Showing papers on "Orthorhombic crystal system published in 1984"
TL;DR: The crystal structures of three lithium titanates by neutron diffraction powder profile analysis were determined in this article, where the lithium partially occupies the highly distorted octahedral interstices in the anatase framework in fivefold-coordination with oxygen.
308 citations
TL;DR: CeCu 6 is shown to be a typical substance in the Kondo lattice ground state, having no magnetic ordering, and the anisotropic negative magnetoresistance is found at low temperatures, which probably reflects the orthorhombic crystal structure as mentioned in this paper.
Abstract: CeCu 6 is shown to be a typical substance in the Kondo lattice ground state, having no magnetic ordering. The anisotropic negative magnetoresistance is found at low temperatures, which probably reflects the orthorhombic crystal structure.
136 citations
TL;DR: In this paper, the analysis of Rayleigh wave propagation in crystals is carried out in the cases for which the Christoffel equations split into two parts providing a rayleigh wave polarized in the sagittal plane, and the boundary conditions simplify under the conditions that some elastic constants vanish.
Abstract: The analysis of Rayleigh wave propagation in crystals is carried out in the cases for which, on the one hand, Christoffel equations split into two parts providing a Rayleigh wave polarized in the sagittal plane, and on the other hand, boundary conditions simplify under the conditions that some elastic constants vanish. It is shown that these requirements are satisfied by 16 configurations in crystals belonging to the orthorhombic, tetragonal, cubic, and hexagonal symmetry systems. The three particular cases solved by Stoneley [R. Stoneley, Proc. R. Soc. London, Ser. A 2 3 2, 447–458 (1955)] are included. The equations giving the velocity and the mechanical displacement are established. The influence of the anisotropy factor on the decay constant is emphasized for crystals belonging to the cubic or tetragonal systems. Curves showing the decrease of the longitudinal and transverse components of the mechanical displacement are given for YAG, Si, GaAs, TiO2, and TeO2. Oscillations and a very slow decrease versus depth of the mechanical displacement components were observed for TeO2. These are ascribed to the strong anisotropy of this crystal.
121 citations
TL;DR: In this article, the authors used cross-polarization and magic angle spinning to determine quantitatively the ratio of monoclinic to orthorhombic crystalline phases in compression moalded ultra-high molecular weight polyethylene (UHMWPE) sheet which had been stretched uniaxially.
93 citations
TL;DR: In this paper, it was shown that the symmetry change between monoclinic and orthohombic nature, exhibited in ZSM-5 zeolite, depends not only on the aluminium concentration and the presence of sorbate molecules, but also on the temperature of the sample.
Abstract: X-Ray diffraction experiments have shown that the framework symmetry change between monoclinic and orthohombic nature, exhibited in ZSM-5 zeolite depends not only on the aluminium concentration and on the presence of sorbate molecules, but also on the temperature of the sample.
89 citations
TL;DR: Reversible light-induced EPR signals of the primary donor (bacteriochlorophyll dimer) showed that the RCs in the crystal were fully active, and from the angular dependence of the EPR signal the molecular g anisotropy of the bacteriochlorophical dimer was deduced to be g perpendicular - g parallel = (64 +/- 3) X 10(-5).
Abstract: Reaction centers (RCs), integral membrane proteins that mediate the conversion of light into chemical energy, were crystallized by two different vapor diffusion techniques. In one method, small amphipathic molecules (1,2,3-heptanetriol and triethylammonium phosphate) were added to the RCs that had been solubilized in detergent. In the second method, crystallization occurred near the phase boundaries of a two-phase system created by the addition of polyethylene glycol and NaCl to RCs in octyl beta-D-glucoside. Several different crystal forms were obtained; two were analyzed by x-ray diffraction. One was monoclinic (space group P2) with beta = 105 degrees, and a = 70 A, b = 105 A, and c = 85 A, two RCs per unit cell, and one RC per asymmetric unit; the crystal diffracted to 3.5 A at 17 degrees C. The other crystal form was orthorhombic (space group C222) with a = 185 A, b = 170 A, and c = 105 A, with eight RCs per unit cell and one RC per asymmetric unit. Reversible light-induced EPR signals of the primary donor (bacteriochlorophyll dimer) showed that the RCs in the crystal were fully active. From the angular dependence of the EPR signal the molecular g anisotropy of the bacteriochlorophyll dimer was deduced to be g perpendicular - g parallel = (64 +/- 3) X 10(-5). Linear dichroism measurements were performed on the monoclinic crystal. The two bands at 535 and 544 nm assigned to the Qx transitions of the bacteriopheophytins were resolved and preliminary orientations of some of the pigments were obtained.
89 citations
TL;DR: In this paper, the authors measured the adiabatic single-crystal elastic moduli of three perovskite-structure compounds, i.e., SmAlO3, GdAlO2 and ScAlO 3, under ambient conditions and found that they are nearly equal and insensitive to distortions from cubic symmetry.
89 citations
01 Sep 1984
TL;DR: In this article, the crystal structure of SnS has been investigated as a function of temperature by elastic neutron scattering from 293 K to 1 000 K. The mean square displacement of the Sn atom which is isotropic at room temperature becomes increasingly anisotropic and anharmonic near Tc.
Abstract: 2014 The crystal structure of SnS has been investigated as a function of temperature by elastic neutron scattering from 293 K to 1 000 K. SnS undergoes a second order displacive phase transition from the 03B1-phase (B16, Pbnm) to the high temperature 03B2-phase (B33, Cmcm) at 887 K. The mean square displacement of the Sn atom which is isotropic at room temperature becomes increasingly anisotropic and anharmonic near Tc. Energy dispersive Xray diffraction experiments have been performed on IV-VI semiconductors PbS, PbSe, PbTe, GeS, GeSe, SnS and SnSe as a function of hydrostatic pressure to 340 kbar. PbS, PbSe and PbTe undergo transition from the NaCl type (B1) phase to the orthorhombic phases (B33 or B16) at about 22, 45 and 60 kbar, respectively. The orthorhombic phases of PbS and PbSe have been found to be of TlI type (B33, Cmcm) and that in PbTe has been found to be GeS type (B16, Pbnm). PbS, PbSe and PbTe undergo further phase transitions to the cubic CsCl type (B2) phase at about 215, 160 and 130 kbar, respectively. The orthorhombic IV-VI compounds GeS, GeSe, SnS and SnSe do not undergo any phase transition up to 340 kbar. Revue Phys. Appl. 19 (1984) 807-813 SEPTEMBRE 1984,
85 citations
TL;DR: The cyclic tetramer (2c) as discussed by the authors was derived from the condensation of phenol and formaldehyde but actually obtained by dealkylating p-t-butyl- and p-octylcalix[4]arenes, crystallizes from acetone in two crystal forms.
Abstract: The cyclic tetramer (2c), formally derived from the condensation of phenol and formaldehyde but actually obtained by dealkylating p-t-butyl- and p-octylcalix[4]arenes, crystallizes from acetone in two crystal forms. The first one, obtained in the presence of 1,2,4,5-tetramethylbenzene, is the (2c)–acetone (1 : 1) clathrate, orthorhombic, space group Pnma, a= 17.010(8), b= 14.127(6), c= 10.667(3)A, Z= 4, final R value 0.090. The second, obtained from pure acetone or in the presence of thymol, is the (2c)–acetone (3 : 1) clathrate, space group P63/m, a=b= 14.543(5), c= 18.228(7)A, γ= 120°, final R value 0.070. The geometry of macrocycle (2c) in the two forms, in the ‘cone’ conformation in both cases, is slightly different. The orthorhombic crystals show a molecular arrangement of an intercalatoclathrate type and the hexagonal one a tubulato-clathrate type.
83 citations
TL;DR: In this paper, the surface morphology of a neck portion of two coalescing particles and clusters of Rh6(CO)16 impregnated on the particles are demonstrated for the first time.
Abstract: The γ-alumina particles are produced by a dry method developed by the author. Three types of structures, tentatively called δ' (orthorhombic; Pmn21; a=8.2, b=16.4, c=11.8 A), θ1 (monoclinic; B2/b; a=11.1, b=12.1, c=17.7 A, β=103° ) and θ2 (monoclinic, B2/m; a=11.1, b=12.1, c=2.9 A, β=103°) are found. The particle is spherical but facetted with flat {111} and {100} surfaces; {110} surfaces consist of many small {111} facets. As a new approach to ceramics and catalysis research, surface morphology of a neck portion of two coalescing particles, and clusters of Rh6(CO)16 impregnated on the particles are demonstrated for the first time.
70 citations
Journal Article•
TL;DR: In this paper, the unit-cell dimensions and crystal structure of andalusite Al2SiO5 have been refined from X-ray data on single crystals mounted in a diamond anvil cell at pressures of 12,25, and 37 kbar.
Abstract: The unit-cell dimensions and crystal structure of andalusite Al2SiO5 have been refined from X-ray data on single crystals mounted in a diamond anvil cell at pressures of 12,25, and 37 kbar. Structure refinements with anisotropic temperature factors yielded weighted R factors of 3.4, 4.9, and 5.2%o respectively. The bulk modulus of andalusite is 1.35t0.10 mbar and the axial compression ratios of orthorhombic unit-cell axes a:b:c are approximately 2.1:1.5:1.0. The relatively greater compressibility of the A(IFOD bond results in a being the most compressible axis. Those bonds that compress )3obetween I bar and 37 kbar at room temperature, are the bonds that also expand significantly between 25 and 1000"C at room pressure. Polyhedral bulk moduli for the Al(l) octahedron, the Al(2) trigonal bipyramid and the Si tetrahedron are 1.3t0.2, 1.6!0.5, and 4.1+1.5 mbar' respectively. Thus, the aluminum polyhedra are significantly more compressible than the silicon tetrahedron. The omega step-scanning technique of X-ray intensity data collection results in a significant improvement in accuracy and is recommended for structure determination with the diamond-anvil high-pressure cell. Introduction High pressure structure determination contain valuable data on the equations of state, interatomic forces and chemical bonding in minerals. The Al2SiO5 polymorphs, andalusite, sillimanite and kyanite, provide an interesting system where aluminum occurs in three types of coordinations; in addition to the octahedral coordination found in all three minerals, aluminum also occurs in tetrahedal coordination in sillimanite and in five-fold trigonal bipyramidal coordination in andalusite. Knowledge of the response to pressure and temperature of these different types of Al-O bonds in the presence of relatively rigid SiOa tetrahedra is necessary for an understanding of the stability relations and phase transformation within the Al2SiO5 system. The temperature efects on the crystal structures of andalusite, sillimanite and kyanite have been determined by Winter and Ghose (1979). The elastic constants of andalusite and sillimanite have been determined by Vaughan and Weidner (1978), who used the Brillouin scattering technique. From infrared and Raman 0003-004)v84l0506-05 l 3$02 . 00 5 I 3 spectroscopic data, the phonon spectra ofandalusite and their temperature dependence have been determined and interpreted on the basis of a rigid-ion model by Iishi et al. (1979). In this paper are presented data on the high pressure structural response of andalusite to 37 kbar, as well as correlations between high-pressure changes and hightemperature response, elasticity, and phonon spectra. It has been possible to observe directly the structural elements of andalusite that are responsible for the compressibility and, hence, the elastic constants. The present data on andalusite at high-pressure, combined with high-temperature data of Winter and Ghose (1979), may be used to test the inverse relationship betwedn structural responses due to temperature versus pressure (Hazen and Finger, 1982). Andalusite is a light-atom structure with a small unit-cell and orthorhombic symmetry and thus also constitutes a test case for the improvement in accuracy of Xray intensity data collected at high pressure by the omega step-scanning technique. The resulting improvement in 514 RALPH ET AL.: ANDALUSITE AT HIGH PRESSURE the data resulted in a successful refinement of the anisotropic temperature factors in a complicated silicate structure at high pressure.
TL;DR: The cubane form of the bromide was discovered during high-resolution solid-state 31P NMR spectral studies on a series of cuprous halide-triphenylphosphine complexes as discussed by the authors.
Abstract: Crystal structure analysis of the tetrameric 1:l adduct of PPh3 with CuBr, [CuBrPPhpl4, recrystallized from refluxing toluene, shows that it has crystallized in a 'cubane" rather than the previously recorded "step" form. A residual of 0.044 was obtained for 3708 independent observed diffractometer reflections recorded at 295 K after full-matrix least-squares refinement; crystals are isomorphous with the chloride, with an orthorhombic Pbcn cell, a = 17.662 ( 5 ) A, b = 20.748 (7) A, c = 18.351 (6) A, and Z(tetramer) = 4. The existence of the cubane form of the bromide was discovered during high-resolution solid-state 31P NMR spectral studies on a series of cuprous halide-triphenylphosphine complexes.
TL;DR: In this article, a tetragonal and an orthorhombic modification of CH2Cl2-toluene were determined to have a centred crown skeletal geometry.
Abstract: [Au9{P(C6H4OMe-p)3}8](NO3)3crystallizes from CH2Cl2–toluene in two crystalline modifications one tetragonal and the other orthorhombic; single crystal X-ray crystallographic determinations on the two modifications have demonstrated that the tetragonal modification has a skeletal geometry derived from an icosahedron and the orthorhombic modification a centred crown skeletal geometry.
TL;DR: The crystal structures of the title compounds, Cu(SCN)L, L = 2-methylpyridme (l),2,6-dimethylpyridine (2), and Cu( SCN)b, L= 2-, 3-, and 4-methyl pyridine, respectively, have been established by single-crystal X-ray diffraction at 295 K and refined by full-matrix least squares to residuals of 0.026, 0.058, and 0.048,0.
Abstract: The crystal structures of the title compounds, Cu(SCN)L, L = 2-methylpyridme (l),2 ,6-dimethylpyridine (2), and Cu(SCN)b, L = 2-, 3-, and 4-methylpyridine (3-5, respectively), 2,4-dimethylpyridine (6), quinoline (7), have been established by single-crystal X-ray diffraction at 295 K and refined by full-matrix least squares to residuals of 0.026,0.039,0.048,0.032, 0.054,0.058, and 0.029 for 1164, 1339, 1499, 1731, 903, 1748 and 468 independent "observed" reflections, respectively. Crystals of 1 are triclinic, PI, with a = 9.452 (3) A, b = 8.077 (3) A, c = 5.779 (1) A, a = 104.33 (2)O, @ = 96.64 (2)O, y = 100.83 (3)O, and 2 = 2; the structure is a polymer consisting of pairs of CuL(SCN)CuL(SCN) strands linked by centrosymmetric four-membered Cu2S2a nd eight-membered CU(SCN)~CrUin gs. Crystals of 2 are monoclinic, P2,/c, with a = 7.721 (2) A, b = 7.753 (2) A, c = 16.1 13 (4) A, @ = 90.67 (2)O, and 2 = 4; the structure is a single-stranded polymer-CuL(SCN)CuL(SCN). Crystals of 3 are orthorhombic, Fdd2, with a = 43.68 (1) A, b = 16.402 (4) A, c = 8.064 (3) A, and 2 = 16. Crystals of 4 are monoclinic, P2]/n, with a = 17.68 (1) A, b = 5.874 (4) A, c = 14.367 (8) A, @ = 112.91 (4)O, and 2 = 4. Crystals of 5 are monoclinic, El, with a = 14.59 (2) A, b = 5.823 (6) A, c = 8.953 (10) A, @ = 106.44 (lo)', and 2 = 2. Crystals of 6 are monoclinic, P21/c, with a = 28.93 (3) A, b = 5.867 (4) A, c = 20.19 (3) A, @ = 112.70 ( 8 ) O , and 2 = 8. Crystals of 7 are orthorhombic,P 212121wr ith a = 16.219 (4) A, b = 12.838 (3) A, c = 8.032 (2) A, and 2 = 4. In spite of the diverse crystal symmetries found for 3-7, all contain single-stranded CuL2(SCN)CuLz(SCN)CuLpzo lymers, with different conformational types. All complexes were synthesized by reaction of copper(1) thiocyanate with the parent base, with or without the presence of acetonitrile as solvent.
TL;DR: The dihydrate of ammonia has been isolated for the first time as discussed by the authors, and its x-ray powder diffraction pattern can be indexed on a cubic unit cell a=7.118 A with a 95% confidence limit of 0.015 A at ∼105 K, and Z=4.1 A or longer.
Abstract: The dihydrate of ammonia has been isolated for the first time. Its x‐ray powder diffraction pattern can be indexed on a cubic unit cell a=7.118 A with a 95% confidence limit of 0.015 A at ∼105 K, and Z=4. The number of diffraction lines, neglect of the hydrogen atoms, and the assumption that the atoms are on sites of multiplicity 4 or 8 yield P213 or P4232 as possible space groups. The infrared spectra suggest O–H‐‐O distances of ∼2.76 A, short O–H‐‐N distances of 2.74±0.02 A, and N–H‐‐‐O distances of 3.1 A or longer. A structure which fits these bond lengths well has been found in P213, with the oxygen and nitrogen atoms all on the 4a sites, of site group C3, with x=0.141 and 0.7111 for the oxygen atoms and x=0.3635 for nitrogen. The infrared spectra also show ν3(NH3) as a triplet, which means that the correct structure, including the hydrogen atoms, must have a lower symmetry than cubic, probably the orthorhombic P212121. That the crystal cannot be cubic is also seen from consideration of the apparent s...
TL;DR: The crystal structure of ferrierite (Nao.2Ko.sCao.sMg2)Al7Si290n 18H20 was reexamined using X-ray diffractometer data.
Abstract: The crystal structure of ferrierite (Nao.2Ko.sCao.sMg2)Al7Si290n 18H20 was reexamined using X-ray diffractometer data. This refinement confirmedthe orthorhombic structure of Vaughan. According to electron diffraction analyses of ferrierites from three localities most crystals show no deviation from the Immm structure. However, several diffraction patterns werefound to exhibit streaking parallel to (010)* and (110)*. Models of conservativeand non-conservative faults were derived which could account for these diffraction patterns.
TL;DR: In this paper, X-ray crystal structure analysis of Na[Cr(1,3-PDTA)]·3H2O and (-)DNa[Rh(1 3 -PDTA)·3 H2O was performed, and the structures were determined on the basis of 1699 and 2928 diffractometer data points.
TL;DR: In this paper, the synthesis and characterisation of the macrocycle 1,7-dimethyl-1,4,7,10-tetra-azacyclododecane (L1) are reported.
Abstract: The synthesis and characterisation of the macrocycle 1,7-dimethyl-1,4,7,10-tetra-azacyclododecane (L1) are reported. The basicity constants of L1 and the stability constant of the complex [CuL1]2+ have been determined by potentiometry at 25 °C in 0.5 mol dm–3 KNO3. The macrocycle L1 behaves as a diprotic base in the pH range investigated; pD–13C n.m.r. studies indicate that only the two secondary nitrogens are involved in the protonation process. Copper(II) and nickel(II) complexes with L1 have been prepared and studied spectrophotometrically both in aqueous solution and in the solid state. The reflectance spectrum of dry yellow NiL1(ClO4)2 shows that a square-planar geometry, with the nickel(II) in the low-spin state, is achievable also with this partially methylated twelve-macrocycle. The molecular structure of the complex [NiBr(H2O)L1]Br has been determined by single-crystal X-ray analysis. The compound crystallises in an orthorhombic unit cell (space group P212121) with lattice constants a= 13.478(5), b= 11.186(4), and c= 10.585(4)A for Z= 4. Least-squares refinement converged at R= 0.046 for 910 observed reflections. The complex shows a cis-octahedral geometry, with the macrocycle co-ordinated in a folded configuration to four sites around the central nickel atom. The chirality of each nitrogen atom of the macrocycle is the same. The bromide ion and the oxygen atom of the water molecule are cis to each other. The chelate rings are all asymmetric.
TL;DR: In this article, a hexagonal/orthorhombic transformation was observed in partially Si-substituted Fe2P and the transformation temperature dependence was shown to increase linearly with increasing P Si substitution.
TL;DR: In this paper, high pressure x-ray diffraction study at room temperature has revealed a narrow gap semiconductor PbTe undergoes a new phase transition from the orthorhombic GeS-type to the cubic CsC1-type structures at 16 ± 1 GPa on compression, in addition to the previously known NaCl-to-GeS one at 4.5 GPa.
TL;DR: Electron diffraction measurements on epitaxially grown crystals of orthorhombic n-hexatriacontane, n-C(36)H(74), give evidence for the chain-defect mechanism for linear chain melting.
Abstract: Electron diffraction measurements on epitaxially grown crystals of orthorhombic n-hexatriacontane, n-C36H74, give evidence for the chain-defect mechanism for linear chain melting. The derived structural model is also in accord with recent spectroscopic studies of odd-chain n-alkanes, and the diffraction data specifically exclude models based on helices or rigid chain rotors. Stability of a kinked chain structure, moreover, is indicated by an observed hysteresis effect that gives different pretransition temperatures for solution-grown and annealed crystals.
TL;DR: In this article, the structural details for Y 2 Ni 3 Si 5 have been determined and the structure was refined to wR = 0.074 for 422 independent reflections, which can be interpreted as an intergrowth of two kinds of structural slabs, one related to the CaBe 2 Ge 2 structure and the other is related to BaNiSn 3 structure.
Abstract: The following structural details were determined for Y 2 Ni 3 Si 5 : M r = 494.37 (orthorhombic); space group, Ibam ; a = 9.5651(4) A ; b = 11.1284(6) A ; c = 5.6453(2) A ; V= 600.91(8) A 3 ; Z = 4; D x = 5.465 Mg m −3 ; Mo Kα, λ = 0.71069 A ; μ (Mo Kα ) = 29.8 mm −1 ; F (000) = 928; T = 293 K . The structure was refined to wR = 0.074 for 422 independent reflections. Ce 2 Co 3 Si 5 , Ce 2 Ni 3 Si 5 and Dy 2 Ni 3 Si 5 have the same crystal structure which is known as the U 2 Co 3 Si 5 type. This structure type can be interpreted as an intergrowth of two kinds of structural slabs, one of which is related to the CaBe 2 Ge 2 structure and the other is related to the BaNiSn 3 structure. The U 2 Co 3 Si 5 and the Sc 2 Fe 3 Si 5 structure types are different stacking variants of identical structural columns.
TL;DR: The phase transition temperatures of rare earth aluminates have been determined by high temperature X-ray diffractometry as discussed by the authors, showing that the phase transitions are reversible and occur for Rh ⇌ C at 500°C (LaAlO 3 ), 1330°C(PrAlO3 ), 1550°c (NdAlO 2 ), and 1950°c(SmAlO 4 ).
TL;DR: In this article, the authors have shown that the distortion from an exactly symmetric conformation being in a direction which increases the separation between the titanium atom and the carbon atom carrying the t-butyl substituent group.
TL;DR: In this paper, the electrical resistivity of black phosphorus has been measured under high pressure and two anomalies are observed at 42 and 108 kbar, associated with the transition from the orthorhombic to the rhombohedral phase and from the rhombhedral to the simple cubic phase, respectively.
Abstract: The electrical resistivity of black phosphorus has been measured under high pressure. Two anomalies are observed at 42 and 108 kbar, associated with the transition from the orthorhombic to the rhombohedral phase and from the rhombohedral to the simple cubic phase, respectively. The former occurs in the vicinity of the vanishing of the energy gap of the orthorhombic phase. The simple cubic phase has a clear positive temperature coefficient of resistivity, but the absolute value of the resistivity is higher than those of usual metals. A preliminary experiment under very high pressure using "sintered-diamond" anvils has shown a sign of a phase transition from the simple cubic phase to a new phase at 0.8–1 Mbar.
TL;DR: In this article, two distinctly different morphologies were characterized using Laue X-ray diffraction methods and an optical trace analysis, both involving a stereographic projection description Microindentation experiments were performed on different prominent growth surfaces of several selected laboratory-grown crystals having the conventional morphology type.
Abstract: RDX (cyclotrimethylenetrinitramine) explosive crystals, typically approaching 5 mm in size, were grown by evaporation from acetone solution using production-grade crystals as starting material Two distinctly different morphologies resulted, including one that apparently has not been previously reported in other investigations These morphologies were characterized using Laue X-ray diffraction methods and an optical trace analysis, both involving a stereographic projection description Microindentation experiments were performed on different prominent growth surfaces of several selected laboratorygrown crystals having the conventional morphology type The hardness results are compared with measurements made directly on several production-grade crystals having a different morphology, and are compared with preceding measurements on a crystal having the previously unreported morphology The latter crystal exhibited highly localized plastic deformation at the indentations as revealed by dislocation etch-pitting Observations are made regarding the dislocation structure and cleavage properties of RDX based on its orthorhombic unit cell
TL;DR: In this paper, it was revealed that the unknown phase is another polymorph of Mg 2 Ni hydride which is easily transformed into the low temperature form by grinding the powder in a mortar at room temperature.
Abstract: The high temperature form of Mg 2 Ni hydride has an f.c.c. lattice with the metal atoms occupying antifluorite positions. It transforms to the low temperature form at 235°C. In earlier work the structure of the low temperature form was determined from its X-ray powder diffraction data. It can be described as a monoclinic distortion of the high temperature cubic lattice. However, the low temperature phase is usually contaminated with a small amount of an unknown phase which shows a similar powder pattern to the high temperature form. In the present investigation it was revealed that this unknown phase is another polymorph of Mg 2 Ni hydride which is easily transformed into the low temperature form by grinding the powder in a mortar at room temperature. This intermediate phase was found to be stabilized by substituting cobalt for 10 wt.% Ni. This structure can also be described as a distortion of the high temperature cubic lattice and the main peaks were indexed with an orthorhombic cell with a = 6.572 A , b = 4.520 A and c = 4.560 A . However, the presence of several weak peaks indicates that longer-range ordering exists and that the true unit cell is larger than this.
TL;DR: In this paper, the molecular structure of a new monoclinic modification of the PMe2Ph derivative has been determined: space group P21/n with a = 19.698(4), b = 10.9440(20), and c = 21.360(6) A.
TL;DR: The crystal and molecular structures of cis- and trans-phenyltellurium(IV) tri-iodide and two polymorphs of diphenyl tellurium (IV) diiodide have been determined from diffractometer data as mentioned in this paper.
Abstract: The crystal and molecular structures of cis- and trans-phenyltellurium(IV) tri-iodide and two polymorphs of diphenyltellurium(IV) di-iodide have been determined from diffractometer data : cis-(PhTeI3)2, orthorhombic, space group Cmc21, a= 19.915(5), b= 12.617(2), c= 8.867(2)A, Z= 4, 1 267 reflections, R= 0.044; trans-(PhTeI3)2, orthorhombic, space group Pnnm, a= 8.911 (2), b= 11.559(2), c= 13.506(2)A, Z= 2, 1 201 reflections, R= 0.048; α-Ph2TeI2, tetragonal, space group I41, a= 11.684(3), c= 10.196(2)A, Z= 4, 575 reflections, R= 0.030; and β-Ph2TeI2, monoclinic, P21/c, a= 9.722(1), b= 15.627(2), c= 19.338(7)A, β= 107.08(2), Z= 8, 3 303 reflections, R= 0.034. Both tri-iodides form iodine-bridged dimers with square-based pyramidal geometry at the tellurium. The phenyl rings are both on one side of this plane (cis), or on opposite sides (trans). No Te ⋯ I secondary bonds occur but they contain I ⋯ I interactions. Both polymorphs of the di-iodide have pseudo-trigonal bipyramidal geometry (with one vacant position), and have either one or two Te ⋯ I secondary bonds occupying the fifth and sixth positions of distorted octahedra. Te–I distances are: 2.775(2)–2.792(2) and 3.152(2)–3.285(1)A(tri-iodide, terminal and bridge, respectively); 2.883(1)–2.959(1)A(di-iodide).
TL;DR: The new compound Ca₃AlSb ₃ crystallizes in the orthorhombic system (space group Pnma (No. 62)) with lattice constantsa = 1283.5(5) pm, b = 448.9(2) pm, c = 1428.2(3) pm as discussed by the authors.
Abstract: The new compound Ca₃AlSb₃ crystallizes in the orthorhombic system (space group Pnma (No. 62)) with lattice constantsa = 1283.5(5) pm, b = 448.9(2) pm , c = 1428.2(5) pmIn the structure there are AlSb₄ tetrahedra connected by common corners to form chains. The new compound Ca₅Al₂Bi₆ crystallizes in the orthorhombic system, too (space group Pbam (No. 55)) with lattice constantsa = 2333.3(8) pm, b = 758.2(3) pm, c = 452.9(2) pmAlBi₄ tetrahedra are connected by common corners and Bi₂ groups to form double chains. Both compounds are classified as Zintl phases.