Volume 173, Issue 1-2

Two homologous series of cyclically twinned sulphosalt structures are defined in the present paper, with different atomic configurations around the site of six- and threefold axes. The zinckenite homologous series, M 6+ x +N(N+5) A 12+N(N+7) , contains zinckenite, a Pb – Sb sulphosalt, and sulphohalogenides of Bi and Pb. The Ba – Bi sulphide homologous series, M 12+ x +N(N+5) A 18+N(N+7) , contains complex sulphides of Bi and alkaline earths. Degenerate (or approximate) cyclic twinning with only local threefold symmetry occurs in the structures of several Pb – Bi – Sb – (Cu,Fe) sulphosalts and Eu 3 Sb 4 S 9 . The known and the missing members of these series are discussed and related hypothetical structures derived.

An X-ray study of 2,4-hexadiyne-1,6-di(p – n-hexyloxy)benzoate was carried out ( R = 0.060 for 3223 reflections). The molecule has a skew conformation with the pseudotorsion angle relative to the linear diacetylene moiety equal to −110.0(9)°. The non-ability to polymerization in solid state of the studied diacetylene is explained on the basis of crystal chemistry criteria. Cell parameters of two nearest homologues of the studied compound are determined (for one of them on a polymeric state).

The crystal structure of jurbanite, Al(SO 4 )(OH) · 5H 2 O, was refined from 1470 independent reflections measured on a computer-controlled single-crystal diffractometer. The positional and anisotropic thermal parameters (isotropic for hydrogen atoms) were refined by full-matrix least-squares calculations to a final R = 0.047, for 581 reflections with I > 3 σ ( I ). Hydrogen atoms were located on a ΔF map. Lattice parameters are a = 8.3965(6), b = 12.479(2), c = 8.1549(9) Å and β = 101.917(6)°; space group P 2 1 / n ; Z = 4. In the structure pairs of Al(OH) 2 (H 2 O) 4 octahedra and isolated SO 4 groups are connected by a hydrogen bonding system. The atomic arrangement is discussed in relation to other hydrated aluminum sulfates, such as aluminite Al 2 (SO 4 )(OH) 4 · 7H 2 O, and rostite Al(SO 4 )F · 5H 2 O. It is pointed out that jurbanite and rostite, so far considered as dimorphs, have really a different chemical composition, with (OH) − in jurbanite and F − in rostite.

A new family of space-filling polyhedra (parallelohedra) leading to 4-connected 3D-packings (four edges connected at each vertex) is identified, which includes trivalent polyhedra with any even number, F , of faces, larger than fourteen. The number of different space-fillers with a given F increases with F (one for F = 14, 16, two for F = 18, seven for F = 20). The individual polyhedra are isomorphic to convex polyhedra. They can be packed in a bcc lattice with one polyhedron per lattice point. The new space-fillers are derived from the Dirichelet domains of the bcc lattice (Kelvin's tetrakaidodecahedra) by performing successive neighbour switching operations at all edges of the same translation-equivalence class. Each space-filler derived by this method is face-adjacent to a particular set of lattice neighbours and can be identified by this set (order of the neighbours and their orientation in space). A particular solution for the geometry of a space-filler with 20 faces is obtained, with straight edges but curved faces.

The room temperature electron density distribution in potassium trithionate, K 2 S 3 O 6 , has been investigated using single crystal X-ray data taken from the literature. The conventional all-data refinement yielded R / R w values of 0.045/0.042 for 3010 observed reflections, (sin θ / λ ) max = 1.08 Å −1 . In order to reduce parameter bias introduced by bonding effects, various refinements with high order data were performed. In addition, two multipole expansion refinements were carried out, which yielded the significantly improved residuals R / R w of 0.032/0.028 and of 0.028/0.026 respectively. The resulting static deformation density maps reproduce satisfactorily the main features of the X – X HO syntheses. The charge redistribution in the [S 3 O 6 ] 2− anion due to chemical bonding is discussed. No significant single bond peaks are observed on the midpoints of the S – S bonds, which are different in lengths and in their deformation density appearances. The two SO 3 groups are also found to differ mainly with respect to the bonds in the anion plane. The differences can be rationalized in terms of the rather different cation environments of the two SO 3 groups.

The crystal structure of leonite, K 2 Mg(SO 4 ) 2 · 4H 2 O, was determined using 3-dimensional X-ray single crystal data. Leonite crystallizes in space group C 2/ m with lattice constants a = 11.769(3), b = 9.539(3), c = 9.889(3) Å, β = 95.31(2)°. The final weighted R value for 2120 independent reflexions (according to a limit of sin ϑ / λ = 0.8 Å −1 ) was 0.031. The structure is built up by sulphate groups, interconnected by 6 coordinated Mg and 9 to 10 coordinated K atoms, as well as by hydrogen bonds. One of the two crystallographically different sulphate groups is slightly disordered.

Coleonol isolated from the Indian plant Coleus Forskohlii crystallizes in space group P 2 1 2 1 2 1 with four molecules in the unit cell. The doubt regarding the identity of Coleonol with Forskolin has been clarified.

The structure of a synthetic protopyroxene, Mg 0.7 Co 0.1 Li 0.1 -Sc 0.1 SiO 3 , at high temperatures has been studied by precession photography and four-circle diffractometry using a gas flame heater as heat source. Protopyroxene, isotypic with protoenstatite, was sluggishly transformed at around 1250°C to a twinned enstatite IV with approximately retaining the c axis. Diffraction-intensity data of protopyroxene have been collected at 25°C and 1140°C and a refinement of the crystal structure at each temperature has been carried out. Comparison of the effect of temperature on the structures of protopyroxene and protoenstatite has revealed that the variation modes of M2 – O3 distances and O3 – O3 – O3 angles, which are important indicators for the structural characteristics of pyroxenes before transition, are different between protopyroxene and protoenstatite. The M2 – O3 and O3 – O3 – O3 of protoenstatite remain unchanged with increasing temperature while those of protopyroxene increase; M2 – O3 is 2.384 Å and 2.468 Å at 25°C and 1140°C, respectively and O3 – O3 – O3 is 166.64° and 172.2° at 25°C and 1140°C, respectively. Such a mode of structural variation of protopyroxene is similar to those of clinohypersthene and ferrohypersthene.

The structures of Cd 5 (PO 4 ) 2 SiO 4 and Cd 5 (PO 4 ) 2 GeO 4 have been determined by X-ray diffractometer data. Both compounds crystallize with the structure of silicocarnotite Ca 5 (PO 4 ) 2 SiO 4 (Dickens and Brown, 1971). Space group Pnma , Z = 4; Cd 5 (PO 4 ) 2 SiO 4 : a = 669.2(2), b = 1499(1), c = 1014.0(5) pm; Cd 5 (PO 4 ) 2 GeO 4 : a = 673.4(1), b = 1510.7(2), c = 1021.0(2) pm. The tetrahedral centers in position 4c are occupied exclusively by P, those in position 8d are occupied equally by P and Si (or Ge) in random distribution.

The crystal and molecular structure of disperse dye 4-(4′-N-diethylaminoazo) phthalimid has been determined by X-ray diffraction techniques. It crystallizes in the monoclinic system with cell parameters a = 20.44(1) Å, b = 7.945(5) Å, c = 20.808(8) Å, β = 100.9°. The space group is C 2/ c and there are 8 mol per unit cell. The structure was solved using SHELX-76 program and refined to R of 0.06. The hydrogen atoms have been included but not refined. Each molecule is paired with a second one by hydrogen bonding of the phthalimid group about a center of symmetry.

The crystal structure of covellite has been studied under pressure up to 33 kbar based on single-crystal diffraction intensities collected with a four-circle diffractometer. The contraction of the unit cell takes place in such a way that the axial ratio c / a is kept nearly constant, the cell volume at 1 bar being reduced by about 5% at 33 kbar . With the contraction of the Cu – S bonds the sulfur-sulfur bond of the S 2 group shows a trend of lengthening in a way similar to the relation between S – S and M – S bonds in the compounds MS 2 (M = Cu, Ni, Co, Fe) having the pyrite structure type.

A new method of deriving groups of conformal antisymmetry and complex antisymmetry in E 2 \{0} is proposed in this work and the result of it is a catalogue of groups of conformal antisymmetry and complex antisymmetry of one-sided rosettes of the M m type.

(NH 4 ) 2 MnCl 4 · 2H 2 O undergoes a transition from the tetragonal high temperature phase into an orthorhombic low temperature phase at ca. 270 K. Thermal expansion, elastic and thermoelastic constants are strongly affected by the transition. The temperature derivatives of the elastic constants c 11 , c 33 , c 44 and ( c 11 – c 12 )/2 are positive. Different elastic modes exhibit different attenuation and hysteresis effects from which four distinguishible states between 300 and 250 K are derived. The pressure derivatives of the elastic constants show no significant anomalies. The pressure derivative of the transition temperature is negative ( dT / dp = −93 K GPa −1 ) in accordance with a positive volume increment in the transition region of ca. 2%, starting from the high temperature phase.