Crystal structure and physical properties of a new CuTi2S4 modification in comparison to the thiospinel

A new modification of CuTi(2)S(4) was prepared from the elements at 425 degrees C. It crystallizes in the rhombohedral space group Rm, with lattice parameters of a = 7.0242(4) A, c = 34.834(4) A, and V = 1488.4(2) A(3) (Z = 12). Two topologically different interlayer regions exist between the close-packed S layers that alternate along the c axis: one comprises both Cu (in tetrahedral voids) and Ti atoms (in octahedral voids), and the second exclusively Ti atoms (again in octahedral voids). In contrast to the known modification, the spinel, Cu-Ti interactions of 2.88 A occur that have bonding character according to the electronic structure calculations. Both CuTi(2)S(4) modifications are metallic Pauli paramagnets due to Ti d contributions. The Pauli susceptibility of the Rm form is larger than that of the thiospinel in quantitative agreement with the LMTO-ASA band structure calculations. The irreversible transformation to the spinel takes place at temperatures above 450 degrees C.     

HfMoSb4, the first nonmetallic early transition metal antimonide

HfMoSb4, isostructural with the isoelectronic NbSb2, exhibits nonmetallic properties, as predicted via electronic structure calculations made before the actual discovery of HfMoSb4.     

Die Seltenerdmetallpolyselenide Gd8Se15, Tb8Se15−x,Dy8Se15−x,Ho8Se15−x,Er8Se15−x und Y8Se15−x (0 < x ≤ 0.3) – Zunehmende Fehlordnung in ausgedünnten,planaren Selenschichten

The Rare Earth Metal Polyselenides Gd₈Se₁₅, Tb₈Se_15?x, Dy₈Se_15?x, Ho₈Se_15?x, Er₈Se_15?x, and Y₈Se_15?x – Increasing Disorder in Defective Planar Selenium Layers Single crystals of the rare earth metal polyselenides Gd₈Se₁₅, Tb₈Se_15?x, Dy₈Se_15?x, Ho₈Se_15?x, Er₈Se_15?x, and Y₈Se_15?x (0 < x ≤ 0.3) have been prepared by chemical transport reactions (1120 K→ 970 K, 14 days, I₂ as carrier) starting from pre‐annealed powders of nominal compositions between LnSe₂ and LnSe_1.9. The isostructural title compounds adopt a 3 × 4 × 2 superstructure of the ZrSSi type and can be described in space group Amm2 with lattice parameters of a = 12.161(1) Å, b = 16.212(2) Å and c = 16.631(2) Å (Gd₈Se₁₅), a = 12.094(2) Å, b = 16.123(2) Å and c = 16.550(2) Å (Tb₈Se_15?x), a = 12.036(2) Å, b = 16.060(2) Å and c = 16.475(2) Å (Dy₈Se_15?x), a = 11.993(2) Å, b = 15.999(2) Å and c = 16.471(2) Å (Ho₈Se_15?x), a = 11.908(2) Å, b = 15.921(2) Å and c = 16.428(2) Å (Er₈Se_15?x), and a = 12.045(2) Å, b = 16.072(3) Å and c = 16.626(3) Å (Y₈Se_15?x), respectively. The structure consists of puckered [LnSe] double slabs and planar Se layers alternating along [001]. The planar Se layers contain a disordered arrangement of dimers, Se^2? and vacancies. All compounds are semiconducting and contain trivalent rare earth metals (Ln³⁺).     

Crystal structure predictions: the crystal and electronic structure of Zr1−δV1+δAs

Zr_1−δV_1+δAs is accessible via arc-melting of different mixtures of ZrAs, VAs, Zr, and V. It crystallizes in the tetragonal La₂Sb type, with a phase range of −0.43(4)?δ?0.15(1). The lattice dimensions (a=382.4(1) pm, c=1486.8(6) pm for Zr_1.43(4)V_0.57As; and a=375.77(7) pm, c=1400.2(3) pm for Zr_0.85(1)V_1.15As) strongly depend on δ because of the different sizes of the Zr and V atoms. The ZrVAs structure comprises sheets of (empty) M₆ octahedra, whose triangular faces are capped by the main group atoms Q. The sheets are interconnected via M−Q bonds to a truly three-dimensional structure. Like in the isostructural ZrTiAs, the smaller 3d M atom prefers the site in the densely packed square planes. In addition to the dominating M−As bonds, the structure comprises strong M−M bonding. Independent of the exact Zr:V ratio, Zr_1−δV_1+δAs is calculated to have three-dimensional metallic properties.     

Crystal and Electronic Structures of the New Carbomolybdates(III), RE2[Mo2C3] with RE = Ce,Sm, Tb,and Dy

Four new ternary carbometalates of the general formula RE₂[Mo₂C₃] with RE = Ce, Sm, Tb and Dy have been prepared by a high temperature synthesis route. The Ce, Tb and Dy compounds crystallize isotypic to Er₂[Mo₂C₃], Sm₂[Mo₂C₃], however, is an isotype of Ho₂[Cr₂C₃]. The crystal structures comprise polyanionic layers [(Mo₂C₃)^6?] with the rare‐earth metal ions in between. The layers are constructed by edge and vertex connected MoC₄ tetrahedra, which display strong covalent Mo–C bonds. The compounds show metallic behaviour close to the classical limit of 100 μΩ cm for metallic conductors. The magnetic properties are quite different, however they are consistent with the presence of trivalent RE³⁺ ions with the exception of Ce₂[Mo₂C₃], which contains nonmagnetic Ce species. Electronic structure calculations reveal that the additional electron mainly populates the Ce partial structure. The title compounds extend the series of known carbomolybdates RE₂[Mo₂C₃]. The late lanthanides Gd, Tb, Dy, Ho, Er, Tm, and Lu with comparatively small RE³⁺ ions and Ce as Ce⁴⁺ adopt the Er₂[Mo₂C₃] structure type, whereas the early lanthanides Sm and Pr with larger RE³⁺ ions crystallize in the structure types of Ho₂[Cr₂C₃] and Pr₂[Mo₂C₃], respectively.     

Ternary rare earth and actinoid transition metal carbides viewed as carbometalates

Ternary carbides A_xT_yC_z (A=rare earth metals and actinoids; T=transition metals) with monoatomic species C⁴⁻ as structural entities are classified according to the criteria (i) metal to carbon ratio, (ii) coordination number of the transition metal by carbon atoms, and (iii) the dimensionality of the anionic network [T_yC_z]ⁿ⁻. Two groups are clearly distinguishable, depending on the metal to carbon ratio. Those where this ratio is equal to or smaller than 2 may be viewed as carbometalates, thus extending the sequence of complex anions from fluoro-, oxo-, and nitridometalates to carbometalates. The second group, metal-rich carbides with metal to carbon ratios equal to or larger than 4 is better viewed as typical intermetallics (“interstitial carbides”). The chemical bonding properties have been investigated by analyzing the Crystal Orbital Hamilton Population (COHP). The chemical bonding situation with respect to individual T-C bonds is similar in both classes. The main difference is the larger number of metal-metal bonds in the crystal structures of the metal-rich carbides.