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

Abstract

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: (NH4)2Fe2(HPO4)­(PO4)­Cl2F (1) and K2Fe2(HPO4)­(PO4)­Cl2F (2) exhibit similar composition and closely related structural features. Both structures consist of {Fe2(HPO4)­(PO4)­Cl2F}2– macroanions and charge balancing ammonium or potassium cations. Their open framework structure contains layers and chains of corner-linked {Fe(1)­O2Cl4} and {Fe(2)­F2O4} octahedra, respectively, interconnected by PO4 tetrahedra forming 10-ring channels. KFe­(PO3F)­F2 (3) is built up by {Fe­[(PO3F)4/3F2/2]}­{Fe­(PO3F)2/3F2/2F2} layers separated by K+ cations. Chains of alternating {FeF2O4} and {FeO2F4} octahedra, which are linear for 1 but undulated for 2, are linked to each other via corner-sharing {PO3F} 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. 1 reveals a strong ground state spin anisotropy with a spin 5/2 state and a magnetic moment of 5.3 μB/Fe3+. Specific heat and magnetic data unveil three magnetic transitions at 95, 50, and 3.6 K. Compound 2 has a very similar crystal structure as compared to 1 but exhibits a different magnetic behavior: a slightly lower magnetic moment of 4.7 μB/Fe3+ and a magnetic transition to a canted antiferromagnetic state below 90 K. Compound 3 exhibits typical paramagnetic behavior close to room-temperature (5.71 μB/Fe3+). 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.

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

“…In contrast, the bridging F position has no active metals as possible electron donors leading to the shortening of the bond lengths being comparable to similar bonds in other iron fluorophosphates. 27 The LiO 4 tetrahedra are quite irregular with a relatively large spread in interatomic distances, ( d Li–O = 1.93–2.16(2) Å). P–O and P–F distances in the corresponding fluorophosphates tetrahedra are in the ranges 1.467–1.525(5) and 1.523–1.580(6) Å, respectively.…”

“…Crystalline samples of all compounds could be yielded via an ionothermal synthesis approach in which ILs were used as a solvent, structuredirecting agent, and mineralizer supporting crystal growth. 7,25,27,42 Single crystal X-ray diffraction (SCXRD) analyses reveal that NaFe(PO 3 F) 2 (1a) crystallizes orthorhombically (SG Fdd2, a = 9.728(1) Å, b = 42.246(5) Å, c = 8.506(1) Å, V = 3495.4(8) Å 3 , and Z = 24) and is a polymorphic modification of the previously reported monoclinic analogue (1b). 4 3 The crystal structure of NaFe(PO 3 F) 2 (1a) is built up of distorted FeO 6 octahedra and PO 3 F tetrahedra.…”

“… 7 , 23 − 25 Iron phosphates can form porous structures 26 and a variety of such frameworks have been obtained in the laboratory by the hydrothermal approach. 27 − 32 The obtained porous materials are particularly interesting due to their magnetism. For that reason, they have been investigated as magnetic sensors or magnetic separation media.…”

Tin(II)-Induced Large Birefringence Enhancement in Metal Phosphates

“…All of the peaks between 900 and 1300 cm –1 are attributed to the symmetric stretching vibration of O–P–O, and the peaks at around 400–630 cm –1 may correspond to the fundamental frequency of the PO 4 tetrahedral groups . In Rb­[SnF­(HPO 4 )], the peak at 457 cm –1 is the infrared absorption peak of Sn–F, and the broad peaks at 1610, 2347, and 2738 cm –1 are attributed to the bending and stretching vibrations of hydroxy groups. − In Rb­[SnF­(HPO 4 )], hydrogen atoms associate with PO 4 groups to form HPO 4 groups, and hydrogen bonds are formed between adjacent HPO 4 groups. The formation of hydrogen bonds affects the polarization of PO 4 and causes the absorption peak to become wider.…”

Developing design tools for introducing and tuning structural order in ionic liquids

“…[11][12][13][14][15] They lead to the formation of supramolecular structures, which can be beneficially used in the designed synthesis of new materials. For example, they can be used for templating open-framework materials, 16 to allow the morphological control of nanoparticles 17 and even for phase control of polymorphic materials. 18 These effects rely both on the interaction of the IL ions with each other, leading to the formation of a highly structured solvent where clear segregation of domains occurs, 19,20 but also on the interaction of the IL ions with the solutes and nuclei of materials formed in them during synthesis.…”