Electrospray ionization of divalent transition metal ion bipyridine complexes: spectroscopic evidence for preparation of solution analogs in the gas phase

Laser photofragmentation mass spectrometry provides the first spectroscopic evidence that electrospray ionization (ESI) produces gas-phase clusters containing transition metal ion complexes analogous to those found in solution. In solution, the tris(2,2′-bipyridyl)iron(II) and ruthenium(II) coordination complexes exhibit strong metal-to-ligand charge transfer (MLCT) absorption bands in the visible. The characteristic MLCT absorption bands are intact in gas-phase methanolic clusters containing these complexes, indicating that the metal oxidation state is preserved during ESI. Comparison of the ionic species produced by ESI and other ionization/volatilization techniques offers some insight on stabilization of the +2 charge in these gas-phase systems.