Search

In this work the magnetic properties of bimetallic phases M′0.2Mn0.8PS3·0.25H2O (M′ = CoII, NiII, CuII or ZnII) have been explored and compared with those of the pristine phase MnPS3. Magnetic susceptibility, high field magnetization and electron paramagnetic resonance (EPR) studies reveal that the transition temperature between the antiferromagnetic and paramagnetic order for the pristine phase is shifted to lower values in the bimetallic phases. From magnetization measurements the critical field of the spin-flop transition is found to be dependent on the nature of the added secondary transition metal ion. EPR spectra of all compounds in the temperature range of 8–300 K present a single resonance line shape. Temperature dependence of the EPR parameters, like line width, g values and double integrated area (IDIN), are obtained from the spectra and present a scenario compatible with the magnetization results. The temperature dependence of the first derivative of the product (IDINT) shows two maxima for all samples, with exception of the CoII phase, indicating two critical temperatures, while these critical temperatures could not be clearly determined by dc susceptibility. [ABSTRACT FROM AUTHOR]

A new iron(III)/vanadium(III) phosphate, K3[Fe3.26V0.74(OH)O(PO4)4(H2O)2]·2H2O (1), has been obtained by hydrothermal synthesis and characterized by single crystal X-ray diffraction, Scanning electron microscopy–energy dispersive X-ray spectroscopy, Inductively coupled plasma atomic emission spectroscopy (ICP), thermogravimetric analysis, and FTIR spectroscopy. Single crystal X-ray diffraction reveals a 3D open framework (monoclinic, space groupP21/n,a = 9.6391(7) Å,b = 9.8063(7) Å,c = 9.7268(7) Å,β = 100.71(1)°, andV = 903.38(11) Å3). This structure presents FeIIIand VIIIin a 4.4 : 1 M ratio with the metal ions in two different crystallographic sites. Both metallic centers have distorted octahedral environments, linked by PO4tetrahedra, forming channels along thea-axis. The asymmetric unit of K3[Fe3.26V0.74(OH)O(PO4)4(H2O)2]·2H2O presents a {M4(OH)O(PO4)4(H2O)2}3−anionic entity, charge balanced by three K+, which are located within the channels. It is also possible to distinguish M4O2units whose MIIIpolyhedra are linked by vertex and edges. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties of [(VO)3(μ-PO4)2(2,2′-bpy)(μ-OH2)]1/3H2O (1) and (VO)2H4P2O9 (2), a tubular and a layered vanadium(IV) phosphates containing triply oxido bridged VIV dimers, are analyzed considering the Bleaney–Bowers S =1/2 dimer model. In compound 1 the presence of an additional VIV connected with the VIV dimers through μ1,2-PO4 3− bridges is described with a Curie–Weiss type correction. This model reproduces the magnetic properties of compound 1 with g =1.956, J dim =−102.1cm−1, θ =−0.4cm−1 and Nα =278×10−6 emumol−1. In compound 2, the presence of a small percentage of paramagnetic impurity has to be considered to account for the divergence of χm at low temperatures. This simple model reproduces the magnetic data of compound 2 with g =1.99, J =−62.4cm−1 and a 1.2% of monomeric impurity. The moderate antiferromagnetic coupling found in the triply oxido bridges VIV dimers is justified from the structural parameters of the bridge. These studies confirm that the coupling through –O–P–O– bridges is antiferromagnetic and relatively weak, as well as previous magneto-structural correlations in this kind of oxido bridges. DFT calculations on a dinuclear fragment model for the two systems gave the following values of J calc =−72.4cm−1 for 1 and J calc =−5.2cm−1 for 2. These values reproduce the antiferromagnetic nature of the superexchange interactions between the VIV centers. [Copyright &y& Elsevier]

Abstract: The hybrid 2D compound [{Cu(bpy)}2(VO)3(PO4)2(HPO4)2]·2H2O (1), has been investigated due to its interesting magnetic and catalytic properties. Compound (1) acts as an efficient catalyst in the epoxidation of cyclohexene and styrene. The chemoselectivity towards the epoxidation of cyclohexene is notoriously higher than the one observed towards styrene. The bulk antiferromagnetic behaviour of [{Cu(bpy)}2(VO)3(PO4)2(HPO4)2]·2H2O (1) can be well described with a pentanuclear model, using five J values. Both antiferromagnetic and ferromagnetic interactions mediated by phosphate bridges are found to be present in this hybrid copper(II)–vanadium(IV) material. [Copyright &y& Elsevier]

Abstract: In this work, we describe for first time, the structure and magnetic characterization of the one dimensional catena cis-[Ni(μ-ox)(H2O)2]∞ (1), which was obtained by solvothermal synthesis. Cis-[Ni(μ-ox)(H2O)2]∞ crystallizes in a C2/c spatial group. The asymmetric unit contains only one type of nickel atom, oxalate ligand and water molecules. The chain backbone is constructed by the bis-chelating coordination mode of the oxalate ligand, presenting a zigzag chain in the [101] direction. The nickel ions have a distorted octahedral geometry, surrounded by six oxygens, four of them from two different oxalate ligands and the other two from the cis-coordinated water molecules. Thermal dependence of the magnetic susceptibility of (1) was studied in a temperature range of 2.5–255K, at applied fields of 0.10 and 0.25kOe. The plot of χ M T(T) shows antiferromagnetic interactions between the Ni(II) centres. The experimental data were fitted between 255 and 30K, using an empirical expression for a chain of equally spaced Ni(II) centres. The best fit of the experimental date gave a J value of −57cm−1, which is much higher that the obtained for the trans-analogue. Irreversibility between ZFC and FC measurements below 9K was observed, indicating some kind of magnetic ordering. [Copyright &y& Elsevier]

Abstract: The hybrid organic/inorganic copper oxovanadium diphosphonates of formula [Cu(bipy)(VO2)2(O3PCH2PO3)H2O] 1, which crystallizes in the orthorhombic symmetry, and [Cu(bipy)(VO2)(O3P(CH2)2PO2OH)]·1.5H2O 2, which crystallizes in the monoclinic symmetry, were obtained by the soft hydrothermal route. The layered VPOC structure of 1 may be described as a undulating (VO2)2(O3PCH2PO3)(H2O)2− network formed by the link between the V2PCO10 rings via the diphosphonate fragments, creating 18-membered {V4P5C2O7} cavities. The corrugated lamellar structure of 2 is obtained by the interconnection of four oxovanadium phosphorus V4P8C8O8 anionic rings with diphosphonate fragments, forming 28-atom cavities. In both compounds the copper diimine cation groups are coordinated to the chelating oxygen atoms of the PO3 and oxovanadium groups, and do not participate in building the 2D-structure. [Copyright &y& Elsevier]

In this work the magnetic properties of bimetallic phases M′0.2Mn0.8PS3·0.25H2O (M′ = CoII, NiII, CuII or ZnII) have been explored and compared with those of the pristine phase MnPS3. Magnetic susceptibility, high field magnetization and electron paramagnetic resonance (EPR) studies reveal that the transition temperature between the antiferromagnetic and paramagnetic order for the pristine phase is shifted to lower values in the bimetallic phases. From magnetization measurements the critical field of the spin-flop transition is found to be dependent on the nature of the added secondary transition metal ion. EPR spectra of all compounds in the temperature range of 8–300 K present a single resonance line shape. Temperature dependence of the EPR parameters, like line width, g values and double integrated area (IDIN), are obtained from the spectra and present a scenario compatible with the magnetization results. The temperature dependence of the first derivative of the product (IDINT) shows two maxima for all samples, with exception of the CoII phase, indicating two critical temperatures, while these critical temperatures could not be clearly determined by dc susceptibility. [ABSTRACT FROM AUTHOR]

Abstract: Dinuclear [{M(phen)2}2V4O12]·C6H12O·H2O (M=CoII 1, MnII 2, NiII 3 and CuII 4) and [{Cu(phen)2}2V4O12]·3.5H2O 5 has been prepared by biphasic and hydrothermal syntheses, respectively. All five structures exhibit the {V4O12}4− cluster in a chair-like configuration, covalently bonded to two [M(phen)2]2+ fragments, producing a super-exchange magnetic phenomenon. The magnetic study of complexes 1–5 shows that they are very weak antiferromagnetically coupled systems, with J values of −0.14, 2; −0.64, 3 and −0.23, 4 cm−1. Complexes 1 to 3 correspond to isostructural compounds in which the cyclovanadate group acts as a bidentate bridged ligand. In the copper complexes (4 and 5) the {V4O12}4− anion presents the novel monodentate bridging mode, and therefore a more significant distortion from the chair-like configuration. The mentioned complexes, together with that reported in the literature, permit to conclude that it is quite common for a single molecular species to exist in more than one crystalline arrangement. A detailed analysis of the structures of 1–4 shows that the crystal symmetry cannot be strictly centrosymmetric, due to the presence of the cyclohexanol molecule with a single –OH group in the lattice. [Copyright &y& Elsevier]