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, Ba3Fe(PO4)F6, Ba3Ga(PO3.5F0.5)O0.5F5.5 and Ba3Fe(PO3F)F7, have been synthesized through fluoride-rich hydrothermal reactions. Isostructural Ba3Fe(PO4)F6 and Ba3Ga(PO3.5F0.5)O0.5F5.5 revealed a three-dimensional structure comprised of [M(PO4-x)F4]4−x chains and two-dimensional [Ba3F2-xOx]4+x layers [M ​= ​Fe,Ga; x ​= ​0,0.5], while Ba3Fe(PO3F)F7 contained distorted two-dimensional [Ba3F2]4+layers and [Fe(PO3F)F5]4- dimers. Two-dimensional [Ba3F2]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.