M.I. Arriortua

Hydrothermal synthesis of a new layered inorganic–organic hybrid cobalt(II) phosphite: (C2H10N2)[Co3(HPO3)4]: Crystal structure and spectroscopic and magnetic properties

The (C2H10N2)[Co3(HPO3)4] phosphite templated by ethylenediamine has been prepared by hydrothermal synthesis. It crystallizes in the triclinic space group P-1 with the parameters: a=5.351(2), b=5.347(4), c=14.010(6) A, α=80.98(5), β=85.66(4), γ=60.04(4)°, V=343.0(3) A3 and Z=1. The compound shows a layered structure stacked along the c-axis. The ethylenediammonium cations are placed between the sheets. Ionic interactions and hydrogen bonds are present between the ethylenediammonium cations and the inorganic layers. The layers are formed by Co3O12 trimeric entities which contain face-sharing CoO6 octahedra interconnected by (HPO3)2− tetrahedral phosphite anions. The spectroscopic study by diffuse reflectance allowed us to obtain the Dq=725 cm−1 and the Racah parameters, B=880 and C=3950 cm−1 for the high spin octahedral Co(II) ions. Magnetic measurements reveal the presence of antiferromagnetic exchange interactions in the trimeric units of (C2H10N2)[Co3(HPO3)4].

Magnetic properties of the LiMPO4 (M = Co, Ni) compounds

Abstract Powder samples of LiNiPO 4 , LiCoPO 4 together with LiMgPO 4 doped with 0.1% of Co 2+ were prepared by solid state reactions. Magnetic susceptibility measurements of the LiNiPO 4 and LiCoPO 4 compounds are consistent with 3D antiferromagnetic behaviour. The magnetic exchange value for the LiNiPO 4 phase is −5.61 K, with a g -value of 2.15. The EPR study of LiMgPO 4 doped with 0.1% of Co 2+ shows the large magnetic anisotropy of the Co 2+ ion in a distorted octahedral geometry. The obtained values at 4.2 K for the spin Hamiltonian parameters are g 1 = 6.16, g 2 = 4.14, g 3 = 2.53 and A 1 = 246 × 10 −4 , A 2 = 89 × 10 −4 and A 3 −4 cm −1 .

Crystal Structure and Spectroscopic Properties of the Monoaquobis (N-thiocyanate) (2,2′-dipyridylamine)copper(II) Complex

The monoaquobis (N-thiocyanate)(2,2′-dipyridylamine)copper(II) complex has been synthesized and characterized. Its crystal structure has been resolved at room temperature. The complex crystallizes in the monoclinic space group P21/n, with a = 10.688(1) A, b = 11.104(2) A, c = 12.982(2) A β = 102.63(1)° and Z = 4. The structure consists of discrete molecules in which the copper(II) ion is pentacoordinated with a distorted square pyramidal geometry. The ESR and diffuse reflectance spectra are in good agreement with the structural results. The covalence factor has been calculated from the ESR and reflectance measurements (K = 0.79).

Structural phase transitions in the ordered double perovskite Sr2MnTeO6

The crystal structure of the ordered double perovskite Sr2MnTeO6 has been refined at ambient temperature from high resolution neutron and x-ray powder diffraction data in the monoclinic space group P 121/n 1 with a = 5.7009(1) A, b = 5.6770(1) A, c = 8.0334(1) A and β = 90.085(1)°. This represents a combination of in-phase (+) and out-of-phase (−) rotations of virtually undistorted MnO6 and TeO6 octahedra in the (−−+) sense about the axes of the ideal cubic perovskite. High temperature x-ray powder diffraction shows three structural phase transitions at approximately 250, 550 and 675 °C, each corresponding to the disappearance of rotations about one of these axes. The first transition was analysed by differential scanning calorimetry and showed a thermal hysteresis with an enthalpy of 0.55 J g−1. We propose the () sequence of structural transitions which has not been previously reported for a double perovskite oxide.

Solid-state transformation of the MOF [Ni2(bipy)1.5(PDC)2(H2O)2]·3.5H2O

The combination of non-centrosymmetric ligands and dipyridyl spacers produces a MOF that potentially can be porous with formula [Ni2(bipy)1.5(PDC)2(H2O)2]·3.5H2O (bipy = 4,4′-bipyridine and PDC = pyridine-2,5-dicarboxylate). Dehydration of this compound results in a new MOF in which the formation of additional bonds between the carboxylate groups of PDC and the metal ion has occurred. This solid-state transformation takes place with no significant changes in the coordination sphere of the metal ion, which is unusual for coordination polymers. Both compounds exhibit the same unprecedented topology where the connectivity between nodes is remarkably high.

Spectroscopic and magnetic study of the (Mg,M)3(ASO4)2·8H2O (M = NI2+, CO2+) arsenates

Abstract Compounds of general formula (Mg,M) 3 (AsO 4 ) 2 ·8H 2 O (M = Ni 2+ , Co 2+ ) have been synthesized and characterized. The crystal structure of the (Mg 2.5 Ni 0.5 )(AsO 4 ) 2 ·8H 2 O compound has been refined using the Rietveld method. The final reliability factors are R p = 5.62, R wp = 7.06, and R B = 5.29. Crystallographic studies reveal that both the ionic radius of the cations and the symmetry of the octahedral sites can play an important role in determining the cation ordering in these compounds. Diffuse reflectance spectra indicate a significant covalence in the nickel and cobalt-oxygen bonds. The analysis of the magnetic measurements and the structural features shows a strong dimer ferromagnetic interaction in the compounds.

Crystal structure and magnetic properties of two metal–picolinate systems obtained from degradation of bis(2-pyridylketone) through reaction with Mn(II) and Cu(II)

Abstract The bis(2-pyridyl-ketone) compound is expected to have great potential as a multidentate ligand with transition metals. However, similar ketone-containing compounds, bis(2-pyridyl-ketone) could undergo metal-promoted hydration. With the aim of determining its behaviour, bis(2-pyridyl-ketone) was reacted with Cu(II) and Mn(II). X-ray characterisation of the products reveals the formation of complexes containing picolinate anions as products of the degradation of bis(2-pyridyl-ketone). ESR spectroscopy for the compound with Mn(II) ( 1 ) indicates an important zero-field splitting term originating from the strong distortion of the resulting Mn(II) octahedra. The ESR spectra for the compound with Cu(II) ( 2 ) are consistent with the elongated Cu(II)-octahedra. These octahedra form a monodimensional arrangement which shows the occurrence of antiferromagnetic exchange couplings.

Structure and spectroscopic study of an azide-copper(II) dinuclear complex : [Cu(pymep)(N3)2]2•2H2O

Abstract The compound of formula [Cu(C14H15N3)(N3)2]2·2H2O [where C14H15N3 is N-(2′-(6-methyl)pyridyl)methylene-2-(2

Synthetic pathways to obtain phosphates and arsenates of Co (II) and Ni (II) related to minerals: magnetic properties

Abstract Different methods to prepare phosphates and arsenates of transition metals related to minerals are described. M 3 (XO 4 ) 2 ·8H 2 O (M=Co, Ni; X=P, As) vivianite-like compounds were prepared by solution chemistry procedures. (Ni, Mg) 3 (PO 4 ) 2 (related to sarcopside) solid solutions were obtained by thermal treatments of the octahydrated phases. Using hydrothermal conditions three new compounds were synthesized: Co 3 (HPO 4 ) 2 (OH) 2 (related to lazulite) and M 12+ x H 4−2 x (PO 4 ) 6 (HPO 4 ) 2 (OH) 6 (M=Co, Ni), dumortierite-like hexagonal phases. In every case, the magnetic properties are discussed with respect to the crystal structure and the nature of the transition-metal ion.

Hydrothermal synthesis, crystal structure, and spectroscopic and magnetic properties of a new organically templated mixed-anion fluoro-arsenate-phosphate iron(III) compound, (C6H14N2)[Fe3(HAsO4)1.33(HPO4)0.67(AsO4)0.84(PO4)0.16F4]0.5(H2O)

Abstract The new organically templated mixed-anion fluoro-arsenate–phosphate iron(III) compound, with formula (C6H14N2)[Fe3(HAsO4)1.33(HPO4)0.67(AsO4)0.84(PO4)0.16F4]0.5(H2O), has been synthesized by using mild hydrothermal conditions under autogeneous pressure. The crystal structure has been solved from X-ray single crystal data. The unit-cell parameters are a=18.267(1), b=10.085(1), c=20.436(2) A, β=105.97(1)°. Monoclinic, C2/c with Z=8. The structure consists of a three-dimensional inorganic framework formed by [Fe3(HAsO4)1.33(HPO4)0.67(AsO4)0.84(PO4)0.16F4]2− inorganic layers linked by hydrogen-arsenate/phosphate anions. There are three iron atoms crystallographically independent per unit-formula. The sheets are constructed from Fe(1)Fe(3)O6F4 and Fe(2)2O8F2 dimeric units with edge-sharing octahedra. The 1,4-diazabicyclooctane dications are located inside the cavities of the inorganic skeleton. The IR and Raman spectroscopies confirm the simultaneously existence of both the arsenate/hydrogenarsenate and phosphate/hydrogenphosphate anions. From the diffuse reflectance spectrum the Dq=1080 and Racah parameters B=1040 and C=2620 cm−1 for the d5-high spin iron(III) cation in octahedral geometry have been calculated. The Mossbauer spectrum at room temperature is characteristic of high spin iron(III) cations. The ESR spectra are isotropic with a g-value of 1.99(1), which remains unchanged with variation in temperature. Magnetic measurements indicate the presence of antiferromagnetic interactions with a maximum in the susceptibility at around 6.0 K.