Neue Suboxid-Cluster [O5Ba18] in den Kristallstrukturen von Ba21M2O5 (M = Si, Ge)

La26Ge19M5O5 (M = Ag, Cu): Rare-Earth Metal Suboxide Superconductors with [La18O5] Cluster Units

Herein we report two reduced rare-earth metal-based superconductors, La₂₆Ge₁₉M₅O₅ (M = Ag, Cu), that feature an unprecedented [La₁₈O₅] cluster composed of five oxygen-centered [La₆O] octahedra condensed through shared faces and capped with [Ge₄] butterfly rings. The structure, determined by single-crystal X-ray diffraction, crystallizes in a tetragonal space group (P4/nmm), with a = 15.508(2) Å and c = 11.238(2) Å. Resistivity and magnetic susceptibility measurements show onsets of superconductivity at T_c = 5.4 and 6.4 K for the Ag and Cu compounds, respectively. Applying high pressures, up to 1.3 GPa, results in increased superconducting transition temperatures (T_c = 6.8 K for Ag and 7.2 K for Cu compounds), with no sign of saturation.

Remarkable rare-earth metal silicide oxides with planar Si6 rings

New rare-earth silicide oxides, La10Si8O3 (1) and Ce10Si8O3 (2), were synthesized through high-temperature reactions of the pure elements under controlled oxygen atmosphere conditions. The remarkable silicides crystallize in a unique crystal structure (space group P6/mmm; a = 10.975(3) A (La) and 10.844(1) A (Ce); c = 4.680(1) A (La) and 4.561(1) A (Ce)) that features a 3-D framework of corner-shared O-centered (La/Ce)6 octahedra, reminiscent of hexagonal tungsten bronzes, with planar Si6 rings enclosed within its hexagonal channels. Band structure calculations indicate the compounds are metallic, with optimized La-Si bonds, and a benzene-like [Si6]6- anion. Compound 1 exhibits temperature independent paramagnetism. Compound 2 exhibits Curie-Weiss paramagnetism, and an antiferromagnetic ordering below 7 K.