The Short of It

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Science  04 Feb 2000:
Vol. 287, Issue 5454, pp. 769
DOI: 10.1126/science.287.5454.769g

Chromous acetate, first reported in the 1840s, adopts a ‘paddlewheel’ structure (I, where R is a methyl group and the ligand L is water). Elimination of the water ligands should allow an additional bond (presumably a fourth or ‘quadruple’ bond) to form between the chromium atoms and shorten the bond distance from 2.34 angstroms (Å), but x-ray studies show that the oxygen atoms of the carboxylates play the role of axial ligands. An electron-diffraction study of the water-free gas-phase compound gave a bond distance of 1.97 Å, but theoretical studies and the lack of crystal structures cast some doubt on whether such a short bond would form.

Cotton et al. now report that, with judicious design of the carboxylate ligand (III), a species with no axial ligands can be crystallized that has a Cr-Cr bond distance of 1.97 Å. These results should stimulate new theoretical studies of Cr-Cr quadruple bonds, which are among the shortest seen between any pair of atoms relative to their size.—PDS

J. Am. Chem. Soc.122, 416 (2000).

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