Disorder in Cyclodextrin Clathrates: X-ray Diffuse Scattering Analysis of α-Cyclodextrin Cyclopentanone Hydrate

1997 ◽  
Vol 53 (4) ◽  
pp. 673-679 ◽  
Author(s):  
G. Le Bas ◽  
J. Doucet
Keyword(s):  
Crystal Growth ◽  
Neutron Diffraction ◽  
Structure Determination ◽  
Diffuse Scattering ◽  
The Other ◽  
Water Molecules ◽  
Hydroxyl Groups ◽  
Asymmetric Unit ◽  
Orientational Disorder ◽  
X Ray

Most of the cyclodextrin clathrates display disorder, consequently the structure determination is often difficult to carry out. Previous studies by X-ray and neutron diffraction have shown that the \alpha-cyclodextrin cyclopentanone hydrate crystallizes in a channel-like structure with hexagonal P6 symmetry. Two inclusion complexes were found in the asymmetric unit; there is an orientational disorder of the guest with six positions found in one host cavity, three in the other. In addition, certain host hydroxyl groups and water molecules were found to be disordered and their disorder was correlated with the guest disorder. In this paper we investigate X-ray diffuse scattering phenomena in order to go further in the interpretation of disorder. Complicated diffuse scattering patterns revealed a variety of disorder phenomena. Some were not shown by the average structure determination. The interpretation of the results (structure in domains, supercell and vacancies) helps to explain the rotational disorder of the guest and some observed strains of the averaged structure. The description of different microstructures may be of interest for crystal growth and inclusion chemistry.

Hydrogen-bond network in cyclodecaamylose hydrate at 20 K; neutron diffraction study of novel structural motifs band-flip and kink in α-(1→4)-D-glucoside oligosaccharides

2001 ◽  
Vol 57 (6) ◽  
pp. 833-841 ◽  
Author(s):  
K. Imamura ◽  
O. Nimz ◽  
J. Jacob ◽  
D. Myles ◽  
S. A. Mason ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Neutron Diffraction ◽  
Diffraction Study ◽  
Structure Refinement ◽  
Neutron Diffraction Study ◽  
The Other ◽  
Water Molecules ◽  
Hydroxyl Groups ◽  
Neutron Density ◽  
Asymmetric Unit

A single-crystal neutron diffraction study of cyclodecaamylose (CA10) was carried out at 20 K. CA10 crystallizes with 27.18 water molecules [(C6H10O5)10·27.18H2O] in space group C2 with unit-cell constants a = 29.31 (5), b = 9.976 (10), c = 19.34 (2) Å, β = 121.07 (2)°. The asymmetric unit contains a half molecule of CA10 and 13.59 water molecules, the other half being related by a crystallographic twofold rotation axis. All H atoms except two water H atoms could be located from difference neutron-density maps; structure refinement converged at R = 0.635. Two of the five CH2—O6 groups and one of the 15 O2, O3 hydroxyl groups of CA10 are twofold orientationally disordered. A total of 13.59 water molecules in the asymmetric unit are distributed over 23 positions; 20 of which are in the CA10 cavity, and the other three occupy intermolecular interstices. Of the 123 symmetry-independent hydrogen bonds, 25 (= 20%) are three-centered and 7 (= 6%) are four-centered. Water molecules and O—H groups of CA10 form an extended network with cooperative O—H...O—H...O—H hydrogen bonds. They are arranged in 11 polygons with three, four, five, six and eight O—H bonds and in homodromic, antidromic and heterodromic arrangements. Nine polygons are located within the cavity and the others are outside.

Study of Diffuse Scattering by Means of High Resolution Structure Images

1976 ◽  
Vol 34 ◽  
pp. 476-477
Author(s):  
Sumio Iijima ◽  
G. R. Anstis
Keyword(s):  
High Resolution ◽  
Neutron Diffraction ◽  
Diffuse Scattering ◽  
Reciprocal Space ◽  
The Other ◽  
X Ray ◽  
Actual Model ◽  
High Resolution Structure ◽  
Made In ◽  
Resolution Structure

Disorders in crystals with relatively simple structures which gave diffuse scattering have been extensively studied by X-ray or neutron diffraction methods. All these investigations were based on traditional diffraction methods and observations were made in reciprocal space (note observable diffraction intensities can be considered only in terms of interatomic vectors) and therefore the results obtained there leaves considerable ambiguity, particularly when we try to derive an actual model of the disordered crystals. A solution of this problem will be given only by knowing all atom positions in an assembly of atoms and for this case the observable diffracted intensity is given bywhere (xi,yi) and (xj,yj) represent position vectors of the i th and j th atoms with scattering factors fi and fj from an arbitrary origin. On the other hand, a crystal containing imperfections can be defined by

Opening and Narrowing of the Water H—O—H Angle by Hydrogen-Bonding Effects: Re-inspection of Neutron Diffraction Data

1998 ◽  
Vol 54 (4) ◽  
pp. 464-470 ◽  
Author(s):  
T. Steiner
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Neutron Diffraction ◽  
Diffraction Data ◽  
Water Molecules ◽  
Hydroxyl Groups ◽  
Secondary Effects ◽  
X Ray Diffraction ◽  
X Ray ◽  
Sample Average

For 71 water molecules donating two Ow—H...O hydrogen bonds, the correlation of the covalent H—O—H angle and the O...Ow...O angle is inspected from 49 well refined organic and organometallic neutron diffraction crystal structures. Compared to sample average, the water angle is opened for large and narrowed for small O...Ow...O angles. Notably, the H—O—H angle is widened compared with the gas phase value even for small O...Ow...O. Related behavior is observed for chloride anion acceptors. The correlation exhibits a considerable scatter which should not be interpreted as experimental inaccuracies, but as secondary effects. Possible secondary effects are multi-center hydrogen bonding and effects of coordination to the water O atom. In a comparative test, low-temperature X-ray diffraction data were shown to be completely unsuitable for this type of analysis. The dependence of the C—O—H angle on the C—O...O angle in hydrogen bonds donated by hydroxyl groups in carbohydrates is also shown.

Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXI. The 1 : 1 Adducts of the Copper(I) Halides (Cl, Br, I) With Bis(2-diphenylphosphinoethyl)phenylphosphine, 'triphos'

1991 ◽  
Vol 44 (7) ◽  
pp. 919 ◽  
Author(s):  
RD Hart ◽  
BW Skelton ◽  
AH White
Keyword(s):  
Single Crystal ◽  
Structure Determination ◽  
Copper Atom ◽  
Phosphorus Atom ◽  
Lewis Base ◽  
The Other ◽  
Asymmetric Unit ◽  
X Ray

The 1 : 1 adducts between the copper(I) halides, CuX , X = Cl , Br, I, and the title ligand, 'triphos', Ph2P(CH2)2P(Ph)(CH2)2PPh2, have been synthesized and characterized by single-crystal X-ray structure determination. The three complexes are isomorphous : monoclinic P21/c, a ≈ 14.5, b ≈ 20.5, c ≈ 24.5 Ǻ, β ≈ 118.5°; the asymmetric unit of each structure is the binuclear [Cu2X2( triphos )2] unit (with one acetonitrile solvate). Residuals were 0.047, 0.049 and 0.065 for 6006, 4832 and 5108 'observed', independent reflections respectively. About each copper atom, the four-coordinate environment comprises a terminal halogen [Cu- Cl,Br,I , 2.305(3), 2.311(2); 2.441(2), 2.443(2); 2.614(2), 2.614(2)Ǻ], two phosphorus atoms (central and distal) from the same ligand , and one distal phosphorus atom from the other ligand.

scholarly journals SbVO4 Catalyst Structure Determination Using Electron, X-ray and Neutron Diffraction

2012 ◽  
Vol 18 (S5) ◽  
pp. 95-96 ◽  
Author(s):  
J. Hernández-Velasco ◽  
J. García-García ◽  
A. Landa-Cánovas
Keyword(s):  
Neutron Diffraction ◽  
Structure Determination ◽  
Current Method ◽  
Oxidation Catalysts ◽  
Catalyst Structure ◽  
X Ray

SbVO4 series of compounds could be used as oxidation catalysts of industrial interest yielding 20% cheaper acrylonitrile by the ammoxidation of propane compared to current method producing 8×106 ton/year based on propylene as starting reactant.

scholarly journals Diosgenin hemihydrate

2012 ◽  
Vol 68 (8) ◽  
pp. o2357-o2357 ◽  
Author(s):  
María-Guadalupe Hernández Linares ◽  
Sylvain Bernès ◽  
Marcos Flores-Alamo ◽  
Gabriel Guerrero-Luna ◽  
Anselmo A. Martínez-Gallegos
Keyword(s):  
Crystal Structure ◽  
Water Molecule ◽  
Dimethyl Sulfoxide ◽  
Starting Material ◽  
Water Molecules ◽  
Asymmetric Unit ◽  
Acta Cryst ◽  
X Ray ◽  
Hydroxy Groups ◽  
Hydrogen Bonded

Diosgenin [or (22R,25R)-spirost-5-en-3β-ol] is the starting material of the Marker degradation, a cheap semi-synthesis of progesterone, which has been designated as an International Historic Chemical Landmark. Thus far, a single X-ray structure for diosgenin is known, namely its dimethyl sulfoxide solvate [Zhanget al.(2005).Acta Cryst.E61, o2324–o2325]. We have now determined the structure of the hemihydrate, C27H42O3·0.5H2O. The asymmetric unit contains two diosgenin molecules, with quite similar conformations, and one water molecule. Hydroxy groups in steroids and water molecules form O—H...O hydrogen-bondedR54(10) ring motifs. Fused edge-sharingR(10) rings form a backbone oriented along [100], which aggregates the diosgenin molecules in the crystal structure.

Crystal Structure of Calcium Picrate Pentahydrate: A New Eight-Coordinate Stereochemistry for [M(bidentate)2(unidentate)4]

1979 ◽  
Vol 32 (2) ◽  
pp. 301 ◽  
Author(s):  
V Diakiw ◽  
TW Hambley ◽  
DL Kepert ◽  
CL Raston ◽  
AH White
Keyword(s):  
Crystal Structure ◽  
Water Molecule ◽  
Single Crystal ◽  
Title Compound ◽  
Lattice Site ◽  
The Other ◽  
Water Molecules ◽  
X Ray Diffraction ◽  
Triangular Face ◽  
X Ray

The crystal structure of the title compound, Ca(C6H2N307)2,5H2O, has been determined by single-crystal X-ray diffraction at 295(1) K and refined by least squares to a residual of 0.049 for 1513 'observed' reflections. Crystals are orthorhombic, Pmab, a 24.169(6), b l0.292(7), c 8.554(2) �, Z 4. The stereochemistry about the calcium has not been observed previously for the system [M(bidentate)2- (unidentate)4]; in the present structure, the calcium is coordinated by a pair of bidentate picrate ligands and the four water molecules in an array in which three of the water molecules occupy a triangular face of a square antiprism, the overall array having m symmetry. The remaining water molecule occupies a lattice site with no close interaction with the other species.

Kristallstrukturen der selenid- bzw. sulfidverbrückten Gold(I)verbindungen [Se(AuPPh3)+3]PF6- und [S(AuPPh3)2] · CH2Cl2/Crystal Structures of the Selenide- and Sulphide-Bridged Gold(I) Complexes [Se(AuPPh3)3]+PF6- and [S(AuPPh3)2] · CH2Cl2

1982 ◽  
Vol 37 (8) ◽  
pp. 944-949 ◽  
Author(s):  
Cornelia Lensch ◽  
Peter G. Jones ◽  
George M. Sheldrick
Keyword(s):  
Crystal Structures ◽  
Structure Determination ◽  
Asymmetric Unit ◽  
Light Atom ◽  
X Ray ◽  
Ray Methods

Abstract The Compound [S(AUPPh3)2] · CH2Cl2 was prepared from Ph3PAuCl and H2S in CH2Cl2 and characterised by X-ray structure determination [P21/c, a = 1851.6(4), b = 2225.1(6), c = 880.3(2) pm, β = 96.32(1)°, Z = 4, R = 0.053]. A constrained refinement of the light atom positions was necessary because of pseudosymmetry. Ph3PAuPF6 reacts with Se(Sn)(CH3)3)2 to give [Se(AuPPh3)3]+PF6- which was also characterised by X-ray methods [P1̄, a = 1539.5(6), b = 1800.5(7), c = 2289.5(9) pm, α = 89.35(3), β = 72.44(3), γ = 69.75(3)°, Z = 4, R = 0.061]. There are two formula units in the asymmetric unit. Both structures show short Au···Au contacts (ca. 300-340 pm).

Strukturen cäsiumhaltiger Fluoride, II1 Die Kristall- und Magnetische Struktur von CsFeF4 / Crystal and Magnetic Structure of CsFeF4

1974 ◽  
Vol 29 (3-4) ◽  
pp. 139-148 ◽  
Author(s):  
D. Babel ◽  
F. Wall ◽  
G. Heger
Keyword(s):  
Neutron Diffraction ◽  
Single Crystals ◽  
Magnetic Structure ◽  
Structure Determination ◽  
Mean Value ◽  
X Ray ◽  
Magnetic Structures ◽  
Powder Samples ◽  
Crystal And Magnetic Structure ◽  
Improved Model

The results of an X-ray structure determination on single crystals of CsFeF4 are reported. The compound crystallizes tetragonally with α = 7.794, c = 6.553 Å, z = 4, in spacegroup P4/nmm-D4h7 and is a hitherto unknown superstructure variant of the TlAlF4-type. Cesium exhibits 12-coordination (mean value Cs-F = 3.25 Å); the FeF6-octahedra are characteristically shortened normal to the FeF4⁻-layers (Fe-F = 1.962/1.861Å). An improved model is proposed and verified for a related structure of RbFeF4, showing the same features. Neutron diffraction studies on powder samples of CsFeF4 show that both compounds are identical as for their magnetic structures.

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