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).     

Survey of the phase formation in the Yb2O3Ga2O3MO and Yb2O3Cr2O3MO systems in air at high temperatures (M: Co,Ni, Cu,and Zn)

The phase relations in the Yb₂O₃Ga₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃CuO system at 1000°C and the Yb₂O₃Ga₂O₃ZnO system at 1350 and 1200°C, the Yb₂O₃Cr₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃CuO system at 1000°C, and the Yb₂O₃Cr₂O₃ZnO system at 1300 and 1200°C were determined in air by means of a classical quenching method. YbGaCoO₄ (a = 3.4165(1) and c = 25.081(2) Å), YbGaCuO₄ (a = 3.4601(4) and c = 24.172(6) Å), and YbGaZnO₄ (a = 3.4153(5) and c = 25.093(7) Å), which are isostructural with YbFe₂O₄ (space group: $\text{R}\text{3}\text{m, a = 3.455(1)}$ and c = 25.109(2) Å, were obtained as stable phases. In the Yb₂O₃Ga₂O₃NiO system and the Yb₂O₃Cr₂O₃MO system (M: Co, Ni, Cu, and Zn), no ternary stable phases existed.     

Dimorphism in triple orthovanadates MIILaTh (VO4)3 (MII = Sr or Pb)

Triple orthovanadates, SrLaTh(VO₄)₃ and PbLaTh(VO₄)₃ are found to be dimorphic, the crystalline form depending upon the firing temperature. The low-temperature form has zircon structure and the corresponding high-temperature form exhibits its well-known monoclinic modification. The X-ray powder diffractograms and infrared spectra are recorded and discussed in comparison with those of structurally related compounds.     

Hyperfine interactions in MgF2:Fe2+ and ZnF2:Fe2+ by Mössbauer spectroscopy

Measurement of the magnetic hyperfine interaction in paramagnetic Fe²⁺ in ZnF₂ and MgF₂ by Mössbauer spectroscopy is reported. The results, ?275 ± 3 kOe and ?270 ± 3 kOe for ZnF₂:Fe²⁺ and MgF₂:Fe²⁺ respectively are compared with a previous analysis of hyperfine interactions in the rutile fluorides.     

Magnetic superexchange involving tetrahedral anions: One-dimensional antiferromagnetic interactions via sulfate anions in M(2,9-di-CH3-1,10-phenanthroline)SO4 (M = Mn,Fe, Co,Ni, Cu)

The magnetic susceptibilities of powder samples of the polymeric compounds M(dmp)SO₄ (M = Mn, Fe, Co, Ni, Cu; dmp = 2,9-di-CH₃-1,10-phenanthroline) have now been studied at temperatures between 1.5 and 305 K. There is clear evidence of one-dimensional, antiferromagnetic interactions in the Mn, Fe, Co, and Ni compounds: from $\text{T ? 300}\text{to}\text{1.7}\text{K}$, the magnetic moment decreases steadily from a value that is approximately the spin-only moment of the high-spin configuration to a value that is ～20% of the spin-only moment, and the susceptibility-vs-temperature curve contains a broad maximum atT ≤ 30 K. Cu(dmp)SO₄, however, exhibits almost perfect Curie-Weiss paramagnetism. These results when combined with the results of various spectroscopic studies lead to proposed molecular structures (chainlike polymers of cis-MN₂O₄ chromophores and bridging-chelating sulfates) and estimated energies of intrachain antiferromagnetic exchange ($\text{?0.5}\text{K}\text{≥}\text{J}\text{k}{}_{\mathrm{<mtext>B</mtext>}}\text{≥ ?10}\text{K}$).     

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.     

Spinel, YbFe2O4, and Yb2Fe3O7 types of structures for compounds in the In2O3 and Sc2O3---A2O3---BO systems [A: Fe, Ga, or Al; B: Mg, Mn, Fe, Ni, Cu, or Zn] at temperatures over 1000°C

In the Sc₂O₃---Ga₂O₃---CuO, Sc₂O₃---Ga₂O₃---ZnO, and Sc₂O₃---Al₂O₃---CuO systems, ScGaCuO₄, ScGaZnO₄, and ScAlCuO₄ with the YbFe₂O₄-type structure and Sc₂Ga₂CuO₇ with the Yb₂Fe₃O₇-type structure were obtained. In the In₂O₃---A₂O₃---BO systems (A: Fe, Ga, or Al; B: Mg, Mn, Fe, Ni, or Zn), InGaFeO₄, InGaNiO₄, and InFe³⁺MgO₄ with the spinel structure, InGaZnO₄, InGaMgO₄, and InAlCuO₄ with the YbFe₂O₄-type structure, and In₂Ga₂MnO₇ and In₂Ga₂ZnO₇ with the Yb₂Fe₃O₇-type structure were obtained. InGaMnO₄ and InFe₂O₄ had both the YbFe₂O₄-type and spinel-type structures. The revised classification for the crystal structures of AB₂O₄ compounds is presented, based upon the coordination numbers of constituent A and B cations.     

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.     

The phase relations in the In2O3A2O3BO systems at elevated temperatures [A: Fe or Ga, B: Cu or Co]

The phase relations in the In₂O₃Fe₂O₃CuO system at 1000°C, the In₂O₃Ga₂O₃CuO system at 1000°C, the In₂O₃Fe₂O₃CoO system at 1300°C, and the In₂O₃Ga₂O₃CoO system at 1300°C were determined by means of a classical quenching method. InFeCuO₄ (a = 3.3743(4) Å, c = 24.841(5) Å), InGaCuO₄ (a = 3.3497(2) Å, c = 24.822(3) Å), and InGaCoO₄ (a = 3.3091(2) Å, c = 25.859(4) Å) having the YbFe₂O₄ crystal structure, In₂Fe₂CuO₇ (a = 3.3515(2) Å, c = 28.871(3) Å), In₂Ga₂CuO₇ (a = 3.3319(1) Å, c = 28.697(2) Å), and In₂FeGaCuO₇ (a = 3.3421(2) Å, c = 28.817(3) Å) having the Yb₂Fe₃O₇ crystal structure, and In₃Fe₃CuO₁₀ (a = 3.3432(3) Å, c = 61.806(6) Å) having the Yb₃Fe₄O₁₀ crystal structure were found as the stable ternary phases. There is a continuous series of solid solutions between InFeCoO₄ and Fe₂CoO₄ which have the spinel structure at 1300°C. The crystal chemical roles of Fe³⁺ and Ga³⁺ in the present ternary systems were qualitatively compared.     

Cyclic transport of Fe3+ As H[FeCl4] and H[FeBr4] through a dibutyl ether-benzene membrane

Cyclic transport of Fe³⁺ as H[FeX₄], where X is Cl or Br, across solvent-type liquid membranes has been demonstrated. H[FeCl₄] was transported from HCl into HBr across a dibutyl ether—benzene mixture. In HBr the transported species reacted to H[FeBr₄], which moved out to the HCl side against the concentration gradient of Fe³⁺. On the HCl side it was reconverted into H[FeCl₄]. This continued till equilibrium was achieved. Likewise, Fe³⁺, present as H[FeBr₄] in HBr, migrated from HBr into HCl and then back to HBr across the same membrane.     

The stereochemistry of transition metal cyclooctatetraenyl complexes: di-h3,h3′ cyclooctatetraenedinickel,a sandwich compound with two enveloped nickel atoms

The crystal structure of dicyclooctatetraenedinickel, [(COT)Ni]₂, has been determined from three-dimensional, single crystal X-ray data collected by counter methods. Crystals of [(COT)Ni]₂, belong to the monoclinic system with a = 8.2906(3), b = 11.4185(5), c = 7.2340(3) Å, β = 115.978(2)°, d(calc) = 1.757 gcm^?3, Z = 2. The space group is C²_2h-P2₁/a. The structure was refined anisotropically (hydrogen atoms and a nickel atom fragment isotropically) by fullmatrix least-squares techniques. Final values of R and R_w were 0.046 and 0.079, respectively, for the 1055 unique, absorption and extinction corrected reflections with I > 2σ(I). Crystals of [(COT)Ni]₂ consists of discrete molecules with crystallographic C_i ($\text{1}$) symmetry. The compound possesses a sandwich structure with both metal atoms between the COT rings. Each nickel atom forms π-allyl type bonds to three carbon atoms of each COT ring. The nickel atoms are disordered over three sites. The effect of this disorder on the interpretation of the derived structural parameters is discussed.     

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.     

Structural investigation of K+ and Tl+ β-aluminas

Structures of K⁺ and Tl⁺ aluminas were investigated by single-crystal X-ray diffraction. In the final refinements, corresponding to R values of 0.034 and 0.058, respectively, the distribution of conducting ions was found to be similar to that of Na β-alumina. In K⁺ β-alumina clear evidence of additional electronic density in the spinel-like blocks is obtained and is interpreted as due to a Frenkel defect.     

Systematics of the librational modes of water in the IR spectra of MSO4 · H2O (M = Mn,Co, Ni,Zn)

In the isomorphous hydrates MSO₄ · H₂O (M = Mn, Co, Ni, Zn), where M-O_W distance is the only variable, the frequencies of the wagging, rocking and bending modes of water and of metal-oxygen stretching have been shown to correlate smoothly with the distance r(M-O_W). Quantitative relations have been found for ν_W and ν(M-O_W) which vary linearly, while ν_R and ν^C₂ vary non-linearly with r(M-O_W).     

Jahn-Teller distortion and electronic structure of the O− center in CaF2: an MS Xα study

The O^? center in CaF₂ is investigated by performing multiple scattering Xα calculations on the (OF₆)^7? cluster. In agreement with experiment, a strong Jahn-Teller distortion of tetragonal symmetry is predicted. Finally the ground state electronic structure of the cluster is discussed.     

Microdomains in the reduction of Ca2LaFe3O8+z

The reduction of Ca₂LaFe₃O_8+z in the electron microscope shows this solid to decompose into Ca₂ Fe₂O₅ and LaFeO₃, two perovskite-related line-phases which, under these conditions, appear to be thermodynamically more stable. In kinetic terms, the decomposition appears to be of the nucleation and growth type. Microdomains appear to be an essential characteristic of the system since they are present in both the reactants and the reaction products. Up to nine sets of structurally-related microdomains can simultaneously be present within the same crystal. This leads to quite elaborate electron diffraction patterns which can be interpreted in terms of perovskite superstructures. These results are discussed in terms of diffusion data on perovskite-like ferrites.     

Aqueous polymerization of acrylonitrile initiated by the Mn3+/citric acid redox system

Kinetics of polymerization of acrylonitrile initiated by the redox system Mn³⁺/citric acid were investigated in aqueous sulphuric acid in the range of 20–25°; initial rates of polymerization and Mn³⁺ disappearance etc. were measured. The effects of certain water miscible organic solvents and certain cationic and anionic detergents on the rate of polymerization have been examined. A mechanism has been suggested involving formation of a complex between Mn³⁺ and citric acid, decomposition of which yields the initiating free radical and with polymerization being terminated by mutual interaction of growing radicals.