Zhen-Chao Dong

A8Tl11 (A = K, Rb, or Cs) phases with hypoelectronic Tl117− cluster anions: Syntheses, structure, bonding, and properties

The title compounds, which are synthesized from be elements, are shown to be isostructural with K8In11 (R3¯c Z=6) and to contain pentacapped trigonal prismatic clusters that have been compressed along the three-fold axes so as to bring the two types of capping atoms within bonding distances. These are arranged in double-ccp layers separated by double alkali--metal layers. Extended Hückel calculations show a substantial energy gap and the end of significant intracluster bonding for the hypoelectronic (by Wades rules) 18-electron Tl117−. Correspondingly, all three compounds are metallic (ρ298 ≈ 400 μΩ · cm) and Pauli-paramagnetic (χM ≈ 4 x 10−4 emu. mol−1, consistent with their formulation as metallic (A+)8Tl117− e− phases. Factors thought to be responsible for the cluster distortion, the metallic salt characteristics, and the unusual chemistry of thallium am noted.

Synthesis, structures and properties of cubic R3In and R3InZ phases (R = Y, La; Z = B, C, N, O): The effect of interstitial Z on the superconductivity of La3In

Abstract Samples of La3In, Y3InCx and La3InZx for 0.3 ⩽ x ⩽ 1.5 , Z = C and O, La3InBx for 0.7 ⩽ x ⩽ 1.5, and La3InN were synthesized in welded Ta containers by powder sintering, fusion and annealing techniques. Y3In and La3Ga could not be obtained. All of the R3InZx examples were single phase between x ≈ 0.3–0.5 and x ≈ 1.0 and had the inverse perovskite structure (stuffed Cu3Au). Single crystal refinements for Y3InC and La3InN confirmed the type and stoichiometry (Pm¯3m, a = 4.9023(7)A˚, 5.102(1)A˚, and R(F)/Rw = 1.1/1.3%, 2.2/2.4% respectively). Magnetic susceptibilities measured for both normal and superconducting states showed Tc ≈ 10K and 104χRT ≈ 4 emu mol−1 were retained through the B and O series, with some enhancement of density and supercurrent shielding for B and a reduction of both for O. The absence of superconductivity (greater than 2 K) for Y3InC, La3InC and La3InN parallels their 104χRT values of less than or equal to 2 emu mol−1; the temperature dependencies of χ for these were also notably less than for the superconductors. These last phases are also more brittle. Extended Hu¨ckel band calculations indicated appreciable In and B (La In and La B) contributions at EF for La3InB. Thereafter, the La Z bonding states rapidly fall in energy as does the amount of La In bonding at EF, the last returning somewhat with the electron-richest oxygen interstitial. The decrease in Tc with increasing x in La3InCx parallels a decrease in densities-of-states at EF.