Band 212, Heft 3

Brightness decay in electroluminescent (EL) phosphors is a diffusion-related phenomenon. Copper is shown to be the most easily diffusing species, although all diffusion is strongly influenced by the presence of sulfur vacancies or, to a lesser extent, halogen atoms substituting on sulfur sites. Diffusion is facile in the Cu 2− x S which decorates the defects in EL phosphors, and bond valence sums harmonize well with the existence of a plethora of copper sulfide binary phases. Strategies for improving the useable lifetimes of EL phosphors are examined.

Single crystals of optical quality and dimensions up to 60 mm of sulfanilates of Li, Na, K, Rb, Cs, Tl, NH 4 , CH 3 NH 3 and C(NH 2 ) 3 have been grown from aqueous solutions by controlled lowering of temperature and slow evaporation between 315 K and 290 K. All species except the sulfanilates of methylammonium and guanidinium form hydrated phases within that temperature range. Thallium sulfanilate crystallizes simultaneously in two phases, a metastable monohydrate and a stable hemihydrate. The sulfanilates of Na, K, Rb and Tl (monohydrate) possess orthorhombic symmetry, the others monoclinic symmetry. Except the cesium salt they all exhibit an inversion center. The elastic constants C ij and their derivatives T ij = d log C ij /d T , T temperature, have been determined from ultrasonic resonance frequencies of thick plates and their variation with temperature, respectively. In addition, the tensor of thermal expansion has been measured. The anisotropy of the longitudinal elastic stiffness shows a close relation to the arrangement of the sulfanilic anions. The contribution of the hydrogen bonds to the elastic stiffness is clearly recognizable. The structurally inhomogeneous group obeys to a large extent the rules governing the mean elastic and thermoelastic behaviour of ionic crystals.

Six selected area electron diffraction (SAED) patterns and two HREM images from Pb 5 MoO 8 single crystals are presented and used to solve their structure. The unit cell parameters of these crystals confirm the known powder diffraction data.

Parascholzite (SG: I 2/ c , a = 17.186(6) Å, b = = 7.413(3) Å, c = 6.663(2) Å, β = 95.39(3)°, Z = 4, ϱ = = 3.12g/cm 3 , ϱ = 3.118g/cm 3 , V = 845(5) Å 3 , R ( F ) = = 3.0%) and the idealized substructure of scholzite, SG: Pbcn , a = 17.149(3) Å, b = 7.421(1) Å, c = 6.667(1) Å, Z = 4, are “building unit structures” with layer compositions of [ZnPO 4 ] − 2 n and [Ca · 2H 2 O] 2+ n . The respective phase of CaZn 2 [PO 4 ] 2 · 2H 2 O originates from both the conformation of the crystal water together with the oxygens of the zinc phosphate and two alternatives of octahedrally coordinated interstices for the Ca 2+ -ions. The prediction of the parascholzite structure, which had been made earlier with the aid of order-disorder considerations (Taxer, 1992), was confirmed experimentally.

Mixed chalcogen rings (Se/S) 6 and (Se/Te) 6 are obtained in CuBrSe 2.36 S 0.64 , CuISe 2.6 S 0.4 , and CuISe 1.93 Te 1.07 . These compounds can be prepared by reaction of mixtures of CuBr/CuI, Se, and S/Te in the corresponding stoichiometric amounts. They crystallise in a structural type isotypic with CuISe 3 , space group R [unk] m (No. 166), Z = 18, a = 13.729(1) Å, c = 13.781(1) Å, V = 2249.3(2) Å 3 (CuBrSe 2.36 S 0.64 ), a = 13.967(1) Å, c = 14.166(1) Å, V = 2393.1(1) Å 3 (CuISe 2.6 S 0.4 ), and a = 14.549(3) Å, c = 14.383(4) Å, V = 2636.6(9) Å 3 (CuISe 1.93 Te 1.07 ). In CuISe 3 up to 50% of selenium can be substituted by tellurium.

A redetermination of the crystal structure of ganomalite, with composition Pb 9 Ca 5.44(1) Mn 0.56(1) Si 9 O 33 , using new single crystal X-ray diffraction data is reported. Hexagonal space group symmetry P [unk], with Z = 1 and unit cell parameters a = 9.8456(3) Å and c = 10.1438(4) Å. The refinement of a structural model based on the Pb 5 Ge 3 O 11 structure, with a partially occupied manganese position, resulted in an R -value of 0.031. The arrangement of the SiO 4 tetrahedra in ganomalite is an intermediate between the nasonite and pyromorphite structure, and the structure can be described as containing “lead tunnels” based on Pb 9 O 21 units extending through the structure.

Topological properties and the Laplacian function of the electron density of 1,2,4-triazole have been determined from X-ray diffraction data collected at 15 K. 1,2,4-Triazole, C 2 H 3 N 3 , orthorhombic, space group Pbca , Z = 8, lattice parameters a = 9.717(4) Å, b = 9.304(4) Å and c = 6.912(4) Å. The results are compared with those derived from ab initio -wavefunctions at the Hartree-Fock and MP2 level of theory. The different C–N bonds are analyzed in terms of bond topological parameters. The result reveals considerable aromaticity which seems to be enhanced by the strong hydrogen bonds.

The crystal structure of the title compound D(H)LAP with chemical formula (D 2 N) 2 CND · (CH 2 ) 3 CH(ND 3 )CO 2 · D 2 PO 4 · D 2 O has been determined by single crystal neutron diffraction. Positional and thermal parameters of atoms were refined by block diagonal matrix least-squares technique. A final R f value of 0.048 was obtained for 1040 observed independent reflections. The crystal structure consists of alternate layers of phosphate groups and ariginine molecules stacked along the a -axis and held together by hydrogen bonds. By deuteration of HLAP, the deuteriums occupy hydrogen positions except those hydrogen atoms bonded to carbon atoms. All the D(H) bond lengths in D(H)LAP are about 10% to 30% longer than those in HLAP And bond angles are obviously different from references [1] and [2].

Crystal structures of the title compounds were determined by single crystal X-ray diffraction. Absolute configuration of the barium salt of (+)-( S )-acid was revealed by means of the Bijvoet's method. Compared to theoretical calculations, the conformations in the solid state are severely influenced by hydrogen bonding and/or coordination to barium ion. In all the crystal structures investigated except the racemic acid, there are two distinct bipyridine rotamers differing in the torsion angle around the biaryl axis and corresponding to syn -clinal and anti -clinal arrangements. The self-assembly patterns of the free (optically active as well as racemic) acids are closely similar: in crystal, their molecules are organized in layers by short intermolecular hydrogen bonds between the hydroxyl and the N -oxide. In contrast, the supramolecular patterns of the corresponding barium salts differ totally from each other. The anions are coordinated to barium through their oxygen atoms by four different modes, from monodentate to η 6 , μ 6 . This, together with the coordination of terminal and bridging water molecules, results in octa-, nona- and decacoordinated barium ions arranged in polymeric chains (in the S -salt) or layers (in the R,S -salt), linked by hydrogen bonds.