Band 177, Heft 1-2

The crystal structure of ε -Mg 2 PO 4 OH ( Pnma , a = 8.239(1), b = 6.135(1), c = 7.404(1) Å, Z = 4) was solved by direct methods and Fourier syntheses and refined to a final R -value of 0.017 for 637 high-angle reflections. Slightly distorted trans -MgO 4 (OH) 2 octahedra form chains along b by edge-sharing, the chains being connected laterally by pairs of corner-sharing, highly distorted PO 4 and MgO 4 (OH) polyhedra. From steric considerations and a bond-strength calculation, the OH group is found to be essentially unbonded. Morphological study has revealed ten crystal forms. Optical data are: n α = 1.5790, n β = 1.5830, n γ = 1.5870 (all ± 0.0005 at 589 nm and 22.1 ± 0.1° C); 2V X = 88.1(2)° (from spindle-stage extinction data); X = b , Y = a , Z = c . A phase diagram showing the stability fields of five polymorphs of Mg 2 PO 4 OH is presented. The structures of four of these are briefly compared. Infra-red spectra are given for ε - and α -Mg 2 PO 4 OH.

The crystal structure of β -Mg 2 PO 4 OH ( P 2 1 / c , a = 9.656(3), b = 12.859(3), c = 12.069(4) Å, β = 108.49(3)°, Z = 16) has been refined isotropically to a final R -value of 0.052 for 1863 high-angle reflections. Fairly regular PO 4 tetrahedra, distorted cis -MgO 4 (OH) 2 octahedra, and distorted MgO 4 (OH) trigonal bipyramids are sharing either edges or vertices to build up a complex three-dimensional network. The variation in cell parameters for the solid-solution series Mg 2 PO 4 F – Mg 2 PO 4 OH with wagnerite structure is shown graphically. There are indications of preferred substitution of OH for F in the two ‘largest’ F/OH sites. Low valence sums in the bond-strength calculation are correlated with long Mg – O distances. Hydrogen bonding is relatively weak with strongly bent O – H⋯O bonds. The infra-red spectrum is briefly discussed.

X-ray studies of orthorhombic- I tridymite, especially focussed on atomic mean-square displacements (m.s.d.'s) at 443, 493, 573, 653 and 693 K respectively, were carried out on the basis of the usual second-order refinement of the Dollase model. The m.s.d.'s for O are highly anisotropic, and large in the planes perpendicular to Si – Si axes. Plots of temperature vs. m.s.d.'s point to a disorder of O atoms in the orthorhombic- I form. The transition, from the orthorhombic- I to the hexagonal high form or vice versa, is an example of a displacive structure transition from a disordered structure to another disordered one. When temperature falls from 693 K, any two SiO 4 tetrahedra joined by O on the two-fold axes parallel to a move away from the hexagonal positions, rotating progressively around the two-fold axes, and then symmetry is lowered to orthorhombic. The pair-wise rotations are accompanied by anisotropic changes of the thermal ellipsoids for two kinds of O atoms forming the basal planes of silica tetrahedra, nearly normal to c ; the thermal ellipsoids are distorted to elliptical shapes in the sections perpendicular to Si – Si axes when temperature falls. On the other hand, the thermal ellipsoid for the apical O atom is approximately circular in that section.

Two least-squares methods based on the Gram-Charlier expansion and the Edgeworth expansion were applied to a test structure to examine their usefulness in analysing multimodal density distribution of atoms. The Gram-Charlier expansion was more successful to reproduce the test structure than the Edgeworth expansion. The least-squares method based on the Gram-Charlier expansion was applied to the high temperature forms of tridymite to analyse density distribution of O atoms. The obtained density distribution of O was concave and nearly concentric at both 693 and 733 K (hexagonal), but clearly bimodal, at 493 K (orthorhombic), with the mean positions of low densities.

The crystal structure of AgTaO 3 has been determined with the intensities of 778 independent reflections measured on a X-ray four-circle single-crystal diffractometer at 295 K. The unit cell is rhombohedral with a R = 5.5758 Å, α R = 59.434°, a H = 5.5281(1) Å, c H = 13.7159(5) Å, γ H = 120°, V H = 363.00 Å 3 , Z H = 6, D c = 9.24 gcm −3 . The refinement was carried out in the two possible space groups: R 3 c and R [unk] c , and converged to R w = 2.6 and 2.8%, respectively. The acentric space group R 3 c was chosen as the proper one for AgTaO 3 .

Crystals of [(CH 3 ) 2 N(CH 2 ) 2 (CH 2 ) 2 O] 2 NaAg 3 I 6 · 2H 2 O (in which the organic ion is N,N-dimethylmorpholinium) belong to space group Ibam with Z = 4 and a = 18.002(11), b = 23.409(15), c = 7.295(3) Å. Unlike the arrangement in NaI · 2H 2 O, tetrahedra of water molecules surround the Na + ions at 2.36 Å. The tetrahydrated Na + ions are in turn surrounded by edge-sharing tetrahedra of iodide ions forming an infinite chain parallel to the c axis. These tetrahedra share edges with two infinite chains of [AgI 4 ] tetrahedra, together forming a triple infinite chain of edgesharing [AgI 4 ] tetrahedra. There is also a single infinite chain of edgesharing [AgI 4 ] tetrahedra parallel to the c axis. The infinite chains are isolated from each other by the N,N-dimethylmorpholinium ions.

The comparative crystal study of the title compound Midalcipran, Et 2 N – C(O) – C(Ph) – CH(CH 2 ) in its active Cis-form with its trans isomer form crystallizing under two varieties, Trans I and Trans II, has been carried out for a better understanding of the mechanism of its antidepressant activity. The crystal data have also been compared with existing theoretical CNDO/2 studies. The Cis-form crystallizes in the orthorhombic system, Trans I is monoclinic and Trans II triclinic. Their crystal structures have been determined using conventional X-ray single crystal analysis. The active compound is characterized by a strong intramolecular hydrogen bond.

The crystal structure of the title compound has been determined from three-dimensional X-ray diffraction data for 2997 observed unique reflections [ I > 2 σ ( I )]. The crystals are triclinic, space group P [unk], with: a = 10.328(6), b = 10.868(4), c = 10.243(3) Å, α = 117.18(2), β = 96.26(3), γ = 96.48(3)°, V = 999.26 Å 3 and Z = 2. The structure was solved by the heavy-atom method and refined by least-squares to a final R = 0.030 ( R w = 0.037). Antimony is in pseudooctahedral coordination with the two axial positions occupied by chlorine atoms [Sb – Cl 2.510(2), 2.550(1) Å] and three of the equatorial apices occupied by the carbonyl oxygen [Sb – O 2.110(4) Å], a hydrazide nitrogen [Sb – N 2.202(5) Å] and a pyridine nitrogen [Sb – N 2.326(4) Å] of the organic ligand, which acts as a tridentate chelate. The fourth apex is occupied by the non-bonding electron pair of Sb(III). The molecules, which are essentially planar due to the extended fused ring system formed by the organic ligand, are held together by van der Waals forces. The IR and UV spectra are in accordance with the established geometrical features of the structure.

Neutron powder diffraction data of cubic CsNO 2 at room temperature (space group Pm 3 m , a = 4.389 Å) are analyzed with several models for the orientationally disordered NO 2 group. The density distribution of O and N atoms are expanded on spherical shells with cubic harmonics. The density of the O atoms is concentrated close to the <100> axes. The shell radii refine to 0.40(2) and 1.19(2) Å for N and O, respectively. Split-atom and Frenkel models constructed on this basis are consistent with the experimental data. There are two Frenkel models (superposition of rigid NO 2 groups) which can coexist in the crystal: in the first model the O – O direction of a molecule is parallel to <100> and in the second parallel to <110>. The configurational entropy and the two distinct orientations are consistent with published thermodynamic and Raman data.

The π -overlap between the phenyl ring and the side chain, in acetanilides and acetophenones, is not directly related to the coplanarity of these moieties.

The crystal structure of Na 2 S 4 O 6 · 2H 2 O has been redetermined from three-dimensional X-ray intensity data and refined to R = 0.025 ( R w = 0.018) for 1620 observed reflections. The structure is monoclinic, space group C 2, with a = 14.4726(5), b = 6.3716(3), c = 5.4402(3) Å, β = 105.53(1) °, Z = 2. Except for the chirality of the structure and the hydrogen positions, for which no information is given in the earlier work of Foss and Hordvik (1964), their structural model was confirmed by the present study. The tetrathionate anion possesses a two-fold symmetry axis. From the two independent S – S bonds of the anion the central bond is significantly shorter than the terminal one [2.019(1) Å versus 2.115(1) Å]. The S–S–S bond angle formed about the central S – S bond by the sulfur atoms is 89.55(2)°. The terminal SO 3 groups of the anion have almost perfect trigonal symmetry [S–O: 1.447(1)–1.450(1) Å, O–S–O: 113.39(6)– 113.82(5)°]. The sodium cation is surrounded by six oxygen atoms in a distorted octahedral arrangement. [Na–O: 2.358(1)–2.465(1) Å]. By sharing opposite faces, columns of NaO 6 octahedra are formed, which run parallel to b axis and are linked together through the sulfonate groups of the tetrathionate anions and through hydrogen bonds, in which the water molecules are involved. The chirality of the structure was determined with the Hamilton and the Bijvoet methods. Both indicated that the earlier structure proposal of Foss and Hordvik (1964) should be inversed for our crystal.

The crystal structure of BiSeCl has been determined with 667 independent reflections, using three-dimensional intensities. The cell constants, obtained by least-squares calculation from direct θ -value measurements on the diffractometer, are: a = 8.0787(8), b = 9.3046(6), c = 4.2182(4) Å with Z = 4 formula units per unit cell; the space group is Pnαm . The positional and vibrational parameters, with anisotropic temperature factors, were refined by full-matrix least-squares calculations to a final R = 0.032. Each Bi atom is six-coordinated by three Se atoms at distances 2.727 – 2.855 Å and three Cl atoms at distances 2.899–3.186 Å. Two of the Se atoms and two Cl atoms form a parallelogram parallel to c , with the remaining atoms occupying the apices of the pyramids formed on either side of this parallelogram. The coordination polyhedron is linked to a symmetry-equivalent polyhedron by a common Se – Se edge. This characteristic double-polyhedron system is repeated along the c axis, thus forming an infinite double chain of composition {Bi 2 Se 4 Cl 6 } n . The chain is further linked to each of four similar chains by a common (Cl – Cl) n – row parallel to c . The structure constitutes a new type within the group of compounds of the general formula A[unk]B[unk]C[unk], with A = As, Sb, Bi; B = S, Se, Te; C = Cl, Br, I.

Single crystals of optical quality of l -glutamic acid chloride, bromide and iodide with dimensions up to 80 × 30 × 20 mm have been grown from aqueous solutions by controlled lowering of temperature from 315 to 300 K. The isotypic crystals possess quite similar physical properties. Strong anisotropic effects are found with respect to elastic constants, coefficients of thermal expansion and piezoelectric constants. The dielectric constants show only a very weak anisotropy. The piezoelectric and electrooptic constants are smaller than those of α -quartz.

Complete third-order elasticity tensors of cubic NaBrO 3 , Na 3 SbS 4 · 9H 2 O and NaH(CH 3 COO) 2 have been determined from stressinduced shifts of ultrasonic resonance frequencies of thick plates. The observed third-order elastic constants are negative, except c 456 of NaBrO 3 and c 123 of NaH(CH 3 COO) 2 . The constant c 111 is the largest and c 144 and c 456 are the smallest in absolute magnitude. The pressure derivatives of the inverse compressibility are slightly larger than those of the alkali halides. The third-order elastic properties of NaBrO 3 and Na 3 SbS 4 · 9H 2 O resemble those of NaCl-type crystals and α -alums, respectively.

FePO 4 was obtained by reaction of Fe 2 O 3 with H 3 PO 4 at 5 kP, and 520 K, and subsequent dehydration at 750 K. The structure is isotype to AlPO 4 -quartz (berlinite). The structure was investigated by neutron scattering of a powder sample.

The structure of harstigite, MnCa 6 Be 4 [SiO 4 ] 2 [Si 2 O 7 ] 2 (OH) 2 from Värmland, Sweden, is orthorhombic with space group Pnam , a = 9.793(2), b = 13.636(3), c = 13.830(3) Å, Z = 4 and D x = 3.19 g cm −3 . It was refined to R (unweighted) = 0.053 and R (weighted) = 0.050 using 3630 non-equivalent reflections. Harstigite is a mixed-anion silicate which contains [SiO 4 ] tetrahedra (mean Si – O distance 1.637 Å), [Si 2 O 7 ] groups (mean Si – O distance 1.623 Å), and in addition [Be(O,OH) 4 ] tetrahedra (mean Be – (O,OH) distance 1.651 Å), [MnO 6 ] polyhedra (mean Mn – O distance 2.222 Å) and [CaO 8 ] polyhedra (mean Ca – O distance 2.507 Å). The ratio of single tetrahedra [SiO 4 ] to double tetrahedra [Si 2 O 7 ] in the structure is 1:1.

The crystal structure and lattice constants of P 4 O 10 were redetermined applying diffractometer data and Guinier powder data, respectively [ R 3 c ; a = 10.3035(9), c = 13.5102(19) Å; R w = 0.023]. In contrast to earlier investigations the geometry of P 4 O 10 in the crystalline state proved to be in accordance with T d -symmetry.