Volume 187, Issue 1-2

Single crystals of tertiary-butyl-alcohol (TBA) have been grown by a zone refining technique. A review of the phases and the properties of TBA crystals is presented. The crystal structure of phase IV has been determined at 295 K: space group P [unk], a = 6.393(2), b = 9.481(3), c = 15.126(4) Å, α = 85.47(2)°, β = 79.60(2)°, γ = 76.01(2)°, V = 874.3 Å 3 , Z = 6. The molecules are arranged in helical chains along the a -axis and connected by hydrogen bonds. The optical properties have been studied and interference fringes have been used to determine the birefringence of the crystals: n 1 −n 3 = 2.55 · 10 −3 , n 2 −n 1 = 7.98 · 10 −4 ( λ = 488 nm, T = 294.7 K). The angle between two optical axes is 69° ± 1.5° and a mean index of refraction is [unk] = 1.41 ± 0.02.

Structural properties of three varieties of dioptase, namely natural green dioptase, Cu 6 Si 6 O 18 · 6H 2 O, synthetic blue dioptase, Cu 6 Si 6 O 18 ·6H 2 O, and synthetic black dioptase, Cu 6 Si 6 O 18 , are discussed, based on a structure determination of the latter. For blue dioptase a structural model is proposed. All three structures are closely related. The rather sluggish transition green-blue is interpreted as a mobilization of the H 2 O molecules within the structure. The structural background of the dehydration to black dioptase is discussed.

The crystal structures of PbBr 2 · SC(NH 2 ) 2 (form I) [ a = 6.026(2), b = 15.369(4), c = 4.259(2) Å, β = 110.71(5)°, Z = 2, space group P 2 1 ] and of PbBr 2 · 2[SC(NH 2 ) 2 ] (form II) [ a = 10.583(2), b = 12.457(3), c = 4.088(2) Å, β = 95.61(5)°, Z = 2, space group P 2 1 ] have been determined by single-crystal X-ray diffraction analysis. There is rather similar fivefold primary coordination around Pb 2+ in both complexes, conveniently described as distorted square pyramidal with the most strongly bound bromine at the apex of the pyramid. In PbBr 2 · SC(NH 2 ) 2 (form I) there are 2 sulphurs and 2 bromines in the base of the pyramid and in PbBr 2 · 2[SC(NH 2 ) 2 ] (form II) 4 sulphurs. In PbBr 2 · SC(NH 2 ) 2 (form I) the bases of the pyramids are linked through S – Br edges to form columns along [001], with the coordination around Pb 2+ increased to sevenfold by weaker links to two apex bromines of adjacent pyramids. There is also NH ⋯ Br hydrogen bonding within and between the columns. In PbBr 2 · 2[SC(NH 2 ) 2 ] (form II) the bases of the pyramids are linked via the sulphur atoms to form columns extending along [001], with additional links between adjacent Pb 2+ ions through loosely-held Br − ions, thus increasing the overall coordination to sevenfold. There are two NH ⋯ Br hydrogen bonds within each column and two additional such hydrogen bonds between adjacent columns; there are also two NH ⋯ S hydrogen bonds between adjacent columns. Re-examination of the structure of PbCl 2 · 2[SC(NH 2 ) 2 ] [Nardelli and Fava, Acta Crystallogr. 12 (1959) 727 – 732] shows that it is isostructural with PbBr 2 · 2[SC(NH 2 ) 2 ] (form II). The sevenfold overall coordination around Pb 2+ in these three complexes can be described as capped trigonal prismatic, with varying degrees of distortion from an ideal geometry; an alternative description is as octahedral with one site split between two more remote ligands. The split links are ascribed to sp hybridization of the 6s 2 lone pair, as proposed by Orgel [J. Chem. Soc., pp. 3815 – 3819 (1959)].

Crystals of Na-nephelines of two different compositions have been studied. For both compositions the structure has been determined at room temperature in order to study the effect of different Si/Al ratios. A second objective is to corellate the structural parameters with conductivity measurements of this one-dimensional ionic conductor. A meroedric twinning of the crystals has been accounted for. Two other data sets of 573 K and of 773 K have been evaluated using anharmonic temperature coefficients in order to determine the probability density for the highly mobile ion in the central channel of the structure.

The new organoboron compound (oxalato)(2,4-hexanedionato)boron(III), 1, has been synthesized by the reaction of boric acid with 2,4-hexanedione and oxalic acid. Crystals of 1 are trigonal, a = b = 9.008(5), c = 10.824(7) Å, α = β = 90°, γ = 120°, Z = 3, space group P 3 1 ϱ c = 1.39 g cm −3 . The structure was solved by direct methods and was refined by full-matrix least-squares procedures to a R value of 0.054 for 1583 reflections with F > 3 · σ ( F ) ( R w = 0.048). The structure consists of discrete molecules containing tetrahedrally coordinated boron atoms with average B – O distances of 1.461(6) Å. The acetylacetonato moiety is consistent with the fully delocalized and symmetric description of the (acac) ligand, where acac ≙ [CH 3 COCHCOC 2 H 5 ] − .

Conditions for vapour growth of tin films containing α 2 -Sn, a recently observed unusual tin structure, are described. The formation of tin films consisting of unusual tin structures was found to depend on the temperature of the tin source, and on the distance between the tin source and the growing film.

The crystal structures of bis(N-isopropyl)-salicylaldiminato zinc iodide [I 2 Zn(C 20 H 26 N 2 O 2 )] (adduct 1 ) and of bis-chelate-N-isopropyl-salicylaldiminato zinc (complex 2 ) Zn (C 20 H 24 N 2 O 2 ) have been determined at room temperature by X-ray diffraction methods. Adduct 1 crystallizes in space group P 2 1 / c with a = 9.229(2), b = 10.610(2), c = 24.711(4) Å, α = γ = 90°, β = 94.04°, V = 2413.68 Å 3 , with Z = 4 units. The structure confirms the adduct nature of the compound; it shows an asymmetry with respect to the I – Zn – I plane and some additional disorder in one of the two N-isopropyl groups. Bis-chelate 2 crystallizes in orthorhombic form, space group Pbca , with a = 13.225(2), b = 19.476(2), c = 15.155(4) Å, V = 3903.47 Å 3 , with Z = 8 units. The structure consists of monomeric units in which the zinc atom shows a slightly distorted tetrahedral geometry. The structures have been solved by direct methods and refined by least-squares calculations to a final R value of 0.0296 for 3146 unique observed reflections [ I ⩾ 3 σ ( I )] for adduct 1 , and to an R value of 0.0339 for 2376 unique observed reflections for bis-chelate 2 .

The crystal structure of the title compound has been examined at room temperature. Crystals are triclinic, space group P [unk] with a = 4.2859(7), b = 6.036(1), c = 10.6563(5) Å, α = 73.35(1), β = 83.81(1), γ = 89.11(2)°, V = 262.5(2) Å 3 , Z = 2, D x = 1.621 g cm −3 . The structure was refined by a full-matrix least-squares procedure to final R = 0.063 for 1003 reflections with I ⩾ 3.0 σ ( I ) measured on a CAD4 diffractometer. The molecule is essentially planar and exists in the lactam-thione form with the C(2) – S(2) and C(4) – O(4) distances being 1.683(3) and 1.227(4) Å respectively. Intermolecular hydrogen bonding, involving the sulphur and oxygen atoms, leads to infinite ribbons which stack in a layer structure; the vertical distance between successive layers is approximately 3.48 Å.

A thorough study on α , β -unsaturated ketonic derivatives was initiated in order to correlate conformation of the O = C – C = C group and circular dichroism (CD) of the R band. A new compound, (−)-3-[( o -chlorobenzoyloxy o -chlorophenyl) α -methylene] nopinone was prepared from (+)-nopinone and its structure determined by X-ray analysis [ P 2 1 2 1 2 1 , a = 15.728(2), b = 17.773(2), c = 7.3204(7) Å]. Final refinement with anisotropic temperature factors resulted in R = 0.035 and R ( w ) = 0.033 for 3941 unique reflections. The ester has the Z configuration with the o -chlorinated ring greatly twisted due to steric effects. This structure inhibits entirely conjugation and lowers the Δε of the R band, thus proving the direct dependence of the CD of this band upon electronic effects. Furthermore, the helicity of the O = C – C = O group is positive, as is the sign of the CD of the R band and this is consistent with Snatzke's rule concerning α , β -unsaturated cisoid ketones.

The crystal structure of the title compound (DPXI hereafter) was determined from three-dimensional intensities of 2397 independent reflections. The cell constants obtained from direct θ value measurements of 100 reflections and refined by least-squares, are a = 10.637(1), b = 10.440(2), c = 7.844(1) Å, α = 82.53(2)°, β = 107.75(1)°, γ = 102.42(1)°, Z = 2, space group P [unk], ϱ meas = 1.69 Mg m −3 . The structure was solved by Patterson and Fourier methods and the positional and anisotropic thermal parameters were refined by full-matrix least-squares calculations. The final R value was 0.069 ( wR = 0.071). The structural unit of DPXI is a dimer formed by two centrosymmetrically related formula units bridged by I … S secondary bonds. The coordination around the I atom is distorted planar tetragonal comprising two normal I – C ar bonds and two secondary I … S bonds to different xanthate ligands.

The monoclinic form of LiMgBO 3 has been synthetized and its crystal structure studied by single crystal X-ray diffraction methods. The space group is C 2/ c , Z = 8, with unit cell parameters a = 5.161(1) Å, b = 8.880(2) Å, c = 9.911(2) Å and β = 91.29(2)°. The structure which is isotypic to that of i.a . LiZnBO 3 , has been refined versus the amplitudes of 368 X-ray reflections with sin( θ )/ λ ≤ 0.8 Å −1 to an R -value of 0.042. LiMgBO 3 has a well ordered Mg arrangement, the Li positions are disordered. The Mg atoms are five-coordinated, square bipyramidal, by the O atoms with a distance range of 1.97 to 2.12 Å. The coordination of the average Li atom position is trigonal bipyramidal, with three shorter bonds in the trigonal plane. The Li atoms are disordered around the average position. The disorder can be described by two half-occupied positions about 0.3 Å above and below the trigonal plane, half-way towards the centroids of the two face-sharing tetrahedra forming the bipyramid. The disordered Li atoms thus become essentially four coordinated by the oxygen atoms with the bond distances ranging from 1.88 to 2.33 Å. Estimated bond valences of Mg and Li are in agreement with the expected formal charges of the metal ions.

The crystal structure of Ca 11 Ga 7 , determined from single crystal X-ray data, is a new cubic type, space group Fm [unk] m , cF 144, a = 16.109(2) Å, Z = 8. Direct methods were used for the structure determination. Refinement with anisotropic temperature factors led to R = 0.029 for 297 structure factors. Out of the two gallium atoms, one is coordinated by a monocapped square antiprism of nine calcium atoms, while the other forms a tetrahedral Ga 4 cluster, surrounded by a four-capped truncated tetrahedron of 16 calcium atoms. The structure shows a tridimensional connection of the truncated tetrahedra, which leaves in between channels filled up by the other gallium and calcium coordination polyhedra.

The crystal structure of Hg 4 As 2 I 3 ( Pa [unk]) has been solved and refined to R = 0.030 ( Rw = 0.038) for 565 unique observed reflections. The framework, isostructural to that of Cd 4 As 2 I 3 , is described either as a pseudo-cubic close packing of Hg atoms with As and I in the interstices or as a complex arrangement of two sorts of polyhedra surrounding Hg, sharing corners or edges. The cohesion of the structure is assumed to be due to As atoms with strong bonds As – Hg and As – As. A discussion about Hg – I distances is proposed, involving a iono-covalent character to the corresponding bond.

Single crystals were studied by X-ray diffraction at 20, 500 and 750°C. The structures are homeotypic with α -quartz (low temperature) and have been refined in the space group P 3 1 21 leading to R F -values between 0.026 and 0.037. In contrast to the isotypic compound AlPO 4 and to quartz, but in accordance with the known literature no displacive α-β phase transformation has been found in the range of temperature up to 750°C. In this range interatomic distances and angles show only small variations, which is also true for the angle Al – O – As (135.5 – 140.1°). The orientation of the vibrational ellipsoids and the dependence on temperature of lattice constants, interatomic distances and angles and of tilt angles of the metal – oxygen tetrahedra around their twofold axes are discussed.

Krinovite, a meteoritic silicate mineral with ideal crystal chemical formula Na 2 Mg 4 Cr 2 [Si 6 O 18 ]O 2 , is triclinic, space group P [unk], with a = 10.238(4), b = 10.642(4), c = 8.780(3) Å, α = 105.15(3)°, β = 96.50(4)°, γ = 125.15(3)°. The crystal structure of krinovite has been refined to R = 0.065, R w = 0.067 for 1661 independent reflections. Krinovite is a member of the aenigmatite group, and is characterized by octahedral walls connected through tetrahedral chains with appendices and additional insular octahedra.

A uniform description of the crystal structures of β -Si 3 N 4 and of compounds with the phenakite type structure is proposed, based on the fact that the latter are superstructures of the former. The cation ordering in α -LiGaSiO 4 that leads to space group R 3 is explained in terms of a superstructure of β -Si 3 N 4 with space group P 6 3 from which the two-fold screw axes are removed. Remnants of the same screw axis are present in phenakite type structures with space group R [unk] as well.

Crystal structure refinement ( R = 0.057 for 811 observed reflections) based on neutron diffraction data of a strontian piemontite (S. Marcel, Italy), with unit cell a = 8.884(3) Å, b = 5.684(1) Å, c = 10.202(3) Å), β = 115.23(2)°, lead to the following crystallochemical formula: Ca(Ca 0.84 Sr 0.16 ) (Al 0.81 Mn 0.17 Fe 0.02 ) Al(Al 0.06 Mn 0.61 Fe 0.33 ) [O(SiO 4 ) (Si 2 O 7 ) OH]. Because of the Jahn-Teller effect, Mn 3+ prefers the octahedral site M(3) whose distortion is quite independent from the composition.

Single crystals of guanidinium tetrafluoroborate of optical quality and dimensions up to 60 × 60 × 30 mm have been grown from aqueous solutions. They possess a distinct polar morphology of point symmetry group 3 m and strong pyroelectric, piezoelectric, electrooptic and nonlinear optic effects similar to those observed in hexagonal guanidinium iodide. Further, their elastic anisotropy represents one of the largest so far observed in crystals. The crystals are suited for technical applications which require the simultaneous existence of different species of large polar effects.

The crystals of the title compound are orthorhombic, space group Pca 2 1 with the following parameters: a = 16.387(4), b = 7.507(2), c = 28.612(8) Å, V = 6343.8 Å 3 , Z = 4, D x = 1.35 g cm −3 , μ (Mo Kα ) = 0.753 mm −1 , Final R = 0.11, R w = 0.12 with 1.00/[ σ 2 ( F o ) + 0.0005 | F o | 2 ] for 1073 unique redections [ I > 3 σ ( I )]. The nickel atom has an approximate square planar configuration. The nitrogen atom of the cation exhibits a tetrahedral configuration. The anions are arranged along the a -axis at Z = 0.25 and 0.75 with the Nickel atoms nearly collinear.