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

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(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:".

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INDIAN J. CHEM., VOL. HA, AUGUST 1976

U.IUZ

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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