Douglas M. Collins

Crystal and molecular structure of bis(pentamethylcyclopentadienyl)dicarbonyldicobalt

The compound (η 5 -Me 5 C 5 )Co(μ-CO) 2 Co(η 5 -Me 5 C 5 ) has been prepared and characterized. The crystal structure has been determined and the CoCo distance found to be 2.327(2) A. This structure completes the information on MM distances in the series of compounds CpM(EO)(E′O)MCp, where Cp = C 5 H 5 or Me 5 C 5 , M = Fe or Co and E = C or N, several members of which were previously studied by others. The EAN rule would predict a double bond here as in the isoelectronic compound CpFe(NO) 2 FeCp and the MM distances are virtually identical in the two molecules. Disordered packing of the molecules limits the accuracy with which the molecular dimensions, other than CoCo, may be determined. However, the structure is in generally close agreement with those of the other molecules in the set previously mentioned. The crystals are monoclinic with a 7.433(2) A, b 14.704(8) A, c 9.671(2) A, β 101.84(2)° and V 1034.6(7) A 3 ; Z = 2. The structure was refined to R 1 = 0.062 and R 2 = 0.074 using a disordered model in space group P 2 1 / m .

The molecular structure and dynamic NMR spectrum of bis[(η5-cyclopentadienyl)dicarbonylmolybdenum]-μ-ethyne(MoMo)

Abstract The title compound, (η5-C5H5)2Mo2(CO)4(μ-HC CH) has a molecular structure practically identical to that of its previously described analog containing μ-EtC CEt. Its13C NMR at −144°C has a broad doublet in the terminal CO region; this sharpens at −118°C then again broadens (-100°C) and finally coalesces below −58°C to a single resonance. The appearance of a semi-bridging CO (SBCO) ligand in the title compound and its EtC CEt analog, but not in a related compound with μ-H2C C CH2 is attributed to internal crowding and it is suggested that these compounds may provide the most unambiguous examples of such an effect.