Metal complexes of a novel heterocyclic benzimidazole ligand formed by rearrangement-cyclization of the corresponding Schiff base. Electrosynthesis, structural characterization and antimicrobial activity.

The electrochemical oxidation of anodic metals (M = cobalt, nickel, copper, zinc and cadmium) in a solution of the ligand 1H-anthra[1,2-d]imidazol-6,11-dione-2-[2-hydroxyphenyl] [H2L] afforded homoleptic [ML] compounds. The addition to the electrochemical cell of coligands (L') such as 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) allowed the synthesis, in one step, of heteroleptic [MLL'] compounds. The crystal structures of H2L (1), [CoL(MeOH)]2 (2), [CoL(phen)]2 (3), [NiL(bpy)]2 (4), [CuL(bpy)] (5), [CuL(phen)] (6) and [CdL(bpy)]2 (7) have been determined by X-ray diffraction techniques. The crystal structures of 2, 3, 4 and 7 consist of dimeric species in which both metallic atoms are connected through two phenolate bridges in a penta-coordinated (2) or hexa-coordinated (3, 4 and 7) environment. Copper compounds 5 and 6 are monomeric species with the metal in a pentacoordinated [N4O] environment. In all the compounds, the main interactions responsible for the crystal packing are classic (N-HO, O-HN and O-HO) and non-classic (C-HO and C-HN) hydrogen bond interactions, and π interactions (π-π-stacking and C-Hπ). All compounds were also characterized by microanalysis, IR spectroscopy, FAB mass spectrometry and 1H NMR spectroscopy. Magnetic susceptibility data were measured for 2-4 over the temperature range 2-300 K, and their analysis has revealed the occurrence of intramolecular antiferromagnetic coupling for 2 (J = -2 cm-1) and ferromagnetic coupling for 3 (J = 7.8 cm-1) and 4 (J = 2.8 cm-1) [J being the isotropic magnetic coupling parameter]. The nature of the magnetic coupling in 2-4 is correlated with the magnitude of the M-Ophenolate-M angle between the phenolate bridge and the metallic centers [M(ii) = Co, Ni]. The in vitro antimicrobial properties of the novel ligand and its metal complexes were detected against Gram positive and Gram negative bacteria and fungi. [NiL(bpy)]2 and all tested Cd(ii) complexes were the most active compounds, showing the highest inhibitory effect against bacilli (MIC 1.5-3 µg mL-1) and Sarcina, Streptococci and Haemophilus influenzae bacterial strains (MIC 12-50 µg mL-1), while almost no antifungal properties were observed.

Zinc(II), cadmium(II), mercury(II), and ethylmercury(II) complexes of phosphinothiol ligands.

Neutral zinc, cadmium, mercury(II), and ethylmercury(II) complexes of a series of phosphinothiol ligands, PhnP(C6H3(SH-2)(R-3))3-n (n = 1, 2; R = H, SiMe3) have been synthesized and characterized by IR and NMR ((1)H, (13)C, and (31)P) spectroscopy, FAB mass spectrometry, and X-ray structural analysis. The compounds [Zn{PhP(C6H4S-2)2}] (1) and [Cd{Ph2PC6H4S-2}2] (2) have been synthesized by electrochemical oxidation of anodic metal (zinc or cadmium) in an acetonitrile solution of the appropriate ligand. The presence of pyridine in the electrolytic cell affords the mixed complexes [Zn{PhP(C6H4S-2)2}(py)] (3) and [Cd{PhP(C6H4S-2)2}(py)] (4). [Hg{Ph2PC6H4S-2}2] (5) and [Hg{Ph2PC6H3(S-2)(SiMe3-3)}2] (6) were obtained by the addition of the appropriate ligand to a solution of mercury(II) acetate in methanol in the presence of triethylamine. [EtHg{Ph2PC6H4S-2}] (7), [EtHg{Ph2P(O)C6H3(S-2)(SiMe3-3)}] (8), [{EtHg}2{PhP(C6H4S-2)2}] (9), and [{EtHg}2{PhP(C6H3(S-2)(SiMe3-3))2}] (10) were obtained by reaction of ethylmercury(II) chloride with the corresponding ligand in methanol. In addition, in the reactions of EtHgCl with Ph2PC6H4SH-2 and with the potentially tridentate ligand PhP(C6H3(SH-2)(SiMe3-3)) 2, cleavage of the Hg-C bond was observed with the formation of [Hg{Ph2PC6H4S-2}2] (5) and [Hg(EtHg) 2{PhP(O)(C6H3(S-2)(SiMe3-3))2}2] (11), respectively, and the corresponding hydrocarbon. The crystal structures of [Zn3{PhP(C6H4S-2)2}2{PhP(O)(C6H4S-2)2}] (1*), [Cd2{Ph2PC6H4S-2}3{Ph2P(O)C6H4S-2}] (2*), 3, 5, 6, [EtHg{Ph2P(O)C6H4S-2}] (7*), 8, 9, [{EtHg}2{PhP(O)(C6H3(S-2)(SiMe3-3))2}] (10*), and 11 are discussed. The molecular structures of 1, 2, 4, 7, and 10 have also been studied by means of density functional theory (DFT) calculations.

Bis[2-(diphenylphosphinoyl)benzene] disulfide.

The title compound, [2-Ph(2)P(O)C(6)H(4)S](2) or C(36)H(28)O(2)P(2)S(2), obtained by electrochemical oxidation of 2-(diphenylphosphino)benzenethiol, has twofold crystallographic symmetry. Principal dimensions include S-S 2.0212 (15) A, S-C 1.786 (3) A and C-S-S-C 81.34 (14) degrees.