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 gaseous ions (py)₂Cu⁺ and (py)₂CuCl⁺, 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)₂Cu⁺, whereas an expulsion of atomic chlorine largely prevails for (py)₂CuCl⁺. Theoretical studies using density functional theory predict a bond dissociation energy (BDE) of BDE[(py)₂Cu⁺ ‐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 CuI/CuII redox couple. Copyright © 2010 John Wiley & Sons, Ltd.