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

Abstract

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.