V(CO)7‎+‎: A capped octahedral structure completes the 18-electron rule

Molecular structures, relative energies, vibrational spectra and bond dissociation energies of the seven-coordinate, 18-valence-electron vanadium carbonyl complex, V ( CO ) 7 + , are predicted theoretically. A C3v symmetry capped octahedral structure is found to be the global minimum and predicted CO vibrational frequencies range from 2023 to 2122 cm−1, generally consistent with experiment for known cationic carbonyl complexes. The lowest energy structure of V ( CO ) 6 + is also determined, a triplet D3d structure. The resulting bond dissociation energy, De, for CO ligand loss is predicted to be 11 kcal mol−1 with B3LYP, in good agreement with experiment, while BP86 and MP2 predict much higher values of 30 and 39 kcal mol−1.