Showing papers in "Zeitschrift Fur Kristallographie in 1982"

Polymorphie, Leitfähigkeit und Kristallstrukturen von Oxo-phthalocyaninato-titan(IV)

Abstract: Oxo-phthalocyaninato-titan(IV) (PcTiO) shows weak electrical conductivity of 5 · 10~ Ω\" 1 cm\" 1 at room temperature. Doping of PcTiO with I2 is accompanied by an increase of conductivity up to 5· 10\" Ω \" 1 cm\" 1 . PcTiO was found to exist in two modifications built up by monomeric complexes: Phase I crystallizes monoclinic in the space group Ρ 2 l /c with the lattice constants a = 1341.1(6) pm, b = 1323.0(3) pm, c = 1381.0(4) pm, β = 103.72(3)°, Ζ = 4. Phase II forms a triclinic structure in space group PT and an unit cell of dimensions a = 1216.6(4)pm, b = 1258.4(5)pm, c = 864.1 (3)pm, α = 96.28(3)°, β = 95.03(4)°, y = 67.86(4)°, Ζ = 2. In both modifications the Ti-atom exhibits a square pyramidal coordination with a short Ti — Ο distance of 165 pm and 163 pm, respectively. Close contacts exist between the phthalocyaninato planes of neighbouring molecules.

Electron-density distributions of three orthopyroxenes, Mg2Si2O6, Co2Si2O6, and Fe2Si2O6

Abstract: The crystal structures, net atomic charges and electron-density distributions of three synthetic orthopyroxens, Mg2Si206 (orthoenstatite), Co2Si206, and Fe2Si206 (orthoferrosilite), have been studied using single crystal X-ray diffraction intensities. In accordance with the fact that the size of Co + is intermediate between those of Mg and Fe + , the structure of Co2Si206, newly determined, is in every respect intermediate between those of orthoenstatite and orthoferrosilite. An average of the net charges of Co in Co2Si206 has been found to be -I0.95 and that of Fe in orthoferrosilite + 1.12. These values are considerably smaller than +1.82 for Mg in orthoenstatite. In the same species of orthopyroxene, which has two distinct octahedral sites Ml and M2, the cation at Ml tends to be more ionic than that at M2; in the case ofCo2Si2Oe, the former has a charge of + 1.3 and the latter + 0.6, both with estimated errors of + 0.1. The net charges determined for Si in the three materials yield an average value of +2.25. Residual Fourier-peaks occurring between Si and bridge oxygen atoms are significantly different, in peak height and distances from Si, from those between Si and non-bridge oxygen atoms. Those occurring around Fe atoms at the Ml and M2 sites of orthoferrosilite, each having a point symmetry 1, have features which are similar respectively to those around M2 and Ml of fayalite, Fe2Si04, the former having point symmetry m and the latter i. * Present address: Department of Earth and Space Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794, U.S.A. 280 S. Sasaki et al . : Elect ron density of o r t h o p y r o x e n e s

Crystal structure of synthetic makatite Na2Si4O8(OH)2 · 4H2O

Abstract: The crystal structure of synthetic makatite, Na2Si408(0H)2 • 4 H 2 0 , [monoclinic, a = 7.3881(5) A, b = 18.094(3)Ä, c = 9.5234(5)Ä, β = 90.64(1)°, Pljc, ζ = 4] was solved by direct methods, (MULTAN), and Fourier syntheses and refined to R = 0.051 for 834 independent reflexions. The makatite structure is built up of corrugated [Si204(0H)j; ~ layers containing rings of six tetrahedra. The layers are connected by octahedral [Na(H20)4]JJ rods and sodium atoms coordinating five oxygens which form distorted trigonal bipyramids. Hydrogen atoms positions have not been determined. Introduction As a part of a general study of zeolites with ion exchange properties for the treatment of nuclear power station wastes we have synthesized a large number of different zeolites. Exclusion of the aluminium component from the N a 2 0 —A1203 —Si02 —H20 system led to the preparation of a number of hydrous layer silicates, of which some are known as minerals, e.g. magadiite (NazO · 14SiOz · 9 H 2 0 ) (McAtee, House, and Eugster, 1968), kenyaite (Na 20 · 22SiOz · 10H 20) (Eugster, 1967) and makatite (Hay, 1968), and some as purely synthetic products, e.g. sodium polysilicate (Na 2 0 • 8 Si02 · 9 H 2 0 ) previously reported by McCulloh (1952) and Iler (1964). Many of these layer silicates have interesting ion exchange properties and this present structure determination was undertaken in order to understand the mechanism of the ion exchange. The details of the syntheses will be published elsewhere but in general most of the preparations yielded crystals to small for single crystal X-ray work. However, in the case of makatite, the introduction * Permanent adress: School of Chemistry, University of Western Australia, Nedlands, 6009. W. Australia 204 Η. Annehed et al.: The crystal structure of makatite of the complexing agent triethanolamine (Charnell, 1971) resulted in the growth of larger, more suitable crystals. Recently Dent Glasser et al. (1980) have proposed by help of electron microscopy methods a new chain type structure for makatite with a repeat distance of 3.4 A in the fibre direction which by our investigation is shown not to be the case.

Dynamisches Verfahren zur Messung von elektostriktiven und elektrooptischen Effekten. Beispiel: Tinkalkonit Na2B4O5(OH)4· 3 H2O

Abstract: A method for the dynamic measurement of electrostrictive and electrooptical effects basing on the principle of a Michelson interferometer has been developed. Changes of optical pathways as small as 0.1 Å can be determined with good accuracy. The linear electrostrictive and the linear electrooptical tensors of tincalconite, Na2B4O5(OH)4 · 3 H2O have been measured.

A new layer structure of MgCl2 with hexagonal close packing of the chlorine atoms

Abstract: The new crystalline β modification of MgCl2 was prepared by dehydration of MgCl2 • 6 H 2 0 with SOCl2 and its crystal structure was determined on the basis of X-ray powder patterns. The crystals are trigonal (space-group Ρ3ml) with lattice parameters a = b = 3.641(3), c = 5.927(6) Α; Ζ = 1 . ̂ caic = 2.323 g · cm . Chlorine atoms are in a hexagonal close packed array and the arrangement of the Mg + and CI\" ions corresponds to a layer structure. The cation coordination is octahedral and Mg—CI distances amount to about 2.51 A. For the samples examined comparison between observed and calculated intensities is only qualitative due to the presence of stacking faults in the succession of the layers of chlorine atoms along the c axis.

Metrik und Raumgruppe von BiB3O6

Abstract: Die Verbindung BiB306 wurde von Levin und McDaniel bei der Untersuchung des Systems Bi 2 0 3 — B 2 0 3 nachgewiesen. Kleine Kristalle von BiB306 ließen sich durch sehr langsames Abkühlen einer Schmelze gleicher Zusammensetzung erhalten. Ihre röntgenographische Untersuchung, insbesondere durch Buerger-Präzessions-Aufnahmen der reziproken Netzebenen AO/, Al/ und A2/, ergab monokline Symmetrie und aufgrund der Reflexionsbedingung hkl: h + k = 2 η die möglichen Raumgruppen C2, Cm und C2/m. diesen kommt jedoch wegen eines starken longitudinalen piezoelektrischen Effekts in Richtung [010] nur die Raumgruppe C2 in Betracht. Die Gitterkonstanten wurden aus einer Pulverdiffraktometeraufnahme ermittelt, deren

Die Kristallstrukturen der Bleiniobate vom Pyrochlor-Typ

Abstract: Several phases of lead niobates have closely related crystal structures of the pyrochlore type: Pb! 5 N b 2 0 6 5 (a = 10.567Ä; Fd3m), Pb 2 Nb 2 0 7 (a = 7.472Ä, c = 28.351Ä; P3ml), P b 2 3 1 N b 2 0 7 31 {a = 7.472 A, c = 66 .75Ä;Ä3m)andPb 2 4 4 Nb 2 0 7 . 4 4 ( a = 7.460 A ,c = 96.26Ä; R 3m). As in the case of the ideal cubic pyrochlore structure in P b 1 5 N b 2 0 6 5 interconnected layers of NbOe-octahedra parallel (111) form a stacking sequence AaBbCc of hexagonal tungsten bronze (HTB) like layers A, B, C and layers consisting of single octahedra a, b, c. The structures of the three trigonal phases can be considered as superstructures of the pyrochlore structure. For the compounds Pb 2 Nb 2 0 7 , Pb2 3 1 N b 2 0 7 31 and Pb2 4 4 N b 2 0 7 44 the stacking sequences of layers can be described as AaBbaBbCc, AaBbCcbCcAaBbaBbCcAac and AacAaBbaBbCcbCcAacAaBbaBbCcbCc. Consequently these crystal structures are formed by blocks of 9, 7 or 5 layers. All these structures have oxygen vacancies. Only in the structures of Pb t 5 N b 2 0 6 5 and P b 2 N b 2 0 7 the sites of lead are partly occupied.

The crystal structure of synthetic TISb3S5

Abstract: The crystal structure of a new synthetic sulfosalt nSb 3 S 5 has been determined. Four formula units are contained in the monoclinic unit cell of dimensions*! = 7.225(2)A,b = 15.547(3)A, c = 8.946(3) Ä, β = 113.55(3)°, the space group is f21/c. The structure was determined by Patterson methods and refined with anisotropic temperature factors and anomalous dispersion correction to a final R-value of 0.067 for all observed reflections. The T1 atom is surrounded by eight S atoms (mean: Tl—S = 3.301 A). The coordination polyhedron around the Tl atom is a trigonal prism with two S atoms against the side faces. The Tl — S prisms share a common basis and build up chains parallel to the c-axis. The Sb atoms have a trigonal pyramidal coordination [mean: S b ( l ) S = 2.488A, Sb(2)-S = 2.531 A, Sb(3)-S = 2.515 A], The Sb(2) atom has an additional fourth S atom at a distance of 2.849 A. The Sb pyramids form oo[Sb3S5] infinite layers parallel to the (010)plane, which are connected by the fourth longer Sb(2) — S bond. The Tl S chains are within the layers. nSb3S5 is the fourth sulfosalt which shows a layer structure, the others being hutchinsonite, imhofite and parapierrotite.

Crystal morphology of monoclinic potassium feldspars

Abstract: The influence of the crystal structure on the crystal morphology of monoclinic potassium feldspar has been investigated according to the theory of Hartman and Perdok. There are a limited number of PBCs, i.e., uninterrupted chains of strong bonds, consisting exclusively of T(=Si,Al) — O bonds. These are parallel to [001], <^0>, [101], [100], <&1>, [010] and [102], Many other PBCs are present having both Τ—O and Κ —O bonds as strong bonds, e.g., < f t l> , , [TOI], <§¿0>, <&2>, [201] and. The most important crystal faces can now be classified as either F t faces parallel to at least two PBCs having only T—O, or as F2 faces parallel to at least two PBCs, one of which contains in addition Κ —O bonds. The F t faces are {110}, {001}, {010}, {201} and {111}. The F2 faces are {130}, {021}, {221}, {112}, {10 0} and {101}. The remaining faces parallel to the various PBCs are S faces. Crystals grown in nature display only F faces as the most important faces. The presence of S faces is induced by internal factors other than crystal structure or by external factors such as impurities and supersaturation. 1. Relation between crystal structure and crystal morphology

Neutron diffraction study of the structure of p-benzenedicarbonitrile

Abstract: A new structure refinement of p-C6H4(CN)2 was performed by means of neutron-diffraction-measurements at room temperature. The results are compared with former X-ray analyses by Rij and Britton, and Drück and Littke. The agreement of the parameters of the non-hydrogen atoms is found to be satisfactory.

The crystal structure of iron(II) diphosphate, Fe2P2O7

Abstract: The preparation of Fe2P207 is described, with a technique to produce single crystals. The triclinic ( P I ) unit cell has the dimensions a = 5.517(2), b = 5.255(2), c = 4.488(l)Ä, α = 98.73(2)°, 0 = 98.33(4)°, γ = 103.81(2)°, V= 122.6(2)Ä (Ζ = 1). The formula weight is 285.64atomic units, and the calculated density is 3.868 g · cm 3 . The crystal structure has been determined by direct methods and refined to RF = 0.049 on the basis of 722 independent X-ray single-crystal reflections (PW1100 diffractometer data). The building elements of the structure are two distinct FeOe octahedra in combination with diphosphate ions. Each FeO e octahedron shares three edges with octahedra of the other type. The FeO e octahedra are distorted, with F e Ο distances in the ranges 1.98 — 2.44A (mean: 2.16Ä) and 2.04 —2.63 A (mean: 2.21 A). The diphosphate anion h a s a P — Ο — Ρ angle of 153°. The P 0 4 tetrahedra are also distorted, with a Ρ—Ο grand mean distance of 1.536 A.

Crystal structure of N3P3Cl4[HN(CH2)3NH] at 133 K: a spiro cyclic cyclotriphosphazene

Abstract: N3P3G4[HN(CH2)3NH] crystallizes in the hexagonal system, space group /6122; the cell parameters are a = 9.271(2), c = 26.09(1)Â, V — 1942(1) À at 133 Κ. The crystal structure determined with a reliability index R = 0.049 shows that the diamino loop is fixed on the same phosphorus atom P(1 ) setting the spiro form. Some distortion occurs in the cyclophosphazenic ring, especially at the level of the bond length P(l) —N(l) of 1.609(5)Â and the bond angle N(l)P(l)N(li) pinched to 111.5°. The packing of the molecule piled up along the [001] direction clearly shows a network of hydrogen bonding.

The distribution of Fe3+ and Ga3+ between octahedral and tetrahedral sites in garnets, Y3(Fe,Ga)5O12, at different temperatures

Abstract: The distribution of Fe + and Ga + between the octahedral and tetrahedral sites in two garnets with the compositions Y 3 FeGa 4 0 1 2 and Y3Fe3Ga2012 was studied after heating at temperatures between 1000°C and 1500 °C using Mössbauer and electronic absorption spectroscopy. Fe + shows preference for the octahedral sites and Ga + for the tetrahedral sites. At elevated temperatures, a more disordered distribution is observed. The standard Gibbs free energy change AG° per exchange pair according to the reaction Fe(oct) + Ga(tet)<± Ga(oct) + Fe(tet) is 4 .7-5 .3 kcal and the enthalpy change ΔΗ° is of the same magnitude. ΔΗ° may be correlated with the ¿-electron site preference for the tetrahedral coordination, which is considerably larger for d 1 0 than for d 5 configurated cations. The rather slow kinetics of the cation exchange between octahedral and tetrahedral sites at temperatures below 1200 ° C is probably due to the cornersharing topology of the coordination polyhedra.

A new refinement of monoclinic tetracyanoethylene (TCNE) from X-ray and neutron data

Abstract: The monoclinic phase of TCNE (C6N4) was submitted to a new X-ray and neutron diffraction analysis. Contrary to the results reported by Bekoe and Trueblood (1960) we found a slight disorder, such that 3.8—5 % of the molecules are rotated about 90 degrees in the molecular plane around their center of gravity. The final Ä-values are 0.035 for the X-rayand 0.033 for the neutron-data. The resulting X —N-map showed clearly resolved peaks, whose hights correspond well with theoretical calculations. Introduction The cubic phase of TCNE has been subject of extended studies with X-ray and neutron diffraction [Little, Pautler, and Coppens (1971); Becker, Coppens, and Ross (1973)]. The resulting difference density however did not correspond well with theoretical calculations [Haase, Schulte, and Schweig (1977)]. Therefore and in order to compare with results of aromatic nitriles [Drück et al. (1981); Drück and Kutoglu (1983)], a new investigation of monoclinic TCNE (space group P2l/n, Ζ = 2) was performed with X-ray and neutron diffraction. Earlier work on TCNE was reported by Bekoe and Trueblood (1960). Experimental Monoclinic TCNE was crystallized from solution in ethyl-acetate. For X-ray investigation a crystal with dimensions of 0.35 χ 0.4 χ 0.53 mm was sealed in a thin glas capillary and mounted on an automatic four-circle diffractometer (Stoe AED). Reflections were measured in the ω/2 θ scan mode using 104 U. Drück a n d Η. G u t h : Monoc l in i c te t racyanoethylene Table 1. Crystal da ta of T C N E (monocl inic phase)