Band 210, Heft 12

Single crystals of monoclinic β -succinic acid, (CH 2 ) 2 (COOH) 2 , possess an extreme anisotropy of the longitudinal elastic stiffness. The maximum of 12.56 × 10 10 Nm −2 is observed along the hydrogen-bonded infinite chains, the minimum of 0.99 × 10 10 Nm −2 near a perpendicular direction within the cleavage plane (010). This anisotropy is the largest hitherto found in ionic or molecular crystals. The tensor of thermal expansion exhibits a considerable anisotropy, too, in accordance with the Grueneisen rule.

Coordination sequences for five 3-dimensional, ten 4-dimensional and eleven higher-dimensional lattices have been determined and all but one can be expressed as simple polynomials. Some regularities in these polynomials are observed. The correlation between topological and geometric density is demonstrated for 4-dimensional lattices. It is conjectured that hexagonal closest packing is topologically the densest packing in three dimensions.

The DIRDIF program system for solving crystal structures using Patterson procedures and direct methods applied to difference-structure factors, uses a variety of X-ray intensity scaling procedures based on the formulae of Wilson (1942), and when part of the structure is known, Parthasarathy (1966), and Gould, Van den Hark and Beurskens (1975). Applications of these procedures to various heavy atom structures are discussed. A new scaling procedure is presented which is based on the relative frequency of calculated partial structure factors being larger than the observed structure factors on an absolute scale. This procedure is especially useful for structures with superstructure effects.

The crystal structure of In 7 Br 9 has been determined on the basis of single crystal data. In 7 Br 9 is a mixed valence compound according to the crystal-chemical formulation (In + ) 6 In 3+ (Br − ) 9 , and it crystallizes isotypically with In 7 Cl 9 in space group Pa [unk] with a = 1268.10(3) pm. While trivalent indium is octahedrally coordinated by bromine with a bond length of 268 pm, univalent indium resides in a slightly distorted bisdisphenoid, the bond lengths ranging from 307 pm to 377 pm.

Crystals of EuZnGe were prepared by a reaction of the elemental components in tantalum tubes. EuZnGe crystallizes in the hexagonal space group P 6 3 / mmc with the lattice constants a = 437.2(1) pm, c = 860.4(2) pm and V = 0.1424(1) nm 3 . The structure belongs to the ZrBeSi-type, a ternary ordered version of the AlB 2 -type. It was refined from single-crystal diffractometer data to wR 2 = 0.0297 for 146 F 2 values and eight variables. The crystal chemistry of EuZnGe is discussed in comparison with the structure of binary EuGe 2 . Susceptibility measurements show Curie-Weiss behavior above 40 K with μ exp = 7.8(1) μ B /Eu, indicating Eu 2+ . Below 0.01 T EuZnGe shows two magnetic transitions at 12.2(5) K and 9.5(5) K, respectively. Magnetization measurements at 2 K indicate metamagnetism with a critical field of 0.60(5) T. The saturation magnetic moment per Eu atom at 2 K is 5.8(1) μ B .

C 10 H 16 NH 3 (SeO 3 ) 2 , M r = 407.18, orthorhombic, Pbca (No. 61), a = 9.840(1) Å, b = 24.416(5) Å, c = 12.2489(8) Å, V = 2943(1) Å 3 , Z = 8, D x = 1.838 gcm −3 , X-ray diffraction, λ = 0.7093 Å, μ = 49.927 mm −1 , | F (000)| = 1616, T = 22(2)°C, R ( F ) = 1.96%, wR ( F ) = 2.36%, S = 0.80 for 1127 reflections with I > 3 σI out of 2286 unique data and 16044 measured reflections. Synthesis, thermal behavior and crystal structure at room temperature are reported. Transitions at −78.6 °C, −25.8 °C and 1.7 °C are observed on DSC measurements. The structure contains chains of HSeO 3 − ions and H 2 SeO 3 molecules connected by a network of hydrogen bonds, the organic cations acting as spacers between the chains.

The crystal structure of squaric acid [3,4-dihydroxy-3-cyclobutene-1,2-dione, H 2 C 4 O 4 , M = 114.1] has been determined from neutron diffraction data at 15 K, T c − 21 K, T c − 13 K and T c + 5 K below and above the phase transition at 374 K. The space group of the material is monoclinic P 2 1 / m from 15 K and up to T c and tetragonal I 4/ m above. After corrections for absorption and thermal diffuse scattering, least-squares refinements were carried out with 69 variable parameters in the model below T c and 25 above T c . The analysis of difference vibrational parameters along the C–O internuclear direction strongly suggest that the high-temperature structure has a disordered C 4 O 4 unit. In agreement with previous findings, the protons are distributed on two principal positions 0.53 Å apart along the O … O hydrogen bond above T c . In the low-temperature phase, an increasing amount of disorder with increasing temperature is found, particularly in the protonic positions. However, the protons in the two different hydrogen bonds show distinctly different behavior, and hence immediately below T c different degrees of order are found along the x - and z -directions. These structural findings are discussed in the light of the 1-D correlations observed in the material.

The title compound C 11 H 19 N 2 · C 6 H 2 N 3 O 7 crystallizes in the monoclinic space group P 2 1 / n with a = 778.9(3) pm, b = 1349.4(3) pm, c = 1950.7(3) pm, β = 101.10(2)°, Z = 4 and D x = 1.345g · cm −3 . R = 0.076 for 2458 unique reflections with I > 2 σ ( I ) at 294 K. The π -system of the dye cation is polarized by intermolecular interactions resulting in a bond length alternation. Stacks of dye molecules, which corresponds to J -aggregate structures could not be found.

There is essential stereochemical difference between the molecules of the monoclinic and triclinic polymorph of tris(1,3-diphenylpropane-1,3-dionato)-cobalt(III), C 45 H 33 CoO 6 . The monoclinic form crystallizes with the space group P 2 1 / c . The crystal data are: a = 17.257(4) Å, b = 9.951(2) Å, c = 20.786(5) Å, β = 92.73(2)°, V = 3565(1) Å 3 , Z = 4, λ (Mo K α ) = 0.7107 Å, μ Mo K α ) = 0.53 mm −1 , D x = 1.358 g cm −3 . The structure was solved by the heavy-atom method. The structure was refined by full-matrix least-squares technique with terminal phenyl rings taken as ideal hexagons to R = 0.050 for 3652 unique reflections. Only very weak intermolecular attraction forces keep the individual molecules together and the contacts between neighboring molecules correspond to the normal van der Waals interactions. The cobalt environment is a distorted octahedron with Co–O bond lengths ranging from 1.872(3) Å to 1.897(3) Å. The rotation of the terminal phenyl rings in relation to the chelate plane depends on the intramolecular steric hindrances and the tendency of the ligand to achieve planarity as a delocalized π -electron system.