Open-Framework Iron Fluoride Phosphates Based on Chain, Trinuclear, and Tetranuclear Chain Fe-III Building Units: Crystal Structures and Magnetic Properties

We report the synthesis and characterization of a series of new openframework iron fluoride-fluorophosphates based on linear, trinuclear, and tetranuclear chain Fe-III building units. KFe2(PO3F)(2)F-3 (I) consists of {Fe-2(O3F)(2)F-2}(10-) zigzag chains interconnected by P(O/F)(4) tetrahedra forming a three-dimensional (3D) open framework. K2Fe(PO2.5F1.5)(2)F-2 (II) is built up by {Fe(PO2.5F1.5)(2)F-2}(2-) chains separated by K+ cation layers. The framework for K3Fe3(PO4)(PO3F)(2)F-5 (III) contains two-dimensional {Fe3O4F4(PO3F)(2)}(2-) sheets, which are built from trimeric Fe-octahedra insulated by PO3F tetrahedra. The macroanionic framework of K3Fe4(PO4)(2)F-9 (IV) comprises linear {Fe4O8F9}(10-) chains consisting of tetranuclear magnetic clusters of [Fe4O8F9]10- formed via corner-sharing fluorine atoms decorated with PO4 groups. The magnetic characterization of three iron fluorophosphates reveals diversified magnetism: S = 5/2 spin chains for I, antiferromagnetically coupled triangular Fe units for III, and coupled tetrahedral S = 5/2 spin chains for IV. IV shows strong geometric frustration thanks to its spin motifs of corner-shared tetrahedral clusters.