Volume 197, Issue 1-2

Solid-state high-resolution 29 Si-NMR experiments were used to study the structure of the silicate layers in makatite and its crystalline silicic acid obtained by a cation exchange reaction from makatite. For each of the studied samples two well-separated NMR signals have been recorded which could be assigned to Q 3 – [ − O Si (OSi ≡ ) 3 ] – units of the silicate layers of the corresponding compounds and to Q 4 – [ Si (OSi ≡ ) 4 ] – units of quartz impurities. Compared with makatite in the silicic acid a high-field shifted Q 3 -signal and a splitting of this signal into two component lines have been detected. These observations were attributed to structural changes which appeared as a result of the cation exchange reaction.

Na 2 CaSiO 4 , Na 2 SrSiO 4 , and Na 2 (Ca 0.5 Sr 0.5 )SiO 4 , are shown by X-ray powder diffraction to have the cubic, Fm [unk] m crystal structure of orientationally disordered Na 3 PO 4 . The distribution of SiO 4 orientations are well described by cubic harmonics and show a high probability of Si – O bonds pointing within about 20° of 〈100〉 and low probabilities in other directions. The disordered SiO 4 groups form a cubic close packed array with cations in both “tetrahedral” and “octahedral” interstices. There is apparent preference of the divalent Ca and Sr cations for the tetrahedral sites over the octahedral sites. About 92% of the cations in the ideal formulae are accounted for on these two sites. Electron microprobe analyses suggest that at least part of any remaining deficit is attributable to loss of Na atoms during synthesis but additional, weakly occupied sites may also be present in the structure.

HAlSi 4 O 10 was prepared from natural petalite (castor), LiAlSi 4 O 10 , by Li/H exchange in H 2 SO 4 (300°C). The crystal structure was determined by X-ray methods from a twinned crystal [ a = 5.867(3), b = 4.927(3), c = 7.524(4) Å, α = 93.0(l), β = 113.1(1), γ = 90.1(1)°, space group P 1, Z = l, R = 0.053 for 1011 reflections and 133 variables]. The topology of the Si 4 O 10 layers of petalite is not affected by ion exchange. The Al atoms are rearranged, however: Half of the Al atoms are on positions corresponding with those in petalite, the other Al atoms are on former Li positions. The remaining tetrahedral positions are empty. As a consequence the a translation in HAlSi 4 O 10 is only half as long as in petalite. The SiO 4 and AlO 4 tetrahedra are rotated during site exchange: one of the former O – O edges in AlO 4 resp. LiO 4 tetrahedra (now a vacant tetrahedral site) is shortened to 2.567(2) Å. Neutron powder patterns were recorded on HAlSi 4 O 10 and DAlSi 4 O 10 at 5 K and 293 K. Rietveld refinement allowed the location of the hydrogen atom in the short O … O contact.

Crystal structures of two ortho-substituted diaryl sulphur diimides have been determined by three-dimensional X-ray analysis. C 14 H 14 N 2 O 2 S is orthorhombic, space group P 2 1 2 1 2 1 , Z = 4, a = 21.391(3), b = 8.148(1), c = 7.717(1) Å. C 20 H 14 N 2 S is monoclinic, space group P 2 1 / n , Z = 4, a = 21.969(3), b = 5.311(1), c = 13.255(2) Å, β = 96.86(5)°. Results are reported and discussed also in comparison with the ones previously obtained by X-ray analysis on related compounds.

The crystal structure of a substituted pyranocarbazole alkaloid has been determined by X-ray diffraction method on a single crystal using Mo K α radiation. The compound crystallizes in the monoclinic system with the space group P 2 1 / c and Z = 4. The unit cell dimensions are a = 5.521(1), b = 15.314(2), c = 19.989(2) Å and β = 93.19(1)°. The structure was solved by direct methods and refined by full-matrix least squares to a final R value of 0.063 with 1551 ‘observed’ reflections. The molecule is not quite planar. The carbazole moiety adopts a slight boat conformation; the dihedral angle between the two six-membered rings is 3.9(2)°. The pyran ring is not planar and makes an angle of 5.2(3)° with the plane of the carbazole moiety. The N(l) – C(19) bond distance is slightly shorter than the single C – N bond value.

Na 4 SrSi 3 O 9 is monoclinic, C 2, a = 10.706(2), b = 10.866(2), c = 6.509(1) Å, β = 144.14(2)°, Z = 2. The structure was determined using 411 independent reflexions measured on a Nicolet P3 4-circle diffractometer; the coordinates (including anisotropic temperature factors for Sr only) refined to R = 10.4%. Extra very weak reflexions on film (with Cu K α suggested a superstructure, but these could not be detected using the diffractometer (with Mo K α ). The compound contains infinite SiO 3 chains, of a conformation not described previously. Bond lengths and angles are normal, although the Si – O – Si angle is nearly 180°; this rather large value is associated with large temperature factors for the bridging oxygen atoms. The structure is compared with those of other compounds of formula M 4 ′M″(TO 3 ) 3 where M′ = Na, K; M″ = Ca, Sr, Ba; T = Si, Ge.

A new sodium vanadyl(IV) orthophosphate NaVOPO 4 has been synthesized by solid-state and hydrothermal method and characterized by single-crystal X-ray diffraction and magnetic susceptibility. It crystallizes in the monoclinic space group P 2 1 / c with a = 6.524(1), b = 8.455(4), c = 7.119(1), β = 115.29(1)°, Z = 4, R = 0.027, and is structurally similar to the triclinic analog LiVOPO 4 . The structure can be described as close-packed infinite chains of trans-corner-sharing VO 6 octahedra with the holes around each chain filled with Na and P atoms. These infinite chains have alternating short and long V – O bonds and are similar to those found in β -VOPO 4 . The Na atom has six close oxygen neighbors at distances of 2.268 to 2.511 Å.

High temperature experimental study of a leucite single crystal was carried out using heating-quenching and heating-cooling-heating processes. We observed that in the heating process, the transition temperatures, Tc 1 and Tc 2 were 655°C and 675°C, respectively. After quenching, in heating process (before cooling), transition temperatures were found at 640°C and 660°C, respectively. It is concluded that this hysteresis is not due to the first order transition because there is no existence of hysteresis in heating-cooling-heating process nor an abrupt volume change at the transition. Moreover, the reflections of 200, 020, and 002 were always observed in the temperature range 21°C – 900°C. Our results do not confirm the existence of I 4 1 / a low temperature form, or Ia 3 d high temperature form including a transient phase I 4 1 / acd .

Packing considerations suggest that within an arithmetic crystal class the number of examples of a space-group type should decrease exponentially with the number of mirror planes [ m ] and twofold axes [2]. After allowing for various other factors, quantitative agreement ( R 2 ≤ 0.05) could be obtained, but in the crystal class mmm the discrepancies between observed and calculated frequencies greatly exceeded the statistical sampling errors. Kitajgorodskij's prediction that molecules with inherent mirror symmetry will adopt preferentially certain space groups (in particular Pnma ) satisfactorily explains the discrepancy.

The title compound, C 43 H 79 O 2 NPt, crystallizes in the monoclinic system, space group P 2 1 / c , with a = 20.444(8) Å, b = 12.220(4) Å, c = 18.303(7) Å, β = 101.6(4), Z = 4. The coordination of Pt is slightly distorted square-planar, the backbone of the hydro -aldoamidic ligand is almost planar; its mean plane is orthogonal to the coordination plane of Pt. The crystal structure has been refined to R = 0.054 for 3518 observed reflections.

A crystallographic and crystal chemical study has been performed on a new mineral, an orthorhombic MnSO 3 · 3H 2 O occurring in manganese ores at the Gambatesa Mine (Val Graveglia, Italy), associated with tephroite, bementite, braunite, hausmannite and hematite. Gravegliaite, appearing mainly as few radial aggregates of prismatic crystals, elongated parallel to [010] and up to 0.5 mm long, crystallizes in Pnma space group with a = 9.763(1) Å, b = 5.635(1) Å and c = 9.558(1) Å. It is colourless, transparent, optically biaxial and nonpleochroic with n α = 1.590, n β = 1.596, n γ = 1.636 and 2 V γ = 41° ( Z = b ). The strongest lines in the powder pattern are ( d Å) 6.83, 4.33 and 3.43. Microprobe analyses reveal a good compositional homogeneity and a quasi-ideal chemical composition. The crystal structure refinement confirms this mineral to be the natural analogue of synthetic MnSO 3 · 3H 2 O described by previous authors. The attempt to localize hydrogen atoms and to assign hydrogen bonds is discussed, since hydrogen bonds seem to play the major role in assuring cohesion to the structure.

The technique of oblique-texture diffraction on powder mounts with a strong preferred orientation of platelets, which has been used in electron diffraction, is extended to X-rays. It allows an easy recording of reflections that are otherwise lost in composite peaks or difficult to observe and measure in powder patterns. The technique is flexible and has important advantages: the photographs can be taken on any instrument permitting a controlled tilting of the mount, such as the widely available precession or Weissenberg single-crystal cameras; the sample is X-rayed in air, not in vacuum, and hydrated phases can thus be examined; by varying tilt of the sample and the X-ray wavelength, a good resolution of diffraction spots can be achieved that, in turn, facilitates interpretation of the patterns or measurement of intensities. As the preferred orientation approaches ideality, the information provided by an oblique-texture X-ray photograph approaches that from a single-crystal rotation pattern.

The reaction of Si(O 2 C 6 H 4 ) 2 (MeOH) x ( x = 1 − 2) with Ph 4 PCl yields besides other products crystals of [PPh 4 ] [( μ -Cl) {l,2-(HO) 2 C 6 H 4 }] ( 1 ), in which the anion consists of a chloride ion solvated by the catechol molecule via the hydrogen atoms. No anion-cation interactions are observed. 1 crystallises in the monoclinic space group P 2 1 / n (No. 14) ( T = 295 K) with a = 13.661(4), b = 16.059(5), c = 12.640(4) Å, β = 112.68(5)°, V = 2558.5 Å 3 and Z = 4. The refinement gives the final R values R = 0.078 and R w = 0.053 for 1940 observed symmetry-independent reflections.

The crystal structure of solid dichlorodifluoromethane has been solved from powder neutron diffraction data. A single solid phase exists between the melting point and 1.5 K. The structure is orthorhombic, Fdd 2, Z = 8 , with a = 10.1676(3) Å, b = 14.9638(4) Å, and c = 5.1004(2) Å at 1.5 K. The molecules form columns with their dipole moments aligned ferroelectrically along the c direction.

The crystal structure of Mo 5 Ge 3 has been refined on the basis of single crystal data. Mo 5 Ge 3 crystallizes isotypically with W 5 Si 3 in space group I 4/ mcm – D 4 h 18 (no. 140). The lattice constants are a = 984.5(2) pm and c = 496.5(1) pm.