bluuebunny/crossref_metadata_2025_split huggingface dataset:
Room- and high-temperature single crystal diffraction studies on γ-Na2Si2O5: an interrupted framework with exclusively Q3-units
Authors: Kahlenberg V. , Rakić S. , Weidenthaler C. 
Published: December 2003

Abstract
Single crystals of γ-Na2Si2O5 have been obtained from the crystallization of a stoichiometric glass at 520 °C. The monoclinic crystals belong to space group C2/c (a = 33.326(2) Å, b = 14.1457(7) Å, c = 26.206(2) Å, β = 108.60(2)°, V = 11709.0(1.5) Å3, Z = 96, D
calc = 2.48 g cm–3). The diffraction pattern showed the typical features of a superstructure. The structure was solved by direct methods including the pseudo-translational effects as a prior information for the normalization process and subsequently refined to a residual of R1 = 0.058. The compound can be classified as an interrupted tetrahedral framework with exclusively Q3-units. Basic building units are spiral achter single chains running parallel [010]. Every four of these chains are linked via common corners, surrounding a central tunnel where the sodium atoms are located for charge compensation. The framework density has a value of 16.4 T-atoms/1000 Å3. At 563°C the monoclinic phase undergoes a structural phase transition into a tetragonal high temperature modification (space group I41/a, a = 11.869(2) Å, c = 7.176(2) Å, V = 1011.0(6) Å3, Z = 4). The transition is induced by cooperative rotations of the tetrahedra and involves a bisection of the translation period along the spiral chains. The symmetries of both modifications are in a close relationship: the space group of the RT-phase is a subgroup of index 24 of the space group of the HT-phase. Focussing on the connectivity of the tetrahedra the two phases are identical and can be characterized as defect—cristobalites where 20 of the tetrahedra have been removed. Topologically they can be described as three dimensional 3-connected nets of a type which has been already observed in the intermetallic compounds LiGe and LiSi, as well as in the mineral grumantite.
General structural relationships between rutile-type VO2 and the Magnéli-phases VnO2

n

–1
Authors: Katzke H. , Schlögl R. 
Published: December 2003

Abstract
The structures of the Magnéli-phases V
n
O2

n

–1 (3 ≤ n ≤ 7) are reviewed with respect to their structural relationships to rutile-type VO2. The general expressions for the transformation matrices P and Q = P
–1 are derived allowing the prediction of lattice parameters and atomic coordinates for hypothetical structures of V
n
O2

n

–1 with n ≥ 8.
Crystal structures of N-(trichloroacetyl)morpholine and 2,6-di(trichloroacetyl)cyclohexanone
Authors: Özbey Süheyla , Kaynak F. B. , Şenöz H. , Tunoğlu N. 
Published: December 2003

Abstract
The crystal and molecular structure of the title compounds have been determined by X-ray analysis (N-(trichloroacetyl)morpholine, C6H8Cl
3NO2, P21/a, a = 9.869(1) Å, b = 12.287(1) Å, c = 16.060(1) Å, β = 98.773(7)°, Z = 8; 2,6-di(trichloroacetyl)cyclohexanone, C10H8Cl
6O3, Pbca, a = 10.553(1) Å, b = 15.405(2) Å, c = 18.435(2) Å, Z = 4). The morpholine and cyclohexane rings of both compounds adopt the chair conformation. There are some intra- and intermolecular hydrogen bonds in the title compounds, so the crystal structures of them are stabilized by C—H...Cl and C—H...O intra- and inter molecular hydrogen bonds.
Hydroxy-alkyl bisphosphonic acid partial esters (HABPA-PE): Structures of two symmetrical and non-symmetrical members of a new class of prodrugs in bone disease treatments
Authors: Barbey C. , Lecouvey M. , Mallard I. , Prangé Th. , Neuman A. , Lance M. , Navaza A. 
Published: December 2003

Abstract
Two new hydroxy alkyl bisphosphonate partial esters (HABPA-PE) have been crystallised. The first compound C6H15NaO7P2C2H5O, crystallises as an ethanol solvate and forms rigid infinite β-sheet-like ribbons. The second, C6H16O7P2, displays self-association in dimers. In these new structures, packing analyses confirm the enhanced hydrophobic character due to partial esterification compared to naked hydroxybisphosphonic acids and the simplification of their H bonding patterns.
Ab-initio XRPD structural characterization of coordination polymers: the case of [Ag(C3H3N2CS2)]
Authors: Masciocchi N. , Brenna S. , Galli S. , Maspero A. 
Published: December 2003

Abstract
The crystal structure of the one-dimensional polymer [Ag(C3H3N2CS2)] has been determined from conventional X-ray powder diffraction methods, through simulated annealing and Rietveld refinement techniques [Ag(C3H3N2CS2)] is monoclinic, P21/c; a = 8.409(1), b = 11.740(1), c = 6.721(1) Å, β = 101.86(2)°, V = 649.3(2) Å3; Z = 4; ρ = 2.566 g cm-3 Final Rwp
, Rp
and RF
agreement factors, for 3100 data points collected in the 8–70° 2θ range, are 0.091, 0.071 and 0.058, respectively Anisotropic peak shapes and high-angle tails for the 0k0 (and neighboring) reflections suggest that the polymeric chains, aligned along b, suffer from a partial disorder, in that packing of adjacent molecules does not conform to a rigorous crystalline, truly periodic, tiling.
Preparation and crystal structure of a new high-pressure phase (V0.5Re0.5)O2 with rutile-type structure
Authors: Bramnik K. G. , Ehrenberg H. , Theissmann R. , Fuess H. , Morán E. 
Published: December 2003

Abstract
The new complex oxide (V0.5Re0.5)O2 has been synthesized under high pressure of 60 kbar at 1000°C, and its crystal structure determined by single crystal X-ray diffraction data analysis (S.G.: P42/mnm, a = 4.6357(4) Å, c = 2.8292(3) Å, V = 60.80(1) Å3). This compound adopts a rutile-type structure with random cat ion distribution on one crystallographic site. The substitution of 50 vanadium by rhenium stabilizes the high temperature form of VO2 at room temperature. The cation ratio of 1 : 1 was confirmed by EDX analysis performed by electron microscopy on the same crystals used for X-ray diffraction.
Electron crystallography of zeolites. 1. Projected crystal structures of ZSM-5 and ZSM-11
Authors: Dorset Douglas L. 
Published: December 2003

Abstract
The prospect of carrying out quantitative crystal structure analyses by direct methods with electron diffraction intensity data from zeolites is evaluated for two related materials: ZSM-5 and ZSM-11. The stacked plate-like arrays of ZSM-5 induce intensity perturbations from secondary electron scattering; nevertheless, the T-site positions can be found by direct methods. Intensity data from smaller ZSM-11 microcrystals are more favorable for ab initio analysis so that some oxygen positions are found during Fourier refinement. For intergrowths of one zeolite in the other, the nature of the inclusions has been found to depend on the dominant species. If ZSM-5 is dominant, the apparent ZSM-11 inclusions (assuming a preferred platy orientation) could be rather large, whereas if ZSM-11 is dominant, the ZSM-5 inclusions extend over only 3 or 4 unit cells.
The structures of ZrNCl, TiOCl and AlOCl in the light of the Zintl-Klemm concept
Authors: Vegas A. , Santamaría-Pérez D. 
Published: December 2003

Abstract
The structures of ZrNCl on one hand and TiOCl and AlOCl on the other hand are analysed in comparison with the Zintl phases Ca[Al2Si2] and Na[AlSi], respectively. In the former, the [ZrN]+ sublattice is isostructural to the [Al2Si2]2- skeleton whereas the latter are orthorhombic distortions of the Na[AlSi] structure. The three structures can be rationalised by means of an inverse Zintl-Klemm concept, in similarity with the Zintl-Klemm concept which accounts for the structures of the Zintl phases. In addition, Ca[Al2Si2] presents the same structure than the hexacelsian oxide Ca[Al2Si2O8] providing a new example of how the cation arrays, in oxides, maintain the structure of their respective alloy.
Single crystal neutron diffraction study of the phase transition in (NH4)H5(PO4)2
Authors: Troyanov Sergej I. , Kosterina E. V. , Loose A. , Reehuis M. , Kemnitz Erhard 
Published: December 2003

Abstract
The crystal structure of NH4H5(PO4)2 was investigated at 298 and 80 K by single crystal neutron diffraction. The room temperature modification II crystallizes monoclinic (space group C2/c), a = 10.156(4), b = 7.554(3), c = 9.507(4) Å, β = 100.71(4)°, Z = 4. It is characterized by disorder of the NH4
+ cations and short symmetrical hydrogen bonds (2.422(8) Å) connecting the layers of H2PO4 tetrahedra. The low temperature modification I is monoclinic, (space group P21/c), a = 10.040(4), b = 7.628(2), c = 9.558(3) Å, β = 102.51(4)°, Z = 4. Below the phase transition the NH4
+ cations become ordered and the layers of PO4 tetrahedra are connected by asymmetrical hydrogen bonds (2.427(7) Å) allowing to formulate the phase I as (NH4)(H2PO4)(H3PO4). The changes in the thermal ellipsoids and a possible mechanism of the phase transition are discussed.
The crystal structure of Er(HPO4)(NO3)·3 H2O: ab initio determination from X-ray powder diffraction data
Authors: Ivashkevich L. S. , Lyakhov A. S. , Selevich A. F. , Petrusevich Yu. I. 
Published: December 2003

Abstract
The crystal structure of orthorhombic Er(HPO4)(NO3)·3 H2O has been determined from X-ray powder diffraction data. The unit cell dimensions are a = 10.1653(4) Å, b = 11.9178(5) Å, c = 6.8533(3) Å, V = 830.26(6), Z = 4. The space group is Pbcm (No. 57) or Pbc21 (No. 29). The structures were solved ab initio using EXPO program and refined by FULLPROF package. Because geometrical features of the two solutions are the same, the crystal structure has been described in the scope of the centrosymmetric Pbcm space group. Positions of the hydrogen atoms were not defined. The erbium atom is eight coordinated. It is surrounded by one nitrate anion, one water molecule and four phosphate groups. [ErO8] polyhedra are linked together through their edges forming infinite chains extended along the c axis. The chains are connected by phosphate groups to form layers palallel to the yz plane. Probable hydrogen bonds are discussed.
Molecular and crystal structure of 5-amino-1H-[1,2,4]triazole-3-carboxylic acid derivatives
Authors: Wawrzycka-Gorczyca I. , Rzeszotarska B. , Dżygiel A. , Masiukiewicz E. , Kozioł A. E. 
Published: December 2003

Abstract
The analysis of molecular structures of three derivatives: 5-amino-3-carbomethoxy-1-methyl-1H-[1,2,4]-triazole (1), 1-acetyl-5-amino-3-carbomethoxy-1H-[1,2,4]-triazole (2) and 5-acetylamino-3-carbomethoxy-1-methyl-1H-[1,2,4]triazole (3) indicate the sensitivity of the N2–N1–C5 fragment of the triazole ring to the substitution. Molecular conformations are influenced by several intra- and intermolecular contacts. In all structures very extensive N–H···N/O and C–H(methyl)···O/N net of secondary interactions is formed. This kind of interactions is common in crystal structures which are proton-deficient and for this reason various types of multi-point interactions are forced. Besides, triazole π···π stacking interactions are observed.
Synthesis and structural investigation of (4-methoxy-phenyl)-[4-(4-methoxy-phenyl)-1-(1-phenylethylidene-amino)-2-thioxo-1,2-dihydro-pyrimidin-5-yl]-methanone
Authors: Akkurt M. , Sarıpınar E. , Öztürk S. , Yılmaz C. , Fun H.-K. 
Published: December 2003

Abstract
The crystal structure of (4-methoxy-phenyl)-[4-(4-methoxy-phenyl)-1-(1-phenylethylideneamino)-2-thioxo-1,2-dihydro-pyrimidin-5-yl]-methanone, has beeen determined by single-crystal X-ray diffraction at 183(2) K. The compound crystallizes in the monoclinic system, space group P21/c. The O3 and C19 atoms in the methoxy group shows conformational disorder. In the title compound, the pyrimidine ring is slightly nonplanar. The angle between the planes formed by the ring atoms N2–C2–C3 and C1–N1–C4 is 4.0 (1)°. The three phenyl rings form dihedral angles of 147.9 (1), 113.0 (1) and 103.2 (1)° with the pyrimidine ring. The structure is stabilized by weak intermolecular C–H...O interactions.
Structural and spectral studies of N-(3-hydroxypyridine-2-yl)salicylideneimine and N-(3-hydroxypyridine-2-yl)-5-bromosalicylideneimine and their dimethyltin(IV) complexes
Authors: Öztaş S. G. , Şahin E. , Ancın N. , İde S. , Tüzün M. 
Published: December 2003

Abstract

N-(3-hydroxypyridine-2-yl)salicylidineimine (1), N-(3-hydroxypyridine-2-yl)-5-bromo salicylideneimine (2) and their diorganotin(IV) complexes formulated as Me2Sn(OC6H4CH=NC5H3NO) (3) and Me2Sn(OC6H3BrCH=NC5H3NO) (4) were prepared and characterized by 1H-NMR, IR, mass spectroscopy and single crystal x-ray diffraction study. The crystal structures of 3 [orthorhombic, Pbna (no 60); a = 10.439(1) Å, b = 13.388(3) Å, c = 19.340(2) Å, Z = 4; V = 2703(1) Å3] and 4 [monoclinic, P21/a (no 14); a = 7.528(4) Å, b = 16.576(7) Å, c = 12.017(7) Å, β = 97.97(5), Z = 4; V = 1485(1) Å3] have been solved by standard methods and refined by full-matrix least squares (carried out on F
2) to R values of 0.066 and 0.046 respectively. The studied tin(IV) complexes (3 and 4) exhibit the distorted trigonal-bipyramidal geometries around Sn atoms, separately. The tautomeric effects of ligands and the substitution of Br atom to the common molecular structure were discussed beside of the coordination geometries of 3 and 4.
Synthesis, crystal structure and electrochemical behaviour of [2,6-bis(3,5-dimethylpyrazolyl)pyridine](dithiocyanato)cobalt(II)
Authors: Arıcı C. , Ülkü D. , Kurtaran R. , Emregül K. C. , Atakol O. 
Published: December 2003

Abstract
A mononuclear cobalt(II) complex, [Co(dmpp)(SCN)2], was synthesized using 2,6-bis (3,5-dimethylpyrazolyl)pyridine (dmpp) and thiocyanate anion (SCN), and characterized by IR spectroscopy and single-crystal X-ray diffraction. In addition, cyclic voltammetric studies have been performed. The complex crystalizes in monoclinic space group C 2/c, with unit cell dimensions a = 15.2469(15), b = 9.1120(9), c = 14.0302(11) Å, β = 95.823(3)°. The cell containes 4 molecules.
Crystal structure and properties of L-arginine diphosphate
Authors: Haussühl S. , Karapetyan H. A. , Petrosyan A. M. 
Published: December 2003

Abstract
Single crystals of L-arginine diphosphate (L-HN:C(NH2)NH(CH2)3CH(NH2)COOH·2 H3PO4, abbreviated as LADP) with dimensions of ca 15 × 20 × 40 mm and of optical quality were grown by controlled evaporation of aqueous solutions. A structure analysis showed that LADP (space group P212121, a
1 = 9.681(2), a
2 = 21.756(4), a
3 = 7.000(14) Å, Z = 4 at 293 K) is isotypic to L-arginine·2 H3AsO4. The tensors of thermal expansion as well as of dielectric, elastic, thermoelastic, piezoelastic and piezoelectric properties were measured and compared with corresponding properties of L-arginine·H3PO4·H2O (LAP).
The (3 + 1)-dimensional superspace description of the commensurately modulated structure of p-chlorobenzamide (α-form) and its relation to the γ-form
Authors: Schönleber A. , Pattison P. , Chapuis G. 
Published: December 2003

Abstract
The room temperature structure (α-form) of the organic compound p-chlorobenzamide, C7H6ClNO, can be described as a classical three-dimensional periodic superstructure (α
S) and also as a commensurately modulated structure (α
M) in (3 + 1)-dimensional superspace. The diffraction pattern is characterized by a clear difference in intensity between main and satellite reflections. All reflections can be indexed with four indices hklm in a triclinic unit cell and one modulation vector in the superspace group P1̅(αβγ) with the modulation vector q⃗ = 1/3·a⃗*. The structure undergoes a phase transition at higher temperature. In this phase transition the modulation vanishes as indicated by the disappearance of the satellite reflections. The resulting high temperature phase (γ-form) contains one molecule in the asymmetric unit, the space group is P1̅. The high temperature structure (γ) is very close to the reference structure of the modulated model at room temperature. The phase transition can therefore be understood as a loss of the modulation at high temperature.
Rietveld refinement of incommensurate low tridymite
Authors: Graetsch H. A. 
Published: December 2003

Abstract
The incommensurate modification of SiO2 low-tridymite was refined in the 3 + 1 dimensional superspace group Cc(α0γ) 0 at 295 and 325 K from X-ray powder diffraction data. The displacive modulation mainly consists of tiltings of rigid SiO4/2 tetrahedra with the wave vector r = 0.656a* – 0.496c* (dimensions of the average cell: a = 5.005 Å, b = 8.598 Å, c = 8.213 Å and β = 91.50°). The largest amplitude is ca. 0.6 Å for oxygen and ca. 0.3 Å for silicon. Wave vector and amplitudes of the displacive modulation functions vary only very little with increasing temperature.
Wickenburgite, a double-layer silicate Pb3Al[6][Ca[6]Al[4]Si[4]
10O27(H2O)3]·H2O: Crystal chemistry and thermal behaviour
Authors: Hesse K.-F. , Liebau F. , Eulert H.-H. 
Published: December 2003

Abstract
To clarify discrepancies in the literature with regard to the water content and crystal structure of wickenburgite, chemical and thermal analyses and IR spectroscopic measurements were made and the structure was redetermined with single-crystal X-ray diffraction data. It was found that the idealised composition of the mineral is Pb3Al2CaSi10O27·4 H2O rather than Pb3Al2CaSi10O27·3 H2O as reported by Lam et al. in 1994. Based on chemical analysis and crystal structure determination, there is considerable isomorphous replacement on the cation positions, leading to the crystal-chemical formula
Pb3(Al0.79Pb0.22)Σ1.01
[6]{
uB
, 4, 2∞
2} [Ca1.02
[6](Al0.81Fe0.06Si0.14)Σ1.01[4]Si10.00
[4]O27(H2O)3]·H2O.
With regard to crystal structure, that described by Lam et al. is found to be essentially correct, except for an additional H2O molecule per formula unit, whereas the structure suggested by Penna & Giese in 1968 and by Hesse & Liebau in 1992 and 1993 is incorrect. The wickenburgite structure contains silicate double-layers in which one out of twelve [(Al, Si)O4] tetrahedra is replaced by an [O3Ca(H2O)3] octahedron. Adjacent double layers are held together by Al3+ and Pb2+ cations that are octahedrally and irregularly eight-fold coordinated, respectively. The fourth H2O molecule per formula unit occupies a small cavity which is formed by six oxygen atoms from two adjacent double layers and three interlayer lead ions, thus shielding the repulsive forces between the lone-pair electrons of the latter. Minor but varying amounts of adhering, non-crystalline water is reversibly lost upon heating below 100°C. The cavity water is steadily and irreversibly lost between approximately 100 and 550°C (at a heating rate of 10°C per minute). Before all cavity water has been driven out, water coordinating the Ca2+ ions begins to escape. This dehydration process is accompanied by an approximately 4.4 percent reduction of the unit-cell volume without substantial disruption of the structure. At 740 °C the dehydration is not yet complete. The structure of wickenburgite is related to that of jagoite which contains both silicate single- and double-layers. In the double-layers of wickenburgite one out of twelve [(Al, Si)O4] tetrahedra is replaced by an [O3Ca(H2O)3] octahedron whereas in jagoite within the double-layers two out of twelve [(Fe, Si)O4] tetrahedra are replaced by [PbO3] pyramids.
Structure characterization of molecular complexes for non-linear optical materials I. X-ray analysis and AM1 calculations of 1 : 1 complexes of 8-hydroxiquinoline (1) and isonicotinamide (2) with 2,4,6-trinitrophenol
Authors: Carvalho C. C. , Camargo A. J. , Teijido Maurício Vega , Isolani P. C. , Vicentini G. , Zukerman-Schpector Julio 
Published: December 2003

AbstractC6H2N3O7–·C9H8NO+(1), Mr = 374.27,P21/c,a= 8.2606(9),b= 9.2574(9),c= 19.906(2) Å,β= 91.441(8)°,Z= 4,R1= 0.0405. C6H2N3O7–·C6H7N2O+, (2), Mr = 351.24,P21/n,a= 14.3064(6),b= 7.4451(7),c= 14.7209(7) Å,β= 116.626(3)°,Z= 4,R1= 0.0385. The packing units in both compounds consist of hydrogen bonded cation-anion pairs. The basic first and second-level graph set analysis are given. The (hyper)polarizabilities have been calculated for the crystallographic and optimized molecules, by the semi-empirical quantum method AM1.
The twinned and disordered crystal structure of tetrakis(triphenylphosphine)silver(I)bis(trifluoroacetato)triphenylstannate(IV)
Authors: Ng Seik Weng , Rae A. David 
Published: December 2003

Abstract
The crystal structure of tetrakis(triphenyl-phosphine)silver(I)bis(trifluoroacetato)triphenylstannate(IV), [(C6H5)3P]4Ag (C6H5)3Sn(O2CCF3)2 [R3: a = 16.238(1), c = 52.354(3) Å], consists of discrete four-coordinate te trahedral cations and five-coordinate trans-C3SnO2 trigonal bipramidal anions. The asymmetric unit consists of a third of each of two cations and two anions. The structure is a 0.675(3): 0.325 twin of a 0.783(1): 0.217 disorder of an R3 structure that uses a 2-fold rotation operation of R32 for the twinning and the disorder. The structure is refined on 234 variables and 6276 reflections with I > 3σ(I) to R
F = 0.053.
Theoretical explanation of the octahedral distortion in FeF2and MgF2
Authors: Riss Alexander , Blaha Peter , Schwarz Karlheinz , Zemann Josef 
Published: December 2003

AbstractThe equilibrium geometries of rutile type FeF2and MgF2are determined using precise density functional theory calculations that lead to good agreement with experimental data. The strong deviation from the “ideal” octahedral geometry in FeF2comes from the Fe2+ion with thed6configuration in the high-spin state, which would require a singly occupied spin-downdorbital. The stability can only be understood by going beyond the first coordination shell considering direct Fe–Fe interactions mainly along thec-axis. The orbital population of the various Fe-dorbitals is analyzed using constarint distortions between the ideal and the equilibrium structure. Above a critical Fe–Fe distance of about 3.15 Å the population numbers change drastically, a single Fe-dspin down orbital becomes occupied and the system can relax to an insulating state. In MgF2no suchd-orbitals are present and thus the distortions are much smaller.
Rational approximants to 5, 8 and 7-fold two-dimensional tilings
Authors: Subramaniam Anandh , Ramakrishnan Krishnamurthy 
Published: December 2003

Abstract
The strip projection method is used to generate rational approximants to Penrose, octagonal and 7-fold tilings. Two types of approximants to the Penrose tiling are considered, wherein the basis vectors of the approximants are either orthogonal or are 72° apart. Various types of approximants including those with partially retained quasiperiodicity are generated and the pseudosymmetries arising therein analyzed. A simplified approach based on uniform distortions of perpendicular space is put forth for the analyses.
The cubic limiting complexes of the tetragonal lattice complexes
Authors: Koch Elke , Fischer Werner 
Published: December 2003

AbstractFor all tetragonal lattice complexes the limiting complexes with cubic characteristic space-group type have been derived. These limiting complexes are caused by a specialization of the axial ratioc/a. However, they may require in addition special coordinate parameters.The limiting complexes have been determined with the aid of group-subgroup relationships. In order to check the material, the occurrence of cubic sphere packings within tetragonal lattice complexes was used. The results are presented in four separate tables referring to the 4 invariant, the 24 univariant, the 38 bivariant and the 48 trivariant tetragonal lattice complexes.