Band 213, Heft 5

The crystal structures of rare-earth metal sesquisulfides and some related compounds (Tm 5 S 7 , Tm 8 S 11 , Tm 15 S 22 ) of orthorhombic or monoclinic symmetry with the mirror plane perpendicular to the translation of 3.7 Å – 4.1 Å have been studied using an analysis of close-packed atomic nets. The cation and the anion matrices have been shown to possess a similar construction for all compounds. A system of parallel mirror planes (∼2 Å apart) causes all atoms to be located only in these planes; in fact, this means that a crystal structure becomes pseudo two-dimensional. It was found that in each structure there were sets of cation close-packed crystallographic planes perpendicular to the mirror planes; when intersecting they form a node net close to the ideal 3 6 net. Because of the proximity of the neighbouring mirror planes the cation node in one mirror plane corresponds with a vacancy in the adjacent mirror plane. Hence the cation matrices can be represented by a single-layer hexagonal structure whose basal planes split into the two mirror planes with half the cations moving onto each of the mirror planes (the AA′ type according to our classification). The anion matrices have a similar construction but they are less regular and on a smaller scale. Each structure type has an inherent law governing the distribution of atoms and vacancies in the net and the proper conditions for the compatibility between the cation and anion matrices that determine the unit cell dimensions. So, the system of the nearest mirror planes is the main factor which regulates the atomic arrangement, that is, keeps to the minimum the number of arbitrarily changed coordinates or, more properly, degrees of a freedom of the structure.

The results of an ab initio structure determination of a series of CuO powder samples are reported. It is shown that the thermal treatment affects the peak broadening and overlapping and determines the possibility to get the cell size and the atomic positions. It is also demonstrated that the highest level of sintering not always assures the best results in the ab initio procedure as can be seen from the CuO sample prepared at 1273 K. This study suggests that, when possible, it is better to apply the ab initio procedure to a series of samples differently annealed than to use directly the highest sintered powder.

The new compounds K 2 Cu 2 (SeO 3 ) 3 and K 2 Cu 3 (SeO 3 ) 4 were synthesized in the course of low-hydrothermal experiments on natrochalcite-type selenate representatives. The crystal structures were determined by direct methods from single-crystal X-ray diffraction data. K 2 Cu 2 (SeO 3 ) 3 : space group Cmcm , Z = 4, a = 5.312(1) Å, b = 9.858(3) Å, c = 17.595(5) Å, V = 921.4(4) Å 3 , R 1 = 0.023. K 2 Cu 3 (SeO 3 ) 4 : space group P [unk], Z = 1, a = 5.443(1) Å, b = 7.158(2) Å, c = 8.369(3) Å, α = 95.26(2)°, β = 108.58(2)°, γ = 92.17(2)°, V = 307.0(2) Å 3 ; R 1 = 0.035. Both compounds contain sheets built from edge- or cornersharing CuO n polyhedra ( n = 5,6) and trigonal pyramidal selenite groups. These units are linked via the potassium atoms. In K 2 Cu 2 (SeO 3 ) 3 one of the two selenite groups is strongly disordered.

The ordering in DyFe 6 Sn 6 was studied by conventional X-ray single crystal diffraction. Two inequivalent structure models fitted the observed intensities equally well. Model I comprises three twinned individuals with the TbFe 6 Sn 6 superstructure ( Cmcm , a = 8.912(1) Å, b = 18.672(1) Å, c = 5.390(1) Å, R F = 0.061, wR F 2 = 0.155 for all 2050 reflections and R F = 0.100, wR F 2 = 0.196 for 317 superstructure reflections). Model II corresponds to a novel superstructure ( Cmcm , a = 8.912(1) Å, b = 37.343(2) Å, c = 21.560(2) Å, R F = 0.057, wR F 2 = 0.130 for all 2050 reflections and R F = 0.097, wR F 2 = 0.190 for 317 superstructure reflections). The preferences is given to model I.

The crystal structures of two polymorphic, hydrothermally synthesized cobalt selenite monohydrates, CoSeO 3 · H 2 O II ( a = 568.1(1) pm, b = 476.7(1) pm, c = 1348.0(2) pm, μ = 101.37(1)°) and CoSeO 3 · H 2 O III ( a = 477.2(1) pm, b = 1320.9(3) pm, c = 568.6(1) pm, β = 90.54(1)°), both mP 32, P 2 1 / n , Z = 4, have been determined by single crystal X-ray diffraction. Both structures are built up from buckled trans layers 2 ∞ [CoSeO 3 · H 2 O] consisting of strongly distorted CoO 5 (H 2 O) octahedra and trigonal pyramidal SeO 3 2− ions. The structures differ with respect to the stacking of the layers, which originates in their pseudosymmetry and in the stereochemical requirements of the selenite lone electron pair. Only intra-layer H bond schemes are built, i.e., the layers are held together by van der Waals interactions.

Three phosphates with (NaM II PO 4 ) x composition have been synthesized and characterized structurally. The low temperature modifications of NaMgPO 4 and Na 2 CaMg(PO 4 ) 2 crystallize in the orthorhombic space group P 2 1 2 1 2 1 , and the monoclinic space group P 2 1 / c , respectively. The phase transitions at high temperature were investigated by thermal analysis and powder diffractometry. The high-temperature modification of Na 2 CaMg(PO 4 ) 2 is isotypic with glaserite, K 3 Na(SO 4 ) 2 as determined by Rietveld refinement. Na 18 Ca 13 Mg 5 (PO 4 ) 18 crystallizes in the trigonal space group R [unk] m . The structures of all of these phosphates can be related to the arrangement of cations and phosphate tetrahedra in the glaserite structure.

The compression of cadmium orthosilicate, Cd 2 SiO 4 , was studied by high-pressure single-crystal diffraction carried out in a diamond-anvil cell. The equation of state at room temperature (third-order Birch-Murnaghan: V 0 = 695.71(3) Å 3 , K 0.298 = 119.2(5) GPa, K ′ = = 6.17(4)) was determined from unit-cell volume data to 9.51 GPa. Compression of the orthorhombic structure ( Fddd , Z = 8) was found to be anisotropic with relative compressibilities of 2.10:1.00:4.77 for the a , b , and c axes. The variation of the lattice parameters with pressure is described by: a / a 0 = 0.99989(7) − 3.10(3) × × 10 − GPa −1 × P + 8.2(3) × 10 −5 GPa −2 × P 2 ; b / b 0 = = 1.00007(8) − 8.8(9) × l0 −2 GPa −1 × P ; c / c 0 = 1.00001(5) − 4.16(3) × 10 −3 GPa −1 × P + 6.5(2) × 10 −5 GPa −2 × P 2 . Crystal structures were determined at pressures of 3.01 GPa, 5.44 GPa, and 8.69 GPa. The anisotropy of the unit-cell compression is controlled by the distortion of the CdO 6 and SiO 4 polyhedra due to their unusual interconnection through shared edges. Cation-cation repulsion between Cd and Si atoms, which results in short and long Cd–O bonds, was found also to be responsible for unusual compressional behaviour related to the strength of the bond: the shorter the Cd–O bond the higher its compressibility. The large uniaxial distortion of the silicate tetrahedron is responsible for the relatively higher compressibility along the c axis. The compressional differences between the a and b axis result from the compressional anisotropy of the CdO 6 octahedron.

The 5-nitro-2-tosylaminobenzaldehyde di(morpholin-4-yl)aminal forms a stable complex with carbon tetrachloride in the crystal phase. X-ray structural study of this complex indicates an essentially shortened intermolecular contact of 2.89 Å between the oxygen atom of the nitro group and one of the chlorine atom of the CCI 4 molecule. Quantum-chemical calculations by semiempirical AMI method showed that the formation of such complex did not cause considerable decrease of system energy or change of charge distribution in molecules. It was supposed that this associate has van der Waals character.

The crystal and molecular structure of disordered triphenyl(pyridine-2-thiolato)tin(IV), [Ph 3 Sn(2-pyS)], C 23 H 19 NSSn, has been determined at room temperature. The colorless crystals are monoclinic, space group C 2/ c with unit cell dimensions a = 17.179(5) Å, b = 15.256(1) Å, c = 8.142(5) Å, β = 109.55(3)°, Z = 4 and D x = 1.520 Mgm −3 . A molecule of [Ph 3 Sn(2-pyS)] with half occupancy comprises the asymmetric unit and this molecule is 1:1 disordered about the 2-fold rotation axis with the Sn 0.38 Å off axis. Constrained refinement using 95 variables plus additional restraints gave a final R = 0.046 for 1608 reflections with I ≥ 3.0 σ ( I ). The title compound is molecular and features a distorted tetrahedral tin-atom geometry defined by a thiolate S(2) atom [Sn–S 2.456(3) Å] and three phenyl groups; distortion from the ideal geometry can be traced, in part, to the close approach of the pyridine-N atom, i.e. Sn–N(l) is 2.831(6) Å.

The crystal and molecular structure of [Hdmtp] 2 [SnCl 6 ], C 14 H 18 Cl 6 N 8 Sn, (where Hdmtp is 5,7-dimethyl-[1,2,4]triazololium-N3-[1,5-a]pyrimidine) has been determined at room temperature. The colorless crystals are triclinic, space group P [unk] with unit cell dimensions a = 9.259(1) Å, b = 9.479(1) Å, c = 7.9447(9) Å, a = 113.245(9)°, β 114.810(9)°, γ = 62.523(8)°, Z = 1 and D x = 1.931 Mg m −3 . The structure was refined by a full-matrix least-squares procedure on F to final R = 0.026 using 2529 reflections. The lattice is comprised of centrosymmetric [SnCl 6 ] 2− dianions and [Hdmtp] + cations in the ratio 1:2. The [Hdmtp] + cation has been shown to be protonated at N(3) and to be associated to a centrosymmetrically related cation via N(3)–H … N(4) hydrogen bonding.

The crystal and molecular structure of {8-[2-(6-methoxy-2-naphthyl)-1-ethynyl]-1-naphthyl}-trimethyl-stannane, [Me 3 Sn(C 10 H 6 C=CC 10 H 6 OMe)], C 26 H 24 OSn, has been determined at room temperature. The colorless crystals are triclinic, space group P [unk] with unit cell dimensions a = 9.489(1) Å, b = 16.931(4) Å, c = 7.174(2) Å, α = 97.61(2)°, β = 106.58(1)°, γ = 94.76(2)°, Z = 2 and D x = 1.441 Mg m −3 . The structure was refined by a full-matrix least-squares procedure on F to final R = 0.049 using 3736 reflections with I ≥ 3.0 σ ( I ). The tin center exists in a distorted tetrahedral geometry defined by four carbon atoms with Sn–C in the range 2.137(6) Å to 2.168(5) Å. Steric hindrance in the molecule, indicated by a close Sn … C≡C contact of 3.192(5) Å, is responsible for the major distortions from the ideal geometry.