Ahuja, I. S.

Singh, Raghuvir

English

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INDIAN J. CHEM., VOL. 15A, JUNE 1977Methylpyrazine Complexes of Ag(I), Zn(II) &Cd(II) NitratesReceived30June 1976;accepted17December19761. S. AHUJA & RAGHUVIRSINGHChemistry Department,Banaras Hindu UniversityVaranasi 2210051:1, 1:4 and 1:2 complexesof Ag(I), Zn(I1)andCd(I1) nitrates, respectively,with methylpyrazinehavebeenpreparedandcharacterizedonthebasisofmolarconductance,molecularweightand IR andfarIR data. The Ag(I) complexis suggestedto havealinearpolymericstructurewith a planarthree-coor-dinateenvironmentaroundthe silver atomswithbridgingmethylpyrazineand terminalmonodentatenitrategroups. The Zn(II) complexis suggestedtohaveatetrahedralenvironmentoffournitrogenatomsof terminallybondedmethylpyrazinemoleculesandionic nitrates. The Cd(II) complexis suggestedtohavea monomericoctahedralenvironmentaroundthecadmiumatoms with monodentatemethy1pyrazinemoleculesandbidentatechelatingnitrategroupsattrans-positionsto eachother.IN continuationof our workl,2 on the complexesof pyrazineand its derivatives,we report thepreparationandcharacterizationofAg(l), Zn(II) andCd(II) nitratecomplexesof methylpyrazine.Thecomplexeswerepreparedby addinganexcessof theligandto hot solutionsof therespectivemetalnitratesin ethanol,Ag(l) complexcrystallizedoutimmediatelywhile Zn(II) and Cd(II) complexescrystallizedonconcentrationof thesolutionsby slowevaporation.The complexeswerefiltered,washedwith ethanolanddriedin vacuo[theAg(I) complexwas dried at "",90°].Metal and nitrate wereestimatedgravimetricallya.Thecomplexesarefairlysolublein dimethylformamideand methanol. IRspectrawere recordedin nujol and hexachloro-butadienemulls on a Perkin-Elmer 621 spectro-photometer.Ag(methylpyrazine)N03;m.p. 176°[Found: Ag,41·1;NOa,23·7. Calc.:Ag, 40,9;NOa•23·5%J.Zn(methylpyrazine)4(N03)2;m.p. 66°[Found:Zn,22·0;NOa,11·6. Calc.: Zn, 21'9;NOa, 11-5%].Cd(methylpyrazine)2(NOa)2;m.p.130°[Found:Cd,26·5;N03, 29·0. Calc.: Cd, 26,4;NOa,29·2%J.AnalyticaldatashowthatAg(l), Zn(II) andCd(II)nitratesform 1:1, 1:4 and 1:2 complexesrespec-tively with methylpyrazine.Molar conductivitiesof "",10-31\1solutions in dimethylformamideandmethanol demonstratethat the Ag(l) complexbehavesas 1:1 electrolyte(AM =110ohm-I cm2mole-I)whiletheZn(II) (160-170ohm-Icm2mole-I)and Cd(II) ("",180ohm-1cm2 nlOle-1)complexesbehaveas 1:2 electrolytes.Strong bandsin theIR spectra(IR banelpositionsin cm-I)in theregion1500-1300assignedto nitrate groups mask some5. KEITH, J. LAIDLER, Chemical kinetics (McGraw-Hill,New York), 1965,Chapter I, pp. 16.6. LONG,F. A. & PAUL, M. A., Chern.Rev., 57 (1957),1.7. JAMESON,R. F. & SALMON, J. E.,].chem.Soc.,(1955),360.[H3P04] 103 kobs(M)(min-I)3·06·413·02·281363·0· 911-52·07294,67 84,10·emperature=28'0°±0·10; ionic strength=3'0]TABLt 1- DEPENDENCE OF THE RATE CONSTANT ON THEOLARITY OF THE METAL COMPLEX AND ACIDK,I +Hf+H2PO;j~ Cr(Ox)(H2P04MH20)-+Ox2-+2H+III"-II -t·'"productss10This eadsto the rate law:ate=kIKIK2[ComplexJ[H2PO;jJ2[ox~Tlhoauthorsare thankful to Prof. M. N. Sastriful discus:sions.mediill aplotof logkobsversus- H0wasmade. Thevalue of the rate Constantsobtained.by varyirgthe c ncentrationof the metalcomplexandortho-phos loric acid arepresentedin Table 1. An in-creas in ionic strengthfrom 0·5 to 3-0 increaseskobs rom 0·97xI0-3 min-l to 6'36xlO-3 min-l([comlex]=0·006M and [H3P04]=3·0M). Thisis in agreementwith the change expectedina rea ionbetweentheionsof thesamechargetype.It w s found that an increasein added[oxalate]from '002to 0'008M decreasedthekobsfrom2·26X10-3 min-I to 1·21X10-3 min-l ([complex]=0·006 ; [H3P04] =3'OM; [J. =3·0).Th grassgreenproductobtainedin thesestudiesappe s to be identical with that formedin thesubst'ution of Cr(OxH- by H3P04with two broadabsortion peaks around430-450nm (EM =28,2)and 5 0-610nm (EM =21·3). Ion exchangestudiesfailed to show the presenceof either cationicoranionc phosphatocomplexin the product. Hencethe p oduct speciesmay be possiblyof the typeCr(H2 04)(HP04)(ref.2 and 7).Th followingmechanismis suggestedto explainall tl experimentalobservations.K.Cr(O 2(H20)2+H++H2PO;j~ Cr(Ox)(OxH)(H2P04).(H20):;Refer1. LA~HRI'S. C., j. Indian chem.Soc., 52 (1975),478.2. RA , V. M., ANANTARAMAM,V. & SASTRI,M. N., CurroS i., 45 (1976),451-3. PAL ER, W. G., Experimentalinorganicchemistry(Cam-b idge University P ess, Lond n), 1954,387.4. KRI HNAMURTY,K. V. & HARRIS, G. M., j. phys. Chem.,6 (1960),346.562!il! II"NOTESof ,thebandsdue to the organicmoiety in thisregIOn.Methylpyrazinemay act as a unidentateor abidentateligand. Geometryof this moleculepre-cludeschelationbut favours coordinationof thetwo donorsitesto differentmetalionsthusleadingto the formation of polymeric structures. IRspectralstudieshaveshownthatin metalcomplexeswheremethylpyrazineis bondedthroughonly oneof its nitrogenatomsmediumintensitybandsappearin the regions950-1000 and --1250 (refs 1, 2).Such bandsare absentin methylpyrazine-bridgedpolymersof long chain but weak bands appearwhenthe chain lengthis short. The intensityofthese bands has been consideredas a measureof chain lengthin metalcomplexes1,2.Ag(I), Zn(Il) and Cd(Il) beingd10ions, do notshow d-:;..d transitions and, therefore,electronicspectraland magneticsusceptibilitymeasurementsare not helpfulin assigningthe stereochemistryofthese complexes.Information on the tentativestereochemistryof the presentcompoundshasbeenderivedmainlyfroma comparisonof the IR bandsdue to nitrategroupswith similarmodesin com-poundsof establishedstructures.The freenitrateion (D3h symmetry)showsthreeIR active fundamentals- \12, \13 and \14'\11isnormally IR-inactivebut is usuallyobservedas aweak band in the IR spectraof solid compoundscontainingionic nitratesprobablybecauseof thecrystal interactions.On coordination4-9the localsymmetryof the nitrate group is loweredto C2vwith theresultthatall themodesbecomeIR-active,shiftsin thebandpositionsoccurandthedegeneracyof \13and \14is lifted. Since the local symmetryof the mono-and bi-dentatenitrategroupsis thesame, both the bonding types exhibit similarsplittingsof the fundamentalmodes4-9•However,themagnitudeof separationof \11and\14frequenciesof coordinatednitrate groups affords a usefulcriterionfor distinguishingbetweenthe mono-andbi-dentatenitrates6.The magnitudeof separationof thesebandsis smallerfor the mono-than forthebi-dentatenitrates. Recentlyit hasbeenestab-lished that the numberand the relativeenergiesof the nitrate combinationmodesin the region1800-1700maybeusedin distinguishingthevariouscoordinationmodesof thenitrategroups6,10.Com-poundswith ionic nitratesexhibit only one weakband in this region while those with mono- orbidentatenitratesshowtwo bandsthe separationof which is generallysmaller(6-26) for the mono-than for the bi-uentate(20-66)nitrates.IR spectrumof the 1:1 Ag(I) complexshowsadditionalbanesat 1260 and 980 indicatingthatthemethylpyrazineis bondedthroughboththeringnitrogensandthecomplexhasa shortchain-lengthpolymericstructure1.2.In additionto ligandbands,Ag(I) complexshowsbandsat 1442, 1312, 1015,820, 730 and 718 whichare assignedto \14'\11'\12'\16,\15and\13modes,respectively,dueto coordinatednitrate group. Moreover,two weak bands (1760,1745)with a separationof 15 appearin the region1800-1700. The observedseparation(130) (ref. 6)of \14at 1442 and of VI at 1312and of the com-binationmodes(15) (ref. 10) indicatethe presence~U~~_~ ~~~m 'IIIof terminallybondedmonodentatenitrate group.From a considerationof bidentatebridgednatureofmethylpyrazine(vt"desupra) and terminallybondedmonodentatenitrategroupit is suggestedthat thiscomplexhasa shortchainlengthpolymericstructurewith a three-coordinatedenvironmentof ligandatoms(twonitrogensfrombridgingmethylpyrazinemoleculesand an oxygenatom of the terminalmonodentatenitrategroup)aroundthesilveratoms.The 1:4Zn(n) complexexhibitsmediumintensitybandsat 1255and 980 characteristicof terminallybondedmethylpyrazinemolecules1.2•It behavesasa 1:2 electrolyteindicatingthat both the nitrategroupsare ionic in solution. IR spectrumof thiscomplexshowsa strongbroadbandat 1370dueto\13and mediumintensity bands at 833 and 720dueto \12and \14modes,respectively.Moreover,aweakbandat 1045dueto \11(normallyIR-forbiddenin ionic nitrates)is observedprobablydueto site-symmetryeffects. Further, IR spectrumexhibitsonly one band of very weak intensity in thecombinationmoderegion,1800-1700.Thesefeatures.clearlyindicatethepresenceof ionicnitratesin thesolidstatein this compound4-1O.From a considera-tion of terminallybondedmethylpyrazineIllolecules.andionicnitratesthecomplexis tentativelyassigneda four-coordinatedmonomerictetrahedralstructurein the solidstate.Besidesthe mediumintensitybandsat 1260and940 dueto terminallybondedmethylpyrazinemole-cules1,2,the 1:2 Cd(Il) complexshowsbandsat1470, 1290, 1050, 816, 735 and 710 assignedto\I., \14'\12,\16,\13and \15modes,respectively,due tocoordinatednitrategroups. Thesebandsareabsentin the uncoordinatedmethylpyrazineand Cd(Il)chloride,bromide,iodideor thiocyanatecomplexesreportedearlier1.Two weak bands at 1765and1725 with a separationof 40, and the observedseparationof 180 of \11and \14modes due tocoordinatednitrategroups,suggesthe presenceofonly bidentatenitrate groupsin this complex8,10.Withbidentatechelatingnitrategroupsandterminal-ly bondedmethylpyrazinemolecules(vide supra)the 1:2 Cd(Il) complexis tentativelyassignedamonomericoctahedralstructurein the solid state.The absenceof a band in the region 1800-1790in the IR spectrumof Cd(Il) complexeliminatesthepossibilityof polymericstructuresinvolvingmono-dentate,M-0(N02)-M, or bidentate,M-O(NO)-O-M, bridgingnitrategroupsll. Finallymolecularweightdeterminationof this compoundby Rast'smethod(observed475, calc.424) is also consistentwiththemonomericstructurefor thecomplexin thesolid state. Sincethe fundamentalmodesdue tocoordinatednitrategroupsin this compound o notexhibit greatersplitting than expectedfor C2trsymmetry,the two nitrategroupsmustbe trans toeachother5. The metalatomsin this complexarethus likely to have a six-coordinatedmonomericoctahedralenvironmentof four oxygenatoms(fromtwo terminallybondedbidentatechelatingnitrategroups)and two nitrogenatomsof the terminallybondedmethylpyrazinemolecules.Becauseof the'/0,,-weakAg--ONO~2and Cd NO bonds7,12, the"-0/563INDIAN J. CHEM., VOL. 15A, JUNE 1977Ag-{ (nitrate) and Cd-O (nitrate) stretchingmode couldnot be observedabove200.W thank Prof. O. P. l\falhotra,Head of theChen'stry Department.BHU, Varanasi,for pro-vidi facilities.Refer,nces1. A$:UJA, I. S. & RASTOGI, P., ]. chem.Soc., (1970),2161,nd refs. 9-13 therein.2. AiTJA' I. S. & GARG, A., Indian]. Chem.,9 (1971), 1307.3 V GEL, A. I., A textbookof quantitativeinorganicanalysis( ongmans. Green, London), 1971.4. F LD, B. O. & HARDY, C. ]., Q. R v. chem.Soc., 18964), 361; ADDISON, C. C., LOGAN, N., WALLWORK,· C. & GARNER, C. D., Q. Rev. chem.Soc.,25 (1971),89; ADDISON, C. C. & SUTTON, D., Prog. inorg. Chem.,(1967), 195.5. G4TEHOUSE, B. M., LIVINGSTONE, S. E. & NYHOLM, R. S.,· chem.Soc., (1957), 4222.6. C1fRTIS, N. F. & Cl:RTIS, Y. M., Inorg. Chem.,5 (1965),04.7. AJ)DISON, C. C. & GATEHOUSE, B. M., ]. chem.Soc.,960), 613.8. HbT, F. A. & LAMING, F. P., ]. inorg.nucl. Chem.,27965), 1605; 1825.9. Blj'LLOCK, ]. I., J.inorg. nucl. Chem.,29 (1967), 2257.10 LnvER, A. B. P., MANTOVANI, E. & RAMASWAMY B. S.,an. J. Chem.,49 (1971), 1957. KARAYANNIS, N. M.,IKULSKI, C. M., PVTLEWSKI, L. L. & LABES, M. M.,· inorg.nucl. Chem.,34(1972), 3139; Inorg. Chem.,13974), 1146. SPECA, A. N., PYTLEWSKI, L. L., KARA-ANNIS, N. M. & OWENS, C., J. inorg. nucl. Chem.,6 (1974), 3151; AHUJA, 1. S., SINGH, Ro\GHUVIR &INGH, RAJINDAR, SPectrochim.Acta, 32A (1976), 547.11. R~SENTHALL' M. R. & DRAGO, R. S., Inorg. Chem.,4( 965), 840.12. F RRARO, J. R. & WALKER, A., ]. chem.Phys., 42( 965), 1273.PolarographicStudyof Zn(II)-TryptophanSystemJ. C. KHATRI, MUKRTAR SINGH & S. K. JRAepartmentof Chemistry,AgraCollege,Agraceived9 March 1976; revised24 December1976accepted6 January 1977Pol rographicbehaviourofZn(I1)in thepresenceofDL-trptophanand NaCIO as supportingelectrolytehas een studied.The systemyields two waves,howeer,thesecondis maskedbya maximumat lowtrypt hanjZn(I1)ratios. The maximumdisappearson in reasingthe [tryptophan]but at this stagethesecon waveis considerablysuppressedandis finalIyelimi atedon furtherincreaseof tryptophanjZn(I1)ratio. Thefirstwavewhichrepresentsanirreversibleelectrdeprocessis duetoZn(I1)-tryptophancomplex.Ther teconstantandtheproduct'ana' for theelec-trode eactionhavebeenevaluated.CH LATES of Pb(II), Cu(II) and Cd(II) withL tryptophanwere first reportedby Quintinand oglizzo1.Pleticha2hasreportedpolarographicstudi s of complexesof Co(II), Ni(II), Fe(II) andMn(! ) with severalaminoacidsincludingL-trypto-phan. ChandraandSrivastava3andLal andChris-tian4 have also dealt with different aspectsofNi(II -L-tryptophansystem.Th presentnotedealswith polarographicstudyof Zn II)-tryptophansystemin NaC104assupporting564electrolyte.Sodiumperchloratehas beenspeciallyusedto avoidany possibilityof complexformationof Zn(Il) with the anionof the supportingelectro-lyte. The use of buffer has also been avoidedfor thesamereason, Sincethekineticstudieswereenvisaged,useof any surface-activeagenthasalsobeenavoided.The d.m.e. (Sargent,USA) had the followingcharacteristicsm2J3tlJ6 =2·140mg2J3 sec-l/2 in O·lMNaCl04 at -0,11 V versusSCE. All thechemicalsusedwereof BDH or E. Merck (AR grade). ZnC12was used as ,the depolarizer.The experimentalset up and the procedurewere similar to thosereportedearlier5.ThediffusioncoefficientshavebeenexperimentallydeterminedusingDawsoncell6 and tn' calculatedthereafterby Ilkovic equation,correspondingto thefirst wavehas beenfound to be between1·7and2·2. Suchdiscrepanciesin calculatedvaluesof "n'are not unusual7.The potentialdependentheterogeneousrate con-stant kJ,h is relatedto E by the followingtworelations8,9(1) and (2).kJ,h =k/h exp[-a.:naF(E+O·2412)(RTJ ... (1)[-LlGt+a.:naF(E +0'2412)]kJ,h = KT (h'O exp RT ... (2)Equatingthevalueof log kJ,h at E =° from thetworelationswegetLlGt (kcal)at 25°ar.disobtainedby the relation(3).+ -5·706') 0 816 7 '!J.G+= 4.18 Log kJ,h-' rxna-6· 9J ... (3)Zn(II) yields a singlewell definedwave withE1/2 =-1·0365 V (versusSCE) and slope0·040Vin O·lM NaCl04. On the additionof tryptophanto thesystem[1mM Zn(II), 1mM tryptophanandO·lM NaCl04J the followingsignificantchangesareobservedin the current-potentialcurves:(a)E1/2 is shiftedto morenegativepotentialandbecomes0·1066V.(b) The wave becomesmore drawn out withslope=0'095V.(c) The waveis closelyfollowedby a maximum.However,it is not on the rising portion and thusdoes not interfere with the quantitativestudyof the wave.AsthetryptophanjZn(II)ratiois increasedkeepingZn(II) constant at 1 mM, the wave records agradualshift towardsmorenegativepotentialstill[tryptophan]reaches5 mM. There is no changeat [tryptophan]=6 mM. This is followedby apositiveshift at 7 mM and between[tryptophan]7 mM to 20 mM, the E1/2 remainspracticallyconstant.The heightof the maximiumgraduallydecrease~with an increasein [tryptophan]till 4 roM andfrom 4 mM to 6 mM it is reducedto a roundedhump.. At 7 mM theroundedhumpalsodisappearsandIII Its placea smallsecondwaveappearswhichchangesneitherin shapenor in positiontill 15roMtryptophan(id =1·088and-Et =1·225V). How-ever, this secondwave disappearscompletelyat20 mM tryptophan.The ~act~haton the addition of tryptophanthe Et IS shIftedto morenegativepotentialsandI ."~' I"III

Methylpyrazine Complexes of Ag(I), Zn(II) & Cd(II) Nitrates

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Methylpyrazine Complexes of Ag(I), Zn(II) & Cd(II) Nitrates

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