Volume 213, Issue 11

Large single crystals of optical quality of nickel zirconium bis (nitrilotriacetate) · 8.5 hydrate (space group C 222 1 ) have been grown from aqueous solutions. Complete elastic, thermoelastic and piezoelastic tensors were determined by the aid of ultrasonic methods. In addition, the indices of refraction, the tensor of thermal expansion, dielectric and piezoelectric constants have been studied. Most physical properties investigated show a strong anisotropy. E.g. the relative dielectric constants ∈ 33 and ∈ 11 have values of 335 and 7, respectively. The static piezoelectric constant d 312 surmounts 750 pC/N (by more than a factor of 300 larger than d 111 of α -quartz), whereas d 123 remains as low as 4 pC/N. Anomalous features are the sharp bend of the temperature dependence of ∈ 33 at about 287 K, and, above 280 K the increasing attenuation of transversal ultrasonic waves propagating along [100] with displacement vector parallel to [010] and vice versa. These waves are related to the elastic constant c 66 . The anomalies and the large values of ∈ 33 and d 312 hint at a higherorder ferroelectric transition.

Expressions for the calculation of multiple diffraction patterns for perfect crystals spheres are given in the kinematical approach. Two experimental ψ -scans of the ‘almost forbidden’ 222 reflection of silicon, measured with Ag K α -radiation and with synchrotron radiation at λ = 0.5612 Å, are compared with simulations performed with the program UMWEG-97. It is shown that multiple diffraction patterns of perfect spherical crystal samples can be satisfactorily predicted on absolute scale.

In contrast to earlier structure determinations of SnGa 6 Te 10 and PbGa 6 Te 10 (space group R 32), which showed disordered distributions of Sn and Pb, it could be shown for SnGa 6 Te 10 , PbGa 6 Te 10 and the new SnAl 6 Te 10 , that weak superstructure reflections can be observed in well crystallized samples, which indicate an ordering of Sn(Pb) in all three phases. The black, air stable solids (exept the Al-compound, which is air-sensitive) crystallize trigonally in one of the two enantiomorphic space groups P 3 1 21 and P 3 2 21. Symmetry considerations based on group-subgroup relations show the relationship between β -manganese and the trigonal structures of the title compounds, which are actually nonmetallic, filled β -manganese phases. Their structures consist of a sublattice of Te atoms, closely related to the topology of the β -manganese structure, in which two of four distorted octahedral (“metaprismatic”) holes per pseudocubic unit cell are occupied by Sn(Pb). Furthermore 12 of 100 distorted tetrahedral holes are occupied by Al(Ga) atoms. It can be shown, that only the ordered Sn (Pb) distribution breaks the rhombohedral symmetry of R 32 and requires P 3 1 21/ P 3 2 21. The complex three-dimensional connection pattern of tetrahedra and metaprisms is discussed with respect to the crystal chemical functionality of distinct atoms and the aid of electrostatic lattice energy calculations based on the MAPLE formalism. Finally some comments concerning the probably isotypical structures of CaAl 6 Te 10 , CaGa 6 Te 10 and PbIn 6 Te 10 are given.

At increasing temperature sulfate groups in LiNaSO 4 undergo rotational disorder which lead to an enhanced mobility of the cationic species. This disorder results in a phase transition above which the material is a superionic conductor. In order to understand the nature of the phase transition we have carried out extensive X-ray and calorimetric studies of LiNaSO 4 . This includes the first reported single crystal X-ray investigation on the high temperature phase. The α – β phase transition in LiNaSO 4 is strongly first order ( T tr = 788 K) with a volume change of 6%. However, the α and β -form bear a close structural relationship. Precursor effects indicate the approaching phase transition. We found a strongly anisotropic thermal expansion in the low temperature phase. The λ -like increase of specific heat suggests the onset of the SO 4 -rotation well below T tr . Short range order in the high temperature phase which considerably affects the heat capacity and the volume as well as indications for a further phase transition are discussed within the scope of Landau-theory. Finally, we introduce a transition-model combining the features of a continuous part and a discontinuous part of the phase transition.

X-ray single-crystal structure analyses of green and brown pyromorphites, Pb 5 (PO 4 ) 3 Cl, from Kamioka Mine and Mikura Mine both in Japan, respectively, were performed at room temperature. They are hexagonal, P 6 3 / m , and the cell dimensions are 10.022(3) Å and 9.993(2) Å for a axis, and 7.348(9) Å and 7.334(6) Å for c axis for green and brown ones, respectively. The structures were refined to R 's of 0.031 for green and 0.029 for brown ones. No significant difference was observed between their structures. In both of the pyromorphites, the site occupancies of Pb atoms which have two crystallographically independent sites, M(1) and M(2), are slightly larger at M(2) than at M(1), and those of impurities (minor cations) are slightly larger at M(1) than at M(2). The thermal ellipsoids of the Cl atoms in the two pyromorphites were nearly isotropic. In the chlorapatite group, M 5 (PO 4 ) 3 Cl, the amplitude along [001] of the thermal ellipsoid of Cl atom becomes quantitatively large with decreasing the value of the ionic radius of M atom, r M 2+ .

Cs 2 ZnI 4 belongs to the family of A 2 BX 4 compounds which at room temperature have a structure isomorphous to β -K 2 SO 4 . At low temperatures it is known to undergo a sequence of phase transitions. The room temperature structure crystallizes in space group Pnam with lattice parameters a = 10.812(11) Å, b = 14.464(5) Å, c = 8.306(2) Å. The structure was refined to a final R ( F ) value of 5.68% for 1104 reflections. As β -K 2 SO 4 the structure is pseudohexagonal. The [ZnI 4 ] 2− tetrahedra are only slightly distorted. Csl + ions have nine nearest I − neighbours, Cs2 + have 11 nearest neighbours. Structures of type A 2 BX 4 ( β -K 2 SO 4 ) are closely related to compounds of type A 3 BX 5 (A = Cs, NH 4 + ; B = Co, Zn, Hg; X = Cl, Br, I) yet phase transitions have only been observed in the first. A detailed comparison of the two structure types shows that strong “underbonding” of one of the A cations, short X–X distances and the size of the cavities in which the A ions are incorporated are parameters closely connected to the occurrence of phase transitions at low temperatures.

The crystal structure of β -sodium acetate, NaC 2 H 3 O 2 , has been determined from X-ray powder diffraction data. Grid search and Rietveld refinement have been used to determine the structure. The crystal symmetry is orthorhombic (space group Pmn 2 1 , Z = 2) and the unit cell parameters are a = 3.4517(5) Å, b = 9.9123(11) Å and c = 5.1864(6) Å. Soft constraints have been applied to the molecule. The final R F value obtained was 7.5%.

The molecular and crystal structures of two terminally blocked diastereomeric -Pro-Ala-(Aib) 4 - hexapeptide sequences, p BrBz-L-Pro-D-Ala-(Aib) 4 -O t Bu ( 1 ) and p BrBz-D-Pro-D-Ala-(Aib) 4 -O t Bu dihydrate ( 2 ), have been determined by X-ray diffraction. The two compounds are characterized by the following parameters: ( 1 ) orthorhombic, P 2 1 2 1 2 1 , a = 15.827(2) Å, b = 22.625(2) Å, c = 11.336(2) Å, and Z = 4; ( 2 ) triclinic, P 1, a = 10.225(2) Å, b = 12.474(2) Å, c = 8.827(1) Å, α = 104.2(1)°, β = 92.8(1)°, γ = 85.0(1)°, and Z = 1. The structures were solved by direct methods. The least-squares refinements led to R values of 0.057 and 0.079 for ( 1 ) and ( 2 ), respectively. The heterochiral L-Pro-D-Ala- sequence of hexapeptide ( 1 ) is folded in a type-II β -bend conformation, which is followed by a left-handed 3 10 -helix spanning the sequence -D-Ala-(Aib) 3 -. Conversely, the homochiral -D-Pro-D-Ala- sequence of hexapeptide ( 2 ) adopts a distorted type-II′ β -bend conformation, which induces a right-handed 3 10 -helix in the following -D-Ala-(Aib) 3 - sequence. Interestingly, in compound ( 2 ) the D-Ala residue is forced to take a φ torsion angle typical of an L-amino acid.

The crystal and molecular structures of four Me 3 Sn(O 2 CCH 3− x Cl x ), x = 0 – 3, compounds have been determined at 200 K. The colorless crystals of [Me 3 Sn(O 2 CCH 3 )] are orthorhombic, space group Pnma with unit cell dimensions a = 10.569(4) Å, b = 7.876(9) Å, c = 9.719(9) Å, V = 809(1) Å 3 , Z = 4 and D x = 1.829 Mg m −3 . The colorless crystals of [Me 3 Sn · (O 2 CCH 2 Cl)] are monoclinic, space group P 2 1 / c with unit cell dimensions a = 12.564(6) Å, b = 10.093(5) Å, c = 14.44(1) Å, β = 98.62(5)°, V = 1810(1) Å 3 , Z = 8 and D x = 1.888 Mg m −3 . Crystals of colourless [Me 3 Sn · (O 2 CCHCl 2 )] are monoclinic, space group P 2 1 / n with unit cell dimensions a = 10.013(5) Å, b = 16.60(1) Å, c = 12.467(6) Å, β = 103.71(4)°, V = 2012(1) Å 3 , Z = 8 and D x = 1.925 Mg m −3 . The colorless crystals of [Me 3 Sn(O 2 CCl 3 )] are monoclinic, space group P 2 1 / n with unit cell dimensions a = 9.124(4) Å, b = 9.941(6) Å, c = 12.119(5) Å, β = 102.22(4)°, V = 1074.3(8) Å 3 , Z = 4 and D x = 2.016 Mg m −3 . The structures were solved by direct methods and each refined by a full-matrix least-squares procedure to final R = 0.034 using 876 reflections for [Me 3 Sn(O 2 CCH 3 )]; to R = 0.041 using 2556 reflections for [Me 3 Sn(O 2 CCH 2 Cl)]; to R = 0.045 using 3301 reflections for [Me 3 Sn(O 2 CCHCl 2 )]; and to final R = 0.038 reflections for [Me 3 Sn(O 2 CCl 3 )]. Each of the four structures adopts a similar polymeric motif owing to the presence of bidentate bridging carboxylate ligands. This arrangement leads to the presence of trans -R 3 SnO 2 tin atom geometries. There is no apparent correlation between the pK a values of the carboxylate ligands and the derived interatomic parameters, suggesting that crystal packing effects may exert an influence on these parameters. The solution structures of these compounds are shown by spectroscopy (infrared, 1 H NMR) to be monomeric with tetrahedral tin atom geometries.

(Phenyldichlorophosphino)chlorogold(I), (Cl 2 PPh)AuCl 1 crystallizes with two independent but closely similar molecules. The coordination at gold is linear, with Au–P 2.206(2) Å, 2.204(2) Å and Au–Cl 2.273(2) Å, 2.271 (2) Å. Molecules are linked into chains by aurophilic contacts of 3.382(1) Å, 3.419(1) Å. In phenyltrichlorophosphonium tetrachloroaurate, [PhPCl 3 ] + [AuCl 4 ] − 2 , the cation displays crystallographic m symmetry and the two independent anions each 2/ m symmetry. The Au–Cl bond lengths differ appreciably [2.261(2) Å, 2.279(1) Å]. Anions and cations are linked by Cl … Cl contacts. The phenyl groups and one AuCl 4 − cation form stacks.