Ionothermal Synthesis, Structures, and Magnetism of Three New Open Framework Iron Halide-Phosphates.

A set of different open framework iron phosphates have been synthesized ionothermally using a task-specific ionic liquid, 1-butyl-4-methylpyridinium hexafluorophosphate, that acts in the synthesis as the reaction medium and mineralizer: (NH)Fe(HPO)(PO)ClF () and KFe(HPO)(PO)ClF () exhibit similar composition and closely related structural features. Both structures consist of {Fe(HPO)(PO)ClF} macroanions and charge balancing ammonium or potassium cations. Their open framework structure contains layers and chains of corner-linked {Fe(1)OCl} and {Fe(2)FO} octahedra, respectively, interconnected by PO tetrahedra forming 10-ring channels. KFe(POF)F () is built up by {Fe[(POF)F]}{Fe(POF)FF} layers separated by K cations. Chains of alternating {FeFO} and {FeOF} octahedra, which are linear for but undulated for , are linked to each other via corner-sharing {POF} tetrahedra with the fluorine pointing into the interlayer space. The compounds were characterized by means of single crystal and powder X-ray diffraction, infrared spectroscopy, and magnetic measurements. reveals a strong ground state spin anisotropy with a spin 5/2 state and a magnetic moment of 5.3 μ/Fe. Specific heat and magnetic data unveil three magnetic transitions at 95, 50, and 3.6 K. Compound has a very similar crystal structure as compared to but exhibits a different magnetic behavior: a slightly lower magnetic moment of 4.7 μ/Fe and a magnetic transition to a canted antiferromagnetic state below 90 K. Compound exhibits typical paramagnetic behavior close to room-temperature (5.71 μ/Fe). There are no clear indications for a phase transition down to 2 K despite strong antiferromagnetic spin-spin interactions; only a magnetic anomaly appears at 50 K in the zero-field cooled data.