M(CO)2(NO)(L-L) moiety. The remarkahle dif-ference in the regions of C-O bands (",150 em-I) ofnitrosylated derivatives and their parent M(CO)a(L-L)(CsH6N) compounds is probably due to thereplacement of pyridine molecule by NO in theparent compound. A strong band around 1660cm-1 was also observed which may be attributedto terminal NO stretching vibrations'', The positionof this band indicates" the nature of bonding arisingfrom prior transfer of the odd electron from NO tothe metal followed by lone pair donation of NO+.Bands attributable to bridging CO or bridging NOgroups are absent in the IR spectra. This spectraldata along with non-ionic nature and diamagneticbehaviour of complexes in magnetic field suggest sa dinuclear structure for nitrosylated complexesin which both M(CO)2(NO)(L-L) moieties are solelylinked by a M-M bond in such a way that groupsaround one metal atom are effectively trans to thecorresponding groups around the other metal atom.Nitrosyl groups are colin ear with M-M bond andcarbonyl groups are arranged in a configuration ofC2" symmetry. Appearance of only two C-O bandsis indeed due to the expected IR-active (Au+Bu)stretching modes. Except for minor variations,the nature and region of IR bands resemble closelythose of the dirneric complex [Mo(CO)2(NO) (2,2'-bipyi], . prepared earlier! by the action of nitricoxide on carbonyl bridged complex [MO(CO)3(2,2'-bipy)J2'

All experiments were carried out under an inertatmosphere of dry nitrogen. M(CO)3(L-L)(CsHsN)complexes were prepared by established methodss-",

Author is indebted to Dr P. P. Singh, ChemistryDepartment, M.L.K. College, Balrampur, for hisconstructive suggestions.

References1. PATHAK, D. N., Transition Met. Chem. (in press).2. HOUK, L. W. & DOBSON, G. R, Inorg, Chem., 5 (1966),

2119.3. JOHNSON, B. F. G. & MCCLEVERTY, J. A., Progress in

inorganic' chemistry, Vol. 7. edited by F. A. Cotton(Interscience, New York), 1966, 277.

4. LINDNER, E., BEHRENS, H. & LEHNERT, G., Z. Natur-[orscli., B25 (1970), 104.

5. HOUK, L. W. & DOBSON, G. R, J. chem, Soc., (1966),317.

Stabilities of Mixed Ligand Chelates ofCadmium- Thiocyanate- Maleate/I taconate/

Adipate

P. D. JADHAVt & R A. BHOBE*

Department of Chemistry, Marathwada UniversityAurangabad 431004

Received 29 April 1978; revised 3 July 1978accepted 6 September 1978

The mixed ligand complex formation by Cd(II)with some dicarboxylic acids (maleate. itaconate andadipate) has been investigated polarographically at

tPresent address: Regional Research Laboratory,M.P. & I.C. Division, Hyderabad 500009.

(

N.O T E S

250 ± 0.50 and JI. = 2'5M (KNOs) in aqueous medium.The reduction of all the three systems exhibits atwo-electron reversible diffusion-controlled. wave.Evidence is obtained for the formation of mixed ligandchelates having 1: 1 : 1. 1 : 2; 1. 1: 1 : 2 ratios of Cd(II) :maleate: SCN. Cd(II): itaconate: SCN and Cd(II):adipate: SCN respectively. The absence of thecomplexes [Cd(maleate)(SCN)2]2- and [Cd(itaconate)3-(SCN)]'- is inferred from the negative values of theirstability constants.

THE stability constants of the. mixed ligandcomplexes of Cd(II) with dicarboxylic acids

have been already reported from this laboratory+-.The enhancement in the stabilities of these mixedcomplexes were interpreted in terms of electrostaticeffects and possibility of simultaneous -e-bondingbetween the metal ion and ligands. The presentstudy is in continuation of our earlier work="on mixed ligand complexes of various dicarboxylicacids and inorganic anions with Cd(II). The di-carboxylate anions chosen are maleate (MEL),itaconate (ITA) and adipate (ADPT) and the thio-cyanate is chosen as the inorganic anion.

All the chemicals used here were of AR qualityand the solutions were prepared in an air-free con-ductivity water. Potassium maleate, potassiumitaconate, potassium adipate and potassium thio-cyanate were used as complexing agents at pH 7·0.The concentration of stock solution of Cd(U) waschecked complexometrically by EDTA titration.

Experiments were performed with deaerated1 111M cadmium (II) solution. Polarographic waveswere recorded at 25° using a Cambridge pen-record-ing type polarograph with a saturated calomelelectrode as reference electrode. The droppingmercury electrode had the characteristics: t =3·33 see, in 0'5M KCI (open circuit); m = 1·75mg/sec; m2/3 X t1/6 = 1·77 mg2/3 sec-t. The half-wave potentials '\rere corrected for iR drop acrossthe cell and were obtained from the log plots.

Though the studies of the complexation ofmaleates, itaconate, adipate and thiocyanate ionsindividually with Cd(II) have been carried out bypolarographic method1,3,6-12, the systems were re-investigated as Cd(II)-meleate6•7, Cdfl Ij-itaconates,Cd(II)-adipate8•9 and Cd(II)-thiocyanate1.10,1l witha view to obtaining their stabilities under identicalexperimental conditions mai.ntained for mixedsystems studied here. The reduction of Cd(II)in the presence of these ligands was found to bereversible and di.ffusion-controlled. In the studiesinvolving individual ligands, the usual procedurewas followed.

The experimental data and Fi[X] values for thesingle ligand systems have not been included here,for the sake of brevity but only the results obtainedby DeFord and Hume treatment= are given below:

Cd(II)-maleate complexes: l)g ~1 = 1·90 ± 0·05;log ~2= 2·30±0·04; and log ~3= 3·32±0·05.

Cd(II) -itaconate complexes: log ~l = 1·73±0·05; log ~2 = 3·36 ± 0·09; and log ~3= 3·20 ± 0·05.

Cd(II)-adi.pate complexes: log ~l = 1·41 ± 0·05;log ~2= 2·11 ± 0·07; and log ~3= 3·16 ± 0·04.

Cd(II) -thiocyanate complexes : log ~1 = 1·11 ±0·06; log ~2= 1·85 ± 0·03 and log ~3= 1-18 ± 0·08.

311

INDIAN J. CHEM., VOL. 17A, MARCH 1979

TABLE 1 - MIXED FORMATIONCONSTANTS

[Temp. 298K; [L = 2·5M (KN03)]

System log A log B log C log D log ~ll log ~12 log ~21 log ~30

Cd(II)-MEL-SCN1·00 2·18±0·06 2·57±0·06 3·68±0·02 2-59 2·75 = 3'43(a) 0'16M [SCN] -ve

(b) 0·40M [SCN] 1-47 2-36±0'03 2·70±0·04 3·46±0·02 (2'34) (2'73)Cd(II)-ITA-SCN

1'98±0'02 2·18±0·06 ,> 3'20±0'04 . 2·30 2·74 = 3'20(a) 0'16M [SCN] 0·95 -ve(b) 0·40M [SCN] 1'51 2'28±0'02 2·30±0·04 3·39±0·06 \2'29) (2'61)Cd(II)-ADPT-SCN

0'90 1'85±0'03 2·30±0·02 3·08±0·07 2·34 2·65 2'54 = 3·15(a) 0·1IiM [SCN](b) 0'40M [SCN] 1·47 2'20±0'03 2'47±0'03 3'38±0'05 (2'19) (2·60) (2-53)

Values in parentheses are theoretically calculated according to the procedure by Watters et al.15•

I t will be seen that these values are in closeagreement with the results obtained by otherworkers1,2,6-11, allowing for the different experi-mental set up in each case.

The observed order with respect to stabilityconstants of single ligand system, i.e. ~icd-MEL >

_~i:d-ITA >~i:d-ADPT >~icd-SCN' can be explained asfollows. In the case of maleate, fairly stronglydeveloped catiophilic property is seen, probablydue to -CH=CH- group and mutual effect ~fthe two carboxylic groups.' The decrease of thistendency in itaconate and adipate is possibly dueto the presence of -CH2=C- group in the firstand methylene group in the latter and al~o due toa greater strain in Cd(II)-itaconate and. still greaterstrain in the Cd(II)-adipate chelate nngs.

Bonding mainly occurs through both the carbo~y-lr te groups in maleic, itaconic and adipic acidswhile thiocyanate is an ambident anion. Cadmi~mhas same affinity for the both donor atoms of th.1O-cyanate ion, the softer S is preferred by soft acidssuch as Cd(II) , Cu(I), Ag(II) , etc. and the harderN preferred by hard acids such as Fe(III), Co(III),U02(II) etc.P, It can, therefore, be safely inferredthat cadmium thiocyanate binding occurs throughsulphur atom.

Mixed ligand systems: Cd(IJ)-MEL-SCN, Cd(IJ)-IT A-SCN and Cd(IJ)-ADPT-SCN - The concen-tra1ion of maleate, itaconate and adipate ions werevaried while that of thiocyanate ions was keptc onstant at two different values such that at thesetwo values of SCN concentration, 1: 1 and 1: 2complexes predominated for the simple Cd(II)-thiocyanate complex.

Solutions containing 1 X 10-3M Cd(II) , 0·16Mthiocyanate and' requisite amount of KN03 at'pH7·0 and T = 298°K were polarographed at vanousmaleate, itaconate and adipate ion concentrationsfor Cd(II)-MEL-SCN, Cd(II)-ITA-SCN and Cd(II)-ADPT-SCN systems respectively. The processeswere repeated under identical conditions, keepingthiocyanate ion concentration constant at 0·40M,for all the other systems.

In each case, the plot of Ed.e. versus log (i/id-i)was found to be linear with a slope of 30 ± 1 mVindicating that the reduction is reversible involvingtwo electrons. The direct proportionality ofthe diffusion current to square root of the effective

312

{

height of mercury head showed that the reductionis entirely diffusion-controlled.

As the concentrations of maleate, itaconate andadipate ions were increased, the half-wave potentialshifted to more negative values at each constantthiocyanate concentration. The shift in El values,observed in the ternary systems is greater than thosefor the corresponding binary systems, conclusivelyproving the presence of mixed ligand complexes.

Here again, the mean values of coefficient Dwhich coincides with stability constant ~30 for [Cd(MEL) 3]4-, [Cd (ITAla]4- and [Cd(ADPTla]4- com-plexes in all the three systems support the aboveconclusion. Here log ~30= 3·43, 3·20 and 3·15respectively are the mean values for log Dare 3·57,3·29, 3·23 respectively.

The values of the mixed formation constants(A, B, C and D) obtained with the help of Schaapand McMasters method-s for all the systems aregiven in Table 1. From these values, the stabilityconstants (log ~11'log ~12and log ~.I) were calculatedfor all mixed lijand complexes existing in thesolution and the values are recorded in Table 1.It may be pointed out that the negative valuesfor ~12 and ~21 show the absence of the complexes[Cd(ITA)(SCN)2J2- and [Cd(MEL)2(SCN)]3- in solu-tion. The values in the parentheses in Table 1 arethe theoret.ically predicted stability constantsaccording to the procedure suggested by Watterset al.15•

It is seen from the data in Table 1 that theexperimentally observed values are higher than thepredicted ones. Such increase may be attributedto some mutual interaction between the differentkinds of ligands in mixed complexes. It couldbe concluded from the data (Table 1) that thestability constants of the mixed ligand complexesdecrease as the size of the organic ligand increases(MEL>ITA>ADPT). This gradual decrease inthe stability constants may be due to steric hindrance.

The authors wish to thank Prof. K. A. Thakarfor his constant encouragement.

References

1. JADHAV, P. D., BlDKAR, R. G., DHULEY, D. G. &BHOBE, R. A., J. Indian chem, Soc., 53 (1976), 451.

2. BlDKAR,R. G., DHULEY,D. G. & BHOBE,R. A., IndianJ. Chem., 15A (1977), 63.

3. JADHAV, P. D. & BHOBE, R. A., Indian J. cu«; 15A(1977), 760.

4. JADHAV, P. D. & BHOBE, R. A., Curro Sci., 46 (1977), 339.5. J.ADHAV, P. D. & BHOBE, R. A., J. inorg. nucl, cs-«;

39 (1977), 2290.6. NOZAKI, T., MISE, T. & HIGAKI, K., Chem, A bstr. , 68

117598.7. KHURANA, S. C. & GUPTA, C. M., J. inorg. nucl. Chem.,

35 (1973), 269.8. YASUDA, M., YAMASAKI, K. & OHTAKI, H., Bull. chem,

Soc. Japan, ·33 (1960), 1067.9. BIDKAR, R. G., Polarographic studies in metal comptixes,

Ph.D. thesis, Marathwada University, 1976.10. DHOOT, L. N. & KARMALKAR, P. K., Vikaram Univ. J.,

4 (1960), 81.11. SENISE, P. & NEVAS DE ALMEIDE, E. F., J. Am. chem,

Soc., 83 (1961), 4146.12. DEFoRD, D. D. & HUME, D. N., J. Am. chem, Soc., 73

(1951), 5321.13. PEARSON, R. G., J. Am. chem, Suc., 82 (1963), 3533.14. SCHAAP, W. B. & McMASTERS, D. L., J. Am. chem, Soc.,

83 (1961), 4699.15. WATTERS, J. 1. & DEWITT, R. L., 1. Am. chem. Soc.,

82 (1960), 1333.

Stability Constants of Cu(II), Zn(II), Ni(II),Co(II) & Mn(II) Comple:x;es of Some

Sulpha Drugs

KEEMTI LAL

Chemistry Department, D.N. College, Meerut 250002

Received 24 June 1978; accepted 29 July 1978

Stability constants of Cu(II), Zn(II), Ni(II), Co(II)and Mn(lI) complexes with sulphapyridine, sulpha-dimethoxine, sulphamethoxypyridazine and sulpha-phenazole have been determined potentiometrically at27° and 0·1, 0·05 and O'OlM ionic strengths (NaClO.) bythe method of Irving and Rossotti, in 50% (v/v) ethanolmedium. The thermodynamic formation constantshave been obtained by extrapolating the values atvarious ionic strengths to zero ionic strength.

ALTHOUGH studies on the chelating propertiesof some sulpha drugs have been reported in the

literature=+, no work has been done on theprotonation and formation constants of the metalcomplexes of sulphapyridine (Spy), sulphadimeth-oxine (Sdi) , sulphamethoxypyridazine (Sme) andsulphaphenazole (Sph). In the present note, theprotonation constants of Spy, Sdi, Sme and Sph,and stability constants of their complexes withCu(II), Zn(II), Ni(II), Co(II) and Mn(II) have beendetermined in 50% (vJv) ethanol medium at 27°and various ionic strengths, 0·1, 0·05 and O·OIM(NaCl04), by the method of Irving and Rossott i",The thermodynamic formation constant and freeenergy change (llGO) have also been calcul itcd.

The sulphadrugs (pure chemicals) were used assuch. All the metal ions solutions were preparedfrom the corresponding sulphates (BDH, AR).Sodium hydroxide and perchloric acid were standar-dized by usual methods. Chemically pure sodiumperchlorate was used to keep. the ionic strengthconstant.

Potentiometric tit rations were carried out asreported earlier", The following mixtures (total

(

NOTES

volume 40 ml, ionic strength adjusted with 1MNaCl04) in 50% (vJv) ethanol medium were titratedpotentiometrically ag-ainst standard O·OSM NaOH.-

(i) 2·0 ml HCl04 (0·05M),(ii) (i) + 10·0 ml sulphadrug solution (O·OIM),(iii) (ii)+2·5 ml metal ion solution (0·008M).In all the cases' correction for change in volume

occurring during the fltrations due to the additionof sodium hydroxide was made. The hydrogen IOnconcentration in a mixed non-aqueous media is givenby the following relationshipt":

-log [H+] = B+ log UH

where B is the pH -meter reading, log UH is thePH correction factor for a fixed composition. Thevalue of U H was obtained from the differencebetween the observed pH value 'B' and thetheoretical value of -log [H+J.

The value of log UH at a fixed temperaturecan be obtained for any ionic strength from theexpression:

log UH = log U~ + log Y ±

where Y ± is the activity coefficient and log U~ isthe correction factor independent of ionic strength,i.e. correction at zero ionic strength in the solventunder consideration. The values of log UHand·log U~ are found to be 0·18 and 0·94 respectivelyfor 50% (v/v) ethanol at 27°. The value oflog UH increases with increase in Y ± .

Formation functions nH, nand pL were calcu-lated using the standard expressions" from thetitration curves for (i), (ii) and (iii).

The pK values of the Iigands at different ionicstrengths were evaluated by plotting log nH /(I-nH)versus pH when linear plots of intercept equal toPK~ 2nd slope equal to 1 were obtained. Thevalues of proton-ligand stability constants are givenin Table 1. The order of log K~ values for thesesulpha drugs is Spyc-Sdio-Smec-Sph. Log K~ valuefor sulphanilamide (H2N,C6H4.S02NH2) is reportedto be 11·2 (ref. 10). The lower values of log K~for the present sulpha drugs may be due to thesubstitution of the electron attracting groups inplace of the proton in -S02NH2 grouping.

The n values were plotted against correspondingpL values to get formation curves for the metalcomplexation equilibria. The maxsmum value ofn was about 1·7 for the systems under investigation.The values of log K) and log K2 were calculatedusing the half-integral method of Irving and Ros-sotti", The values are reported in Table 1. Theorder of stabilities of bivalent metal complexeswith the present drugs is: Cuc-Zn c-Ni c-Coc-Mn.This order is in agreement with Irving-Williamsorder of stability of complexes with bivalent metalions of 3d-seriesll.

It may be observed from Table 1 that the valueof stability constant increases with the decrease :in the ionic strength. This is in agreement with thefindings of Debyev.

The thermodynamic formation constants (Table 2)were obtained by extrapolation of the overallstability constants to zero ionic strength (fL) in theplot of log ~2 versus yfJ.. The total free energy

313