Search results for "Octahedron"
showing 10 items of 405 documents
Complexes of Co(II) and Zn(II) with ofloxacin. Crystal structure of [Co(oflo)2(MeOH)2].4MeOH.
2002
Abstract Ofloxacin (oflo) is able to interact with Co(II) and Zn(II) salts to form complexes with the general formula [M(oflo) 2 ] · 4H 2 O, (M = Co, Zn). Bonding takes place through one of the oxygen atoms of the carboxylate group (acting as a monodentate) and the oxygen atom of the ketonic group. The IR bands of the carboxylic and ketonic group at 1713 and 1622 cm −1 , respectively, shift to 1615 and 1575 cm −1 in the complexes. After dissolution in methanol, complex [Co(oflo) 2 ] · 4H 2 O crystallizes as [Co(oflo) 2 (MeOH) 2 ] · 4MeOH, where Co(II) ion is in an octahedral environment of oxygen atoms. This compound crystallizes in the triclinic system, spatial group P‐1, with unit cell di…
Crystal structure of a novel bismuth phthalocyanine-bismuth iodide complex
1999
Abstract A new phthalocyaninato complex of bismuth with formula [(BiPc) 4 (Bi 4 I 16 )] was obtained in the reaction of bismuth with 1,2-dicyanobenzene in iodine vapour. The crystal and molecular structure of the complex was determined by single crystal X-ray diffraction. The unit cell consists of four discrete (BiPc) + cations and (Bi 4 I 16 ) 4− anions. The (Bi 4 I 16 ) 4− complex anion is formed by four edge-sharing BiI 6 octahedra. The arrangement of molecules in the crystalline structure of the complex is mainly determined by ionic attraction between the (BiPc) + and (Bi 4 I 16 ) 4− moieties, i.e. each (Bi 4 I 16 ) 4− complex anion is encapsulated between four (BiPc) + cations. The str…
Solid- and solution-state studies of the novel mu-dicyanamide-bridged dinuclear spin-crossover system {[(Fe(bztpen)]2[mu-N(CN)2]}(PF6)3 x n H2O.
2005
The mononuclear diamagnetic compound {Fe(bztpen)[N(CN)2]} (PF6)CH3OH (1) (bztpen = N-benzyl-N,N′,N′- tris(2-pyridylmethyl)ethylenediamine) has been synthesized and its crystal structure studied. Complex 1 can be considered to be the formal pre-cursor of two new dinuclear, dicyanamide-bridged iron(II) complexes with the generic formula {[(Fe(bztpen)]2[μN(CN)2]}(PF6) 3·nH2O (n = 1 (2) or 0 (3)), which have been characterized in the solid state and in solution. In all three complexes, the iron atoms have a distorted [FeN6] octahedral coordination defined by a bztpen ligand and a terminal (1) or a bridging dicyanamide ligand (2 and 3). In the solid state, 2 and 3 can be considered to be molecu …
Proton presence and motion in rhenium-oxide films and their application to liquid-crystalline cells
2007
Disordered solid phases, containing appreciable amounts of hydrogen ions, are grown at the surface of rhenium oxide crystals, because of the high reactivity of this compound with ambient moisture. To investigate such phenomena, a comparative study is performed on ground powder and thermally evaporated or sputtered films using x-ray diffraction and micro-Raman spectroscopy. Two types of solid phases were found in the films: HxReO3 distorted perovskite structures, based on corner-sharing ReO6 octahedra as in the bulk crystals, and ordered HReO4 crystalline structures, based on tetrahedral perrhenate ions. The complex impedance measurements on ReO3 films support the hypothesis of mobile hydrog…
Structural phase transitions on the nanoscale: The crucial pattern in the phase-change materialsGe2Sb2Te5and GeTe
2007
Phase-change materials are of immense importance for optical recording and computer memory, but the structure of the amorphous phases and the nature of the phase transition in the nanoscale bits pose continuing challenges. Massively parallel density functional simulations have been used to characterize the amorphous structure of the prototype materials ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ and GeTe. In both, there is long-ranged order among Te atoms and the crucial structural motif is a four-membered ring with alternating atoms of types $A$ (Ge and Sb) and $B$ (Te), an ``$ABAB$ square.'' The rapid amorphous-to-crystalline phase change is a reorientation of disordered $ABAB$ …
On structural phase transitions in the (C 5 H 12 N) 2 SbCl 5 crystals
2000
Abstract The results of the X-ray (at 295 and 355 K), dilatometric, differential scanning calorimetry and dielectric studies on a new piperidinium crystal, (C5H12N)2SbCl5, are presented. The anionic sublattice of the crystal is built up of infinite (SbCl52−)n chains composed of SbCl63− distorted octahedra connected with each other by corners. In voids of anionic sublattice two crystallographically independent piperidinium cations are located. At 295 K they are both in chair conformation. The compound undergoes three first-order phase transitions at 378.5 K (I→II), 339.5 K (II→III) and 205 K (III→IV). The mechanism of the (II→III) transition (Pna21→P212121) was proposed based on the X-ray da…
Mössbauer study of properties and phase transitions of Cd2Nb2–2xSn2xO7–2xF2x
1973
With the aid of Mossbauer spectroscopy the solid solution series Cd2Nb2–2xSn2xO7–2xF2x are investigated in the temperature range 4.2 to 400 K. The crystal structure belongs to the cubic pyrochlore type. The BY6 octahedra (B = Nb, Sn; Y = O, F) are linked three-dimensionally through their corners, forming groups of four octahedra which are extended or compressed in the (111)-direction for x ≤ 0.375 or x ≥ 0.400 respectively. The dependence of the quadrupole splitting ΔEQ on x shows a small but significant discontinuity in the region 0.375 < x < 0.400. This can be attributed to a first order phase-transition which depends on concentration, but not on temperature over the temperature region st…
Crystal Chemistry of CdIn2S4, MgIn2S4, and MnIn2S4 Thiospinels under High Pressure
2012
We report X-ray diffraction measurements in CdIn2S4, MgIn2S4, and MnIn2S4 thiospinels at room temperature and high pressures. The pressure dependences of the structural parameters have been determined and compared to those from theoretical calculations. It is found that the three thiospinels have similar bulk moduli (B-0) between 75 and 80 GPa (B-0' similar to 3). The degree of inversion of these thiospinels has also been determined. The three thiospinels undergo a phase transition toward a defect LiTiO2-type structure above 9.5, 8.3, and 6.8 GPa in CdIn2S4, MgIn2S4, and MnIn2S4, respectively. Interestingly, the low- and high-pressure phases belong to the same symmetry group (Fd-3m), the tr…
Structure Solution of the High-Pressure Phase of CuWO4 and Evolution of the Jahn–Teller Distortion
2011
In this work, we have investigated the structural behavior of cuproscheelite up to 33.9 GPa by means of high-pressure single-crystal X-ray diffraction (SXRD) and extended X-ray absorption fine structure (EXAFS). According to EXAFS, beyond 9 GPa a phase transition takes place. On the basis of SXRD, the transition is from the triclinic (P1) structure to a monoclinic (P2/c) structure isotypic to wolframite. The transition implies abrupt changes of CuO6 and WO6 octahedra, but no coordination change. Further, we report the role played by the Jahn–Teller distortion of the CuO6 octahedra on the mechanism of the phase transition as well as the changes in the behavior of the Cu–O bonds for the tricl…
Cation Environment of BaCeO3−Based Protonic Conductors II: New Computational Models
2011
Quantum chemical calculations have been carried out to simulate Y-doped BaCeO(3) derivatives. Hartree-Fock energy functional was used to study octahedral site environments embedded in a Pmcn orthorhombic framework, showing local arrangement characterized by Ce-O-Ce, Ce-O-Y, and Y-O-Y (Z-O-Ξ) configurations and including or not hydrogen close to the moieties encompassing those configurations. The latter are, in fact, representative of - and, in our modeling approach, were treated as - local arrangements that could be found in Y:BaCeO(3)-doped materials. The geometrical optimizations performed on the structural models and a detailed orbital analysis of these systems allowed us to confirm and …