Showing papers in "Zeitschrift Fur Kristallographie in 1969"

The crystal structure of the synthetic zeolite L

Abstract: The crystal structure of the synthetic zeolite, Linde L, K6N aaA19Si27072 . 21H20, has been determined from powder data at room temperature. The zeolite is hexagonal with unit-cell dimensions a = 18.4 A and c = 7.5 A. The structure has been refined assuming space group P6/mmm. The aluminosilicate framework is based upon the polyhedral cages which are formed by five six-membered and six four-membered rings and are found in can- crinite, erionite and offretite. These cavities are linked through the planes of their upper and lower six-membered ring, thus forming columns in which hexagonal

Struktur und Fehlordnung des Vaterits

Abstract: Single-crystal photographs of vaterite (/1 CaC03) show numerous diffuse streaks II e* with maxima which require an increase in the previous lattice parameter a by a factor -y3 to 7.15 A, and doubling (sometimes trebling) of e to 16.94 A; moreover satellite reflections were observed. The structure of vaterite can be considered as a disordered stacking sequence of single layers of trigonal symmetry which are mostly related by glide reflections and sometimes by a screw operation lie. Sequences of two layers AA' and of four layers AA'BB' may be considered as states of order which are approached; the partial sequences ABAB and A'B'A'B' correspond to the principle of the hexagonal closest packing. For a more exact treatment one has to consider the deformations of the primitive hexagonal partial lattice array of the calcium atoms also. The average structure agrees in general with KAMHI'S proposal; but the C03 group has to be centered around (i) of space group P 63/mme with an occupancy of one sixth only. The least-squares refinement reduced R to 0.115. The oxygen atoms form distorted cubes around the calcium atoms. Conclusions are drawn concerning the structures of rare-earth borates and of the bastnaesite-vaterite series.

The crystal structure of fresnoite, Ba2(TiO)Si2O7

Abstract: Auszug Die KristaIIstruktur von Fresnoit, Ba2(TiO)Si207, wurde aus der PattersonProjektion P(uv) bestimmt und nach der Methode der kleinsten Quadrate aus hkl-Interferenzen verfeinert. Eigentfunlich fur die Struktur ist die tetragonalpyramidale Umgebung des Titans. Schichten aus heterozyklischen Hinfgliedrigen Ringen, die von tetragonalen Ti-O-Pyramiden und Si-O-Tetraedern gebildet sind, werden durch Ba-O-Bindungen zusammengehalten. Die Bindungen innerhalb der Schichten sind vorwiegend kovalcnt; zwischen den Schichten ist Ionenbindung vorherrschend.

The crystal structure and chemical composition of pollucite

Abstract: The structure of pollucite from Rumford, Maine has been determined and refined. The space group is Ia3d with cell edge a = 13.69 A. The structure was investigated using 213 independent reflection intensities measured on a single crystal diffractometer. Pollucite has the analcime framework with the cesium atoms occupying the large voids in the framework, as initially suggested by NARAY-SZABO. The water molecules occupy the large voids of this same set which are not occupied by the cesium atoms. The sodium atoms are located in equipoint 24c, at t t 0, in the positions between the water molecules. The water molecules and the sodium atoms occupy the same positions as they do in analcime, but they occur only in randomly distributed clusters of atoms whose outer members are restricted to water molecules. The final structure was refined by least squares to an R value of 0.050 for all reflections. The chemical composition of pollucite can be expressed by a general formula similar

The crystal structure of orthoenstatite

Abstract: The crystal structure of a natural orthorhombic enstatite (orthoenstatite) from the Bishopville meteorite, has been refined by the least-squares method using 680 three-dimensional reflections. The space group and the cell dimensions of this orthoenstatite are Pbca and a = 18.210, b = 8.812 and c = 5.178 A. The crystal structure of orthoenstatite is compared with that of clinoenstatitc and the geometric relationship between the two polymorphs is described. The orthoenstatite structure is shown to be an exact twin of clinoenstatite on a unitcell scale. The orthorhombic cell is composed of two monoclinic cells of clinoenstatite joined on (100) through a b-glide plane. The orthoenstatite structure is also compared with the structures of hypersthene and orthoferrosilite. The corresponding interatomic distances show the following characteristics. \Vith increasing Fe replacement of Mg the interatomic distances M-O in the metal octahedra increase. The mean interatomic distances, M-O, of the octahedra can thus be used to determine the Mg:Fe

Refinement of the crystal structure of hardystonite, Ca2ZnSi2O7

Abstract: The structure of hardystonite, Ca2ZnSi207, was refined to R = 5.30/0 from three-dimensional diffractometer data. The Zn-O and Si-O bonds are predominantly covalent, and the adjacent covalent sheets of [ZnSi207 ]4- are linked by Ca2+ ions, with the interlayer bonding being predominantly ionic in character.

Die Kristallstruktur des 2.6-Diphenyl-4-(4-bromphenyl)-N-(p-oxy-m,m'-diphenyl)-phenyl-pyridinium-betain-monoäthanolats

Abstract: The structure of CuHi&NOBr · C2H5OH was solved by the heavy atom method with three-dimensional estimated intensity data. 3514 reflections with θ <. 60° (Λ = 1.5418 A) were used, 327 of which were unobserved. Space group Ρ2ija, a = 18.83 ± 3, b = 17.12 ± 3, c = 11.62 ± 2 Α, β = 111.7 ± ± 0.2°, Dm = 1.32, Dz = 1.29 g · cm\"1 . B y least-squares methods with anisotropic temperature factors, the structure was refined to R = 11.6°/o· The N—C bonds in the pyridinium ring are of usual length (1.36 A), as is also the Ν—C bond (1.48 A) that links the pyridinium and the phenolate ring. The dihedral angle between these rings is 65°. The dihedral angle between an outer phenyl group and the corresponding inner ring ranges from 18° to 70°. The C—Ο bond of the phenolate oxygen is very short (1.29 A). The two adjacent C—C bonds are stretched (1.45 A). A hydrogen bond ( 0 H 0 = 2.71 A) connects the ethanol to the negatively charged phenolate oxygen.

Structural principles and classification of sulfosalts

Abstract: Ein Uberblick uber die Dimensionen der Anionengruppe TSa, T = As, Sb, Bi, in Sulfosalzen ergibt fUr die Abstiinde T-S bzw. S-T-S 2,26 und 2,31 A fur AsSa, 2,46 und 2,54 A fUr SbSa und 2,62 und 2,79 A fUr BiSa. Unter Berucksichtigung der moglichen Deformationen der Bindungswinkel werden die Abstande S-S zu 3,4-3,6A fUr AsSa, 3,6-3,8 A fur SbSa und 3,8-4,1 A fUr BiSa angenommen. Aus den bisher bestimmten Strukturen von Sulfosalzen konnte gefolgert werden, dal3 das Strukturprinzip dieser. Gruppe auf der raumlichen Beziehung zwischen den Koordinationspolyedern urn die Metall- und die T-Atome beruht und dal3 die Radien dieser Atomc als Mal3 fUr die Klassifikation dienen konnten. Aber die Radien, vor all em der Metallatome, lassen sich wegen der wechselnden Koordination dieser Atome nicht eindeutig angeben. Deshalb wurden statt der Atomradien versuchsweise die Hauptquantenzahlen der Valenzelektronen als Ordnungsgrol3e benutzt. Die Sulfosalze wurden in ein Diagramm mit dem Mittel aus den Hauptquantenzahlen iiA als Abszisse und der Summe dieser Quantenzahlen, dividiert durch die Summe der Hauptquantenzahlen der T-Atome, IiiA/InT, eingetragen. 1m Diagramm sind deutlich vier Gebiete zu erkennen, von denen ein jedes nur Strukturen eines gemeinsamen Bauschemas aufweist. Das eine Gebiet umfal3t kupferreiche Verbindungen und ist durch Verknupfungen von CuS4-Tetraedern allein oder mit TSa-Pyramiden charakterisiert; das zweite hat hohen Silbcrgeha\t und wird hauptsachlich durch die Bindungen der Silberatome bestimmt; die Strukturen des dritten Gebiets sind bleireich oder silberarm und nah verwandt mit der Bleiglanz-Struktur; das vierte Gebiet enthalt Blei-Sulfosalze mit relativ hohem Gehalt an T -Atomen. Die Strukturen dieses Gebiets wurden auch in der Abhangigkeit von nT (statt iiA als Abszisse) klassifiziert; fUr sie sind die Grol3enunterschiede zwischen den Blei-Polyedern und den TSa-Pyramiden mal3gebend.

The crystal structure of trechmannite, AgAsS2*

Abstract: The crystal structure of treehmannite, AgAsS2, has been determined with the use of three-dimensional intensity data. The crystal is rhombohedral,

Die Kristallstruktur von Li4GeO4

Abstract: The crystal structure of l i thium orthogermanate has been determined by means of three-dimensional Fourier syntheses and the least-squares method. The lattice parameters of the orthorhombic uni t cell are: β = 7.76, b = 6.05 and c = 7.36 Ä; space group Bmmb—DLLiGeOi is built up by [GeOi] tetrahedra, being linked together by [LiO<] tetrahedra. The average interatomic distances are found to be: Ge—Ο = 1.77 and Li—Ο = 1.98 A. Auszug Die Kristallstruktur des Lithiumorthogermanats wurde mit Hilfe dreidimensionaler Fourier-Synthesen und nach der Methode der kleinsten Quadrate bestimmt. Die Gitterparameter der rhombischen Elementarzelle (Raumgruppe Dll—Bmmb) betragen: a = 7,76, b = 6,05 und c = 7,36 Ä. Li4Ge04 enthält [GeC>4]-Tetraeder, welche durch [LiOij-Tetraeder verknüpft sind. Als mittlere Atomabstände wurden erhalten: Ge—Ο = 1,77 und Li—Ο = 1,98 Ä. Einleitung Kürzlich wurde die Elementarzelle des Lithiumorthogermanats bestimmt· und in einer kurzen Mitteilung ein Strukturvorschlag für diese Verbindung gegeben. Experimentelles Zur Herstellung wurden L12CO3 (reinst, Merck) und GeC>2 (99,999%, Loba-Chemie; Quarzform) im molaren Verhältnis 2:1 bei 1 A . WITTMAHN u n d E . MODERN, U n t e r s u c h u n g e n i m Z w e i s t o f f L12O—GeC>2. Mh. Chem. 96 (1965) 581—582. 2 A. WiTTMANif, Beiträge zur Strukturchemie der Germanate. Fortschr. Miner. 43 (1966) 230—272. 3 H . VÖLLENKLE u n d A . WITTMAHN, Z u r K r i s t a l l s t r u k t u r v o n LUSiOi u n d LUGeO«. Naturwiss. 54 (1967) 441. Die Kristallstruktur von LiiGeOi 67 1300°C im Platintiegel geschmolzen. Aus der erstarrten Schmelze konnten Einkristalle für die Drehkristallund Weissenberg-Aufnahmen isoliert werden. Für die rhombische Elementarzelle (Z = 4) ergeben sich die Abmessungen: a = 7,76, b = 6,05 und c = 7,36 A. Aus Weissenberg-Aufnahmen wurden folgende systematischen Auslöschungen festgestellt: hkl mit A + i = 2n + 1 und hkO mit k = In + 1. Diese Auslöschungen sind für die Raumgruppen (?2® und charakteristisch; wie sich in der Folge zeigte, liegt die Raumgruppe D^—Bmmb vor. Um sämtliche mit CuÜTa-Strahlung erfaßbaren Reflexe zu erhalten, wurden Equi-inclination-Aufnahmen um [010] und [101] (0. bis 3. Schichtlinie) sowie um [001] (0. bis 5. Schichtlinie) ausgewertet. Die Intensitäten wurden durch visuellen Vergleich mit einer geeichten Schwärzungsskala bestimmt. Zur Angleichung der Intensitäten von Aufnahmen der verschiedenen Schichtlinien wurden jeweils zwei sich überschneidende Ebenenscharen im reziproken Gitter herangezogen und zwar Aufnahmen um [010] und [001] sowie um [010] und [101]. Die Berechnung der Skalenfaktoren für die einzelnen Schichtlinien erfolgte aus den gemittelten Quotienten der J^-Werte gleich indizierter Reflexe. [-Fol\"Werte identischer Netzebenen, welche aus der Auswertung verschiedener Aufnahmen vorlagen, wurden für die weiteren Berechnungen gemittelt. Bestimmung der Kristalls truktur Die Anordnung der Germanium-Atome wurde auf Grund von zweidimensionalen zugespitzten Patterson-Synthesen P(u0w) und P(uv0) ermittelt. Die aus der Strukturfaktorrechnung mit den Ge-Positionen resultierenden Vorzeichen wurden für zweidimensionale Fourier-Synthesen ρ (xyO) und ρ (xOz) verwendet. Damit konnte auch die Lage der Sauerstoffatome festgelegt werden. Die Verfeinerung erfolgte mittels dreidimensionaler FourierSynthesen (Fig. lo). Zur Lokalisierung der Lithiumionen wurde eine dreidimensionale Differenzsynthese der Form (F0—Fc[Ge0ii) ausgeführt. Wie aus Fig. 1 b hervorgeht, läßt sich daraus die Lage der Lithiumionen eindeutig bestimmen. Nunmehr wurden drei Zyklen einer Ausgleichs-Rechnung mit isotropen Temperaturfaktoren ange-

Die Kristallstruktur von Baumhauerit

Abstract: The crystal structure of baumhauerite Pbn.eAsis.TAgo.eSse is redetermined. The unit cell is triclinic with a = 22.80 ± 0.01 A, b = 8.357 ± 0.005 A, e = 7.894 ± 0.005Ä, α = 90°3' ± 2', β = 97°16' ± 4', γ = 89°55' ± 2'. The space group is Ρ1. Among twelve independent Pb atoms, the eight \"paired\" (1, 2, 6, 7, 8, 9, 11, 12) are surronded by nine S atoms, the four \"unpaired\" (3, 4, 5, 10) are surrounded by seven S atoms. The As atoms are coordinated by S atoms in a trigonal pyramidal configuration. The Pb(4) is partially replaced by As. The As(5) occupies statistically two neighbouring places 5 a, 5b. The Ae(4) is partially replaced by Ag. AsSs pyramids form chains of finite length.

The crystal structure and one-dimensional disorder of the orange modification of HgI2

Abstract: The metaatable orange modification of Hgl2, described earlier b y several authors , was obta ined by recrystallization of H g l i f rom 2-chloroethanol in the form of square, platelike crystals ranging in color f rom red-orange to yellow-orange. The x-ray photographs of t he yellow-orange crystals indicated one-dimensional disorder along c, whereas the reflections f rom the red-orange * Present address : Depar tment of Chemistry, Universi ty of California, Los Angeles, California 90024. Z. Kriätallogr. Bd. 128, 1/2 7 98 D . S C H W A R Z E S B A C H form were sharp. The Friedel symmetry is 4'mmm and the lattice constants are twice those of the red form, i.e., a = 8.776. c = 24.723 Ä, cja ~ 2) 2 . Both the hkO and hhl reciprocal-net planes are identical with the hkO plane of the red form and there are many systematic extinctions. The structure was solved from these observations. The structural motif is a Hgnlio group, consisting of four corner-linked Hgli tetrahedra in a tetrahedral arrangement. These groups are connected into Hgl2 layers which are stacked with I—I contacts in the same way as the Hgl4 tetrahedra in the red form. In contrast to the red form, there exist two kinds of stacking, leading to a cubic close packing of the iodine atoms. One results in a four-layer structure (red-orange crystals), the other in a two-layer structure. The disorder of the yellow-orange crystals is caused by an irregular succession of the two kinds of stacking. The intensity of the diffuse scattering arising from the disorder was calculated, and is in qualitative agreement with the observations. Introduction Mercury (II) iodide, Hgl2, has an orange modification in addition to the well-known red and yellow forms (BIJVOET, CLAASSEN and KARSSEN, 1926; GORSKY, 1934a; JEFFREY and VLASSE, 1967). It was first observed by KOHLSCHÜTTER (1927) who obtained from Hgl2 vapor, orange tetragonal crystals with many faces. These crystals were more stable at room temperature than the yellow modification. Small orange plates were also obtained by precipitation from alcohol. GORSKY (19346; 1935) prepared the orange modification by crystallizing Hgl2 from acetone at room temperature. The crystals were metastable at all temperatures between 15 and 140°C. Laue and oscillation photographs showed that they were tetragonal, with space group* My/amd or 74imd, and lattice constants almost exactly twice those of the red form, i.e., a = 8.73 A and c = 24.45 Ä. The systematic absences were not reported. GORSKY also described orange crystals with a = 17.4 Ä and suspected them to be twins. JEFFREY and VLASSE (1967) prepared the orange modification by GORSKY'S method. The Friedel symmetry was 4/mmm and the lattice constants c = a = = 24.85 Ä. Very unusual systematic extinctions were observed and the hkO and Olcl reciprocal-net planes were found to be identical with the hkO plane of the red modification. These crystals were described as twins. It is probable that they were identical with the crystals having a = 17.4 Ä, reported by GORSKY (1935). The a axis used by JEFFREY and VLASSE corresponds to [110] in GORSKY'S axial system. * The space group is misprinted in the publication of 1934. Tlx· crystal structure and one-dimensional disorder of Hgl2 99 Crystal data Crystals of the orange form were prepared by cooling a solution of Hgl2 in 2-chloroethanol saturated at the boiling point. Thin square plates with side lengths between 0.2 and 0.5 mm were obtained, together with crystals of the red and yellow forms. Their color ranged from red-orange to yellow-orange. The phase transformation into the red modification could be started simply by touching them. The redorange crystals turned red slowly in the course of a day, whereas the yellow-orange crystals were more unstable and often took only minutes to transform. This sensitivity caused difficulty in mounting the crystals for photography and none remained orange for longer than about three days. They were examined by the precession and Weissenberg methods. The lattice constants were measured on a Picker 4-circle single-crystal dififractometer and refined by least squares. The x-ray data for the red-orange crystals are as follows: Friedel symmetry: 4jmmm a = 8 . 7 7 6 (a = 0 . 0 0 1 ) A c = 2 4 . 7 2 3 (σ = 0 . 0 0 2 ) A c/a = 2 . 8 1 7 ~ 2 · ] / 2 The following reflections hkl are present: h,k = 2η and h-\\-k = 4n: I = 8n h,k = 2η and h+k = 4n + 2: I = 2n, but not 8η h + k = 2 n + l : I = 2n+l h,k = 2n + 1 : no reflections. The hkO and hhl reciprocal-net planes both were found to be identical with the hkO plane of the red form. The estimated intensities are given in Table 1. The space group which explains the largest fraction of the extinctions is Mi/amd, in agreement with GORSKY ( 1 9 3 5 ) . Since the red form contains two formula units per cell, sixteen formula units can be expected per cell of the orange form. The calculated density is then 6.34 g · cm 3 , as compared to 6.38 g · c m 3 calculated for the red form (JEFFREY and VLASSE, 1967) . The yellow-orange crystals gave x-ray photographs indicating one-dimensional disorder along c. They had the same lattice constants as the red-orange crystals. No crystal was found to have an α-axis length of 17.4 A. as reported by GORSKY. The reflections with h,k = 2η were sharp with the same intensities as with the red-orange

Refinement of the crystal structure of parahopeite

Abstract: The crystal structure of parahopeite, Zna(P04)2. 4H20, has been refined using three-dimensional intensity data. The refined atomic positions obtained in this paper provided more regular coordination polyhedra with interatomic distances in better agreement with those found in other compounds.