Three new fluoride phosphates and fluorophosphates Ba3Fe(PO4)F6, Ba3Ga(PO3.5F0.5)O0.5F5.5 and Ba3Fe(PO3F)F7: Combinations of varied building blocks and two-dimensional [Ba3F2]4+ layers derived from fluorine-centred tetrahedra

Three new fluoride phosphates and fluorophosphates, Ba 3 Fe(PO 4 )F 6 , Ba 3 Ga(PO 3.5 F 0.5 )O 0.5 F 5.5 and Ba 3 Fe(PO 3 F)F 7 , have been synthesized through fluoride-rich hydrothermal reactions . Isostructural Ba 3 Fe(PO 4 )F 6 and Ba 3 Ga(PO 3.5 F 0.5 )O 0.5 F 5.5 revealed a three-dimensional structure comprised of [M(PO 4-x )F 4 ] 4−x chains and two-dimensional [Ba 3 F 2-x O x ] 4+x layers [M ​= ​Fe,Ga; x  ​= ​0,0.5], while Ba 3 Fe(PO 3 F)F 7 contained distorted two-dimensional [Ba 3 F 2 ] 4+ layers and [Fe(PO 3 F)F 5 ] 4- dimers. Two-dimensional [Ba 3 F 2 ] 4+ layers are formed by fluorine-centred tetrahedra. Close examinations of bond length and bond strength in fluorine-centred tetrahedron complexes suggested that fluorine-centred tetrahedra are indeed reasonable structural subunits.