Search results for "tetrahedron"

Diisopropyl [(2-hydroxy-1-naphthyl)methyl]phosphonate

2003

The bond lengths and angles in the title compound, C17H23PO4, are in accordance with anticipated values. There are two conformers in the asymmetric unit. They differ from each other in the orientation of the C and P tetrahedra. Analysis of the structure does not reveal any significant differences between the bond distances and angles of the mol­ecules in the asymmetric unit. In the crystal structure, the conformers are linked by O—H⋯O=P and C—H⋯O hydrogen bonds.

A hollow tetrahedral cage of hexadecagold dianion provides a robust backbone for a tuneable sub-nanometer oxidation and reduction agent via endohedra…

2007

We show, via density functional theory calculations, that dianionic Au16(2-) cluster has a stable, hollow, Td symmetric cage structure, stabilized by 18 delocalized valence electrons. The cage maintains its robust geometry, with a minor Jahn-Teller deformation, over several charge states (q = -1,0,+1), forming spin doublet, triplet and quadruplet states according to the Hund's rules. Endohedral doping of the Au16 cage by Al or Si yields a geometrically robust, tuneable oxidation and reduction agent. Si@Au16 is a magic species with 20 delocalized electrons. We calculate a significant binding energy for the anionic Si@Au16/O2- complex and show that the adsorbed O2 is activated to a superoxo-s…

A New Heptanuclear Cobalt(II) Cluster Encapsulated in a Novel Heteropolyoxometalate Topology:  Synthesis, Structure, and Magnetic Properties of [Co7(…

2004

The synthesis and the structural and magnetic characterization of a novel heptanuclear cobalt cluster encapsulated in a heteropolyoxotungstate is reported. This complex shows how it is possible to control the nuclearity of the Co clusters formed in a tungstate solution by slightly changing the synthetic conditions, and the relevance of pH in this regard. This heptanuclear complex [Co7(H2O)2(OH)2P2W25O94]16- (Co7) crystallizes in the triclinic space group P1 (a = 12.3403(6) A, b = 22.5966(11) A, c = 23.2645(12) A, α = 68.7830(11)°, β = 83.7981(12)°, γ = 78.5423(13)°, V = 5922.4(5) A3, Z = 2) and is formed by six CoO6 octahedra from two Co3 trimers sustained by Keggin trivacant fragments held…

Kirkman's tetrahedron and the fifteen schoolgirl problem

2011

We give a visual construction of two solutions to Kirkman's fifteen schoolgirl problem by combining the fifteen simplicial elements of a tetrahedron. Furthermore, we show that the two solutions are nonisomorphic by introducing a new combinatorial algorithm. It turns out that the two solutions are precisely the two nonisomorphic arrangements of the 35 projective lines of PG(3,2) into seven classes of five mutually skew lines. Finally, we show that the two solutions are interchanged by the canonical duality of the projective space.

X-ray-absorption fine-structure study of ZnSexTe1−x alloys

2004

X-ray-absorption fine-structure experiments at different temperatures in ZnSexTe1−x (x=0, 0.1, 0.2, 0.55, 0.81, 0.93, 0.99, and 1.0) have been performed in order to obtain information about the structural relaxation and disorder effects occurring in the alloys. First and second neighbor distance distributions have been characterized at the Se and Zn K edges, using multiple-edge and multiple-scattering data analysis. The first neighbor distance distribution was found to be bimodal. The static disorder associated with the Zn–Te distance variance did not depend appreciably on composition. On the other hand, the static disorder associated with the Zn–Se distance increased as the Se content dimi…

Retraction notice to “trans-Tetrakis(pyridine)dichloroiron(II) as catalyst for Suzuki cross-coupling in ethanol and water” [Tetrahedron Lett. 49 (200…

2009

Structure and Magnetic Properties of the Ferromagnetic Cu3Cl126- Trimer in [(NH3C2H4)3NH]2Cu3Cl14

2004

The crystal structure consists of a strongly hydrogen bonded network of tris(N-ethylammonium)ammonium cations, Cu3Cl12(6)- trimeric species, and Cl- anions. The Cu3Cl12(6)- trimers are formed by two distorted tetrahedral CuCl4(2)- anions linked to a central square planar CuCl4(2)- anion via semicoordinate Cu-Cl...Cu mu1 bridges. The central copper ion shows only small deviations from ideal D4h symmetry, while the terminal copper ions show a mild distortion from D2d symmetry with an average trans Cl-Cu-Cl angle of 136.0 degrees. The semicoordinate linkages provide a ferromagnetic exchange pathway between the copper ions with J/k = 6.91(3) K. Short Cl...Cl contacts (3.67-3.90 angstoms) lead t…

Crystallographic study of a family of Cs2BX4compounds

1990

Abstract Five compounds of the Cs2BX4 family with B = Zn, Co, Cu and X = Cl, Br were grown and studied. They belong to Pnma space group with 4 formula units per cell. From the full determination of the structure it appears that the ZnX4 tetrahedra are almost regular while the CuX4 tetrahedra are strongly distorted. This seems to be due to a strong Jahn-Teller effect induced by the Cu ions. This remark is extended to other compounds of the general family A2BX4.

Amorphous Ge15Te85: density functional, high-energy x-ray and neutron diffraction study

2011

The structure and electronic properties of amorphous Ge15Te85 have been studied by combining density functional (DF) simulations with high-energy x-ray and neutron diffraction measurements. Three models with 560 atoms have been constructed using reverse Monte Carlo methods constrained to (1) agree with the experimental structure factors S(Q), and have (2) energies close to the DF minimum and (3) a semiconducting band structure. The best structure is based on the melt-quenched DF structure and has a small number of Ge–Ge bonds. It shows interlocking networks of Te and GeTe with a significant fraction (22–24%) of voids (cavities). Ge occurs with both tetrahedral and 3 + 3 defective octahedral…

Tetrahedra from Aryleneethenylenes – From small Molecules to Luminescent Glasses

2004

AbstractThe fourfold Horner olefination of tetraphenylmethane or –silane with fourp-methyl- phosphonate groups and a variety of aromatic aldehydes with donor groups or extended conjugated systems results in the formation of tetrahedra from four chromophores connected via a central atom. Electronic spectra in solution reveal an electronic interaction between the π-systems. In the solid state, the emission of compounds with a dense packing is nearly identical to the solution spectra, more open structures show significant red shifts. The emission of scaffolds with 1-styrylpyrene chromophores is nearly completely quenched. Most of these tetrahedra are thermally stable up to 420°C. Depending on …