Treatment of the dimeric dianionic bisdithiolene complexes of iron and cobalt, [MS4C4R4]22–(R = CN and CF3), [Fe(S2C6H3Me)2]– and [M(S2C6Cl4)2]nn–(n= 1 or 2), with Lewis bases such as pyridines, alkyl- and arylphosphines and phosphites, arsines, stibines, and phenylisonitrile, results in the dissociation of the dimers and the formation of five-co-ordinate complexes, [M(L)–(S–S)2]–(L = monodentate Lewis base). The monomeric, monoanionic iron bis(toluenedithiolene) forms with pyridines and phosphines weak complexes which are labile in solution; one complex of the corresponding cobalt dithiolene, [Co(PEt3)(S2C6H3Me)2]–, has been obtained. Fission of [FeS4C4(CN)4]22– with CN–, NCO–, and N3– results in the formation of the unstable complexes [Fe(X)–(S–S)2]2–(X = pseudohalide ion). With bidentate four-electron-donor Lewis bases such as 2,2′-bipyridyl, o-phenanthroline, ethylenediamine, and dimethylglyoxime, six-co-ordinate complexes of the type [M(N–N)–(S–S)2]– have been prepared. The voltammetry of those complexes which were not labile in dichloromethane solution is described, and the spectral and magnetic properties of the complexes are discussed. A tentative MO description of the five-co-ordinate complexes is suggested.