Polyhedral {Ag 12 } and {Ag 16 } Clusters: Synthesis, Structural Characterization and Third-Order Nonlinear Optical Properties.

Two polyhedral silver-thiolate clusters, [S@Ag 16 (Tab) 10 (MeCN) 8 ](PF 6 ) 14 (Ag 16 ) and [Ag 12 (Tab) 6 (DMF) 12 ](PF 6 ) 12 (Ag 12 ), were synthesized by using electroneutral Tab species as protective ligands (Tab=4-(trimethylammonio)benzenethiolate, DMF=N,N-dimethylformamide, MeCN=acetonitrile). Ag 16 has a decahedral shape composed of eight pentagon {Ag 5 } units and two square {Ag 4 } units. The structure of Ag 12 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(CH 3 ) 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.