Ligand field photofragmentation spectroscopy of [Ag(L)N]2+ complexes in the gas phase: experiment and theory

Experiments have been undertaken to record photofragmentation spectra from a series of [Ag(L)N]2+ complexes in the gas phase. Spectra have been obtained for silver(II) complexed with the ligands (L): acetone, 2-pentanone, methyl-vinyl ketone, pyridine, and 4-methyl pyridine (4-picoline) with N in the range of 4-7. A second series of experiments using 1,1,1,3-fluoroacetone, acetonitrile, and CO2 as ligands failed to show any evidence of photofragmentation. Interpretation of the experimental data has come from time-dependent density functional theory (TDDFT), which very successfully accounts for trends in the spectra in terms of subtle differences in the properties of the ligands. Taking a sample of three ligands, acetone, pyridine, and acetonitrile, the calculations show all the spectral transitions to involve ligand-to-metal charge transfer, and that wavelength differences (or lack of spectra) arise from small changes in the energies of the molecular orbitals concerned. The calculations account for an absence in the spectra of any effects due to Jahn-Teller distortion, and they also reveal structural differences between complexes where the coordinating atom is either oxygen or nitrogen that have implications for the stability of silver(II) compounds. Where possible, comparisons have also been made with the physical properties of condensed phase silver(II) complexes.