Zeitschrift fur Kristallographie - Crystalline Materials
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VII. The crystal structure of pseudobrookite
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 73 Số 1-6 - Trang 97-112 - 1930
Crystal structure of bis[chloro-1<i>k</i>Cl-<i>μ</i>-hydroxo-<i>μ</i>-oxo-(tetraphenyl-1<i>K</i> <sup>2</sup>C,2<i>K</i> <sup>2</sup>C)ditin], [Cl(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>Sn(OH)OSn(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>]<sub>2</sub>
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 209 Số 7 - Trang 622-623 - 1994
Structural characteristics of cadmium(II) bis(<i>N</i>,<i>N</i>-dialkyldithiocarbamate) compounds Abstract
The crystal and molecular structures of four colorless Cd(S2 CNR2 )2 compounds have been determined. The crystals of Cd(S2 CNi Pr2 )2 , C14 H28 CdN2 S4 , (determined at 293 K) are monoclinic, space group P 21 /n with unit cell dimensions a = 11.611(5) Å, b = 11.228(9) Å, c = 16.767(2) Å, β = 108.90(2)°, Z = 4 and D
x = 1.494 Mg m−3 . Crystals of Cd(S2 CN(Et)Cy)2 , C18 H32 CdN2 S4 , (200 K) are monoclinic, space group P 21 /c with unit cell dimensions a = 8.541(4) Å, b = 19.688(8) Å, c = 13.847(3) Å, β = 94.29(3)°, Z = 4 and D
x = 1.479 Mg m−3 . Crystals of Cd(S2 CNCy2 )2 as a 1/1 CH2 Cl2 solvate, C27 H46 CdCl2 N2 S4 , (293 K) are triclinic, space group P [unk] with unit cell dimensions a = 13.557(7) Å, b = 14.49(2) Å, c = 9.604(2) Å, α = 100.70(6)°, β = 91.55(3)°, γ = 115.58(6)°, Z = 2 and D
x = 1.421 Mg m−3 . Crystals of Cd(S2 CNi Bu2 )2 , C18 H36 CdN2 S4 , (293 K) are monoclinic, space group C 2/c with unit cell dimensions a = 49.97(5) Å, b = 9.597(3) Å, c = 23.675(8) Å, β = 116.41(3)°, Z = 16 and D
x = 1.361 Mg m−3 . The structures were solved by direct methods and each refined by a full-matrix least-squares procedure to final R = 0.059 using 3485 reflections for Cd(S2 CNi Pr2 )2 ; to R = 0.055 using 2849 reflections for Cd(S2 CN(Et)Cy)2 ; to R = 0.079 using 3069 reflections for Cd(S2 CNCy2 )2 ; and to final R = 0.060 for 4851 reflections for Cd(S2 CNi Bu2 )2 . The Cd(S2 CNR2 )2 structures adopt a common dimeric motif in the solid state consistent with that observed for related systems. In the centrosymmetric dimeric unit, each cadmium atom is chelated by two dithiocarbamate ligands, one of which forms quite disparate Cd–S distances owing to a bridge formed to the second cadmium atom. The coordination geometries are distorted trigonal bipyramidal.
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 214 Số 10 - Trang 670-676 - 1999
Thermal conductivity of the Al-based quasicrystals and approximants Abstract
At high temperatures above 200 K, significant increase in thermal conductivity (κ ) was observed for the Al-based icosahedral quasicrystals and their corresponding approximants. By comparing the measured κ of the Al—Re—Si 1/1-cubic approximants with their electronic density of states at the Fermi level (ε
F ) determined by the low temperature specific heat measurements, we found that the increase in κ at high temperature was most pronounced when ε
F is located at the bottom of the pseudogap. This fact indicates that the large increase in κ is not brought about by the lattice but by the conduction electrons in associated with the narrow pseudogap at ε
F . It is also found that the behavior of κ at high temperature is well accounted for in terms of the bipolar diffusion effect of conduction electrons that is generally employed to analyze κ of the narrow-gap semiconductors and semimetals.
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 224 Số 1-2 - Trang 35-38 - 2009
The crystal structure of Benzoic Acid: a redetermination with X-rays at room temperature; a summary of neutron-diffraction work at temperatures down to 5 K Abstract
The crystal structure of benzoic acid, C6 H5 CO2 H, has been redetermined by X-ray diffraction at room temperature. Extensive neutron-diffraction measurements have also been made: by single-crystal methods at room temperature and 130 K; and, at 130 K and 5 K, by powder-profile analysis on C6 D5 CO2 H.
The structure consists of centrosymmetric dimers [formula (1)], in which two molecules are linked by a pair of hydrogen bonds between their carboxyl groups. Better precision attaches to the X-ray results. Full-matrix refinement, on 1011 independent reflexions, converged at R = 3.7%. This refinement was indeed based on a model that was formally ordered, so far as concerns all atoms except the acidic hydrogen. However the structural results implied an averaged molecule, with the C – O distances 1.258, 1.268(2) Å and the C – C – O angles 118.7, 117.8(1)°; and the acidic hydrogen appeared as two “half atoms” on the hydrogen bond, 0.9 Å from each oxygen atom. These findings are most simply interpreted as due to disorder: the two configurations, A and B (of Fig. 1), occur randomly and in nearly equal proportions.
Owing to difficulties inherent in the crystal texture of benzoic acid, the neutron results were less satisfactory. Large single crystals were affected by twinning. Though the powder method avoids this difficulty, the structure, further confused by modulation, is rather too complicated for profile refinement. At 5 K however, the structure may be ordered, consisting wholly of dimers in the A -configuration.
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 157 Số 3-4 - Trang 215-231 - 1981
The role of OH and H<sub>2</sub>O in oxide and oxysalt minerals Abstract
Hydrogen plays an extremely important role in the structure and chemistry of the oxide and oxysalt minerals. The characteristics of this role can be profitably analyzed in a simple and intuitive fashion using bond-valence theory. For any crystal structure, the structural unit may be defined as the strongly bonded part of the structure; structural units are linked together by interstitial species , usually alkali or alkaline earth cations and (H2 O)0 groups that are involved in much weaker bonding. This scheme gives a binary representation of even the most complex structure. The interaction between the structural unit and the interstitial species can be quantitatively evaluated using the valence-matching principle (Brown, 1981).
As components of the structural unit, (OH)− and (H2 O)0 play a major role in dictating the dimensional polymerization of the structural unit because of the very asymmetric nature of the donor-hydrogen and hydrogen…acceptor interactions. As an interstitial component, (H2 O)0 can play three different roles. Interstitial (H2 O)0 may bond to an interstitial cation, essentially forming a complex cation . In this role, (H2 O)0 acts as a bond-valence transformer, moderating the Lewis acidity of the interstitial cations such that it matches the Lewis basicity of the structural unit and the valence-matching principle is satisfied. Interstitial (H2 O)0 need not bond to an interstitial cation to occupy well-ordered atomic positions; a stable hydrogen-bonded network can occur in the interstitial regions between structural units. The role of such (H2 O)0 is to satisfy the bond-valence requirements of H atoms that are part of the structural unit, propagating the bonding across the interstitial space to other parts of the structural unit. Occluded (H2 O)0 may occur in some minerals. Such (H2 O)0 is not bonded to interstitial cations and does not participate in a static ordered hydrogen-bond network. However, this type of (H2 O)0 will still affect many of the physical properties of a mineral.
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 201 Số 3-4 - Trang 183-206 - 1992
The crystal structure of K<sub>2</sub>{Cu[TeO<sub>4</sub>(OH)<sub>2</sub>]} · H<sub>2</sub>O Abstract
K2 {Cu[TeO4 (OH)2 ]} · H2 O was synthesized under moderate hydrothermal conditions. The structure was solved from single crystal X-ray data; a = 9.589(2), b = 6.235(1), c = 12.014(3) Å, β = 90.44(2)°, space group Cc , wR (F ) = 0.038 for 2875 observed reflections with sin([unk]/λ < 0.90 Å−1 . CuO4 squares and TeO4 (OH)2 octahedra alternatingly share O–O edges to form chains in [110]. This part of the structure is pseudocentrosymmetric and shows in addition an approximate Cccm symmetry. The higher symmetry is violated by hydrogen bonds; refinements in C 2/c or Cccm resulted in large anisotropic displacement parameters or split positions for K and Ow atoms. The {Cu[TeO4 (OH)2 ]} chains are connected by potassium atoms and by hydrogen bonds of hydroxil groups (Oh …O = 2.643 and 2.650 Å) and water molecules (Ow …O = 2.782 and 2.955 Å), respectively.
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 205 Số 1 - Trang 41-53 - 1993
The Crystal Structure of TlSe, Thallous Thallic or Thallosic Selenide
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 101 Số 1-6 - Trang 396-405 - 1939
The crystal structure of the binary iridium-aluminum IrAl<sub>2.75</sub> and rhodium-aluminum RhAl<sub>2.63</sub> phase Abstract
The crystal structures of IrAl2.75 (“Ir2 Al5 ”) and RhAl2.63 (“Rh2 Al5 ”) phases have been studied with single crystal methods: space group P 23, IrAl2.75 , a = 7.674(1) Å, Z = 8, RF
= 0.053 (457 hkl , 29 parameters) and RhAl2.63 , a = 7.6692(1) Å, RF
= 0.042 (684 hkl , 29 parameters). The unit cell contains three transition metal sites and five aluminum sites. Most aluminum sites reveal strong defects in the occupations, some of them are described as being split. The overall number of atoms in the unit cell is 30(1) for IrAl2.75 and 29.0(3) for RhAl2.63 . Ordering and full occupation lead either to the AuZn3 (space group Pm [unk]n ) or to the hypothetical “Ir4 Al13 ” structure (space group Pm [unk]).
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 212 Số 6 - Trang 439-444 - 1997
The crystal structure of the ternary alloy <i>c</i>-Al<sub>68</sub>Pd<sub>20</sub>Ru<sub>12</sub> Abstract
The crystal structure of cubic Al68 Pd20 Ru12 was investigated by means of single crystal X-ray structure analysis: space group P 23 (No. 195), a = 15.540(2) Å, V = 3753(1) Å3 , Pearson symbol cP 296–46.85. The chemical composition was determined by microprobe analysis: Al68 Pd20 Ru12 , M
r = 6316, Z = 2, D
calc = 5.59 Mg m−3 ; MoKα
, refined as Al87 Pd38 , F (000) = 5758, μ = 9.89 mm−1 , R (wR ) = 0.056(0.052) for 1289 reflections with F > 3σ (F ) and 133 variables, goodness of fit S = 2.21. The structure contains 35 different orbits. Body centred pseudo symmetry is broken by the distribution of atoms, the non-centrosymmetric point symmetry 23 of this structure is close to m [unk] in space group Pn [unk]. Disorder of Al atoms is observed at a number of positions. Interatomic distances cover the ranges of 2.98 Å to 3.20 Å, 2.43 Å to 3.12 Å and 2.54 Å to 3.66 Å, for contacts TM–TM, Al–TM and Al–Al, respectively (TM: transition metal). The coordination shells contain triangular and/or quadrangular faces forming icosahedra, rhombic dodecahedra or respective combinations of these two basic forms. Links to cubic approximants of icosahedral phases are shown and relationships to neighboring crystalline and decagonal phases are discussed.
Zeitschrift fur Kristallographie - Crystalline Materials - Tập 211 Số 1 - Trang 17-24 - 1996
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