Tetrahalogenomercury(II) complexes. A study of their electronic spectra, formation constants, ionic strength, and cation effects

Abstract

The unambiguous electronic absorption spectra of HgX₄²⁻(X = Cl, Br, or I) in methanol have been determined for the first time. The spectra were resolved into their component Gaussian bands, and assigned using a correlation diagram for T_d symmetry. The effects of second-order spin–orbit coupling account satisfactorily for the observed band intensities and splittings. The formation constants, K₄, as a function of ionic strength were computed over the complete spectral range by multiple linear regression analysis and were, extrapolated to infinite dilution, 0.4 ± 0.1 for Hgl₄²⁻ and HgBr₄²⁻, and 5.7 ± 0.2 for HgCl₄²⁻. Significant cation effects were observed upon the spectra of HgX₂ with added X⁻, and may partially be explained in terms of the extended Debye–Hückel equation. Key words: electronic absorption spectra, mercury(II) halide complexes, formation constants, ionic strength, Gaussian band analysis.