Band 161, Heft 1-2

Integrated neutron intensities for rutile (TiO 2 ) were measured up to sin ∂/λ = 0.94 Å −1 with two crystals of volumes 1.2 mm 3 and 8.9 · 10 −3 mm 3 . Statistical treatment showed the data not to be normally distributed. From statistics of symmetry-equivalent intensities there was no evidence of anisotropic extinction. Isotropic extinction parameters were refined for both crystals. There is no significant difference between the neutron and X-ray refined structure parameters. Thermal motion of titanium is larger than that of oxygen.

Pu(SO 4 ) 2 · 4 H 2 O has been prepared in two polymorphic forms, α - and β -. The α -form crystals are orthorhombic, space group Fddd , with eight formula units in a cell of dimensions a = 26.527(19), b = 11.995(9) and c = 5.687(4) Å. The β -form crystals are also orthorhombic, space group Pnma with four formula units in a cell of dimensions a = 14.544(10), b = 10.980(8) and c = 5.667(3) Å. The structure of the β -form has been determined from three dimensional X-ray data obtained on Weissenberg films. Least-squares refinement has led to a value of the conventional R index of 0.089 for 476 observed reflections. The coordination geometry about the Pu(IV) ion is an archemedian square – antiprism formed by oxygen atoms from four sulphate groups and four water molecules. Each sulphate group is shared by two Pu(IV) ions. Hydrogen bonds operate between the water molecules and sulphate oxygen atoms not bonded to plutonium. The structure of the α -form derived from powder data shows that it differs from the β -structure only in the functional nature of the hydrogen bonds. The α - to β -transformation can be achieved by slow heating upto 120°C.

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], 〈1/21/20〉, [101], [100], 〈1/21/21〉, [010] and [102]. Many other PBCs are present having both T – O and K – O bonds as strong bonds, e.g., 〈unk/21/21〉, 〈3/21/21〉, [unk01], [100], 〈3/21/210〉, 〈1/21/22〉, [201] and 〈111〉. The most important crystal faces can now be classified as either F 1 faces parallel to at least two PBCs having only T – O, or as F 2 faces parallel to at least two PBCs, one of which contains in addition K – O bonds. The F 1 faces are {110}, {001}, {010}, {[unk]01} and {[unk]11}. The F 2 faces are {130}, {021}, {[unk]21}, {[unk]12}, {100} and {[unk]01}. 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.

The morphological relationship of compounds of glaserite-, Na 2 SO 3 -, low1-K 2 SO 4 - and olivine types is examined. The crystal structures can be retraced to a common basic structure. The morphological lattice is determined by a sign determination with the help of the Goldschmidt complication rule and with Fourier methods. The crystal growth of olivine, having a morphology similar to that of barite, deviates from the other compounds. The differences are indicated with the help of partitions of the three-dimensional space into Dirichlet domains of morphological points. The packings of space-filling polyhedra allow conclusions on growth mechanisms.

C 9 H 10 O 3 , Mol. wt. = 166.1, monoclinic, P 2 1 / c , Z = 4, F 000 = 352, a = 13.868(1) Å, b = 5.153(1) Å, c = 11.896(1) Å, β = 102.17(1)°, V = 831.05 Å 3 , ϱ c = 1.327 gm cm −3 , m.p. = 418(1) K. The structure of paramethylphenoxyacetic acid is redetermined accurately by direct methods and refined by full-matrix least-squares to R = 0.048. The molecules dimerise about a centre of symmetry, as is usual with simple carboxylic acids, and the O … O distance is 2.610(5) Å. The geometry of the carboxyl group suggests that the group is disordered.

The crystal structure of NaCrP 2 O 7 has been determined by X-ray diffraction. The crystal data are: space group P 2 1 / c , a = 7.294(2), b = 7.838(2), c = 9.484(2) Å, β = 111.72(2)°, V = 503.8(4) Å 3 , D m = 3.26, D c = 3.282 Mg m −3 , Z = 4, μ (Mo Kα ) = 2.89mm −1 . The structure was refined to R = 0.029 for 2381 independent reflections (| F o |≥ 4 σ | F o |). In addition, the lattice parameters of compounds isostructural with NaCrP 2 O 7 were measured.

The crystal structure of 6′-acetamido-6-bromo-2-cyano-4′-diethylamino-4-nitroazobenzene has been determined by single-crystal X-ray analyis. The crystals are monoclinic, a = 7.070(3), b = 12.409(4), c = 23.439(7) Å, β = 101.35(3)°, space group P 2 1 / c , Z = 4. The structure was refined to R = 0.078 and R w = 0.065 by block-diagonal least-squares methods, using 2743 independent reflections measured with a single-crystal diffractometer. The conformation found has the acetamide group trans to the Br atom, and is apparently stabilized by intramolecular hydrogen bonding.

The structure of the title compound has been determined and refined to R 0.032 [ P 2 1 , a = 28.045(6), b = 6.767(2), c = 6.719(2) Å, β = 90.30(2)°, Z = 4]. The two independent molecules differ mainly in relative ring orientation. Bond lengths at the acetal centre are not significantly different.

The crystal structure of the title compound has been determined and refined to R 0.031 [ P 2 1 2 1 2 1 , a = 4.700(2), b = 13.314(3), c = 20.876(5) Å, Z = 4]. The acetal bond lengths are not significantly different. The crystal packing involves a system of hydrogen bonds.

Refinement of the crystal structure of the title compound to R = 0.043 with new diffractometer data provides the most accurate description to date of the undistorted β -hydroquinone host lattice.

The unit-cell dimensions of phases with the CsCl structure that contain Cu, Ag or Au(A) are examined as a function of the diameters of the component atoms, D A and D B and compared with those of phases of other A components. The cell dimensions of phases with upper composition of the B component limited by an electron concentration of 1.5 electrons per atom are controlled by the A – B contacts. The cell dimensions of phases containing the rare earths (B) are controlled by the A – B and B−B contacts acting cojointly. The Li and Mg phases of Ag and Au have unusually small cell dimensions. Whereas the Ag and Au phases with composition limited by electron concentration 1.5 have the same cell sizes, the Li, Mg, Sc, Y and rareearth phases of Au have cell sizes on the average 0.051 Å smaller than the Ag phases. This is accounted for in terms of the electronegativity differences for this group of Au phases. The Au phases of the alkali metals are discussed; the size of the Au − ion is deduced; the essential metallic nature of AuLi is demonstrated, and the non-existance of AuNa and AuK is rationalized. The AgMg phase with a range of homogeneity, is particularly considered.

The monoclinic phase of TCNE (C 6 N 4 ) 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 R -values are 0.035 for the X-ray- and 0.033 for the neutron-data. The resulting X – N-map showed clearly resolved peaks, whose hights correspond well with theoretical calculations.

The crystal structure of SbSeI has been determined with the intensities of 821 independent reflections, measured on a computer-controlled Philips PW 1100 single-crystal diffractometer. The cell constants, obtained by least-squares calculations from direct ∂ -value measurements on the diffractometer, are: a = 8.6862(9), b = 10.3927(9), c = 4.1452(3) Å, Z = 4; space group Pnam . The positional and thermal parameters, with anisotropic temperature factors, were refined by full-matrix, least-squares calculations to a final R = 0.054. The compound is isotypic with BiSCl (Voutsas and Rentzeperis, 1980). Each Sb atom is seven-coordinated by three Se atoms at distances 2.601 to 2.796 Å and four iodine atoms at distances 3.150 to 3.822 Å. The four I atoms form a square parallel to c , while the three Se atoms form an isosceles triangle perpendicular to (001), with its base parallel to c . The I atoms and two of the Se atoms are at the vertices of a triangular prism parallel to c and of height equal to c . The third Se atom is at the apex of a pyramid whose base is one of the Se 2 I 2 faces of the triangular prism. The composite coordination polyhedron (prism + pyramid) is linked to a symmetry-equivalent polyhedron by a common Se, Se edge of the corresponding pyramids. This characteristic double-polyhedron system is repeated along the c axis, thus forming an infinite double chain of composition {Sb 2 Se 4 I 8 } n . The chain is further linked to each of four similar chains by a common (I,I) n row parallel to c . This system of chains explains very well the needle-like growth of the crystals along c .

A simple graphical method for deriving the various settings of an orthorhombic crystal from what has been called the “standard” setting is briefly discussed. The “standard” setting is not necessarily the most useful one to use when a crystal is to be oriented according to the relative dimensions of its three cell translations.

The crystal structure of the title compound has been determined (space group P 2 1 , a = 14.267(7), b = 7.486(3), c = 15.368(6) Å, β = 101.10(3)°, Z = 4) and refined to R 0.038 for 3477 unique observed reflections. The two independent molecules show some torsion angle differences about the C(l) – O(1) bond but are otherwise similar. The relationship between acetal bond lengths and electronegativity of the aromatic group, noted in a previous paper (Jones et al., 1982b), is maintained. A partially occupied water site leads to disorder of the hydrogen bonding network.

The crystal structure of the title compound ( 1 ) was determined (space group P 2 1 2 1 2 1 , a = 5.654(3), b = 16.700(7), c = 25.905(10) Å, Z = 4) and refined to R 0.053 for 2170 unique observed reflections. The introduction of the four acetal groups has very little effect on the geometry at the acetal centre (cf. the parent glucoside, see preceding paper).

We have measured the electrogyration effect in Sr(NO 3 ) 2 , Ba(NO 3 ) 2 , and Pb(NO 3 ) 2 as a function of temperature and wavelength. Only Pb(NO 3 ) 2 displays a slight temperature dependence. The optical transitions responsible for electrogyration are centred between the onset of absorption and the resonance determined by the dispersion of refractive indices. We suggest a latent chirality of O 2− -arrangements as the main source of the effect.

Indexing of powder pattern and refinement of unit cell parameters of cholinium salt with dipicrylamine, (C 5 H 14 NO) + (C 12 H 4 N 7 O 12 ) − are reported. The crystals belong to the triclinic system, a = 10.2012(2) Å, b = 10.5394(2) Å, c = 22.3001(5) Å, α = 95.797(2)°, β = 91.226(3)°, γ = 89.962(1),° Z = 4.