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

The new lanthanum vanadium oxyselenides LaVSe₂O, La₅V₃Se₆O₇, La₅V₃Se₇O₅, La₇VSe₅O₇, and La₁₃V₇Se₁₆O₁₅ were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined using single-crystal and powder X-ray diffraction experiments. LaVSe₂O and La₅V₃Se₆O₇ adopt known structure types, whereas La₅V₃Se₇O₅, La₇VSe₅O₇, and La₁₃V₇Se₁₆O₁₅ crystallize in hitherto unknown structure types. The main building blocks of these compounds are chains of edge-sharing VSe₆, VSe₅O, and/or VSe₄O₂ octahedra, linked together by edge-sharing OLa₄ and/or OLa₃V tetrahedra forming fluorite-like ribbons. LaVSe₂O, La₅V₃Se₇O₅, and La₇VSe₅O₇ contain only V(iii) ions, whereby La₅V₃Se₆O₇ and La₁₃V₇Se₁₆O₁₅ 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 La₅V₃Se₆O₇, metamagnetism for La₅V₃Se₇O₅, ferromagnetism for La₇VSe₅O₇ and a complex magnetic structure for La₁₃V₇Se₁₆O₁₅.