CHEMICAL BONDING IN METALLAHETEROCUMULENE COMPLEXES .1. NEUTRON-DIFFRACTION STUDY ON A SINGLE-CRYSTAL OF PENTACARBONYLDIETHYLCYANAMIDECHROMIUM AT 110-K

The crystal structure of the complex [Cr(NCNEt2) (CO)5] has been deter mined by neutron diffraction at 110 K. The crystal used was twinned an d the twin law was analysed. The structure is composed of layers of mo lecules parallel to the twin plane which are held together by van der Waals interactions and intermolecular hydrogen bonds. The cyanamide li gand has an intermediate sigma-donor:tau-acceptor ratio, stronger, for example, than the carbene ligand. There are two types of cis-carbonyl groups in the structure, resulting from the conjugation effect of the cyanamide skeleton in the molecule. Charge transfer, which is charact eristic of the delocalization of the lone pair of the amino nitrogen a long the six-atom linear chain, is observed along the bonds on the bin ary molecular axis, including the transcarbonyl group.