Synthesis and characterization of the rare-earth vanadium oxyselenides Ln₇VO₄SE₈ (Ln = Nd, Sm, Gd)

The new compounds Ln₇VO₄Se₈ (Ln = Nd, Sm, Gd) were each prepared by heating V, Se, and the corresponding rare-earth sesquioxide at 1223 K in a sealed fused-silica tube. Single crystals have been grown through the use of an antimony flux. They have been characterized by single-crystal and powder X-ray diffraction measurements and by energy dispersive X-ray analysis. These isostructural compounds crystallize with two formula units in the orthorhombic space group Pbam in cells (at 153 K) of dimensions: Nd₇VO₄Se₈, a = 14.3419(9) Å, b = 15.5528(10) Å, c = 3.9948(3) Å; Sm₇VO₄Se₈, a = 14.200(2) Å, b = 15.451(2) Å, c = 3.9511(6) Å; Gd₇VO₄Se₈, a = 14.075(8) Å, b = 15.424(6) Å, c = 3.903(1) Å. The new structure type comprises four crystallographically independent Ln atoms with three different coordination geometries and one V atom in an octahedral environment. Magnetic measurements reveal that Gd₇VO₄Se₈ is paramagnetic down to 5 K. (C) 2000 Academic Press.