Guided Ion Beam Studies of the Collision-Induced Dissociation of CuOH+(H2O)n (n=1-4): Comprehensive Thermodynamic Data for Copper Ion Hydration

Threshold collision-induced dissociation (TCID) using a guided ion beam tandem mass spectrometer is performed on CuOH+(H2O)n where n = 1-4. The primary dissociation pathway for the n = 2-4 reactants consists of loss of a single water molecule followed by the sequential loss of additional water molecules at higher collision energies. The n = 1 reactant departs from this trend by losing the OH ligand and the H2O ligand competitively. Loss of the OH ligand is thermodynamically favored, whereas H2O loss is the kinetically favored process, consistent with heterolytic cleavage of the dative bond. The data are analyzed using a statistical model after accounting for internal and kinetic energy distributions, multiple collisions, and kinetic shifts to obtain 0 K bond dissociation energies (BDEs). These are also converted using a rigid rotor/harmonic oscillator approximation to yield thermodynamic values at room temperature. Experimental BDEs are compared to theoretical BDEs determined at the B3LYP, cam-B3LYP, B3P86, M06, CCSD(T), 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. In addition, BDEs for the loss of OH from CuOH+(H2O)n where n = 0, 2-4 are derived using the experimental BDEs for dissociation of CuOH+(H2O)n and literature values for Cu+(H2O)n.