Heba M. Refaat

Synthesis, Electrochemical Behavior, Spectral, and Magnetic Studies of Copper(II) Complexes with Ferrocene-Containing Hydrazones

ABSTRACT A new series of copper(II) complexes of the stoichiometry [L2Cu]·nH2O and [(HL)2CuCl2]·2H2O, where HL is 1-acetyl-ferrocene-benzoylhydrazone, 1-acetylferrocene-4-chlorobenzoyl-hydrazone, 1-acetylferrocene-4-hydroxy-benzoylhydrazone or 1-acetylferrocene-4-methylbenzoylhydrazone, HL1, HL2, HL3 or HL4, respectively, were synthesized and characterized. IR data showed that all ligands act as monobasic or neutral bidentates coordinated to copper ion via the oxygen and azomethine N atoms. ESR spectra and magnetic data showed that [(L1)2Cu]·-H2O and [(L3)2Cu]·2H2O are polymeric exhibiting magnetic exchange interaction. ESR data also indicate that all complexes are associated with a d x 2−y 2 ground state. The electrochemical behavior of the free ligands and their copper(II) complexes were studied and are discussed.

Homogeneous oxidative coupling catalysts: stoichiometry and product characterization of the oxidation of copper(I) complexes [(Pyr) n CuX]4 ( n = 1 or 2, Pyr = pyrrolidine, X = Cl, Br or I) by dioxygen in aprotic media

Copper(I) halides react quantitatively with pyrrolidine (Pyr) in dioxygen-free methylene chloride or nitrobenzene to form tetranuclear copper(I) complexes [(Pyr) n CuX]4O2; n = 1 or 2, X = Cl, Br or I. These complexes are very soluble and completely reduce dioxygen to a dioxo bridging ligand with stoichiometry, Δ[Cu(I)]/Δ[O2] = 4.0. Analytical and cryoscopic data establish the formation of discrete tetranuclear products. The stable oxo solids [(Pyr) n CuX]4O2 mimic the tyrosinase copper protein and are homogeneous oxidative coupling catalysts for phenols. Electronic transition spectra in the near infrared for [(Pyr) n CuX]4O2 are explained as charge transfer from a minimum of three halo ligands to a copper(II) site, (LMCT). Therefore, one can expect a higher molar absorptivity when X = I, as in the [(Pip) n CuX]4O2 system. However, molar absorptivity is about half of expected. The lower absorptivity explains the step structure of [(Pyr) n CuI]4O2, in which only two copper(II) sites, instead of four as in [(Pyr) n CuX]4O2, X = Cl or Br, have three iodo ligands per copper center. In addition to infrared and electronic spectra for [(Pyr) n CuI]4O2, EPR bands are observed, and it is concluded that two different types of copper(II) sites are present as represented in scheme 1.

Structure evaluation of bismuth telluride (Bi2Te3) nanoparticles with enhanced Seebeck coefficient and low thermal conductivity

ABSTRACT Bismuth telluride (Bi2Te3) nanoparticles with different morphologies were synthesized using solvothermal process. The composition, the size and the micro-structure of the synthesized nanoparticles were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). Band gap energy was determined using UV-vis spectrometer. The absorption peaks were shifted from 278 to 284 nm which confirm that the effect of the size and the nanostructure morphology. Moreover, the direct band gap (E g ) of ST–Bi2Te3, STEd–Bi2Te3, STNaEd–Bi2Te3, STPv–Bi2Te3 and STNaPv–Bi2Te3 were equal to 3.95,4.7,4.8,4.7 and 4.5 eV. Thermal and electrical conductivity of the prepared nanoparticles were also investigated at room temperature. Plainly, thermal conductivity measurement concludes that thermal conductivity of ST–Bi2Te3 sample prepared without any additives was high. The study revealed that, the addition of NaOH to the reaction medium as an alkali modifier has a great effect on the morphology and the size of the produced nanoparticles. The additions of PVP in absence and in presence of NaOH strongly affect the size and the morphology of the product. The effect of changing the morphology and the particle size were determined on the band gap energy and the Seebeck coefficient of the prepared samples and the negative sign of all Seebeck coefficients indicate n-type semiconductor.

COMPARATIVE STUDY BETWEEN N,N'-BIS (ACETYLACETONE)-O-PHENYLENEDIAMINE AND (MONOACETYLACETONE)-O-PHENYLENEDIAMINE SCHIFF BASE COMPLEXES

Co(II) , Ni(II) and Cu(II) complexes formed from the Sciff base [ (2Z,4Z)-4-[(2-aminophenyl)imino-]pent-2-en-2-ol] , were prepared in situ and characterized on the basis of elemental analyses, magnetism, UV-vis., IR and ESR spectra . Thermal analyses of the complexes were studied in order to confirm the proposed structures and determine their thermal stability . Comparison between geometries, ESR and thermal studies obtained from direct condensation and in situ preparation of complexes were discussed. The in situ data show that the Schiff base form complexes with 1:1 (metal : ligand) stoichiometry with Cu(II) and Ni(II) ions compared to 2:1 (metal : ligand) formed from direct condensation between schiff base and metal ions. However, the Co(II) in situ complex formed 1:2 (metal: ligand ) stoichiometry. Square-planar geometry was suggested for the Cu(II) and Ni(II) in situ complexes, while, octahedral geometry was suggested for the Co(II) complex. The ESR spectrum of the in situ Cu(II) complex was isotropic to suggest a geometry involving grossly misaligned tetragonal axes .The thermal behavior of the complexes showed good agreement with the formulae suggested from the analytical data . Thermal decomposition of the complexes took place in several stages. The order of stability was [Cu L.(H2O)] 3H2O ˃ NiL.H2O ˃ CoL2.H2O. The thermodynamic parameters , energy of activation ∆ E * a , enthalpy of activation ∆H * , order of reaction n and entropy of activation ∆S * of the complexes were calculated. All the reactions were found to be first order. The high values of activation energies reveal the high stability of these complexes.

Synthesis, crystal structure and comparative DFT studies of a 1D Ni(II) polymeric complex of 2-Hydroxypyridine-N-oxide

A novel Nickel (II) complex of 2-hydroxypyridine-N-oxide has been prepared and characterized by X-ray crystal structure analysis, FT-IR, UV spectra and thermogravimetry. The X-ray diffraction study reveals that the nickel complex is a 1D linear polymer in space group Pī with axa0=xa06.250(1), bxa0=xa08.746(2), cxa0=xa09.462(2)xa0Å, αxa0=xa081.76(3)o, βxa0=xa079.55(3)o and γxa0=xa081.17(3)o. Two nickel ions are present in the unit cell related by the crystallographic centre of symmetry at ½ ½ ½. There are two different short non-bonded Ni to Ni separations in the polymeric structure: 3.454 and 3.467xa0Å respectively. Both room temperature magnetic moment measurements, and theoretical calculations are in favor of a simple paramagnetic system. As a complementary study, plane wave pseudopotential DFT calculations were performed, utilizing eight different XC functionals. The PBE and PBE0 functionals reproduce well the X-ray crystal structure of the complex, while the HSE functional gives a band gap which corresponds reasonably to the experimentally estimated value. The results of antimicrobial properties and thermal analysis of the complex are also reported.Graphical AbstractThe preparation, crystallization and X-ray analysis of a novel 1D polymeric Nickel (II) complex of 2-hydroxypyridine-N-oxide and its characterization by FT-IR, UV spectra, thermogravimetry and possible therapeutics via antimicrobial studies are described.

The Ni(II) Complex of 2-Hydroxy-Pyridine- N-Oxide 2-Isothionate: Synthesis, Characterization, Biological Studies, and X-ray Crystal Structures using (1) Cu Kα Data and (2) Synchrotron Data

C 12 H 20 N 6 NiO 6 S 2 or NiL 2 (SCN) 2 ](NH 4 ) 2 .2H 2 O, where L is 2-hydroxy-pyridine-N-oxide, has been prepared and characterized using elemental analyses, IR, UV and visible spectrometry, magnetic moment measurements, thermal analyses and single crystal X-ray analyis. The results indicate that the complex reacts as a bidentate ligand and is bound to the metal ion via the two oxygen atoms of the ligand (HL). The activation energies, ∆ E*, entropies ∆S*, enthalpies ∆H* and order of reactions have been derived from differential thermogravimetric (DTA) curves. Based on inhibition zone diameter measurements, the complex exhibited significant antibacterial activity against both Staphylococcus aureus and Escherichia coli. It also exhibited significant antifungal activity against Candida albicans, but no activity was found against Aspergillus flavus . The crystal structure of the Ni(II) complex [C 12 H 20 N 6 Ni O 6 S 2 ], Mr = 467.17, was determined from Cu Kα X-ray diffraction data, λ = 1.54178 A, at 100 K using direct methods. The crystals are monoclinic, space group P2 1 /n with Z = 4 and a = 8.9893(2) A, b = 17.6680(5) A, c = 12.5665(3) A, β = 108.609(1)°. In parallel with this study corresponding results were derived for the crystal structure determined independently from synchrotron X-ray diffraction data, λ = 0.61990 A, at 100 K. The unit cell parameters derived in this experiment are a = 9.000(2) A, b = 17.700(4) A, c = 12.590(3) A, β = 108.61(3)°. Both studies show 4 O and 2 N atoms coordinating Ni in a distorted octahedral arrangement. Each of the Ni 2-hydroxy-pyridinium-N-oxide moieties is highly planar and the S=C=N-Ni ligands are approximately linear. The crystal structure is characterised by a number of strong hydrogen bonds.