Flux synthesis, crystal structures, and physical properties of new lanthanum vanadium oxyselenides.

The new lanthanum vanadium oxyselenides LaVSeO, LaVSeO, LaVSeO, LaVSeO, and LaVSeO were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined using single-crystal and powder X-ray diffraction experiments. LaVSeO and LaVSeO adopt known structure types, whereas LaVSeO, LaVSeO, and LaVSeO crystallize in hitherto unknown structure types. The main building blocks of these compounds are chains of edge-sharing VSe, VSeO, and/or VSeO octahedra, linked together by edge-sharing OLa and/or OLaV tetrahedra forming fluorite-like ribbons. LaVSeO, LaVSeO, and LaVSeO contain only V(iii) ions, whereby LaVSeO and LaVSeO contain mixtures of either V(iii)/V(iv) or V(iii)/V(v) cations. Magnetic measurements indicate Curie-Weiss paramagnetism and magnetic ordering of the vanadium moments at low temperatures. More precisely, we observe antiferromagnetism for LaVSeO, metamagnetism for LaVSeO, ferromagnetism for LaVSeO and a complex magnetic structure for LaVSeO.