Structural Science

 

Acta Cryst. (2001). B57, 221-230  [ doi:10.1107/S0108768100019960 ]

X-ray diffraction study of the phase transition of K₂Mn₂(BeF₄)₃: a new type of low-temperature structure for langbeinites

A. Guelylah, G. Madariaga, V. Petricek, T. Breczewski, M. I. Aroyo and E. H. Bocanegra

Synopsis: The twinned low-temperature monoclinic (P112₁) structure of K₂Mn₂(BeF₄)₃ has been determined. Unlike the known structures of langbeinite, the low-temperature unit cell is doubled along the crystallographic b axis with respect to the parent phase. In the monoclinic phase the BeF₄ tetrahedra occupying the same position in the cubic phase along two consecutive unit cells rotate differently.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 231-236  [ doi:10.1107/S0108768100020322 ]

Structural basis for the phase transitions of Cs₂HgCl₄

B. Bagautdinov, A. Jobst, J. Ludecke and S. van Smaalen

Synopsis: The low-temperature 2c₀ superstructure of Cs₂HgCl₄ has been determined by X-ray scattering. The comparison of the parent structure with the 2c₀, 3c₀ and 5a₀ superstructures shows that the phase transitions are driven towards increased bonding of the underbonded Cs(1)-type atoms.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 237-243  [ doi:10.1107/S0108768101001628 ]

Neutron diffraction study of -Bi₈Pb₅O₁₇: structure refinement and analysis of cationic ordering

L. Righi, G. Calestani, M. Gemmi, A. Migliori and M. Bettinelli

Synopsis: The -Bi₈Pb₅O₁₇ triclinic structure, recently solved by the synergic use of electron and powder X-ray diffraction, has been refined on neutron diffraction data. The occurrence of cationic ordering, indicated by valence bond and charge distribution analysis, has been confirmed by site occupancy refinements. The structure was found to be ordered to a large extent, with Bi and Pb atoms occupying preferentially different lattice sites.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 244-250  [ doi:10.1107/S0108768101002038 ]

Electron density in the sodium vanadium oxide bronze -Na_xV₂O₅ at 9  K

R. P. Ozerov, V. A. Streltsov, A. N. Sobolev, B. N. Figgis and V. L. Volkov

Synopsis: The crystal structure and the electron density in -Na_xV₂O₅ [x = 0.282  (3)] have been studied at 9.6  K.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 251-260  [ doi:10.1107/S0108768101004141 ]

General method for the description, visualization and comparison of metal coordination spheres: geometrical preferences, deformations and interconversion pathways

J. W. Yao, R. C. B. Copley, J. A. K. Howard, F. H. Allen and W. D. S. Motherwell

Synopsis: A Euclidean dissimilarity index, R_c(x), based on L-M-L valence angles is defined which permits the intercomparison and mapping of the coordination sphere geometries of ML_n species in crystal structures of metal complexes. Taking account of atomic permutational symmetry, the technique identifies clusters of observations that represent geometrical preferences and local distortions, together with pathways that map geometrical interconversions of coordination sphere geometries.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 261-270  [ doi:10.1107/S010876810100297X ]

Study of rare-earth -complexes by means of Voronoi-Dirichlet polyhedra

O. A. Blatova, V. A. Blatov and V. N. Serezhkin

Synopsis: An investigation of 135 -complexes of rare-earth atoms was carried out with Voronoi-Dirichlet polyhedra. A novel method for the evaluation of the sizes of polyatomic ligands and steric effects in the structure of organometallic compounds was developed.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 271-277  [ doi:10.1107/S010876810100101X ]

Commensurate structure of Ca₂CoSi₂O₇, a new twinned orthorhombic structure

K. Hagiya, K. Kusaka, M. Ohmasa and K. Iishi

Synopsis: The structure of the commensurate phase of Ca₂CoSi₂O₇ has been derived from the modulated structure described in (3  +  2)-dimensional space and refined by a least-squares method in three-dimensional space. The structure is composed of twins of orthorhombic individuals.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 278-287  [ doi:10.1107/S0108768101003068 ]

Relationship between bond valence and bond softness of alkali halides and chalcogenides

St. Adams

Synopsis: Detailed studies on the significance of higher coordination shells and a novel empirical correlation of the bond-valence parameter b to the softness of a bond permit the systematic determination of softness-sensitive bond-valence parameters.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 288-295  [ doi:10.1107/S0108768101002737 ]

Dipyrimidine-copper(II) dinitrate complexes showing magnetic interactions

M. Yasui, Y. Ishikawa, N. Akiyama, T. Ishida, T. Nogami and F. Iwasaki

Synopsis: The crystal structures of [Cu(NO₃)₂(pm)₂]_n (pm = pyrimidine), [Cu(NO₃)₂(H₂O)₂(pm)]_n and Cu(NO₃)₂(H₂O)₂(pm)₂ were determined and relations between chain structures and magnetic interactions were discussed.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 296-302  [ doi:10.1107/S0108768101001525 ]

Structure of the X-phase of 38% brominated betaine calcium chloride dihydrate

L. G. Vieira, O. Hernandez, J. L. Ribeiro, A. Cousson, J.-M. Kiat, M. R. Chaves, A. Almeida and A. Klöpperpieper

Synopsis: The structures of the Pnma and P2₁2₁2₁ phases of 38% brominated betaine (trimethylammonioacetate) calcium chloride dihydrate have been determined by single-crystal neutron diffraction at 295 and 20  K, respectively. The distortion with respect to the high-temperature Pnma phase is characterized by anti-symmetric displacements of the betaine molecules as well as of the Ca octahedra. The direct phase transition that occurs around 80  K between these two phases is interpreted in the scope of a symmetry-mode analysis.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 303-310  [ doi:10.1107/S0108768101004426 ]

Hydrogen-bonded hexagonal and pseudo-hexagonal grid motifs in supramolecular cobalt(II) and nickel(II) cupferronato complexes incorporating neutral N-donors with intermolecular NH₂ connectors and solvent molecules

A. Deák, A. Kálmán, L. Párkányi and I. Haiduc

Synopsis: The self-assembly of cobalt(II) and nickel(II) octahedra formed by cupferronato and neutral N-donor ligands and their NH₂ functions leads to extended two-dimensional hexagonal and pseudo-hexagonal grid-type networks. The solvent molecules play a key role in such systems.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 311-316  [ doi:10.1107/S0108768101003779 ]

Asymmetric hydrogen bonds in centrosymmetric environment: neutron study of very short hydrogen bonds in potassium hydrogen dichloromaleate

I. Olovsson, H. Ptasiewicz-Bak, T. Gustafsson and I. Majerz

Synopsis: The very short hydrogen bonds in potassium hydrogen dichloromaleate have been studied by neutron diffraction at 30 and 295  K. The hydrogen bonds are asymmetric, although the environment is centrosymmetric.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 317-328  [ doi:10.1107/S0108768100020280 ]

Hydrated metal complexes of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)glycinate: interplay of molecular, molecular-electronic and supramolecular structures

J. N. Low, J. M. Moreno Sánchez, P. Arranz Mascarós, M. L. Godino Salido, R. López Garzon, J. Cobo Domingo and C. Glidewell

Synopsis: The title anion forms finite molecular aggregates with Li⁺ and Mn²⁺, simple aquated salts with Mg²⁺ and Zn²⁺, but organic-inorganic hybrid sheets with Na⁺ and K⁺.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 329-338  [ doi:10.1107/S0108768100019832 ]

Hydrated salts of 3,5-dihydroxybenzoic acid with organic diamines: hydrogen-bonded supramolecular structures in two and three dimensions

C. J. Burchell, G. Ferguson, A. J. Lough, R. M. Gregson and C. Glidewell

Synopsis: 3,5-Dihydroxybenzoic acid forms hydrated salt-type adducts with a range of organic diamines. The molecular components are linked by an extensive series of N-HO, O-HO and O-HN hydrogen bonds into continuous arrays in two or three dimensions.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 339-345  [ doi:10.1107/S0108768100015184 ]

X-ray and neutron structure of 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol (P326); some pitfalls of automatic data collection

R. A. Palmer, B. S. Potter, J. N. Lisgarten, R. H. Fenn, S. A. Mason, O. S. Mills, P. M. Robinson and C. I. F. Watt

Synopsis: The structure of the crown ether P326, the parent compound for a series of derivatives, is presented as determined by room-temperature X-ray diffraction and low-temperature neutron diffraction. Forming a very useful pedagogical example, a variety of situations arose through the two simultaneous and interdependent data collections and analyses, complicated by an extremely unusual combination of lattice geometry and pseudosymmetry.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 346-352  [ doi:10.1107/S010876810100489X ]

Variable-temperature crystal structure studies of m-nitroaniline

G. Wójcik and J. Holband

Synopsis: The thermal evolution of the lattice parameters, expansion tensor coefficients, and rigid-body translation and libration tensors, as well as the torsional vibration of the nitro group, were studied in order to understand the molecular interactions and dynamics leading to thermodynamic transitions.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 353-358  [ doi:10.1107/S0108768101004359 ]

Experimental electron density of urea-phosphoric acid (1/1) at 100  K

B. L. Rodrigues, R. Tellgren and N. G. Fernandes

Synopsis: The crystal formed by urea and phosphoric acid is stabilized by hydrogen bonds, including the very short d(OO) = 2.410  (2)  Å. Deformation maps obtained from multipole refinements show the hydrogen bonding effect on P-O bonds and the covalent character of the two O-H interactions of the short hydrogen bond.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 359-365  [ doi:10.1107/S0108768100020048 ]

Chemical bonding in energetic materials: -NTO

E. A. Zhurova and A. A. Pinkerton

Synopsis: The electron density and related properties of the quasi-stable form of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO; space group P2₁/c) have been determined from low-temperature X-ray diffraction.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 366-371  [ doi:10.1107/S010876810100218X ]

X-ray studies on crystalline complexes involving amino acids and peptides. XXXVII. Novel aggregation patterns and effect of chirality in the complexes of DL- and L-lysine with glutaric acid

N. T. Saraswathi, N. Manoj and M. Vijayan

Synopsis: The complexes exhibit novel patterns of amino acid aggregation. They also illustrate the profound effect reversal of chirality can have on aggregation.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 372-377  [ doi:10.1107/S0108768100019121 ]

Structure of -trimyristin and -tristearin from high-resolution X-ray powder diffraction data

A. van Langevelde, R. Peschar and H. Schenk

Synopsis: The crystal structures of -1,2,3-tritetradecanoylglycerol (-trimyristin or -MMM) and -1,2,3-trioctadecanoylglycerol (-tristearin or -SSS) have been determined from high-resolution synchrotron X-ray powder diffraction data using grid-search techniques and refined with Rietveld refinement to final R_p values of 0.053 and 0.041, respectively.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 378-385  [ doi:10.1107/S0108768100020218 ]

Superspace description of the structure of the composite crystal urea/n-octane at room temperature

I. Peral, G. Madariaga, V. Petricek and B. Breczewski

Synopsis: The structure of the composite crystal urea/n-octane has been solved using the superspace formalism [superspace group P6₁22(00)0. A comparison of the proposed model with that of the urea/heptadecane crystal shows that the modulation of n-alkane molecules is provoked by the shape of the urea tunnels.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 386-393  [ doi:10.1107/S0108768101002166 ]

Average structure of the composite crystal urea/octanedioic acid at room temperature within the superspace formalism

I. Peral, G. Madariaga, V. Petrícek and T. Breczewski

Synopsis: The average structure of the composite crystal urea/octanedioic (suberic) acid has been solved using the superspace formalism under the superspace group H'3₁21(00)00. The strong orientational disorder shown by the guest molecules has been modelled using 12 equiprobable orientations of suberic acid molecules within the urea tunnels.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 394-398  [ doi:10.1107/S010876810002108X ]

Inclusion compounds of binaphthol with picolines: structures, selectivity and kinetics of desolvation

L. R. Nassimbeni and H. Su

Synopsis: The structures of binaphthol with picoline isomers have been elucidated. The lattice energies are correlated with their thermal stabilities, selectivities and activation energies of desolvation.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 399-409  [ doi:10.1107/S0108768101001963 ]

Non-covalent interactions in the crystallization of the enantiomers of 1,7-dioxaspiro[5.5]undecane (olive fly sex pheromone) by enantiospecific cyclodextrin hosts, hexakis(2,3,6-tri-O-methyl)--cyclodextrin and heptakis(2,3,6-tri-O-methyl)--cyclodextrin

S. Makedonopoulou, K. Yannakopoulou, D. Mentzafos, V. Lamzin, A. Popov and I. M. Mavridis

Synopsis: Weak but numerous host-guest interactions and induced fit of the hosts are responsible for the observed enantioselectivity. The difference of the hosts to selectively bind one of the optical antipodes is reflected in very subtle differences in the C-HO intermolecular distances between host and guest.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 410-414  [ doi:10.1107/S0108768101002154 ]

Influence of hydrogen bonding on the second harmonic generation effect: neutron diffraction study of 4-nitro-4'-methylbenzylidene aniline

J. M. Cole, J. A. K. Howard and G. J. McIntyre

Synopsis: 4-Nitro-4'-methylbenzylidene aniline (NMBA) was studied by neutron diffraction in order to rationalize its large second-harmonic generation output via its structural characteristics: C-HX hydrogen bonding and very close interplanar separations are shown to be important supramolecular features in this regard.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 415-427  [ doi:10.1107/S010876810100430X ]

Interplay between dipolar, stacking and hydrogen-bond interactions in the crystal structures of unsymmetrically substituted esters, amides and nitriles of (R,R)-O,O'-dibenzoyltartaric acid

U. Rychlewska and B. Warzajtis

Synopsis: The results presented demonstrate the importance of dipole/dipole interactions between CO and C*H groups in stabilizing the molecular conformation, and between carbonyl groups in stabilizing crystal packing of molecules that lack classical hydrogen-bond donor groups. An illustration is provided as to how a small change in mutual orientation of molecules arranged in a close-packed fashion causes a change in the character of intermolecular interactions from van der Waals to sandwich stacking and to dipolar. Hydrogen bonds with ester carbonyls as acceptors are formed by the amide but not by carboxyl donor groups.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 428-434  [ doi:10.1107/S0108768101005171 ]

Topochemically controlled solid-state methyl rearrangement in thiocyanurates

M. Greenberg, V. Shteiman and M. Kaftory

Synopsis: Some thiocyanurates undergo intermolecular methyl rearrangement in the solid state. The crystal structures and DSC thermographs of representatives of thiocyanurates are described and discussed. It is shown that this type of reaction in the solid state is topochemically controlled.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 435-439  [ doi:10.1107/S0108768100018875 ]

Migration of the proton in the strong O-HO hydrogen bond in urea-phosphoric acid (1/1)

C. C. Wilson

Synopsis: The position of the H atom in the strong O-HO hydrogen bond in urea-phosphoric acid is monitored by neutron diffraction using a multiple single crystal sample. The proton position is found to change significantly as a function of temperature, migrating along the hydrogen bond to become more centred as the temperature increases.

Online 25 May 2001

 

Acta Cryst. (2001). B57, 440  [ doi:10.1107/S0108768101006796 ]

Perspectives in structural biology

Online 25 May 2001

 

Acta Cryst. (2001). B57, 440  [ doi:10.1107/S0108768101007935 ]

Crystal structure determination

Online 25 May 2001