Crystal structure of bis(benzyltriethylammonium) hexachlorotellurate(IV), [C7H7(C2H5)(3)N](2)(TeCI6)

C26H44Cl6N2Te, monoclinic, P12(1)/n1 (no. 14), a = 9.3981(5) Angstrom, b = 14.606(1) Angstrom, c = 12.4524(7) Angstrom, beta = 108.335(5)degrees, V = 1622.6 Angstrom(3), Z = 2, R-gt(F) = 0.024, wR(ref)(F-2) = 0.065, T = 293 K.

Crystal structure of potassium trifluoro(2-methyl-1,3-dithiano)borate, K(C5H9BF3S2)

C5H9BF3KS2, triclinic, P (1) over bar (no. 2), a = 11.9238(5) angstrom, b = 13.6060(5) angstrom, c = 14.0280(3) angstrom, alpha = 114.995(2)degrees, beta = 92.035(2)degrees, gamma = 92.390(2)degrees, V = 2057.4 angstrom(3), Z = 8, R-gt(F) = 0.049, wR(ref)(F-2) = 0.117, T = 296 K.

Crystal structure of a lectin from Canavalia maritima (ConM) in complex with trehalose and maltose reveals relevant. mutation in ConA-like lectins

The crystal structure of Canavalia maritima lectin (ConM) complexed with trehalose and maltose revealed relevant point mutations in ConA-like lectins. ConM with the disaccharides and other ConA-like lectins complexed with carbohydrates demonstrated significant differences in the position of H-bonds. The main difference in the ConM structure is the replacement of Pro202 by Ser202, a residue that promotes the approximation of Tyr12 to the carbohydrate-binding site. The O-6' of the second glucose ring in maltose interacts with Tyr12, while in trehalose the interaction is established by the O-2' and Tyr12, explaining the higher affinity of ConM for disaccharides compared to monosaccharides. (c) 2006 Elsevier B.V. All rights reserved.

Crystal structure of 1,1,3-trimethyl-2-(2-(2,2,6-trimethyl-cyclohexyl)ethyl) cyclohexane, C20H34

C20H34, monoclinic, P12(1)/n1 (no. 14), a = 10.647(l) angstrom, b = 6.6844(9) angstrom, c = 11.723(1) angstrom, beta = 99.75(1)degrees, V = 822.3 angstrom(3) Z = 2, R-gt(F) = 0.043, wR(ref)(F-2) = 0.110, T = 93 K.

Crystal structure of bis(acetylacetonato)-bis(3-methylpyridine)-nickel(II) dihydrate, Ni(C6H7N)(2)(C5H7O2)(2)center dot 2H(2)O

C22H32N2NiO6, triclinic, P (1) over bar (no. 2), a = 8.335(1) angstrom, b = 9.314(1) angstrom, c = 17.045(2) angstrom, alpha = 88.45(1)degrees, beta = 82.12(1)degrees, gamma = 70.296(9)degrees, V = 1233.7 angstrom(3), Z = 2, R-gt(F) = 0.050, wR(ref)(F-2) = 0.177, T = 293 K.

Crystal structures and luminescence properties of La3Zr4F25 and alpha-LaZr3F15

During a study of the LaF3-ZrF4 system, both La3Zr4F25 and alpha-LaZr3F15 compounds have been evidenced. Their crystal structures have been determined from single-crystal X-ray diffraction data. La3Zr4F25 crystallises in the cubic system with a= 12.384 Angstrom and I (4) over bar 3d space group (no. 220). Its crystal structure is built up of (ZrF6)(2-) octahedra and (LaF8)(5-) dodecahedra sharing corners. The low temperature form, alpha, of LaZr3F15 is orthorhombic (space group Pmmn, no. 59) with a = 15.721 Angstrom, b = 16.299 Angstrom, c= 8.438 Angstrom. Its structure is built of corner-sharing tricaped trigonal prisms surrounding the La3+ ions and both octahedra and monocapped trigonal prisms encompassing the Zr4+ ions. This structure is characterised by dynamically disordered (ZrF6)(2-) complex anions.The Eu3+ luminescence properties of these phases have been investigated and are discussed in relationship with their crystal structures.

Mixed pseudohalide complexes of copper(II). Crystal and molecular structure of [Cu(N-3)(NCS)(tmen)](n) and of [Cu(N-3)(NCO)(tmen)]2 (tmen = N,N,N ',N '-tetramethylethylenediamine)

The compounds [Cu(N-3)(NSC)(tmen)](n) (1), [Cu(N-3)(NCO)(tmen)](n) (2) and [Cu(N-3)(NCO)(tmen)](2) (3) (tmen = N,N,N',N'-tetramethylethylenediamine) were synthesized and studied by i.r. spectroscopy. Single crystals of compounds (1) and (3) were obtained and characterized by X-ray diffraction. The structure of compound (1) consists of neutral chains of copper(II) ions bridged by a single azido ligand showing the asymmetric end-to-end coordination fashion. Each copper ion is also surrounded by the other three nitrogen atoms: two from one N,N,N',N'-tetramethylethylenediamine and one from a terminal bonded thiocyanate group. Compound (2) decomposes slowly in acetone and the product formed [Cu(N-3)(NCO)(tmen)](2) (3) crystallizes in the monoclinic system (P2(1)). The structure of (3) consists of dimeric units in which the Cu atoms are penta-coordinated and connected by p(1,3) bridging azido and cyanate ligands. In both cases the five coordinated atoms give rise to a slightly distorted square-based pyramid coordination geometry at each copper ion. The thermal behavior of [Cu(N-3)(NSC)(tmen)](n) (1) and [Cu(N-3)(NCO)(tmen)](n) (2) were investigated and the final decomposition products were identified by X-ray powder diagrams.

Exchange and crystal field effects in the ESR spectra of Eu(2+) in LaB(6)

Electron spin resonance of Eu(2+) (4f(7), S=7/2) in a La hexaboride (LaB(6)) single crystal shows a single anisotropic Dysonian resonance. From the observed negative g shift of the resonance, it is inferred that the Eu(2+) ions are covalent exchange coupled to the B 2p-like host conduction electrons. From the anisotropy of the spectra (linewidth and field for resonance), we found that the S ground state of Eu(2+) ions experience a cubic crystal field of a negative fourth order crystal field parameter (CFP), b(4)=-11.5(2.0) Oe, in agreement with the negative fourth order CFP, A(4), found for the non-S ground state R hexaborides. These results support covalency as the dominant contribution to the fourth order CFP for the whole R hexaboride family.

Synthesis, crystal structure and theoretical studies of aryltellurenyl tetramethylthiourea(tmtu) iodine complexes: Ph-Te(tmtu)I (1) and beta-naphtyl-Te(tmtu)I (2)

(1) C11H17IN2STe, Mr = 463.83, P2(1)/n, a 7.6582(8), b = 13.8008(9), c = 15.026(3) angstrom, beta = 96.233(12)degrees, Z = 4, R-1 = 0.0318. (2) C15H19IN2STe, Mr = 513.88, P2(1)/n, a = 8.434(5), b = 11.697(5), c = 18.472(5) angstrom, beta = 98.556(5)degrees, Z = 4, R-1 = 0.0236. The synthesis of the aryltellurenyl N,N',-tetramethylthiourea (tmtu) iodide has been performed by ligand exchange with potassium iodide and the corresponding aryltellurenyl(tmtu) bromide. In both structures the tellurium atom is primarily three-coordinated, being bonded to a carbon atom of the organic ring and, in directions nearly perpendicular to the Te-C bond, to one tmtu sulfur atom and one iodine. In addition there are Te...secondary bonds, joining the molecules in centrosymmetric dimers, which in turn are joined through C-H...1 and C-H... S interactions, in (1) and (2), respectively.

Effect of niobia on the crystal structure and dielectric characteristics of Pb(Zr0.45Ti0.55)O-3 prepared from polymeric precursor

The influence of niobia addition on the phase formation and dielectric properties of Pb(Zr0.45Ti0.55)O-3 powder prepared from polymeric precursor was analyzed. The weight fraction and unit-cell volume of the tetragonal phase decreased, and the mass fraction of the rhombohedral phase increased, with increasing niobia concentration. The rhombohedral unit-cell volume increased up to 5 mol% of added Nb and then decreased. Small amounts of pyrochlore and tetragonal zirconia phases were observed in PZT powder with more than 10 mol% Nb. These results were interpreted as an indication that the Nb ion was substituted for the zirconium ion in the tetragonal phase. For sintered PZT samples at 1100 degrees C, no free-zirconia phase was observed. The dielectric constant increased with the niobia addition up to 5 mol% and decreased for higher concentrations. The Curie temperature decreased with niobia addition up to 10 mol% before the formation of pyrochlore phase. (C) 2000 Elsevier B.V. Ltd. All rights reserved.

Simulation of electron density maps for two-dimensional crystal structures using Mathematica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Vibrational spectroscopy of the seselin crystal

Seselin, C14H12O3, is a coumarin which crystallizes in a monoclinic structure P2(1)/b(C-2h(5)) with four molecules per unit cell. In a Fourier-transform Raman spectroscopic study performed at room temperature, several normal modes were observed. Vibrational wavenumber and wave vector calculations using density functional theory were compared with experiment, which allowed the assignment of a number of normal modes of the crystal. Temperature-dependent Raman spectra were recorded between 10 and 300 K. No anomalies were observed in the phonon spectra, indicating that the monoclinic structure remains stable. Copyright (c) 2007 John Wiley & Sons, Ltd.