Browsing by Author "Costes, Jean-Pierre"

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MAGNETIC INVESTIG ATION OF AN UNUSUAL DISSYMMETRIC BINUCLEAR MANGANESE CARBOXYLATE COMPLEX
(Academia de Știinițe a Moldovei, 2006) Novitchi, Ghenadie; Costes, Jean-Pierre; Popovschi, Lilia; Shova, Sergiu; Gulea, Aurelian
The magnetic susceptibility (χT) of an unusual dissymmetric binuclear manganese corboxylate complex has been measured from 2 to 300K. The magnetic data which have been fted with help of the Heisenberg Dirac Van Vleck HDVV spin-exchange Hamiltonian
MAGNETIC INVESTIGATION OF AN UNUSUAL DISSYMMETRIC BINUCLEAR MANGANESE CARBOXYLATE COMPLEX
(Institute of Chemistry of ASM, 2006) Novitchi, Ghenadie; Costes, Jean-Pierre; Popovschi, Lilia; Shova, Sergiu; Gulea, Aurelian
The magnetic susceptibility (χT) of an unusual dissymmetric binuclear manganese corboxylate complex has been measured from 2 to 300K. The magnetic data which have been fitted with help of the Heisenberg Dirac Van Vleck HDVV spin-exchange Hamiltonian HJSS=−urur, indicate that an antiferromagnetic interaction equalto J = 0.90(1) cm-1 ispresent. A correlation between J values andMn-H2O-Mn angles has been tempted.
MAGNETIC INVESTIGATION OF AN UNUSUAL DISSYMMETRIC BINUCLEAR MANGANESE CARBOXYLATE COMPLEX
(2006) Novițchi, Ghenadie; Costes, Jean-Pierre; Popovschi, Lilia; Șova, Sergiu; Gulea, Aurelian
The magnetic susceptibility (χT) of an unusual dissymmetric binuclear manganese corboxylate complex has been measured from 2 to 300K. The magnetic data which have been fitted with help of the Heisenberg Dirac Van Vleck HDVV spin-exchange Hamiltonian H = −J S1S2ur ur, indicate that an antiferromagnetic interaction equal to J = -0.90(1) cm-1 is present. A correlation between J values and Mn-H2 O-Mn angles has been tempted.
SYNTHESIS, STRUCTURE, ERP AND MAGNETIC PROPERTIES OF SOME NEW CHROMIUM(III) HETEROMETALLIC NITRILOTRIACETATES
(Academia de Ştiinţe a Moldovei, 2006) Ciornea, Valeriu; Borta, A.; Galeev, R.; Mingalieva, L.; Voronkova, V.; Costes, Jean-Pierre; Filippova, Irina; Novitki, Ghenadie; Gulea, Aurelian
Four heterometallic compounds with general formula MII(2,2′-bpy)2Cr2(OH)2(nta)2∙nH2O (MII = Mn (n=8) (1); Co (2), Ni(3) and Zn (4) (n=9); bpy = 2,2′-bipyridine, nta = nitrilotriacetate ion) have been prepared by reaction of Ba[Cr2(OH)2(nta)2]5H2O and corresponding MII-sulphates in presence of 2 mol of 2,2′-bipyridine. Substances 1-4 have been characterised by magnetic susceptibility measurements and X-ray crystal structure analysis. Compounds 2-4 are isostructural and consist of non-centrosymmetric dimeric anion [Cr2(μOH)2(nta)2]2-, complex cation [MII(bpy)2(H2O)2]2+ and solvate water molecules. The octahedral coordination of chromium atoms implies four donor atoms of the nta3- ligands and two bridging OH groups. Adjacent anions are connected to each other by strong OH...Ocarb hydrogen bonds and form chains along a axis. Multiple hydrogen bonds of coordinated and solvate water molecules link the anions with the cations in a 3-D network. A similar [Cr2(μ-OH)2(nta)2]2ˉ unit is found in 1. One carboxylate oxygen atom of nta ligand performs the bridging function that leads to formation of a trinuclear complex [Mn(bpy)(H2O)2Cr2(μ-OH)2(nta)2]. The Cr-dimers are joined together by OH...Ocarb hydrogen bonds. The experimental and calculated frequency and temperature dependences of EPR spectra of the new compounds are presented. The program for the simulation of EPR spectra for polycrystalline samples of the compound consisting of Cr-dimers taking into account the isotropic and anisotropic exchange, dipole-dipole interaction and zero-field splitting tensor of chromium was compiled. The temperature dependence of the fine structure of EPR spectra of compound 4 is analyzed in details. It is established that the main part of EPR signals is due to the transitions in the spin states of a spin multiplet with S=2. The analysis of temperature dependences of experimental and calculated spectra of compounds 1-4 showed the absence of the interaction between ions of metals (MII) and Cr-dimers in 2-3 and the presence of the weak interaction Mn –Cr in 1. The temperature dependence of magnetic susceptibilities for 1-4 was fitted on the basis of the expression derived from isotropic Hamiltonian including a bi-quadratic exchange term. The values of the coupling interaction between chromium ions (J) ranges from -14.02(2) cm-1 to 5.80(2) cm-1 and the bi-quadratic terms (j) from +0.71(2) to 2.35(2) cm-1. The experimental and theoretical (calculated, with the Glerup-Hodgson-Pedersen model) values of J have been discussed.