Solvation of Transition Metal Ions by Water. Sequential Binding Energies of M+(H2O)x (x = 1-4) for M = Ti to Cu Determined by Collision-Induced Dissociation

Abstract

Thresholds for collision-induced dissociation of M^+(H_2O), (x = 1-4, M = Ti to Cu) with xenon are measured by using guided ion beam mass spectrometry. In all cases, the primary product is endothermic loss of one water molecule. The cross-section thresholds are interpreted to yield 0 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the clusters, and dissociation lifetimes. Overall, the results presented here are consistent with previously reported values for x = 1 and 2 and resolve several discrepancies in these values. Theory is shown to accurately predict the BDEs of x = 1 and 2 as well as the sign of the difference between them. For all ions but Mn^+, the bond dissociation energies (BDEs) of the first and second water molecules are large compared with those of the third and fourth water molecules. Trends in BDEs are discussed in terms of hybridization and spin changes occurring at the transition metal center.