Halometallate Complexes of Germanium(II) and (IV): Probing the Role of Cation, Oxidation State and Halide on the Structural and Electrochemical Properties

The Ge IV chlorometallate complexes, (EMIM)2- (GeCl6), (EDMIM)2(GeCl6) and (PYRR)2(GeCl6) (EMIM = 1-ethyl- 3-methylimidazolium; EDMIM = 2,3-dimethyl-1-ethylimidazo- lium; PYRR = N-butyl-N-methylpyrrolidinium) have been syn- thesised and fully characterised; the first two also by single- crystal X-ray diffraction. The imidazolium chlorometallates exhibited significant CH···Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solu- tion 1 H NMR data also showed cation-anion association. The synthesis and characterisation of Ge II halometallate salts (EMIM)(GeX3 )( X= Cl, Br, I) and (PYRR)(GeCl3), including single-crystal X-ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the in- termolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solu- tion. Cyclic-voltammetry experiments on the Ge IV species in CH2Cl2 solution showed two distinct, irreversible reduction waves attributed to Ge IV -Ge II and Ge II -Ge 0 , whereas the Ge II species exhibited one irreversible reduction wave. The po- tential for the Ge II -Ge 0 reduction was unaffected by chang- ing the cation, although altering the oxidation state of the precursor from Ge IV to Ge II does have an effect; for a given cation, reduction from the (GeCl3) � salts occurred at a less cathodic potential. The nature of the halide co-ligand also has a marked influence on the reduction potential for the Ge II -Ge 0 couple, such that the reduction potentials for the (GeX3) � salts become significantly less cathodic when the halide (X) is changed Cl!Br!I.