M. Antonia Mendiola

Synthesis, spectral and electrochemical properties of divalent metal complexes containing thiohydrazone and thiosemicarbazone ligands

Abstract The L1H4 and L2H6 complexes of metal halides MX2 (M = Cu, Ni, Co, Zn, Cd or Hg, X = Cl, Br or I) have been prepared. The complexes were characterized on the bases of 1H NMR, IR, electronic and mass spectra, magnetic studies, conductance and analytical data. The stoichiometry and the spectroscopic data indicate that the complexes 1–8, 11, 12 and 15 the metal ions are coordinated by ligand anions and the complexes 9, 10, 13, 14 and 16 contain the neutral ligand. Electrochemical behaviour of nickel and cobalt complexes was determined by cyclic voltammetry. The reduction of complexes are related to metal-centred reductions. In addition, complexes 3, 11 and 12 show irreversible waves associated to Ni(II)/Ni(III) process. The reduction/oxidation potentials depend on the unsaturation grade present in the complexes.

Macrocyclization of cyclic thiosemicarbazones with mercury salts

Abstract A new cyclic Schiff base L1H3 derived from benzil and thiosemicarbazide has been prepared in the presence of NaBH4. Reactions of the new molecule and the cyclic 5-methoxy-5,6-diphenyl-4,5-dihydro-2H-[1,2,4]triazine-3-thione L2H2 with mercury chloride and nitrate are reported. Complexes of 1:2 stoichiometry are obtained from L1H3, but the reactions from L2H2 yield complexes of the macrocyclic Schiff base 5,6,11,12-tetraphenyl-1,2,4,7,8,10-hexaaza-cyclododeca-4,6,10,12-tetraene-3,9-dithione L3H2, which indicates the macrocyclization of L2H2. A mechanism for the cyclization reaction based on the rupture of the C–N single bond in L2H2 is proposed. The electrochemical results of complex L3Hg makes it and its precursors, L2H2 and L3H2, outstanding candidates for mercury determination by appropriate electrode modification.

Structural diversity of benzil bis(benzoylhydrazone): Mononuclear, binuclear and trinuclear complexes

The coordination behaviour of the Schiff-base, benzil bis(benzoylhydrazone), LH(2) towards divalent nickel, lead, cadmium, zinc and copper ions has been investigated. The complexes have been fully characterized by techniques including (113)Cd and (207)Pb NMR, as well as (13)C and (113)Cd CP/MAS NMR and by single crystal X-ray diffraction. All the complexes have the general formula [ML](n) (n = 1-3 depending on the metal ion), with the ligand doubly deprotonated. The nickel complex [NiL] is a monomeric compound, the lead complex [PbL](2) shows a binuclear structure, whereas zinc [ZnL](3) and copper [CuL](3) complexes are trinuclear helicates. The cadmium complex seems to be a dimer with a structure similar to that of . In the nickel and lead derivatives, the ligand behaves as a tetradentate N(2)O(2) chelate and in complex also as a bridge through one of the O atoms. In the crystal structures of Zn and Cu complexes [ML](3) each metal is in a pentadentate N(3)O(2) environment formed by two different ligands, one tridentate chelate and the other bidentate chelate, giving rise to trinuclear helicates. These results point out the versatility of benzil bis(benzoylhydrazone) on its coordination.

Synthesis and antimicrobial activity of tetradentate ligands bearing hydrazone and/or thiosemicarbazone motifs and their diorganotin(IV) complexes.

Four novel ligands derived from 2,3-butanedione have been synthesized, two dissymmetric thiosemicarbazone/3-hydroxy-2-naphthohydrazone ligands, H2L1 (bearing 4-isopropyl-3-thiosemicarbazone) and H2L2 (containing 4-cyclohexyl-3-thiosemicarbazone) and the symmetric H2L3, diacetyl bis(3-hydroxy-2-naphthohydrazone), and H2L4, diacetyl bis(4-cyclohexyl-3-thiosemicarbazone). Their reactivity with SnR2Cl2 (R=methyl, n-butyl and phenyl) was explored and the resulting complexes were characterized by elemental analysis, molar conductivity, mass spectrometry, IR, 1H, 13C and 119Sn NMR and seven of them also by single crystal X-ray diffraction. The results showed that the reactivity of the dissymmetric ligands is strongly different and while the cyclohexyl derivative is very stable, with isopropyl easily undergoes a symmetrization reaction to yield the corresponding symmetric ligands. The antimicrobial activity of the ligands and the corresponding diorganotin(IV) complexes was investigated in vitro against seven species of microorganisms and minimum inhibitory concentrations (MICs) were determined. The results showed that the ligand H2L2 and several of its derivatives, together with methyl and phenyl complexes of H2L1, have the ability of inhibiting the growth of tested bacteria and fungi to different extents. Bacillus subtilis and Staphylococcus aureus Gram positive strains were the most sensitive microorganisms.

Tin(IV), titanium(IV) and vanadium(IV) chloride complexes with 2-aminobenzimidazole and 2(2'-aminophenyl) benzimidazole

Summary2-Aminobenzimidazole (abi) and 2(2′-aminophenyl)benzimidazole (apbi) react with tin, titanium and vanadium tetrachlorides to yield complexes of formulae: [MCl4(abi)](M=Sn or Ti), [TiCl4(abi)2], [VCl3(abi-H)] ((abi-H) being the deprotonated ligand) and [MCl4(apbi)] (M=Sn, Ti or V).Abi is monodentate, with the metal in a pseudooctahedral environment, so that a dimeric structure is proposed for [SnCl4(abi)] and [TiCl4(abi-], monomeric for [TiCl4(abi)2] and polymeric for [VCl3(abi-H)]. Apbi acts as a bidentate ligand in all complexes showing a hexacoordinated environment for the metal.

Synthetic and physicochemical studies of divalent metal complexes with cyclic hydrazone and semicarbazone ligands

SummaryThe syntheses of 3,4,10,11-tetraphenyl-1,2,5,6,8,9,12,13-octaazacyclotetradeca-7, 14-dione-2,4,9,11-tetraene (dbdch) and 6-methoxy-1,6-diphenyl-4-oxo-3,4,5,6-tetrahydro-2,3,5-triazine (bsc) and their complexes with divalent metal ions (copper, nickel, cobalt, zinc, cadmium and mercury) are reported. All compounds were characterized by 1H n.m.r., 13C n.m.r., i.r. and u.v.-vis. spectroscopy and by FAB mass spectrometry; possible structures are presented and discussed.

Syntheses and characterization of cobalt(II) and iron(III) complexes with the Schiff basesN-(o-hydroxybenzylidene)-2-aminobenzimidazole andN-(o-hydroxybenzylidene)-2(2′-aminophenyl)benzimidazole

SummaryN-(o-hydroxybenzylidene)-2-aminobenzimidazole (HL) andN-(o-hydroxybenzylidene)-2(2′-aminophenyl)benzimidazole (HL′) react with CoX2 (X=Cl, Br, or NCS) and FeCl3 yielding complexes of general formulae [Co(HL)2X2], [Co(HL′)2X2], [FeCl2(HL)2] [FeCl4], and [FeCl2(HL′)2][FeCl4]. Moreover, it was possible to isolate the complexes [Co(HL)Br2] [Co(L)Cl] and [Co(L′)Cl]. The complexes were characterized by elemental analyses, i.r. and electronic spectroscopies and conductivity and magnetic measurements at different temperatures.

Gold(III) bis(thiosemicarbazonate) compounds in breast cancer cells: Cytotoxicity and thioredoxin reductase targeting

Gold(III) compounds have received increasing attention in cancer research. Three gold complexes of general formula [AuIIIL]Cl, where L is benzil bis(thiosemicarbazonate), compound 1, benzil bis(4-methyl-3-thiosemicarbazonate), compound 2, or benzil bis(4-cyclohexyl-3-thiosemicarbazonate), compound 3, have been synthesized and fully characterized, including the X-ray crystal structure of compound 3, confirming square-planar geometry around the gold(III) centre. Compound 1 showed moderate cytotoxicity and accumulation in MCF7 breast cancer cells but did not inhibit thioredoxin reductase (TrxR) activity and did not induce reactive oxygen species (ROS) production. Compound 2, the least cytotoxic, was found to be capable of modestly inhibiting TrxR activity and produced low levels of ROS in the MCF7 cell line. The most cytotoxic compound, 3, had the highest cellular accumulation and its distribution pattern showed a clear preference for the cytosol and mitochondria of MCF7 cells. It readily hampered intracellular TrxR activity leading to a dramatic alteration of the cellular redox state and to the induction of cell death.

Structural diversity and supramolecular architectures of Zn(II), Cu(II) and Ni(II) complexes by selective control of the degree of deprotonation of diacetyl bis(4-isopropyl-3-thiosemicarbazone)

The reactivity of the new potentially tetradentate ligand diacetyl bis(4-isopropyl-3-thiosemicarbazone) (H2L) with zinc(II), copper(II) and nickel(II) nitrates using different amounts of lithium hydroxide was studied. The results obtained show that with zinc(II), selective ligand deprotonation was completely achieved and complexes [Zn(H2L)(OH2)](NO3)2 (1), [Zn(HL)(EtOH)]NO3 (2) and [ZnL]2 (3) were synthesized, where the ligand acts as a neutral, singly or doubly deprotonated donor, respectively. In contrast, in the case of copper(II), only complexes [Cu(HL)]NO3 (4) and [CuL] (5) were isolated, whereas with nickel(II) the double deprotonation of the ligand took place even in the absence of a base, to yield complex [NiL] (6). The structural preferences of the metals also influence the structure of the complexes; whereas copper(II) and nickel(II) are in a square-planar arrangement, zinc(II) prefers a square-base pyramid geometry. In all the complexes containing a NO3− ion, the ion is not coordinated to the metal and acts as a counter-ion. The different degrees of deprotonation of the ligand, together with the presence or the absence of nitrate and solvent molecules bonded to the metal, make the existence of different supramolecular architectures based on different hydrogen bond arrays possible. The topological analysis shows the formation of 2D (1) and 1D (3 and 5) networks, tetranuclear aggregates (2 and 5·DMF) and dimers (6·DMF), which are linked by other weak interactions to give 2D or 3D nets.

Titanium(III) and vanadium(III) chloride complexes with 2-pyridylphenylacetonitrile and 1,2-dicyano-1,2-diphenyl-1,2-di(2′-pyridyl)ethane

Summary2-Pyridylphenylacetonitrile (ppa) and 1,2-dicyano-1,2-diphenyl-1,2-di(2′-pyridyl)ethane (dcppe) react with titanium(III) and vanadium(III) chlorides yielding complexes of formulae: [TiCl3(ppa)2], [TiCl3(ppa)3], [VCl3(ppa)], [TiCl3(dcppe)] and [(VCl3)2(dcppe)]. The results obtained suggest pentacoordinated structures for complexes, except for [TiCl3(ppa)3] where an hexacoordinated stereochemistry around the metal is proposed.