Silver-Water Clusters: A Computation of Agn(H2O)m for n = 1-6; M = 1-8

Calculations of the equilibrium structure and properties of silver-water neutral, cation, and anion clusters Agn(H2O)m, n = 1-6; m = 1-8 are reported. Density functional theory using the PBE1PBE functional is applied to determine stationary points on the energy surface. Several basis sets were compared in this study of cluster thermodynamic properties in the gas and aqueous phases. Clusters of each charge state show Ag-O coordination and a significant number of H bonded water molecules forming a second sphere. This is apparent for neutral clusters that have Ag-O and Ag-H coordination and a chain of H bonded water molecules. Cation clusters have Ag-O coordination in the first sphere with the next water ligands attached by H bonds. The anion structures involve Ag-H coordination, and at sizes of four silver atoms and above the Ag-O coordination mode is also observed. The hydration free energies at room temperature and energy were computed and are consistent with aggregation to larger particles in gas and aqueous phases. The free energy of solvation of charged silver clusters decreases with size in contrast to several neutral clusters. The calculated value for Ag+ solvation free energy and bond strengths compared well with experiment. Possible reactions in aqueous phase involving nucleation, silver ion adsorption, or electron acceptance from reducing agents were evaluated, and trends were found to be consistent with experiment. A reaction pathway under mild reducing conditions for nucleation and growth of small silver clusters in the aqueous phase involving catalysis by neutral particles is proposed based on calculated thermodynamic properties. © 2017 American Chemical Society.