Complexes of indium with unsaturated bidentate sulphur-donor ligands

Abstract

THERE is an extensive literature on the chemistry of transition-metal complexes with unsaturated bidentate ligands in which sulphur is the donor atom,l but, of the main-group elements, only zinc(rr) and tin(1v) compounds have been reported. The structure of [Zn(MNT),]2(MNT2= maleonitriledithiolate anion) is not known;2 the tin(1v) complexes are polymeric unless aryl groups are also bonded to the metal.3 We find that the reaction of indium(II1) chloride with MNT2gives rise to the anionic complexes [In(MNT),]or [In(MNT) 3]3-, depending on the In : MNT2mole ratio used in the preparation. Treatment of [In(MNT),]with neutral bidentate donor ligands in alcohol gave anionic complexes of the type [In(MNT) 2L] [L = 2,2’-bipyridyl, 1,lOphenanthroline, 8-hydroxyquinoline, ethylenediamine, or 1 , 2-bis(diphenylphosphino)ethane] . The Et,N+ salts of all of these anions are yellow; salts of the adduct species are 1 : 1 electrolytes in acetonitrile, except that the 8-hydroxyquinoline adduct has a conductivity ca. 50% lower than expected; Et,N[In(MNT),] is a 1 : 1 electrolyte, and (Et,N),[In(MNT),] a 3 : 1 electrolyte in this solvent. No reaction of [In(MNT),]was detected either chemically or spectroscopically with monodentate donors (pyridine, ammonia, urea, Ph3P) other than NN’-dimethylacetamide (dma) , which gave an unstable adduct Et,N [In(MNT),(dma),] (decomp. 60’). From similar reactions involving indium chloride and TDT2(TDT2= toluene3,4-dithiolate anion) we obtained the 1 : 1 electrolytes Et,N[In(TDT),] and [In(TDT),L] (L = bipy, phen) , and the 3 : 1 electrolyte (Et,N) [In(TDT) ,I. The acceptor ability of the [In(MNT),]and [In(TDT),]complexes, while in keeping with the ability of the metal in this oxidation state to form [InCl,L,]species,, is markedly different from the behaviour of the complexes of transition-metal ions other than cobalt(rr1) with di-sulphur 1igands.l ,6 Polarographic reduction of these complexes in aqueous or absolute methanol showed in almost each case a series of reversible one-electron changes, formally 1,111 -+ In11 -+ In1 -+ Ino. This behaviour is in sharp contrast to the usual aqueous phase In111 -+ Ino polarographic reduction,6 and represents the first identification of a formally In11 complex, although this oxidation state has been reported’ in a matrix of frozen aqueous sulphuric acid irradiated with y-rays at -77’. In view of earlier workl, however, it seems highly probable that the added electrons are associated with the metalligand ring system rather than being in purely metal orbitals. In those analogous transition-metal complexes for which structure determinations have been reported,* the MS, co-ordination is either a precise or distorted trigonal prismatic arrangement. An X-ray structure determination on (Et,N) [In(MNT),] shows that the Ins, kernel in this anion has a distorted octahedral structure, with the In-S bond length 2.59 A. The S-In-S angle within the chelate ring is 80°, and the S-S distance in the ring 3.39 A. A three-dimensional electron-density difference map shows the positions of all the remaining non-hydrogen atoms ; refinement by block-diagonal least-squares method is presently being undertaken with the 25 atoms of the anion (R = 0.24 for 1866 reflexions). The [In(MNT),],anion is thus the first example of a di-sulphur ligand complex with the “classical” distorted octahedral symmetry associated with tris (bidentate ligand) co-ordination, yet showing the stabilization of unusual formal oxidation states. This work was supported in part by Operating Grants from the National Research Council of Canada.