Binding of ammonia to small copper and silver clusters

We report equilibrium geometries, harmonic frequencies, and thermochemical data for the metal cluster-ammonia complexes Ag-n(NH3) and Cu-n,(NH3) (n = 1,2,3,4), Ag-4(NH3)(2), and Cu-4(NH3)(2) calculated by a density functional method. The calculated shifts in ammonia umbrella mode frequency correlate with the observed shifts and the calculated enthalpies of complexation. Th e preferred site for NH3 adsorption and the calculated bond enthalpies can be rationalized by considering atomic charges obtained from a natural popul ation analysis and polarization of the metal electron density. (C) 1999 Els evier Science B.V. All rights reserved.