Sequential bond energies of Cr(CO)_x⁺, x = 1-6

The sequential bond energies of Cr(CO)_x⁺, _x = 1-6, are determined by collision-induced dissociation in a guided ion beam tandem mass spectrometer. Values for the 0 K bond energies (in eV) are determined to be D(Cr⁺-CO) = 0.93 ± 0.04, D[(CO)Cr⁺-CO] = 0.98 ± 0.03, D[(CO)₂Cr⁺-CO] = 0.56 ± 0.06, D[(CO)₃Cr⁺-CO] = 0.53 ± 0.08, D[(CO)₄Cr⁺-CO] = 0.64 ± 0.03, and D[(CO)₅Cr⁺-CO] = 1.35 ± 0.08. The sum of these bond dissociation energies, 4.99 ± 0.14 eV, is in good agreement with literature thermochemistry. The observation that the relative bond strengths vary nonmonotonically with the number of ligands is discussed in terms of spin conservation and ligand field theory. The bond energy for Cr⁺-Xe is also determined as 0.7 ± 0.1 eV and compared with values for other transition metal ion rare gas species.