The influence of substituents at the C2 carbon of thiosemicarbazones on bonding and nuclearity of silver(I) complexes

Several thiosemicarbazones of the type (R1R2C2N3–N2H–C(S)N1H2) 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, HL1, has formed a sulfur-bridged dimer, [Ag2Cl2(μ-S–HL1)2(PPh3)2] 2, while a similar reaction with 2-acetylpyridine thiosemicarbazone, HL2, has formed a mononuclear complex {AgCl(η1-S–HL2)2(PPh3)] 1, with an unusual Ag:ligand:PPh3 stoichiometry of 1:2:1. Reaction of silver(I) nitrate/acetate with benzophenone thiosemicarbazone, HL3, and acetone thiosemicarbazone, HL4, have yielded mononuclear complexes, [Ag(ONO2)(η1-S–HL3)(PPh3)2] 3, and [Ag(N3,S–HL4)(PPh3)2]X (XNO34, CH3COO 5). In complexes 1 and 3 and in dimeric complex 2, the ligands exhibit the usual η1-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 N3,S-chelation with the methyl substituents at the C2 carbon of the thiosemicarbazones.

The substitution at C2 carbon has led to a change in stoichiometry, nuclearity and dentacy of thiosemicarbazone complexes of silver(I). For example, 2-acetylpyridine thiosemicarbazone (HL2) has yielded complex 1, while 2-benzoylpyridine thiosemicarbazone (HL1) has yielded a sulfur-bridged dimer 2.Figure optionsDownload as PowerPoint slide