Volume 213, Issue 4

It is shown that the coordinates of the atoms in a crystal can be derived by purely algebraic and analytical means from form and structure factors without the need to search a Fourier grid map.

It is shown that coordination numbers ( CN ) of alkali atoms can be determined in crystal structures by means of Voronoi-Dirichlet polyhedra without using crystal-chemical radii. It is found that a domain with constant volume corresponds to an alkali atom at CN ≥ 6. The conclusion about correctness of application of the model of deformable spheres for the description of alkali atoms in a crystal field is drawn.

Structure data for both triclinic α - and γ -CuMoO 4 have been delivered with anisotropic temperature factors at 190 K. The complete tensors of linear thermal expansion coefficients were derived for α - and γ -CuMoO 4 using the temperature dependence of lattice parameters within the temperature range 20 K–300 K and 20 K–260 K, respectively. The orientation of principal axes and values of principal expansion coefficients are given for selected temperatures. Their relation to the structure is discussed. The volume expansion coefficient of α -CuMoO 4 becomes negative below 80 K.

The structures of HN(SO 2 R) 2 , R=F, CF 3 are formed by molecules linked by hydrogen bonds to infinite chains. While KN(SO 2 F) 2 is composed of alternating cations and anions, HN(SO 2 CF 3 ) 2 exhibits a pronounced layer structure. In the acids, the substituents – R are in trans configuration being on the opposite sides of the plane defined by S–N–S bonds but in the salts the cis configuration with both substituents on the same side of the S–N–S plane is preferred, probably due to numerous metal-anion interactions.

Hydrothermal synthesis in the systems LaCl 3 (CeCl 3 )–Al(OH) 3 (Ga 2 O 3 )–GeO 2 yielded crystals of composition La 3 AlGe 5 O 16 , La 3 GaGe 5 O 16 and Ce 3 GaGe 5 O 16 , respectively. The syntheses were carried out at temperatures of 1023 K–1073 K under pressures of 1000 bar. The space group of the three substances was determined as P [unk] with the pseudosymmetry P 2 1 / c . All compounds are isostructural. The lattice parameters are a = 4.794(4) Å, b = 8.102(8) Å, c = 15.722(8) Å, α = 90.42(3)°, β = 94.46(2)°, γ = 89.91(2)° for La 3 AlGe 5 O 16 , a = 4.827(4) Å, b = 8.090(4) Å, c = 15.707(6) Å, α = 90.76(5)°, β = 94.01(7)°, γ = 90.01(7)° for La 3 GaGe 5 O 16 and a = 4.768(7) Å, b = 8.088(5) Å, c = 15.600(2) Å, α = 90.55(4)°, β = 94.46(4)°, γ = 89.63(4)° for Ce 3 AlGe 5 O 16 . There are two formula units in the unit cell.

The crystal structure of α -Cu 3 SbS 3 at 493 K and 403 K was determined from single crystal data. The high-temperature modification, which is stable above 394 K, crystallizes in the orthorhombic system, space group Pnma (No. 62), a = 7.808(1) Å, b = 10.252(2) Å, c = 6.587(2) Å, and Z = 4 ( T = 493 K). From single crystal data the distribution of the disordered copper atoms in the three-dimensional arrangement of [SbS 3 ] 3− units was determined. The atomic displacement parameters of the disordered copper atoms were refined using a Gram-Charlier non-harmonic development and a suggestion for a pathway for mobile copper atoms is derived. Copper atoms are distributed over five sites with trigonal planar or tetrahedral coordination and empty octahedra S 6 are the bottlenecks for a three-dimensional movement. The crystal structure of γ -Cu 3 SbS 3 , which is stable below 264 K, was determined from X-ray powder data by the Rietveld method. The low-temperature modification crystallizes also in the orthorhombic system, space group P 2 1 2 1 2 1 (No. 19), a = 7.884(1) Å, b = 10.221(1) Å, c = 6.624(1) Å, and Z = 4 ( T = 223 K). Whereas the arrangement of the thioantimonate(III) polyhedra keeps almost unchanged the copper atoms in the low-temperature modification γ -Cu 3 SbS 3 are no longer disordered but are located in three different positions with triangular coordination by sulfur.

The crystal structure of dichlorine oxide is reported. Cl 2 O crystallizes in the tetragonal space group I 4 1 / amd with a = 772.46(5) pm, c = 926.06(7) pm, and Z = 8 at 90 K. Basically a molecular structure ( d (O–Cl) = 170.92(4) pm) with weak secondary Cl–O interactions ( d (O … Cl) = 279.86(4) pm) results in a distorted tetrahedral coordination of the oxygen atom. Cl 2 O is isostructural to the high-pressure modification of water, ice VIII.

Pb monoborate hydrate, Pb 5 B 3 O 8 (OH) 3 H 2 O, was synthesized in the hydrothermal system PbCO 3 –Li 2 B 4 O 7 –H 2 O ( T = 543 K, p = 100 bar; PbCO 3 /Li 2 B 4 O 7 = 0.25–0.5; 10–14 days). The hexagonal structure was established from X-ray single crystal diffraction, λ (Mo K α ) = 0.71073 Å; space group P 6 3 cm ; a = 9.067(3) Å, c = 24.637(9) Å, V = 1753.19 Å 3 ; M = 7592.58; D x = 7.19 g/cm 3 ; Z = 6; μ = 707.4 cm −1 ; F (000) = 3156; R = 0.067 for 624 reflections. The new phase is characterized by the alternation along [001] of simple and complex layers, formed by only Pb-polyhedra, or by Pb-polyhedra and B-triangles, respectively. The asymmetric coordination of the most Pb atoms, similar with lead oxide and Pb 6 B 10 O 21 , is connected with two 6 s electrons, emphasizing the similarity in the nature of bonding between these compounds. The Pb(6)-atoms are disordered around 12 d site with 50% occupancy. The distance between the two potential crystallographic sites is 1.24 Å. The similar split of the Pb-position was recently reported for PbBi 12 Mo 5 O 34 . The B(O,OH) 3 groups are weakly aplanar with the apex pointing towards sheets, formed by Pb-polyhedra, due to the polarizing effects of the central cations. Similarly to other relevant examples, the B atoms in two B,O-triangles have the forth relatively near O atom neighbours, which could cause a tendency towards a tetrahedral environment of the B atoms. The pyramidal distortion of the three other borate complexes is rather to be attributed to the polarizing power of Pb atoms. Preliminary investigations of the non-linear optical behaviour of lead monoborate hydrate (powder technique) are also discussed.

2-Benzoylpyridine piperidinyl- and hexamethyleneiminylthiosemicarbazones, HBzpip and HBzhexim, respectively, crystallize in a hydrogen bonded Z isomeric conformation with respect to the C7–N2 bond. The intramolecular hydrogen bond is between N3–H…N1, but the S atom is E to the azomethine nitrogen, N2, for HBzpip and Z for HBzhexim. HBzpip is the second ZE isomer known, but the first that does not have a formal hydrogen bond to N2.

The crystal and molecular structure of diaquabis-(2,4-dinitrophenolato)cobalt(II) tetrahydrate, [Co(dnp) 2 · (OH 2 ) 2 ] · 4 H 2 O, C 12 H 18 CoN 4 O 16 , has been determined at room temperature. The red-brown crystals are triclinic, space group P [unk] with unit cell dimensions a = 8.961(3) Å, b = 11.573(3) Å, c = 4.872(1) Å, α = 93.05(2)°, β = 90.72(2)°, γ = 90.16(2)°, Z = 1 and D x = 1.755 Mg m −3 . The structure was refined by a full-matrix least-squares procedure on F to final R = 0.037 using 1644 reflections with I ≥ 3.0 σ ( I ). The cobalt(II) atom (which lies on a center of inversion) exists in a slightly distorted octahedral geometry with the basal plane being defined by two phenoxide (2.001(2) Å) and two nitro oxygen atoms (2.110(2) Å) and the axial positions by two oxygen donor atoms derived from two symmetry related H 2 O molecules (2.092(2) Å). The lattice is stabilised by a network of hydrogen-bonding contacts.