Bhobe, R. A.

Bidkar, R. G.

Dhuley, D. G.

English

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NOTESTABLE 1- VALUES OF El AND THE SLOPESOF THEPLOTSOF Ede VERSUSLOG [i/(id-i)][Cd(II) = l~mM; fL = 1·0M (KNO.);temp. 25°±0'5°;-(El)' = 0,5850V]± O·lt, log ~02 =2·25± 0·12and log ~08 =3,44+0,04. ' l",-In the mixedligand system,the concentrationsof phthalateionwereconstantat 0'08M and0·16Mbecauseat theseconcentration.s1: 1and1:2 Cd(II)-phthalatecomplexspecieswerefoundto be pre-dominant.In thefirstset,thesolutions((.Co =l'OM) contain-ing 1 mM Cd(II), 0·08M potassiumphthalateanddifferentconcentrationsof oxalate were polaTo-graphed. The sameprocedurewasadoptedin thesecondset in which phthalateion concentrationwaskeptconstantat 0·16M.In all the systems,a well-definedand diffusion-controlledsingle wave was observed.The linearrelationshipbetweenEde VS log ij(id-i) with slopevaluesin therangeof 30-33mV indicateda rever-siblereductioninvolvingtwo electrOIJs.The valuesof -(EI/2)e and the slopesat .thesetwo concentrationsof phthalateions are given inTablES1 and 2.Theshift in half-wavepotentialof Cd(II) in thepresenceof the mixture of phthalateand oxalateIons is greaterthan that of in oxalateion alone.This suggeststhe formation of Cd(II)-oxalate-phthalatemixedcomplexes.O'OM0'08M[phthalate][phthalate)0·020·6180·63000' 61530·00·04, 338 42, 9066425, 857, 89 5·1052567 910 7·3,27 813· 9 947 70 651TABLE 2 - VALUES OF El AND THE SLOPESOF THEPLOTSOF EdeVERSUSLOG i/(id-i)[Cd(II) = 1 mM; IL = 1·0M (KNOa), temp. 25°±0·5°,-(El)s = 0,5850V][Ox]-El (vs SCE) atlog 1m/IeSlopeM-------------- (mY)O'OM16 ]4·' 789,413. 2221 3'1-- -PolarographicStudyofMixed Ligand Complexes:Cd(1I)-Oxalate-PhthalateSystemR. G. BIDKAR, D. G. DHULEY & R. A. BHOBEDepartmentof Chemistry,MarathwadaUniversityAurangabad431002Received25 Septembey1975;accepted24 May 1976Themixedli~andcomplexationof oxalate(Ox)andphthalateionswithCd(II)hasbeenstudiedpolaroli\ra-phicaliyin aqueousmediumat 25°±0·5° and Ii =l·OM (KNOa). Theformationofthreecomplexspecies[Cd(Ox)(phthalate)]a-,[Cd(OxMphthalate)]&-and[Cd(Ox)(phthalate)a]&-is observed.By applyin~Schaapand McMasterstreatmenthe stabilityconstantsofthesecomplexesarefoundto belo~Pll=3·75,lo~Pal=5'02andlogP13 = 3·89respectively.Thecomplexationconstantsofthesespecieswerealsoevaluatedfol1owin~theproceduresu~~estedby Watters.IN recentyearspolarographictechniquehasreceivedconsiderableattentionin the study of mixt:-dligandcomplexesafter the notablework of Schaapand McMasters1.The presentneteis in continua-tion of an earlierpublication2fromour laboratoriEsdescribingthepolarographicdeterminationof stabi-lity constantsof mixedligandcomplexesof oxalateandsalicylateionswith Cd(II).Cadmium nitrate was of BDH (AR) grade.Oxalate(Ox) and phthalicacidswereused in theformof their potassiumsalts,whichwererecrystal-lizedfromdoublydistilledwater. All the solutionswere preparedin a doubly distilled water. Thepolarogramsof deaeratedsolutionswererecordedat 25°±0'5° and !J. = l'OM (KNOs) with the helpof a CambridgePen recordingpolarograph.Thed.m.e.hadthefollowingcharacteristics:t = 3·2 see,in O'lM (opencircuit); and m = 1'97mg sec-l.SCE used as a referenceelectrodehad negligiblecell resistance.Half-wave potential values wereobtainedfrom log plots. The polarogramswererecordedat a fixedconcentrationof Cd(II) (1 mM)and varyingconcentrationof oxalate (0'02-0'5M)and phthalate(0·02-1·OM).The conditionsmaintainedfor Cd(II)-oxalate-phthalate-mixedsystem were similar to thosereported1-Sfor Cd(II)-oxalateand Cd(II)-phthalatesystems.For the system Cd(II)-oxalate, the plct of-(EI/2)e vs log CL (whereCL = oxalateion concen-trations) indicatesthe presenceof 1:1, 1:2 and1: 3 Cd(II)-oxalatecomplexspecies.The DeFordand Hume treatment'was appliedto determinethe stability constantsof thesespeciesand thevalues are: log ~l>o=2·70± 0,04, log~2'o=4·07± 0·15and log ~3'O=5·14± 0·06. Thesevaluesare in good agreementwith those obtainedbySchaap and McMaster~1and Kanemura andWattersli.The applicationof DeFord and Humemethod'for Cd(II)-phthalatesystemsuggest(dthe forma-tion of 1:1, 1:2 and 1:3 complexspecies.Thestabilityconstantsthusobtainedare:log~O,1= 1·90[Ox]M-El (vs SCE) at log 1m/Ie Slope(mY)63INDIAN J. CHEM., VOL. 15A,JANUARY 1977Sch.me'l' e method of Schaap and McMa<;terslwasappledto evaluatethe cotfficientsA, B, C andDin b th the sets. The value,>of the,>ecoefficient,>are iven below:A 0'08M phthalate:log A = 1'30;log B = 3·0±0 9; log C = 4,30± 0'09; and log D =5'17+ O' 6- A I 0·16M phthalate: log A = 1,78; log B= 3' 0 ± 0·03; log C =4'47± 0'03; and log D=5' 7 +0·08l' e ~ean value of logD = 5·17 agree,>wellwith the log ~ao= 5,14,the stability constantof[Cd( x)a]4-.l' e valuesof A, B, C andD wereusedin calcu-latin the stablity constantsof mixed species.The mixed complex~pecies[Cd(Ox) (phthalate)]a-[Cd( x)a (phthalate)]4-and [Cd(Ox) (phthalate)a]4-wer~1foundto havethe stability constantslog ~11=3, 5, log ~al= 5·02and log ~12= 3,89respec-tivel .l' observedstability constantsof the mixedcom lexes have b en comparedwith calculatedfromI thoseof the simplecomplexesfollowingtheprocduresuggestedby Watten,6. The calculatedvalu s for complexationconstantsare: (i) 3X~~:~X~ll = 104.35as comparedto 105'02observedfor0,[Cd( x)a(phthalate)]4-and(ii) 3X Al/3X Aa/3 = 103'69t'3,0 t'0,2as omparedto 103'89of [Cd(Ox)(phthalate)2]4-.The ncreasein the valuesfor thesespecieswererespetive1y10+0'67and 10+0'20.Th statisticalfactorfavouringthe formationofmixe complex[Cd(Ox) (phthalate)]2-is two. Theobsered value(103'75)is largerthan the calculated(103-4)by 10+0'29.The greatestenhancementisobsered for the [Cd(Ox)2(phthalate)]4-complex.Th variouscomplexationreactionsalong withtheir log stepwisestability constantsare showninSche e 1.log J( value for [Cd(Ox)]to [Cd(Ox)a]a-is 1·40whil thevaluefor Cd(phthalate)to [Cd(Ox)(phtha-late)]- is 1·85. The largervalueof log K for thelater reactionshowsthat the formationof mixedspecis is favoured. A similar argumentholdsgoodfor the mixedcomplex[Cd(Ox)(phthalate)]a-whenformedfrom[Cd(Ox)]. It is seenthat log Kvalu4rin the formationof [Cd(Ox) (phthalate)2-fromiCd(OX)]is muchhigherthanin the form ion64!Iiof [Cd(phthalate)a]a-from [Cd(phthalate)]being1·05in the fannerand0,35in thelatter case.Oneof themodesin whichmixedligar:dcomplex[Cd(Ox)(phthalate)J2-candisproportior:ateis:2[Cd(Ox)(phthalate)Ja-~[Cd(Ox)2]2-+[Cd(phthalate)a]a-andreactionhasthelogK =-1,18 in the directionwritten whichclearlyshowsthat the formationofthe mixedcomplexis preferred.That the saturatedmixed complexes[Cd(Oxla-(phthalate)]4-and[Cd(Ox)(phthalate)a]4-arefavoundcan be seenby comparingthe formationconstantsfor the additionof oxalateanionas a third ligandto [Cd(Ox)a]a-,[Cd(Ox)(phthalate)]a-and [Cd(phtha-late)a]a-.Log K valuesare respectively1,07,1·25and 1,65.The authorswish to expresstheir deepsenseofgratitudeto Prof. D. D. Khanolkar for his keeninterestand encouragement.References1. SCHAAP, W. B. & McMASTERS, D. L., J. Am. chem.Soc.,83 (1961),4699.2. DHULEY, D. G., JAHAGIRDAR, D. V. & KHANOLKAR, D. D.,J. inorg. nucl. Chem.,37 (1975),2135.3. JAIN, D. S., ANAND KUMAR & GAUR, J. N., J. Polarogt'.Soc., 13 (1967),120.4. DEFORD, D. D. & HUME, D. N., J. Am. chem.Soc., 73(1951),5321.5. KANEMURA, Y. & WATTERS, J. I., J. inorg. nucl. Chem.,29 (1967),1701.6. WATERS, J. 1. & DEWITT, R., J. Am. chem.Soc.,82 (1960),1333.A Studyof Cu(II) Monochloroacetate&Trich1oroacetateat d.m.e.H. S. SHARMA, S. S. SINGH & H. L. NIGAMDepartment of Chemistry, University of AllahabadAllahabad 211002Received13 January 1976; accepted22 May 1976Copper(lI)mono-and trichloroacetateshavebeenobservedto undergodiffusion-controlled,irreversiblereductionat d.m.e.in 25%ethanoland25%acetone.But in aqueousmediumcopper(lI)monochloroacetateundergoesdiffusion-controlledreversiblesingle-elec-tronelectroreductionwhiletheothershowsirreversibleelectroreduction.Kineticparametersof all irrever-sibleelectrodeprocesseshavebeenevaluatedalongwithotherpolarographicharacteristics.COPPER (II) monochloroacetatexhibit" metal-metal exchangeinteraction,while Cu(II) tri-chloroacetateshowsnormal magneticpropertiesof a paramagneticomplexin solid "tatel. Sl.:chatypical behaviourof thesetwo alkanoateshasalsobeenestablisbedin organic solvent<;2of low di-electric coPstant and having le,><;coordinatingability thanwater. In aqueousolution,thedimeri-zation reaction appearsto be destroyed.Theseconclusionshave beenarrivedat on the basisofspectraland magneticpropertiesof these alka-noates. Recentpolarographicinvestigatior:s3showthat Cu(II) monochloroacetategives double wave!'II, I1',11 1"11 I

Polarographic Study of Mixed Ligand Complexes: Cd(II)-Oxalate-Phthalate System

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Polarographic Study of Mixed Ligand Complexes: Cd(II)-Oxalate-Phthalate System

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