Showing papers in "Zeitschrift Fur Kristallographie in 1996"
93 citations
TL;DR: In this paper, a statistical analysis based on 1924 [LX m ] polyhedra is presented, where L are cations having one electron lone-pair and X=O, S or Se.
Abstract: According to the current bond-valence concept, the valence V i of an atom A i is a function of the distances D ij to its neighbors X j and can be calculated using V i = ΣS ij = Σexp[(r o -D ij )/0.37] , where the bond-valence parameter r o is considered to be constant for each element pair A-X. A statistical analysis based on 1924 [LX m ] polyhedra is presented, where L are cations having one electron lone-pair and X=O, S or Se. According to this analysis, for i r o for each individual [LX m ] polyhedron is dependent on the stereochemical influence of the lone-pair electrons on the geometry of the polyhedron. This influence is expressed by a vector Φ i = Φ(LX j -L i -X j , D ij ). As a result, the formal bond-valence sum for an individual lone-pair cation L i can be calculated with ΣS ij = Σexp[(E|Φ i |+F-D ij )/0.37] where E and F are constants.
62 citations
TL;DR: For the calculation and drawing of Dirichlet domains and coordination polyhedra in crystal structures or point sets, two programs, DIDO95 and VOID95, have been derived as mentioned in this paper.
Abstract: For the calculation and the drawing of Dirichlet domains and coordination polyhedra in crystal structures or point sets two programs - DIDO95 and VOID95 - have been derived. A third program - DEMODIDO - shows how the Dirichlet domain of a point changes if the metrical parameters or the coordinates vary along a one-dimensional path. All three programs are written in FORTRAN and may be used on an ordinary PC under DOS.
56 citations
TL;DR: In this article, the authors compare refinement results of crystal structures on the basis of neutron powder data of orthorhombic NdGaO 3 (300 K) and of rhombohedral LaGaO3 (573 K).
Abstract: From neutron powder diffraction intensities it is often problematic to distinguish between centrosymmetry and non-centrosymmetry. X-ray single crystal diffraction may be more accurate. In this paper we compare refinement results of crystal structures on the basis of neutron powder data of orthorhombic NdGaO 3 (300 K) and of rhombohedral LaGaO 3 (573 K), obtained from non-centrosymmetric and centrosymmetric starting models. By using of X-ray single crystal measurements, the structures of LaGaO 3 and NdGaO 3 could be determined as being centrosymmetric corresponding to the space group R3c and Pbnm, respectively.
48 citations
37 citations
TL;DR: In this paper, the authors describe the crystal chemistry and chemical bonding of EuPtIn, EuZnSn, and EuPsn in comparison with other intermetallic europium compounds, all of which crystallize with structures related to CeCu 2 and TiNiSi.
Abstract: The title compounds were prepared from the elements in sealed tantalum tubes at 1320 K and subsequent annealing at 970 K. EuZnIn adopts the CeCu 2 structure (space group Imma) with a random distribution of the Zn and In atoms on the Cu position. EuPtIn and EuZnSn crystallize with the ordered CeCu 2 structure (space group Pnma). The three structures were refined from single crystal X-ray diffractometer data: a = 482.3(1) pm, b = 780.7(2) pm, c = 827.6(2) pm, wR2 = 0.0773, 367 F 2 values and 13 variables for EuZnIn, a = 746.94(8) pm, b = 447.27(6) pm, c = 843.46(9) pm, wR2 = 0.0689, 381 F 2 values and 20 variables for EuPtIn, and a = 789.4(1) pm, b = 476.7(1) pm, c = 807.9(1) pm, wR2 = 0.0955, 474 F 2 values and 20 variables for EuZnSn. The site occupancies for the transition metal and indium (tin) atoms are different in EuPtIn and EuZnSn. The more electronegative atoms, Pt and Sn, occupy the energetically favored positions with the maximum Pt-Pt and Sn-Sn separation in the rhombus of the [PtIn] and [ZnSn] polyanions. The crystal chemistry and chemical bonding of EuZnIn, EuZnSn, and EuPtIn is discussed in comparison with other intermetallic europium compounds, all of which crystallize with structures related to CeCu 2 and TiNiSi.
35 citations
TL;DR: In this article, the Rietveld method has been applied to refine the structure of magnesium substituted β-tricalcium phosphate at a magnesium content of about 14 mol% and the results of the refinements, which show a final agreement factor R WP = 0.12, are in agreement with an almost complete substitution in two of the five crystallographically independent cation sites.
Abstract: Rietveld method has been applied to refine the structure of magnesium substituted β-tricalcium phosphate at a magnesium content of about 14 mol%. The results of the refinements, which show a final agreement factor R WP = 0.12, are in agreement with an almost complete substitution in two of the five crystallographically independent cation sites. The preference of magnesium for these two sites can be explained on the basis of the coordination geometry of the five different cation sites. Furthermore the results allow to interpret the discontinuity found around 10 magnesium mol% in the variation of the c axis as a function of magnesium content.
33 citations
TL;DR: In this article, the crystal structure of cubic Al 68 Pd 20 Ru 12 was investigated by means of single crystal X-ray structure analysis: space group P23 (No. 195), a = 15.540(2) A, V = 3753(1)A 3, Pearson symbol cP296-46.85.
Abstract: The crystal structure of cubic Al 68 Pd 20 Ru 12 was investigated by means of single crystal X-ray structure analysis: space group P23 (No. 195), a = 15.540(2) A, V = 3753(1)A 3 , Pearson symbol cP296-46.85. The chemical composition was determined by microprobe analysis: Al 68 Pd 20 Ru 12 , M r = 6316, Z = 2, D calc = 5.59 Mg m -3 ; MoK α , refined as Al 87 Pd 38 , F(000) = 5758, μ = 9.89 mm -1 , R(wR) = 0.056(0.052) for 1289 reflections with F > 3σ(F) and 133 variables, goodness of fit S = 2.21. The structure contains 35 different orbits. Body centred pseudo symmetry is broken by the distribution of atoms, the non-centrosymmetric point symmetry 23 of this structure is close to m3 in space group Pn3. Disorder of Al atoms is observed at a number of positions. Interatomic distances cover the ranges of 2.98 A to 3.20 A, 2.43 A to 3.12 A and 2.54 A to 3.66 A, for contacts TM - TM, Al - TM and Al - Al, respectively (TM: transition metal). The coordination shells contain triangular and/or quadrangular faces forming icosahedra, rhombic dodecahedra or respective combinations of these two basic forms. Links to cubic approximants of icosahedral phases are shown and relationships to neighboring crystalline and decagonal phases are discussed.
27 citations
TL;DR: In this paper, the satellite reflections and s-layers in urea inclusion compounds with guest molecules of varying lengths were investigated between room temperature and 30 K, and it was found that diffuse s-layer widths, which are due to weak lateral correlations of the guest molecules, are not sharp parallel c* at room temperature as assumed previously, but show a broadening of their widths with increasing order.
Abstract: X-ray diffuse scattering phenomena and satellite reflections in urea inclusion compounds with guest molecules of varying lengths (tridecane, tetradecane, pentadecane, heptadecane and a mixture of pentadecane and hexadecane) were investigated between room temperature and 30 K. It was found that diffuse s-layers, which are due to weak lateral correlations of the guest molecules, are not sharp parallel c* at room temperature as assumed previously, but show a broadening of their widths with increasing order. With decreasing temperature the widths of the s-layers decrease and become sharp within the resolution limit at very low temperature, i.e. there is an ordering of the guest molecules along the urea host tunnels. The modulations of the s-layers point towards a lateral correlation of the guest molecules at room temperature which can be described by a box-shaped distribution function. A model is described which explains the existence of (numerous) satellite reflections and satellite s-layers at low temperatures. Some of the satellites are also observable at room temperature in inclusion compounds with guest molecules longer than tetradecane. They can be assigned to a non-negligible interaction between host and guest. Possible commensurations of these satellite reflections with main (guest-) reflections have been a source of misinterpretations in the literature.
25 citations
TL;DR: The crystal structures of the mixed skutterudites CoGe 1.5 and CoGe1.5 were determined by X-ray diffraction of powder samples and pseudomerohedral multiple twins as mentioned in this paper.
Abstract: The crystal structures of the mixed skutterudites CoGe 1.5 S 1.5 and CoGe 1.5 Se 1.5 were determined by X-ray diffraction of powder samples and pseudomerohedral multiple twins (space group R3, No. 146, Z = 24, CoGe 1.5 S 1.5 : a = 1133.63(10)pm, c = 1391.76(9) pm, R(F) = 2.2%, 4288 unique reflections; CoGe 1.5 Se 1.5 : a = 1173.00(8) pm, c = 1441.1(3) pm, R(F)= 2.8%, 828 unique reflections). The triple pseudomerohedral twins are connected by three twofold rotation axes, which are linked by a threefold rotation axis. An absorption correction was performed by an intensity and volume ratio weighted empirical method. The intensity data for CoGe 1.5 Se 1.5 were collected in two different azimuth and θ positions in order to minimise the absorption effects. The structures obtained are compared with those of binary skutterudites with respect to symmetry relations of the space groups and bonding of the rhombic Ge 2 X 2 units (X = S, Se), which partly reveal antiaromatic 4π electron behavior.
24 citations
TL;DR: The crystal structure of [Fe II (bpy) 3 ] 2+ n [AgCr III (ox) 3 ], where bpy = bipyridine, ox = oxalate, C 36 H 24 AgCrFeN 6 O 12, has been determined by X-ray diffraction at room temperature.
Abstract: The crystal structure of [Fe II (bpy) 3 ] 2+ n [AgCr III (ox) 3 ] n 2n- , where bpy = bipyridine, ox = oxalate, C 36 H 24 AgCrFeN 6 O 12 , has been determined by X-ray diffraction at room temperature. Cubic crystals of tetrahedral shape have space group P2 1 3, a= 15.486(3) A, Z = 4. The absolute structure, with respect to the crystal form {111}, based on the four indexed crystal faces, was refined on F 2 by using a full-matrix procedure to final R = 0.050. The three-dimensional three-connected polymeric anionic silver(I)-chromium-(III)tris-oxalate network consists of [Ag I (ox) 3 ] and [Cr III (ox) 3 ] subunits. These subunits and the cationic complex [Fe II (bpy) 3 ] 2+ , which templates the structure, are all chiral and exhibit the Λ configuration. The chirality of the anionic decagon connected network corresponds to right-handed helicity. The cationic complexes fill the voids within the anionic network, and the iron(II) centers occupy sites with symmetry 3 at positions x, x, x (Wyckoff letter a). The Ag and Cr atoms occupy also special positions on three-fold rotation axes (Wyckoff letter a). The shortest distance between Ag and Cr in the three-dimensional network is 5.579(2) A. There are only weak hydrogen bonding contacts of type C-H...O between the bpy ligands and the oxalate oxygen atoms as acceptors. Overall, this structure represents a rare case of a chiral polymeric decagon framework type which has been accomplished because of the special coordination algorithm of the linking metal ions as well as of the choice of the bis-chelating ligands.
TL;DR: In this paper, the conformation of non-substituted porphyrins with small mesosubstitutents was investigated by determination of the crystal structures of 2,3,7,8,12,13,17,18-octaethyl-5-(Nsuccinimidyl)porphyrin.
Abstract: Studies on highly substituted porphyrins bearing eight β-substituents and at least one bulky mesosubstitutent have shown that peripheral steric strain leads to considerable macrocycle distortion. While this is well established for porphyrins with dodecasubstitution ; the situation is less clear for nonasubstituted porphyrins with meso-substituents such as methyl, aryl or ester groups. In order to further study this situation we have investigated the conformation of nonasubstituted porphyrins with small meso-substitutents by determination of the crystal structures of : 2,3,7,8,12,13,17,18-octaethyl-5-(N-succinimidyl)porphyrin, 1 ; 2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-5-methoxymethylporphyrin, 2 ; pyridine(2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-5-methoxymethylporphyrinato) zinc(II), 3 ; methanol(5-acetoxy-2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-porphyrinato) zinc(II) methanol solvate, 4 ; and (2,3,7,8,12,13,17,18-octaethyl-5-methylporphyrinato)zinc(II), 5. The compounds show only small deviations from planarity which might be due to packing effects, however, all compounds show some degree of rhomboic elongation of the porphyrin core.
TL;DR: In this paper, the tetragonal structure of Cu(C 4 H 4 O 4 )H 2 O was established from X-ray single crystal diffraction, λ (CuK α = 1.5418 A); space group P4 2 2 1 2; a = 8.853(4)A, c = 14.1 A 3 ; M = 197.63; D x = 2.25 g/cm 3 ; Z = 8; μ = 5.049 mm -1 ; F(000) = 792; R = 0.
Abstract: Cu succinate was obtained by treating of naturally occuring azurite with detergent which presumedly contained succinic acid. The tetragonal structure of Cu(C 4 H 4 O 4 )H 2 O was established from X-ray single crystal diffraction, λ (CuK α = 1.5418 A); space group P4 2 2 1 2; a = 8.853(4)A, c = 14.866(8)A, V = l165.1 A 3 ; M = 197.63; D x = 2.25 g/cm 3 ; Z = 8; μ = 5.049 mm -1 ; F(000) = 792; R = 0.078 for 366 reflections. The new phase is characterized by a layered structure, which consists of Cu cations linked by chelating - bridging dicarboxylate anions. The structure is closely related to that of copper maleate hydrate.
TL;DR: For the first time single crystal diffraction experiments on individually mounted kaolinite crystals with volumes of 8μm 3 to 04 μm 3 are reported in this article, where diffraction patterns prove that no reflections violating the C-centering exist.
Abstract: For the first time single crystal diffraction experiments on individually mounted kaolinite crystals with volumes of 8 μm 3 to 04 μm 3 are reported The diffraction patterns prove that no reflections violating the C-centering exist, confirming the space group C1 for kaolinite Preliminary refinements confirm the structural model of kaolinite in C1 Non-hydrogen atoms could be refined anisotropically and the hydrogen positions could be refined as well The diffraction patterns show diffuse scattering in streaks along 001 through hkl reflections with hk not equal zero, which is caused by stacking faults The diffraction pattern of the smallest (04 μm 3 ) sample also reveals micro twinning and diffuse scattering This sample consists of domains of left and right handed kaolinite
TL;DR: In this paper, the crystal structure of the low temperature form of ZSM-11 (structure code MEL) was refined from high-resolution synchrotron X-ray powder diffraction data, recorded at 20 K. Based on the results of 2D 29 Si NMR investigations, a model was obtained by energy minimization the Rietveld refinement of which converged in space group I4 (No. 82) [a = 20.019(2)A; c = 13.380(1)A] to R I = 0.
Abstract: The crystal structure of the low temperature form of ZSM-11 (structure code MEL) was refined from high resolution synchrotron X-ray powder diffraction data, recorded at 20 K. Based on the results of 2D 29 Si NMR investigations a model was obtained by energy minimization the Rietveld refinement of which converged in space group I4 (No. 82) [a = 20.019(2)A; c = 13.380(1)A] to R I = 0.143 and R wp = 0.126. Comparison of the theoretically predicted and experimentally determined structures against results from NMR experiments using the average T-T distance relationship between the structural parameters and the isotropic 29 Si chemical shifts did not show any correlation with the results of the structure refinement. However, with the values obtained from the energy-minimized structure model a good correlation between the structural parameters and the chemicals shifts of Si was obtained for one of the two possible assignments of the NMR chemical shifts to Si-sites. The fit of the energy minimized model to the experimental data set gave R I = 0.179 and R wp = 0.157. Since the NMR experiment gives direct information about the local ordering and structural state of the material this demonstrates the potential of the modeling experiment and also reveals the limits in accuracy and precision of the Rietveld structure refinement.
TL;DR: In this article, the structure of three hydrated germanates K 3 HGe 7 O 16.3.1 H 2 O, Rb 3 HG 7 O16.3 HG, Rb 2 HG 6 O 16.3 A, and Rb 1.56660(4) A were determined from Rietveld refinement of powder diffraction patterns collected using synchrotron radiation.
Abstract: The structures of three hydrated germanates K 3 HGe 7 O 16 . 3.1 H 2 O, Rb 3 HGe 7 O 16 . 3.1 H 2 O and Cs 3 HGe 7 O 16 . 2.3 H 2 O have been determined in space group 123, no. 197, Z = 8, with a = 15.34960(4) A, 15.45998(4) A and 15.56660(4) A, respectively, from Rietveld refinement of powder diffraction patterns collected using synchrotron radiation. The structure of these germanates consists of a three-dimensional framework of tetrahedrally and octahedrally coordinated Ge atoms, with charge compensating cations and water molecules occupying the interconnecting channels. The cations occupy sites near the centres of two types of window approximately 3.3 A across. One window is nearly circular whilst the other is more elliptical. On partial dehydration, the body-centred superstructure is lost for the Rb and Cs compounds. The structures of Rb 3 HGe 7 O 16 . 0.69 H 2 O and CS 3 HGe 7 O 16 . 0.70 H 2 O have been refined in space group P43m, no.215, Z = 1, with a = 7.66990(1) A and 7.73347(3) A, respectively. In these materials the window apertures are now identical and are circular. For the partially dehydrated K form a 2 x 2 x 2 face-centred cubic structure forms, with a lattice parameter similar to the body-centred hydrated form, a = 15.0844(2) A.
TL;DR: In this paper, the real symmetry of the room-temperature modification of K 3 [Nb 3 O 6 |(BO 3 ) 2 ] was determined using a single-domain crystal.
Abstract: The anhydrous potassium niobate borate K 3 [Nb 3 O 6 |(BO 3 ) 2 ] has been grown from potassium borate flux to crystals of good optical grade and dimensions of up to 6 x 6 x 20 mm 3 . Incorrectly described earlier as trigonal P31m, K 3 [Nb 3 O 6 |(BO 3 ) 2 ] normally forms multidomain crystals at room temperature, composed of three different orientation states. The reported crystal structure of the room-temperature modification of K 3 [Nb 3 O 6 |(BO 3 ) 2 ], determined using a single-domain crystal, shows that the real symmetry is orthorhombic with space group P2 1 ma (No. 26) (a = 17.506(2) A, b = 15.162(3) A, c = 3.968(4) A, Z = 4, D X = 3.845 g/cm 3 , μ(MoK α ) = 4.122 mm -1 , R(F) = 0.030 for 2752 unique reflections (I > 4σ(I)).
TL;DR: In this article, the coordination sequence for simple 4-connected nets such as occur in zeolite frameworks can be expressed by sets of equations, quadratic in shell number.
Abstract: It is shown that the coordination sequence for many simple 4-connected nets such as occur in zeolite frameworks can be expressed by sets of equations, quadratic in shell number. In some instances a set of equations can be reduced to one equation utilizing trigonometric functions. The coefficient of the quadratic term is well correlated with the geometrical density. Low-density nets with a high proportion of three rings are described; they form a group separate from typical zeolite nets as far as density correlations are concerned.
Journal Article•
TL;DR: In this article, the structures of aluminum oxides (β-alumina and tohdite), hydroxides (gibbsite, bayerite and nordstrandite) and oxihydroxides were analyzed on the basis of their cation arrays.
Abstract: The structures of aluminum oxides (β-alumina and tohdite), hydroxides (gibbsite, bayerite and nordstrandite) and oxihydroxides (diaspore and bohmite) are analyzed on the basis of their cation arrays. In all of them, the Al - Al distances and their topologies, can be related to the structure of the parent Al metal. In hydroxides and oxihydroxides, a direct relationship can be also established between their cation arrays and the α- and β-Ga structures. The A1 3+ cation arrays can be also compared with the Al subarray in Zintl phases and intermetallic compounds.