From a Dense Structure to Open Frameworks: The Structural Plethora of Alkali Metal Iron Fluorophosphates

[Image: see text] By employing the pyridinium hexafluorophosphate task-specific ionic liquids 1-butyl-4-methylpyridinium hexafluorophosphate ([C(4)mpyr][PF(6)]) and 1-ethylpyridinium hexafluorophosphate ([C(2)pyr][PF(6)]) as the reaction medium, mineralizer, structure-directing agent, and, in the case of the smaller pyridinium cation, even a structural component, it was possible to obtain five new alkali metal iron phosphates featuring interconnected FeX(6) octahedra and PX(4) (X = F, O, or OH) tetrahedra. NaFe(PO(3)F)(2) (1) is a dense 3D structure, RbFe(PO(3)F)(PO(2)(OH)F)(PO(2)(OH)(2)) (2) features 1D strands, (C(2)pyr)LiFe(PO(3)F)(3)(PO(2)F(2))F (3) has 2D layers, and LiFe(PO(3)F)(PO(2)F(2))F (4) as well as Cs(0.75)Fe(PO(2.75)(OH)(0.25)F)(PO(2)F(2))(2) (5) are 3D open frameworks. While in 1–2 as well as in 4 and 5, FeX(6) octahedra and PX(4) (X = F, O, or OH) tetrahedra alternate, 3 features octahedra dimers, Fe(2)X(11) (X = F, O, or OH). The magnetic behavior of all compounds is governed by antiferromagnetic interactions. Interestingly, 3 exhibits a broad maximum in the temperature dependence of the magnetic susceptibility, characteristic of a low-dimensional magnetic system consistent with the presence of Fe–Fe dimers in its crystal structure.