Volume 212, Issue 12

A new method is developed for interpreting the difference Patterson function in surface X-ray structure analysis. The difference Patterson function has negative parts which arise from subtracting the integral Patterson function from the true Patterson function. This suggests, that by adding a judiciously chosen function one may utilize the information contained in the positivity constraint for the true Patterson function. We formulate conditions on this function and find a method to construct this function. It is shown that in many cases this function coincides with the integral Patterson function of the so-called “complementary structure”. The proposed new Patterson function obtained by adding the so constructed function to the difference Patterson function is easier to interpret than the conventional difference Patterson function.

Single crystals of the new monophosphate Nb 0.787 W 0.213 OPO 4 both with Nb(V) and W(V), have been isolated. This phase is close to α -NbOPO 4 but crystallizes in a different space group ( P 4/ nmm ) with a = 6.3524(7) Å and c = 4.0916(5) Å. The structure consists of a random stacking of two kinds of layers along c , named α and α ′ built up of [MPO 8 ] ∞ chains running along a . The first kind of layer ( α ) is identical to that observed for α -NbOPO 4 , whereas the second kind ( α ′) corresponds to the enantiomorphous form α ′-NbOPO 4 that has never been observed. It is because such layers are only linked through the apical oxygen atoms of the [MO 6 ] octahedra that their assemblage is made possible, so that this new phase can be considered as a α - α ′ racemic structure.

Single phase samples of the new intermetallic compound Mo 7 Sn 12 Zn 40 are synthesized from the elements at 1023 K. Mo 7 Sn 12 Zn 40 crystallizes cubic ( Fm 3 c ) with a = 25.447 Å. The complex crystal structure is characterized by two different polyhedra of high symmetry, which are built up by two shells. Besides chiral polyhedra MoZn 14 Sn 24 there are nearly undistorted Mackay polyhedra Mo 13 Zn 42 of symmetry I h , which are connected to a 3D net via Zn 6 octahedra. Thereby twelve icosahedra MoZn 10 Sn 2 , which form the homogeneous cubic “bauverband” cP 2[12 i ] condense to a “supericosahedron”. The crystal structure can be regarded as a model structure for the crystallisation of intermetallic phases and shows a remarkable self similarity.

The structure of Sr 4 Fe 6 O 13 is orthorhombic, space group Iba 2, with unit cell dimensions a = 11.278(3) Å, b = 18.953(6) Å, c = 5.546(3) Å, Z = 4. The crystal structure was refined by full-matrix leastsquares to R = 0.010 using 301 reflections measured with an imaging plate using a Weissenberg camera and mono-chromatized synchrotron radiation of wavelength 1.000 Å. The result is essentially the same with the previously reported structure (Yoshiasa, Ueno, Kanamaru, Horiuchi, 1986) but has yielded some details of the structure in which Fe–O bondings are involved. The polyhedral distortions and ionic radii for the five coordinated Fe 3+ ions in the structure have been discussed in comparison with those of related structures.

The X-ray structures of a high temperature α -phase (monoclinic, P 2 1 / c , Z = 24) and a low temperature β -phase (orthorhombic, Pbca , Z = 8) of trichlorophosphazo- N -sulfurylchloride Cl 3 PNSO 2 Cl were determined at 173 K and 150 K, respectively. Both modifications are composed of isolated molecules arranged in layers with no strong intermolecular interactions with numerous Cl … O intermolecular interactions. The molecules in both modifications are fairly eclipsed along the P … S direction, the largest deviation from an ideal position being −17.4(2)° and 22.7(3)°. The bond lengths and angles of all molecules are equal within 4 σ limits with an exception of P–Cl bonds.

The crystal structure of a multiple domain crystal of composition YbV 4 O 8 has been determined and refined as a commensurate composite crystal with two subsystems. Subsystem 1 is formed by the V 2 O 4 atoms, subsystem 2 contains the Yb atoms. All reflections in the diffraction pattern can be indexed using a lattice with a = 9.057(1) Å, b = 21.238(5) Å and c = 5.7560(9) Å yet three different types of domains have to be taken into account to explain the diffraction pattern. Domains I and II correspond to two twin domains of β -YbV 4 O 8 with symmetry A 2 1 / d 11 (≡ P 2 1 / n 11) while domain III with symmetry P 12 1 / n 1 has the structure of α -YbV 4 O 8 . Refinement was carried out in higher dimensional space using the reflections of all domains simultaneously and converged at a final R ( F ) value of 0.050 ( R w ( F ) = 0.038). The results are discussed.

The substructure of natural clinotobermorite Ca 5 [Si 3 O 8 (OH)] 2 · 4 H 2 O \p=n-\ Ca 5 [Si 6 O l7 ] · 5 H 2 O from the Wessels mine, Kalahari manganese field, South Africa, was determined from single-crystal X-ray data. The diffraction pattern (monoclinic: a = 11.19 Å, b = 7.29 Å, c = 22.46 Å, β = 96.97°) is characterised by rather diffuse reflections of the type hkl with h , k = 2 n + 1. The substructure (space group I 2/ m , Z = 1, a /2 = 5.593(6) Å, b /2 = 3.645(4) Å, c = 22.46(3) Å, β = 96.97(2)°) was solved from the sharp Bragg reflections ( hkl , with h , k = 2 n ) and refined on the basis of 1877 unique reflections to R ( F ) = 6.7%. The structure of clinotobermorite is closely related to the one of so called 11 Å tobermorite Ca 5 Si 6 O 16 (OH) 2 · 2 H 2 O (pseudo-orthorhombic, a = 11.17 Å, b = 7.38 Å, c = 22.6 Å). In both minerals layers parallel (001), formed by seven-fold co-ordinated Ca, are flanked on either side by wollastonite-like [Si 3 O 9 ] single chains (ca. 7.3 Å periodicity along b ) creating a sandwich-like assemblage. The short b /2 axis (3.645 Å) and the short a /2 axis (5.593 Å) of the subcell are caused by an overlay of two half-occupied single chains of tetrahedra with one shifted by b /2 against the other. In clinotobermorite the sandwich-like layers are stacked along c yielding an interlayer distance of 4.5 Å with a free aperture of 3.2 Å where additional Ca ions and H 2 O molecules connect the sandwich units. Clinotobermorite with 4–5 H 2 O represents a much denser structure than 11 Å tobermorite with only 2 H 2 O or 14 Å tobermorite with ca. 6 H 2 O (pseudo-orthorhombic, a = 11.17 Å, b = 7.38 Å, c = 27.94 Å). The substructure of clinotobermorite can be interpreted as either composed of ‘Dreiereinfachketten’ leading to the formula Ca 5 [Si 3 O 8 (OH)] 2 · 4 H 2 O, or of ‘Dreierdoppelketten’ leading to the formula Ca 5 [Si 6 O 17 ] · 5 H 2 O, or of a mixture of both variants. The surface structure of clinotobermorite was studied by atomic force microscopy (AFM) where low magnifications reveal a complex layering or twinning parallel (001). High resolutions scans parallel (100) establish enhanced contrast fringes with a periodicity of ca. 10 Å interpreted as the repeat distance of the Ca polyhedral layers parallel to c .

At room temperature, tris(1,1′-dimethyl-4,4′-bipyridinium) bishexachlorobismuthat(3-) dihydrate, [C 12 H 14 N 2 ] 3 [BiCl 6 ] 2 · 2H 2 O, crystallizes in the triclinic space group C i 1 ; P [unk]; (No. 2) with a = 797.0(2) pm, b = 1215.8(2) pm, c = 1303.9(3) pm, α = 88.76(1)°, β = 83.01(1)°, γ = 73.86(1)°, Z = 1, D x = 1.977 g/cm 3 . The cell contains three [C 12 H 14 N 2 ] 2+ cations (methyl viologen), two slightly distorted BiCl 6 octahedra ([unk] Bi–Cl = 269.4(2) pm) and two water molecules.

Preliminary Weissenberg photographs, showed that crystals of the title compound (C 22 H 26 N 2 O 2 ), belonged to the orthorhombic system with systematic absences consistent with the space group P 2 1 2 1 2 1 . The unit-cell dimensions and their standard deviation, obtained at room temperature (293 K) were a = 10.583(6) Å, b = 18.812(2) Å, c = 9.962(1) Å, Z = 4. The unit cell volume ( V ) was 1983(1) Å 3 and the absorption coefficient ( μ ) was 0.075 mm −1 , D c was 1.174 and Dm measured by flotation was 1.18 Mgm −3 ; F (000) = 752, λ (Mo K α ) = 0.7107 Å. The structure was solved by direct methods and refined by full-matrix least squares methods to a final R ( F ) = 0.041 and Rw ( F 2 ) = 0.12. This work unambiguously establishes the overall conformation of the title molecule and the configuration for the new chiral centre C 2 is R . The pyrrolidine ring adopts a perfect envelope 2 E conformation. Crystal cohesion is only governed by van der Waals contacts.

The crystal and molecular structure of l -hypaphorine hydroiodide, C 14 H 19 IN 2 O 2 , has been determined at room temperature. The colorless crystals are tetragonal, space group P 4 1 , with unit cell dimensions a = 7.168(2) Å, c = 30.497(9) Å, Z = 4 and D x = 1.586 Mg m −3 . The structure was solved by direct methods and refined by a full-matrix least-squares procedure on F to final R = 0.029 using 877 reflections. The structure determination shows that the indole ring is almost perpendicular to the roughly planar C γ –C β –C α –N α chain. The lattice is stabilised by I … H hydrogen bonding interactions.

The attempt to synthesize an oligomer of aluminium dichloro- iso -propoxide · iso -propanol led to crystals of two interesting compounds: trialuminium pentachloro-tetra- iso -propoxide · iso -propanol, Al 3 Cl 5 (O- i -Pr) 4 · i -PrOH ( 1 ), and trialuminium hexachloro-oxo- iso -propoxide · 3 iso -propanol, Al 3 Cl 6 O(O- i -Pr) · 3 i -PrOH ( 2 ). Both of them crystallize with the monoclinic space group P 2 1 / n . The lattice parameters of 1 area a = 10.1863(7) Å, b = 28.276(2) Å, c = 18.8681(12) Å, β = 93.512(1)°, Z = 8; the data of 2 are a = 11.300(2) Å, b = 14.920(2) Å, c = 15.816(2) Å, β = 97.14(3)°, Z = 4. In 1 , as well as in 2 , two of the aluminium atoms are tetrahedrally coordinated, while the other displays octahedral coordination. Compound 1 is closely related to Al 3 Cl 5 (O- i -Pr) 4 ( 3 ), which was previously published in 1978 [1].

The crystal structure analysis of two benzoxazole containing molecules is reported: 2-[4- N , N -bis(2-hydroxyethyl)]phenyl-6-nitrobenzoxazole monohydrate ( 1 ) and 2-[4- N -(6-hydroxyhexyl)-/ N -methyl] phenyl-6-nitrobenzoxazole ( 2 ). These compounds are monomer precursors of polymers with nonlinear optical properties of the second order. The crystal structures have been determined at room temperature by direct methods and refined by full-matrix least-squares method. Some differences have been found in the molecular geometry of 1 and 2 as compared to published data on similar benzoxazole containing compounds. These differences are due to the strong electron donor effect of the amino group and indicate enhanced conjugation in the molecules. The pattern of hydrogen bonding in the two compounds is also discussed.

Single crystals of tetragonal (NH 4 ) 2 PF 7 with dimensions of up to 20 × 20 × 15 mm have been grown from aqueous solutions of NH 4 PF 6 after partial decomposition. Two phase transitions of character close to secondorder occur at 231 K and 178 K. Elastic constants and their temperature and pressure derivatives have been evaluated from ultrasonic resonance frequencies of thin plates. The shear stiffness exhibits a positive temperature derivative T 66 which increases as the crystal approaches the transition at 231 K. Below 231 K all elastic modes, in which c 66 is essentially involved, are strongly attenuated. Under the polarizing microscope both transitions are recognizable by the formation of characteristic domain patterns. From DSC runs we found transition enthalpies of 0.08 J g −1 at 231 K and 1.8 J g −1 at 178 K. Slight anomalies are observed also in the thermal expansion curves. The anomalous behaviour of (NH 4 ) 2 PF 7 is comparable to that of K 2 SnCl 6 . Apparently in both species the librational motions of the octahedral anions contribute substantially to the interactions driving the transitions.