The influence of substituents at the C 2 carbon of thiosemicarbazones on bonding and nuclearity of silver(I) complexes

Abstract

Several thiosemicarbazones of the type (R 1R 2C 2 N 3–N 2H–C( S)N 1H 2) were reacted with silver salts, yielding a variety of complexes with different ligand coordination modes, nuclearities and stoichiometries. Reaction of silver(I) chloride with 2-benzoylpyridine thiosemicarbazone, HL 1, has formed a sulfur-bridged dimer, [Ag 2Cl 2(μ-S–HL 1) 2(PPh 3) 2] 2, while a similar reaction with 2-acetylpyridine thiosemicarbazone, HL 2, has formed a mononuclear complex {AgCl(η 1-S–HL 2) 2(PPh 3)] 1, with an unusual Ag:ligand:PPh 3 stoichiometry of 1:2:1. Reaction of silver(I) nitrate/acetate with benzophenone thiosemicarbazone, HL 3, and acetone thiosemicarbazone, HL 4, have yielded mononuclear complexes, [Ag(ONO 2)(η 1-S–HL 3)(PPh 3) 2] 3, and [Ag(N 3,S–HL 4)(PPh 3) 2]X (X NO 3 4, CH 3COO 5). In complexes 1 and 3 and in dimeric complex 2, the ligands exhibit the usual η 1-S-bonding and μ-S-bridging coordination commonly observed for thiosemicarbazone ligands with tetrahedral coinage metal ions. In complexes 4 and 5, however, weak binding properties of nitrate or acetate anions to silver favored N 3,S-chelation with the methyl substituents at the C 2 carbon of the thiosemicarbazones.