Body-centered Packing Research Articles

Synthesis and Atomic Structure of the Yb-Ga-Au 1/1 Quasicrystal Approximant.

The Yb-Ga-Au 1/1 quasicrystal approximant (AP) composition ranges from Yb14.0Ga20.6Au65.4 to Yb14.8Ga46.3Au38.9, and single crystals of the 1/1 AP having the composition Yb13.8Ga26.1Au60.1 were obtained by the self-flux technique. X-ray structural analysis demonstrated that the atomic structure [space group Im3; a = 14.6889(9) Å] can be described by the body-centered packing of Tsai-type rhombic triacontahedron (RTH) clusters. The positional disorder in these clusters, interpreted as the average of an orientationally disordered tetrahedron and triangle, results in positional disorder in the outer shells. The elemental distributions and positions of mixtures of Au and Ga atoms in the RTH clusters correspond to those in the isostructural Yb15Al36Au49 1/1 AP.

Combining Linker Design and Linker-Exchange Strategies for the Synthesis of a Stable Large-Pore Zr-Based Metal-Organic Framework.

A Zr(IV)-based metal-organic framework (MOF), termed reo-MOF-1 [Zr6O8(H2O)8(SNDC)4], composed of 4-sulfonaphthalene-2,6-dicarboxylate (HSNDC2-) linkers and Zr6O8(H2O)8(CO2)8 clusters was synthesized by solvothermal synthesis. Structural analysis revealed that reo-MOF-1 adopts the reo topology highlighted with large cuboctahedral cages (23 Å). This structure is similar to that found in DUT-52 (fcu topology), however, reo-MOF-1 lacks the body-centered packing of the 12-connected Zr6O4(OH)4(CO2)12 clusters, which is attributed to the subtle, but crucial influence in the bulkiness of functional groups on the linkers. The control experiments, where the ratio of H3SNDC/naphthalene-2,6-dicarboxylate linkers was varied, also support our finding that the bulky functionalities play a key role for defect-controlled synthesis. The reo-MOF-1A framework was obtained by linker exchange to yield a chemically and thermally stable material despite its large pores. Remarkably, reo-MOF-1A exhibits permanent porosity (Brunauer-Emmett-Teller and Langmuir surface areas of 2104 and 2203 m2 g-1, respectively). Owing to these remarkable structural features, reo-MOF-1A significantly enhances the yield in Brønsted acid-catalyzed reactions.

Packing schemes of cavities in selected clathrasils and zeolites and the analogous packings of atoms in crystal structures

Sizes of cavities and their packing schemes in selected zeolites and clathrasils were studied by means of least squares fitting of circumscribed spheres to them. Resulting packing of spheres of different diameters was analyzed by the coordinates of their centers, their volumes and sphericity, and interpreted by comparison with analogous packings of atoms in inorganic compounds and alloys. The topology is described qualitatively as “negative” structures formed by the cavities. Melanophlogite and dodecasils 3C and 1H are all clathrasils with isolated cavities. They all have pentagonal dodecahedral [5 12 ] cages, associated with other cavity types. The packing of cavities in melanophlogite is analogous to the packing of atoms in the structure of Cr 3 Si, where the Cr atoms form icosahedra around the Si sites. Dodecasil 3C has a cubic arrangement of [5 12 ] cavities, which is described as ABC stacking of kagome nets and its cavity packing is an analog to the packing scheme of atoms in the cubic Laves phase MgCu 2 . Dodecasil 1H has an arrangement of [5 12 ] cavities in an AA stacking of kagome nets and is analogous to the alloy structure type CaZn 5 . Edingtonite and natrolite are built from two types of cavities, tetragonal scalenohedra and [8 6 ] cavities. The [8 6 ] cavities have different shape and packing in the two structures. In paulingite, the largest cavity, a large rhombicuboctahedron [4 12 6 8 8 6 ] with a diameter of 11.02 A is in a body centered configuration. It is interspaced by six other types of cavities with diameters from 5.10 to 8.20 A, arranged in a complex pattern. In this structure, there are three non-intersecting channel systems. Their cavity arrangements mimic sodalite and a modified ReO 3 structure. The cubic structure of sodalite has only one type of cavity, a truncated octahedron [4 6 6 8 ] with a diameter of 6.41 A, arranged in a body-centered packing analogous to α-Fe. Chabasite has a rhombohedral packing of elongate cavities [4 12 6 2 8 6 ], whereas Linde Type A has [4 6 6 8 ] and [4 12 6 8 8 6 ] cavities in a CsCl-type arrangement. The cavity representation used here gives a clear picture of cavities and interconnections even for complicated cases.

Copper–indium ordering in RECu 6In 6 ( RE=Y, Ce, Pr, Nd, Gd, Tb, Dy)

The rare earth metal–copper–indides RECu 6In 6 ( RE=Y, Ce, Pr, Nd, Gd, Tb, Dy) were synthesized from the elements by arc-melting. Well-crystallized samples were obtained by slowly cooling the melted buttons from 1320 to 670 K in sealed silica tubes in a muffle furnace. They were investigated by X-ray diffraction on powders and single crystals: ThMn 12 type, space group I4/ mmm, Z=2, a=916.3(2), c=535.8(2) pm, w R 2=0.063, 216 F 2 values, 15 variables for YCu 6In 6, a=926.5(4), c=543.5(3) pm, w R 2=0.064, 314 F 2 values, 15 variables for CeCu 6In 6, a=925.7(4), c=540.1(3) pm, w R 2=0.075, 219 F 2 values, 15 variables for PrCu 6In 6, a=923.1(4), c=540.3(3) pm, w R 2=0.071, 218 F 2 values, 15 variables for NdCu 6In 6, a=917.7(4), c=540.2(3) pm, w R 2=0.076, 207 F 2 values, 15 variables for GdCu 6In 6, a=917.0(5), c=540.5(4) pm, w R 2=0.062, 215 F 2 values, 15 variables for TbCu 6In 6, a=915.2(8), c=540.7(7) pm, w R 2=0.108, 218 F 2 values, 15 variables for DyCu 6In 6. The structures have been refined with a split position (50% Cu+50% In) for the 8 j site. They can be explained by a tetragonal body-centered packing of CN 20 polyhedra (10Cu+10In) around the rare earth atoms. The ordering models of the copper and indium atoms and the limitations/resolution of X-ray diffraction for this topic are discussed.

Supramolecular adduct of tetrachlorogallate with cucurbituril: (H7O3)4[GaCl4]2Cl2·C36H36N24O12·2H2O

During the investigation of the Ga3+–HCl–cucurbituril system, we prepared crystals of the title compound, tetrakis(hydroxonium) bis(tetrachlorogallate) dichloride cucurbituril decahydrate, by slow evaporation of an aqueous hydrochloric solution containing Ga3+and cucurbituril at room temperature in air. The compound appeared to be isostructural with the cucurbituril tetrachloroferrate(III) adduct. The structure contains H7O3+cations, [GaCl4]−anions, cucurbituril and water molecules. The centres of the cucurbituril molecules are arranged as body-centered packing and [GaCl4]−anions are situated in space between them. There is a complicated network of hydrogen bonds in the structure.

Teaching Crystal Structures with 3?D Surfaces

Using mathematics from the method of the exponential scale, crystals inner and outer structures are given. A number of fundamental crystal structures are described as mathematical functions. Plotting the equations gives the classical ball representation of the structures. In the case of intricate structures, the pedagogical interest lies in the possibility of describing the whole structure as the sum of very simple partial structures, each corresponding to a part of the equation. Structures given are primitive cubic packing, primitive hexagonal packing, face-centered-cubic close-packing, hexagonal close-packing, body-centered packing, CsCl, diamond, zinc blende, CaF2, ReO3, perovskite, NaCl, Mg3NF3, SiO2, Cu3Au, NiAs, wurtzite, and graphite.

Synthesis and Structure of a Neutral SiAl14 Cluster

A metastable AlCl solution obtained by co-condensation of the high-temperature molecule AlCl and a mixture of toluene/diethyl ether reacted with SiCp*2 or SiCl4/AlCp*, giving a unique SiAl14 cluster species that bears six Cp* ligands protecting the compound from disproportionation and formation of the bulk material (elemental Al or an Si/Al alloy). The structure of the SiAl14 core represents a section of the body-centered packing where a Si atom resides in the center of an Al cube. Each of the six faces of the cube is capped by an additional Al(η5 Cp*) moiety. This cluster compound was investigated by mass spectrometry, X-ray diffraction, 27Al NMR spectroscopy, and ab initio theory. The solid-state structure contains minor amounts of molecules with additional Cl atoms bonded to the Al atoms at the corners of the cube, and the presence of Cl-containing molecules in the crystal is rationalized on basis of the suggested reaction path.

Crystal Structure, Specific Heat, and119Sn Mössbauer Spectroscopy of CeRu4Sn6: A Ternary Stannide with Condensed, Distorted RuSn6Octahedra

CeRu4Sn6was prepared from the elements by a reaction in an arc-melting furnace and subsequent annealing at 1123 K. It crystallizes with the tetragonal YRu4Sn6type structure of space groupI42m:a=688.1(1),c=975.2(2) pm,V=0.4617(1) nm3, wR2=0.0472, 554F2values, and 19 variables. The cerium atoms in CeRu4Sn6have coordination number 16 formed by 12 tin and 4 ruthenium atoms. These polyhedra are arranged in a tetragonal body-centered packing and are linked by common Sn1 atoms. The strongest bonding interactions are between ruthenium and tin atoms. The ruthenium atoms have 6 tin neighbors at distances from 256.9 to 276.8 pm in the form of a strongly distorted octahedron. Four of such octahedra are condensed via common edges and faces forming [Ru4Sn6] units. These groups are packed in a tetragonal body-centered arrangement. The cerium atoms occupy the space between the [Ru4Sn6] units. The [Ru4Sn6] substructure of CeRu4Sn6is discussed in comparison with the structures of Ru2Sn3, LaRuSn3, and Ru3Sn15O14which also contain condensed RuSn6octahedra or trigonal prisms as characteristic structural motifs. Despite the two different tin sites the119Sn Mössbauer spectroscopic measurements show only one signal atδ=1.99 mm/s subjected to quadrupole splitting. Heat capacity measurements indicate that CeRu4Sn6behaves like a heavy-fermion compound.

Darstellung und Lithiumteilstruktur von Lithiumnitridtribromid, Li6NBr3 und Lithiumnitridtriiodid, Li6NI3 / Preparation and Lithium Sublattice of Lithium Nitride Trihalides, Li6NHal3 (Hal = Br, I)

Abstract Single phase Li6NBr3 was prepared by the reaction of Li3N and dry, OH-free LiBr at 450°C. It is the most bromide rich compound in the quasi binary system Li3-2xN1-xBrx. The crystal structures of Li6NBr3 and of isotypic Li6NI3, have been redetermined from neutron powder diffraction data. Both compounds crystallize in the cubic space group Fm3m (No. 225), a(Li6NBr3) = 894.18(7), a(Li6NI3) = 951.7(1) pm with 4 formula units per unit cell. The anion sublattice comprises a rock salt like arrangement of N with one of the three halogen atoms (Hal1), with the remaining halogen atoms in the resulting N4Hal4 cubes. The structure may be regarded as an ordered AX3 variation of a body-centered packing. The lithium atoms are disordered over the 96 (distorted) tetrahedral NX3 holes in such a way that of the four neighbouring, face-sharing NBr3 tetrahedra along an N-H all-connection line only one is occupied. The resulting Li coordination polyhedron around N (and Hal1) is a distorted octahedron with 6 equidistant Li atoms. Hal2 is surrounded by 12 Li atoms. The Li6NHal3 structure may be regarded as an anti-form of the cryolite structure.

Icosahedral and decagonal quasicrystals of intermetallic compounds are multiple twins of cubic or orthorhombic crystals composed of very large atomic complexes with icosahedral point-group symmetry in cubic close packing or body-centered packing: Structure of decagonal Al 6 Pd

A doubly icosahedral complex involves roughly spherical clusters of atoms with icosahedral point-group symmetry, which are themselves, in parallel orientation, icosahedrally packed. These complexes may form cubic crystallites; three structures of this sort have been identified. Analysis of electron diffraction photographs of the decagonal quasicrystal Al(6)Pd has led to its description as involving pentagonal twinning of an orthorhombic crystal with a = 51.6 A, b = 37.6 A, and c = 33.24 A, with about 4202 atoms in the unit, comprising two 1980-atom doubly icosahedral complexes, each involving icosahedral packing of 45 44-atom icosahedral complexes (at 0 0 0 and 1/2 1/2 1/2) and 242 interstitial atoms. The complexes and clusters are oriented with one of their fivefold axes in the c-axis direction.

A novel hydridic high-nuclearity rhodium cluster: synthesis and x-ray crystal structure of the anion [Rh 14H(μ-CO) 15(CO) 10] 3−

The novel anion [Rh 14H(CO) 25] 3− has been obtained by reaction of the tetra-anion [Rh 14(CO) 25] 4− with acids. Its structure can be related to that of the parent species, but there are differences in the cluster geometry and in the carbonyl stereochemistry. The metal atom polyhedron can be described as an array intermediate between a cubic body-centered packing and a cubic close-packed arrangement.

Physical Properties and Crystal Structure of 1,1,1,2-Tetrachloro-2-methylpropane

Abstract 1,1,1,2-Tetrachloro-2-methylpropane is cubic at room temperatures. X-ray date may be interpreted on the basis of a body-centered packing of molecules in disorder, orientational or rotational. The cube edge of the unit containing two molecules is a=7.4Å. The crystal undergoes transition at about −62.2°C, when cooled, and at −39.7°C,when heated starting at a lower temperature.