On the factors controlling the crystal packing of first-row transition-metal binary carbonyls

The crystal packings of [V(CO)6], [Cr(CO)6], [Mn2(CO)10], [Fe(CO)5], [Fe2(CO)9], [Co2(CO)8], and [Ni(CO)4] have been examined. It is shown that each molecule except [Ni(CO)4] is enclosed in a 12-molecule shell. Two basic packing motives are recognized, namely the cubo-octahedron and the anti-cubo-octahedron. Crystal and molecular qualifiers, such as molecular volumes, and packing coefficients have been calculated. The atom–atom pairwise potential-energy method has been used to estimate the separate contributions to the total packing potential energy (p.p.e.) of each kind of intermolecular interaction; given the same number of metal atoms, a CO group contributes a fairly constant amount to the p.p.e. The CO-group intermolecular mutual orientations have also been examined, showing that the CO axes are preferentially orthogonal in projection.