Three in a Column

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Science  24 Aug 2007:
Vol. 317, Issue 5841, pp. 1010
DOI: 10.1126/science.317.5841.1010c

Numerous compounds comprising two bonded metal centers stabilized by bulky organic ligands have been characterized. However, zinc, cadmium, and mercury, which straddle the boundary between d-block and p-block metals, have only very recently been observed in this motif. Zhu et al. previously prepared zinc and cadmium dimers bearing bis(diisopropylphenyl) phenyl ligands, and have now synthesized a mercury dimer with the same ligand set to complete a homologous series. The compounds were accessed by reduction of metal halide precursors, and their solid-state structures characterized by x-ray crystallography. As predicted by theoretical calculations, the mercury-mercury bond is longer (and thus likely weaker) than the analogous zinc linkage, but shorter than the cadmium bond. The calculations implicate relativistic effects in this bond shortening, in keeping with a higher proportion of s-orbital character (as well as a measure of dz2 overlap) in the mercury dimer's highest occupied molecular orbital (HOMO). All three compounds have effectively linear C-M-M-C geometries, with the terminal phenyl rings canted at an approximate right angle relative to one another. The authors also prepared zinc and cadmium dimers incorporating bridging hydride ligands for structural comparison; the mercury hydride proved monomeric and was characterized spectroscopically. — JSY

J. Am. Chem. Soc. 129, 10.1021/ja072682x (2007).

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