Web Release Date: May 21,
Bonding of Seven Carbonyl Groups to a Single Metal Atom: Theoretical Study of M(CO)n (M = Ti, Zr, Hf; n = 7, 6, 5, 4)
Center for Computational Quantum Chemistry, South China Normal University, Guangzhou, 510631 China, School of Chemistry and Chemical Engineering, Central South University, Changsha, 410083 China, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080 China, Institute of Chemical Physics, Beijing Institute of Technology, Beijing 100081, China, and Department of Chemistry and Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602
Received January 16, 2008
Abstract:
The equilibrium geometries, thermochemistry, and vibrational frequencies of the homoleptic metal−carbonyls of the group 4 elements, M(CO)n (M = Ti, Zr, Hf; n = 7, 6, 5, 4) were predicted using density functional theory. Analogous M(CO)n structures were found for all three metals. The global minima for the 18-electron M(CO)7 molecules are all singlet C3v capped octahedra. The global minima for the 16-electron M(CO)6 species are triplet M(CO)6 structures distorted from Oh symmetry to D3d symmetry. However, the corresponding singlet M(CO)6 structures lie within 5 kcal/mol of the triplet global minima. The global minima for M(CO)n (n = 5, 4) are triplet structures derived from the D3d distorted octahedral structures of M(CO)6 by removal of one or two CO groups, respectively. Quintet D3h trigonal bipyramidal structures for M(CO)5 and singlet Td tetrahedral structures for M(CO)4 are also found, as well as higher energy structures for M(CO)6 and M(CO)7 containing a unique CO group bonded to the metal atom through both M−C and M−O bonds. The dissociation energies M(CO)7 → M(CO)6 + CO are substantial, indicating no fundamental problem in bonding seven CO groups to a single metal atom.
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