ORIGIN OF INEQUIVALENT CHROMIUM CARBONYL BOND LENGTHS IN CHLOROTETRACARBONYLETHYLIDYNECHROMIUM
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In the reported crystal structure of Cl(CO)4CrCCH3, two distinct pairs of Cr-Cco bond distances are reported. The difference Cr-Cco bond distances were attributed to two possible effects: (1) a hyperconjugative interaction of the methyl group on the chromium atom and (2) the effects of crystal packing on the molecule. In this paper, the molecule Cl(CO)4CrCCH3 is studied with use of ab initio full-gradient geometry optimization techniques in order to ascertain what causes the inequivalent Cr-Cco bond distances. From the results of the optimizations, it can be concluded that a tilt of the methyl group such that its local 3-fold axis is no longer collinear with the CrC axis is the cause of the inequivalent Cr-Cco bond distances. This tilt is caused by close contacts of the methyl hydrogens with chlorine atoms of neighboring molecules, an effect of crystal packing. The tilted methyl group then induces a charge flow between the chromium and carbyne carbon atoms, which, in turn, causes the Cr-CO bond distances to differ. 1990, American Chemical Society. All rights reserved.
