Perovskite, LiNbO3, corundum, and hexagonal polymorphs of (In(1-x)M(x))MO3

LiNbO(3) (LN), corundum (cor), and hexagonal (hex) phases of (In(1-x)M(x))MO(3) (x = 0.143; M = Fe(0.5)Mn(0.5)) were prepared. Their crystal structures were investigated with synchrotron X-ray powder diffraction, and their properties were studied by differential thermal analysis, magnetic measurements, and M?ssbauer spectroscopy. The LN-phase was prepared at high pressure of 6 GPa and 1770 K; it crystallizes in space group R3c with a = 5.25054(7) ?, c = 13.96084(17) ?, and has a long-range antiferromagnetic ordering near T(N) = 270 K. The cor- and hex-phases were obtained at ambient pressure by heating the LN-phase in air up to 870 and 1220 K, respectively. The cor-phase crystallizes in space group R-3c with a = 5.25047(10) ?, c = 14.0750(2) ?, and the hex-phase in space group P6(3)/mmc with a = 3.34340(18) ?, c = 11.8734(5) ?. T(N) of the cor-phase is about 200 K, and T(N) of the hex-phase is about 140 K. During irreversible transformations of LN-(In(1-x)M(x))MO(3) with the (partial) cation ordering, the In(3+), Mn(3+), and Fe(3+) cations become completely disordered in one crystallographic site of the corundum structure, and then they are (partially) ordered again in the hex-phase. LN-(In(1-x)M(x))MO(3) exhibits a reversible transformation to a perovskite GdFeO(3)-type structure (space group Pnma; a = 5.2946(3) ?, b = 7.5339(4) ?, c = 5.0739(2) ? at 10.3 GPa) at room temperature and pressure of about 5 GPa.     

Control of magnetic ordering by Jahn--Teller distortions in Nd(2)GaMnO(6) and La(2)GaMnO(6).

The substitution of Ga(3+) into the Jahn--Teller distorted, antiferromagnetic perovskites LaMnO(3) and NdMnO(3) strongly affects both the crystal structures and resulting magnetic ordering. In both compounds the Ga(3+) and Mn(3+) cations are disordered over the six coordinate sites. La(2)GaMnO(6) is a ferromagnetic insulator (T(c) = 70 K); a moment per Mn cation of 2.08(5) mu(B) has been determined by neutron powder diffraction at 5 K. Bond length and displacement parameter data suggest Jahn--Teller distortions which are both coherent and incoherent with the Pnma space group symmetry of the perovskite structure (a = 5.51122(4) A, b = 7.80515(6) A, c = 5.52947(4) A) at room temperature. The coherent distortion is strongly suppressed in comparison with the parent LaMnO(3) phase, but the displacement ellipsoids suggest that incoherent distortions are significant and arise from local Jahn--Teller distortions. The preparation of the new phase Nd(2)GaMnO(6) has been found to depend on sample cooling rates, with detailed characterization necessary to ensure phase separation has been avoided. This compound also adopts the GdFeO(3)-type orthorhombically distorted perovskite structure (space group Pnma, a = 5.64876(1) A, b = 7.65212(2) A, c = 5.41943(1) A at room temperature). However, the B site substitution has a totally different effect on the Jahn--Teller distortion at the Mn(3+) centers. This phase exhibits a Q(2) mode Jahn--Teller distortion similar to that observed in LaMnO(3), although reduced in magnitude as a result of the introduction of Ga(3+) onto the B site. There is no evidence of a dynamic Jahn-Teller distortion. At 5 K a ferromagnetically ordered Nd(3+) moment of 1.06(6) mu(B) is aligned along the y-axis and a moment of 2.8(1) mu(B) per Mn(3+) is ordered in the xy plane making an angle of 29(2) degrees with the y-axis. The Mn(3+) moments couple ferromagnetically in the xz plane. However, along the y-axis the moments couple ferromagnetically while the x components are coupled antiferromagnetically. This results in a canted antiferromagnetic arrangement in which the dominant exchange is ferromagnetic. Nd(2)GaMnO(6) is paramagnetic above 40(5) K, with a paramagnetic moment and Weiss constant of 6.70(2) mu(B) and 45.9(4) K, respectively. An ordered moment of 6.08(3) mu(B) per Nd(2)GaMnO(6) formula unit was measured by magnetometry at 5 K in an applied magnetic field of 5 T.     

High-pressure synthesis and neutron diffraction investigation of the crystallographic and magnetic structure of TeNiO3 perovskite

TeNiO(3) has been prepared under moderate pressure conditions (3.5 GPa), starting from a reactive TeO(2) and Ni(OH)(2) mixture contained in a sealed platinum capsule under the reaction conditions (850 °C for 2 h). The sample has been studied by neutron powder diffraction (NPD) data and magnetization measurements. TeNiO(3) crystallizes in an orthorhombically-distorted perovskite structure (space group Pnma) with the unit cell parameters a = 5.9588(1) ?, b = 7.5028(1) ? and c = 5.2143(1) ?. The NiO(6) octahedral network is extremely tilted, shaping a trigonal-pyramidal environment for the Te, where it is effectively coordinated to three oxygen atoms at Te-O distances of 1.92 ?. Below T(N) ≈ 130 K, it experiences an antiferromagnetic ordering, as demonstrated by susceptibility and NPD measurements. Above the Néel temperature, a paramagnetic moment of 3.24(1) μ(B)/f.u. and θ(Weiss) = -199(1) K are obtained from the reciprocal susceptibility. Below T(N), the magnetic reflections observed in the neutron patterns can be indexed with a propagation vector k = 0. The magnetic structure corresponds to the magnetic mode G(y)F(z). The magnetic moments are oriented along the y-direction, with a canting along the z-axis. This ferromagnetic component explains the weak ferromagnetism observed in the magnetization isotherms; the infrequent shape of the magnetization cycles suggests a metamagnetic transition below 0.2 T. At T = 2.5 K, the ordered magnetic moment for the Ni(2+) ions is 1.88(5) μ(B) for the G(y) mode and 0.9(2) μ(B) for the F(x) mode.     

Syntheses, crystal and electronic structures, and characterizations of quaternary antiferromagnetic sulfides: Ba2MFeS5 (M = Sb, Bi)

Two new quaternary sulfides, Ba(2)SbFeS(5) and Ba(2)BiFeS(5), were synthesized by using a conventional high-temperature solid-state reaction method in closed silica tubes at 1123 K. The two compounds both crystallize in the orthorhombic space group Pnma with a = 12.128(6) ?, b = 8.852(4) ?, c = 8.917(4) ?, and Z = 4 for Ba(2)SbFeS(5) and a = 12.121(5) ?, b = 8.913(4) ?, c = 8.837(4) ?, and Z = 4 for Ba(2)BiFeS(5). The crystal structure unit can be viewed as an infinite one-dimensional edge-shared MS(5) (M = Sb, Bi) tetragonal-pyramid chain with FeS(4) tetrahedra alternately arranged on two sides of the MS(5) polyhedral chain via edge-sharing (so the chain can also be written as (1)(∞)[MFeS(5)](4-)). Interestingly, the compounds have the structural type of a Ba(3)FeS(5) high-pressure phase considering one Ba(2+) is replaced by one Sb(3+)/Bi(3+), with Fe(4+) reduced to Fe(3+) for in order to maintain the electroneutrality of the system. As a result, the isolated iron ions in Ba(3)FeS(5) are bridged by intermediate MS polyhedra in Ba(2)MFeS(5) (M = Sb, Bi) compounds and form the (1)(∞)[MFeS(5)](4-) chain structure. This atom substitution of Ba(2+) by one Sb(3+)/Bi(3+) leads to a magnetic transition from paramagnetic Ba(3)FeS(5) to antiferromagnetic Ba(2)MFeS(5), resulting from an electron-exchange interaction of the iron ions between inter- or intrachains. Magnetic property measurements indicate that the two compounds are both antiferromagnetic materials with Ne?el temperatures of 13 and 35 K for Ba(2)SbFeS(5) and Ba(2)BiFeS(5), respectively. First-principles electronic structure calculations based on density functional theory show that the two compounds are both indirect-band semiconductors with band gaps of 0.93 and 1.22 eV for Ba(2)SbFeS(5) and Ba(2)BiFeS(5), respectively.     

Interplay between the structural and magnetic probes in the elucidation of the structure of a novel 2D layered [V4O4(OH)2(O2CC6H4CO2)4]·DMF

The title compound has been synthesized under solvothermal conditions by reacting vanadium(V) oxytriisopropoxide with terephthalic acid in N,N-dimethylformamide. A combination of synchrotron powder diffraction, infrared spectroscopy, scanning and transmission electron microscopy, and thermal and chemical analysis elucidated the chemical, structural and microstructural features of a new 2D layered inorganic-organic framework. Due to the low-crystallinity of the final material, its crystal structure has been solved from synchrotron X-ray powder diffraction data using a direct space global optimization technique and subsequent constraint Rietveld refinement. [V(4)O(4)(OH)(2)(O(2)CC(6)H(4)CO(2))(4)]·DMF crystallizes in the monoclinic system (space group P2/m (No. 10)); cell parameters: a = 20.923(4) ?, b = 5.963(4) ?, c = 20.425(1) ?, β = 123.70(6)°, V = 2120.1(9) ?(3), Z = 2. The overall structure can be described as an array of parallel 2D layers running along [-101] direction, consisting of two types of vanadium oxidation states and coordination polyhedra: face-shared trigonal prisms (V(4+)) and distorted corner-shared square pyramids (V(5+)). Both configurations form independent parallel chains oriented along the 2-fold symmetry crystallographic b-axis mutually interlinked with terephthalate ligands in a monodentate mode perpendicular to it. The morphology of the compound exhibits long nanofibers, with the growth direction along the layered [-101] axis. The magnetic susceptibility measurements show that the magnetic properties of [V(4)O(4)(OH)(2)(O(2)CC(6)H(4)CO(2))(4)]·DMF can be described by a linear antiferromagnetic chain model, with the isotropic exchange interaction of J = -75 K between the nearest V(4+) neighbours of S = 1/2.     

Vanadium(IV) Complexes with Mixed O,S Donor Ligands. Syntheses, Structures, and Properties of the Anions Tris(2-mercapto-4-methylphenolato)vanadate(IV) and Bis(2-mercaptophenolato)oxovanadate(IV)

Reaction of VO(acac)(2) with 2-mercaptophenol (mpH(2)) in the presence of triethylamine gives the mononuclear tris complex (Et(3)NH)(2)[V(mp)(3)] (1), in which the vanadyl oxygen has been displaced. An analogous reaction using 2-mercapto-4-methylphenol (mmpH(2)) afforded (Et(3)NH)(PNP)[V(mmp)(3)] (2), which was structurally characterized. 2 crystallizes in the orthorhombic space group Pna2(1 )with unit cell parameters (at -163 degrees C) a = 23.974(7) ?, b = 9.569(4) ?, c = 25.101(6) ?, and Z = 4. The coordination geometry around the vanadium is between octahedral and trigonal prismatic. Reaction of VO(acac)(2 )with the sodium salt of 2-mercaptophenol produces the vanadyl(IV) complex Na(Ph(4)P)[VO(mp)(2)].Et(2)O (3), which crystallizes in the triclinic space group P&onemacr; with unit cell parameters (at -135 degrees C) a = 12.185(4) ?, b = 12.658(4) ?, c = 14.244(4) ?, alpha = 103.19(2) degrees, beta = 100.84(2) degrees, and gamma = 114.17(2) degrees. The unit cell of 3 contains a pair of symmetry-related [VO(mp)(2)](2)(-) units bridged through vanadyl and ligand oxygen atoms by a pair of sodium ions, in addition to two PPh(4)(+) ions. The coordination geometry around the vanadium is square pyramidal, with a V=O bond length of 1.611(5) ?. 1, 2, and 3 are characterized by IR and UV-vis spectroscopies, magnetic susceptibility, EPR spectroscopy, and cyclic voltammetry. 1 and 2 can be oxidized by I(2, )Cp(2)Fe(+), or O(2) to [V(mp)(3)](-) and [V(mmp)(3)](-), respectively, which in turn can be reduced back to the dianions by oxalate ion. These reversible redox processes can be followed by UV-vis spectroscopy.     

New vanadium selenites: centrosymmetric Ca2(VO2)2(SeO3)3(H2O)2, Sr2(VO2)2(SeO3)3, and Ba(V2O5)(SeO3), and noncentrosymmetric and polar A4(VO2)2(SeO3)4(Se2O5) (A = Sr2+ or Pb2+)

Five new vanadium selenites, Ca(2)(VO(2))(2)(SeO(3))(3)(H(2)O)(2), Sr(2)(VO(2))(2)(SeO(3))(3), Ba(V(2)O(5))(SeO(3)), Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), have been synthesized and characterized. Their crystal structures were determined by single crystal X-ray diffraction. The compounds exhibit one- or two-dimensional structures consisting of corner- and edge-shared VO(4), VO(5), VO(6), and SeO(3) polyhedra. Of the reported materials, A(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) (A = Sr(2+) or Pb(2+)) are noncentrosymmetric (NCS) and polar. Powder second-harmonic generation (SHG) measurements revealed SHG efficiencies of approximately 130 and 150 × α-SiO(2) for Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), respectively. Piezoelectric charge constants of 43 and 53 pm/V, and pyroelectric coefficients of -27 and -42 μC/m(2)·K at 70 °C were obtained for Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)) and Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), respectively. Frequency dependent polarization measurements confirmed that the materials are not ferroelectric, that is, the observed polarization cannot be reversed. In addition, the lone-pair on the Se(4+) cation may be considered as stereo-active consistent with calculations. For all of the reported materials, infrared, UV-vis, thermogravimetric, and differential thermal analysis measurements were performed. Crystal data: Ca(2)(VO(2))(2)(SeO(3))(3)(H(2)O)(2), orthorhombic, space group Pnma (No. 62), a = 7.827(4) ?, b = 16.764(5) ?, c = 9.679(5) ?, V = 1270.1(9) ?(3), and Z = 4; Sr(2)(VO(2))(2)(SeO(3))(3), monoclinic, space group P2(1)/c (No. 12), a = 14.739(13) ?, b = 9.788(8) ?, c = 8.440(7) ?, β = 96.881(11)°, V = 1208.8(18) ?(3), and Z = 4; Ba(V(2)O(5))(SeO(3)), orthorhombic, space group Pnma (No. 62), a = 13.9287(7) ?, b = 5.3787(3) ?, c = 8.9853(5) ?, V = 673.16(6) ?(3), and Z = 4; Sr(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), orthorhombic, space group Fdd2 (No. 43), a = 25.161(3) ?, b = 12.1579(15) ?, c = 12.8592(16) ?, V = 3933.7(8) ?(3), and Z = 8; Pb(4)(VO(2))(2)(SeO(3))(4)(Se(2)O(5)), orthorhombic, space group Fdd2 (No. 43), a = 25.029(2) ?, b = 12.2147(10) ?, c = 13.0154(10) ?, V = 3979.1(6) ?(3), and Z = 8.     

Synthesis, structure and magnetic properties of Nd3+ and Pr3+ 2D polymers with tetrafluoro-p-phthalate

Two lanthanide tetrafluoro-p-phthalate (L(2-)) complexes, Ln(L)(1.5)·DMF·H(2)O (Ln = Pr(3+) (1), Nd(3+) (2)), were synthesized using pyridine as a base. The compounds were found to be isostructural, and the structure of 1 has been determined by single crystal X-ray diffraction (monoclinic, space group C2, a = 22.194(2) ?, b = 11.4347(12) ?, c = 11.7160(12) ?, β = 94.703(2)°, V = 2963.3(5) ?(3), Z = 4). The crystal structure of 1 consists of dinuclear Pr(3+) units, which are connected by tetrafluoro-p-phthalate, forming separate 2D polymeric layers. The Ln(3+) ions in the dinuclear Ln(2) units are linked by two μ-O atoms and by two bridging O-C-O groups. The structure is porous with DMF and water molecules located between layers. Non-coordinated DMF molecules occupy about 27% of the unit cell volume. A systematic analysis of reported structures of Ln(III) polymers with p-phthalate and its derivatives shows that the ca. known 60 structures can be divided into six possible structural types depending on the presence of certain structural motifs. The magnetic properties of compounds 1 and 2 were studied. The dependence of χ(M)T on T (where χ(M) is magnetic susceptibility per dinuclear lanthanide unit) for 1 and 2 was simulated using two different models, based on: (i) the Hamiltonian ? = Δ?(z)(2)+ μ(B)g(J)H?, which utilises an axial splitting parameter Δ and temperature-independent paramagnetism (tip) and (ii) crystal field splitting. It was found that both models gave satisfactory fits, indicating that the Ln-Ln exchange interactions are small and the symmetry of the coordination environment is the main factor influencing the magnetic properties of these compounds.     

Orthogonal spin arrangement in quasi-two-dimensional La2Co2O3Se2

The crystal, electronic, and magnetic structures of the cobalt oxyselenide La(2)Co(2)O(3)Se(2) were investigated through powder neutron diffraction measurements and band structure calculations. This oxyselenide crystallizes in a tetragonal layered structure with space group I4/mmm. The Co ion is sixfold-coordinated by two oxide ions and four selenide ions, and the face-sharing CoO(2)Se(4) octahedra form Co(2)OSe(2) layers. The band structure calculations revealed that the Co ion is in the divalent high-spin state. Rietveld analysis of the neutron diffraction profiles below 200 K demonstrated that the Co moments have a noncollinear antiferromagnetic structure with the propagation vector k = (?, ?, 0). The ordered magnetic moment was determined to be 3.5 μ(B) at 10 K, and the directions of the nearest-neighbor Co moments are orthogonal each other in the c plane.     

Syntheses and characterization of nine quaternary uranium chalcogenides among the compounds A2M3UQ6 (A = K, Rb, Cs; M = Pd, Pt; Q = S, Se)

Nine compounds from the series A(2)M(3)UQ(6) (A = K or Rb or Cs; M = Pd or Pt; Q = S or Se) were synthesized by reacting U, M, and Q in ACl or A(2)Q(x) fluxes. These compounds crystallize with eight formula units in the NaBa(2)Cu(3)O(6) structure type, in space group Fmmm of the orthorhombic system. The structure contains hexagons formed from six edge-sharing square-planar coordinated M atoms, which in turn edge-share with trigonal-prismatically coordinated U atoms, forming layers along (010). These layers are separated by A atoms. Electrical resistivity measurements along the [100] direction of Rb(2)Pd(3)US(6) show typical semiconductor behavior. Magnetic susceptibility measurements on Rb(2)Pd(3)US(6) display marked magnetic anisotropy and unusually low magnetic moments owing to crystalline electric field effects.     

Stabilization and study of SrFe(1-x)Mn(x)O2 oxides with infinite-layer structure

A series of layered oxides of nominal composition SrFe(1-x)Mn(x)O(2) (x = 0, 0.1, 0.2, 0.3) have been prepared by the reduction of three-dimensional perovskites SrFe(1-x)Mn(x)O(3-δ) with CaH(2) under mild temperature conditions of 583 K for 2 days. The samples with x = 0, 0.1, and 0.2 exhibit an infinite-layer crystal structure where all of the apical O atoms have been selectively removed upon reduction. A selected sample (x = 0.2) has been studied by neutron powder diffraction (NPD) and X-ray absorption spectroscopy. Both techniques indicate that Fe and Mn adopt a divalent oxidation state, although Fe(2+) ions are under tensile stress whereas Mn(2+) ions undergo compressive stress in the structure. The unit-cell parameters progressively evolve from a = 3.9932(4) ? and c = 3.4790(4) ? for x = 0 to a = 4.00861(15) ? and c = 3.46769(16) ? for x = 0.2; the cell volume presents an expansion across the series from V = 55.47(1) to 55.722(4) ?(3) for x = 0 and 0.2, respectively, because of the larger effective ionic radius of Mn(2+) versus Fe(2+) in four-fold coordination. Attempts to prepare Mn-rich compositions beyond x = 0.2 were unsuccessful. For SrFe(0.8)Mn(0.2)O(2), the magnetic properties indicate a strong magnetic coupling between Fe(2+) and Mn(2+) magnetic moments, with an antiferromagnetic temperature T(N) above room temperature, between 453 and 523 K, according to temperature-dependent NPD data. The NPD data include Bragg reflections of magnetic origin, accounted for with a propagation vector k = ((1)/(2), (1)/(2), (1)/(2)). A G-type antiferromagnetic structure was modeled with magnetic moments at the Fe/Mn position. The refined ordered magnetic moment at this position is 1.71(3) μ(B)/f.u. at 295 K. This is an extraordinary example where Mn(2+) and Fe(2+) ions are stabilized in a square-planar oxygen coordination within an infinite-layer structure. The layered SrFe(1-x)Mn(x)O(2) oxides are kinetically stable at room temperature, but in air at ~170 °C, they reoxidize and form the perovskites SrFe(1-x)Mn(x)O(3-δ). A cubic phase is obtained upon reoxidation of the layered compound, whereas the starting precursor SrFeO(2.875) (Sr(8)Fe(8)O(23)) was a tetragonal superstructure of perovskite.     

Intermolecular Ferromagnetic and Antiferromagnetic Interactions in Halogen-Bridged Copper(I) Imino Nitroxides: Crystal Structures and Magnetic Properties of [Cu(I)(&mgr;-X)(imino nitroxide)](2) (X = I or Br)

Reaction of CuI or CuBr with some imino nitroxides in methanol gave the halogen bridged dinuclear Cu(I) complexes [Cu(&mgr;-I)(impy)](2) (1), [Cu(&mgr;-I)(immepy)](2) (2), [Cu(&mgr;-Br)(immepy)](2) (3), and [Cu(&mgr;-Br)(imph-NO(2))](2) (4), respectively (impy = 2-(2'-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl, immepy = 2-(6'-methyl-2'-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl, imph-NO(2) = 2-(4'-nitrophenyl)-4,4,5,5-tetramethyl-4,6-dihydro-1H-imidazolyl-1-oxyl). Crystal structures and magnetic properties have been studied. Complexes 1-4 have dimeric structures where two copper ions are doubly bridged by halide ions in a &mgr;(2) fashion. In 1-3, each copper ion is tetrahedral with a bidentate imino nitroxide and two halide ions, and the two copper ions are separated by 2.592(2), 2.6869(8), and 2.7357(6) ?, respectively. In 4, triangular coordination sites of the copper ions are completed with a nitrogen atom from the imino nitroxide and two bromide ions bridging the two copper ions with a separation of 3.074(2) ?. Ligand imino nitroxides in 1-4 form one-dimensional radical chains, and the chains are linked with halocuprate dimer units. Structural and magnetic susceptibility data support that radicals in 1 and 4 are ferromagnetically stacked, while radicals in 2 and 3 form an antiferromagnetic chain. The magnetic behaviors are discussed in connection with the stacking modes of the radicals and bridging conformations. Crystal data (Mo Kalpha, lambda = 0.71069 ?): 1, orthorhombic, space group P2(1)2(1)2(1), a = 17.807(2) ?, b = 8.595(2) ?, c = 19.336(6) ?, and Z = 4; 2, monoclinic, space group P2(1)/c, a = 9.941(2) ?, b = 18.482(2) ?, c = 8.337(2) ?, beta = 96.41(2) degrees, and Z = 2; 3, monoclinic, space group P2(1)/c, a = 9.964(6) ?, b = 18.167(4) ?, c = 8.009(7) ?, beta = 95.81(6) degrees, and Z = 2; 4, monoclinic, space group P2(1)/c, a = 11.991(7) ?, b = 17.998(8) ?, c = 7.215(6) ?, beta = 104.07(6) degrees, and Z = 2.     

Two new noncentrosymmetric (NCS) polar oxides: syntheses, characterization, and structure-property relationships in BaMTe2O7 (M = Mg2+ or Zn2+)

Two new noncentrosymmetric (NCS) polar oxides, BaMgTe(2)O(7) and BaZnTe(2)O(7), have been synthesized and characterized, with their crystal structures determined by single crystal X-ray diffraction. The iso-structural materials exhibit structures consisting of layers of corner-shared MgO(5) or ZnO(5), Te(6+)O(6), and Te(4+)O(4) polyhedra that are separated by Ba(2+) cations. The Te(4+) cation is found in a highly asymmetric and polar coordination environment attributable to its stereoactive lone-pair. The alignment of the individual TeO(4) polar polyhedra results in macroscopic polarity for BaMgTe(2)O(7) and BaZnTe(2)O(7). Powder second-harmonic generation (SHG) measurements revealed a moderate SHG efficiency of approximately 5 × KDP (or 200 × α-SiO(2)) for both materials. Piezoelectric charge constants of 70 and 57 pm/V, and pyroelectric coefficients of -18 and -10 μC·m(-2)·K(-1) were obtained for BaMgTe(2)O(7) and BaZnTe(2)O(7), respectively. Although the materials are polar, frequency dependent polarization measurements indicated that the materials are not ferroelectric, that is, the observed macroscopic polarization cannot be reversed. Infrared, UV-vis diffuse spectroscopy, and thermal properties were also measured. Crystal data: BaMgTe(2)O(7), orthorhombic, space group Ama2 (No. 40), a = 5.558(2) ?, b = 15.215(6) ?, c = 7.307(3) ?, V = 617.9(4) ?(3), and Z = 4; BaZnTe(2)O(7), orthorhombic, space group Ama2 (No. 40), a = 5.5498(4) ?, b = 15.3161(11) ?, c = 7.3098(5) ?, V = 621.34(8) ?(3), and Z = 4.     

Hydrothermal Syntheses and Structural Characterization of Layered Vanadium Oxides Incorporating Organic Cations: alpha-, beta-(H(3)N(CH(2))(2)NH(3))[V(4)O(10)] and alpha-, beta-(H(2)N(C(2)H(4))(2)NH(2))[V(4)O(10)

Four new layered mixed-valence vanadium oxides, which contain interlamellar organic cations, alpha-(H(3)N(CH(2))(2)NH(3))[V(4)O(10)] (1a), beta-(H(3)N(CH(2))(2)NH(3))[V(4)O(10)] (1b), alpha-(H(2)N(C(2)H(4))(2)NH(2))[V(4)O(10)] (2a), and beta-(H(2)N(C(2)H(4))(2)NH(2))[V(4)O(10)] (2b), have been prepared under hydrothermal conditions and their single-crystal structures determined: 1a, triclinic, space group P&onemacr;, a = 6.602(2) ?, b = 7.638(2) ?, c = 5.984(2) ?, alpha = 109.55(3) degrees, beta = 104.749(2) degrees, gamma = 82.31(3) degrees, Z = 1; 1b, triclinic, P&onemacr;, a = 6.387(1) ?, b = 7.456(2) ?, c = 6.244(2) ?, alpha = 99.89(2) degrees, beta = 102.91(2) degrees, gamma = 78.74(2) degrees, Z = 1; 2a, triclinic, P&onemacr;, a = 6.3958(5) ?, b = 8.182(1) ?, c = 6.3715(7) ?, alpha = 105.913(9) degrees, beta = 104.030(8) degrees, gamma = 94.495(8) degrees, Z = 1; 2b, monoclinic, space group P2(1)/n, a = 9.360(2) ?, b = 6.425(3) ?, c = 10.391(2) ?, beta = 105.83(1) degrees, Z = 2. All four of the compounds contain mixed-valence V(5+)/V(4+) vanadium oxide layers constructed from V(5+)O(4) tetrahedra and pairs of edge-sharing V(4+)O(5) square pyramids with protonated organic amines occupying the interlayer space.     

The series of molecular conductors and superconductors ET4[AFe(C2O4)3]·PhX (ET = bis(ethylenedithio)tetrathiafulvalene; (C2O4)2- = oxalate; A+ = H3O+, K+; X = F, Cl, Br, and I): influence of the halobenzene guest molecules on the crystal structure and superconducting properties

An extensive series of radical salts formed by the organic donor bis(ethylenedithio)tetrathiafulvalene (ET), the paramagnetic tris(oxalato)ferrate(III) anion [Fe(C(2)O(4))(3)](3-), and halobenzene guest molecules has been synthesized and characterized. The change of the halogen atom in this series has allowed the study of the effect of the size and charge polarization on the crystal structures and physical properties while keeping the geometry of the guest molecule. The general formula of the salts is ET(4)[A(I)Fe(C(2)O(4))(3)]·G with A/G = H(3)O(+)/PhF (1); H(3)O(+)/PhCl (2); H(3)O(+)/PhBr (3), and K(+)/PhI (4), (crystal data at room temperature: (1) monoclinic, space group C2/c with a = 10.3123(2) ?, b = 20.0205(3) ?, c = 35.2732(4) ?, β = 92.511(2)°, V = 7275.4(2) ?(3), Z = 4; (2) monoclinic, space group C2/c with a = 10.2899(4) ?, b = 20.026(10) ?, c = 35.411(10) ?, β = 92.974°, V = 7287(4) ?(3), Z = 4; (3) monoclinic, space group C2/c with a = 10.2875(3) ?, b = 20.0546(15) ?, c = 35.513(2) ?, β = 93.238(5)°, V = 7315.0(7) ?(3), Z = 4; (4) monoclinic, space group C2/c with a = 10.2260(2) ?, b = 19.9234(2) ?, c = 35.9064(6) ?, β = 93.3664(6)°, V = 7302.83(18) ?(3), Z = 4). The crystal structures at 120 K evidence that compounds 1-3 undergo a structural transition to a lower symmetry phase when the temperature is lowered (crystal data at 120 K: (1) triclinic, space group P1 with a = 10.2595(3) ?, b = 11.1403(3) ?, c = 34.9516(9) ?, α = 89.149(2)°, β = 86.762(2)°, γ = 62.578(3)°, V = 3539.96(19) ?(3), Z = 2; (2) triclinic, space group P1 with a = 10.25276(14) ?, b = 11.15081(13) ?, c = 35.1363(5) ?, α = 89.0829(10)°, β = 86.5203(11)°, γ = 62.6678(13)°, V = 3561.65(8) ?(3), Z = 2; (3) triclinic, space group P1 with a = 10.25554(17) ?, b = 11.16966(18) ?, c = 35.1997(5) ?, α = 62.7251(16)°, β = 86.3083(12)°, γ = 62.7251(16)°, V = 3575.99(10) ?(3), Z = 2; (4) monoclinic, space group C2/c with a = 10.1637(3) ?, b = 19.7251(6) ?, c = 35.6405(11) ?, β = 93.895(3)°, V = 7128.7(4) ?(3), Z = 4). A detailed crystallographic study shows a change in the symmetry of the crystal for compound 3 at about 200 K. This structural transition arises from the partial ordering of some ethylene groups in the ET molecules and involves a slight movement of the halobenzene guest molecules (which occupy hexagonal cavities in the anionic layers) toward one of the adjacent organic layers, giving rise to two nonequivalent organic layers at 120 K (compared to only one at room temperature). The structural transition at about 200 K is also observed in the electrical properties of 1-3 and in the magnetic properties of 1. The direct current (dc) conductivity shows metallic behavior in salts 1-3 with superconducting transitions at about 4.0 and 1.0 K in salts 3 and 1, respectively. Salt 4 shows a semiconductor behavior in the temperature range 300-50 K with an activation energy of 64 meV. The magnetic measurements confirm the presence of high spin S = 5/2 [Fe(C(2)O(4))(3)](3-) isolated monomers together with a Pauli paramagnetism, typical of metals, in compounds 1-3. The magnetic properties can be very well reproduced in the whole temperature range with a simple model of isolated S = 5/2 ions with a zero field splitting plus a temperature independent paramagnetism (Nα) with the following parameters: g = 1.965, |D| = 0.31 cm(-1), and Nα = 1.5 × 10(-3) emu mol(-1) for 1, g = 2.024, |D| = 0.65 cm(-1), and Nα = 1.4 × 10(-3) emu mol(-1) for 2, and g = 2.001, |D| = 0.52 cm(-1), and Nα = 1.5 × 10(-3) emu mol(-1) for 3.     

Synthesis,Crystal Structure and Magnetic Property of Ternary Neodymium Zirconium Sulfide,Nd_2ZrS_5

A new ternary neodymium zirconium sulfide Nd_2ZrS_5 was synthesized by high-temperature solid-state reaction and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the orthorhombic space group Pnma(No. 62) belonging to the Y_2HfS_5 structure-type with a = 11.461(4), b = 8.009(3), c = 7.315(3) ?, Z = 2 and V = 671.5(4) ?~3. Its structure features NdS_8 and ZrS_7 polyhedra-constructed a 3-D network. The data of magnetic susceptibility indicate its antiferromagnetic-like behavior without magnetic order down to 2 K.     

Spectroscopic and magnetic properties of a series of μ-cyano bridged bimetallic compounds of the type M(II)-NC-Fe(III) (M = Mn, Co, and Zn) using the building block [Fe(III)(CN)5imidazole]2-

In this contribution, we describe the preparation and single-crystal X-ray diffraction of a new building block for bimetallic solid state materials. X-ray diffraction data of these complexes indicate that (PPh(4))(2)[Fe(CN)(5)imidazole]·2H(2)O crystallizes in the triclinic space group P1 with a = 9.8108(15) ?, b = 11.1655(17) ?, c = 23.848(4) ?, α = 87.219(2)°, β = 85.573(2)°, γ = 70.729(2)°, and Z = 2, while its precursor Na(3)[Fe(CN)(5)(en)]·5H(2)O crystallizes in the monoclinic space group P2(1)/n with a = 8.3607(7) ?, b = 11.1624(9) ?, c = 17.4233(14) ?, β = 90.1293(9)°, and Z = 4. Spectroscopic and magnetic properties of a series of bimetallic materials were obtained by reaction of the complex [Fe(CN)(5)imidazole](2-) with hydrated transition metal ions [M(H(2)O)(n)](2+) (M = Mn, Co, Zn; n = 4 or 6). The new bimetallic materials obtained are [Co(H(2)O)(2)][Fe(CN)(5)imidazole]·2H(2)O (1), [Mn(CH(3)OH)(2)][Fe(CN)(5)imidazole] (2), Zn[Fe(CN)(5)imidazole]·H(2)O (3), and [Mn(bpy)][Fe(CN)(5)imidazole].H(2)O (4). All of the complexes crystallize in the orthorhombic system. X-ray single-crystal analysis of the compounds identified the Imma space group with a = 7.3558(10) ?, b = 14.627(2) ?, c = 14.909(2) ?, and Z = 4 for 1; the P2(1)2(1)2(1) space group with a = 7.385(5) ?, b = 13.767(9) ?, c = 14.895(10) ?, and Z = 4 for 2; the Pnma space group with a = 13.783(2) ?, b = 7.167(11) ?, c = 12.599(2) ?, and Z = 4 for 3; and the Pnma space group with a = 13.192(3) ?, b = 7.224(16) ?, c = 22.294(5) ?, and Z = 4 for 4. The structures of 1, 2, and 4 consist of two-dimensional network layers containing, as the repeating unit, a cyclic tetramer [M(2)Fe(2)(CN)(4)] (M = Mn, Co). H bonding between the layers in the structure of 1 results in a quasi-three-dimensional network. The structure of 3 was found to be three-dimensional, where all of the cyano ligands are involved in bridging between the metal centers. The bridging character of the cyano is confirmed spectroscopically. The magnetic properties have been investigated for all of the bimetallic systems. Compound 1 shows ferromagnetic behavior with an ordering temperature at 25 K, which is higher than the corresponding Prussian Blue analogue Co(x)[Fe(CN)(6)](y)?·zH(2)O. Compound 2 shows weak ferromagnetic behavior and an interlayer antiferromagnetic character, while 3, as expected, shows paramagnetic character due to the diamagnetic character of Zn(2+). Compound 4 shows antiferromagnetic behavior.     

High-pressure synthesis, crystal structure, and properties of BiPd2O4 with Pd2+ and Pd4+ ordering and PbPd2O4

BiPd(2)O(4) and PbPd(2)O(4) were synthesized at high pressure of 6 GPa and 1500 K. Crystal structures of BiPd(2)O(4) and PbPd(2)O(4) were studied with synchrotron X-ray powder diffraction. BiPd(2)O(4) is isostructural with PbPt(2)O(4) and crystallizes in a triclinic system (space group P1, a = 5.73632(4) ?, b = 6.02532(5) ?, c = 6.41100(5) ?, α = 114.371(1)°, β = 95.910(1)°, and γ = 111.540(1)° at 293 K). PbPd(2)O(4) is isostructural with LaPd(2)O(4) and BaAu(2)O(4) and crystallizes in a tetragonal system (space group I4(1)/a, a = 5.76232(1) ?, and c = 9.98347(2) ? at 293 K). BiPd(2)O(4) shows ordering of Pd(2+) and Pd(4+) ions, and it is the third example of compounds with ordered arrangements of Pd(2+) and Pd(4+) in addition to Ba(2)Hg(3)Pd(7)O(14) and KPd(2)O(3). In PbPd(2)O(4), the following charge distribution is realized Pb(4+)Pd(2+)(2)O(4). PbPd(2)O(4) shows a structural phase transition from I4(1)/a to I2/a at about 240 K keeping basically the same structural arrangements (space group I2/a, a = 5.77326(1) ?, b = 9.95633(2) ?, c = 5.73264(1) ?, β = 90.2185(2)° at 112 K). BiPd(2)O(4) is nonmagnetic while PbPd(2)O(4) exhibits a significant temperature-dependent paramagnetic moment of 0.46μ(B)/f.u. between 2 and 350 K. PbPd(2)O(4) shows metallic conductivity, and BiPd(2)O(4) is a semiconductor between 2 and 400 K.     

Importance of halogen···halogen contacts for the structural and magnetic properties of CuX2(pyrazine-N,N′-dioxide)(H2O)2 (X = Cl and Br)

The structural and magnetic properties of the newly crystallized CuX(2)(pyzO)(H(2)O)(2) (X = Cl, Br; pyzO = pyrazine-N,N'-dioxide) coordination polymers are reported. These isostructural compounds crystallize in the monoclinic space group C2/c with, at 150 K, a = 17.0515(7) ?, b = 5.5560(2) ?, c = 10.4254(5) ?, β = 115.400(2)°, and V = 892.21(7) ?(3) for X = Cl and a = 17.3457(8) ?, b = 5.6766(3) ?, c = 10.6979(5) ?, β = 115.593(2)°, and V = 950.01(8) ?(3) for X = Br. Their crystal structure is characterized by one-dimensional chains of Cu(2+) ions linked through bidentate pyzO ligands. These chains are joined together through OH···O hydrogen bonds between the water ligands and pyzO oxygen atoms and Cu-X···X-Cu contacts. Bulk magnetic susceptibility measurements at ambient pressure show a broad maximum at 7 (Cl) and 28 K (Br) that is indicative of short-range magnetic correlations. The dominant spin exchange is the Cu-X···X-Cu supersuperexchange because the magnetic orbital of the Cu(2+) ion is contained in the CuX(2)(H(2)O)(2) plane and the X···X contact distances are short. The magnetic data were fitted to a Heisenberg 1D uniform antiferromagnetic chain model with J(1D)/k(B) = -11.1(1) (Cl) and -45.9(1) K (Br). Magnetization saturates at fields of 16.1(3) (Cl) and 66.7(5) T (Br), from which J(1D) is determined to be -11.5(2) (Cl) and -46.4(5) K (Br). For the Br analog the pressure dependence of the magnetic susceptibility indicates a gradual increase in the magnitude of J(1D)/k(B) up to -51.2 K at 0.84 GPa, suggesting a shortening of the Br···Br contact distance under pressure. At higher pressure X-ray powder diffraction data indicates a structural phase transition at ～3.5 GPa. Muon-spin relaxation measurements indicate that CuCl(2)(pyzO)(H(2)O)(2) is magnetically ordered with T(N) = 1.06(1) K, while the signature for long-range magnetic order in CuBr(2)(pyzO)(H(2)O)(2) was much less definitive down to 0.26 K. The results for the CuX(2)(pyzO)(H(2)O)(2) complexes are compared to the related CuX(2)(pyrazine) materials.     

Chemistry in Molten Alkali Metal Polyselenophosphate Fluxes. Influence of Flux Composition on Dimensionality. Layers and Chains in APbPSe(4), A(4)Pb(PSe(4))(2) (A = Rb, Cs), and K(4)Eu(PSe(4))(2)

The reaction of Pb and Eu with a molten mixture of A(2)Se/P(2)Se(5)/Se produced the quaternary compounds APbPSe(4), A(4)Pb(PSe(4))(2) (A = Rb,Cs), and K(4)Eu(PSe(4))(2). The red crystals of APbPSe(4) are stable in air and water. The orange crystals of A(4)Pb(PSe(4))(2) and K(4)Eu(PSe(4))(2) disintegrate in water and over a long exposure to air. CsPbPSe(4) crystallizes in the orthorhombic space group Pnma (No. 62) with a = 18.607(4) ?, b = 7.096(4) ?, c = 6.612(4) ?, and Z = 4. Rb(4)Pb(PSe(4))(2) crystallizes in the orthorhombic space group Ibam (No. 72) with a = 19.134(9) ?, b = 9.369(3) ?, c = 10.488(3) ?, and Z = 4. The isomorphous K(4)Eu(PSe(4))(2) has a = 19.020(4) ?, b = 9.131(1) ?, c = 10.198(2) ?, and Z = 4. The APbPSe(4) have a layered structure with [PbPSe(4)](n)()(n)()(-) layers separated by A(+) ions. The coordination geometry around Pb is trigonal prismatic. The layers are composed of chains of edge sharing trigonal prisms running along the b-direction. [PSe(4)](3)(-) tetrahedra link these chains along the c-direction by sharing edges and corners with the trigonal prisms. A(4)M(PSe(4))(2) (M = Pb, Eu) has an one-dimensional structure in which [M(PSe(4))(2)](n)()(n)()(-) chains are separated by A(+) ions. The coordination geometry around M is a distorted dodecahedron. Two [PSe(4)](3)(-) ligands bridge two adjacent metal atoms, using three selenium atoms each, forming in this way a chain along the c-direction. The solid state optical absorption spectra of the compounds are reported. All compounds melt congruently in the 597-620 degrees C region.