Quantum-chemical study of the geometric and electronic structure of the CoC2 molecule

DFT (B3LYP) calculations have been performed to study the CoC2 molecule in its different geometric conformations and electronic states. The energies have been refined using ab initio multiconfigurational CASSCF/CASPT2 calculations. Both approaches are in a good semi-quantitative agreement between themselves and predict the symmetric triangular (C-2 nu) structure to be more stable than the linear (C-infinity nu) conformation. The ground state has been found to be a quartet, which can formally be regarded as an ionic Co2+-C-2(2-) complex, resulting from a transfer of the two 4s electrons of the cobalt atom to the 3 sigma(g) orbital of the C-2 ligand and distributing the remaining seven valence electrons over the split 3d orbitals. (C) 2000 Elsevier Science B.V. All rights reserved.