bluuebunny/crossref_metadata_2025_split huggingface dataset:
Search for structure-forming components in molecular crystals of binary compounds: a topological approach
Authors: Peresypkina E. V. , Blatov V. A. 
Published: December 2003

Abstract
Molecular crystal structures of 81 polymorphs of binary compounds are investigated with the method of coordination sequences and with the uniformity criterion for atomic sublattices. It is shown that using these tools one can estimate semi-quantitatively the relative force of inter-molecular interactions and to find so-called structure-forming lattice, i.e. the atomic sublattice, where the most stable long-wavelength phonons are likely to spread. When a crystal consists of molecules with distinguished central atoms, the polarizability of surrounding atoms is found to dictate mainly the composition of the structure-forming lattice. If the polarizability is small, crystal structure is formed by molecules as a whole, otherwise surrounding atoms form the structure basis themselves, and it is their lattice that often is one of the close packings. It is shown that if the central atom of a molecule has stereoactive lone pair the central atom can form the structure-forming lattice together with surrounding atoms.
On the treatment of settings of space-groups and crystal structures by spezialized short Hermann-Mauguin space-group symbols
Authors: Burzlaff H. , Zimmermann H. 
Published: December 2003

Abstract
From the short Hermann-Mauguin space-group symbol a set of generating operators can be derived. The matrix description of the operators depends on three free parameters related to the origin of the setting. Simple rules allow the specification of an origin, the origin of the symbol. The use of any other origin is notated by appending a shift vector from the symbol origin to the new one selected.
Phase extension to weaker reflections of proteins via a partial structure based tangent formula
Authors: Burla M. C. , Carrozzini B. , Cascarano G. L. , Giacovazzo C. , Polidori G. 
Published: December 2003

Abstract
When some molecular fragment is well located, the so called partial structure based tangent formula may be used to recovery the complete crystal structure. The formula has been extensively applied to small molecules and initial applications to proteins have also been performed. We will show in this paper that the formula may be successfully applied to macromolecules, to refine phase values and to extend the phase information to weaker reflections, even in absence of prior information (at atomic level) on part of the crystal structure. Experimental tests have been performed via a modified form of the program SIR2000.
Synthesis of zoning-free BaSO4-PbSO4 solid solution and its structural characterizations
Authors: Wang Hsiu-Ru , Lee Jiann-Shing , Yu Shu-Cheng 
Published: December 2003

Abstract
Natural Pb-bearing barite, (Ba,Pb)SO4 “hokutolite”, is a radioactive sulfate mineral occurring in hot-spring deposit. An attempt to synthesize (Ba,Pb)SO4 crystal with a flux-growth process was made in this study. BaSO4 and PbSO4 in various proportions were used as precursor materials with Na2SO4 as a flux agent. The growth was carried out in a platinum crucible at 750-850ºC and ambient pressure conditions. The nucleation and growth were activated by a slow-cooling process at 2ºC/hr cooling rate. The flux-grown (Ba,Pb)SO4 crystals up to 1 mm in dimension were obtained and their chemical compositions were found to cover the entire range between BaSO4 and PbSO4. Thus there does exist a complete solid solution series between the barite (BaSO4) and anglesite (PbSO4) binary system. This result is consistent with that reported for (Ba,Pb)SO4 synthesized with a hydrothermal method. Both natural and hydrothermally synthesized (Ba,Pb)SO4 crystals display a distinct domain structure in which the Ba/Pb ratio varied among different domains. This type of chemical zoning is recognized under an optical microscope to be a banded texture in which dark bands (Ba-rich area) alternate with bright bands (Pb-rich area). In contrast, the (Ba,Pb)SO4 samples synthesized in this work contain no detectable optical bands, and this dramatic difference is believed to be a direct consequence of different growth kinetics. The flux-grown (Ba,Pb)SO4 crystals were determined to be a barite type of structure with the Ba and Pb atoms substituting each other in a fully disordered arrangement. The cell parameters vary continuously and systematically from the Ba-rich end toward the Pb-rich end as dictated by an ideal solid solution series.
Stacking disorder in 2H-NbS2 and its intercalation compounds K
x
(H2O)
y
NbS2 II. Stacking disorder in K
x
(H2O)
y
NbS2
Authors: Katzke H. 
Published: December 2003

Abstract
The intercalation reaction of hydrated K+ ions into the layered structure of 2H-NbS2 was studied using in situ X-ray diffraction. A structurally complex intercalation mechanism was observed showing several highly one-dimensionally disordered intercalated phases. A quantitative modelling of the disorder in K
x
(H2O)
y
NbS2 is presented allowing a complete understanding of the intercalation mechanism.
Phase transformation of ammonium monomolybdate. The structure of the low temperature modification, (NH4)2[MoO4] (mP60, P21/a)
Authors: Schweda E. , Hofmann M. , Dittmann M. , Glaser J. 
Published: December 2003

Abstract
(NH4)2[MoO4] (mS60) undergoes on cooling a phase transition at 190 K. The investigation of this phase transition by means of time and temperature resolved X-ray powder diffraction showed that the phase transition appears on heating at a temperature of 250 K. From this hysteresis and the abrupt changes in the peak positions of the diffractograms it is assumed that this is a first order transition. A diffractogram of the low temperature modification was recorded between 10° and 100° in 2θ. The structure was determined using direct methods and was refined by Rietveld methods. The low temperature modification of (NH4)2[MoO4] (mP60, P21/a) crystallizes in space group P21/a (No. 14) and lattice constants a = 767.57(5) pm, b = 1120.53(7) pm, c = 712.64(4) pm and β = 115.727(2)°.
Topological analysis of DL-arginine monohydrate at 100 K
Authors: Kingsford-Adaboh R. , Dittrich B. , Wagner A. , Messerschmidt M. , Flaig R. , Luger P. 
Published: December 2003

Abstract
The charge density of DL-arginine monohydrate has been extracted from a synchrotron data set of 212121 reflections collected at 100 K with a Bruker CCD area detector up to a resolution of sin θ/λ = 1.40 Å-1 (d = 0.36 Å). DL-arginine monohydrate is characterised by a neutral α-amino group and a notable different hydrogen bond pattern compared to previously examined free arginine structures. All bond critical points of the electron density at the covalent and hydrogen bonds were located. We compare the local topological indices of ρ(r) with other amino acids. The conformation obtained from the experimental structure is found to be different from the Hartree-Fock (HF) optimization for the isolated molecule, thus the topology obtained from the static experimental charge density is compared to that derived from calculations at experimental and optimized geometry at HF and B3LYP levels of theory.
Synthesis, structural and spectral studies of bis-[N-(2,4-dimethoxy benzylidene)-2-mercaptoanilinato] Ni(II)
Authors: Şahin E. , İde S. , Ancın N. , Öztas S.G. , Tüzün M. 
Published: December 2003

Abstract
The Ni(II) complex of N-(2,4-dimethoxy ben-zylidene)-2-mercaptoaniline, [Ni(C15H14NO2S)2] was prepared and investigated. The structure derived from the two dimensional (2-D) NMR techniques, the infrared spectra, elemental analysis and mass spectra is consistent with that of the single crystal X-ray diffraction. Crystal system is monoclinic, space group Cc(no:9), number of formulae per unit cell Z=4. Cell parameters are a=14.283(4), b=13.828(4), c=14.345(5) Å, β=102.84(3)°, V= 2762(2) Å3. Two singly deprotonated ligands coordinate the metal atom in a distorted square planar geometry. The molecular geometry was also effected by C-H⋅⋅⋅N and C-H⋅⋅⋅O intramolecular hydrogen bonds.
Neural network investigation of borate crystal properties
Authors: Barber M. J. , Becker P. 
Published: December 2003

Abstract
Correlations between crystal chemical properties of anhydrous oxoborate crystals wereanalysed using artificial neural networks. Using structuralproperties of oxoborate crystal structures described inthe literature, we developed several neural network modelsthat capture statistical relations between crystalchemical properties of the anhydrous oxoborates from the existingdata sets. This indicates the suitability of neural networks forthe prediction of structural propertiesof crystals.
Influence of high hydrostatic pressure on lattice parameters of a single crystal of La3Nb0.5Ga5.5O14
Authors: Pavlovska A. , Werner S. , Boehler R. 
Published: December 2003

Abstract
Unit-cell parameters of La3Nb0.5Ga5.5O14 (langanite) have been determined at a number of pressures up to 23GPa in diamond anvil high pressure cells with single crystal X-ray diffraction techniques. The anisotropic behaviour of unit cell parameters of langanite is caused by differences of bonding strength in direction parallel to the a- and c-axis. Within the investigated pressure range, the c/a-ratio increases from 0.6232 to 0.6503. The volume compressibility of trigonal langanite (space group P321) is the 0.007 GPa-1, with calculated bulk modulus of 145(3)GPa (B'0=1.4(8)). At a pressure of 12.4(3)GPa a first-order phase transition was detected, characterised by a discontinuity in the pressure dependence of lattice parameter c. The high-pressure phase (presumably monoclinic, A2) with a volume compressibility of 0.011 GPa-1 (B0=93(2) GPa, B'0=1.9(9)) is more compressible as compared to the initial phase due to an abnormal pressure dependence of lattice parameter a.
Intramolecular hydrogen bond and proton transfer in 3-(2-benzimidazolylthio)-2,4-pentanedione. Crystallographic evidence and theoretical calculations
Authors: Smrčok L. , Tunega D. , Langer V. , Koóš M. 
Published: December 2003

AbstractCrystal structure of the title compound is orthorhombic,Pbca,a=7.8689(2) Å,b=9.6519(3) Å,c=31.3579(9) Å. The structure was solved by direct methods and refined by a full-matrix least squares procedure to finalR(all)=0.0682 for 2853 unique diffractions merged from 24459 measured at 183(2)K. The molecule is formed by two planar moieties joined through an atom of sulphur. The short intramolecular O...O contact is 2.430(2) Å, the intramolecular hydrogen bond is slightly asymmetric. Theoretical ab initio calculations done at B3LYP/SVP and ONIOM(MP2/SVP:B3LYP/SVP) levels showed that the experimental geometry of pentanedione pseudoring is close to the geometry corresponding to a transition state on the asymmetric potential energy curve. Calculated energy difference between two minima is only –4.72 kJ/mol and the energy barrier –6.02 kJ/mol, which agrees well to ~6.6kJ/mol found in microwave spectroscopic study of malonaldehyde.
On the discovery of new low temperature monoclinic phases with Cm and Cc space groups in Pb(Zr0.52Ti0.48)O3: an overview
Authors: Pandey D. , agini R 
Published: December 2003

Abstract
The decades old phase diagram of the technologically important Pb(Zr
x
Ti1–

x
)O3 (PZT) ceramics in the vicinity of the morphotropic phase boundary has been under review during the last few years. This article summarises the results of the discoveries of two new mono clinic phases (F
M
HT) and (F
M
LT) with Cm and Cc space group by the Brookhaven group and our group, respectively, in the PZT ceramics.
Investigation of transition from decagonal to vacancy ordered phase on replacement of Co by Cu in Al70Co15–

x
Cu
x
Ni15
Authors: Yadav T. P. , Shaz M. A. , Tiwari R. S. , Srivastava O. N. 
Published: December 2003

Abstract
The alloy with composition Al70Co15Ni15 forms one of the important quasicrystalline phase exhibiting formation of decagonal variants [1, 2]. In the present investigation, copper has been substituted in place of cobalt i.e. the phases corresponding to Al70Co15–

x
Cu
x
Ni15, have been investigated. It is found that when copper concentration reaches to a value of 10 atomic percent with the composition corresponding to Al70Co5Cu10Ni15, the decagonal phase starts yielding to give rise to vacancy ordered phase. When all cobalt is replaced by copper i.e. when the composition corresponds to Al70Cu15Ni15, the decagonal phase disappears and the only phase observed is the vacancy ordered phase. It can thus be said that copper substitution brings in decagonal to vacancy ordered (VOP) phase transition. It has also been observed that gradual increase in concentration of Cu in Al70Co15–

x
Cu
x
Ni15 leads to cellular to dendritic transition in morphology.
White beam synchrotron X-ray topography studies of twinning in GdFeO3-type perovskite crystals
Authors: Savytskii D. , Senyshyn A. , Matkovskii A. , Vasylechko L. , Wieteska K. , Wierzchowski W. , Lukasiewicz T. , Bismayer U. 
Published: December 2003

Abstract
The twin structure of NdGaO3 and YAlO3 : Dy crystals was examined using white beam synchrotron X-ray topography. The relation of the orthorhombic lattice basis vectors has been obtained for every domain pair in the crystals with GdFeO3-type structure. A new computer program has been used to generate Laue simulation patterns and to calculate the image shifts in topographs. The proposed approach allow for the analysis of both, sample images for specified reflections and Laue patterns as a whole. Topography was used to map domain patterns, to show misorientations and to detect symmetric aspects of ferroelastic twins. Information on twin laws and the twin distribution was obtained simultaneously.
Synthesis, X-ray crystal structure and dielectric measurements of a tetragonal tungsten bronze: Pb0.75K1.80Li1.70Nb5O15
Authors: Elaatmani M. , Zegzouti A. , Capitelli F. , Moliterni A. G. G. , Migliori A. , Calestani G. 
Published: December 2003

Abstract
Typical crystals Pb0.75K1.80Li1.70Nb5O15, belonging to tetragonal tungsten bronze materials, were grown by the slow cooling technique. The crystals were characterized at room temperature by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HREM). The structure, solved combining information obtained by HRTEM images and Direct Methods application to single crystal XRD data, was refined by full-matrix least-squares technique in the P4bm space group to a final R = 0.031. The lattice constants are a = 12.540(2), c = 4.037(1) Å, V = 634.8(2) Å3, at 293 K. There are two formulas per unit cell, for a calculated density of 4.928 Mg/m3. Dielectric measurements, carried out along the [001] direction in the frequency 103 Hz, showed the existence of the paraelectric-ferroelectric transition at 628 K and of a further maximum of ε′r (with a very weak intensity) at T
1 = 150 K.
Ab initio structure determination of In2H2(P2O7)(P4O12) from X-ray powder diffraction data
Authors: Ivashkevich L. S. , Lyakhov A. S. , Selevich A. F. , Lesnikovich A. I. 
Published: December 2003

Abstract
The crystal structure of In2H2(P2O7)(P4O12) has been determined from X-ray powder diffraction data. The structure is orthorhombic, space group Pmmn (No. 59), with unit cell dimensions a = 12.9398(2) Å, b = 11.3725(3) Å, c = 5.0385(1) Å, V = 741.45(3) Å3, Z = 2, and D
x = 3.23 g/cm3. The structure has been solved by direct methods using EXPO program and refined by FULLPROF package. The final R
Bragg value was 4.6%. Positions of hydrogen atoms were not defined. Indium cation has sixfold oxygen coordination being surrounded by two diphosphate and four cyclotetraphosphate groups. Probable scheme of hydrogen bonding is discussed.
EXAFS and XRD investigations of zeunerite and meta-zeunerite
Authors: Hennig C. , Reck G. , Reich T. , Roßberg A. , Kraus W. , Sieler J. 
Published: December 2003

Abstract
In this paper EXAFS was used to determine bond lengths in the structures of zeunerite and meta-zeunerite. The atomic distances between heavy and light scatterers observed using EXAFS in meta-zeunerite deviate approximately 0.1 Å from literature data of single-crystal X-ray diffraction measurements. Because this difference is significant higher than the error limits of EXAFS measurements, the complete crystal structure of meta-zeunerite, Cu[UO2AsO4]2·8 H2O, is revised by X-ray structure analysis. The bond length determinations by EXAFS and the revised XRD data agree within the experimental error limits. In this study EXAFS spectroscopy has proven to be an useful tool for determining precise local bond lengths in the environment of heavy atoms. Moreover, the crystal structure of zeunerite, Cu[UO2AsO4]2·12 H2O, hitherto not been described in the literature, was investigated. Reflex broadening effects and intergrowth relationship between zeunerite and meta-zeunerite show that meta-zeunerite grows in nature due to dehydration of zeunerite. The structural transition from zeunerite to meta-zeunerite is connected with a change in the uranyl arsenate layer arrangement and the crystal water content.
Crystal and molecular structures of 4-aryl-1,4-dihydropyrimidines: Novel calcium channel antagonists
Authors: Chandra Mohan K. , Ravikumar K. , Shetty M. M. , Velmurugan D. 
Published: December 2003

Abstract
The solid-state structures of three calcium channel antagonists viz. 1,4-dihydro-6-methyl-5-N-methyl-carbamoyl-4-(3′,4′-dichlorophenyl)-2(3 H)-pyrimidinethione, C13H13N3OSCl2 (1); 1,4-dihydro-6-methyl-5-N-methyl-carbamoyl-4-(4′-methoxyphenyl)-2(3 H)-pyrimidinethione, C14H17N3O2S (2) and 1,4-dihydro-6-methyl-5-N-methyl-carbamoyl-4-(2′,4′-dichlorophenyl)-2(3 H)-pyrimidineone monohydrate, C13H13N3O2Cl2·H2O (3), are reported here. The structures show that these compounds can adopt the important structural features of 1,4-dihydropyridine calcium channel blockers. In (2), the compound crystallized with three molecules in the asymmetric unit. The dihydropyrimidine ring adopts a half-chair in (1) and boat conformation in (2) and (3). The 4-aryl substituents occupies a pseudo-axial position approximately orthogonal to the plane of the dihydropyrimidine ring [95.1(2)° (1); 97.5(3)°, 79.8(2)° & 88.2(2)° (2) and 78.8(3)° (3)]. The C3 substituent, carbamoyl group, is in an extended conformation and oriented anticlinical in (1) and (3), but in (2) two molecules are anticlinal and the other one is synperiplanar, respectively. Intra- and inter- molecular interactions may be influencing the orientation of the C3 carbamoyl group. The 2-chlorophenyl substituent in (3) is in the axial synperiplanar orientation.
Crystal structure of anhydrous potassium O-n-propyldithiocarbonate. Theoretical calculations of O-alkyl dithiocarbonates
Authors: Buntine M. A. , Cox M. J. , Lim Y. X. , Yap T. C. , Tiekink Edward R. T. 
Published: December 2003

Abstract
The xanthate anion in the structure of K[S2COnPr] displays the expected features, i.e. planar S2CO chromophore and variation in C—S and C—O distances. The K cation exists in a distorted cubic geometry defined by an O2S6 donor set. Cubes are face-shared so as to form a layer structure with cohesion between layers afforded by hydrophobic interactions. A series of theoretical gas-phase structures have been calculated for isolated S2COR anions. These show that there is a remarkable consistency in geometric parameters across the series. This observation indicates that the nature of the R substituent does not influence greatly the electronic structure of the central S2CO chromophore.
Synthesis and crystal structure of diaquabis(diketohydrindene-diketohydrindamine)manganese(II)
Authors: Derebe M. G. , Retta N. , Moliterni A. G. G. , Capitelli F. 
Published: December 2003

AbstractDiaquabis(diketohydrindene-diketohydrindamine)manganese(II), Mn(II) complex of Ruhemann's purple, a condensation product of ninhydrin andα, L-alanine (or anyα-amino acid), was synthesized for the first time and its structure determined by X-ray diffraction methods. The study revealed that the metal ion is seven-coordinated with two Ruhemann's purple ligands, one behaving as a didentate ON donor and another as a tridentate ONO donor, both monobasic, and two additional water ligands. The structure closely resembles a distorted pentagonal bipyramid (D5h) geometry.
Ab initio structure determination of cytochrome c6 by combined reciprocal space-real space approach
Authors: Chowdhury K. , Ghosh S. , Mukherjee M. 
Published: December 2003

Abstract
The direct method program SAYTAN has been applied successfully to redetermine the structure of cytochrome c6, a heme-containing redox protein with 89 amino acids, a Fe atom and 151 solvent water molecules in the asymmetric unit and data to 1.1 Å resolution. The crystal system is rhombohedral with space group R3, cell parameters a = b = c = 40.43(10) Å, α = β = γ = 80.25(5)°. Starting with initially random phases, useful phase sets could be obtained from multiple trials of direct methods based on reciprocal space. The E-map corresponding to the phase set with the lowest mean phase error, 45.4°, showed a distorted octahedral coordination around the Fe site. The phase estimates from the metal atom and a few neighbouring atoms in the initial E-map have been improved by density modification procedure (PERP) operating in direct space. The resulting electron density map can be interpreted readily by an automated procedure to build up the protein structure.
Tricalcium silicate Ca3SiO5, the major component of anhydrous Portland cement: on the conservation of distances and directions and their relationship to the structural elements
Authors: de Noirfontaine M.- N. , Dunstetter F. , Courtial M. , Gasecki G. , Signes-Frehel M. 
Published: December 2003

Abstract
Tricalcium silicate, the major component of Portland cement exhibits a complex phase diagram, surprisingly still not completely understood. In this letter, new results are highlighted including a comprehensive study of the superstructure relationship between the polymorphs, and new ideas about the structural analysis. The organisation of the silicate skeleton can be described in terms of 1-D or 2-D elements, from which arise new hypotheses about the cohesion and the chemical origin of the observed superstructures.