A(VO2F)(SeO3) (A = Sr, Ba) and Ba(MOF2)(TeO4) (M = Mo, W): first examples of alkali-earth selenites/tellurites with a fluorinated d0-TM octahedron

Abstract

Four new compounds of A(VO₂F)(SeO₃) (A = Sr 1, Ba 2) and Ba(MOF₂)(TeO₄) (M = Mo 3, W 4) oxyfluorides have been synthesized successfully by hydrothermal reactions. They represent the first examples of alkali-earth selenites or tellurites with a fluorinated d⁰-TM octahedron. Their crystal structures were determined by single-crystal X-ray diffraction. They exhibit two different types of structures. Compounds 1 and 2 are isostructural and crystallize in the orthorhombic crystal system with the space group of Pbca (no. 61). Their structures feature a 3D network composed of 0D [V₂O₄F₂(SeO₃)₂]⁴⁻ dimers which are further bridged by Sr²⁺ or Ba²⁺ cations. Isostructural compounds 3 and 4 are crystallized in the monoclinic crystal system with the space group of P2₁/c (no. 14). Their structures can be described as 2D [(MOF₂)(TeO₄)]²⁻ (M = Mo, W) anionic layers separated by Ba²⁺ cations. Out-of-center distortion studies show that the magnitude of the distortion of the (MO_xF_6−x) octahedron is comparable to that of MO₆ (M = d⁰ transition metal). Infrared spectroscopy, thermal stability, optical property studies and theoretical calculations based on density functional theory methods were also performed.