Polyhedral {Ag₁₂} and {Ag₁₆} Clusters: Synthesis, Structural Characterization and Third-Order Nonlinear Optical Properties

Two polyhedral silver-thiolate clusters, [S@Ag₁₆(Tab)₁₀(MeCN)₈](PF₆)₁₄ (Ag₁₆) and [Ag₁₂(Tab)₆(DMF)₁₂](PF₆)₁₂ (Ag₁₂), were synthesized by using electroneutral Tab species as protective ligands (Tab=4-(trimethylammonio)benzenethiolate, DMF=N,N-dimethylformamide, MeCN=acetonitrile). Ag₁₆ has a decahedral shape composed of eight pentagon {Ag₅} units and two square {Ag₄} units. The structure of Ag₁₂ is a cuboctahedron, a classical Archimedean structure composed of six triangular faces and eight square faces. The former configuration is discovered in silver-thiolate cluster for the first time, possibly benefited from the more flexible coordination between the Tab ligand and Ag⁺ facilitated by the electropositive -N(CH₃)₃ ⁺ substituent group. Third-order nonlinear optical studies show that both clusters in DMF exhibit reverse saturate absorption response under the irradiation of 532 nm laser.