Search results for "X-ray crystallography"

Conformation of the galactose ring adopted in solution and in crystalline form as determined by experimental and DFT 1H NMR and single-crystal X-ray …

2003

The solution-state conformations of various galactose derivatives were determined by comparison of the experimental (1)H-(1)H vicinal coupling constants to those calculated using density functional theory (DFT) at the B3LYP/cc-pVTZ//B3LYP/6-31G(d,p) level of theory. The agreement between the experimental and calculated vicinal coupling constants for 1,2:3,4-di-O-isopropylidene-alpha-d-galactopyranose was good, thereby confirming an (O)S(2) skew conformation for it and its derivatives on the basis of their similar observed couplings. Single-crystal X-ray analysis of 1,2:3,4-di-O-isopropylidene-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-beta-d-glucopyranosyl)-alpha-d-galactopyranose and …

Effects of high-pressure on the structural, vibrational, and electronic properties of monazite-type PbCrO4

2012

We have performed an experimental study of the crystal structure, lattice dynamics, and optical properties of PbCrO 4 (the mineral crocoite) at ambient and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band gap have been accurately determined. X-ray-diffraction, Raman, and optical absorption experiments have allowed us also to completely characterize two pressure-induced structural phase transitions. The first transition is from a monoclinic structure to another monoclinic structure. It maintains the symmetry of the crystal but has important consequences in the physical properties; among others, a band-gap collapse is induced. The second one invo…

Preliminary studies on the synthesis of alkaline-free large crystals of ZSM-5

1988

Single crystals of ZSM-5 were synthesized in three systems containing Na + -TPA, Li + -TPA, and NH 4 + -TPA, respectively. Applying a reaction mixture of the molar composition 8 TPA + 123(NH 4 ) 2 O + Al 2 O 3 + 59 SiO 2 + 2280 H 2 O, alkaline-free, homogeneous, and pure single crystals of ZSM-5 were prepared up to a length of 350 μm. The crystal size and yield were found to be dependent on the water content of the starting reaction mixture and on the type of aluminium source; for example, boehmite and aluminiumtriisopropylate.

An improved goniometer head for high-temperature single-crystal X-ray diffraction

1999

A reliable and inexpensive goniometer head has been designed. Its stability, resulting from its compact construction, makes it very suitable for accurate measurements. Moreover, its space-saving design facilitates its application in X-ray data collection using charge-coupled device (CCD) detectors. This head has been improved for high-temperature measurements and has been tested by comparison of accurate K0.88Rb0.12TiOPO4data collected both at room temperature and at 973 K on the same crystal. The excellent structure results obtained at 973 K during the 360 h of measurements prove the stability of the goniometer head.

Synthesis and Electrochemistry of Aluminum Porphycenes. Crystal and Molecular Structure of Methyl-σ-Bonded Aluminum Etioporphycene

1997

The synthesis and characterization of three monomeric aluminum porphycenes with anionic or σ-bonded axial ligands is reported. The investigated compounds are represented as ( EtioPc ) Al ( CH 3) and ( EtioPc ) AlX where EtioPc represents the dianion of etioporphycene and X = Cl − or OH −. Each synthesized complex was characterized by mass spectrometry. 1 H NMR, IR and UV-visible spectroscopies as well as by electrochemistry. Comparisons are made between the properties of complexes in the aluminum etioporphycene series and related chloro- or methyl σ-bonded Al ( III ) porphyrins containing octaethylporphyrin ( OEP ) or tetraphenylporphyrin ( TPP ) macrocycles. Comparisons are also made betw…

Grazing-Incidence X-ray Diffraction Study of Octadecanoic Acid Monolayers

1998

We report the observation of X-ray scattering profiles from monolayers of octadecanoic acid in the vicinity of room temperature and evidence for the existence near room temperature of all four hexatic rotator phases L2d, Ov, L‘1, and LS, which differ in the details of their molecular tilt. While the incontrovertible triple-reflection signature of the chiral L‘1 phase was not observed, we propose that the previously reported rapid annealing behavior in this phase can lead to the disappearance of one, and in some cases two, of the three peaks.

Structural diversity of cyanide-bridged bimetallic clusters based on hexacyanometallate building blocks

2002

Abstract Four new cyanide-bridged bimetallic complexes, with different geometries and nuclearities, have been synthesized and characterized by single crystal X-ray crystallography. The trinuclear compound {〚Zn(bpy)2(OH2)〛2〚Fe(CN)6〛}Cl (1)·2 MeOH·12 H2O crystallizes in the triclinic space group P 1 , with a = 12.010(2) A, b = 16.316(3) A, c = 16.325(3) A, α = 97.47(3)°, β = 92.14(3)°, γ = 92.43(3)°, V = 3166(1) A3 and Z = 4. The tetranuclear compound {〚Zn(phen)2〛2〚Fe(CN)6〛2}2– (2) cocrystallizes with 〚Zn(bpy)3〛2+ and 32 H2O molecules in the monoclinic space group C2/c with a = 42.047(8) A, b = 13.541(2) A, c = 28.781(5) A, β = 120.23(3)°, V = 14158(4) A3 and Z = 2. The pentanuclear compound …

Effect of coherency of domain walls on X-ray diffraction diagrams: Case a crystal with a low tetragonality

2000

Les diagrammes de diffraction des rayons X d'une poudre ou d'une ceramique de BaTiO 3 tetragonal ont ete etudies. Une correlation entre les caracteristiques des profils des raies de diffraction (intensite, forme, position,...) et la microstructure en domaines ferroelectriques a ete mise en evidence. A partir d'une approche numerique, le calcul des diagrammes de diffraction montre que la modification des profils des raies de diffraction du compose tetragonal est fortement dependante de la microstructure en domaines ferroelectriques. Ce a du prendre en compte l'existence d'un certain degre de coherence dans les murs de domaines entre deux domaines a 90° adjacents. Il a par ailleurs ete mis en…

Alternative Motifs for Halogen Bonding (Eur. J. Org. Chem. 9/2013)

2013

Unravelling the fine structure of stacked bipyridine diamine-derived C-3-discotics as determined by X-ray diffraction, quantum-chemical calculations,…

2011

An in depth investigation of the fine structure adopted by the helical stacks of C3-discotics 1 incorporating three 3,3'-diamino-2,2'-bipyridine units is described. In the bulk the molecules display liquid crystalline behaviour in a temperature window of >300 K and an ordered rectangular columnar mesophase (Colro) with an inter-disc distance of 3.4 Å is assigned. X-Ray diffraction on aligned samples has also revealed a helical superstructure in the liquid crystalline state, and a rotation angle of 13–16° between consecutive discs. The proposed superstructure in the bulk phase has been further substantiated by a combination of quantum-chemical calculations and solid-state NMR spectroscopy…