title: Competing non-covalent interactions in alkali metal ion-acetonitrile-water clusters.
abstract: Competitive ion-dipole, ion-water, and water-water interactions were investigated at the molecular level in M+ (CH3CN)n(H2O)m cluster ions for M = Na and K. Different [n,m] combinations for two different n + m cluster sizes were characterized with infrared predissociation spectroscopy in the O-H stretch region and MP2 calculations. In all cases, no differences were observed between the two alkali metal ions. The results showed that at the n + m = 4 cluster size, the solvent molecules interact only with the ion, and that the interaction between the ion and the large dipole moment of CH3CN decreases the ion-water electrostatic interactions. At the n + m = 5 cluster size, at least two different hydrogen-bonded structures were identified. In these structures, the ion-dipole interaction weakens the ability of the ion to polarize the hydrogen bonds and thus decreases the strength of the water-water interactions in the immediate vicinity of the alkali metal ion.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Vaden
authors.forename: James M
authors.initials: JM
authors.lastname: Lisy
mesh_terms: D000097:Acetonitriles / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D006860:Hydrogen Bonding; D007477:Ions; D008670:Metals / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D012997:Solvents / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D055672:Static Electricity; D014867:Water / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D007477:Ions; D008670:Metals; D012997:Solvents; D014867:Water; C032159:acetonitrile