Volume 209, Issue 12

A generating routine for an icosahedral quasicrystal, using local rules, is described. The triacontahedral morphology of a larger polyhedral model, the corresponding projections of the atomic positions and their Fourier transforms are illustrated. The existence of an icosahedral surface dividing the structure into two disjoint and interpenetrating parts, is reported.

Correction for absorption in ground single crystals is analyzed for crystal shapes determined by convex hulls. In particular, the case of superellipsoidal morphology is pursued. The results are used to determine the effects of asphericity of a sample on the transmission factor and to computer routine that performs the absorption correction for a given sample.

Neutron powder diffraction data of α -MnMoO 4 (space group C 2/ m ) are presented, which were collected with the diffractometer DN5 at the CEN Grenoble at T = 50 K and between 13 K and 5.5 K. Below T = 15.3 K, α -MnMoO 4 is antiferromagnetically ordered. The translational symmetry of the magnetic structure is described by a propagation vector (1,0, 1/2), i.e. the magnetic unit cell is a , b , 2 c . The magnetic moments corresponding to the two nonequivalent crystallographic sites of the magnetic Mn ions in the unit cell of the crystal structure are aligned in the (0 1 0) plane. Magnetic moments belonging to different sites are canted by an angle of 9°. Within one site they are collinear. The angles between the moment directions and the α -axis are 67° and 58°, respectively.

The structure of two polymorphs of manganese dioxide, λ -MnO 2 and γ -MnO 2 and the spinel oxide LiMn 2 O 4 have been refined by Rietveld analysis of powder neutron diffraction data. λ -MnO 2 , Fd 3 m , a = 8.0639(3) Å, R Bragg = 1.81%, γ -MnO 2 , Pnam , a = 9.3229(11) Å, b = 4.4533(7) Å, c = 2.8482(3) Å, R Bragg = 1.34% and LiMn 2 O 4 , Fd 3 m , a = 8.2468(2) Å, R Bragg = 2.33%.

The preparation and the X-ray single-crystal structure determination of {Mg[CH 3 CON(CH 3 ) 2 ] 6 } · [MgCl 4 ] are described. The crystals (C 24 H 54 Cl 4 Mg 2 N 6 O 6 ) are triclinic, space group P [unk], with a = 10.069(5) Å, b = 10.474(4) Å, c = 18.733(8) Å, α = 85.86(3)°, β = 77.84(4)°, γ = 87.55(4)° and Z = 2. The structure was solved by direct methods and refined using full-matrix least-squares leading to final R = 0.080 and R w = 0.091. The obtained compound shows an ionic structure in which the Mg cation is coordinated by six dimethylaccetamide moieties through the oxygen atoms and the tetrahedral [MgCl 4 ] 2− acts as counteranion.

The new compound La 2 Fe 25 P 12 was prepared by reaction of the elements in a tin flux. Its crystal structure was determined from single-crystal X-ray diffractometer data: Pbam , a = 1475.6(4) pm, b = 1814.9(4) pm, c = 363.6(2) pm, Z = 2, R = 0.037 for 1765 unique structure factors and 120 variable parameters. The compound belongs to a large family of structures with a metal: phosphorus ratio close to 2:1. An unusual feature in the structure of La 2 Fe 25 P 12 are strings of edge-sharing Fe 4 tetrahedra extending along the short translation period.

Single-crystal structure refinements of the low-temperature quartz modification of GaPO 4 were performed up to 6.80(7) GPa. The refinements were carried out in space group P 3 1 21. At ambient conditions the lattice parameters are a = 4.9043(7) Å and c = 11.4079(5) Å. They decrease to a = 4.6421(8) Å and c = 10.8022(6) Å at 6.80(7) GPa. Powder diffraction studies indicate that a pressure induced amorphization takes place at about 9 GPa. The high pressure behavior of GaPO 4 is similiar to that of the homeotypic compounds quartz and GeO 2 , and to that of the isotypic compounds AlPO 4 and AlAsO 4 . Structural changes with increasing pressure are characterized by an increasing c / a axial ratio, increasing distortions of the GaO 4 and PO 4 tetrahedra, and decreasing (Ga–O–P) angles which indicate a cooperative tilting of the tetrahedra. As in the case of other quartz-type structures, the high-pressure behavior of GaPO 4 is determined by changes of the oxygen packing towards a cubic body-centered lattice. Structural changes occuring at varying temperatures are slightly different from pressure-induced changes.

Dibutyltin salicyldehydethiosemicarbazate (C 4 H 9 ) 2 Sn[OC 6 H 4 -2-CH = N–N = C(NH 2 )S] and dibutyltin salicyldehydesemicarbazate (C 4 H 9 ) 2 Sn[OC 6 H 4 -2-CH = N–N = C(NH 2 )O] crystallize isomorphously in the hexagonal R [unk] space group as isostructural molecules with the tin atoms in a cis -trigonal bipyramidal geometry (Sn–S = 2.537(2) Å, Sn–O = 2.103(6) Å, Sn <–N = 2.227(4) Å,C–Sn–C = 127.2(4)°; Sn–O = 2.137(9) Å, 2.09(1) Å, Sn <–N = 2.149(8) Å, C–Sn–C = 132.0(7)°).

The title compound is monoclinic, space group P 2 1 / c , Z = 4. Cell dimensions are a = 12.644(2) Å, b = 14.905(3) Å, c = 17.945(3) Å and β = 95.68°(14). A total of 5829 reflections were measured with a PC-computer-controlled PHILIPS PW1100 automatic diffractometer using MoK α radiation. The structure was refined by full-matrix least squares to a conventional R = 0.0668 for 4359 observed reflections. The charge of the [Ni(enR) 2 tfac] + entity is counterbalanced electro-statically by the perchlorate anion. The nickel(II) ion is six-coordinated and it is positioned at the centre of a nearly regular octahedron. The best (equatorial) plane encompasses the β -dionato metallocyclic ring and one nitrogen of each of the bidentate diamino ligands. The other donor atoms occupy the remaining apical positions and are equidistant from the metal centre. The Ni–O bond lengths are virtually identical (average Ni–O 2.006 Å) despite the proximity of the strongly electron-attracting trifluoromethyl group to one of the oxygens. The 1,2-diamine forms five-membered chelate rings, adopts the gauche conformation and the meso form in accordance with the appearance of a double band in the infrared absorption spectrum attributable to the N–H stretching vibrations. The N–C distances connecting the phenyl groups are on average shorter by 0.05 Å than those within the chelate rings. The perchlorate group, [ClO 4 ] − , exhibits a distorted tetrahedral structure that causes splitting in the relevant infrared absorption band at ∼ 1900 cm−1.

N,N′-ethylene-bis-(tetronic-acid-3-formiminato)-copper(II)/K1 crystallizes in space group P 2 1 / n : C 12 H 10 CuN 2 O 6 × H 2 O; a = 8.439(5) Å; b = 12.762(1) Å; c = 12.582(1) Å; β = 99.02(3)°; V = 1338.3 Å 3 ; Z = 4; D x = 1.783 gcm −3 ; Mo K α = 0.71069 Å; μ = 16.71 cm −1 ; F (000) = 732; T = 293 K; Conventional R = 0.037; R w = 0.040 for 1633 observed reflections. N,N′-ethylene-bis-(tetronic-acid-3-formiminato)-nikkel(II)/K2 crystallizes in space group C 2/ c : C 12 H 10 N 2 O 6 Ni × 4 H 2 O; a = 20.232(5) Å; b = 12.983(5) Å; c = 14.038(10) Å; β = 120.01(3)°; V = 3193.0 Å 3 ; Z = 8; D x = 1.702 gcm −3 ; Mo K α = 0.71069 Å; μ = 12.74 cm −1 ; F (000) = 1696; T = 293 K; Conventional R = 0.087; R w = 0.090 for 2877 observed reflections. N,N′-ethylene-bis-(1,5,5-trimethyltetramic-acid-3-formiminato)-copper(II)/K3 crystallizes in space group P 2 1 / n : C 18 H 24 N 4 O 4 Cu × 1 H 2 O; a = 15.981(9) Å; b = 7.293(8) Å; c = 18.742(4) Å; β = 114.06(4)°; V = 1994 Å 3 ; Z = 4; D x = 1.472 gcm −3 ; Mo K α = 0.71069 Å; μ = 11.31 cm −1 ; F (000) = 924; T = 293 K; Conventional R = 0.129; R w = 0.142 for 2900 observed reflections. In K1 and K3 copper is coordinated by two nitrogen and two oxygen atoms of the ligand molecule as well as by one water molecule on top of a tetragonal pyramid. In K2 two water molecules are included in the complex formation. These and two nitrogen as well as two oxygen ligand atoms form a nearly regular octahedron.

The crystal structure of the title compound has been determined from three-dimensional X-ray diffraction data. The crystals are triclinic, space group P [unk], with a = 11.218(1) Å, b = 11.680(1) Å, c = 15.360(1) Å, α = 93.422(5)°, β = 110.575(8)°, γ = 90.951(6)°, V = 1879.36 Å 3 , Z = 2. The structure was solved by the heavy-atom method and refined by least-squares to a final R = 0.043 ( R w = 0.044) for 4897 observed unique reflections [ F o > 5 σ ( F o )]. The complex consists of dimeric (C 18 H 14 N 4 O 3 PbS) 2 units. Each Pb atom is coordinated by one 1-(2-thenoyl)-2-(2,2′-dipyridyl methylene)hydrazine ligand, (TDPH), and one acetyl ligand. The TDPH ligand behaves as a tridentate chelate by linking to Pb through the thenoyl oxygen, the azomethine nitrogen and one pyridine nitrogen [mean metal-to-ligand distances: Pb–N(azomethine) 2.492(5) Å, Pb–N(pyridine) 2.640(6) Å and Pb–O(thenoyl) 2.370(4) Å]. The acetyl group, on the other hand, acts as a bibentate chelate with one Pb–O distance significantly larger than the other [short bond distance range: 2.275(1)–2.320(7) Å; long bond distance range: 2.709(7)–3.354(9) Å]. Moreover, there is an additional Pb…O interaction with the acetyl group of the other member of the dimeric unit, giving rise to a strongly distorted pentagonal pyramidal environment around the metal atom with the thenoyl oxygen lying at its apex. The IR and electronic spectra are in accordance with the established structure from the X-ray data. Conductivity measurements indicate the non-electrolytic character of the complex.

The title compound was obtained by acylation reaction of the corresponding “free” cyclohexanol derivative using chloroacetyl chloride. It crystallizes from n -pentane in the monoclinic system, space group P 2 1 / n , with a = 1077.7(2) pm, b = 1483.8(3) pm, c = 890.2(2) pm, β = 90.46(2)°, Z = 4.

The electrical conductivity of Tl 3 BX 4 -crystals (B = V, Nb, Ta; X = S, Se) has been investigated in the temperature range between 268 and 333 K. The crystals show both electronic and Tl + ionic conduction at room temperature. By impedance and DC-conductivity measurements the total conductivity σ t as well as the electronic and ionic partial conductivity were determined. The σ t values range between 9.3 · 10 −6 (Tl 3 VSe 4 ) and 1.4 · 10 −7 ( Ω cm) −1 (Tl 3 TaSe 4 ). Apart from Tl 3 VSe 4 the Tl + ionic conduction predominates.