PROBING SOLVATAION SHELLS OF Ni(H2O)m2+ (m=4-10) AND NiOH(H2O)n+ (n=2-5) WITH CRYOGENIC ION VIBRATIONAL SPECTROSCOPY.

The solvation of metal cations, a process that dictates chemistry in both catalytic and biological systems, has been well studied using gas-phase spectroscopy. However, until recently the solvation of cation-anion pairs has been poorly explored. Here we present gas-phase spectra of chem{Ni(H_2O)_m}$^{2+}$ (m=4-10) and chem{NiOH(H_2O)_n}$^{+}$ (n=2-5) obtained via cryogenic ion vibrational spectroscopy (CIVS). Our results indicate that as cluster size decreases, the chem{NiOH(H_2O)_n}$^{+}$ moiety becomes more favorable over the chem{Ni(H_2O)_m}$^{2+}$ moiety. Analysis of the spectral data in conjunction with density functional theory calculations shows that both species have a 1$^{st}$ solvation shell consisting of six lingands. However, the chem{NiOH(H_2O)_n}$^{+}$ clusters show evidence of strong interactions between a first solvation shell water ligand and the OH$^{-}$ group of the metal, similar to the interactions previously observed in chem{CaOH(H_2O)_n}$^{+}$ and chem{MgOH(H_2O)_n}$^{+}$