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 open-framework iron fluoride-fluorophosphates based on linear, trinuclear, and tetranuclear chain Fe III building units. KFe 2 (PO 3 F) 2 F 3 ( I ) consists of {Fe 2 (O 3 F) 2 F 2 } 10- zigzag chains interconnected by P(O/F) 4 tetrahedra forming a three-dimensional (3D) open framework. K 2 Fe(PO 2.5 F 1.5 ) 2 F 2 ( II ) is built up by {Fe(PO 2.5 F 1.5 ) 2 F 2 } 2- chains separated by K + cation layers. The framework for K 3 Fe 3 (PO 4 )(PO 3 F) 2 F 5 ( III ) contains two-dimensional {Fe 3 O 4 F 4 (PO 3 F) 2 } 2- sheets, which are built from trimeric Fe-octahedra insulated by PO 3 F tetrahedra. The macroanionic framework of K 3 Fe 4 (PO 4 ) 2 F 9 ( IV ) comprises linear {Fe 4 O 8 F 9 } 10- chains consisting of tetranuclear magnetic clusters of [Fe 4 O 8 F 9] 10- formed via corner-sharing fluorine atoms decorated with PO 4 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.