Javier García-Tojal

Synthesis and spectroscopic properties of copper(II) complexes derived from thiophene-2-carbaldehyde thiosemicarbazone. Structure and biological activity of [Cu(C6H6N3S2)2].

The synthesis, structure and spectroscopic properties on complexes with the formula [Cu(Lm)2] (1) and Cu(NO3)2(HLm)2 (2), where HLm = thiophene-2-carbaldehyde thiosemicarbazone, have been developed. The molecular structure of compound 1 consists of monomeric entities. The copper(II) ions exhibit distorted square-planar geometry with both bidentate thiosemicarbazone ligands placed in a centrosymmetric way. Metal to ligand pi-backdonation is proposed to explain several structural and spectroscopic features in these complexes. The EPR spectra of compound 1 show an orthorhombic g tensor indicating the presence of weak magnetic exchange interactions. The reaction of compound 1 with glutathione causes the reduction of the metal ion and the substitution of the thiosemicarbazone ligand by the thiol ligand. This mechanism seems to be related to the cytotoxicity of this complex against Friend Erithroleukemia cells (FLC) and melanome B16F10 cells.

Spectroscopic and magnetic properties of copper(II) complexes derived from pyridine-2-carbaldehyde thiosemicarbazone. Structures of [Cu(NO3)(C7H8N4S)(H2O)](NO3) and [{Cu(NCS)(C7H7N4S)}2]

Abstract Complexes with the formula CuX(L) (X=N3 1, NCO 2 and NCS 3) and [Cu(NO3)(HL)(H2O)](NO3) 4, where HL=C7H8N4S, (pyridine-2-carbaldehyde thiosemicarbazone), have been characterised. Single-crystal X-ray diffraction studies on compounds 3 and 4 have been carried out. The structure of compound 4 consists of monomeric distorted square pyramidal copper(II) species. The copper(II) ions are coordinated to the NNS atoms from the tridentate thiosemicarbazone ligand and one oxygen atom of a nitrate group in the equatorial position. The oxygen atom of the water molecule occupies the apical position. The structure of compound 3 consists of non-centrosymmetric {Cu2(μ-SR)2} entities in which the copper(II) ions exhibit five-coordinate square–pyramidal geometry. The thiosemicarbazone ligand and one nitrogen atom from the thiocyanate ion are in a basal position. The sulfur atom of the tridentate ligand acts as a bridge occupying the apical position. Structural and spectroscopic results suggest the presence of relevant σ ligand-to-metal charge transfer and metal-to-ligand π-backdonation character in these compounds. The ESR spectra of compounds 3 and 4 show rhombic symmetry. For complexes 1 and 2 the ESR spectra exhibit axial signals. Magnetic measurements on compounds 1, 2 and 3 show antiferromagnetic couplings. The susceptibility data were fitted by the Bleaney–Bowers’ equation for copper(II) dimers. The obtained J/k values are −4.22, −6.10 and −7.33 K for compounds 1, 2 and 3, respectively.

Biological activity of complexes derived from pyridine-2-carbaldehyde thiosemicarbazone: Structure of [Co(C7H7N4S)2][NCS]

Biological studies on [Fe(L)2](NO3).0.5H2O (1), [Fe(L)2][PF6] (2), [Co(L)2](NCS) (3), [Ni(HL)2]Cl2.3H2O (4) and Cu(L)(NO3) (5), where HL=C7H8N4S, pyridine-2-carbaldehyde thiosemicarbazone, have been carried out. The crystal structure of compound 3 has been solved. It consists of discrete monomeric cationic entities containing cobalt(III) ions in a distorted octahedral environment. The metal ion is bonded to one sulfur and two nitrogen atoms of each thiosemicarbazone molecule. The thiocyanate molecules act as counterions. The copper(II) and iron(III) complexes react with reduced glutathione and 2-mercaptoethanol. The reaction of compound 1 with the above thiols causes the reduction of the metal ion and bis(thiosemicarbazonato)iron(II) species are obtained. The redox activity, and in particular the reaction with cell thiols, seems to be related to the cytotoxicity of these complexes against Friend erithroleukemia cells and melanoma B16F10 cells.

SYNTHESIS, STRUCTURE, SPECTROSCOPIC AND MAGNETIC PROPERTIES OF TWO COPPER(II) DIMERS CONTAINING PYRIDINE-2-CARBALDEHYDE THIOSEMICARBAZONATE (L), CUL(X )2 (X=CL OR BR)

The compounds [{CuL(X)}2](X = Cl 1 or Br 2, HL = pyridine-2-carbaldehyde thiosemicarbazone) have been synthesised and structurally characterized. Both crystallize in the triclinic space group P. For compound 1, a= 7.915(3), b= 8.262(5), c= 9.016(2)A, α= 67.97(3), β= 92.26(2), γ= 71.33(4)°, Z= 2, R= 0.046, R′= 0.054. For 2, a= 7.617(1), b= 8.451(3), c= 8.966(2)A, α= 68.50(2), β= 95.94(1), γ= 71.73(2)°, Z= 2, R=R′= 0.035. The copper(II) ions have square-pyramidal environments with the tridentate thiosemicarbazone ligands and the halide atoms in an equatorial position. The sulfur atom of the tridentate ligand acts as a bridging ligand occupying the apical position of the symmetric copper atom in the dimeric structure. Such a disposition of the sulfur bridges is very scarce. Q-Band ESR spectra of the two compounds show rhombic signals with g1= 2.183, g2= 2.053, g3= 2.033 for 1 and g1= 2.161, g2= 2.057, g3= 2.033 for 2. Magnetic measurements on 1 and 2 show antiferromagnetic couplings between the copper(II) cations through the sulfur bridges. The exchange parameter is J/k=–6.8K (–4.7 cm–1). Magnetostructural correlations have been analysed by using extended Huckel molecular orbital calculations.

First end-to-end thiocyanato chain containing 5-coordinate copper(II) ions

The synthesis and crystalstructure of a new ½fCuðLÞðNCSÞ2gncomplex where L ¼ð C8H8N4O Þ¼ 2-methylamino-5-pyridin-2- yl-1,3,4-oxadiazole are reported. The structure is made up of 1D-chains containing monomeric copper(II) units linked by thiocy- anato groups which act as end-to-end bridges. The metalions show a 5-coordinate environment with a stereochemistry cl ose to SP where the basal plane positions are occupied by the N-donor atoms of the bidentate L ligand, a bridging and a terminal thiocyanato group. The apical site is occupied by an S-donor atom from the neighbor molecule. The shortest copper ��� copper distances are 5.599(6) � A A paramagnetic behavior is observed in this compound. 2003 Elsevier Science B.V. All rights reserved.

AN APPRAISAL OF STRUCTURAL, SPECTROSCOPIC AND MAGNETIC ASPECTS OF THE PYRIDINE-2-CARBALDEHYDE THIOSEMICARBAZONECOPPER(II) COMPOUNDS

Abstract Comparative structural studies and approximate molecular orbital calculations have been developed on copper(II) complexes derived from the pyridine-2-carbaldehyde thiosemicarbazone. The results allow to explain: (a) some significant structural differences between complexes containing the neutral ligand and those with the anionic one, (b) the reasons why the formation of either dimers bridged through the S atom of the thiosemicarbazone or the non-thiosemicarbazone coligand, and (c) the formation of monomeric versus dimeric entities with the neutral ligand. Other implications of these studies in the stability, and the spectroscopic and magnetic properties of these systems are also discussed. The partially localized negative charge on the N3 hydrazinic atom in the anionic thiosemicarbazone molecules, the presence of water molecules, the energy and contributions of the frontier orbitals, the influence of the nonthiosemicarbazone ligands and changes observed in the a ligand-to-metal charge transfer and metal-to-ligand π-backdonation are proposed to explain several features in these complexes.

Organic–inorganic hybrids based on four-electron reduced Keggin β-isomer phosphododecamolybdates and diazines

Six salts of diazonium cations (C4H5N2+) with the four-electron reduced β-Keggin phosphododecamolybdate, (1,2-C4H5N2)3[H4PMo12O40]·9H2O (1), (1,3-C4H5N2)2[H5PMo12O40]·(1,3-C4H4N2)·10H2O (2), (1,4-C4H5N2)3[H4PMo12O40]·5H2O (3), (1,2-C4H5N2)3[H4PMo12O40]·2H2O (4), (1,3-C4H5N2)3[H4PMo12O40]·2H2O (5), and (1,4-C4H5N2)2[H5PMo12O40]·½(1,4-C4H4N2)·5H2O (6), have been synthesised in aqueous solution. Compounds 1–3 were obtained photochemically using methanol as electron donor, and compounds 4–6 were prepared using thiophosphate as reducing agent. These compounds contain the four-electron reduced β-Keggin polyanion with a variable degree of protonation. The crystal packing in compound 1 consists of chains formed by pairs of polyanions hydrogen bonded along the [010] direction. The diazonium cations are connected, via NX1–HX1⋯Ow hydrogen bonds, to a ten-membered ring of hydrogen bonded water molecules. The crystal packing in compound 6 is formed by antiparallel chains of polyanions connected through the hydrogen bond OHpoly⋯Opoly along the [010] direction. These polyanion chains are embedded in a 3D-channel structure formed by a helicoidal arrangement of the diazine species hydrogen bonded via the water molecules. The dimensions of these tunnels are approximately 14 × 13.5 A. Ab initio RHF calculations have been performed on idealised α- and β-Keggin isomers in order to get information about stability and protonation sites and interactions between the organic rings and the surface of the Keggin anions.

Synthesis, crystal structure and spectroscopic properties of copper(II) complexes derived from 2-methylamino-5-pyridin-2-yl-1,3,4-oxadiazole

Abstract Two new complexes with the formulae [Cu(L)(oxalatoo)(H2O)]·H2O (1) and [Cu(L)2(H2O)2](NO3)2 (2), where L=(C8H8N4O)=2-methylamino-5-pyridin-2-yl-1,3,4-oxadiazole, have been synthesized and characterized. The structure of compound 1 contains monomeric entities in which the copper(II) ions exhibit five-coordinate square-pyramidal geometry. The oxadiazole bidentate ligand links to the metal ion through the Npyridine and one of the Noxadiazole atoms. Two oxygen atoms from the oxalato ligand complete the basal positions. The oxygen atom of a water molecule occupies the apical one. Solvation water molecules are also present in the lattice. The structure of compound 2 consists of monomeric distorted octahedral copper(II) species. The copper(II) ions are coordinated to both bidentate oxadiazole ligands in the equatorial plane, with the two oxygen atoms of both water molecules placed in the axial positions. Nitrate groups act as counterions. The presence of π–π stacking interactions interconnecting the monomeric entities in both complexes is discussed. The EPR spectra of compounds 1 and 2 show axial symmetries.

Desulfurization processes of thiosemicarbazonecopper(II) derivatives in acidic and basic aqueous media

This work provides structural evidence for different desulfurization processes in aqueous solutions of [CuL]+ derivatives (HL = pyridine-2-carbaldehyde thiosemicarbazone). Structural resolution has been achieved for the [{CuL(SH)}2] (1), [CuLCl]2[Cu(pic)2] (pic− = picolinato, pyridine-2-carboxilato) (2) and [Cu(HL)(NCS)](NO3) (4) compounds, together with a derivative of 4 with formula [Cu(HL)(NCS)][Cu(HL)(NCS)0.72(NO3)0.28](NO3)2 (5), whose HS−, pic− and NCS− ligands come from thiosemicarbazone breakage. The behaviour of the [CuL]+ species in basic aqueous solutions or water under reflux has been compared with that exhibited by iron(III), cobalt(III), zinc(II) and lead(II) derivatives of the same thiosemicarbazone ligand. [Cu(L′)]+ species (HL′ = pyridine-2-carbaldehyde N4-methylthiosemicarbazone) have also been analyzed by infrared spectroscopy or mass spectrometry under the same experimental conditions. In addition, preparative methods for a rational synthesis of the serendipitously obtained compounds are proposed. In this way, the crystal structure of [CuL(pic)]·3H2O (3) has been elucidated too. The partial desulfurization of coordinated thiosemicarbazones could lead to a reinterpretation of their biological activity with consequences for the search for possible therapeutic uses.

Hydrothermal Synthesis at High Pressure and Temperature of the Mg 7.5 Ni 6 H 3 (AsO 4 ) 8 (OH) 6 and Mg 8 Ni 4 H 6 (PO 4 ) 8 (OH) 6 Compounds

The Mg 7.5 Ni 6 H 3 (AsO 4 ) 8 (OH) 6 and Mg 8 Ni 4 H 6 (PO 4 ) 8 (OH) 6 compounds have been synthesized by using hydrothermal techniques at high pressure and temperature. The crystal structure of the arsenate phase has been refined with the Rietveld method. The compounds are isostructural. The structure consists of a three-dimensional framework in which the presence of triangular and hexagonal channels is observed. Reflectance diffuse measurements confirm the hexacoordination of the Ni(II) ions in both compounds. The magnetic behaviour indicates the presence of antiferromagnetic interactions between the Ni(II) ions placed in the double chains.