Structure of mercury(II)–sulfur complexes by EXAFS spectroscopic measurements

We have examined alkaline sulfidic (0.5–0.005 M NaHS−) aqueous solutions of Hg(II)–S complexes [2.8–0.28 mM Hg(II)] using extended X-ray absorption fine structure (EXAFS) and an especially designed spectroscopic cell. The structural environment of Hg in the complex, determined by EXAFS analysis of Hg LIII edge fluorescence spectra taken at 298 and 348K, shows Hg coordinated by 2 S atoms at 2.30 Å. Multiple-scattering analysis reveals a linear [–S–Hg–S–] arrangement in the solution complex. These results are consistent with a low coordination number for Hg as predicted by relativistic models, ab initio calculations, and as determined from the structural environment of Hg in crystalline mercury compounds.