Theoretical calculations of high-pressure phases of NiF<Subscript>2</Subscript>: An ab initio constant-pressure study

We have studied the structural properties of the antiferromagnetic NiF₂ tetragonal structure with P4₂/mnm symmetry using density functional theory (DFT) under rapid hydrostatic pressure up to 400 GPa. For the exchange correlation energy we used the local density approximation (LDA) of Ceperley and Alder (CA). Two phase transformations are successfully observed through the simulations. The structures of XF₂-type compounds crystallize in rutile-type structure. NiF₂ undergoes phase transformations from the tetragonal rutile-type structure with space group P4₂/mnm to orthorhombic CaCl₂-type structure with space group Pnnm and from this orthorhombic phase to monoclinic structure with space group C2/m at 152 GPa and 360 GPa, respectively. These phase changes are also studied by total energy and enthalpy calculations. According to these calculations, we perdict these phase transformations at about 1.85 and 30 GPa.     

Gd5-xYxTt4 (Tt = Si or Ge): effect of metal substitution on structure, bonding, and magnetism

A crystallographic study and theoretical assessment of the Gd/Y site preferences in the Gd 5- x Y x Tt 4 ( Tt = Si, Ge) series prepared by high-temperature methods is presented. All structures for the Gd 5- x Y x Si 4 system belong to the orthorhombic, Gd 5Si 4-type (space group Pnma). For the Gd 5- x Y x Ge 4 system, phases with x < 3.6 and x >or= 4.4 adopt the orthorhombic, Sm 5Ge 4-type structure. For the composition range of 3.6 相似文献   

Dissymmetrization of crystal structures of grossular-andradite garnets Ca<Subscript>3</Subscript>(Al,Fe)<Subscript>2</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The crystal structures of three birefringent grossular-andradite natural garnets Ca₃(Al,Fe)₂(SiO₄)₃ were investigated using single-crystal X-ray diffraction data (MoK_α, number of reflections measured 8065, 10619, 9213; R = 2.81, 2.74, 3.26%). According to the values of unit cell constants, inconsistent intensities of reflections and appearance of additional (forbidden) reflections explored garnets have different symmetry: cubic, sp. gr. (Fe/(Fe + Al) = 0.078, Δn = 0.0002); orthorhombic, sp. gr. Fddd (Fe/(Fe + Al) = 0.58, Δn = 0.0089); triclinic, sp. gr. or I1 and pseudo-orthorhombic (Fe/(Fe + Al) = 0.23, Δn = 0.0066). Careful refinement of all crystal structures in space groups , Fddd and has confirmed the symmetry reduction detected on the diffraction patterns and shown that dissymmetrization of cubic garnets connects with partial ordering of trivalent cations over Y-sites. Direct linear relationship between Fe-occupancy, an average Y–O bond lengths and octahedral O–O edges has been revealed. Cluster models of dissymmetrization have been regarded. Evidence for the “growth dissymmetrization” phenomena (kinetic phase transformations) as the reasons of the symmetry reduction of cubic garnets has been discussed. The reasonable assumption that the garnets crystal structures described as orthorhombic are triclinic, but the deviations from the orthorhombic symmetry so small, that cannot be manifested by of X-ray diffraction study has been taken.     

Phase Evolution and Magnetic Properties of Sn_(1-2x)Fe_xNb_xO_2(0.45≤x≤0.50)

Sn1-2xFexNbxO2(0.45≤x≤0.50) samples were prepared at 1000 ℃ via a simple chemical co-precipitation method.The effects of the concentrations of Sn doped on the structures and magnetic properties of the samples have been investigated.A systematic variation from monoclinic to orthorhombic FeNbO4 structure was observed with increasing Sn content.The phase evolutions were observed from monoclinic structure with x=0.50 to the coexistence of monoclinic and orthorhombic structures with x=0.48,0.47,0.46,and then to orthorhombic structure with x=0.45.Antiferromagnetic behavior was observed for all the samples,and the magnetic ordering temperatures decrease with increasing Sn concentration,which further indicated the sequence of phase transitions.The results suggest that the incorporation of Sn can stabilize the orthorhombic FeNbO4.     

Organic-inorganic hybrid perovskite (C<Subscript>6</Subscript>H<Subscript>5</Subscript>(CH<Subscript>2</Subscript>)<Subscript>2</Subscript>NH<Subscript>3</Subscript>)<Subscript>2</Subscript>CdCl<Subscript>4</Subscript>: Synthesis,structural and thermal properties

The present research work reports the study on crystal structure, vibrational spectroscopy and thermal analysis of organic-inorganic hybrid compound (C₆H₅(CH₂)₂NH₃)₂CdCl₄. Single crystals of bis(phenethylammonium)tetrachlorocadmate (C₆H₅(CH₂)₂NH₃)₂CdCl₄ (PEA–Cd) were obtained by diffusion at room temperature. This compound crystallizes in the orthorhombic space group C2cb with unit cell parameters a = 7.4444(2) Å, b = 38.8965(3) Å, c = 7.3737(2) Å and Z = 4. Single crystal structure has been solved and refined to R = 0.036 and wR = 0.092. The structure consists of an extended [CdCl₄]^2– network and two [C₆H₅(CH₂)₂NH₃]⁺ cations to form a two-dimensional perovskite system. The infrared (IR) spectrum of the title compound was recorded at room temperature. Differential scanning calorimetry (DSC) was used to investigate the phase transition; this compound exhibits a reversible single solid-solid phase transition.     

Phase transition in Tl2TeO3: influence and origin of the thallium lone pair distortion

A new modification of thallium tellurite, beta-Tl(2)TeO(3), has been synthesized by methanolothermal reaction, and its phase transition has been studied by single-crystal X-ray diffraction. At a temperature of 440(10) degrees C an irreversible phase transition from a monoclinic structure (beta-Tl(2)TeO(3): P2(1)/c (No. 14), Z = 4, a = 8.9752(18) A, b = 4.8534(6) A, c = 11.884(2) A, beta = 109.67(2) degrees, V = 487.47(15) A3 at 25 degrees C) to an orthorhombic structure (alpha-Tl(2)TeO(3): Pban (No. 50), Z = 8, a = 16.646(2) A, b = 11.094(2) A, c = 5.2417(8) A, V = 968.0(3) A3 at 25 degrees C) is observed. Both structures are characterized by psi-tetrahedral TeO(3)(2-) anions. In the orthorhombic structure psi-trigonal bipyramidal [TlO(4)] units are found together with psi-tetrahedral [TlO(3)] units whereas in the monoclinic structure the coordination polyhedron around Tl(I) can be best described as a psi-square pyramide, psi-[TlO(4)]. The electronic structure of Tl(2)TeO(3) in both modifications has been studied to explain the influence of the lone pairs. It can be conclusively shown that the minimization of antibonding ns-metal/2p-oxygen interactions is the driving force for "lone pair" distortions which determines the structures of Tl(2)TeO(3).     

Crystal structure and properties of AHoCuS<Subscript>3</Subscript> (A = Sr or Eu)

The structures of complex sulfides AHoCuS₃ (A = Sr or Eu) have been determined by X-ray powder diffraction. The crystals of the compounds belong to the orthorhombic crystal system; they are isostructural (space group, Pnma; structure type Eu₂CuS₃). The unit cell parameters for SrHoCuS₃ and EuHoCuS₃ are a = 10.1487(1) Å, b = 3.9332(1) Å, c = 12.9524(2) Å and a = 10.1484(2) Å, b = 3.9195(1) Å, c = 12.8499(2) Å, respectively. The temperatures and enthalpies of phase transformations of complex sulfides AHoCuS₃ (A = Sr or Eu) have been determined.     

Substitution of Au or Hg into BaTl2 and BaIn2. New ternary examples of smaller CeCu2-type intermetallic phases

The compounds BaAu(0.40(2))Tl(1.60(7)) (1), BaAu(0.36(4))In(1.64(4)) (2), and BaHg(0.92(2))In(1.08(2)) (3) have been prepared by high-temperature techniques. Single-crystal X-ray diffraction shows that these have the orthorhombic CeCu(2)-type structure, Imma, Z = 4 (a = 5.140(1), 5.104(1), 5.145(1) A; b = 8.317(2), 8.461(2), 8.373(2) A; c = 8.809(2), 8.580(2), 8.715(2) A, respectively). The structure consists of a four-linked honeycomblike polyanion (4(2)6(3)8) of infinity3[Tr2]2- (Tr = In or Tl) with encapsulated Ba2+ cations. The Au or Hg randomly replace Tr in a single type of site. The two gold phases exhibit appreciable nonstoichiometry ranges. Band calculations (EHTB) demonstrate that the three compounds are electron-poor and metallic, and the latter has been confirmed for 1 through resistivity and magnetic susceptibility measurements. The orthorhombic structure of 1 contrasts with the hexagonal structure of BaTl2 (CaIn2-type, P6(3)/mmc), a change that appears to be driven by substitution of the smaller Au atoms into the polyanion network. Relativistic effects for the heavier Au and Hg are evidently responsible for decreases in lattice parameters and bond lengths from BaIn2 to those in isostructural 2 and 3.     

(Zr6B)Cl11-xI2+x] (0< or = x < or = 6): a new mixed-halide structure with zigzag cains of clusters in multiply twinned crystals

The new [(Zr6B)Cl11-xI2+x] phase (with 0 < or = x < or = 6) is obtained from reactions of ZrI4, ZrCl4, and elemental Zr and B for 2-4 weeks in sealed Ta tubing at 800-850 degrees C. Single crystals of [(Zr6B)Cl6.44(7)I6.56] have been characterized by X-ray diffraction at room temperature (orthorhombic Pbcn, Z = 4, a = 12.365(2) A, b = 15.485(3) A, c = 13.405(2) A). This structure contains zigzag chains of boron-centered (Zr6B) octahedra that are interconnected by Cl(i-i) halides. Further three-dimensional connectivity is achieved by I(a-a-a) bridges. The noncluster interconnecting two-bonded X(i) sites are occupied statistically by a mixture of Cl and I. For each site both positions were resolved. This structure forms within a phase width of 0 < or = x < or = 6 at temperatures between 800 and 850 degrees C. Crystals of this phase appear to be always multiply twinned.     

New polymorph of CaHPO<Subscript>4</Subscript> (monetite): synthesis and crystal structure

A novel form of anhydrous dicalcium phosphate CaHPO₄ (monetite) is synthesized hydrothermally and characterized by single crystal X-ray diffraction. It crystallizes in the orthorhombic space group Ccm2₁ with a = 6.242(1) Å, b = 6.994(2) Å, c = 7.003(3) Å, V = 305.73(16) ų and it has four independent unit formulas in the unit cell (Z = 4). A three-dimensional crystal structure can be described by {HPO₄}_n infinite zigzag chains linked by Ca–O bonds. The comparison to the crystal structures of other polymorphs is given.     

Crystal structure of EuLaCuS<Subscript>3</Subscript>

The crystal structure of the EuLaCuS₃complex sulfide synthesized for the first time has been solved by X-ray powder diffraction. Crystals are orthorhombic, space group Pnma, Ba₂MnS₃-type structure, a = 8.1297(3) Å, b = 4.0625(1) Å, c = 15.9810(4) Å, V = 527.80(3) ų, Z = 4, and ρ_calc = 5.669 g/cm³. The La and Eu atoms are randomly disordered over two crystallographic positions with a coordination number of 7, and the Eu(La)-S bond lengths range from 2.892(6) to 3.078(6) Å. The CuS₄ tetrahedra with Cu-S interatomic distances of 2.358(5)–2.40(1) Å form chains running along the b axis.     

Uranyl cyanoacetate [UO<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>(NCCH<Subscript>2</Subscript>COO)<Subscript>2</Subscript>]: Synthesis,crystal structure,and absorption spectra

The U(VI) complex with cyanoacetic acid, [UO₂(H₂O)₂(NCCH₂COO)₂] (I), was synthesized from an aqueous solution, and its X-ray diffraction analysis was carried out. The crystals are orthorhombic: space group Pca2 ₁, a = 25.9605(7) Å, b = 6.7634(2) Å, c = 6.3398(2) Å, V = 1113.15(6) ų at 100 K, and Z = 4. The coordination polyhedron of the uranium atom is a distorted pentagonal bipyramid. The cations UO ₂ ²⁺ are bound into infinite zigzag chains by the bridging carboxyl groups of one of the anions of cyanoacetic acid. The carboxyl oxygen atom of the second anion, which is not involved in coordination, and the nitrogen atoms of the cyano groups form hydrogen bonds with the coordination water molecules. The layer structure of the compound is formed through the hydrogen bonds. The absorption spectra in the visible and infrared ranges of the crystalline compound are measured and analyzed.     

Organometallic coordination polymers based on silver carboxylates: [AgCF<Subscript>3</Subscript>CO<Subscript>2</Subscript>(2,3-Et<Subscript>2</Subscript>Pyz)] and [AgCF<Subscript>3</Subscript>CO<Subscript>2</Subscript>(Bpeta)]

Coordination polymers [AgCF₃CO₂(2,3-Et₂Pyz)](I)(2,3-Et₂Pyz-C₈H₁₂N₂) and [AgCF₃CO₂(Bpeta)] (II) (Bpeta is 4′4-bipyridylethane, C₁₂H₁₂N₂) are synthesized. Their structures are determined. The crystals of compound I are monoclinic, space group P2(1)/n, a = 7.185(1), b = 14.754(1), c = 12.317(1)Å, β = 97.09(1)°, V = 1295.7(2) ų, ρ_calcd = 1.831 g/cm³, Z = 4. Structure I consists of infinite chains of doubled polymeric chains joined by silver carboxylate dimers [[Ag₂(CF₃CO₂)₂(Et₂Pyz)₂]_∞. The coordination polyhedron of Ag⁺ is a distorted tetrahedron. The crystals of compound II are orthorhombic, space group Pbca, a = 13.555(3), b = 13.991(3), c = 16.449(3) Å, V = 3119.5(11) ų, ρ_calcd = 1.725 g/cm³, Z = 8. Doubled polymeric chains with the Ag…Ag bond (3.16 Å) are also formed in structure II. Supramolecular layers are formed in the structure due to the weak π-π-stacking interaction between the aromatic groups of chains. The CF₃CO ₂ ^? anion is weakly bound to Ag⁺ (Ag-O_avg 2.790 Å).     

The high-pressure phase transition of TiS2 from first-principles calculations

The structural stability of TiS₂ under high pressures has been investigated by using first-principles plane-wave pseudopotential density functional theory within the local density approximation (LDA). The obtained results predict that TiS₂ undergoes a pressure-induced first-order phase transition from its trigonal 1T-type structure to orthorhombic cotunnite-type structure at 16.20 GPa. The calculated transition pressure agrees quite well with the experimental finding of 20.7 GPa. The equation of state determined from our calculated results yields bulk moduli of 58.91 and 118.10 GPa for the 1T-type and cotunnite-type phases, respectively. This indicates higher incompressibility of the high-pressure phase of TiS₂. In addition, the electronic structures of the two phases of TiS₂ are also calculated and discussed. The results suggest the structural phase transition of TiS₂ at high pressure is followed by a semimetal to metal electronic transition.     

Titanium tetrafluoride complexation with phosphorylated ketone Ph<Subscript>2</Subscript>P(O)(CH<Subscript>2</Subscript>)<Subscript>2</Subscript>C(O)Me in CH<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

The products resulting from the reaction of TiF₄ with Ph₂P(O)(CH₂)₂C(O)Me (L') in CH₂Cl₂ have been studied by ¹⁹F{¹H} and 31P{¹H} NMR spectroscopy. At a twofold excess of L', solution contains cis-TiF₄(L')2 (>90%), trans-TiF₄(L')₂, and fac-[TiF₃L₃']⁺, where L' is coordinated via the P=O group, as well as the dimer [(Ti₂F₇L'₂)₂]+, where L' is coordinated through the P=O and C=O groups. An equimolar solution contains dimeric and polynuclear complexes containing moieties with three terminal cis fluorine ions, while the other coordination sites are occupied by the P=O groups and F^– bridges. At a twofold excess of TiF₄, ligand L' coordinates via the P=O and C=O groups and behaves as a bridge along with F^– ions. Thermodynamic stability of the structures of the TiF₄L'₂ isomers and the structure of [(µ-F)(µ-L')₂(TiF₃)₂]⁺ has been calculated.     

Synthesis and crystal structure of a novel two-dimensional network complex [Mn(O<Subscript>2</Subscript>CCH<Subscript>2</Subscript>Cl)<Subscript>2</Subscript>(phen)]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

A novel two-dimensional network manganese(II) polymer complex [Mn(O₂CCH₂CI)₂-(phen)] _n has been synthesized and characterized by elemental analysis and IR spectrum. The crystal structure of title complex has also been determined, which is in monoclinic of a space group P2₁/c with the following unit cell parameters at 294K:a =1.9738 (4) nm,b=1.1384 (2) nm,c =0.74915(14) nm,V = 1.6795(5) nm³, Z= 2.     

Systems Li<Subscript>2</Subscript>O(Na<Subscript>2</Subscript>O)-CdO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>: Phase composition and phase diagrams

The subsolidus phase composition of the M₂O-CdO-V₂O₅ systems with M = Li or Na is studied. Double orthovanadates MCdVO₄ and MCd₄(VO₄)₃ form solid solutions of composition Li_{1 ? 2x/3}Cd _x/3CdVO₄ (0 ≤ x ≤ 1, orthorhombic space group Cmcm, modulation at x = 0.6) and Na_{3 ? 2x} Cd_{3 + x} (VO₄)₃ (0 ≤ x ≤ 0.10 and 0.30 ≤ x ≤ 1, orthorhombic space group Cmcm and Pn2₁ a or Pnma, respectively). In the range 0.10 < x < 0.30, the end-members of the solid solutions coexist. Isothermal sections of the systems are mapped.     

Interplay between size and electronic effects in determining the homogeneity range of the A9Zn4+xPn9 and A9Cd4+xPn9 phases (0 < or = x < or = 0.5), A = Ca, Sr, Yb, Eu; Pn = Sb, Bi

Seven cadmium- and zinc-containing Zintl phases, A9Zn(4+x)Pn9 and A9Cd(4+x)Pn9 (0 < or = x < or = 0.5), A = Ca, Sr, Yb, Eu; Pn = Sb, Bi, have been synthesized, and their structures have been determined by single-crystal X-ray diffraction. All compounds are isostructural and crystallize in the centrosymmetric orthorhombic space group Pbam (no. 55, Z = 2), and their structures feature tetrahedra of the pnicogens, centered by the transition metal. The tetrahedra are not isolated but are connected through corner sharing to form ribbons, which are separated by the divalent cations. The occurrence of a small phase width and its variation across this family of compounds has been systematically studied by variable temperature crystallography, resistivity, and magnetic susceptibility measurements, and these results have been reconciled with electronic structure calculations performed using the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method. These analyses of the crystal and electronic structure indicate that the polyanionic subnetwork requires 19 additional electrons, whereas only 18 electrons are provided by the cations. Such apparent "electron deficiency" necessitates the presence of an interstitial atom in order for an optimal bonding to be achieved; however, an interplay between the sizes of the cations and anions and the total valence electron concentration (governed by the stoichiometry breadth) is suggested as a possible mechanism for achieving structure stability. The structural relationship between these and some known structures with two-dimensional layers are discussed as well.     

Layered rare-earth gallium antimonides REGaSb(2) (RE = La--Nd, Sm).

The ternary rare-earth gallium antimonides, REGaSb(2) (RE = La--Nd, Sm), have been synthesized through reaction of the elements. The structures of SmGaSb(2) (orthorhombic, space group D(5)(2)-C222(1), Z = 4, a = 4.3087(5) A, b = 22.093(4) A, c = 4.3319(4) A) and NdGaSb(2) (tetragonal, space group D(19)(4h)-I4(1)/amd, Z = 8, a = 4.3486(3) A, c = 44.579(8) A) have been determined by single-crystal X-ray diffraction. The SmGaSb(2)-type structure is adopted for RE = La and Sm, whereas the NdGaSb(2)-type structure is adopted for RE = Ce--Nd. The layered SmGaSb(2) and NdGaSb(2) structures are stacking variants of each other. In both structures, two-dimensional layers of composition (2)(infinity)[GaSb] are separated from square nets of Sb atoms [Sb] by RE atoms. Alternatively, the structures may be considered as resulting from the insertion of zigzag Ga chains between (2)(infinity)[RE Sb(2)] slabs. In SmGaSb(2), all of the Ga chains are parallel and the (2)(infinity)[SmSb(2)] layers are stacked in a ZrSi(2)-type arrangement. In NdGaSb(2), the Ga chains alternate in direction, resulting in a doubling of the long axis relative to SmGaSb(2), and the (2)(infinity)[NdSb(2)] layers are stacked in a Zr(3)Al(4)Si(5)-type arrangement. Extended Hückel band structure calculations are used to explain the bonding in the [GaSb(2)](3-) substructure.     

Über Thiomercurate. 2. Zur Kenntnis von Ba2HgS3

On Thiomercurates. 2. About Ba₂HgS₃ Ba₂HgS₃ (bright red) crystallizes orthorhombic with a = 8.93₁, b = 4.35₇, c = 17.25₇ Å, Z = 4, space group Pnma—D (single crystal data and Guinier-Simon-powder photographs, parameter see text). The structure shows chains of corner linked tetrahedra (976 hkl MoKα, R = 6.4₅%, R_W = 8.9₆%). A new method to describe a structure is used.