Band 172, Heft 1-2

The monoclinic potassium feldspars are observed in various forms. The habit changes due to the growth temperature can be explained by different growth mechanisms. The application of the Fourier transform method led to six different types. Therefore it is obvious that the tetrahedra framework is built up in different ways. Equilibrium and growth forms were calculated. The latter deviate only slightly from experimentally grown crystals or from natural specimens.

In the framework of the Hartman-Perdok PBC theory it is possible for a crystal face ( hkl ) to grow flat if the crystal structure contains intersecting and compatible periodic bond chains (PBCs) in at least two directions [ uvw ]′ and [ uvw ]″ on ( hkl ). Due to the inherent periodicity of the structure the content of these two PBCs determines the composition of a growth layer ∥ ( hkl ), that is an F slice. To arrive at PBCs one must first determine all paths or direct chains in the structure; and to arrive at F slices one must combine often large numbers of PBCs. It is conceptually simpler and computationally more straightforward to view an F slice as an infinite two-dimensional connected network ∥ ( hkl ). F slices can be generated from the direct chains of the structure, thus bypassing the necessity of constructing PBCs. The APL program F FACE determines F slices for ionic structures.

The algebraic relations between one-phase seminvariants and Harker sections are described. One-phase seminvariants of the first rank can be estimated via the Fourier transform of single Harker sections, and one-phase seminvariants of the second rank can be estimated via the Fourier transform of pairs of Harker sections.

Thermal deformations, polymorphic transformations and melting of normal paraffins C n H 2n+2 with odd numbers n = 17, 19, 21 and 23 have been studied by the thermoroentgenographic method. Common traits corresponding to four stages have been distinguished in the thermal deformations of all studied paraffins. A quantitative structural interpretation of the deformation nature is given based on the principle of rotation of the aliphatic chains about their axes. Odd paraffins with n ≤ 21 melt before reaching the hexagonal state, paraffin with n = 23 at heating first undergoes an orthorhombic-hexagonal transformation and then melts. The results obtained can be useful for creating preset plasticity paraffin arrangements.

A neutron-diffraction refinement of the crystal structure of sodium trimetaphosphate-tellurate has been made by using 406 independent reflections to a final R value of 0.054. This neutron analysis has been carried out in order to locate the hydrogen atoms and thereby complete the previous X-ray study. Acid molecules Te(OH) 6 and water molecules as well as their environments are described.

The compound cis-methyl – acetate crystallises in the triclinic space group P [unk] with unit-cell parameters a = 6.413(1), b = 10.501(3), c = 10.862(4) Å, α = 82.71°(2), β = 87.73°(2), γ = 85.29°(2), cell volume = 724.16 Å 3 , d c = 1.24 g/ml, d m = 1.23 g/ml, μ (Mo Kα ) = 0.91/cm, and Z = 2. The gross structure was solved by direct method which on refinement yielded R = 0.055.

β -Bi 5 O 7 I crystallizes in space group C 2/ m with lattice parameters a = 18.387(4), b = 4.2497(9), c = 13.254(2) Å, β = 108.10(1)°, Z = 4. The structure was solved with 747 independent reflections and refined to R = 0.040 ( R w = 0.034); it consists of (Bi 10 O 14 ) n 2n+ columns parallel [010] which are connected by double rows of iodine. Structural relationships to Sb 5 O 7 I exist.

Diffraction intensities from disordered cylindrical crystallites as proposed by Mitra and Bhattacherjee (1975) with two types of layer disorders have been worked out. Numerical computations have been carried out to study the effect of the variation of defect parameters.

4,4′-bis(pentyloxy)azoxy benzene, C 22 H 30 N 2 O 3 , forms a mesophase at 341.5 K and melts at 396.2 K, with an intermediate highly ordered smectic phase. The crystal structure is triclinic P [unk], Z = 2 with a = 7.428(2), b = 8.267(1), c = 17.868(3) Å, α = 97.73(1), β = 98.66(2), γ = 101.25(2)°, D c = 1.323, D m = 1.289 g/cm 3 . The structure was solved using MULTAN80 and refined by full-matrix least-squares calculations to R = 0.0427 for 1960 observed reflections [ I > 2.50 σ ( I )]. The molecules are in their most extended trans conformation. They are nearly planar and packed in alternate sheets in which all the molecular long axes are either in head or tail configuration.

1,2,4,5-Tetra- tert -butyl-1,2,4,5-tetraphospha[2.2]pentane crystallizes in the orthorhombic space group Pbcn with a = 1252.7 pm, b = 1518.6 pm, c = 1167.2 pm and Z = 4 formula units. The crystal structure has been determined by ‘direct methods’ and refined to R F = 0.040 for 958 observed reflections. ( t BuP) 2 C( t BuP) 2 forms a spirocyclic molecule with approximate symmetry [unk]. The endocyclic bond angles in the three-membered rings are remarkable ([unk](C – P – P) = 53.83°, [unk](P – C – P) = 72.35°). The arrangement of the tert -butyl substituents is all-trans . Their bond lengths are in the expected range ([unk](P – C) = 188.85 pm, C – C) = 151.8 pm).

Crystals of Na 5 Cu 3 (PO 4 ) 2 (PO 4 HPO 4 ) were synthesized under hydrothermal conditions. The crystal structure was solved by Patterson methods and was refined to R w = 0.045 ( a = 5.106(2) Å, b = 8.409(3) Å, c = 9.052(3) Å, α = 115.76(3)°, β = 90.09(3)°, γ = 106.01(3)°, space group P [unk], Z = 1). The two crystallographically different Cu atoms display “square planar” coordination; one of them has a fifth O atom neighbour with Cu – O at 2.183 Å. Two of the four phosphate groups per formula unit are connected by an extreme short (symmetry restricted) hydrogen bond with O … O at 2.388 Å.

The crystal structure of 2-[2-aminophenoxy]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, prepared from 2-ethoxy-4,4,5,5-tetramethyl-l,3,2-dioxaborolane and o-aminophenol, was determined from single-crystal X-ray diffractometer data. The compound is orthorhombic, space group Pn 2 1 a , the lattice constants are a = 727.59 pm, b = 1031.10 pm, and c = 1681.50 pm; the unit cell contains Z = 4 formula units; the calculated density is D c = 1.148 Mg · m −3 . The crystal structure has been solved from 679 observed reflections by means of the Patterson method and refined by least-squares calculations to an index of R = 3.0%. The structure contains a tetracoordinated boron atom with a B – N distance of 165.4(6) pm, so that the molecule is better named as an inner trioxoammoniumborate. It consists of the planar aromatic 6-ring, a heterocyclic 5-ring, and the borolane 5-ring.

Single crystals of As 5 Te 7 I were prepared hydrothermally. The crystal structure was determined by using the intensities of 1316 independent reflections, measured on a computer-controlled single-crystal diffractometer (Philips PW 1100). The cell constants, refined by least-squares, are: a = 14.5661(8), b = 4.0353(1), c = 13.8633(7) Å, β = 110.581°(4), Z = 2; space group C 2/ m . Solution of the structure was essentially effected by direct methods combined with successive Fourier syntheses. The positional and anisotropic thermal parameters, were refined by full-matrix least-squares calculations. Correction for absorption and anomalous dispersion was applied for all atoms. The final R value was 0.047. Three of the five As atoms are octahedrally coordinated by six statistically distributed (Te, I) atoms, whereas the other two are surrounded by a composite polyhedron of seven Te atoms, consisting of a tetragonal pyramid and a triangular prism, one face of which coincides with the base of the pyramid. One octahedron is linked to two centrosymmetrically equivalent octahedra on either side by a common (Te, I) – (Te, I) edge. Thus a triple octahedron unit is formed, while two centrosymmetrically equivalent composite polyhedra are linked to the triple octahedron unit on either side through common Te – Te edges. This combination of the polyhedra is repeated along the b axis, forming an infinite band. Adjacent bands are held together by weak As – Te bonds.

The electrical conductivity of Tl 3 BX 4 -crystals (B = V, Nb, Ta; X = S, Se) has been determined in the temperature range between 20 and 200°C. It turned out that the compounds are semiinsulating with conductivities σ at 20°C between 1.2 × 10 −5 (Tl 3 VSe 4 ) and 2.5 × 10 −8 ( Ω cm) −1 (Tl 3 NbS 4 ). They are mixed conductors. T1 3 VS 4 , Tl 3 NbS 4 and Tl 3 VSe 4 show Tl + ionic conduction at room temperature. Very strong piezoelectric effects of the crystals have been observed.

In a PbO/PbF 2 flux (1400°C) a new (Al,Ge)-mullite was grown incorporating Pb 2+ and Nd 3+ ions, the needle like crystals (about 2 mm in length) are orthorhombic: P 2 1 2 1 2, a = 7.6648(4), b = 7.7914(3), c = 2.9213(1) Å, V = 174.46(1) Å 3 , Z = 1, D x = 3.79 g cm −3 . Final R = 0.0211 for 297 observed reflections. Pb 2+ and Nd 3+ are located in the vacancies that are formed by omission of O(3)-atoms.

Single crystals of SrB 4 O 7 with dimensions up to 40 mm have been grown by the Czochralski method. Because of the high viscosity of the melt the pulling rate had to be unusually small (ca. 0.2 mm/h). The linear electrooptical tensor [ r ijk ] and the tensor of the linear electrostriction [ d ijk ] have been determined: r 113 = 0.58(3), r 223 = 0.78(3), r 333 = 0.39(3), r 131 = 0.22(4), r 232 = 0.33(4); d 311 = 1.16(7), d 322 = 1.61(6), d 333 = −0.39(7), d 113 = 0.26(8), d 223 = 0.97(10) (unit: 10 −12 m/V, T = 295 K, λ = 633 nm).

Single crystals of As 2 Te 3 were prepared hydrothermally by heating and gradually cooling a mixture of stoichiometric quantities of powdered As and Te in a HCl 25% w/w solution in a quartz ampoule. The crystal structure was determined by using the intensities of 600 independent reflections, measured on a computer controlled singlecrystal diffractometer (Philips PW 1100). The cell constants, refined by least-squares, are: a = 14.3573(9), b = 4.0199(2), c = 9.8990(7) Å, β = 95.107°(5), Z = 4; space group C 2/ m . The positional and anisotropic thermal parameters were refined by full-matrix least-squares calculations. Correction for absorption and anomalous dispersion was applied for all atoms. The final R value was 0.052. There are two types of As atoms. The first is six-coordinated by Te atoms forming a distorted octahedron. The second type is seven-coordinated by Te atoms forming a composite coordination polyhedron, consisting of a tetragonal pyramid and a triangular prism, with one face of the latter coinciding with the base of the pyramid. Each octahedron is linked to a centrosymmetrically equivalent one with a common Te – Te edge forming thus a double octahedron. To this are linked on either side two centrosymmetrically equivalent composite polyhedra through common Te – Te edges. This unit of polyhedra is repeated along the b axis, forming an infinite band. Adjacent bands are held together by weak As – Te bonds.

The structures of natural and synthetic* α -eucryptites, LiAlSiO 4 , are trigonal with space group R [unk], a = 13.471(3) [13.473(3)]Å, c = 8.998(2) [9.001(2)] Å, Z = 18, D x = 2.66 [2.66] gcm −3 . They were refined to R (unweighted) = 0.055 [0.054] and R (weighted) = 0.043 [0.041] using 1721 [1710] non-equivalent reflections. The structures consist of [LiO 4 ] tetrahedra (mean Li – O distance 1.982 [1.983] Å) and [TO 4 ] tetrahedra with T = Al/Si (mean T – O distance 1.688 [1.688] Å). It is confirmed that α -eucryptite, natural and synthetic, is isostructural with phenakite and willemite, and has a three-dimensional tetrahedral framework. The Li atoms of eucryptite occupy the sites equivalent to the Si positions in phenakite and willemite. The Al and Si atoms of eucryptite are disordered in the sites equivalent to the Be and Zn positions in phenakite and willemite.

The structure of (NH 4 ) 2 S 5 is characterized by tetrahedral NH 4 + cations and helical S 5 2− anions with all-trans conformation (skrew order k = 3.76; [unk](S – S) = 2.057 Å (3×) and 2.073 Å (1×); β (S/S/S) = 107.2° – 109.0°; dihedral angle = 67.1°; 68.0°). The analysis of the rigid body motion does not change the ratio of the different bond lengths. ( P 2 1 / c ; a = 5.427, b = 16.226, c = 9.430 Å, β = 105.31°; Z = 4; 1626 hkl ; R = 0.028).