A(VO 2 F)(SeO 3 ) (A = Sr, Ba) and Ba(MOF 2 )(TeO 4 ) (M = Mo, W): first examples of alkali-earth selenites/tellurites with a fluorinated d 0 -TM octahedron.

Four new compounds of A(VO2 F)(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 [V2 O4 F2 (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 (MOx F6-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.