Nagendram, A

Omprakash, K L

Pal, A V Chandra

Reddy, M L N

English

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IndianJournalof ChemistryVol.27A, March 19RR, p.267FormationConstantsof BinaryComplexesof Lanthanideswith2-Hydroxymethyl-benzimidazoleTableI-FormationConstants(log~2) andThermody-namicParametersofLn- HMB Chelatesin 50%v/vaqdioxanemediumA NAGENDRAM, K L OMPRAKASH,A V CHANDRA PAL* & M L N REDDYDepartmentof Chemistry,OsmaniaUniversity,Hyderabad500007Received19March1987;revisedandaccepted16July 1987Calculationsusingthismethodresultedin nega-tive valuesof K 1 (positiveintercept)and henceonlylog~2 valuesarereportedinTable1.Lane andQuinlan7 havereportedtheformationof only 1:1 complexesof La(IIl) with 2-hydroxy-Proton-ligandand metal-ligandformationconstantsof bi-narycomplexesof La(IlI), Pr(IlI), Nd(IlI), Gd(IlI), Dy(IlI) andY(IlI) with 2-hydroxymethylbenzimidazolehave been deter-minedpH-metricallyin 50% v/v aq dioxanemediumat 30°,40° and 50°C and 1=0.1 M (NaCI04), The thermodynamicparametersof complexformationhavebeenevaluated,Stabi-lities (log 112 values)of the chelatesincreasewith decreaseinionic radiusof the metal[Dy(llI)>Gd(llI) >Y(1l1)>Nd(llI»-Pr(IlI) >La(1l1)].In continuationof our studieson the complexingtendenciesof benzimidazoles1- 3, we reporthereinthe formationconstantsof binary complexesofthe type ML2 [whereM =La(IIl), Pr(IIl), Nd(IIl),Gd(IIl), Dy(IIl), Y(IIl) and L= 2-hydroxymethyl-benzimidazole(HMB)] in 50%v/v aq dioxaneme-diumandI=0.1 M(NaCI04).The proton-ligandand metal-ligandformationconstantsfor binarysystemsweredeterminedus-ing Irving-RossottipH titration technique4•Thegeneralexperimentaldetailswerethesameasdis-cussedearlierl-3• The pH meterreadings(B) intheaq dioxanemediawerecorrectedby themeth-odofVanUitertandHaasS.From the proton-ligand formation curves(0.1<liH <1.8) the proton-ligandformationcon-stantslog KOH and log KNH evaluatedat 30°(12.59and 5.03),40° (12.12and 4,74)and 50°C(11.46and4.52)arein accordancewiththevaluesreportedbyLaneandDurham6•From theformationcurve(Ii vs pL), it is foundthat the log K 1 and log K 2 do not differ muchfromoneanotherandhencetheyhavebeenevalu-atedbytheleast-squaretreatment4ofEq, (1)Ii _ (2 - 1i)(L)(Ii - 1)(L) (Ii - 1) ~2 - K I" , (1)[/=0,1 M(NaCI04)]TempDy(1l1) Gd(1l1)Y(1l )Nd(1l )Pr(1l )La(K) log11230316.7916.554115 89,36313348002489272-~G(kJ mol-I at303K) 97.193289- ~H(kJ mol-I) 28.98.7,~S(JK -I mol-I at303K) 226.12 4.103,.methylnaphthimidazole,The formation of 1:2complexesof Ln(IIl) with HMB in thepresentin-vestigationis quitereasonablebecauseof theless-er steric hindranceof benzimidazolemoiety ascomparedtoanaphthimidazolemoiety.The orderof stabilities(log~2) of Ln(IIl) - HMBcomplexes [Dy(IIl)>Gd(IIl) >Y(IIl) >Nd(IIl) >Pr(IIl)>La(IIl)] is almostin theincreasingorderoftheir Z2/r valuesindicatingthat the metal-ligandbondisprimarilyionic.The thermodynamicparameters,tlG, tlH andtlS of formationof Ln - HMB complexeshavebeen evaluatedusing well known equationsandarepresentedin Table 1.The stabilitiesarefoundto decreasewith increasein temperaturesuggest-ing thatthe interactionof Ln(IIl) ions with the li-gandisexothermicin nature,One of the authors(A N) is gratefulto theCSIR, New Delhi, for the awardof a senior re-searchfellowship.References1 OmprakashK L, ChandraPal A V & ReddyM L N, Indi-an] Chern,(a)21A(1982)322;(b)22A(1983)546,2 OmprakashK L, GoverdhanReddyK, ChandraPal A V &ReddyM L N, Indian] Chern,23A(1984)79.3 GoverdhanReddyK, OmprakashK L, ChandraPal A V &ReddyM L N, Indian] Chern,24A (1985)161.4 (a) Irving H & RossottiH S, ] chernSOl',(1954)2904; (b)(1953)3397.5 Van Uitert L G & Haas C G, ] Arn chernSoc, 75 (1953)451.6 LaneT J & DurhamH B, lnorgChern,2(1963)632,7 LaneT J & QuinlanK P,] Arn chernSoc,82(1960)2997,267

Formation Constants of Binary Complexes of Lanthanides with 2-Hydroxymethylbenzimidazole

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Formation Constants of Binary Complexes of Lanthanides with 2-Hydroxymethylbenzimidazole

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