RING PUCKERING AND METAL-METAL SEPARATIONS IN ONE CLASS OF DIBRIDGED BINUCLEAR COMPLEXES

A recent structure of Cp2M2(NO)2 and a comparison with other Cp2M2(CO)x(NO)2-x structures showed that the two metal atoms and the bridging carbonyls or nitrosyls in nearly all cases lie in a single plane. However, the isolobal compound Co2(CO)8 and related structures with terminal carbonyls have the inner rhomboid puckered. The reasons for the presence or absence of the puckering deformation are traced to the slightly different symmetry properties of the frontier orbitals in the MCp or M(CO)3 cases. Metal-metal bond-length differences with electron count are examined, leading to an apparent contradiction between the theory and the structural facts known for this series of compounds. © 1979, American Chemical Society. All rights reserved.