New nickel gallium boride, B14Ga3Ni27: synthesis and crystal structure.

Crystals of the new compound B(14)Ga(3)Ni(27) were successfully prepared by arc melting of the elements. B(14)Ga(3)Ni(27) crystallizes as a novel structure type in the monoclinic space group P2(1)/m with unit cell parameters a = 8.6859(4) Å, b = 10.7477(4) Å, c = 8.8425(3) Å, ß = 90.707(4)°, and Z = 2. Its structure was solved from single crystal data and refined to R1(F) = 0.0225. The unit cell of B(14)Ga(3)Ni(27) contains boron dumbbells and isolated gallium atoms embedded in a nickel 3D-framework. Its electronic structure, calculated by DFT methods, indicates metallic properties.

Investigation in the binary system Yb-Ga: crystal structure of the Ga-rich compound YbGa3.34.

Compounds within the Yb-Ga binary system were prepared by direct melting of the elements, and their crystal structure was solved from single crystal X-ray diffraction. YbGa(2) crystallizes in the hexagonal system, P6(3)/mmc, a = 4.4527(2), c = 7.1969(3) A, and YbGa(4) is monoclinic, C2/m, a = 6.129(2), b = 6.1096(14), c = 6.097(2) A, beta = 119.05(5) degrees . A new compound of formula YbGa(3.34) was identified in this system, and its crystal structure determined in the orthorhombic Immm space group, a = 4.2049(4), b = 4.3320(5), c = 25.691(3) A. While atoms are fully ordered in YbGa(2) and YbGa(4), partial atomic disorder occurs in YbGa(3.34) where gallium triangular units are found to substitute for some Yb atoms. The electronic structures have been calculated by first principles density functional theory methods using ordered models in supercells. Crystal structures and bonding therein are analyzed on the basis of gallium three-dimensional (3D) anionic networks and are compared with similar compounds. YbGa(3.34) marks the boundary between layered and 3D intergrown gallium frameworks.

Structural versatility of the epsilon-SmGa(x) phase: X-ray, electron diffraction, and DFT studies.

Two new compounds, SmGa(2.67) (hexagonal, P62c, Z = 15, a = 12.861(2), c = 8.4402(8) A) and SmGa(3.64) (orthorhombic, Fmmm, Z = 24, a = 8.493(1), b = 14.912(2), c = 17.080(2) A), have been synthesized and identified in the Sm-Ga system and their crystal structures solved and refined from single-crystal X-ray diffraction. These structures display consistent atomic disorder. Electronic structures have been calculated using first-principle DFT methods with ordered models. Atomic arrangements and bonding are analyzed on the basis of gallium partial anionic networks; they are compared with those of some analogous compounds in the other lanthanide-gallium systems.

Three novel phases in the Sm-Co-Ga system. Syntheses, crystal and electronic structures, and electrical and magnetic properties.

This paper presents the synthesis, identification, and characterization of three novel phases in the ternary system Sm-Co-Ga: SmCoGa5 (tP7, HoCoGa5 type, tetragonal P4/mmm, Z = 1, a = 4.2419(3) A, and c = 6.8559(5) A), Sm4Co3Ga16 (tP23, tetragonal P4/mmm, Z = 1, a = 6.0620(5) A, and c = 11.1495(9) A), and SmCoGa4 (oC24, YNiAl4 type, orthorhombic Cmcm, Z = 4, a = 4.1246(6) A, b = 15.608(2) A, and c = 6.4556(9) A). The structure of SmCoGa5 was obtained from a multiphase X-ray powder Rietveld refinement whereas the crystal structures of the other two phases were determined from single-crystal X-ray analysis. Electronic structures were calculated for all phases by first-principles DFT methods. The atomic arrangements and bonding are discussed on the basis of the partial anionic networks involving Co and Ga atoms, and a strong structural correlation is observed between SmCoGa5 and Sm4Co3Ga16. The latter, which displays paramagnetic behavior, has a resistivity of 4.2 microOmega.cm at 3 K and undergoes a superconducting transition at 2.8 K.

4-[Bis(1,5-dimethyl-1H-pyrazol-3-yl-methyl)amino]phenol monohydrate.

The crystal structure of the title compound, C18H23N5O.H2O, shows molecules containing a phenol group linked perpendicularly to a roughly planar fragment comprising two pyrazole rings. Molecules are stacked perpendicular to the [101] direction, with their phenol groups disposed alternately. The molecular packing in the crystal is stabilized by hydrogen bonding involving water molecules.

Single crystal manganese oxide multipods by oriented attachment.

Nonhydrolytic sol-gel processes in organic solvents have become very popular for the synthesis of metal oxide NCs. We report an affordable, high-yield, shape-control synthesis of MnO multipod nanocrystals with a quick reaction time. The reaction yields exclusively multipods; two to six pod nanocrystals are synthesized. The mechanism leading to this hierarchical nanostructure is studied in relation with an oriented attachment mechanism; all nanocrystals are found to be single crystals. The study is completed by high-resolution TEM, X-ray powder diffraction, and magnetic measurements.

Sm5Ga3.

Single crystals of pentasamarium trigallium, Sm5Ga3, display tetragonal symmetry. The crystal structure was solved and refined in space group P4/ncc. The present work does not confirm the space group I4/mcm previously deduced from powder data measurements. One Sm atom is in a general position, and the other Sm atom and one of the Ga atoms are at sites with fourfold symmetry. The remaining Ga atom is at a site with twofold symmetry.

Two cubic polymorphs of AlGeLi.

Aluminium germanium lithium, AlGeLi, crystallizes in two cubic dimorphs. The structure of the F-43m form, already inferred from powder data, has been confirmed by both powder and single-crystal X-ray diffraction studies. The second dimorph, not previously identified, adopts a disordered centrosymmetric structure with space group Fm-3m.

Li15Al3Si6 (Li14.6Al3.4Si6), a compound displaying a heterographite-like anionic framework.

The title compound, lithium aluminium silicide (15/3/6), crystallizes in the hexagonal centrosymmetric space group P6(3)/m. The three-dimensional structure of this ternary compound may be depicted as two interpenetrating lattices, namely a graphite-like Li(3)Al(3)Si(6) layer and a distorted diamond-like lithium lattice. As is commonly found for LiAl alloys, the Li and Al atoms are found to share some crystallographic sites. The diamond-like lattice is built up of Li cations, and the graphite-like anionic layer is composed of Si, Al and Li atoms in which Si and Al are covalently bonded [Si-Al = 2.4672 (4) A].

Atomic structure of the (Al,Si)CuFe cubic approximant phase.

The structure of the alpha-(Al,Si)CuFe approximant phase is determined by a single-crystal X-ray diffraction study and compared to the ideal structure obtained by the perpendicular shear method of the parent icosahedral phase. It is shown that the local environments (typical atomic clusters) of the two phases are similar and expand significantly farther than the size of the unit cell of the approximant. The orbit Al(2) issuing from the theoretical icosahedral model corresponding to the inner dodecahedron of the Mackay-type cluster is not found in the approximant and is replaced by a partially occupied inner icosahedron with an unusually large Debye-Waller factor.

Heteroatomic Centering of Icosahedral Clusters. Crystal and Electronic Structure of the K(6)(NaCd)(2)Tl(12)Cd Compound Containing the Not-So-Naked Tl(12)Cd(12-) Polyanion.

The title compound was synthesized in a niobium container by fusion of the elements followed by slow cooling. In the first stage, the stoichiometric proportion KNaCd(3)Tl(7) yielded a heterogeneous product containing a few single crystals of the compound K(6)(Na(2.36(9))Cd(1.64(9)))Tl(12)Cd, the structure of which was established by a single crystal X-ray diffraction technique (cubic, Im&thremacr;, a = 11.352(2) Å, Z = 2, R(F) = 3.24%, Rw(F) = 4.60%). Occurrence of a stoichiometry range for the compound was indicated after a new reaction starting from the composition K(6)Na(2)Cd(3)Tl(12) gave a quite homogeneous and well-crystallized product (refined composition K(6)(Na(1.93(7))Cd(2.07(7)))Tl(12)Cd, Im&thremacr;, a = 11.321(2) Å, Z = 2, R(F) = 3.98%, Rw(F) = 4.99%). The structure of K(6)(NaCd)(2)Tl(12)Cd is distinguishable from that reported for Na(4)K(6)Tl(13) by replacement of the icosahedron centering thallium and of half the sodium cations by cadmium. Statistical occupation disorder occurs on the 8(c) position of the outer Cd/Na atom. The structure contains the 50-electron closed shell centered Tl(12)Cd(12-) icosahedral cluster with &thremacr;m symmetry (T(h)). Extended Hückel molecular orbital and band calculations were carried out to analyze the centering effect on the anion stability and look at the electron transfer, especially from cadmium lying within the first coordination shell of the icosahedral cluster. Electron localization within the Cd-centered icosahedron is not as evident as in the Tl-centered thallium icosahedral clusters described elsewhere; actually, cadmium is found to bridge icosahedra within a more three-dimensional network than sodium by forming bonds that are mainly covalent. The compound is a semiconducting Zintl phase with closed shell bonding.