Makale 2000-2009 yılları
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Browsing Makale 2000-2009 yılları by Publisher "Elsevier"
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Item A theoretical analysis of the explanation of the significant differences in antiferromagnetic interactions between homologous μ-alkoxo and acetate bridged dicopper(II) complexes: ab initio and semi-empirical calculations(Elsevier, 2004-07) Zeyrek, C. Tuğrul; Elmalı, Ayhan; Elerman, Y.; 0000-0001-6744-7841; TAEK-ANAEMA magnetostructural classification of dimmers, containing the Cu (μ-alkoxo) Cu core, based on data obtained from X-ray diffraction analysis reported in the literature has been performed. In these complexes, the local geometry around the copper ions is generally a square planar and each copper ion is surrounded by one N atom and three O atoms. The influence of the overlap interactions between the bridging ligands and the metal (Cu) d orbitals on the super-exchange coupling constant has been studied by means of ab initio Restricted Hatree–Fock molecular orbital calculations. The interaction between the magnetic d orbitals and highest occupied molecular orbitals of the acetate oxygens has been investigated in homologous μ-acetato-bridged dicopper(II) complexes which have significantly different −2J values (the energy separation between the spin-triplet and spin-singlet states). In order to determine the nature of the fronter orbitals, Extended Hückel molecular Orbital calculations are also reported. Ab initio restricted Hartree–Fock calculations have shown that the acetato bridge and the alkoxide bridge contribute to the magnetic interaction countercomplementarily to reduce antiferromagnetic interaction.Item An EPR study on tea: Identification of paramagnetic species, effect of heat and sweeteners(Elsevier, 2009-10) Bıyık, Recep; Tapramaz, Recep; 0000-0001-7929-4395; TAEK-ÇNAEMTea (Camellia Sinensis) is the most widely consumed beverage in the world, and is known to be having therapeutic, antioxidant and nutritional effects. Electron paramagnetic resonance (EPR) spectral studies made on the tea cultivated along the shore of Black Sea, Turkey, show Mn2+ and Fe3+ centers in green tea leaves and in black tea extract. Dry black tea flakes and dry extract show additional sharp line attributed to semiquinone radical. The origins of the paramagnetic species in black tea are defined and discussed. Effect of humidity and heat are investigated. It is observed that dry extract of black tea melts at 100 ◦C and the semiquinone radical lives up to 140 ◦C while Mn2+ sextet disappears just above 100 ◦C in tea extract. Natural and synthetics sweeteners have different effects on the paramagnetic centers. White sugar (sucrose) quenches the Mn2+ and semiquinone lines in black tea EPR spectrum, and glucose, fructose, lactose and maltose quench Fe3+ line while synthetic sweeteners acesulfam potassium, aspartame and sodium saccharine do not have any effect on paramagnetic species in tea.Item EPR spectra of Cu2+ in KH2PO4 single crystals(Elsevier, 2007-03-18) Bıyık, Recep; Tapramaz, Recep; TAEK-ÇNAEMCu2+ doped single crystals of KH2PO4 were investigated using EPR technique at room temperature. The spectra of the complex contains large number of overlapping lines. Five sites are resolved and four of them are compatible with the tetragonal symmetry, and the fifth one belongs to an interstitial site. The results are discussed and compared with previous studies. Detailed investigation of the EPR spectra indicate that Cu2+ substitute with K+ ions. The principal values of the g and hyperfine tensors and the ground state wave function of Cu2+ ions are obtained.Item Magnetic characterization, synthesis and crystal structure of a heterodinuclear CuIIGdIII Schiff base complex bridged by the two phenolic oxygen atoms(Elsevier, 2005-04) Zeyrek, C. Tuğrul; Elmalı, Ayhan; Elerman, Y.; 0000-0001-6744-7841; TAEK-ANAEMA novel heterodinuclear complex formed by the reaction of gadolinium nitrate with Schiff base complex of copper(II) has been synthesized and characterized. Preparation, crystal structure and magnetic properties of the heterodinuclear complex, LCu(Me2CO)Gd(NO3)3, (L=(N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane) are reported. The complex is consisting of a deca-coordinated GdIII ion which is bridged to four coordinated CuII via both phenolate oxygen atoms of the L Schiff base ligand. The average Cu⋯Gd separation is 3.475(2) Å. There is also one non-coordinating acetone molecule in the crystal structure. The magnetic susceptibility of the complex was measured over the range 4.5–350 K and the observed data were successfully simulated by the equation based on the spin-Hamiltonian operator H=−JSCu·SGd. The values of the intrachain interaction parameters have been deduced from the magnetic data: exchange integral J(Cu–Gd)=7.3 cm−1, gCu=2.17, gGd=2.09. This indicates a weak ferromagnetic spin exchange interaction between CuII and GdIII ions. The nature of the magnetic super-exchange interaction of the title compound is compared with similar CuIIGdIII heterodinuclear complexes.