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 co
nsiderable technical challenge. Charge transfer prevents such species from
being "grown" as cluster ions and techniques, such as electrospray, do not
always produce the desired charge state or allow for experiments to be perf
ormed on a broad range of ligands. Discussed here are new results from a te
chnique which promises to overcome some of these problems, and appears capa
ble of producing complexes from a wide variety of metals and ligands. Data
are-presented for complexes based on silver(II) in association with a broad
range of ligands, including pyridine, tetrahydrofuran, and benzene. For ea
ch [AgLn](2+) system, two important quantities are identified: (i) the mini
mum number of ligands required to form a stable unit and (ii) the value of
n for which the intensity distribution reaches a maximum. For nitrogen-cont
aining ligands these numbers are 2 and 4, respectively, and for oxygen-cont
aining ligands 4 and 5. A series of aromatic ligands all exhibit coordinati
on numbers of 2. For several of the nitrogen-based ligands the most stable
combinations correspond to those identified in the condensed phase, and [Ag
(pyridine)(4)](2+) is a very good example of such behavior. In the case of
the oxygen-containing ligands, there are no direct condensed phase analogue
s, but some of the more stable combinations identified may offer prospects
for future preparative work. Within the latter group, not only was the pres
ence of stable silver(II)/CO2 complexes very unexpected, but with [Ag(CO2)(
4)](2+) being the most stable combination, the pattern of behavior is marke
dly different from that of other oxygen-containing ligands. The composition
and charge states of many of the stable complexes were confirmed via colli
sional activation, where both ligand loss and charge-transfer processes cou
ld be identified. Only one example of a chemical reaction could be clearly
identified as being initiated by the presence of silver(II).