Band 188, Heft 1-2

C 15 H 23 OBr 2 Cl, M r = 411.98, orthorhombic, P 2 1 2 1 2 1 , a = 7.232(7), b = 11.923(16), c = 19.046(19) Å, V = 1642.3 Å 3 , Z = 4, D x = 1.67 Mgm −3 , Mo Kα , λ = 0.71069 Å, μ = 49.7 cm −1 , F (000) = 832, T = 293 K, R = 0.089 for 1263 reflexions. The two rings are joined at the spiro carbon C(6) and adopt chair [C(1) → C(6)] and half-chair [C(6) → C(11)] conformations. Extensive decomposition of the crystals occurred in the X-ray beam.

The crystal structure of lead-lithium monophosphate has been solved by single crystal X-ray techniques. The cell constants are: a = 7.945(6), b = 18.46(2), c = 4.928(4) Å, Pna 2 1 , Z = 8. The least squares refinement leads to a final R value of 0.032 for 1315 reflections. The three-dimensional framework built up by LiO 4 and PO 4 sharing vertice tetrahedra aligned in the same c direction is a non-common arrangement. The Pb atoms are distributed in the polyhedral cavities of this polar framework.

The choice of reciprocal lattice nodes scan mode ( ω , ω / θ , ω /2 θ ) in single crystal automated diffractometry is examined from an operational point of view, for typical routine situations in mineralogy (Mo Kα radiation, θ < 30°, monochromator). A critical reexamination of the literature (not always free from ambiguities) is attempted and experimental investigations on natural clinopyroxenes are reported. In the above specified conditions, unless extreme cases, what is really important is not primarily the chosen scan mode itself, but rather the size of the horizontal detector aperture in relation to scan mode. If this relationship is correctly chosen, the choice of scan mode itself can be somehow arbitrary and not relevant for refinement accuracy and precision. The criterion of “minimum detector aperture width”, largely emphasized in the literature, is of very limited operative relevance. Even a wrong choice of aperture-scan coupling affects precision but not accuracy of the final crystal chemical model (with the exception of thermal parameters underestimation). The different areas of reciprocal lattice sampled as background with different scan modes do not affect refinement results.

The room temperature electron density distribution in potassium tetrathionate, K 2 S 4 O 6 , was investigated using accurate single-crystal-X-ray diffraction data up to sin ϑ / λ = 0.90 Å−1. The conventional all-data refinement yielded R / R w values of 0.018/0.017, respectively, for 3316 observed reflections. In order to reduce parameter bias introduced by bonding effects, various refinements with high-order data were also performed. The resulting (X – X HO ) dynamic deformation density maps of the two crystallographically independent anion complexes [S 4 O 6 ] 2− agree qualitatively. No significant σ -type single bond peaks are found at the midpoints of the S – S bonds. Instead, extended “lone pair” deformation density maxima are observed close to the S – S bonds, as well as above and below the S – S – S planes, providing evidence for a directional character of the sulfur lone-pair orbitals. The density distributions associated with the terminal SO 3 groups are as expected.

Crystals of KCu 3 (OH) 2 [(AsO 4 )H(AsO 4 )] were synthesized under hydrothermal conditions at ∼ 500 K. The crystal structure was solved from 1386 single crystal X-ray data: a = 10.292(5) Å, b = 5.983(3) Å, c = 7.877(4) Å, β = 117.86(2)°, space group C 2/ m , Z = 2, R = 0.033. One of the two crystallographically different copper coordination polyhedra is a “compressed octahedron” with two “short” (axial) and four “medium” (equatorial) Cu – O bonds [1.899(2) Å, 2× and 2.186(1) Å, 4×]. The other Cu atom as usual is [4 + 2] coordinated [Cu – O = 1.934(1) Å, 2×, 2.000(1) Å, 2×, and 2.428(2) Å, 2×]. Each two arsenate tetrahedra are connected to dimers by a symmetry restricted hydrogen bond of 2.490(6) Å. The structure type of KCu 3 (OH) 2 [(AsO 4 )H(AsO 4 )] is strongly related with that of NaCu 2 (H 3 O 2 )(SO 4 ) 2 (natrochalcite) and Cu 2 O(SO 4 ) (dolerophanite).

The effect of heavy atoms in finding phases of structure factors has been discussed using information theoretic approach in P [unk]. In the present paper, an expression for measuring information content has been derived taking into account the phase and magnitude of the heavy-atom part of the structure. As a test example, a known structure of a derivative of β -lactam has been used and it has been shown that the value of information content gives an indication that the phase prediction is more reliable when information from heavy atom part is taken into consideration.

The crystal structure of the copper(II) complex with the herbicide endothall, (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid = H 2 L), [Cu(H 2 O) 6 ][CuL 2 ], has been determined by X-ray methods and refined to a residual of 0.033 for 1774 observed reflections, collected at 163 K. The complex comprises centrosymmetric tetragonally distorted octahedral [Cu(H 2 O) 6 ] 2+ cations [Cu – O, 1.957, 1.972, 2.321(2) Å and [CuL 2 ] 2− anions [Cu – O, 1.959, 1.995, 2.376(2) Å]. In the complex anions, the four equatorial oxygens are from two unidentate carboxylate groups of each ligand while the axial sites are occupied by oxygens of the oxy-bridged molecular cage.

The crystal and molecular structure of the title compound has been established by means of the X-ray diffraction method on a single crystal using Mo K α radiation. The crystals are monoclinic, space group P 2 1 / a with a = 8.745(2), b = 13.230(8), c = 11.729(2) Å, β = 94.06(2)°. The structure was solved by the heavy-atom method, and refined by full-matrix least squares to a final R value of 0.035 with 1787 ‘observed’ reflections. The five- and six-membered ring are planar and inclined to one another at 0.9°. In the five-membered ring the average C – S bond distance is 1.75 Å and the C – S – C angle is 87.9°.

A new form of molybdenum (V) phosphate has been isolated. The structure of this oxide has been determined from a single crystal X-ray diffraction study. It crystallizes in the triclinic space group P [unk] with a = 8.846(8) Å, b = 8.846(9) Å, c = 10.01(1) Å, α = 56.488(8)°, β = 55.588(7), γ = 68.868(7)°, Z = 1. The refinement has led to R = 0.022 and Rw = 0.026 for 5243 reflections with I ⩾ 3 σ ( I ). The structure consists of corner-sharing MoO 6 octahedra, P 2 O 7 tetrahedra forming tunnels running along [0[unk]1] where the K + ions are located. One original feature of this structure, compared to the other forms – α , β , γ – deals with the existence of Mo 2 P 2 O 15 units formed of one P 2 O 7 group sharing four of its corners with two MoO 6 octahedra.

The absolute configuration of the title compound which shows a pharmacologic activity was determined by the Bijvoet difference method. The compound crystallizes in the orthorhombic system, space group P 2 1 2 1 2 1 , with a = 10.292(2) Å, b = 12.777(2) Å, c = 20.471(2) Å. The final values are R = 0.031 and R w = 0.032 for 2920 reflections. The results establish that the camphosulfonate, modulus A, has the R configuration and the methyl α -(tetrahydro-4,5,6,7 thieno (3,2-c) pyridin-5-yl)-acetate, modulus B, exhibits the S configuration.

The crystal structure of holmquistite Na 0.04 Ca 0.02 Li 1.91 -Mg 1.98 Fe 1.05 Mn 0.03 Ti 0.01 Al 1.93 (Si 7.87 Al 0.13 )O 22 (OH) 2 has been refined by single crystal X-ray methods using 1930 independent reflections. The space group is Pnma with the unit cell dimensions a = 18.254(2), b = 17.636(2), c = 5.270(1) Å and V = 1696.6(4) Å 3 , Z = 4. Chemical and optical data are given. The refinement of the atomic parameters and of the cation distribution gives final R -values of R = 0.023 and R w = 0.027. The cation distribution is dominated by the preferential occupation of M4 by Li and of M2 by Al. M1 and M3 are not statistically occupied by Mg and Fe 2+ . The coordination of M4 is highly irregular with five next oxygens and two longer M4 – O-distances. The A-site is found to be empty.

The structural relationships of high-silica zeolites, an important set of catalysts, are analysed in terms of component sheets which may be used to describe fully their structures. The frameworks of these high-silica zeolites are shown to constitute a sub-set of a much larger group of related frameworks, many of them unknown framework types. The characteristics of a special and unique class of frameworks within this group are also identified.

The symmetry properties of the Bonnet-transformation, the isometric bending of minimal surfaces, are elucidated and the consequences for periodic minimal surfaces are analyzed.

The title compound, (C 12 H 14 NO 3 F), N- p -fluorobenzoyl- l -valine, crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with unit cell parameters a = 10.743(1), b = 11.534(1), c = 20.013(5) Å, Z = 8; D x = 1.281 Mg m −3 . The structure was solved by direct-methods and refined by a full-matrix least-squares procedure on 2757 reflections to final R = 0.045. The two molecules comprising the crystallographic asymmetric unit differ from each other as a result of a rotation about the C(2) – C(3) bond. All potential hydrogen bonding sites on each molecule participate in a complicated, three-dimensional hydrogen bonding network which is described in detail.

We report the thermal decay of extremely long-living metastable states in single crystals of Na 2 [Fe(CN) 5 NO] · 2H 2 O using differential scanning calorimetry. They are generated by laser light in the wavelength range of 350 nm – 580 nm, and their decay was measured in the temperature range of 106 K – 300 K. These states are bulk states which can be generated in molecules with the chemical formula X n [ML 5 NO] · yH 2 O (M = Fe, Ru; L = CN, Cl; X = H, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, NH 4 , Tl, Pb, ZrO, (CH 3 ) 4 N, C(NH 2 ) 3 , (CH 3 ) 3 NCH 2 COO, CH 3 NH 3 . All metastable states decay thermally according to an exponential law. We could not observe any emission of radiation in the energy range of 5 eV – 0.3 eV during the thermal decay. We have evaluated the activation energies E A and frequency factors Z assuming the validity of the Arrhenius law and a first order reaction for three different metastable states ( E A1 = 0.70 eV; E A2 = 0.67 eV; E A3 = 0.50 eV; Z 1 = 5 × 10 15 s −1 ; Z 2 = 5 × 10 15 s −1 ; Z 3 = 8 × 10 14 s −1 ). They all can be completely annihilated with red light. A strong temperature dependence with respect to the generation of the metastable states was observed. The energetic position of these states has been estimated by comparison with Mössbauer data and using absorption spectroscopy.