Coordination and chemistry of stable Cu(II) complexes in the gas phase

A technique has been developed that provides a solution to the very conside rable technical problem of preparing gas-phase complexes from transition me tals in their higher oxidation states, i.e., Cu(II), Cr(III), Fe(LI), etc. Charge transfer prevents complexes, such as [Cu . (H2O)(n)](2+), from being prepared via nucleation about an ion core, and yet these ions are pivotal to an understanding of transition metal chemistry. Discussed here are new r esults from a technique that appears capable of producing complexes from a wide variety of metals and ligands. Data are presented for copper(II) in as sociation with 20 different ligands, including water, ammonia, pyridine, te trahydrofuran, and benzene. For each [Cu .L-n](2+) system, two important qu antities are identified: (i) the minimum number of ligands required to form a stable unit and (ii) the value of n for which the intensity distribution reaches a maximum. The data shaw considerable variation as a function of t he composition and size of solvent molecule, with evidence of stable coordi nation shells containing between 2 and 8 molecules, In most instances, coor dination shells containing more than four molecules can be attributed to th e formation of an extended network of hydrogen bonds. Collisional activatio n of size-selected clusters reveals the presence of extensive ligand-to-met al electron transfer in the smaller complexes, and in several cases, charge transfer is also accompanied by chemical reactivity. The extent of charge transfer is frequently observed to be determined by the stability of the si ngly charged metal-containing product.