Volume 225, Issue 10 -

The stannides Li 8 Rh 7 Sn 8 and Li 1.23 Rh 1.77 Sn were synthesized from the elements in sealed niobium ampoules. The structures were refined on the basis of single crystal X-ray diffractometer data: MnCu 2 Al type (Heusler phase), Fm -3 m , a = 615.5(4) pm, wR 2 = 0.0319, 106 F 2 values, 6 variables for Li 1.23 Rh 1.77 Sn and P -3 m 1, a = 894.4(4) pm, c = 1107.3(4) pm, wR 2 = 0.0600, 1287 F 2 values, 48 variables for Li 8 Rh 7 Sn 8 which crystallizes with a new structure type. The rhodium site in Li 1.23 Rh 1.77 Sn shows Rh/Li mixing. The structure of Li 8 Rh 7 Sn 8 contains two pronounced structural motifs. Layers of edge-sharing RhSn 6 octahedra alternate with layers of six-membered rings of corner-sharing SnRh 4 tetrahedra in UDUDUD orientation. The [Rh 7 Sn 8 ] δ – polyanionic network is characterized by covalent rhodium-tin bonding.

The lithium-rich silicide Li 4.82(2) Pd 2.90(2) Si 2.28(2) was obtained by melting of palladium and silicon in an excess of lithium using a sealed niobium ampoule as container material. The structure of this new silicide was refined on the basis of single crystal X-ray diffractometer data: P 4 3 2 1 2, a = 679.1(1), c = 3774.7(8) pm, wR 2 = 0.0712, Flack 0.03(11), 2072 F 2 values, and 108 variables. The polar Li 4.82(2) Pd 2.90(2) Si 2.28(2) structure consists of a complex three-dimensional [Pd 2.90(2) Si 2.28(2) ] network which leaves larger channels along the c direction which are filled by the lithium atoms. One lithium site shows a mixed occupancy with silicon and two palladium sites show Pd/Si mixing, leading to the composition Li 4.82(2) Pd 2.90(2) Si 2.28(2) for the investigated crystal.

Single crystals of the two title compounds have been synthesised utilising fluoride-based fluxes. X-ray diffraction (XRD) revealed that Ca 5.45 Li 3.55 [SiO 4 ] 3 O 0.45 F 1.55 crystallises in space group R -3 m ( a = 7.1365(6), c = 41.459(3)Å) and Ca 7 K[SiO 4 ] 3 F 3 exhibits space group P 31 m ( a = 10.8161(5), b = 6.6469(3)Å). Both compounds show a non-stoichiometric composition, related to a coupled substitution of mono- and divalent cations compensated by the oxygen–fluorine contents. The Ca/Li ratio in the first compound is derived from the structural refinement, as well as from bond-valence sum (BVS) calculations. Electron microprobe analysis was performed to reveal the K/Ca ratio in the second structure, which shows a slight enrichment in potassium compared to the ideal stoichiometry. The distribution of K and Ca over two cation sites was studied with BVS calculations. Both structures belong to the group of nesosilicates (monosilicates) with additional anions. Furthermore, the structures are discussed in the context of related materials.

Crystal structures of bis(pyridine-2-yl) ketone arylhydrazone derivatives, [ 6 , (py) 2 C=NNHC 6 H 4 X ( X = H, 2-O 2 N, 4-O 2 N and 4-I] have been determined from data collected at 120 K. A third polymorph of ( 6 : X = 4-O 2 N) has been characterized. Compounds, ( 6 : X = 2-O 2 N) and two of the three now known polymorphs of ( 6 : X = 4-O 2 N), β - [Bakir and Brown, J. Mol. Struct. 641 (2002) 183–191] and γ [this study], have similar conformations, which are quite distinct from that of α -( 6 : X = 4-O 2 N) [Bakir et al, Acta Crystallogra. C 61 (2005) o607–o609] and ( 6 : X = 4-I) [this study]. The molecular conformation of ( 6 : X = H) is intermediate between the two extremes. For compound ( 6 : X = H), the supramolecular arrangement is made from C—H···N hydrogen bond, π···π stacking and C—H-(arene) interactions, while that for ( 6 : X = 4-I) is composed of N—H···N, C—H···N and C—H-π interactions. C—HO and π···π stacking interactions are present in γ -( 6 : X = 4-O 2 N). In contrast, ( 6 : X = 2-O 2 N) exists as discrete molecules with no intermolecular contacts within the appropriate sum of van der Waals radii.

X-ray powder diffractometry in a conventional laboratory powder diffractometer was used to discriminate between two chiral diastereoisomeric 7-oxanitronorbornenes that could not be distinguished unambiguously by nuclear magnetic resonance spectroscopy. It was found that the traditional approach consisting of successive steps of molecular modeling, direct-space methods, and crystallographic Rietveld refinement is not efficient for that purpose. This was attributed to the minimization trajectories in the phase spaces becoming trapped in local minima. On the contrary, the use of a final Rietveld refinement incorporating additional energy constraints limited the number of physically-reasonable atomic arrangements, thus allowing in this case unequivocal differentiation between the two nearly identical chiral diasteroisomeric 7-oxanitronorbornenes. This was possible thanks to the use of a multiobjective global optimization procedure (“Pareto optimization”) that searches for the minimum of a cost function defined as the weighted average of the crystallographic and energy residuals.

The molecules of the 7-chloroquinoline-4-hydrazones of the variously substituted benzaldehydes, 5 , of general formula C 16 H 11 ClN 3 X with X = H, o -F, m -F or m -MeO corresponding to compounds ( 5 : X = H), ( 5 : X = o -F), ( 5 : X = m -F) and ( 5 : X = m -MeO), respectively, are formally rather similar. Compounds ( 5 : X = H) and ( 5 : X = o -F) are isostructural but otherwise the molecular packing and intermolecular interactions show unexpectedly wide variation throughout the series. In all 5 hydrogen-bonds link the essentially planar molecules edge to edge to form chains. Combination of intermolecular hydrogen-bonds and π···π interactions creates three-dimensional connectivity in ( 5 : X = H), ( 5 : X = o -F) and, utilising the methoxy oxygen atom as acceptor for a C—H···O hydrogen-bond, ( 5 : X = m -MeO). Significant connectivity is no more than two-dimensional in layers of molecules in ( 5 : X = m -F).

Crystal structures of five tin(IV) complexes containing the tetrahydrothiophene-1-oxide ligand, C 4 H 8 SO, TMSO, with Sn—O interactions, are described. They are trigonal bipyramidal Ph 2 SnCl 2 (TMSO), with TMSO and Cl in axial sites, and the octahedral complexes, Ph 2 SnCl 2 (TMSO) 2 and SnX 4 (TMSO) 2 , where X = Br or Cl. In the octahedral complexes, the TMSO ligands are cis to one another and are trans to the halides. The SnCl 4 (TMSO) 2 complex has been obtained in two crystalline forms, one orthorhombic and isostructural with SnBr 4 (TMSO) 2 , and the other triclinic. Strengths of the interactions of the tin halides with dimethyl sulfoxide, (DMSO), and TMSO ligands are compared.