Band 212, Heft 9

The crystal structure of the orthorhombic ε -Al 4 Cr phase in the Al–Cr system was determined by single crystal X-ray structure analysis: space group Cmcm (No. 63), a = 12.521(1)Å, b = 34.705(2) Å, c = 20.223(1) Å, V = 8787.7(9) Å, Pearson symbol oC 58420.48, Z = 8, M r = 2256, composition Al 56.23 Cr 14.21 , D x = 3.41 g/cm 3 ; F (000) = 8576, λ (Mo K α ) = 0.71069 Å, μ = 4.510 mm −1 , room temperature, R = 0.068 for 2839 reflections, goodness of fit S = 1.084. There are 55 (13Cr + 42 Al) independent atoms in the unit cell, in which 12 Cr atoms and 28 Al atoms have icosahedral coordination. Interatomic distances cover the ranges of 2.570 Å ∼ 2.646 Å, 2.421 Å ∼ 2.978 Å, and 2.480 Å ∼ 2.983 Å, for Cr–Cr, Cr–Al and Al–Al atomic pairs, respectively. The crystalline phase appears obviously as a layered structure perpendicular to the a -axis. A typical aggregation of the icosahedral clusters in the structure of the ε -Al 4 Cr phase has been pointed out.

A simple method is described to suppress the subsidiary maxima occurring in computer simulations of diffraction intensities due to finite sizes of the simulated crystals. This is achieved by multiplying the scattering density of the model crystal by a suitably designed weighting function.

In this series of papers, two types of p 2 gg -4 c l packing of identical ellipses, called p 2 gg -4 c l(a) and p 2 gg -4 c l(b) each, where four ellipses are included in the rectangular unit cell and where every ellipse has six contacting neighbours, are discussed. It is shown, in this first part, that the density of the p 2 gg -4 c 1(a) packing of ellipses does not exceed the maximum density ϱ = π /[unk] through numerical computations and series expansions. The method of computing the density for every parameter values of aspect ratio and tilt angle is given.

A method for the crystal structure refinement of composite crystals with multiple domains of different symmetry is proposed and explained. For this a formula for the integral intensity of domain structures is given and a structure factor formula is derived. The method is applied to the disordered structure of the composite crystal (LaS) 1.18 VS 2 . The crystal consists of two subsystems each of which must be characterized introducing four types of domains. A further domain was introduced simulating all the diffraction intensities of other disordered layer sequences which contribute only to (O kl 0) reflections. All reflections of the LaS subsystem can be indexed assuming a lattice with a I = 5.705(2) Å, b I = 5.830(2) Å, c I = 66.89(1) Å and α I = β I = γ I = 90° and for the VS 2 subsystem with a II = 3.366(1) Å, b II = 5.830(1) Å, c II = 44.59(1) Å and α II = β II = γ II = 90°. The refinement converged at a final R ( F )-value of 0.153 ( R W ( F ) = 0.171) for 1112 reflections. Refinement of modulation amplitudes did not lead to reasonable bond distances and was therefore discarded. The results of the refinement of a non-modulated model are discussed.

The structure of tetrakis- N , N -dibutylamino-ethanolatoisocyanatocopper(II) was determined from single crystal X-ray data at 200 K, since a phase transition at 235 K was proposed from an unsteadiness in the temperature dependence of the magnetic susceptibility data as well as from some disagreement concerning a very reliable magnetostructural correlation. The structure analysis confirmed the phase transition magnetically observed. Below 235 K, eight tetrameric molecules are arranged in a triclinic unit cell with the dimensions a = 24.052(4) Å, b = 13.014(2) Å, c = 39.249(4) Å, α = 72.26(1)°, β = 104.16(1)°, γ = 107.30(1)°, space group B [unk], which is of fourfold volume as compared to the structure at 295 K ( a = 2 a ′, c = 2 c ′). The two crystallographically different molecules show distinct differences mainly concerning the central Cu 4 O 4 -heterocubane moieties. For the first time, an arrangement is observed in which, according to the Mergehenn nomenclature, type-I and transition type Cu 4 O 4 -molecules coexist.

From a solution that contained P 4 S 3 , PPh 3 , and CoCl 2 · 2H 2 O in a mixture of tetrahydrofurane, ethanol and toluene, the new modification γ -P 4 S 3 was crystallized. It is isotypic with β -As 4 S 3 , space group Pbnm , a = 646.2(2) pm, b = 1092.1(3) pm, c = 984.3(2) pm, Z = 4. The four different structure types, α -P 4 S 3 , α -As 4 S 3 , γ -P 4 S 3 , and α -P 4 Se 3 , can be derived from a hexagonal closest-packing of molecules with four varieties of distortion; the symmetry relations are discussed.

The crystal structure of BaMo 3 O 10 has been determined from X-ray and neutron powder diffraction data using no prior structural information. Direct methods and combined X-ray and neutron Rietveld refinements were used to solve the structure. There are two Ba, six Mo and twenty O atoms in the asymmetric unit. The crystal symmetry is monoclinic (space group P 2 1 ; Z = 4), and the unit cell parameters are a = 14.695(2) Å, b = 7.5704(7) Å, c = 6.9618(6) Å, and β = 100.381(8)°. In a combined Rietveld refinement with 124 variables, the R F -values 0.034 and 0.046 were obtained for neutron time-of-flight and X-ray data respectively, although small oscillations in some parameters could not be avoided in the final refinement cycles. The structure is built of layers of [Mo 3 O 10 2− ] linked to each other with barium ions. The Mo–O framework contains distorted MoO 6 octahedra interlinked by corner- and edge-sharing.

The crystal structure of deuterated betaine arsenate, (CH 3 ) 3 NCH 2 COO · D 3 AS 3 O 4 , has been re-investigated from X-ray diffraction data collected with synchrotron radiation at three different wavelengths (0.98 Å, 1.05 Å, 1.15 Å) in the vicinity of the As K -absorption edge (1.04497 Å). Each data set was refined individually, but a joint refinement of all data simultaneously resulted in substantially decreased standard deviations of atomic parameters and derived quantities. The results of a previous structure analysis by Schildkamp, Schäfer and Spilker [Z. Kristallogr. 168 (1984) 187–195] are essentially confirmed. The both paraelectric and ferroelastic room-temperature phase of betaine arsenate crystallizes in space group P 2 1 / n [ Z = 4, a = 9.556(4) Å, b = 12.897(6) Å, c = 8.128(3) Å, β = 91.23(2)°, V = 1001.5(7) Å 3 ]. Its crystal structure consists of AsO 4 3− -tetrahedra which are linked by disordered hydrogen bonds into chains along the c -axis. The betaine zwitterions are attached to these chains in a herring-bone fashion via ordered dimeric hydrogen bonds. These two different hydrogen-bonding schemes are reflected in the AsO 4 3− geometry: there are two shorter and two longer As–O bonds. The shorter distances [1.650(2) Å, 1.653(2) Å] to the oxygens involved in the arsenate chains are typical for double bonded As=O; the longer distances [1.675(2) Å, 1.691(2) Å] correspond with As–OH single bonds.

A crystal of the title compound [{Li(OEt 2 )} 2 Ni(CH 2 NMe 2 ) 4 ] ( 1 ), grown from diethyl ether, was investigated by single-crystal X-ray analysis. 1 crystallizes in the monoclinic space group P 2 1 / n with a = 9.100(2) Å, b = 11.721(2) Å, c = 13.773(3) Å, β = 93.47(3)°, and Z = 2. The crystal structure was solved by the heavy atom method ( wR 2 = 0.1290 for 3532 reflections; R 1 = 0.0453 for 2458 observed reflections). The molecular structure of the very air sensitive compound was found to be centrosymmetric with a square planar arrangement of the four methylene carbon atoms and nickel. The Ni–C bond lengths amount to 2.028(2) Å and 2.037(2) Å, respectively. The lone pair of nitrogen is strongly involved in the lithium coordination (Li–N bond lengths: 1.954(5) Å, 1.995(5) Å). This fact and the absence of β -hydrogen atoms seem to be responsible for an unusual thermal stability of complex 1 ( T dec. = 363–388 K).

The crystal and molecular structures of 1 , [Cu(en) 2 (mtpo) 2 ], C 16 H 26 CuN 12 O 2 , and 2 , [Cu(dach) 2 (OH 2 ) 2 ](mpto) 2 , C 24 H 42 CuN 12 O 4 , (where Hmpto is 4,7-dihydro-5-methyl-7-oxo-[1,2,4]triazolo-[1,5-a]-pyrimidine, en is 1,2-ethylenediamine and dach is cis -1,2-diaminocyclohexane) have been determined at room temperature. The blue crystals of 1 are triclinic, space group P [unk] with unit cell dimensions a = 8.507(2) Å, b = 9.544(1) Å, c = 6.976(1) Å, α = 110.16(1)°, β = 103.65(2)°, γ = 81.24(1)°, Z = 1 and D x = 1.554 Mg m −3 and the purple crystals of 2 are monoclinic, space group C 2/ c with unit cell dimensions a = 16.531(5) Å, b = 12.691(7) Å, c = 15.153(6) Å, β = 112.64(2)°, Z = 4 and D x = 1.418 Mg m −3 . The structures were solved by direct methods and refined by a full-matrix least-squares procedure on F to final R = 0.034 using 1994 reflections for 1 and R = 0.038 using 1849 reflections for 2 . In the structure of centrosymmetric 1 , two mpto anions form Cu…N(3) distances of 2.629(3) Å above and below an essentially square planar CuN 4 geometry. By contrast, in centrosymmetric 2 , the weak Cu…mpto contacts are replaced by weak Cu…OH 2 contacts such that the anions do not associate with the copper center. The study demonstrates two new coordination modes for mtpo. The respective structures are stabilised by extensive intra- and intermolecular hydrogen bonding contacts.