Syntheses, structures and antimicrobial activities of various metal complexes of hinokitiol

Metal–oxygen bonding complexes (M = MgII, MnII, NiII, MoVI, WVI, PdII, SbIII, BiIII, FeIII, TiIV, KI, BaII, ZrIV and HfIV) with a hinokitiol (Hhino; 2-hydroxy-4-isopropylcyclohepta-2,4,6-trienone or β-thujaplicin) ligand, which has two unequivalent oxygen donor atoms, were synthesized and characterized by elemental analysis, TG/DTA, FT-IR and solution (1H and 13C) NMR spectroscopy. Single-crystal X-ray structure analysis revealed various molecular structures for the complexes, which were classified into several families of family, i.e. type A [MII(hino)2(L)]2 (M = MgII, MnII, NiII; L = EtOH or MeOH), with a dimeric structure consisting of one bridging hino− anion, one chelating hino− anion and one alcohol or water molecule, type B, with the octahedral, cis-dioxo, bis-chelate complexes cis-[MVIO2(hino)2] (M = MoVI, WVI), type C, with square planar complex [MII(hino)2] (M = PdII), type D, with tris-chelate, 7-coordinate complexes with one inert electron pair [MIII(hino)3] (M = SbIII, BiIII), type D′, with the bis-chelate, pseudo-6-coordinate complexes with one inert electron pair [MIII(hino)2X] (M = SbIII, X = Br), type E, with tris-chelate, 6-coordinate complexes with Δ and Λ isomers [MIII(hino)3] (M = FeIII), type E′ of bis-chelate, 6-coordinate complex [MIV(hino)2X2] (M = TiIV, X = Cl), type F, with water-soluble alkali metal salts [MI(hino)] (M = KI), and type H, with tetrakis-chelate, 8-coordinate complexes [MIV(hino)4](M = ZrIV, HfIV). These structural features were compared with those of metal complexes with a related ligand, tropolone (Htrop). The antimicrobial activities of these complexes, evaluated in terms of minimum inhibitory concentration (MIC; μg mL−1) in two systems, were compared to elucidate the relationship between structure and antimicrobial activity.