ANS-CHLOROTETRACARBONYL(PHENYLMETHYLIDYNE)CHROMIUM - EXPERIMENTAL ELECTRON DEFORMATION DENSITY

The electron deformation density of the complex Cl(CO)4Cr=CC6H5 crysta llizing in the noncentrosymmetric space group I4(1)md was determined a t 100 K, using Hansen and Coppens' aspherical atom multipolar model. P ositional parameters obtained in this refinement are very close to tho se obtained by a neutron diffraction experiment recorded at the same t emperature. Maps of the electron deformation density show characterist ic features of the C=O and Cr-C ligands interactions, and an important effect of back-bonding between the metal and the carbon atoms is in a greement with the Chatt and Duncanson model. The general features of t he different bonds are the same as those which have previously been ob served in the methyl homolog but are much better resolved. A conjugati on effect between the phenyl ring and the metal-carbyne bond is also e xperimentally observed. The chromium-carbon triple bond charge appears as a flat and deformed ellipsoid centered near the carbon atom and is very similar to theoretical ab-initio results and thus can be conside red as a typical deformation-density feature of the metal-carbyne bond .