The stereochemistry of Tutton's salts X2[M(H2O)6](YO4)2

Neutron structure determinations have been made of Tutton's salts, X₂[M(H₂O)₆] (YO₄)₂, where Y = Se, X = K⁺, M = Cu²⁺; Y = S, X = K⁺, M = Ni²⁺, Cu²⁺, Zn²⁺; X = Rb⁺, Cs⁺, M = Cu²⁺. This work has shown that there are extensive hydrogen networks with almost linear hydrogen bonds from [M(H₂O)₆]²⁺ to (YO₄)^2?. The (H … O) distance increases in the Cu²⁺ series for X = K⁺ to Cs⁺ but there is no difference for the potassium copper salts when Y = Se or S. Three different distorted [M(H₂O)₆]²⁺ octahedra were found in the series (orthorhombic, tetragonal with two long and four short, or four long and two short bonds). The interatomic distances from X⁺ to the neighboring O in a distorted XO₈⁺ dodecahedron increases with increased cation size, implying that the X⁺ polyhedron is maintaining its shape.     

The crystal and magnetic structures of Ca2YRuO6 and the electronic properties of the series M2+2X3+Ru5+O6 (M = Ca,Sr, Ba; X = La,Y)

Profile analysis of constant-wavelength powder neutron diffraction data has been used to refine the crystal structure of the ordered perovskite Ca₂YRuO₆. The material is monoclinic (space group $\text{P2}{}_1\text{n}$) with a disordered arrangement of calcium and yttrium on the A site and one of the B sites, such that the formula is best written as Ca_1.43Y_0.57[(Ca_0.57Y_0.43)Ru]O₆. Low-temperature neutron diffraction experiments showed that the material is a Type I antiferromagnet at 2.5 K with an ordered magnetic moment of 1.2(1)μ_B per Ru⁵⁺. It is suggested that the dominant factor in determining the electronic properties of the series M²⁺₂X³⁺Ru⁵⁺O₆ (M = Ca, Sr, Ba; X = La, Y) is the Ru-Ru separation distance.     

Influence of M2+ ions substitution on the structure of lanthanum hexaaluminates with magnetoplumbite structure

A series of compounds with the initial composition LaM_xAl₁₁O_18+x has been studied with x ranging from 0 to 1, and M = Mn, Co, Cu. They exhibit a more or less distorted and defective magnetoplumbite arrangement. Their effective compositions have been determined by X-ray structure refinement. The smaller the content of M²⁺, the higher the disorder in the crystal lattice, the worse the crystal growth, and more intense the diffuse scattering in (001) planes. The role of M²⁺ is compared to that of M²⁺ stabilizing γ-Al₂O₃ to give MAl₂O₄ spinels.     

Ln(GaM2+)O4 and Ln(AlMn2+)O4 compounds having a layer structure [Ln = Lu,Yb, Tm,Er, Ho,and Y,and M = Mg,Mn, Co,Cu, and Zn]

A series of new compounds Ln(GaM²⁺)O₄ and Ln(AlMn²⁺)O₄ having a layer structure were successfully prepared [Ln = Lu, Yb, Tm, Er, Ho, and Y, and M = Mg, Mn, Co, Cu, and Zn]. The synthesis conditions and the unit cell parameters for 23 compounds have been determined. These compounds are isostructural with YbFe₂O₄ (space group $\text{R}\text{3}\text{m, a = 3.455(1)}$ Å, and c = 25.109(2) Å).     

Ln(Fe3+M2+)O4 compounds with layer structure [Ln : Y,Er, Tm,Yb, and Lu, M : Mg,Mn, Co,Cu, and Zn]

A series of new compounds Ln(Fe³⁺M²⁺)O₄ [Ln : Y, Er, Tm, Yb, and Lu, M : Mg, Mn, Co, Cu, and Zn] were successfully synthesized and their lattice constants were determined. These compounds have the same crystal structure as YbFe₂O₄ and Fe³⁺ and M²⁺ are both surrounded by five oxygen ions forming a trigonal bipyramid. The synthetic conditions are presented. They are strongly dependent upon the constituent cations of the compound.     

Über Ordnungs-Unordnungsphänomene bei Sauerstoff perowskiten vom Typ A2+3B2+M5+2O9

Perovskites of the type A²⁺₃B²⁺M⁵⁺₂O₉, where A²⁺ = Ba, Sr; B²⁺ = Mn, Co, Ni, Zn; M⁵⁺ = Nb, Ta, show order-disorder phenomena. At lower temperatures a thermodynamically unstable disordered cubic perovskite is formed ($\text{1}\text{3}$ formula unit—$\text{AB}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{M}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3$—in the cell), which transforms irreversibly into a 1: 2 ordered high-temperature form with 3L structure (sequence (c)₃). For A²⁺ = Ba this lattice is hexagonal (space group $\text{P}\text{3}\text{m1}$; one formula unit in the cell); with A²⁺ = Sr a triclinic distortion is observed. For Ba₃CoNb₂O₉ a second transformation into a cubic disordered perovskite takes place at 1500°C. This transition is reversible and of the order-disorder type. The vibrational and diffuse reflectance spectra are discussed.     

Lithium-substituted cobalt oxide spinels LixM1−xCo2O4 (M = Co2+, Zn2+; 0 ≤ x ≤ 0.4)

Substitution of Li⁺ into Co₃O₄ and ZnCo₂O₄ gives rise to the solid solution series Li_xM_1?xCo₂O₄ (M = Co²⁺ or Zn²⁺) having the spinel structure upto x = 0.4. X-Ray diffraction intensities show that the spinel solid solutions are likely to have the following cation distributions: (Co²⁺)_t[Li⁺_xCo³⁺_2?3xCo⁴⁺_2x]₀O₄ and (Zn²⁺_1?xCo²⁺_x)_t[Li⁺_xCo³⁺_2?3xCo⁴⁺_2x]₀O₄. Electrical resistivity and Seebeck coefficient data indicate that the electron transport in these systems occurs by a small-polaron hopping mechanism.     

A series of borate-rich metalloborophosphates Na2[MB3P2O11(OH)]·0.67H2O (M=Mg, Mn, Fe, Co, Ni, Cu, Zn): Synthesis, structure and magnetic susceptibility

A series of metalloborophosphates Na₂[M^IIB₃P₂O₁₁(OH)]·0.67H₂O (M^II=Mg, Mn, Fe, Co, Ni, Cu, Zn) have been prepared hydrothermally and their structures have been solved by single-crystal diffraction techniques. They all crystallize in a hexagonal space group P6₃ and form a 3D microporous structure with 12-membered ring channels consisted of octahedral (M^IIO₆), tetrahedral (BO₄, PO₄) and triangular (BO₂(OH)) units, in which the counter Na⁺ cations and water molecules are located. The Na⁺ cations are mobile and can be exchanged by Li⁺ in a melt of LiNO₃. Their open frameworks are thermal stable up to about 500 °C. Completed solid solutions between two different transition metals can also be obtained. Magnetic properties of Na₂[M^IIB₃P₂O₁₁(OH)]·0.67H₂O (M^II=Mn, Co, Ni, Cu) have been investigated.     

Reduction of Eu to Eu in MAl2Si2O8 (M=Ca, Sr, Ba) in air condition

In general, the reduction of Eu³⁺ to Eu²⁺ in solids needs an annealing process in a reducing atmosphere. In this paper, it is of great interest and importance to find that the reduction of Eu³⁺ to Eu²⁺ can be realized in a series of alkaline-earth metal aluminum silicates MAl₂Si₂O₈ (M=Ca, Sr, Ba) just in air condition. The Eu²⁺-doped MAl₂Si₂O₈ (M=Ca, Sr, Ba) powder samples were prepared in air atmosphere by Pechini-type sol-gel process. It was found that the strong band emissions of 4f⁶5d¹-4f⁷ from Eu²⁺ were observed at 417, 404 and 373 nm in air-annealed CaAl₂Si₂O₈, SrAl₂Si₂O₈ and BaAl₂Si₂O₈, respectively, under ultraviolet excitation although the Eu³⁺ precursors were employed. In addition, under low-voltage electron beam excitation, Eu²⁺-doped MAl₂Si₂O₈ also shows strong blue or ultraviolet emission corresponding to 4f⁶5d¹-4f⁷ transition. The reduction mechanism from Eu³⁺ to Eu²⁺ in these compounds has been discussed in detail.     

Crystal structure of Eu-doped M3MgSi2O8 (M: Ba, Sr, Ca) compounds and their emission properties

Emission properties of Eu²⁺-doped M₃MgSi₂O₈ (M: Ba, Sr, Ca) are discussed in terms of the crystal structure. When Ba²⁺ ions account for over one third of M²⁺ ions, M₃MgSi₂O₈ crystallizes in glaserite-type trigonal structure, while Ba-free compounds crystallize in merwinite-type monoclinic structure. Under UV excitation, the Eu²⁺-doped glaserite-type compounds exhibit an intense blue emission assigned to 5d-4f electron transition at about 435 nm, regardless of the molar ratio of Ba²⁺, Sr²⁺ and Ca²⁺ ions. By contrast, the Eu²⁺-doped merwinite-type compounds show an emission color sensitive to the ratio. A detailed analysis of the emission spectra reveals that the emission chromaticity for the Eu²⁺-doped M₃MgSi₂O₈ is composed of two emission peaks reflecting two different sites accommodating M²⁺ ion.     

Metallic Re-Re bond formation in different MRe2O6 (MFe, Co, Ni) rutile-like polymorphs: The role of temperature in high-pressure synthesis

Different polymorphs of MRe₂O₆ (MFe, Co, Ni) with rutile-like structures were prepared using high-pressure high-temperature synthesis. For syntheses temperatures higher than ∼1573 K, tetragonal rutile-type structures (P4₂/mnm) with a statistical distribution of M- and Re-atoms on the metal position in the structure were observed for all three compounds, whereas rutile-like structures with orthorhombic or monoclinic symmetry, partially ordered M- and Re-ions on different sites and metallic Re-Re-bonds within Re₂O₁₀-pairs were found for CoRe₂O₆ and NiRe₂O₆ at a synthesis temperature of 1473 K. According to the XPS measurements, a mixture of Re⁺⁴/Re⁺⁶ and M²⁺/M³⁺ is present in both structural modifications of CoRe₂O₆ and NiRe₂O₆. The low-temperature forms contain more Re⁺⁴ and M³⁺ than the high-temperature forms. Tetragonal and monoclinic modifications of NiRe₂O₆ order with a ferromagnetic component at ∼24 K, whereas tetragonal and orthorhombic CoRe₂O₆ show two magnetic transitions: below ∼17.5 and 27 K for the tetragonal and below 18 and 67 K for the orthorhombic phase. Tetragonal FeRe₂O₆ is antiferromagnetic below 123 K.     

Phase stability and non-stoichiometry in M-phase solid solutions in the system LiO0.5-NbO2.5-TiO2

Phase relations at 1050°C have been determined for M-phase solid solutions in the LiO_0.5-NbO_2.5-TiO₂ ternary phase system by the quench method. Rietveld analysis has been used to help determine phase boundaries and to study structure composition relations. The M-phases have trigonal structures based on intergrowth of corundum-like layers, [Ti₂O₃]²⁺, with slabs of (N−1) layers of LiNbO₃-type parallel to (0001). Ideal compositions are defined along the pseudobinary join LiNbO₃-Li₄Ti₅O₁₂ by the homologous series formula Li_NNb_N−4Ti₅O_3N, N?4. Homologues with N?10 lie to the low-lithia side of the LiNbO₃-Li₄Ti₅O₁₂ join and show extended single-phase solid solution ranges separated by two-phase regions. The composition variations along the solid solutions are controlled by a major substitution mechanism, Li⁺+3Nb⁵⁺↔4Ti⁴⁺, coupled with a minor substitution 4Li⁺↔Ti⁴⁺+3□, where □=vacancy. The latter substitution results in increasing deviations from the stoichiometric compositions A_2N+1O_3N with increasing Ti substitution. The non-stoichiometry can be reduced by re-equilibration at lower temperatures. Expressions have been developed to describe the compositional changes along the solid solutions.     

Über Sauerstoffperowskite mit fünf- und vierwertigem Iridium Verbindungen vom Typ Ba2B3+Ir5+O6 und Ba3B3+Ir4,5+2O9

Perovskites with pentavalent iridium of type Ba₂B³⁺Ir⁵⁺O₆ are for B³⁺ = La, Nd, Sm, Gd, Dy, Y cubic and with B³⁺ = In hexagonal (6 L structure of BaTiO₃ type; sequence (hcc)₂). According to the intensity calculations of powder patterns for Ba₃SmIr₂O₉ and Ba₃YIr₂O₉ the new series Ba₃B³⁺Ir₂O₉ (B³⁺ = Sm, Eu, Gd, Dy, Ho, Yb, Sc, Y, In; mean oxidation state of iridium + 4.5) crystallize in a hexagonal 6 L structure of BaTiO₃ type (space group $\text{P6}{}_3\text{mmc}$; sequence (hcc)₂). The intensity-related R′ value is 8.6% for B³⁺ = Sm and 10.0% for Y. In the octahedral net the double groups of face-connected octahedra are occupied by the iridium atoms, which are dislocated from their ideal positions such that the IrIr distance has increased (2.72₀ Å (Sm) or 2.63₂ Å (Y)). The ir spectra are reported and discussed in connection with the corresponding factor group analysis.     

Synthesis and photoluminescence properties of the high-brightness Eu-doped M2Gd4(MoO4)7 (M=Li, Na) red phosphors

A series of red-emitting phosphors Eu³⁺-doped M₂Gd₄(MoO₄)₇ (M=Li, Na) have been successfully synthesized at 850 °C by solid state reaction. The excitation spectra of the two phosphors reveal two strong excitation bands at 396 nm and 466 nm, respectively, which match well with the two popular emissions from near-UV and blue light-emitting diode chips. The intensity of the emission from ⁵D₀ to ⁷F₂ of M₂(Gd_1−xEu_x)₄(MoO₄)₇ phosphors with the optimal compositions of x=0.85 for Li or x=0.70 for Na is about five times higher than that of Y₂O₃:Eu³⁺. The quantum efficiencies of the entitled phosphors excited under 396 nm and 466 nm are also investigated and compared with commercial phosphors Sr₂Si₅N₈:Eu²⁺ and Y₃A₅O₁₂:Ce³⁺. The experimental results indicate that the Eu³⁺-doped M₂Gd₄(MoO₄)₇ (M=Li, Na) phosphors are promising red-emitting phosphors pumped by near-UV and blue light.     

New compounds A 3+ Te6+M 33+ X 25+ O14 (A = Na, K; M = Ga, Al, Fe; X = P, As, V) with the Ca3Ga2Ge4O14 structure

Compounds A₃⁺Te⁶⁺M₃³⁺X₂⁵⁺O₁₄ (A = Na, K; M = Ga, Al, Fe; X = P, As, V) with the Ca₃Ga₂Ge₄O₁₄ structure (sp. gr. P321) were prepared by solid-phase synthesis at 600–850°C in air. The compounds melt incongruently or decompose in the solid state.     

Chemical composition and crystal structure of β-alumina type R+-gallate (R+ = K+, NH+4)

The crystal structures of β-alumina type K⁺-gallate (K⁺-β-gallate), Mg²⁺-doped K⁺-β-gallate, and NH⁺₄-β-gallate were refined by the single crystal X-ray diffraction method. The positive charges of excess K⁺ ions in K⁺-β-gallate were compensated by O^2? ions in the mO site which coordinated with interstitial Ga³⁺ ions. The charge compensation mechanism mentioned above was changed by doping with Mg²⁺ ions. The excess charges in Mg²⁺-doped K⁺-β-gallate were compensated by the replacement of Mg²⁺ ions for Ga³⁺ ions at the middle of spinel block. No defects were found in NH⁺₄-β-gallate for the charge compensation, which was completely consistent with the result of thermal analysis that indicated a stoichiometric composition of NH⁺₄-β-gallate.     

Influence of titanium oxide on the surface interactions of MO (M=Cu and Ni)/γ-Al2O3 catalysts

The influence of titanium oxide on the surface interactions of MO (M=Cu and Ni)/γ-Al₂O₃ catalysts has been studied by using XRD, LRS and XPS. For the catalysts with titania loadings lower than 0.56 mmol Ti⁴⁺/100 m² Al₂O₃ (i.e., the dispersion capacity), the dispersion of MO oxides on the surface of γ-Al₂O₃ support is significantly suppressed by the dispersed Ti⁴⁺ ions. The inhibiting effect is dependent on the properties of MO oxides. When titania loadings are considerably higher than the dispersion capacity, MO oxides exhibit a rather stronger interaction with the formed TiO₂ particles than the γ-Al₂O₃ support, and some of the dispersed M²⁺ ions might be accommodated by the vacant sites on TiO₂. Therefore, the catalysts can be considered as the compositions of MO/TiO₂ and MO/TiO₂/γ-Al₂O₃ (dispersed titania). TPR results show that either dispersed titania or formed TiO₂ particles can promote the reduction of copper oxide species, but the latter to a greater extent. Based on the consideration of the incorporation model, it is proposed that the surface structure of the support plays an important role in surface interactions.     

The lanthanoid(III) chloride cyclo-tetrasilicates M6Cl10[Si4O12] (M=Sm, Gd-Dy): Synthesis, structure and IR investigations

The chloride derivatized lanthanoid(III) cyclo-tetrasilicates of the composition M₆Cl₁₀[Si₄O₁₂] (M=Sm, Gd-Dy) crystallize monoclinically in space group C2/m (a=1062-1065, b=1036-1052, c=1163-1187 pm, β≈103°, Z=2). They are obtained by the reaction of the sesquioxides M₂O₃ (or the combination of Tb₄O₇ and Tb in 3:2-molar ratio for the terbium case), the corresponding trichlorides MCl₃, and SiO₂ (silica gel) in stoichiometric ratios with double the amount of MCl₃ as flux in evacuated silica tubes (7d at 850 °C) as transparent, pseudo-octagonal, pillar-shaped single crystals with the colour of the respective lanthanoid trication M³⁺. Their crystal structure can be considered as a layered arrangement in which cationic {[(M2)₅Cl₉]⁶⁺} layers are alternatingly piled with anionic ones of the kind {[(M1)Cl[Si₄O₁₂]]⁶⁻}. In the latter, the (M1)³⁺ cations show a slightly distorted hexagonal bipyramidal environment built up by two Cl⁻ and six O²⁻ anions (CN=8), whereas the (M2)³⁺ cations exhibit a coordination number of only seven (five Cl⁻ and two O²⁻ anions in the shape of a distorted pentagonal bipyramid). The cyclo-tetrasilicate units consist of four corner-linked [SiO₄]⁴⁻ tetrahedra in all-ecliptical conformation each, fused to eight-membered rings, which contain two almost linear (178°) and two bent (142°) Si-O-Si bridges. This particular cyclo-[Si₄O₁₂]⁸⁻ situation could be confirmed by theoretical and experimental infrared-spectroscopic investigations.     

On the characterization of BiMO2NO3 (M=Pb, Ca, Sr, Ba) materials related with the Sillén X1 structure

The compounds BiMO₂NO₃, with M=Pb, Ca, Sr, and Ba, were obtained as single-phase products from solid-state reactions in an atmosphere of nitrous gases. The oxide nitrates with Pb and Ca crystallize in the tetragonal space group I4/mmm with two formula units per unit cell; the oxide nitrates with Sr and Ba crystallize in the orthorhombic space group Cmmm with four formula units per unit cell. Lattice parameters at room temperature are a=397.199(4), c=1482.57(2) pm for M=Pb; a=396.337(5), c=1412.83(3) pm for M=Ca; a=1448.76(3), b=567.62(1), c=582.40(1) pm for M=Sr and a=1536.50(8), b=571.67(3), c=597.55(3) pm for M=Ba. The structures, which were refined by powder X-ray diffraction, consist of alternating [BiMO₂]⁺ and [NO₃]⁻ layers stacked along the direction of the long axis. IR and thermogravimetric data are also given. The various M²⁺ cations in BiMO₂NO₃ are compatible with each other; therefore and because of their layer-type structure, these compounds are interesting precursors for oxide materials, e.g., the HTSC compounds (Bi,Pb)₂Sr₂Ca_n−1Cu_nO_x.     

ESR spectra and magnetic constants of α-Al2O3:Co2+,H+ and α-Al2O3 :Co2+,X+

New anisotropic ESR spectra of Co²⁺ doped sapphire, different from hitherto known, are reported. The new spectra which are observed, beside the well-known spectra of α-Al₂O₃:Co²⁺, are shown to form two sets, each one consisting of six spectra (1–6) and (7–12). The spectra of both sets are proven to be interrelated by B_3a symmetry. g and A tensors for each set will be given. Evidence is given that the two sets are to be assigned to the defects α-Al₂O₃:Co²⁺,H⁺ and α-Al₂O₃:Co²⁺,X⁺. The former is concluded to consists of a Co²⁺ ion at the substitutional site (c) and a proton located in a potential minimum along a straight line between O^2- ions situated in O²⁺ triangles above and below the CO²⁺ ion. The potential function for the proton has been calculated by quantum-chemical calculations to clucidate the geometrical structure of the paramagnetic center. The α-Al₂O₃:Co²⁺,X⁺ could not be fully analyzed but some evidence is presented, that X⁺ might be alkali ions.