| Summary |
Developments in experimental technique have made it possible to generate in the gas phase dication complexes consisting of solvated metal ions, [M(L)n]2+, where L is one of twenty possible ligands and M2+ can be Mg2+, Ca2+, Sr2+, Mn2+, Cr2+, Cu2+, Ag2+, Au2+, Zn2+, Pb2+ or Sn2+. Many of the complexes that can be prepared, such as those containing Cu(II), occupy key positions in classical inorganic chemistry. Others, such as those with Au(II) represent oxidation states that are difficult to achieve in the condensed phase. Since these ions are in the gas phase, they offer a unique opportunity to explore topics in spectroscopy, solvation and coordination that cannot be investigated in the condensed phase because of the presence of bulk solvent and counter ions. Two new studies involving metal dications will be discussed in detail.
(i) A quadrupole ion trap apparatus has been developed for recording UV photofragment spectra from cold metal dication complexes. The apparatus has been adapted to store and cool ions via collisions with a helium buff gas that maintains contact with a liq. N2 reservoir. From a cold-ion UV spectrum recorded for the cluster complex [Zn(pyridine)4]2+ it has been possible, using DFT, to identify transitions between individual electronic states. Many of these transitions originate from molecular orbitals associated with the pyridine molecules; however, some transitions appear to involve electronic excitation from zinc-based orbitals of the complex. New results will be presented of spectra recorded on a range of dication metal-solvent clusters.
(ii) From a study of the conditions necessary to stabilise metal dication complexes against charge transfer, it has been possible to derive a molecular view of such fundamental processes as preferential solvation and the hydrolysis mechanism. For the latter, experiments have been undertaken that involve studying a wide range of metal dications each in the presence of small numbers of water molecules. The results show how the Lewis acidity of a metal ion in aqueous solution can be identified with its instability in the presence of a water cluster.
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