Volume 136, Issue 5-6

In average structures so called split atoms are often observable. Atoms are distributed over some sites, which are located close to each other. The sum of the occupation possibilities of such a group of split positions equals one. If the spatial separation of the different split positions is small, the split atoms overlap in Fourier syntheses and appear in the same way as a smeared out electron density. By structure refinements it is possible to determine only a position of gravity for such a group of split atoms. The corresponding anisotropic temperature factor is influenced by the distribution of the split atoms around the position of gravity, this means, it combines the effects of true thermal motion and split atoms. In this paper an equation is derived for a pseudo thermal vibrational ellipsoid of a group of split atoms taken into account the true thermal motion. The results are tested at the example of the average and super structure of the quartz-like structure of β eucryptite (LiAlSiO 4 ). The structure parameters obtained by superstructure refinements are used to calculate a pseudo temperature factor for the oxygen atoms. This result is compared with the temperature factor obtained by the refinement of the average structure. Furthermore the anisotropic temperature factors of the oxygen atoms in quartz-like average structures of composition Li 2 O · Al 2 O 3 · x SiO 2 ( x = 2, 3, 4) are used for an estimation of the short-range order. This is done by comparison of the results of the structure refinements with temperature factors obtained from different split-atom models.

The scattering properties of an anisotropic solid for polarized light allow the observation and the measurement of linear, circular and elliptic birefringence. A general analysis of the phenomenon for any kind of birefringence and any state of polarization of the incident light vibration is given. Scattering by particles with size a [unk] λ (Rayleigh limit) or a ≈ λ is considered. It follows from the theory that the scattering-center distribution is equivalent to a quasi-continuous array of analyzers providing a simultaneous analyzation of the transmitted beam along its whole path in the (in general elliptically) birefringent medium. A new technique based on surface scattering is described. It allows visual observations to be made on very perfect (hence weakly scattering) crystals with low-power light sources and without being forced to achieve complete darkness in the surroundings of the sample. The method of surface scattering is especially adequate for precision measurements; it is thoroughly tested with the elliptic birefringence of quartz. Both methods of surface and bulk scattering are applied to various kinds of birefringence in single crystals of Eu 2 SiO 4 and EuTe.

The compound Ge(OH)PO 4 has been prepared by hydrothermal synthesis. The crystal structure is determined by means of three-dimensional single-crystal data (147 independent reflections, R = 0.122). The structure is built up by octahedral chains of composition [GeO 4 (OH)], which are connected by [PO 4 ] tetrahedra forming a three-dimensional network, which exhibits one-dimensional disorder phenomena (OD structure). The determined crystal structure with the orthorhombic unit cell: a = 12.25 3 , b = 7.01 4 and c = 7.16 1 Å space group Bmam – D 2 h 21 and Z = 8 is a result of superimposed twinned regions, which can be described by a monoclinic unit cell: a = 7.09 6 , b = 7.01 4 and c = 7.16 1 Å, β = 120° 18′, space group C 2/ c – C 2 h 6 and Z = 4. A structural relationship between Ge(OH)PO 4 and the minerals kieserite, titanite (sphene), lazulite and amblygonite is discussed.

The experimental investigation of the mean diamagnetic susceptibility of a set of steroids, derivatives of pregnane, estrane and androstrane, was made by means of the Faraday method. Experimental values χ of the molar magnetic susceptibilities are compared with values predicted using: The empirical systematic developed by P ascal . The empirical revised systematic of P ascal , P acault and H oarau . The empirical systematic related to bonds. The theoretical systematic developed by G uy , T illieu and B audet . Close agreement is obtained between the experimental susceptibilities and the values calculated by the empirical systematic related to bonds. The values calculated by the systematic of P ascal and the theoretical systematic fit better with the experimental ones when corrections for oxygenated groups are made.

Synthetic steroids with anti-inflammatory activity and estrogens are investigated: I. 9 α -Fluorocortisol (9 α -fluoro- Δ 4 -pregnen-11 β , 17 α , 21-triol-3,20-dion). 16 α -Hydroxyprednisolone ( Δ 1,4 -pregnadien-11 β , 16 α , 17 α , 21-tetraol-3,20-dion). Dexamethasone (9 α -fluoro-16 α -methyl- Δ 1,4 -pregnadien-11 β , 17 α ,21-triol-3,20-dion). 6 α -Methylprednisolone (6 α -methyl- Δ 1,4 -pregnadien-11 β ,17 α 21-triol-3,20-dion). II. Estrone ( Δ 1,3,5,10 estratrien-3 β -ol-17-on). Hemihydrated estradiol ( Δ 1,3,5,10 -estratrien-3,17 β -diol). Their diamagnetic anisotropies have been measured and their principal diamagnetic susceptibilities deduced from these.

The influence of heat treatment on the Si,Al-distribution in a sanidine of Volkesfeld, Eifel, was investigated by two complete crystal-structure analyses. Observed differences in the mean T–O distances are compared with simultaneous changes of the optic axial angle and give additional data to such correlations first published by C olville and R ibbe (1968).

1,5-Dichloropentane-urea crystals were grown from a solution of urea and dichloropentane in methanol. From the needle-like crystals single-crystal-type Weissenberg and precession photographs were obtained. The experimentally found extinctions, however, could only be understood if microtwinning of all crystals within the (100) planes was assumed. Based on this interpretation, an orthorhombic unit cell of the space group Pbcn with lattice constants a = 8.260 ± 0.002 Å, b = 14.266 ± 0.004 Å, and c = 10.983 ± 0.005 Å was obtained. The structure of the host molecules appears to be the same as in 1,4-dichlorobutane-urea, but the guest molecules, other than in 1,4-dichlorobutane-urea, are randomly arranged along [001].

The crystalline form of 4-methoxy-6-(5′,6′-dioxymethylene-styryl)-5,6-dihydro- α -pyrone is assigned to space group P 2 1 2 1 2 1 – D 2 4 having parameters a = 28.916, b = 8.504, c = 5.348 Å. The crystal structure was determined by the direct phasing method with the tangent formula [unk] The refinement by the block-diagonal-matrix least squares led to a R value of 0.07 using 1501 reflections. The two ring systems of the molecule are twisted by 73°. The molecules are held together by van der Waals forces only.

The crystalline form of 4-methoxy-6-(1′,2′-dihydrostyryl)-5,6-dihydro- α -pyrone is assigned to space group P 2 1 / c – C 2 h 5 having parameters a = 10.921, b = 7.605, c = 17.014 Å and β = 119°30′. The crystal structure was found by phase assignment with the symbolic-addition procedure. The resulting E map showed the whole molecule. The refinement by the block-diagonal-matrix least squares led to a R value of 0.09 using 2352 reflections. A short discussion of the structure is given.

A new modification of nepheline was obtained by the action of NaF and NaOH on synthetic sodic cancrinite. It has a multiple a axis and a tripled c axis (25.06 Å) and is either hexagonal P 6 1 or possibly monoclinic P 2 1 . The extra reflections disappear on heat treatment at 800°C.