Volume 211, Issue 3

The atomic structure of nanocrystalline particles formed by vapor deposition and subsequent annealing of amorphous thin films of germanium was studied by high resolution electron microscopy (HREM). The HREM images revealed a strongly varied multiply twinned structure. In some regions of adjacent twins contrast features were detected which were caused by an overlapping of twin lamellae. It will be shown by HREM contrast simulations that these interface types can be described by Σ = 3 n boundaries. The influence of lattice relaxations is taken into consideration by molecular dynamics simulations of the structure models.

A new, not yet described double salt K 2 Mn 3 (SO 4 ) 4 · 5H 2 O has been found. Single crystals were prepared using the diffusion-reaction method. It crystallizes in the P 2 1 / a space group with parameters a = 9.969(2) Å, b = 9.750(2) Å, c = 19.168(4) Å, β = 103.96° and Z = 4. The new double salt has been characterized thermogravimetrically, by IR spectra and by X-ray studies. Data for the dielectric constant of K 2 Mn 3 (SO 4 ) 4 · 5H 2 O as function of the temperature have been obtained.

X-ray single crystal structure determinations of sodalite (Na 8 [Al 6 Si 6 O 24 ]Cl 2 , cubic, P [unk]3 n ) were performed under high hydrostatic pressure in diamond anvil cells. Natural (from Bancroft/Canada) and synthetic specimens were investigated. The continuous decrease of the lattice constant with increasing pressure indicates that there are no first order phase transitions in the pressure range investigated. However, the comparison of the results with data obtained from previous experiments and on related structures of tugtupite and helvite, reveals a possible change in the compression mechanism or a phase transition at about 3 GPa. The compression mechanism operates on the intertetrahedral bonding parameters of the alumino-silicate framework structure. The volume reduction is mainly achieved by the deformation of bonding angles between the different TO 4 -tetrahedra. As a result, the size of the β -cages and consequently the size of the [Na 4 Cl] 3+ -clusters decreases. A pressure induced amorphization of the crystal structure was detected at 7.3 GPa. Experiments on the synthetic samples were done to prove this low value of pressure induced amorphization. On lowering the pressure, recrystallization from the amorphous phase occured at 5.8 GPa.

Cadmium perrhenate diureate crystallizes in the monoclinic space group P 2 1 / c with a = 15.185(3) Å, b = 10.257(2) Å, c = 7.561(5) Å, β = 93.69(2)°, Z = 4 and d calc = 3.658g · cm −3 . The hydrated cadmium perrhenate is triclinic with space group P [unk], a = 7.828(1) Å, b = 8.631(1) Å, c = 13.863(1) Å, α = 73.34(1)°, β = 89.39(1)°, γ = 70.42(1)°, Z = 4 and d calc = 5.119 g · cm −3 . The two compounds are built up of topologically equal but differently oriented and interlinked chains of the type [unk][MT 2 ] φ 2 , M = Cd, T = ReO 4 , φ = Urea and H 2 O respectively. In Cd(ReO 4 ) 2 · 2 Urea they are parallel and linked by H-bonds only while in Cd(ReO 4 ) 2 · 2H 2 O the chains lie in alternating layers with crossed orientation. Both bond valence calculations and low-range Raman spectroscopic measurements and estimate pointed out to a stronger Cd–O Urea in comparison to Cd–O H 2 O bonding.

The crystal structure of Be(IO 3 ) 2 · 4H 2 O has been determined by both neutron and X-ray single-crystal studies ( Pccn , Z = 4, a = 1581.0(6) pm, b = 650.66(10) pm and c = 877.5(2) pm, R = 4.20% and 2.50%) on the basis of 402 and 1063 reflections, respectively, and synchrotron X-ray powder diffraction. The layered structure is built up of tetrahedral Be(H 2 O) 4 2+ units linked to adjacent iodate ions by hydrogen bonds. The shortest interionic I…I and I…O distances are with 360.1 pm and 276.8 pm unusually small, the intraionic bond lengths resemble those of other iodate hydrates. The four crystallographically different hydrogen bonds (r H…o : 159.6 pm, 166.0 pm, 167.0 pm and 178.4 pm), which are the strongest bonds known so far of salt hydrates, as also established by the wavenumbers of the uncoupled OD stretching modes, are discussed in connection with the bond valences of the intramolecular OH bonds and the great synergetic effect of Be 2+ ions.

Studies on highly substituted porphyrins bearing eight β -substituents and at least one bulky meso-substitutent have shown that peripheral steric strain leads to considerable macrocycle distortion. While this is well established for porphyrins with dodecasubstitution; the situation is less clear for nonasubstituted porphyrins with meso-substituents such as methyl, aryl or ester groups. In order to further study this situation we have investigated the conformation of nonasubstituted porphyrins with small meso-substitutents by determination of the crystal structures of: 2,3,7,8,12,13,17,18-octaethyl-5-( N -succinimidyl)porphyrin, 1 ; 2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-5-methoxymethylporphyrin, 2 ; Pyridine(2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-5-methoxymethylporphyrinato)zinc(II), 3 ; methanol(5-acetoxy-2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-porphyrinato)-zinc(II) methanol solvate, 4 ; and (2,3,7,8,12,13,17,18-octaethyl-5-methylporphyrinato)zinc(II), 5 . The compounds show only small deviations from planarity which might be due to packing effects, however, all compounds show some degree of rhomboic elongation of the porphyrin core.[unk]