The effect of transition metals on the structure of h-BN intercalation compounds

In this study, hexagonal boron nitride (h-BN) were synthesized by the modified O’Connor method in the presence of various metal nitrates [M(NO₃)_x, M=Cr, Mn, Fe, Co, Ni, Cu, Zn, and Ag]. The composites were analyzed by FTIR, XRF, XRD, and SEM techniques. XRD results indicated a change in the interlayer spacing due to the intercalation of Cr, Mn, Fe and Ag. SEM analyses illustrated the grain growth upon metal intercalation even at a temperature of 1320 K.     

A study of the structure and energy of β-diketonates. XVIII. Molecular structure of chromium and cobalt tris-acetylacetonates according to quantum chemical calculations and gas electron diffraction

The molecular structure of chromium and cobalt tris-acetylacetonates is studied by the synchronous electron diffraction and mass spectrometric experiment and quantum chemically. It is found that molecules have the D ₃ symmetry with internuclear distances r _h1(Cr-O) = 1.960(4) Å r _h1(Co-O) = 1.893(4) Å. Quantum chemical calculations by the DFT methods with different basis sets yield a structure well consistent with that found in the experiment. Changes in the structural parameters of chromium and cobalt β-diketonate complexes whose ligands differ in ?CH₃, ?C(CH₃)₃, ?CF₃ substituents are considered.     

Rare earth transition metal sulfides,LnMS3

Ternary rare earth transition metal sulfides LnMS₃ with Ln = La, Nd, and Gd, and M = V and Cr; as well as Ln = La and M = Mn, Fe, Co, and Ni have been prepared and characterized. The vanadium and chromium sulfides crystallize in a monoclinic layer structure isotypic with LaCrS₃, while the other LnMS₃ sulfides crystallize in a hexagonal structure. Chemical shifts of the metal K-absorption edge and XPS binding energies of core levels indicate that the transition metal is trivalent in the V and Cr sulfides, while it is divalent in the Mn, Fe, Co, and Ni sulfides. Electrical and magnetic properties of the sulfides are discussed in terms of their structures and the electronic configurations of the transition metal ions.     

Antiferromagnetic complexes with a metal-metal bond: XV. Antiferromagnetic heterometallospirane clusters [(CH3C5H4)2Cr2(μ-SCMe3)(μ3-S)2]2M (M = MnII,FeII): Synthesis and molecular structures

The reaction of (CH₃C₅H₄CrSCMe₃)₂S (Ia) with Cp₂Mn in boiling toluene (containing some THF) has been used to prepare a pentanuclear cluster, [(CH₃C₅H₄)₂Cr₂(SCMe₃)(μ₃-S)₂]Mn (II), which is antiferromagnetic and crystallizes into the monoclinic crystal system: space group Cc, a 26.540(10), b 9.208(3), c 21.595(9) Å; β 135.30(2)°, V = 3712.1 ų, Z = 4. According to X-ray analysis, cluster II contains a metallospirane core, Cr₄Mn, which appears to be strongly distorted, compared to its earlier studied cyclopentadienyl analogue [Cp₂Cr₂SCMe₃(μ₃-S)₂]₂Mn, due to the short intramolecular contacts CH₃…S (2.9–3.1 Å). The angle between the metal triangle planes of Cr₂Mn is 109.60°. Here, the two long CrMn bonds (3.019(3) and 3.104(4) Å) are combined with the shorter Cr Cr bond (2.651(6) Å) in one triangle and, vice versa, the less extended CrMn bonds (2.839(4) and 2.967(3) Å) are combined with a longer CrCr bond (2.726(6) Å) in the other triangle of Cr₂Mn. By the reaction of Ia with [CpFe(CO)₂]₂ (taken in the ratio of $\text{2}\text{1}$) in boiling toluene, the antiferromagnetic cluster [(CH₃C₅H₄)₂Cr₂(SCMe₃)(μ₃-S)₂]₂Fe (III) has been synthesized in which the same distortions as in cluster II are present, as revealed by X-ray analysis. In the metallospirane core of the molecule of III, the Cr₂Fe triangles make an angle of 113.84° with each other. In this cluster, the CrCr distances in the peripheral binuclear fragments (CH₃C₅H₄)₂Cr₂(μ-SCMe₃)(μ₃-S)₂ are practically equal (2.688(3) and 2.661(3) Å), whereas the FeCr bond lengths are markedly different (2.749(2) and 2.827(2) Å in on triangle and 2.910(2) and 2.969(2) Å in the other). The dependence of the geometries of clusters II and III on the steric effects of the methyl substituents in the cyclopentadienyl ligands and on the electronic effect of the central metal atom (Mn^II or Fe^II) is discussed.     

Effect of Mn(II) and Ce(IV) Ions on the Oxidation of Lactic Acid by Chromic Acid

The kinetics and mechanism of lactic acid oxidation in the presence of Mn(II) and Ce(IV) ions by chromic acid were studied spectrophotometrically. The oxidation of lactic acid by Cr(VI) was found to proceed in two measurable steps, both of which gave pyruvic acid as the primary product in the absence of Mn(II). 2Cr(VI)+2CH₃CHOHCOOH → 2CH₃COCOOH+Cr(V)+Cr(III) Cr(V)+CH₃CHOHCOOH → Cr(III)+CH₃COCOOHThe observed kinetics was explained due to the catalytic and inhibitory effects of Mn(II) and Ce(IV) on the lactic acid oxidation by Cr(VI). The reactivity of lactic acid depends upon the experimental conditions. It acts as a two-or three-equivalent reducing agent in the absence or presence of Mn(II). It was examined that Cr(III) products resulting from the direct reduction of Cr(VI) by three-equivalent reducing agents. The oxidation of lactic acid follows the complex order kinetics with respect to [lactic acid]. The activation parameters E_a, ΔH^#, and ΔS^# were calculated and discussed.     

Low temperature structural phase transition of Ba3NaIr2O9

Single crystal X-ray and synchrotron X-ray powder diffraction have been used to probe the structure of Ba₃NaIr₂O₉ from 300 K down to 20 K. Ba₃NaIr₂O₉ is found to undergo a structural transition from hexagonal symmetry, P6₃/mmc, at ambient temperature to monoclinic symmetry, C2/c, at low temperature. The evolution of the unit cell volume upon cooling is indicative of a higher order structural transition, and the symmetry breaking becomes apparent as the temperature is decreased. The low temperature monoclinic structure of Ba₃NaIr₂O₉ contains strongly distorted [NaO₆] and [IrO₆] octahedra in comparison to the room temperature hexagonal structure.     

Mixed halide dialkyldithiophosphate derivatives of arsenic(III) and antimony(III)

Mixed chloride dialkyldithiophosphates of arsenic(III) and antimony(III), [(RO)₂PSS]_nMCl_3?n (M = As, Sb; n = 1, 2; R = C₂H₅, n-C₃H₇, i-C₃H₇ and i-C₄H₉) have been synthesized for the first time by the reac metal chlorides with sodium dialkyldithiophosphates or alternatively by co-disproportionation reactions of metal chlorides with metal tris(dialkyldithiophosphates) in different stoichiometric ratios. Mixed halide dialkyl-dithiophosphates of antimony(III) have also been prepared by the cleavage reactions of antimony tris(diisopropyldithiophosphate) with bromine or iodine. Hydrolysis reactions of a few of these compounds have also been studied. The new compounds have been characterized by elemental analyses, molecular weight determinations (cryoscopic) as well as IR and NMR (¹H, ³¹P) data; chelated structures with bidentate dialkyldithiophosphate groups are proposed.     

Conductance Determination of the Ion Association of Tris-(ethylenediamine)chromium(III) Chloride in Dimethyl Sulfoxide–Water Mixtures at Various Temperatures

The electrical conductances of tris-(ethylenediamine)chromium chloride, ([Cr(en)₃]Cl₃; en = ethylenediamine) were measured as functions of temperature and concentration in 20–80 wt% dimethyl sulfoxide (DMSO)–water mixtures. Conductance data were analyzed by the Kraus–Bray and Shedlovsky models. Also, density and viscosity values for 20–80 wt% DMSO–water mixtures have been determined experimentally at temperatures varying from (288.15 to 318.15) K. The limiting molar conductance, Λ ⁰, and the association constant, K _A, for ([Cr(en)₃]Cl₃ were computed by using Shedlovsky’s equation. The Λ ⁰ values decrease with increase in the percentage of DMSO in the mixed solvent. The K _A values increase with increasing temperature and increasing percentage of DMSO in the mixed solvent at all temperatures. This may be attributed to the increase in association constant with the decrease in the relative permittivity of the mixed solvent. Thermodynamic parameters (Gibbs energy, enthalpy and entropy changes) were determined from the temperature dependence of K _A for ([Cr(en)₃]Cl₃. The results of the study have been interpreted in terms of ion–solvent interactions and solvent properties.     

Structural and physical properties evolution in the 6H BaRu1−xMnxO3 synthesized under high pressure

The 6H BaRu_1−xMn_xO₃ with the hexagonal BaTiO₃ structure was synthesized using high-pressure sintering method. It is found that the lattice parameter deviates from Vegard's law at x=0.3 for the solid solutions due to the charge transfer effects at B-site. The substitution of Mn for Ru cations gives rise to the short-range magnetic ordering, due to the disordered arrangement of Ru and Mn cations. The compounds are weak ferromagnetic in the x range 0.05-0.40, with the maximal Curie temperature T_c 175.2 K at x=0.10. They are of spin-glass-like magnetism at lower temperature at x?0.1. With Mn doping, the 6H BaRuO₃ transforms to a semiconductor from the primal metal at x=0.30. The resistance as a function of temperature below about 70 K follows the two-dimensional variable-range hopping conduction mechanism in BaRu_0.50Mn_0.50O₃.     

Magnetic ordering and metal‐atom site preference in tetragonal CrMnAs: Electronic correlation effects

The electronic and magnetic structures of tetragonal, Cu₂Sb‐type CrMnAs were examined using density functional theory. To obtain reasonable agreement with reported atomic and low‐temperature magnetic ordering in this compound, the intra‐atomic electron–electron correlation in term of Hubbard U on Mn atoms are necessary. Using GGA + U, calculations identify four low‐energy antiferromagnetically ordered structures, all of which adopt a magnetic unit cell that contains the same direct Cr Cr and Cr Mn magnetic interaction, as well as the same indirect Mn⋅⋅⋅Mn magnetic interaction across the Cr planes. One of these low‐energy configurations corresponds to the reported case. Effective exchange parameters for metal–metal contacts obtained from SPRKKR calculations indicate both direct and indirect exchange couplings play important roles in tetragonal CrMnAs. © 2018 Wiley Periodicals, Inc.     

A cyano-bridged bimetallic ferrimagnet: Synthesis,X-ray structure and magnetic study

Mixing of trans-[Mn(cyclam)Cl₂]Cl (cyclam = 1,4,8,11-tetraazacyclotetradecane) and potassium hexacyanochromate (K₃[Cr(CN)₆]) aqueous solutions instantaneously yields a 1D infinite chain complex {[Mn(cyclam)(μ-CN)₂Cr(CN)₄]·H₂O}_n (1). The crystal structure of 1, crystallizing in the monoclinic system with space group P2₁/n has been solved from X-ray powder diffraction data following direct space approach and refined by the Rietveld method. The structure analysis of 1 reveals alternating [Cr(CN)₆]³⁻ and [Mn(cyclam)]³⁺ ions generating one-dimensional polymeric (–Cr–CN–Mn–NC–)_n chain propagating along the [0 0 1] direction. The coordination environment of both the metal ions, Mn(III) and Cr(III), is octahedral. While a notable distortion in the coordination environment around Mn(III) centers was observed in complex 1, Cr(III) centers have suffered no such distortion. A ferrimagnetic interaction between the heterobimetallic centers was evidenced through variable temperature magnetic susceptibility measurements. The AC susceptibility measurement reveals that the compound 1 undergoes spontaneous ferrimagnetic ordering. Ferrimagnetic ordering has been rarely observed among the cyano-bridged compounds in the previous studies.     

Magnetic properties of compounds (Mn,Cr)1+xSb,V1+xSb and (Mn,V)1+xSb with B8-type structures

Investigations of the compounds (Mn,Cr)_1+xSb, V_1+xSb and (Mn,V)_1+xSb with B8-type structures are described. The homogeneity ranges of (Mn,Cr)_1+xSb and (Mn,V)_1+xSb shift to metal-richer compositions with increasing temperature. These compounds are ferrimagnetic. The magnetic-ordering temperature and the spontaneous magnetization decrease with increasing $\text{Cr}\text{Mn}$ and $\text{V}\text{Mn}$ ratios, respectively.The homogeneity range of the high-temperature phase V_1+xSb is situated around the composition x = 0.40. V_1.40Sb shows nearly temperature-independent (Pauli) paramagnetism (except at low temperature).     

Préparation et propriétés d'un oxyde de sodium-fer(II,III): NaFe2O3

This compound is prepared, within sealed metallic tubes at 1000°C, through different reactions between components of the FeFe₂O₃NaFeO₂ system. It is black and weakly hygroscopic and gives two forms, α and β, according to oxygen pressure values.The examination of a crystal of the α form leads to a trigonal cell (space group $\text{R3m, R}\text{3}\text{m}$ or R32) with a = 3.047 Å and c = 31.04 Å for the hexagonal cell (Z = 4). The structure is described as a stacking of alternate cationic and anionic planes with a succession of 12 cationic planes: 3 × FFMM (F, plane including Fe; M, mixed plane including $\text{2}\text{3}\text{Na}\text{+}\text{1}\text{3}\text{Fe}$).α-NaFe₂O₃ is paramagnetic above 94°K with μ_eff = 5.40; it is a semiconductor, n type, with E = 0.18 eV. Above 1050°C it dissociates into NaFeO₂ and sodic wustite, which oxidizes easily.The β form is probably a polytype with a hexagonal cell (a = 3.045Å, c = 15.55 Å) with six cationic planes.     

Preparation, structural and magnetic characterization of DyCrMnO5

The title compound has been first synthesized by a citrate technique followed by thermal treatments under moderate oxygen pressure conditions, and characterized by X-ray and neutron powder diffraction (NPD) and magnetization measurements. The crystal structure of DyCrMnO₅ has been refined from NPD data in the space group Pbam; a=7.2617(6) Å, b=8.5161(6) Å, and c=5.7126(5) Å at 295 K. This oxide is isostructural with RMn₂O₅ oxides (R=rare earths) and it contains infinite chains of (Cr, Mn)⁴⁺O₆ octahedra-sharing edges, linked together by (Mn, Cr)³⁺O₅ pyramids and DyO₈ units. The high degree of antisite disordering exhibited by DyCrMnO₅ is noteworthy. The octahedral positions are occupied by roughly 50% of Mn and Cr cations, and the pyramidal groups contain two thirds of Mn and one third of Cr cations. We assume that Mn and Cr cations at the octahedral positions exhibit a tetravalent oxidation state, whereas the metals at the pyramidal positions are trivalent, in order to preserve the electroneutrality of this oxide. The susceptibility vs temperature curve of DyCrMnO₅ does not suggest the establishment of a long-range magnetic structure even at low temperatures; the NPD technique does not provide any signal of magnetic ordering, since the reflections do not show any magnetic contribution.     

Electrical properties and sulfur tolerance of La0.75Sr0.25Cr1−xMnxO3 under anodic conditions

Complex metal oxides with composition of La_0.75Sr_0.25Cr_1−xMn_xO₃(x=0.4,0.5,0.6) (LSCM) have been synthesized and examined as anode materials for solid oxide fuel cells (SOFCs). LSCM compositions show excellent tolerance to both reduction and oxidation but the crystal structure transforms from hexagonal in air to orthorhombic in H₂. The volume change associated with this phase transformation is only about 1%, thus having little effect on other properties. The total electrical conductivity increases with the content of Mn, whereas the resistance to sulfur poisoning increases with the content of Cr. Fuel cells using LSCM as the anode show very good performance when pure hydrogen is used as the fuel. However, they do not appear to be stable in fuels containing 10% of H₂S.     

Spin-crossover in complexes of iron(II) carboranes with tris(pyrazol-1-yl)methane

Synthesis procedures for coordination compounds of iron(II) 1,5,6,10-tetra(R)-7,8-dicarba-nido-undecaborates(-1) (carboranes) with tris(pyrazol-1-yl)methane (HC(pz)₃) of the composition [Fe{HC(pz)₃}₂]A₂·nH₂O (A = (7,8-C₂B₉H₁₂)^? (I), (1,5,6,10-Br₄-7,8-C₂B₉H₈)^? (II), (1,5,6,10-I₄-7,8-C₂B₉H₈)^? (III), n = 0–2) are developed. The compounds are studied by static magnetic susceptibility in the temperature range of 160–500 K, electron (diffuse reflectance spectra), IR, and Mössbauer spectroscopy methods. It is shown that the complexes have high-temperature spin-crossover ¹ A ₁ ? ⁵ T ₂. Transition temperatures (T _c) for I–III are 370 K, 380 K, and 400 K respectively. Spin-crossover is accompanied by thermochromism (color change: pink ? white).     

Low-temperature thermodynamic properties of Ir(C5H7O2)3: Connection of entropy with the molecule volume for tris-acetylacetonates of metals

The heat capacity of Ir(C₅H₇O₂)₃ has been measured by the adiabatic method within the temperature range (5 to 305) K. The thermodynamic functions (entropy, enthalpy, and reduced Gibbs free energy) at 298.15 K have been calculated using the obtained experimental heat capacity data. A connection has been found between the entropy and the volume of the elementary crystalline cell for β-acetylacetonates of some metals. The reasons for this interdependence are discussed. The values of entropies at T = 298.15 K have been calculated for all the metal acetylacetonates on which there are structural data.     

Optically active pseudoctahedral rhodium(III), iridium(III), and ruthenium(II) complexes with α-amino acidato ligands. Crystal structures of RIrSCSN- and SIrSCSN-[(C5Me5)Ir(pro)Cl] · 12H2O (Hpro = l-proline)

The synthesis and characterization of optically active amino acidato complexes of the types [(C₅Me₅)M(aa)Cl], [(p-cymene)Ru(aa)Cl], [(C₅Me₅)M(aa)(PPh₃)]BF₄, and [(p-cymene)Ru(aa)(PPh₃)]BF₄ (M = Rh, Ir; Haa = l-alanine, l-proline), in which the metal is a chiral centre, are reported. The cationic species were prepared via the solvato-complexes [(C₅Me₅)M(aa)(MeOH)]⁺ and [(p-cymene)Ru(aa)(MeOH)]⁺, which epimerize rapidly on the ¹H NMR time scale. The crystal structure of the complex [(C₅Me₅)Ir(pro)Cl] is reported; the asymmetric unit contains two independent molecules differing in the configuration at the metal.     

Mössbauer study of the thermal decomposition products of BaFeO4

A pure sample of a hexavalent iron compound, BaFeO₄, was decomposed at temperatures below 1200°C at oxygen pressures from 0.2 to 1500 atm. In addition to the already known BaFeO_x (2.5 ≦ x < 3.0) phases with hexagonal and triclinic symmetry, two new phases were obtained as decomposition products at low temperatures. One of the new phases, with composition BaFeO_{2.61 – 2.71}, has tetragonal symmetry; lattice constants are a₀ = 8.54 Å, c₀ = 7.29 Å. The phase is antiferromagnetic with Néel temperature estimated to be 225 ± 10 K. Two internal fields observed on its Mössbauer spectra correspond to Fe³⁺ and Fe⁴⁺. In the other new phase, with composition BaFeO_2.5, all Fe³⁺ ions had the same hyperfine field; it too is antiferromagnetic with a Néel temperature of 893 ± 10 K. Mössbauer data on the hexagonal phase coincided with earlier results of Gallagher, MacChesney, and Buchanan [J. Chem. Phys.43, 516 (1965)]. In the triclinic-I BaFeO_2.50 phase, internal magnetic fields were observed at room temperature, and it was supposed that there were four kinds of Fe³⁺ sites. The phase diagram of BaFeO_x system was determined as functions of temperature and oxygen pressure.     

Crystal structure, optical properties and colouring performance of karrooite MgTi2O5 ceramic pigments

Karrooite, MgTi₂O₅, is a promising ceramic pigment due to its high refractoriness and refractive indices, as well as its ability to host transition metal ions in two crystallographically distinct octahedral sites. The colouring performance was investigated combining X-ray powder diffraction with UV-vis-NIR spectroscopy on karrooite doped with V, Cr, Mn, Fe, Co or Ni (M) according to the formula Mg_1−xTi_2−xM_2xO₅, with x=0.02 and 0.05. Transition metals solubility in the karrooite lattice is not complete and a second phase is always present (geikielite or rutile). Structural data proved that incorporation of different chromophore ions into the karrooite structure affects unit cell parameters, bond length distances and angles, site occupancies and therefore cation order-disorder. Optical spectra exhibit broad absorbance bands of Co(II), Cr(IV), Fe(III), Mn(II), Mn(III), Ni(II), V(IV) with distinct contributions by cations in the M₁ and M₂ sites. Karrooite pigments have colours ranging from orange to brown-tan (Cr, Fe, Mn, V) to green (Co) and yellow (Ni) that are stable in low-temperature (<1050 °C) ceramic glazes and glassy coatings.