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

Four new compounds of A(VOF)(SeO) (A = Sr 1, Ba 2) and Ba(MOF)(TeO) (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 d-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 [VOF(SeO)] dimers which are further bridged by Sr or Ba cations. Isostructural compounds 3 and 4 are crystallized in the monoclinic crystal system with the space group of P2/c (no. 14). Their structures can be described as 2D [(MOF)(TeO)] (M = Mo, W) anionic layers separated by Ba cations. Out-of-center distortion studies show that the magnitude of the distortion of the (MOF) octahedron is comparable to that of MO (M = d transition metal). Infrared spectroscopy, thermal stability, optical property studies and theoretical calculations based on density functional theory methods were also performed.