Crystal structure and magnetic properties of Sr4Mn2NiO9

The crystal structure of Sr₄Mn₂NiO₉ has been refined on single crystal. This phase belongs to the series A_1+x(A^′_xB_1–x)O₃ (x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr₄Mn₂NiO₉ is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni²⁺ ions in the spin state configuration S=0.     

On the temperature dependence of proton magnetic resonance lineshapes of tunnelling ammonium in NH4ClO4 and NH4PF6

The proton magnetic resonance lineshapes of NH₄ClO₄ and NH₄PF₆ at liquid helium temperature are narrower than those usually expected for rapidly tunnelling ammonium ions. The narrowing is temperature-dependent, suggesting a kinetic process that involves a modulation of the tunnelling states. A possible “exchange-narrowing” mechanism involving fluctuating molecular torsional states brought about by external lattice perturbations is considered, and is seen to lead to a satisfactory simulation of the observed low-temperature lineshapes. Activation energies of 0.9 ± 0.1 K and 1.7 ± 0.5 K governing the exchange process are derived for the cases of NH₄ClO₄ and NH₄PF₆, respectively.     

Hydrothermal syntheses, structures, and magnetic properties of (NH4)2NaVF6 and Na3VF6

The single crystals of perovskite fluorides (NH₄)₂NaVF₆ and Na₃VF₆ were synthesized under mild hydrothermal conditions. The structures of the compounds were determined by means of single-crystal and powder X-ray diffraction analyses, respectively. (NH₄)₂NaVF₆ has a cubic elpasolite-type structure and crystallizes in the space group with lattice constant a=8.495(0) Å. Rietveld refinement indicates that Na₃VF₆ has a monoclinic structure and is in space group P2₁/n. The compounds were characterized by scanning electron microscopy, thermogravimetric and differential thermal analysis, and variable temperature magnetic susceptibility. With the temperature decreasing, the magnetic studies of the compounds showed the magnetic ordering was related to the crystallographic features and isolated magnetic units.     

Crystal structure of [Cu(NH3)4](ReO4)2

At T = 150 K, the crystal structure of [Cu(NH₃)₄](ReO₄)₂ is studied: a = 6.5167(3) ?, b = 6.7790(3) ?, c = 7.4627(3) ?, α = 67.336(1)°, β = 80.004(1)°, γ = 70.687(1)°, V = 286.70(2) ?³, P-1 space group, Z = 1, d _x = 3.661 g/cm³. We analyze the packing of ions using the translation sublattice isolation technique.     

Crystal structure, thermal and magnetic properties of Cr2V4O13

Cr₂V₄O₁₃, a tetravanadate of Cr³⁺ has been prepared by repeated heating of stoichiometric amounts of Cr₂O₃ and V₂O₅ and its crystal structure is refined by Rietveld refinement of the powder XRD data. This compound crystallizes in a monoclinic lattice with unit cell parameters: a=8.2651(3), b=9.2997(3), c=14.5215(5) Å, β=102.618(3)°, V=1089.21(6) Å³ and Z=4 (Space group: P2₁/c). The U shaped (V₄O₁₃)⁶⁻ formed by corner connected VO₄ tetrahedra links the Cr₂O₁₀ (dimers of two edge shared CrO₆ octahedra) forming a three dimensional network structure of Cr₂V₄O₁₃. This compound is stable up to 635 °C and peritectically decomposes to orthorhombic CrVO₄ and V₂O₅ above this temperature. A possible long range antiferromagnetic ordering below 10 K is suggested from the squid magnetometry and electron paramagnetic resonance (epr) spectroscopic studies of Cr₂V₄O₁₃.     

Crystal structure and vibrational properties of new luminescent hosts K3YF6 and K3GdF6

The luminescence hosts K₃YF₆ and K₃GdF₆ were obtained in a single-crystal form. Their crystal structure was determined from single-crystal X-ray diffraction data. Both crystals adopt monoclinic system with space group P2₁/n, Z=2. Lattice parameters for K₃YF₆ are refined to the following values , , , β=90.65(3) and for K₃GdF₆, , , β=90.80(3). The vibrational analysis, IR and Raman spectroscopy at room temperature, was applied to these compounds in order to study the site symmetry of Y³⁺ and Gd³⁺ ions.     

Crystal growth and structure of a new manganese vanado-antimonate MnVSbO6

Single crystals of a new compound of formula MnVSbO₆ were grown by slow cooling from a V₂O₅-B₂O3₃ flux at 900°C. The compound crystallizes in the orthorhombic space group Pbcn (No. 60), with cell parameters (in the Pcnb setting) a=4.6604(3) Å, b=4.9603(3) Å, c=17.1433(9)Å, Z=4. The crystal structure was solved from 1188 independent reflections to R_w=3.20% and goodness-of-fit 1.5 for 44 refined parameters. The structure can be described as a superstructure of the α-PbO₂ type with a cation ordering similar to that found in Fe₂WO₆. Cations occupy octahedral sites in the PbO₂-like layers. Zigzag chains of edge-sharing MnO₆ octahedra alternate with mixed Sb/V chains following a -Mn-Sb/V-Sb/V- sequence. The magnetic susceptibility of MnVSbO₆ follows the Curie-Weiss law down to ca. 15 K, where it orders antiferromagnetically. The bond lengths and Curie constant are consistent with the expected charge distribution Mn²⁺V⁵⁺Sb⁵⁺O₆.     

Crystal structure of [Pd(NH3)4][Rh(NH3)(NO2)5]

An XRD analysis is used to study the single crystal of [Pd(NH₃)₄][Rh(NH₃)(NO₂)₅] double complex salt at T = 150(2) K. Crystallographic characteristics are as follows: a = 7.6458(5) ?, b = 9.8813(6) ?, c = 9.5788(7) ?, β = 109.469(2)°, V = 682.30(8) ?³, P2₁/m space group, Z = 2, d _x = 2.553 g/cm³. The geometry of the complex [Rh(NH₃)(NO₂)₅]²⁻ anion is described for the first time: Rh-N(NO₂) distances are 2.020(4)–2.060(3) ?, Rh-N(NH₃) 2.074(4) ?, N(NO₂)-Rh-N(NH₃) trans-angle is 178.8(2)°.     

Orientation disorder in ammonium elpasolites: Crystal structures of (NH4)3AlF6, (NH4)3TiOF5 and (NH4)3FeF6

Crystal structures of the known (NH₄)₃AlF₆(I) and (NH₄)₃FeF₆(III) and new (NH₄)₃TiOF₅(II) elpasolites were refined by localizing anions (F⁻, O²⁻) in four acceptable positions of the cubic system Fm3m (Z=4) with a=8.9401(3), 9.1104(3), 9.110(1) Å, respectively. According to the refinement data and a rather large entropy change due to fluorine (oxygen) octahedra disordering in the above compounds and in (NH₄)₃WO₃F₃(IV) elpasolite, it was found that fluorine (oxygen) atoms are randomly distributed in two ways, in general 192l position or in mixed 24e + 96j one. Statistics in fluorine (oxygen) distribution is, probably, the result of domain structure of the crystals.     

Crystal and molecular structure of (NH4)2[UO2(NO3)4] and [(NH4)(18C6)]2[UO2(NO3)4]

Single crystals of diammonium tetranitratouranylate (NH₄)₂[UO₂(NO₃)₄] (I) and a new diammonium tetranitratouranylate complex with 18-crown-6 [(NH₄)(18C6)]₂[UO₂(NO₃)₄] (II) have been synthesized by the reaction of diaquadinitratouranyl tetrahydrate with ammonium nitrate in a nitric acid solution and the reaction of the same reagents with 18C6 in an ethanol solution, respectively. The X-ray diffraction analysis of compounds I and II has been performed. Crystals of compounds I and II are monoclinic, Z = 2, space group P2₁/n, a = 6.4075(5) ?, b = 7.7851(7) ?, c = 12.4461(12) ?, β = 101.239(1)°, V = 608. 94(9) ?³ for compound I and a = 10.542(9) ?, b = 8.590(8) ?, c = 22.5019(19) ?, β = 101.632(1)°, V = 2058.3(3) ?³ for compound II. The [UO₂(NO₃)₄]²⁻ complex anion in compounds I and II contains two monodentate and two bidentate cyclic nitrato groups, and the coordination number of uranyl is 6. The 18C6 molecule in the structure of compound II has the classic crown conformation and combined with the ammonium ion by three hydrogen bonds. Compounds I and II formed by electrostatic attraction forces between counterions are stabilized by (NH₄⁺)NH...O(NO₃⁻) interionic hydrogen bonds.     

Hindered rotation of the ammonium ion in (NH4)2SiF6 and (NH4)2SnCl6

The heat capacity due to the hindered rotation of the ammonium ion has been computed for (NH₄)₂SiF₆ and (NH₄)₂SnCl₆ and compared to that derived from the observed heat capacity. The torsional frequencies for (NH₄)₂SiF₆ and (NH₄)₂SnCl₆ are 226 cm^?1 and 190 cm^?1 respectively, and the barriers to rotation are 3210 calories/mole and 1470 calories/mole, respectively.     

Crystal structure and magnetic properties of Ba2Ni3F10

Ba₂Ni₃F₁₀ is monoclinic (space group $\text{C2}\text{m}$), a = 18.542(7) Å, b = 5.958(2) Å, c = 7.821(3) Å, β = 111°92(10). Ba₂Co₃F₁₀ and Ba₂Zn₃F₁₀ are isostructural. The structure has been refined from 995 reflections by full-matrix least-squares refinement to a weighted R value of 0.048 (unweighted R, 0.047). The three-dimensional network can be described either by complex chains connected to each other by octahedra sharing corners or with an 18L dense-packing sequence. The basic unit (Ni₃F₁₀)^4? is discussed and compared to the different unit existing in Cs₄Mg₃F₁₀. Antiferromagnetic properties of Ba₂Ni₃F₁₀ (T_N = 50 K are described.     

Crystal structure, magnetic properties and conductivity of CuSbTeO3Cl2

CuSbTeO₃Cl₂ has been isolated during an investigation of the system Cu₂O:TeCl₄:Sb₂O₃:TeO₂. The new compound is light yellow and crystallises in the monoclinic system, space group C2/m, a=20.333(5) Å, b=4.0667(9) Å, c=10.778(2) Å, Z=6. The structure is layered and is built up from corner and edge sharing [(Sb,Te)O₄E] trigonal bipyramids that have the lone pair (E) directed towards one of the equatorial positions, those groups build up [(Sb,Te)₂O₃E₂⁺]_n layers. The copper and the chlorine atoms are located in between those layers. There are two different Cu positions. The [Cu1Cl₄] group is a slightly distorted tetrahedron and these tetrahedra make up chains by corner sharing. The electron density for the half occupied Cu2 atom is spread out in the structure like a worm that run along the b-axis in the space in between two chains of [Cu1Cl₄] tetrahedrons. Analysis of the diamagnetic response in magnetic susceptibility measurements is in perfect agreement with a Cu⁺ valence. Conductivity measurements in the temperature range 355–590 K gives an activation energy of 0.55 eV. The delocalised Cu2 position in the structure suggests that the compound is a Cu⁺ ionic conductor along the b-axis.     

Phase relations of NH4ClO4 and NH4BF4 to high pressures

The high pressure phase diagrams of NH₄ClO₄ and NH₄BF₄ were studied by means of differential thermal analysis and volumetric techniques. The high temperature portions of these diagrams are intermediate between those of the corresponding potassium and rubidium salts, but at low temperatures the onset of hydrogen bonding causes the appearance of phases which are unique to the ammonium compounds.     

Deuteron NMR spin–lattice relaxation of NH3D ions in partially deuterated (NH4)2SnCl6 and NH4ClO4

Deuteron spin–lattice relaxation is studied in 5% and 100% deuterated ammonium hexachlorostannate and perchlorate. The relaxation rate is observed to be independent of deuteration down to temperatures slightly lower than that of the maximum. At lower temperatures the rate of the 5% deuterated sample exceeds that of the 100% deuterated sample by four and two orders of magnitude in ammonium hexachlorostannate and perchlorate, respectively. The angular dependence of the deuteron relaxation rate in 5% deuterated ammonium hexachlorostannate at 6 K is explained in terms of existing models on quadrupolar relaxation. In 5% ammonium perchlorate one hydrogen equilibrium position, which lies on the preferred axis for 120° rotations, has a larger probability to be occupied by the deuteron of NH₃D⁺ ions. The deuterons at the other positions are still performing rotational jumps about the preferred C₃ axis and also about the other threefold axes, although at a slower rate. Such observations require a reconsideration of the relaxation process. A somewhat more general expression is derived for the relaxation rate, which agrees with the experimentally observed angular dependence for 5% deuterated ammonium perchlorate at 60 K. At lower temperatures the quadrupole coupling of the deuterons at the preferred axis may become practically time-independent. Then a significant contribution to the relaxation rate can be provided by the deuteron–proton magnetic dipolar interaction, which is still fluctuating fast via the rotation of the three protons about the axis through the stationary deuteron.     

Synthesis, structure and magnetic properties of Na6Co2O6

Na₆Co₂O₆ was synthesized via the azide/nitrate route by reaction between NaN₃, NaNO₃ and Co₃O₄. Stoichiometric mixtures of the starting materials were heated in a special regime up to 500°C and annealed at this temperature for 50 h in silver crucibles. Single crystals have been grown by subsequent annealing of the reaction product at 500°C for 500 h in silver crucibles, which were sealed in glass ampoules under dried Ar. According to the X-ray analysis of the crystal structure (, Z=1, a=5.7345(3), b=5.8903(3), c=6.3503(3) Å, α=64.538(2), β=89.279(2), γ=85.233(2)°, 1006 independent reflections, R₁=8.34% (all data)), cobalt is tetrahedrally coordinated by oxygen. Each two CoO₄ tetrahedra are linked through a common edge forming Co₂O₆^6- anions. Cobalt ions within the dimers, being in a high spin state (S=2), are ferromagnetically coupled (J=17 cm^-1). An intercluster spin exchange (zJ′=−4.8 cm^-1) plays a significant role below 150 K and leads to an antiferromagnetically ordered state below 30 K. Heat capacity exhibits a λ-type anomaly at this temperature and yields a value of 19.5 J/mol K for the transition entropy, which is in good agreement with the theoretical value calculated for the ordering of the ferromagnetic-coupled dimers. In order to construct a model for the spin interactions in Na₆Co₂O₆, the magnetic properties of Na₅CoO₄ have been measured. This compound features isolated CoO₄ tetrahedra and shows a Curie-Weiss behavior (μ=5.14 μ_B, Θ=−20 K) down to 15 K. An antiferromagmetic ordering is observed in this compound below 10 K.     

Crystal structure and phonon properties of noncentrosymmetric LiNaB4O7

A new borate, LiNaB₄O₇, has been synthesized and characterized by single-crystal X-ray structure determination. The material crystallizes in the orthorhombic system, noncentrosymmetric space group Fdd2, with unit cell dimensions a=13.325(2), b=14.099(2), c=10.243(2) Å, Z=16, and V=1924.3(7) Å³. Like Li₂B₄O₇, the structure is built of two symmetrically independent, interpenetrating polyanionic frameworks built from condensation of the B₄O₉ fundamental building block, which is comprised of two distorted BO₄ tetrahedra and two BO₃ triangles. The interpenetrating frameworks produce distinct tunnels that are selectively occupied by the Li and Na atoms. Large single crystals exhibiting an optical absorption edge with λ<180 nm have been grown via the top-seeded-solution-growth method. The SHG signal (0.15× potassium dihydrogen phosphate (KDP)) is consistent with the calculated components of the SHG tensor and the approximate centrosymmetric disposition of the independent and interpenetrating frameworks. A complete analysis of polarized IR and Raman spectra confirms a close relationship between the title compound and Li₂B₄O₇.     

DSC investigation of the thermal behaviour of (NH4)2SO4, NH4HSO4 and NH4NH2SO3

Gaseous products evolved from (NH₄)₂SO₄, NH₄HSO₄ and NH₄NH₂SO₃ during successive heating and cooling cycles were flushed with inert gas into analyzer Dräger tubes hooked tightly to the terminal port of the DSC cell base. This simple procedure allowed the starting temperature of the decomposition to be determined and the amount of the individual gases in the mixture to be identified and even estimated. NH₄NH₂SO₃ at 523 K in humid air produced HNH₂SO₃ initially and, on further cycling, (NH₄)₂SO₄ and NH₄HSO₄ also appeared. The ΔH_f values for NH₄HSO₄ were (kJ mole^?1): in an airtight sample holder 12.67, in a dry argon atmosphere 11.93, and in a static air atmosphere 10.92. Endothermic peaks for (NH₄)₂SO₄ and 498 and 411 K represented the incongruent melting point and the polymorphic transition of (NH₄)₂SO₄·NH₄HSO₄. After the first heating in air to 530 K, (NH₄)₂SO₄ and NH₄HSO₄ exhibited closely similar cyclic DSC curves. The endothermic peaks at about 393–420 K may be assigned to different combinations of (NH₄)₂SO₄ and NH₄HSO₄.     

Crystal structure and magnetic properties of Na2Ni(HPO3)2

Na₂Ni(HPO₃)₂, obtained as light yellow-green crystals under mild hydrothermal conditions, crystallizes in the orthorhombic Pnma space-group with lattice parameters: a=11.9886(3), b=5.3671(2), c=9.0764(3) Å, V=584.01 Å³, Z=4. The structure consists of zig-zag chains of NiO₆ octahedra bridged by two HPO₃²⁻ and the chains are further connected through HPO₃²⁻ to four nearest chains to form a three dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The Na cations reside in the irregular Na(1)O₅, Na-O of 2.276-2.745 Å, and Na(2)O₉, Na-O of 2.342-2.376 Å, environments. The presence of the phosphite monoanion has been further confirmed by IR spectroscopy. Due to the 3D framework of Ni connected by O-P-O bridges, the magnetic susceptibility behaves as a paramagnet above 100 K (C=1.49(2) emu K mol⁻¹, μ_eff=3.45 μ_B, Θ=−39(2) K) and below 6 K, it orders antiferromagnetically as confirmed the sharp drop and the non-Brillouin behavior of the isothermal magnetization at 2 K.     

Crystal structure and magnetic properties of the UFe7Al5 uranium-iron aluminide

The ternary compound UFe₇Al₅ was synthesized by arc melting, followed by annealing at 850°C. The crystal structure was determined by single-crystal X-ray diffraction and refined to a residual value of R=0.039 (S=1.030), with lattice parameters a=8.581(2) Å and c=4.946(1) Å. This compound is a new extreme composition in the family of intermetallics with general formula UFe_xAl_12−x crystallizing in the tetragonal ThMn₁₂-type structure, space group I4/mmm. In contrast to UFe_xAl_12−x within the composition range 4?x?6, in UFe₇Al₅ the additional iron atom is found in the 8i equipositions. Magnetization measurements versus temperature show two magnetic transitions at 363 and 275 K, respectively, with a ferromagnetic behavior below the highest temperature transition. ⁵⁷Fe Mössbauer data indicate that the high-temperature transition is related to the ordering of the iron atoms. The dependence of the isomer shifts and magnetic hyperfine fields on the crystallographic site and on the number of the iron nearest neighbors is similar to that observed in the other UFe_xAl_12−x and rare-earth analogues. The magnetic hyperfine field values of iron atoms on 8i sites is larger than in the other sites, in agreement with previous data obtained for other ThMn₁₂-type compounds.