Formation of Halide Complexes of Methyl- and Inorganic Germanium(IV) in Aqueous Hydrohalogenic Acid Solutions

Article abstract of DOI:10.1246/bcsj.64.3363

The reaction of methyl- and inorganic germanium(IV) hydroxides ((CH3)_nGe(OH)_4-n; n = 1, 2, or 3) with halide ions (X = Cl^-, Br^-, or I^-) to form halide complexes ((CH3)_nGeX_4-n) in aqueous acidic solution has been investigated by liquid-liquid extraction, solid-liquid distribution (ion exchange), and 1H NMR spectrometry.It has been found that methylgermanium moieties are hard Lewis acids similarly to inorganic germanium(IV), because the stability constant of the halide complexes decreases in the order Cl^- > Br^- > I^-.The stability constant for an X^- ion increases as the number of methyl groups attached to the germanium atom increases.The species of inorganic-, monomethyl-, and dimethylgermanium are nonionic and have a tetrahedral structure in HX solution, and OJ^- ions attached to the germanium atom are stepwise substituted by X^- ions with an increase in HX activity.Trimethylgermanium alone forms a cation, when the activity of HX is not sufficiently high.These facts suggest that the transfer of a negative charge from methyl groups to the central germanium atom lowers the stability of the bond between the germanium atom (hard acid) and an OH^- ion (hard base).