Sarkar, H. S.

Sen, D.

English

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------------~~--------------------~,'IndianJournalof ChemistryVol. 15A,June 1977,pp. 531-533Mixed Ligand Complexesof Co(III) with Biguanides& Nitric OxideH. S. SARKAR* & D. SENtDepartmentof Chemistry,IndianInstituteof Technology,Kharagpur721302Received21July 1976;accepted10March 1977A numberof cationichexacoordinatedcomplexesof coba1t(III)with bi~uanidesandnitric oxidehavebeenisolatedand characterizedon the basisof elementalanalysis,con-ductance,spectraland .ma~neticmomentdata. Thecomplexespreparedare of the types[Co(HbgMNO)(H20)]X2and[Co(Hb~MNO)X']XU(whereHb~=bi~uanideoritsderivative,X =ClO'4or !SOj::,X' ~halideor thiocyanateandXu =Cl-, Br, CNS- or ClOV. The complexescontainingSO~-asanionarestablein air in thesolidstatewhileothercompoundsarestable·onlyin anatmosphereofnitrogen.Excepthesulphate,all othercompounds,evenin drystate,aresensitiveto diffusedlight.A NUMBER of transition metal mixed ligandcomplexesinvolving biguanidesand donorslike H20, NHa, oxalate, thiosulphateandN'-amidinoisoureahave been reported1,2.In themajority of mixed ligand nitric oxide complexesofcobalt,oxidationstate+2ofthelatterisobserved.However, other oxidation states have also beenreporteda-s.Nitric oxide can coordinateas NO,NO-f or NO· dependingon the natureof the metalatomand the otherligandsattachedto it. If thealreadypresentligand is 7t-acceptor,nitric oxidecoordinatesasNO+andstabilizestheloweroxidationstates. If theligandpresentis 7t-donor,nitricoxide{;oordinatesas NO- stabilizingthe higheroxidationstate. Since biguanidehas filled 7t-orbital,whichcan overlapwith vacantj>7t or d7torbitalsof metalatom,delocalizationof 7t-electrcnscanoccurthroughthe whole of metal ligand ring systemfavouringhigher oxidationstatesof the metal atom. Thishas been corroboratedby the preparation ofanumberofhighervalentmetalbiguanidecomplexessuchas Ag(IIT)6,Pt(TV)?and Ru(TII)8biguanides.Therefore,it is of interestto studythemixedligandcomplexesof cobaltwith biguanideandnitric oxide.The oxidationstateof cobaltwill be helpfulin in-dicatingthetypeof coordinationexhibitedby nitricoxide giving some ql:alitative informationaboutthe 7t-donorcapacityof biguanide.The general method for the preparation ofcomplexesof the type [Co(R-Hbg)2(NO)X]X(Hbg=biguanide,X =Cl-, Br- or CNS-)involvedactionof nitric oxideon[Co(R-Hbg)2]X2in methanol. Thecomplexes[Co(R-Hbg)2(NO)X]CI04 were isolatedby the treatmentof [Co(R-Hbg)2(NO)(HP)](CI04l2in acetonesolutionwith lithium halide.Materialsand MethodsAll experimentswerecarriedout undernitrogenwhichwaspreviouslypassedthroughalkalinepyro-*Presentaddress:Chemist,Durgapur ChemicalsLtd.West Bengal.tAuthorto whomcorrespondenceshouldbe addressed.gallolsolutionto removeoxygen. The compounds[CoII(Hbg)2]X2where X =Be CIO;, !SO~-,werepreparedfollowingthe methodsdescribedin theliterature9• Nitric oxidewaspreparedandpurifiedas per standard methods1o•No precautionwastakentoremovethetracesofwaterfromthesolvents,sincethereactionwasnotinfluencedby thepresenceor absenceof water in the reactionmedia.(Nitrosyl)(aquo)bis(bi'guanirle)cobatt(1II) perchlorate- Bis(biguanide)cobalt(II) perchlorate (2 g),prepared in situ from [Co(Hbg)2](OH)2 andNH4CI04• was suspendedin oxygen-freemethanol(25 ml). The suspensionwaspurgedwith nitrogenandpurenitric oxidegaswasbubbledthroughthesuspensionat -therateof 70 bubblesperminutefor2 hr whendarkbluishvioletcrystalswereformed.The passageof nitric oxidewas discontinuedandnitrogenwas passedthrough the suspensionforcompleteremovalof unreactednitric oxide. Thecrystalswerefilteredin a goochcrucibleandwashedwith smallportionsof oxygen-freemethanolundernitrogen. Theseweredriedoversodiumhydroxidein a desiccatorin nitrogenatmosphere.The com-'poundswerehighly solublein acetone,methanoland water. From the elementalanalysis, thecompound was characterizedas [Co(Hbgh(NO)-(H20)](CI04)·(Halo)(nittosyl)bis(biguanirle)cobalt(III) perchlorate-The perchloratecomplex, [Co(Hbgh(NO)(H20)]-(CI04)2in acetonesolution,ontreatmentwithlithiumhalidesgivesbluish violet crystals,characterizedas [Co(Hbgl2(NO)X]CI04 whereX =Cl-, Br-or 1-.The compoundswerehighly solublein methanolandwater. The chlorocompoundgavewhite pre-cipitateof AgCI only on long standingand slightheating. The iodo complexis quiteunstableandits detailedstudywasnot possible.(Nitrosyl)(aquo)bis(biguanirle)cobatt(III)sulphate-It was preparedby followingthe samemethodasfor thecorrespondingperchloratecompoundusingbis(biguanide)coba1t(II) sulphatein place of per-chlorate.531INDIAN J. CHEM., VOL. 15A, JUNE 1977(Hy roxo)(nitrosyl)bis(biguanide)cobalt(III) hydro-xide [Co(Hbgh](OH)2 (0'5 g) was suspendedin 1 ml of dry oxygen-freemethanol. Thesuspesion was purged with nitrogen for thecomplte removalof oxygen. Through this sus-pensin, nitric oxidewasbubbledfor 3hr whenthecolou of the contentsturned bluish-violet. Theexces.nitric oxide was removedby purgingwithnitrogn. The bluishvoiletprecipitatewasfilteredand ried over sodiumhydroxidein nitrogenat-mosp ere. The compoundwas also preparedbyreact'n of [Co(BigHMNO)(H20)JS04with bariumhydrxide solutionunderN2·(C oro)(nitrosyl)bis(biguanide)cobalt(III)chloride-It w s preparedby followingthe same methodas fo the perchloratecomplexusing ammoniumchlordesolutionin placeof ammoniumperchlorate.(T iocyanato)(nitrosyl)bis(biguanide)cobalt(III) thio-cyan te- The compoundwaspreparedin the sameway as the corresponding(chloro)(nitrosyl)bis-(bigunide)cobalt(III) chloride compoundexceptthat ammoniumthiocyanatewas usedin placeofammnium chloride. The thiocyanatocompoundrese bles the chloro compoundin physical andche ical properties.T e chloro,bromo and thiocyanatocompoundswere also preparedfrom the (nitrosyl)(aquo)bis-(big nide)coba1t(III)sulphate,[Co(Hbg)2(NO)(H20)]-504,by doubledisplacementreactionswith BaCl2,BaB 2 and Ba(CNS)2respectively.Si ilar complexeswith substitutedbiguanidessuch as methyl-, diethyl- and phenyl-biguanideshav beenpreparedby followingsimilar methodsof eparationas thosefor the simplebiguanidecom ounds. All the compoundsalongwith theiranal tical dataare listedin Table 1..A. thecompoundsof this seriesarelight, air andheatsensitive. They were preservedand studiedin . rk at roomtemperaturein an atmosphereofnitrgen.The conductancesweremeasuredin methanolicsolutionof the compounds.The magneticsuscep-tibilities of the compoundswere measuredusinga Guoybalance. Theinfraredspectrawererecordedon a Beckman-IR 12spectrophotometer.ResultsandDiscussion(Nitrosyl)(aquo)bis(biguanide)cobalt(III) sulphateis fairlystabletowardsaerialoxidation. It is sparing-ly solublein methanolandwater. In thecompoundsof the type [Co(HbgMNO)X]Cl04(whereX =Cl,Br, CNS), the presenceof halide ions in the coor-dinationsphereis indicatedby the fact that thefreshlypreparedsolutiondoesnot giveany preci-pitate of silver halide with AgNOasolution. Theaerialoxidationof nitrosyl groupto N02 dependslargelyon the nature of the ligand in the transposition. [Co(Hbgh(NO)(H20)J504 remains un-changed for several weeks in the presenceofdiffusedsunlight, while [Co(Hbg12(NO)Br]Brgetsoxidizedwithin a few secondson exposureto dryair. This trendis attributedto the strongelectro-negativecharacteraswellaslonepairparticipationof thehalideion trans to the nitrosylgroupin thecomplex.All the present complexesare diamagneticinnature([J.eff =+0·3to -0·5BM). The diamagneticnature of the compoundsshows that all thecomplexeshavecentralmetalatomin the +3 oxida-tion stateandprobablythe complexeshavea bentCo-N-Ogroup.Compoundsofthetype[Co(Hbg)2(NO)X]X' behaveas 1:1 electrolytesin methanol. This indicatesthemolecularformulaas[Co(BigHh(NO)X]X'. Theperchloratecompoundbehavesas a 1:2 electrolyteandhenceit may be representedas [Co(Hbg)2(NO)-(H20)](ClO~)2'The infrared spectra (Table 2) of severalofthese complexeshave been studied. A strongabsorptionat 1600 cm-1indicates the presenceTABLE 1- ANALYTICALAND CONDUCTANCEDATACompoundsFound (%)Calc. (%)AM---'MNSO.XM[Co( bg).(NO)Cl]CI.4H.O13-8135,67-16·0213·30333[Co( gb).(NO)(CNS)JCNS4'4244 42-4 257185 1a[Co( bg).(NO)(H.o)]S .· 48 02 55541 1 b[Co( bg).(NO)(H.o)] (Cl04).1 730'6 452 78bCl]ClO.98·1 -86 269'3 aBr]ClO.2 627 09[Co( eHbg).(NO)C1]C1.4H.o89178 'eHbg).(NO)(H. )](ClO.).790' 6'l o S 43 61[Co leHbg).(NO)Cl]ClO42[ o( leHbg).(NO)CNS]CNS9ietHbg).(NO)Cl]C1.4H.O08-8iet bg . N )CNS]CNS52 41r (H.O)]SO.39[Cor ietHbg) (NO)(H.O)](Cl04).9·24·9,5 07ietHbg). NO C1]ClO.00 9( { h )z19h ).( )CNS] NSr . ( .o) SO.f Hbg .(N )(H.O)] IO.).5676-1X =C1,Br or CNS, a =in methanol,b =in water.532~ - 11SARKAR & SEN: Co(I1I) COMPLEXES WITH BIGUANIDESTABLE 2- INFRARED SPECTRALDATA AND ASSIGNMENTSOF BANDS(Hbg)2S04[Co(Hbg)2(NO)[Co(Hbg)2(NO)C1][Co(Hbg)2(NO)[Co(Hbgh(NO)C1]Assignments(CNS)]CNSC1(H2O)]S04C1043540vs3490VS, 340 vs350 VS, 3430vs46 vs, 34 vs3 50 VS, 3425vsvN-3170vs20 0202532 vs2065VS, 2050 vs-vCNS (coordinated)1650S1685s 168 S1675~N--C-N1610S521v O56 s54 S 545 S-:.c-=N231360S1135S- vS0476 S775 s 78 S7 ssNH bending72 ss was =strong, vs =very strong.of NO- coordinationin the complexsincea bandin the region 1500-1700 cm-1 is expectedforthe coordinatedNO- groupll. The oxidationproduct of the compound [Co(Hbg)2(NO)CI]CIgives a compoundsimilar in all respectstotrans-[Co(HbgMN02)CI]Cl.The nitrosyl biguanidecompoundshave been assignedtrans configura-tions.The thiocyanate complex [Co(Hbg)2(NO)]CNS]showsastrongbandat 2065cm-1dueto coordinatedCNS- group. This indicatesthat the thiocyanatecomplexhas similar configurationas the halidecomplexes.Fromall thesestudiesit appearsthat thenitrosylgroupis coordinatedas NO- in the biguanidecom-plexesof cobalt. It can be concludedthat ligand(biguanide)to metal 7t-donorcapacity (L-+M) isstrongenoughto push the electrondensityfromthe metalto the antibondingmolecularorbital ofnitric oxidewhich in turn coordinatesas NO- andCo-N-Obondbecomesbent.References1. RAY, P., Chern.Rev., 61 (1961),313.2. DUTTA, R. L., J. Indian chern.Soc., 44 (1967),832,842, 863, 866.3. EARNSHAW,A., HEWLETT,P. C. & LARKWORTHY,L. F.,Nature, 199 (1963),483.4. FALTHAM, R. D. & NYHOLM, R. S., Inorg. Chern.,4(1965),1334.5. NAST, R., Chern.A bstr., 58 (1963),3129d.6. SEN, D., J. chern.Soc. (A), (1969),1304.7. SEN, D., J. Indian chern.Soc., 51 (1974),183.8. SEN, D., Sci. Cult., 28 (1962),84.9. RAY, P. & GHOSH,S. P., J. Indian chern.Soc.,20 (1943),291.10. BEANCHARD,A. A., Inorg. synthesis,Vol. 2 (McGraw-Hill,New York), 1950,126.11. MINGOS,D. M. P. & lEERS, J. A., 14 (1974),2610.533

Mixed Ligand Complexes of Co(III) with Biguanides & Nitric Oxide

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Mixed Ligand Complexes of Co(III) with Biguanides & Nitric Oxide

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