Synthesis, crystal structures, and biological activities of 2-thiophene N(4)-methylthiosemicarbazone and its unusual hexanuclear silver(I) cluster

2-Thiophene N(4)-methylthiosemicarbazone (HL) and its Ag(I) complex of formula [Ag6(L)6⋅ 4DMF] 1 have been synthesized and characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction studies. The silver(I) complex 1 with a 1:1 metal–ligand molar ratio is an unusual hexanuclear cluster with 6 silver atoms in different environments: four silver atoms of them are considered to be 3-coordinate form, which are coordinated by two thiolate sulfur atoms and one imine nitrogen and the other two silver atoms are considered to be 4-coordinate form, which are coordinated by three thiolate sulfur atoms and one imine nitrogen, with four thiolate sulfur bridging two silver atoms and two thiolate sulfur bridging three silver atoms. Biological studies, carried out in vitro against bacteria, fungi and SMMC-7721 liver cancer cell line, respectively, have shown that the free ligand and the title complex show distinct difference in the biological property.