Band 122, Heft 3-4

The crystal structure of MgK 2 (SO 4 ) 2 · 6H 2 O, isomorphous with Mg(NH 4 ) 2 (SO 4 ) 2 · 6H 2 O, has been refined from three-dimensional x-ray data using Fourier and least-square methods. The space group is P 2 1 / a , with a = 9.072, b = 12.212, c = 6.113 Å, β = 104°50′ and Z = 2. The magnesium atom has octahedral coordination of six water oxygens (Mg–O = 2.056 to 2.188 Å, O–Mg–O angle = 89° 34′ to 90° 32′) each of which is hydrogen-bonded to two sulfate-oxygen atoms (∼2.75 Å). Thus there are twelve second-nearest neighbours to the magnesium atom and they occupy the corners of a flattened icosahedron. The bond lengths and angles in the sulfate group are close to the tetrahedral values (S–O = 1.442 to 1.507 Å and O–S–O angle = 107° to 112°). One water and five sulfate-oxygen atoms form the nearest neighbours of the potassium atom (K–O ∼2.9 Å). The potassium polyhedra related by a glide share a corner oxygen and run as a chain parallel to the a axis. The structure is built of these parallel chains, the space in between them being filled by So 4 and Mg ++ polyhedra.

The crystal structure of glauberite has been determined from precession data taken on a spherical single crystal. The mineral is monoclinic and its space group is C 2 h 6 – C 2/ c . There are four molecules per unit cell. The parameters, determined by diffractometer data and refined by the least-squares method, are: a = 10.158 Å, b = 8.333 Å, c = 8.551 Å, β = 112°20′. The SO 4 −− tetrahedra are “regular”. Ca atoms are surrounded by eight O atoms placed at the corners of an irregular square antiprism. The Na atoms, binding seven oxygens, form very distorted octahedra with one centered face. The final discrepancy index R is 9.0%.

The instable modifications α I and α II (previously called γ ) of copper phthalocyanine are isomorphous with the stable modifications α I of 4-monochloro-copper phthalocyanine, and α of platinum phthalocyanine respectively. The latter two can be obtained as single crystals and we have determined the essential structural features of them. By isomorphy considerations it was possible to recognize the structural differences between the β , α I and α II modifications of copper phthalocyanine. These α -structures are very similar to those of the α II modification of 4-monochloro phthalocyanine and of the α modification of 4-tetrachloro phthalocyanine. The essential difference between the α structures and the well-known β structure of copper phthalocyanine is a different type of one-dimensional molecular stacking. There are several ways of assembling the stacks into a space lattice so that different α structures are yielded. The substitution of peripheral hydrogen by chlorine (in the 4 position) increases the tendency to form α-type stacks and their stabilization.

The crystallographical expectation of different behaviour of crystals with asymmetric molecules against the optical antipodes of quartz was not exactly proved up to date. The weak asymmetry of the potential field of the crystal surfaces was probably the cause. We awaited a distinct effect from a substance consisting of large complex molecules like vitamin B 12 . The epitaxial effect is extremely selective. The orientation of the vitamin crystals was splendidly positive upon the polished l -quartz surfaces activated by etching with HF, never upon r , quartz. There were found and described 18 laws of orientation of the vitamin crystals upon the faces (10[unk]0), (11[unk]0), ([unk][unk]20), (10[unk]1). (01[unk]1), (0001). The laws could be formulated as one-dimensional structure analogies. The structural interpretation of the molecular kinetics, i.e. adsorption, formation of H bridges between both active groups and seed formation gave a new outlook upon the existence of small molecular matrices of very different size at the surfaces for this catalytic process which leads to the macroscopic appearance of the overranging one-dimensional analogies. The proof of a total mismatch of every matrix system with respect to the vitamin upon the r quartz is especially interesting.

Crystals of arsenic tribromide, AsBr 3 , are orthorhombic, a = 4.33, b = 10.24, c = 12.20 Å, Z = 4, space group P 2 1 2 1 2 1 . The structure was determined by Patterson and Fourier transform methods from visual intensity data, and the positional and anisotropic thermal parameters were refined by three-dimensional least squares; the final R value was 0.19 for 408 observed reflections. The crystal is built up from discrete AsBr 3 molecules, with As–Br = 2.36 ± 0.01 Å, Br–As–Br = 97.7° ± 0.3°. The shortest intermolecular distances are As…Br = 3.72 Å, Br…Br = 3.79 Å, As…As = 4.33 Å.

The structure of cronstedtite is formed by the the stacking together of silicate layers in a regular manner. Stacking faults, each consisting of a misplacement of a layer with respect to its neighbour, occur randomly throughout the crystal, causing streaking of spots on the x-ray diffraction pattern. Measurements of the extent of this streaking have been made using six crystals of cronstedtite, and the results interpreted in terms of Wilson 's theory of diffraction by layer structures containing faults. Values of α , the probability of a layer being misplaced, have been found ranging from 0.08 to 0.30. An alternative model of the disorder in terms of dissociated dislocations is put forward.

Assignment of stoichiometry to interstitial compounds is discussed. It is shown that multiple stoichiometries can occur within the same structural framework where more than one type of interstitial opening is available. These principles are used to clarify the confusion which currently exists in the isotypic series of interstitial compounds derived from alpha-boron. With respect to occupancy of interstitial sites three distinct stoichiometries can exist in this isotypic group; namely, B 12 X 2 Y (B 12 X 3 ), B 12 X 2 and B 12 X. Data are presented on (1) a new form of boron carbide (B 12 C 2 ), (2) a new α -boron derivative containing interstitial aluminum (B 12 C 2 Al), (3) identification and differentiation of two boron subphosphides (B 12 P 2 and B 13 P 2 ), (4) preparation of boron subarsenide, and (5) relationship between metal dodecaborides and α -boron derivatives.

The crystal and molecular structure of bis (hydrazine)zinc bis (hydrazincarboxylate-N′,O), Zn(N 2 H 4 ) 2 (H 2 N′–NH · COO) 2 , has been determined. The crystal structure consists of single molecules bound to one another by hydrogen bonds. Each molecule is an octahedral chelate. The six corners of the coordination octahedron are occupied by two nitrogen atoms belonging to two hydrazine molecules and by two nitrogen atoms and two oxygen atoms, all belonging to two hydrazincarboxylic groups. The bond distances between zinc and surrounding atoms are: Zn–O = 2.05 Å, Zn–N = 2.25 Å and 2.17 Å. The distances between nitrogen atoms, in hydrazinic groups, are: N–N = 1.46 Å, for the hydrazine molecule, and 1.39 Å, for the hydrazinic group of the acid. In the group–NH · COO − the atoms C, N and both O lie in the same plane. The distances C–O = 1.30 Å and 1.25 Å correspond to those found in carboxylic acids and carboxylates.

Chrysazin, C 14 H 8 O 4 , crystallized from the solution of the substance in benzene, is tetragonal, space group P 4 1 or P 4 3 , with four molecules in a unit cell of dimensions a = 5.76 Å and c = 31.45 Å. The trial structure, which was derived from the considerations of strong reflections, molecular packing and hypersymmetry, has been refined by two-dimensional (100)-Fourier projections followed by a few cycles of difference synthesis and least-squares refinement. The refinement of all the three parameters x , y , z has been done using the 0 kl reflections; however, the hk 0 reflections were also included in the least-squares refinement. The molecule is planar within the limits of experimental error and the various bond lengths and bond angles agree with those found in similar compounds. All the intermolecular approaches correspond to the normal van der Waals interactions, the closest being 2.68 Å between O 1 ( x , y , z ) and O 2 ( x –1, y +1, z ). The crystal and molecular structure has been discussed.

The crystal data are: a = 10.280 Å, b = 4.938 Å, c = 28.010 Å, β = 98.12°, D m = 1.37 g · cm −3 , Z = 8, D x = 1.36 g · cm −3 . Space group P 2 1 / c . The structure, which has been solved by conventional methods and refined by least squares, has two molecules per asymmetric unit. Each Cl − ion participates in four hydrogen bonds: the first contacts two O atoms (3.01 and 3.07 Å) and two N atoms (3.18 and 3.19 Å) whilst the second contacts four N atoms (3.13, 3.17, 3.20 and 3.24 Å). The angles are roughly tetrahedral. All eight bonding hydrogen atoms have been detected in a difference map.

Diphenantridylmethane crystallizes in the monoclinic space-group Pc with a = 9.43 Å, b = 15.10 Å, c = 6.53 Å, β = 100°30′. Due to the special position of the two molecules in the pseudo space group P 2 1 / c , it was possible to solve the structure with the method of diffuse scattering without measuring any intensities. The structure has been confirmed and refined (in projections) by the usual x-ray methods.

Details of the construction and instructions for the use of a simple stereographic plotting table are presented. The instrument is the simplest of a number of possible designs and provides a quicker method of drawing stereographic projections. It was originally designed to aid the interpretation of electron-diffraction patterns, but can be of use in the interpretation of any results which involve crystallographic relationships.

All elastic and thermoelastic constants of gypsum have been determined by ultrasonic methods. The observed elastic anisotropy shows close relations to other anisotropic properties. The thermoelastic anisotropy as well as the different deviations from the Cauchy relation c ij = c 9- i-j , 9- i-j are explained as typical for hydrogen bonds with a preferential orientation.

Gadolinium molybdate, Gd 2 (MoO, 4 ) 3 belongs to the tetragonal system, with lattice constants a = 10.396 ± 0.006 Å and c = 10.697 ± 0.004 Å The most probable space group is P 4/ mbm – D 4 h, , 5 P 4 bm – C 4 v 2 or P 4 b 2– D 2 d 7 . Scandium tungstate is orthorhombio (pseudo tetragonal), with lattice constants a = 9.596 ± 0.004, b = 13.330 ± 0.003, and c = 9.512 ± 0.004 Å The space group is Pnca – D 2 h 14 .