Reduction from copper(II) to copper(I) upon collisional activation of (pyridine)2CuCl+

Electrospray ionization of dilute aqueous solutions of copper(II) chloride-containing traces of pyridine (py) as well as ammonia permits the generation of the gaseousions (py)(2)Cu+ and(py)(2)CuCl+, of which the latter is a formal copper(II) compound, whereas the former contains copper(I). Collision-induced dissociation of the mass-selected ions in an ion-trap mass spectrometer (IT-MS) leads to a loss of pyridine from (py)(2)Cu+, whereas an expulsion of atomic chlorine largely prevails for (py)(2)CuCl+. Theoretical studies using density functional theory predict a bond dissociation energy (BDE) of BDE[(py)(2)Cu+-Cl] = 125 kJ mol(-1), whereas the pyridine ligand is bound significantly stronger, i.e. BDE[(py)CuCl+-py]=194 kJ mol(-1) and BDE[(py)Cu+-py]= 242 kJ mol(-1). The results are discussed with regard to the influence of the solvation on the stability of the Cu-I/Cu-II redox couple. Copyright (C) 2010 John Wiley & Sons, Ltd.