Experiment proves that the ions [Cu(H2O)n]2+ (n=1,2) are stable in the gas phase

Electrospray ionization has been used to create the cupric ion hydrate [Cu(H2O)4]2+. Collisional activation and dissociation of this ion in a triple sector electrostatic mass spectrometer leads to the formation of the doubly charged ions [Cu(H2O)3]2+, [Cu(H2O)2]2+ and [Cu(H2O)]2+. The observation of the latter two ions vindicates the results of published theoretical calculations [El-Nahas et al., Chem. Phys. Lett. 318 (2000) 333], which predicted the stability of the cupric ion solvated by one or two water molecules and refutes the belief of Stace et al. [Chem. Phys. Lett. 329 (2000) 173] that their pick-up experiments prove that [Cu(H2O)3]2+ is the lowest stable gas-phase hydrate of the cupric ion.