Maria Brezeanu

Alkoxo-bridged binuclear copper(II) complexes as nodes in constructing extended structures

Abstract Three new compounds exhibiting extended structures have been obtained by using alkoxo-bridged binuclear copper(II) complexes as nodes, and bis(4-pyridyl) derivatives as spacers: [Cu 2 (H 2 tea) 2 (bpe)](ClO 4 ) 2 ·(bpe)·H 2 O ( 1 ), [Cu 2 (Hdea) 2 (4,4′-bipy)](ClO 4 ) 2 ( 2 ), and [Cu 2 (ap) 2 (4,4′-bipy) 2 ](ClO 4 ) 3 ·(4,4′-bipy)·(H 2 ap)·(H 2 O) ( 3 ) (H 3 tea=triethanolamine, H 2 dea=diethanolamine, Hap=aminopropanol; bpe= trans -1,2-bis(4-pyridyl)ethylene, 4,4′-bipy=4,4′-bipyridine). The structure of 1 consists of infinite chains resulted by connecting the bis(alkoxo)-bridged unsymmetrical [Cu 2 (H 2 tea) 2 ] 2+ nodes with bis(4-pyridyl)ethylene rods. The Cu⋯Cu separations are of 2.924 and 13.402 A in an alternate mode. The noncoordinated bpe molecules bind the parallel coordination polymer chains, spread along b axis, through intermolecular H-bonds, resulting in a double zigzag ladder network. In crystal 2 , the 4,4′-bipy molecules connect centrosymmetric [Cu 2 (Hdea) 2 ] 2+ nodes, resulting in infinite chains. The parallel chains are disposed in planes which are parallel to the ab crystallographic plane. The chains directions, [110] or [1−10], alternate in adjacent planes. The stereochemistry of the copper(II) ion is distorted square-pyramidal. The alternate Cu⋯Cu distances within the chain are: 2.9880(5) and 11.0310(5) A. Compound 3 is a two-dimensional coordination polymer. There are two crystallographically independent centrosymmetric [Cu 2 (ap) 2 ] cores. The distances between the alkoxo-bridged copper atoms within the nodes are: 3.071(2) and 3.036(2) A. Each node is connected through four 4,4′-bipy bridges to four other nodes, resulting in a two-dimensional layer with rhombic meshes. The dimensions of the rhomboidal cells are 12.31 and 13.36 A, with an angle between the edges of 83.4°. The uncoordinated 4,4′-bipy and water molecules, the H 2 pa + (monoprotonated aminopropanol species) and perchlorate ions are interconnected through hydrogen bonds resulting in infinite chains. These hydrogen-bonded polymers fill the channels resulted through the stacking of the 2-D layers.

On the structure of manganese ferrite powder prepared by coprecipitation from MnO2 and FeSO4·7H2O

Abstract The microstructure of manganese ferrite powder obtained from MnO 2 and FeSO 4 ·7H 2 O by coprecipitation and aging in isothermal static conditions at temperatures lower than 100°C, has been investigated by X-ray diffraction (XRD), Mossbauer spectroscopy, granulometry and scanning electron microscopy (SEM). The results reveal the influence of the temperature on the particle size distribution as well as on the structure and composition of the ferrite phase. Some magnetic properties of the ferrite powders are presented.

Some Polynuclear Coordination Compounds Precursors of Chromites Synthesis, Physicochemical Characterization and Thermal Stability

The polynuclear coordination compounds LnCr(tartrate)3·nH2O where Ln(III)=La-Er, obtained through a precipitation method, were characterized on the basis of elemental analysis, their electronic and vibrational spectra and magnetic susceptibility measurements. The possibility of obtaining chromites through the transformations of the polynuclear coordination compounds in the solid state was considered. The thermal decompositions of these compounds, studied by TG and DTA methods, were found to follow an almost uniform pattern. The decompositions occurred in six-eight steps. The first two steps involved dehydration, and the third the transformation of tartrate anions to oxalate, followed by conversion to carbonate and oxocarbonate intermediates. The final product in each case was LnCrO3. A non-isothermal kinetic analysis of the first decomposition steps was performed, the most probable decomposition mechanism being selected and the kinetic parameters evaluated. The final products of the transformations were characterized.

Polynuclear coordination compounds as precursors for CuFe2O4

The possibility of obtaining copper ferrite through the thermal decomposition of the two polynuclear coordination compounds: (NH4)8[Fe2Cu(C2O4)8] (I) and [Fe2Cu(C2O4)2(OH)4]·4H2O (II) was considered. The polynuclear compounds were characterized by various physical chemical techniques, e.g., IR, UV-VIS, EPR, Mossbauer spectra, thermal analysis and magnetic measurements. The final products obtained after thermal decomposition of the complex compounds were analysed by X-ray diffraction. A mixture of tetragonal CuFe2O4, α-Fe2O3 and CuO is generated from the thermolysis of compound I, while a clean tetragonal CuFe2O4 with saturation magnetization of 26.89 emu g−1 is obtained from compound II.

Thermal behaviour of some solid coordination compounds with malic acid as ligand

Abstract The authors present the results concerning the synthesis and the characterisation of some coordination compounds with malic acid as ligand: Co(C 4 H 4 O 5 )·2H 2 O, [Fe 2 (C 4 H 4 O 5 )(OH) 4 ]·4H 2 O and [Fe 2 Co(C 4 H 4 O 5 ) 2 (OH) 4 ]·6H 2 O. The heterometallic compound is a precursor of Co-ferrite. The values of the non-isothermal kinetic parameters for the dehydration reactions were determined. These values obtained by three integrals methods are in a satisfactory agreement.

On the formation of manganese ferrite from MnO2 and FeSO47H2O aqueous solutions through coprecipitation

Abstract The formation and evolution of MnFe2O4 ferrite phase coprecipitated with NaOH from MnO2 and FeSO4·7H2O in aqueous solution are discussed, grounded on X-ray diffraction and derivatographic data, IR spectra and magnetic measurements. The results concerning the nature of the initial coprecipitates, their structural changes during ageing in the original solutions at temperatures in the range 25–95°C as well as the structure of the resulting ferritic phases are presented.

Non-isothermal decomposition kinetics of polynuclear coordination compounds

Abstract Results concerning the thermal stability and decomposition kinetics of four polynuclear coordination compounds are presented.

Copper-iron oxides obtained by thermal decomposition of oxalic coordination compounds

The influence of the coordination architecture (materialized by ligand binding mode and content) on the thermal behaviour of coordination compounds containing copper, iron and oxalic anion as ligand was investigated. It was established that the metal-metal connections influence stronger, comparative with ligand content, the stoichiometry of the thermal decompositions.

Nonconventional methods for obtaining hexaferrites

Small particles of PbFe12O19 have been synthesized. X-ray diffraction, thermal analysis and magnetic investigations have been conducted in order to obtain information on the mechanism of lead hexaferrite formation.

Coordination compounds as raw materials for mixed oxides: Part IX. Thermal decomposition of some copper-lanthanide mandelate complexes

Abstract Copper( II )-lanthanide( III ) mandelate complexes, (CuLn 2 (C 8 H 7 O 3 ) 6 (OH) 2 · n H 2 O (Ln = La, Sm, n = 1; Ln = Pr, Nd, Eu, Gd, n = 3), were prepared and characterized by elemental analysis, electrical conductance and magnetic susceptibility measurements, and IR and electronic spectra. The thermal decomposition of these complexes has been studied using TG and DTG techniques in air and argon. The TG curves show three main steps of decomposition. The intermediate oxycarbonate and the final decomposition product were characterized by X-ray diffraction, IR spectroscopy and magnetic susceptibility measurements. The final product is the corresponding CuLn 2 O 4 (Ln = La-Gd), which can be obtained at temperatures even lower than 800 ° C by isothermal decomposition of the coordination compounds.