M.R.P. Kurup

Epr, cyclic voltammetric and biological activities of copper(II) complexes of salicylaldehyde N(4)-substituted thiosemicarbazone and heterocyclic bases

Abstract An interesting series of heterocyclic base adducts of copper(II) complexes have been synthesised by the reaction of copper(II) acetate with salicylaldehyde N(4)-phenylthiosemicarbazone in presence of heterocyclic bases like pyridine (py), piperidine (pip), β/γ-picoline (β/γ-pic), 1,10-phenanthroline (phen) and 2,2′-bipyridine (bipy). IR, electronic, 1H and 13C NMR spectra of the thiosemicarbazone, as well as IR, electronic and EPR spectra of the complexes have been obtained. Based on EPR studies spin Hamiltonian and bonding parameters have been calculated. The g values, calculated for all the complexes in frozen DMF, indicate the presence of the unpaired electron in the dx2−y2 orbital. The metal-ligand bonding parameters evaluated showed strong in-plane sigma and in-plane π bonding. The magnetic and spectroscopic data indicate a square planar geometry for the four-coordinate and a distorted square pyramidal for five-coordinate complexes. From cyclic voltammetric data reversible copper(II)/copper(I) couples are observed for these complexes. The thiosemicarbazone and its copper(II) complexes show growth inhibitory activity against human pathogenic bacteria Salmonella typhi, Shigella dysentariae, non-coagulace Staphylococcus, Photobacterium sp. and Staphylococcus aureus and plant pathogenic fungi Rhizoctonia, Collectotrichium and Aspergillus sp.

Spectral studies and structure of a 2-hydroxyacetophenone 3-hexamethyleneiminyl thiosemicarbazonate(-2) copper(II) complex containing 1,10-phenanthroline

The spectral studies and structure of a ternary complex of copper(II) with 2-hydroxyacetophenone 3-hexamethyliminylthiosemicarbazonate (L(2-)) and 1,10-phenanthroline (phen) are reported. The thiosemicarbazone binds to the metal as a dianionic ONS-donor (L(2-)) ligand, and forms a complex of the stoichiometry [CuLphen]. The copper(II) complex was characterized by IR and UV/Vis spectroscopies, as well as by solid state room-temperature magnetic susceptibility. Spin Hamiltonian and bonding parameters of the compound are calculated from the EPR spectra. Computer simulation of EPR spectrum in DMF at 77 K aided the calculation of magnetic and bonding parameters of the compound. The structure of the compound is solved by single crystal X-ray diffraction. The geometry around copper is distorted square pyramidal.

Synthesis and structural studies of novel Co(III) ternary complexes containing N(4)-substituted thiosemicarbazones of 2-hydroxyacetophenone and heterocyclic bases

Abstract An interesting series of eight neutral ternary Co(III) complexes of 2-hydroxyacetophenone N(4)-substituted thiosemicarbazones (H2L), bidentate heterocyclic bases 2,2′-bipyridine (bipy)/1,10-phenanthroline (phen) and azide with a general formula [MLB(N3)] were prepared. The complexes were characterized by means of spectroscopic methods. The coordination geometry around Co(III) in all the complexes is distorted octahedral with one dibasic tridentate ligand L2−, one bidentate heterocyclic base and one terminally coordinated azide group. Crystal structure of the compound CoL4bipyN3 was completely solved. All the electronic transitions were assigned. All complexes were diamagnetic indicating cobalt in a d6 strong field.

E.s.r. and electrochemical studies of four- and five-coordinate copper(II) complexes containing mixed ligands

Heterocyclic base adducts of salicylaldehyde N(4)- cyclohexylthiosemicarbazone(H2L) copper(II) complexes have been synthesized and characterized. I.r., electronic and e.s.r. spectra of the complexes, as well as i.r., electronic and 1H- and 13C-n.m.r. spectra of the thiosemicarbazone have been obtained. Based on e.s.r. studies, all possible parameters have been calculated. The g values, calculated for all the complexes in frozen solution, indicate the presence of the unpaired electron in the dx2−y2 orbital. The metal–ligand bonding parameters evaluated showed strong in-plane σ- and in-plane π-bonding. The magnetic and spectroscopic data indicate a square-planar geometry for the four-coordinate and a distorted square-pyramidal structure for the five-coordinate complexes. From cyclic voltammetric data quasireversible copper(II)/copper(I) couples are observed for the complexes.

Transition Metal Complexes of Furan-2-aldehyde Thiosemicarbazone

Cu(II), Ni(II), Zn(II), and Co(III) complexes of furan‐2‐aldehyde thiosemicarbazone (HL) have been synthesized and are characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, UV‐Vis, IR, 1H NMR and EPR spectra. The molar conductivities show that all of the complexes are non‐electrolytes. The IR spectra suggest coordination of the thiosemicarbazone to the metal through azomethine nitrogen and thiolate sulfur atoms. The furan oxygen appears not to be coordinated in all complexes. The complexes have the formulas Cu2L2Cl2, NiL2, ZnL2 and CoL3 where L corresponds to the anionic thiosemicarbazone.

Synthesis and Characterization of Iron(III) Complexes of a Substituted 2-Acetyi, Pyridine Thiosemicarbazone

Abstract Iron(III) bis(ligand) complexes of a substituted thiosemicarbazone of 2-acetylpyridine have been prepared and charactmized by physico-chemical and spectroscopic methods. The complex prepared from ferric chloride was found to be a 1:1 electrolyte whereas others are non-electrolytes. The ligand deprotonates and coordinates via the pyridine nitrogen, imine nitrogen, and thiolate sulfur. The neutral ligand coordinates through imine and pyridine nitrogens only. The complex prepared from ferric chloride has an ion pair geometry involving a low-spin iron(III) cation antl high spin iron(III) anion. The EPR studies indicate a high-spin low-spin equilibrium for the nitrato complex. All other complexes are low spin.

TRANSITION METAL COMPLEXES OF 2-FORMYLTHIOPHENE S-METHYLDITHIOCARBAZATE

Transition metal complexes of 2-formylthiophene S-methyldithiocarbazate have been synthesized and characterized. Analytical data show that the complexes are of the type [ML3], where M = Fe3+, and [ML2], where M=Ni2+, Cu2+ or Zn2+. The i.r. spectra suggest coordination to the metal through the azomethine nitrogen and thiolate sulfur. The magnetic and spectroscopic data indicate a square planar geometry for the complexes, except for the Fe3+ complex, which is octahedral. The e.s.r. parameters are indicative of a square planar N2S2 system for the Cu2+ complex.

N′-[(E)-(3-Fluoro­pyridin-2-yl)methyl­idene]benzohydrazide monohydrate

The title compound, C13H10FN3O·H2O, exists in the E conformation with respect to the azomethane C=N double bond. The molecule is close to planar with a maximum deviation of 0.286 (2) Å. The pyridine ring is essentially coplanar with the central C(= O)N2C unit [dihedral angle = 2.02 (3)°] and the phenyl ring exhibits a dihedral angle of 14.41 (10)° with respect to the central unit. The crystal structure features O—H⋯N, N—H⋯O and O—H⋯O hydrogen-bond interactions between the solvent water and the benzohydrazide molecules, as well as C—H⋯O hydrogen bonds and C—F⋯π [3.0833 (18) Å] interactions.

Synthesis, characterization and biological studies of Schiff bases derived from heterocyclic moiety

Some new Schiff bases (H1-H7) have been synthesized by the condensation of 2-aminophenol, 2-amino-4-nitrophenol, 2-amino-4-methylphenol, 2-amino benzimidazole with thiophene-2-carboxaldehyde and pyrrole-2-carboxaldehyde. The structures of newly synthesized compounds were characterized by elemental analysis, FT-IR, 1H NMR, UV-VIS, and single crystal X-ray crystallography. The in vitro antibacterial activity of the synthesized compounds has been tested against Salmonella typhi, Bacillus coagulans, Bacillus pumills, Escherichia coli, Bacillus circulans, Pseudomonas, Clostridium and Klebsilla pneumonia by disk diffusion method. The quantitative antimicrobial activity of the test compounds was evaluated using Resazurin based Microtiter Dilution Assay. Ampicillin was used as standard antibiotics. Schiff bases individually exhibited varying degrees of inhibitory effects on the growth of the tested bacterial species. The antioxidant activity of the synthesized compounds was determined by the 1,1-diphenyl-2-picrylhydrazyl(DPPH) method. IC50 value of synthesized Schiff bases were calculated and compared with standard BHA.

N′-[(E)-Furan-2-yl­methyl­idene]pyridine-3-carbohydrazide

The title compound, C11H9N3O2, exists in the E conformation with respect to the azomethane C=N bond, and has the keto form. There are two independent molecules in the asymmetric unit and each of these features a slight slanting of the pyridine and furan rings, which form a dihedral angle of 14.96 (10)° in one of the molecules and 5.53 (10)° in the other. The crystal structure is stabilized by N—H⋯O and N—H⋯N hydrogen bonds, weak C—H⋯O and C—H⋯N hydrogen bonds and C—H⋯π interactions and π–π interactions [shortest centroid–centroid distance = 3.7864 (15) Å].