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The electronic structures of [(RuCp-(PPh3))2(mu2-(1,4-eta:3,6-eta)Te6)] and [(RuCp(PPh3))2-(mu2-(1,4-eta:3,6-eta)Te6].CH2Cl2 are analyzed with the use of first principles density functional theory. Bond order analysis indicates that the Te-Te bond where fusion occurs has a shared bonding charge of about 2/3 of that found for Te-Te single bonds.

Eleven new quaternary rare-earth tellurides, CsLnZnTe3 (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Y), were prepared from solid-state reactions at 1123 K. The isostructural materials crystalline in the layered KZCuS3 structure type in the orthorhombic space group Cmcm.

The use of direct method analysis and density functional theory (DFT) for the (001) crystal face of SrTio3 with the solution of a c(4x2) unit cell is mentioned. The surface is characterized by a single TiO2 overlayer in which Ti atoms are arranged into edge-shared truncated octahedra.

Research has been conducted on the isostructural RbLnSe (sub)2 compounds. These compounds has been synthesized via the reactive flux methods and their crystal structure, magnetic and optical properties have been studied and are discussed.

The structure, electrical, magnetic, and spectroscopic characteristics of the novel molecular metal tetrabenzoporphyrin iodide (H2(tbp)I) as well as that of nickeltetrabenzpoprphyrin (Ni(tbp)I) were described. Single-crystal reflectance spectroscopy, electrical conductivity, magnetic susceptibility, and electron paramagnetic resonance were utilized. Data revealed that H2(tbp)I and Ni(tbp)I have the same EPR values. The electrical conductivity as well as the Curie constant for Ni(tbp)I were higher than that of H2(tbp)I secondary to the crystal defects and organic impurities.

The preparations of seven new isostructural uranium chalcogenides AMU[Q.sub.3] compounds (where A = alkali metal, M = Cu or Ag, Q = S or Se) via solid-state reactions are reported. The compounds are found to be semiconductors with optical band gaps smaller than 0.73 eV and density-of-state analysis revealed the M-Q orbital to overlap in the valence band and U-Q orbital to overlap in the conduction band.

Research has been conducted on bismuth chalcogenides, AMBiS (sub)4 where A is rubidium and/or cesium and M is silicon and/or germanium. The syntheses and structures of these compounds have been carried our, and the results are reported.

Reports on the synthesis of the compounds RbLnSe[sub 2] by means of the reactive flux method. Crystallization of the isostructural compounds which have the alpha-NaFeO[sub 2]; Occupation of the distorted octahedral sites by the Rb and Ln atoms in alternating layers.

We report the solution of the c(4 × 2) reconstruction of SrTiO[sub 3] (001), obtained through a combination of high-resolution transmission electron microscopy, direct methods analysis, and density functional theory. The structure is characterized by a single overlayer of TiO[sub 2] stoichiometry in which TiO[sub 5] polyhedra are arranged into edge-shared structures, in contrast to the corner-shared TiO[sub 6] polyhedra in bulk. This structural pattern is similar to that reported by us earlier for the (2 × 1) reconstruction of the same crystal face formed at higher temperature. We discuss probable mechanisms of surface stabilization as revealed by these two solutions which are likely to apply to other reconstructions of SrTiO[sub 3] (001) and, possibly, other perovskites in general. [ABSTRACT FROM AUTHOR]

The article examines the use of Zn2(1,4-benzenedicarboxylate)2(1,4-diazabicyclo[2.2.2]octane) metal-organic frameworks (MOF-1) as an adsorbent for alkane separations. The authors simulated a multicomponent mixture in the C5-C7 range using grand canonical Monte Carlo. The absolute adsorption isotherms predicted for a 13-component alkane mixture in MOF-1 are presented.

The A(2)M(4)U(6)Q(17) compounds Rb(2)Pd(4)U(6)S(17), Rb(2)Pd(4)U(6)Se(17), Rb(2)Pt(4)U(6)Se(17), Cs(2)Pd(4)U(6)S(17), Cs(2)Pd(4)U(6)Se(17), and Cs(2)Pt(4)U(6)Se(17) were synthesized by the high-temperature solid-state reactions of U, M, and Q in a flux of ACl or Rb(2)S(3). These isostructural compounds crystallize in a new structure type, with two formula units in the tetragonal space group P4/mnc. This structure consists of a network of square-planar MQ(4), monocapped trigonal-prismatic UQ(7), and square-antiprismatic UQ(8) polyhedra with A atoms in the voids. Rb(2)Pd(4)U(6)S(17) is a typical semiconductor, as deduced from electrical resistivity measurements. Magnetic susceptibility and specific heat measurements on single crystals of Rb(2)Pd(4)U(6)S(17) show a phase transition at 13 K, the result either of antiferromagnetic ordering or of a structural phase transition. Periodic spin-polarized band structure calculations were performed on Rb(2)Pd(4)U(6)S(17) with the use of the first principles DFT program VASP. Magnetic calculations included spin-orbit coupling. With U f-f correlations taken into account within the GGA+U formalism in calculating partial densities of states, the compound is predicted to be a narrow-band semiconductor with the smallest indirect and direct band gaps being 0.79 and 0.91 eV, respectively.

Black single crystals of A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) have been synthesized by the reactive flux method. These isostructural compounds crystallize in the cubic space group Ia ̅3d at room temperature. The structure comprises a three-dimensional framework built from US(6) octahedra and CuS(3) trigonal planar units with A cations residing in the cavities. There are no S-S bonds in the structure. To elucidate the oxidation state of U in these compounds, various physical property measurements and characterization methods were carried out. Temperature-dependent electrical resistivity measurement on a single crystal of K(6)Cu(12)U(2)S(15) showed it to be a semiconductor. These three A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) compounds all exhibit small effective magnetic moments, < 0.58 μ(B)/U and band gaps of about 0.55(2) eV in their optical absorption spectra. From X-ray absorption near edge spectroscopy (XANES), the absorption edge of A(6)Cu(12)U(2)S(15) is very close to that of UO(3). Electronic band structure calculations at the density functional theory (DFT) level indicate a strong degree of covalency between U and S atoms, but theory was not conclusive about the formal oxidation state of U. All experimental data suggest that the A(6)Cu(12)U(2)S(15) family is best described as an intermediate U(5+)/U(6+) sulfide system of (A(+))(6)(Cu(+))(12)(U(5+))(2)(S(2-))(13)(S(-))(2) and (A(+))(6)(Cu(+))(12)(U(6+))(2)(S(2-))(15).

The seven new isostructural quaternary uranium chalcogenides KCuUS 3, RbCuUS 3, RbAgUS 3, CsCuUS 3, CsAgUS 3, RbAgUSe 3, and CsAgUSe 3 were prepared from solid-state reactions. These isostructural materials crystallize in the layered KZrCuS 3 structure type in the orthorhombic space group Cmcm. The structure is composed of UQ 6 octahedra and MQ 4 tetrahedra that share edges to form (2) infinity[UMQ 3 (-)] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing AQ 8 bicapped trigonal prisms. There are no Q-Q bonds in the structure, so the formal oxidation states of A/U/M/Q may be assigned as 1+/4+/1+/2-, respectively. CsCuUS 3 shows semiconducting behavior with thermal activation energy E a = 0.14 eV and sigma 298 = 0.3 S/cm. From single-crystal absorption measurements in the near IR range, the optical band gaps of these compounds are smaller than 0.73 eV. The more diffuse 5f electrons play a much more dominant role in the optical properties of the AMUQ 3 compounds than do the 4f electrons in the AMLnQ 3 compounds (Ln = rare earth). Periodic DFT spin band-structure calculations on CsCuUS 3 and CsAgUS 3 establish two energetically similar antiferromagnetic spin structures and show magnetic interactions within and between the layers of the structure. Density-of-states analysis shows M-Q orbital overlap in the valence band and U-Q orbital overlap in the conduction band.

Eleven new quaternary rare-earth tellurides, CsLnZnTe3 (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Y), were prepared from solid-state reactions at 1123 K. These isostructural materials crystallize in the layered KZrCuS3 structure type in the orthorhombic space group Cmcm. The structure is composed of LnTe6 octahedra and ZnTe4 tetrahedra that share edges to form [LnZnTe3] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing CsTe8 bicapped trigonal prisms. There are no Te-Te bonds in the structure of these CsLnZnTe3 compounds so the formal oxidation states of Cs/Ln/Zn/Te are 1+/3+/2+/2-. Optical band gaps of 2.13 eV for CsGdZnTe3 and 2.12 eV for CsTbZnTe3 were deduced from single-crystal optical absorption measurements. A first-principles calculation of the density of states and the frequency-dependent optical properties was performed on CsGdZnTe3. The calculated band gap of 2.1 eV is in good agreement with the experimental value. A quadratic fit for the lanthanide contraction of the Ln-Te distance is superior to a linear one if the closed-shell atom is included.

Four new compounds, RbSiBiS(4), RbGeBiS(4), CsSiBiS(4), and CsGeBiS(4), have been synthesized by means of the reactive flux method. The isostructural compounds RbSiBiS(4), RbGeBiS(4), and CsGeBiS(4) crystallize in space group P2(1)/c of the monoclinic system with four formula units in cells of dimensions at 153 K of a = 6.4714(4) A, b = 6.7999(4) A, c = 17.9058(11) A, and beta = 108.856(1) degrees for RbSiBiS(4), a = 6.5864(4) A, b = 6.8559(4) A, c = 17.9810(12) A, and beta = 109.075(1) degrees for RbGeBiS(4), and a = 6.5474(4) A, b = 6.9282(4) A, c = 18.8875(11) A, and beta = 110.173(1) degrees for CsGeBiS(4). CsSiBiS(4) crystallizes in a different structure type in space group P2(1)/c of the monoclinic system with four formula units in a cell of dimensions at 153 K of a = 9.3351(7) A, b = 6.9313(5) A, c = 12.8115(10) A, and beta = 109.096(1) degrees. The two structure types are closely related and consist of [MBiS(4)(-)] (M = Si, Ge) layers separated by bicapped trigonal-prismatically coordinated alkali-metal atoms. In each, the M atom is coordinated to a tetrahedron of four S atoms and the Bi atom is coordinated to seven S atoms comprising five close S atoms at the corners of a square pyramid with Bi near the center of the basal plane and the sixth and seventh S atoms further away to complete a distorted monocapped trigonal prism. The optical band gaps of 2.23 eV for RbGeBiS(4) and 2.28 eV for CsGeBiS(4) were deduced from their diffuse reflectance spectra. From a band structure calculation, the optical absorption for RbGeBiS(4) originates from the [GeBiS(4)(-)] layer. The Ge 4p orbitals, Bi 6p orbitals, and S 3p orbitals are highly hybridized.