Band 219, Heft 10

Within the Li-clinopyroxene series LiMe 3+ Si 2 O 6 , a temperature induced C 2/ c → P 2 1 / c phase transition has been observed for Me = Cr, Ga, V, and Sc at temperatures of 330(1), 286(1), 205(3) and 234(1) K, respectively. There is no phase transition for the Al 3+ and the pure In 3+ compound down to 80 K. Within the LiSc 1– x In x Si 2 O 6 solid solution se ries, the transition temperature rapidly decreases with increasing In 3+ content and drops below 90 K between x = 0.26 and 0.30. The C → P phase transition is found only in samples with nearly fully extended tetrahedral chains. The phase transition in LiScSi 2 O 6 , with its “O-rotated” and distinctly more kinked tetrahedral chains in C 2 /c (O3—O3—O3 angle = 175.7(1)° at 298 K), exhibits a different character: the decay of the b -type Bragg reflections hkl : h + k ≠ 2 n and the structural changes in the vicinity of the phase transition are less rapid. The temperature dependent evolution of the order parameter Q 2 (as expressed by the decay of the b -type Bragg reflections) suggests a second order thermodynamic character of the C → P phase transition in the Sc 3+ compound, whereas it is close to a tri-critical behaviour in the other ones. The structural changes, taking place at the phase transition and below are similar to those in LiFeSi 2 O 6 , i.e. dislinkage and appearance of two differently kinked tetrahedral chains in P 2 1 / c , decrease of the coordination number of Li + from 6 to 5, slight alterations of octahedral bond lengths. The structural changes at the phase transition are of similar magnitude in the Ga, Cr, V and Fe compound. LiScSi 2 O 6 is again exceptional. Different thermal expansion of octahedral and tetrahedral sites and increasing site distortion of the M1 site as a consequence of tetrahedral chain kinking in C 2/ c are assumed to be factors inducing the C 2/ c → P 2 1 / c phase transition.

The evolution was studied of structural order/disorder phenomena across the wide stability field of the decagonal phase in the system Al—Co—Ni. Full single-crystal X-ray diffraction data sets were collected of 31 samples annealed at 900 °C. Based on reciprocal space reconstructions of the imaging-plate-scanner data, the variation in Bragg as well as in diffuse scattering is discussed in detail. The samples were also characterized metallographically, by powder X-ray diffraction, differential thermal analysis and energy-dispersive X-ray spectroscopy. The (quasi)lattice parameters vary smoothly over the stability range of decagonal Al 71.5 Co 28.5— x Ni x (8 ≤ x ≤ 20). A smooth variation is also observed for the diffuse scattering related to the ≈8 Å superstructure. These observations indicate a continuous ordering process at 900 °C from the basic Co-rich phase via the type II and type I superstructures to the basic Ni-rich phase.

Based on the latest available crystal data and the reported bond valence parameters, the linear correlation between the bond valence parameter R 0 with B = 0.37 Å for M—O bonds (M = V, Fe and Cu) and the metal oxidation state n is shown for the first time. For V—O bonds, a linear equation of R 0 ∼ n is perfectly established as R 0 = 0.0250 n + 1.674 ( n = 2–5). Similarly, a linear equation for Fe—O bonds is fitted as R 0 = 0.0335 n + 1.648 ( n = 2–4), as well as R 0 = 0.0855 n + 1.482 ( n = 1–3) for Cu—O bonds fitted properly. In addition, the linear correlation between R 0 and n within certain range of B values for V—O and Fe—O bonds is also established. Consequently, the oxidation-state independent parameters ( R 0 , B ) of (1.788, 0.32 Å) for V—O bonds and (1.795, 0.30 Å) for Fe—O bonds can be derived from the zero slope of the R 0 ∼ n straight lines. However, a similar parameter pair for Cu—O bonds cannot be found using this unique approach.

Single crystals of the mixed-valent compounds Hg 7 Se 3 O 13 H 2 ( I ) and Hg 8 Se 4 O 17 H 2 ( II ) were grown under hydrothermal conditions. The crystal structures were solved and refined from single crystal X-ray data collected at room temperature ( I : R 3, Z = 3, a = 5.9239(3), c = 37.096(3) Å, 1465 structure factors, 60 parameters, R [ F 2 > 2 σ ( F 2 )] = 0.0383, wR ( F 2 all) = 0.0970, Goof = 1.047; II : P 31 c, Z = 2, a = 5.8908(6), c = 31.048(3) Å, 1889 structure factors, 69 parameters, R [ F 2 > 2 σ ( F 2 )] = 0.0662, wR ( F 2 all) = 0.1626, Goof = 1.088). Both compounds show a multifarious crystal chemistry and contain triangular Hg 3 4+ cluster cations, Hg 2 2+ dumbbells, Hg 2+ cations, HgO 2 2– mercurate groups, and trigonal-pyramidal SeO 3 2– as well as tetrahedral SeO 4 2– anions and water molecules as simple building units. The description in terms of crystal chemistry leads to the more detailed formulae (Hg IV/3 3 ) (Hg I 2 )(Hg II )(Hg II O 2 )(Se IV O 3 ) 2 (Se VI O 4 )(H 2 O) for I and (Hg IV/3 3 )(Hg I 2 )(Hg II ) 2 (Hg II O 2 )(Se IV O 3 ) 2 (Se VI O 4 ) 2 (H 2 O) for II , respectively. Characteristic features of the closely related structures are building blocks formed by parallel layers of Hg 3 4+ triangles, layers of disordered Hg 2 2+ dumbbells, layers of SeO 4 2– and HgO 2 2– groups, and layers of SeO 3 2– groups which are all stacked along [001]. The layers are linked into a complex three-dimensional framework via common O atoms and H 2 O molecules. In comparison with Hg 7 Se 3 O 13 H 2 , the structure of Hg 8 Se 4 O 17 H 2 contains an additional and disordered HgSeO 4 layer which leads to a significant distortion of parts of the resulting structure.

The Hartman-Perdok theory was used to explain the relation between crystal structure and crystal morphology for Ca 2 AlSi 2 O 7 . Theoretical growth forms were constructed from the calculated attachment energies E hkl a , which are assumed to be directly proportional to the growth rate for F faces. F forms calculated, are {110} {101}, {111}, {021}, {120}, {001}, {100} and {130}. The theoretical growth forms are simulated for different values of the charges (normal and Matsui charges).

Clathrasils are porous framework silicates with cage-like voids. Structural similarities between the clathrasils DOH , MTN , MEP , DD3H and DDR have been analyzed in the context of host/guest interaction and crystallization mechanism. A building unit consisting of 30 T atoms is used as common structural feature to give an alternative description of the well-known layers of [5 12 ]-cages. The [5 12 ]-layers, or Periodic Building Units (PerBU’s), are constructed from two 12-rings connected through a common 6-ring to form two half cages or a 12-ring double cup. These ‘half-cages’ are essentially the bottom of the large ‘inter-layer’ cages in the clathrasils. The rigorous derivation of all possible framework types and their cages based on these principles shows the richness of the concept and makes possible new strategies for the synthesis. The ‘half-cages’ are also possible candidates for precursors which might exist in solution in close contact with templating guest species initiating the nucleation of the crystals.

Single crystals of the title compounds having optical quality and dimensions up to 60 mm have been grown from aqueous solutions. X-ray crystal structure analyses of K 2 H[N(CH 2 COO) 3 ] · H 2 O (I), K 2 H[N(CH 2 COO) 3 ] · 2 H 2 O (II), and Cs 2 H[N(CH 2 COO) 3 ] · H 2 O (III) has been done. Thermal expansion, elastic and thermoelastic properties of the title compounds have been measured employing mechanical and optical dilatometers and ultrasonic resonance techniques, respectively. They possess quite different structural motifs contrary to most other salts having a common anion. An anomalous large molecular volume and a small mean elastic stiffness of K 2 H[N(CH 2 COO) 3 ] · 2 H 2 O is qualitatively interpreted by the small number of Coulomb interactions between the single charged cations and oxygen atoms of the anions. Differences in thermal and elastic properties of corresponding alkali nitrilotriacetates and alkali salts of other large anions are discussed.

C 13 H 16 Cl 2 Te, M r = 370.76, P 2 1 / a , a = 8.1833(8), b = 8.4163(8), c = 20.787(2) Å, β = 99.52(1)°, Z = 4, R 1 = 0,0275. The primary coordination around the Te IV atom is consistent with a pseudo-trigonal bipyramidal bond configuration with two Cl atoms occupying axial positions while the C atoms and the lone pair of electrons occupy the equatorial positions. The Te IV atom is involved in an intermolecular secondary interaction resulting in the self assembly of zigzag-chains supramolecular array. In order to determine the theoretical basis set for the Te atom which leads to the best agreement with the experimental data, a large series of geometry optimizations were performed on dichloro dimethyl Te(IV), as a model compound, and the results compared with the mean distances and angles obtained from 45 X-ray structures. The Ahlrichs basis set plus the Hay & Wadt ECP was selected and used for a series of calculations performed on the title compound.

(±)-1-oxoferruginol and (±)-shonanol, two potential intermediates in the synthesis of tricyclic diterpenoid ferruginol, have been prepared and crystal structures of the compounds have been investigated using single-crystal X-ray diffraction data. The methyl groups of the isopropyl moiety in (±)-shonanol are disordered over two positions with occupation factors 0.65(1) and 0.35(1), respectively. Although the chemical structures of two compounds are very similar, a C—C single bond in the terminal six-membered ring of (±)-1-oxoferruginol is replaced by a C=C bond in (±)-shonanol, the quantitative isostructurality index calculations indicate that the structures are not isostructural. Intermolecular O—H…O hydrogen bonds between pairs of molecules in the compounds related by center of inversion lead to characteristic dimers forming R 2 2 (16) rings. The molecular conformation of (±)-1-oxoferruginol obtained from the semi-empirical quantum mechanical AM1 calculation shows good agreement with the X-ray structures.

The molecular structure of dimeric {[S 2 P(OiPr) 2 ](PPh 3 )} 2 · 2 CHCl 3 is built up about a centrosymmetric eight-membered ring that adopts a chair conformation as a result of bidentate bridging dithiophos phate ligands. The silver atom is in a trigonal planar geometry. Relatively close transannular Ag…S interactions are noted which, if considered significant, leads to a tridentate dithiophosphate ligand and a distorted tetrahedral geometry for silver. The presence of two PPh 3 molecules in the coordination sphere of silver in monomeric Ag[S 2 P(OiPr) 2 ](PPh 3 ) 2 · 3 CHCl 3 as well as a bidentate di thiophosphate ligand gives rise to a tetrahedral geometry. Adducts with lower or greater numbers of PPh 3 ligands could not be obtained pointing to the inherent stability of the characterised structures.

1,1,2,2-Tetrachloroethane, C 2 H 2 Cl 4 (denoted TCE, m.p. 230 K) has been in-situ pressure crystallized in a Merrill-Bassett diamond-anvil cell, and its structure has been determined at 0.5 GPa and 295 K from the single-crystal X-ray diffraction data. TCE crystallizes in the monoclinic space group P 2 1 /c with the molecules located at the inversion centers. The molecules are in the s-trans conformation, while they assume the gauche conformation in the crystal obtained by cooling. This implies that a phase transition may exist between the low-temperature and high-pressure phases of TCE. In the high-pressure phase the HC–CH moiety of the C 2 H 2 Cl 4 molecule is disordered in two sites, one related to the other by the non-crystallographic mirror plane approximately through the four Cl atoms of one molecule. The refined occupancy factors for the disordered sites are 0.77 and 0.23. The role played by the Cl…Cl intermolecular interactions for the disorder, and the phase transition between TCE phases built of s-trans (high-pressure) and gauche (low-temperature) molecules have been discussed.