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

Metal-oxygen bonding complexes (M = Mg-II, Mn-II, Ni-II, Mo-VI, W-VI, Pd-II, Sb-III, Bi-III, Fe-III, Ti-IV, K-I, Ba-II, Zr-IV and Hf-IV) with a hinokitiol (Hhino; 2-hydroxy-4-isopropylcyclohepta-2,4,6-trienone or beta-thujaplicin) ligand, which has two unequivalent oxygen donor atoms, were synthesized and characterized by elemental analysis, TG/DTA, FT-IR and solution (H-1 and C-13) 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 [M-II(hino)(2)(L)](2) (M = Mg-II, Mn-II, Ni-II; 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-[(MO2)-O-VI(hino)(2)] (M= Mo-VI, W-VI), type C, with square planar complex [M-II(hino)(2)] (M= Pd-II), type D, with tris-chelate, 7-coordinate complexes with one inert electron pair [M-III(hino)(3)] (M= Sb-III, Bi-III), type D', with the bis-chelate, pseudo-6-coordinate complexes with one inert electron pair [M-III(hino)(2)X] (M = Sb-III, X = Br), type E, with tris-chelate, 6-coordinate complexes with Delta and Lambda isomers [M-III(hino)(3)] (M= Fe-III), type E' of bis-chelate, 6-coordinate complex [M-IV(hino)(2)X-2] (M = Ti-IV, X = Cl), type F, with water-soluble alkali metal salts [M-I(hino)] (M = K-I), and type H, with tetrakis-chelate, 8-coordinate complexes [M-IV(hino)(4)](M = Zr-IV, Hf-IV). 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; mu g mL(-1)) in two systems, were compared to elucidate the relationship between structure and antimicrobial activity. (c) 2008 Elsevier B.V. All rights reserved.