Chemistry

Heptacoordinate Mercury

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Science  27 Apr 2007:
Vol. 316, Issue 5824, pp. 516-517
DOI: 10.1126/science.316.5824.516d

Although diffraction techniques have offered detailed pictures of atomic arrangements in solids, determining the corresponding structures in solution, where most reactions occur, is hindered by rapid fluctuations in the coordination environment. The solvation shell structure of aqueous mercuric ions is of interest on account of the metal's toxicity, but has proven to be an especially elusive target because of the absence of strong characteristic features in the visible absorption spectrum. Inferences from the solid state have favored a distorted octahedral, or hexacoordinate, arrangement of water molecules around the central Hg(II) ion. Chillemi et al. present experimental and theoretical evidence implicating the presence of an extra water molecule in the shell, giving rise to an unusual seven-coordinate arrangement. Primary support for this claim emerges from x-ray absorption near-edge spectra, which are not consistent with an octahedral shell. Quantum chemical calculations and accompanying molecular dynamics simulations paint a picture of a flexible seven-membered shell that persists for several nanoseconds, while occasionally accepting or expelling water to create much shorter-lived six-and eight-coordinate environments. — JSY

J. Am. Chem. Soc. 129, 10.1021/ja066943z (2007).

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