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)[GeCl(6)], [EDMIM](2)[GeCl(6)] and [PYRR](2)[GeCl(6)] (EMIM=1-ethyl-3-methylimidazolium; EDMIM=2,3-dimethyl-1-ethylimidazolium; PYRR=N-butyl-N-methylpyrrolidinium) have been synthesised and fully characterised; the first two also by single-crystal X-ray diffraction. The imidazolium chlorometallates exhibited significant C–H⋅⋅⋅Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solution (1)H NMR data also showed cation–anion association. The synthesis and characterisation of Ge(II) halometallate salts [EMIM][GeX(3)] (X=Cl, Br, I) and [PYRR][GeCl(3)], including single-crystal X-ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the intermolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solution. Cyclic-voltammetry experiments on the Ge(IV) species in CH(2)Cl(2) 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 potential for the Ge(II)–Ge(0) reduction was unaffected by changing 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 [GeCl(3)](−) 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 [GeX(3)](−) salts become significantly less cathodic when the halide (X) is changed Cl→Br→I.