Binding energies of hydrated cobalt hydroxide ion complexes: A guided ion beam and theoretical investigation

The sequential bond energies of CoOH⁺(H₂O)_x complexes, where x = 1-4, are measured by threshold collision-induced dissociation using a guided ion beam tandem mass spectrometer. The primary dissociation pathway for all reactants consists of loss of a single water molecule. This is followed by the sequential loss of additional water molecules at higher collision energies for the x = 2-4 complexes, whereas the x = 1 reactant loses the OH ligand competitively with the H₂O ligand. The kinetic energy dependent cross sections for dissociation of CoOH⁺(H₂O)_x complexes are modeled to obtain 0 and 298 K binding energies. Our experimental results agree well with theoretically determined bond dissociation energies (BDEs) at the B3LYP, B3LYP-GD3BJ, B3P86, and MP2(full) levels of theory with a 6-311+G(2d,2p) basis set using geometries and vibrational frequencies determined at the B3LYP/6-311+G(d,p) level. Thermochemical information for the loss of OH from CoOH⁺(H₂O)_x where x = 0-4 is also derived by combining the present experimental HO-Co⁺(H₂O) and water loss BDEs from CoOH⁺(H₂O)_x with those for Co⁺(H₂O)_y from the literature. These BDEs are also compared to theory with mixed results.