Na ₅ VO(PO ₄ ) ₂ F as a representative of the Na ₅ <i>M</i> O _{1− <i>x</i>} (PO ₄ ) ₂ F _{1+ <i>x</i>} ( <i>M</i>  = Ti, V, Fe; <i>x</i>  = 0 or 1) family: synthesis, crystal structure and polytypism

Abstract A new sodium vanadyl phosphate fluoride, Na 5 VO(PO 4 ) 2 F, was isolated via hydrothermal synthesis. Its crystal structure was determined using single-crystal X-ray diffraction data and refined against F 2 to R  = 0.061. The compound crystallizes in the orthorhombic space group Pbca , with unit cell parameters a  = 11.7204(6), b  = 10.9986(4), c  = 13.6111(5) Å, V  = 1,754.58(13) Å 3 , Z  = 8. The crystal structure of Na 5 VO(PO 4 ) 2 F features layers of VO 5 F octahedra and PO 4 tetrahedra linked by their vertices. Sodium cations occupy the voids within and between the layers. Magnetically, Na 5 VO(PO 4 ) 2 F consists of isolated V 4+ ions with spin S  = 1/2 and exhibits paramagnetic behaviour down to 2 K. A family with the chemical formula Na 5 M O 1− x (PO 4 ) 2 F 1+ x ( M  = Ti, V, Fe; x  = 0 or 1) has been recognised and symmetry relation between its members are discussed.