| Abstract
| - The preparation and study of gas-phase transition-metal complexes in their higher oxidation states,i.e., Cu(II), Cr(III), Fe(II), etc., presents a considerable technical challenge. Charge transfer prevents suchspecies from being “grown” as cluster ions and techniques, such as electrospray, do not always produce thedesired charge state or allow for experiments to be performed on a broad range of ligands. Discussed here arenew results from a technique which promises to overcome some of these problems, and appears capable ofproducing complexes from a wide variety of metals and ligands. Data are presented for complexes based onsilver(II) in association with a broad range of ligands, including pyridine, tetrahydrofuran, and benzene. Foreach [AgLn]2+system, two important quantities are identified: (i) the minimum number of ligands required toform a stable unit and (ii) the value of n for which the intensity distribution reaches a maximum. For nitrogen-containing ligands these numbers are 2 and 4, respectively, and for oxygen-containing ligands 4 and 5. Aseries of aromatic ligands all exhibit coordination numbers of 2. For several of the nitrogen-based ligands themost stable combinations correspond to those identified in the condensed phase, and [Ag(pyridine)4]2+ is avery good example of such behavior. In the case of the oxygen-containing ligands, there are no direct condensed-phase analogues, but some of the more stable combinations identified may offer prospects for future preparativework. Within the latter group, not only was the presence of stable silver(II)/CO2 complexes very unexpected,but with [Ag(CO2)4]2+ being the most stable combination, the pattern of behavior is markedly different fromthat of other oxygen-containing ligands. The composition and charge states of many of the stable complexeswere confirmed via collisional activation, where both ligand loss and charge-transfer processes could beidentified. Only one example of a chemical reaction could be clearly identified as being initiated by the presenceof silver(II).
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