fETAL & POLYNUCLEAR COMPLEXES
0.7
co 0.6."l"-
I/) 0.5w>a:::>u
:Ja:: 0.1,00
IL
0.6 0.3
0.5 0.2
8 : = ::0.4 01 703 0~~~~~~~~~~~~~~-7~~7-~~~ __ ~
3 4 5 6 7 8 9 10 11 pHo 0.2 0.4 0.6 0.8 10 1.2 1.4 1.6 18 2.0
MOLE RATIO FOR
CURVES 7 & 8
Fig -,2 - CTSC curves [curves 1. 2, 4 and 5: same concentrations
as in Fig. 1]
Curve GCl x 103M
3678
4·02·04·0
Varying
The CTSC analysis showed the divergence of thecurve of the
ternary mixture (curve 2, Fig. 2) fromthat of the bnary one (curve
1). The mmt appearsto start forming around PH 4 and is complete in
thePH range 6-10. At higher pH, precipitation occurs.From a
comparison of a similar curve (curve 3) of aternary mixture with a
higher concentration of Tart(= 2!XCM) it is inferred that initially
mmt andbinary Cu- Tart complex form simultaneously upto pH 8·0 and
that the binary complex thereafter
. transforms into mmt.Molar ratio method was applied at PlI 9·0
taking
constant Ti-Tart and Cu-Tart and varying Cu and Ticoncentrations
respectively (curves 1 and 2, Fig. 3).Curve 1 exhibits a break at
Cu/Ti = 0,5, andcurve 2 at Ti ICu of 0·5 an 1 1·0. In both the
cases,precipitation occurs when the ratio exceeds 2·0.This reveals
the formation of strong complexes withcompositions of 2: 1, 1:1 and
1':2 with respect tothe metal ions. To know the pH range in
whichthe first and third of these mmts are forming,mixtures of Ti ,
Cu and Tart in 2:1:1 and 1:2:1 molarratios were prepared at
different pH values andtheir spectra scanned against Tart blank.
Thoseat pH 9 are included in Fig. 1 (curves 3 and 4). TheCTSC plots
are included in Fig. 2 (curves 6 and 4).These mmts also start
forming around PH 4.Formation of the one with excess titanium
appearsto be complete by PH 7, with no further changeup to pH 9.
Above this PH, precipitation occurs.Formation of mmt with excess
Cu(II) is nearlycomplete' by PH 7 but there appears to be a
further
GTi x103M GTart X 103k!
4·04·0
Varying4·0
10·02·04·04·0
change 11p to PH 11. Above this,pH,precipitationoccurs. ' .
The compositions of mmts with respect to titaniumand copper at
pH 9 were further 'elucidated byapplying the continuous var iat ion
Tc.v.] method indifferent ways. In one case concentrations ofTiand
Cu were continuously varied, keeping that ofTart constant. The
curve obtained at 1000 nmis given in Fig. 4 (curve 1). Since the
breaks inmolar ratio method indicate. a high degree of forma-tion
of complexes, the compositions of the three mmtswith respect to the
metal ions are inferred from theXmax values as well as breaks in
the c.v, curves to be2: 1, 1: 1 and 1; 2. These are in agreement
with thecompositions obtained by molar ratio method. Thesame
compositions can be inferred from the curvesat other wavelengths,
In the other method, con-centrations of titanium and copper were
continuouslyvaried, keeping that of Tart as a constant multipleof
Ccu. Curve 2 (Fig. 4) exhibits an Xmax around0·55 with a break
around 0·3. Solutions beyond0·67 were turbid. This can be taken as
furthersupport to the three compositions arrived at earlieras the
degree of formation of complexes is high. Ifa single highly
dissociating mmt were to formpredominantly Xmax is expected at 0·33
and 0·25 for1:1:1 and 1:2:1 complexes respectively".
The composition with respect to tartrate in thethree cases is
inferred indirectly to be one mole permole of mmt from the minimum
amount requiredto form the complexes, as has been done earlier
byPetit-Ramel et al:".
593
BISWAS el ai.: MIXED METAL & POLYNUCLEAR COMPLEXES
11·0 fall in another straight line, showing that twoabsorbing
species are involved in each of the twotransformations. Taking into
consideration the re-sults of molar ratio method at PH 7 and 9, it
is con-cluded that Ti.Cug.Tart directly forms from Cu~+in the pH
region 4-7 and this mmt changes overto another with the same
composition with respectto the three reactants but differing in the
numberof hydroxyls associated with it in the PH region7-11.
When AmjAlooo was plotted against Aeoo/A1OOOin the above case
(curve 2, Fig. 5) points corres-ponding to PH 4-7 fall in a
straight line, but thosecorresponding to pH 7 to 11 cluster around.
Thelatter is not due to the formation of the sameabsorbing species
but is due to the superimposablespectra of the two species in the
wavelength regionof 725-1100 nm. A similar plot (curve 3, Fig. 5)of
AmfAlooo against A6oofAIOOO brings out thedifference in the slopes
of the two linear portions.In addition, it clearly shows that the
point corre-sponding to pH 7 deviates from either straight
line.This may be attributed to the presence of all thethree
absorbing species, the TiCu2Tart being thepredominant one. On
either side, only two ab-sorbing species are involved.
The spectral data of mixtures prepared for molarratio method at
PH 9 were subjected to CTSCanalysis. Variation of Q•• as a function
of TijCuand Cuj'T! ratios are included ill Fig. 2 (curves 7 and8).
The one in which Ti was varied shows the trans-formation of
Cu'I'art-e-TiCu2Tart-+ TiCuTart-+ Ti2CuTart, while the other shows
TiTart-e- TiCuTart-+TiCu2Tart. The transformation of TiCuTart
toTiCu2Tart, when Cu was varied, is clear in theCTSG plot, while it
is not in molar ratio method.The formation of TizCuTart is
indicated in the molarratio method but not in the CTSC plot. From
thisit is apparent that transformations occurring whenone reactant
is varied can also be studied by theCTSC analysis of the spectral
data.
It may be pointed out that the maximum pH atwhich an mmt is
stable (without precipitation) in-creases with decrease of number
of moles of titaniumand increase of number of moles of copper.
Binary polynuclear complexes - In view of thestability of mmts
with one Tart and three metalions (two of one metal and one of the
other), experi-ments were carried out at PH 7 with mixtures of3:1
and 2:1 of metal to tartrate in the two binarysystems.
Precipitation was observed in the mixtureswith 3:1 ratio, while the
others with 2:1 ratio wereclear even after 24 hr. Since the binary
system withtitanium is colourless, further experiments werecarried
out on Cu-Tart system. Spectra of mixtures
of Cu and Tart (2:1) at different PH values from 3to 11 were
scanned, With increase of PH up to 9,the "max shifts from 800 to
650nm and remains steadybeyond. With increase in PH, the
absorbanceincreases at 600 nm and decreases at 1100 nm. Thespectrum
at PH 9 is shown in Fig. 1 (curve 5). Onanalysing these data by
CTSC (curve 5, Fig. 2), twotransformations are observed, one in the
pH region4-7 and another between PH 7 and 9. To knowthe composition
of the species forming at PH 9, molarratio method was applied,
adding varying amountsof Cu to constant Tart. Curve 4 in Fig. 3 at
900 nmreveals the formation of 1:1 and 2: 1 complexesdepending on
the relative amounts of copper.When job's method was applied around
PH 5, theformation of similar 1:1 (curve 3, Fig. 4) and 2:1(curve
4) complexes is revealed. From this, thefirst transformation in the
CTSC plot appears tocorrespond to the formation of 2:1 complex
frommetal. The second transformation is ascribed tohydroxylation of
the 2: 1 complex with increase inpH. Further confirmation of the
direct formationof 2: 1 complex from metal ion in the PH region
4-6was obtained from the Coleman et al.'s analysis,(curve 4, Fig.
5), which showed the presence of onlytwo absorbing species.
A comparison of spectra in Fig. 1 indicates thatformation of mmt
shifts the "max of the Cu-Tartsystem to higher values. In the
binary Cu-Tartas well as ternary complexes, there is a decrease
of.\max with increase of copper content.
AcknowledgementThe authors thank Dr M. Sankar Das for his
interest in the work.
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