title: Electronic structure of the alkyne-bridged dicobalt hexacarbonyl complex Co(2) micro-C(2)H(2) (CO)(6): evidence for singlet diradical character and implications for metal-metal bonding.
abstract: A series of ab initio calculations are presented on the alkyne-bridged dicobalt hexacarbonyl cluster Co2 micro-C2H2 (CO)6, indicating that this compound has substantial multireference character, which we interpret as evidence of singlet diradical behavior. As a result, standard theoretical methods such as restricted Hartree-Fock (RHF) or Kohn-Sham (RKS) density functional theory cannot properly describe this compound. We have therefore used complete active space (CAS) methods to explore the bonding in and spectroscopic properties of Co2 micro-C2H2 (CO)6. CAS methods identify significant population of a Co-Co antibonding orbital, along with Co-pi* back-bonding, and a relatively large singlet-triplet energy splitting. Analysis of the electron density and related quantities, such as energy densities and atomic overlaps, indicates a small but significant amount of covalent bonding between cobalt centers.
authors.affiliation: School of Chemistry, Cardiff University, Park Place, Cardiff, UK. platts@cf.ac.uk
authors.forename: James A
authors.initials: JA
authors.lastname: Platts
authors.forename: Gareth J S
authors.initials: GJ
authors.lastname: Evans
authors.forename: Michael P
authors.initials: MP
authors.lastname: Coogan
authors.forename: Jacob
authors.initials: J
authors.lastname: Overgaard