Ionothermal synthesis of open-framework metal phosphates with a Kagomé lattice network exhibiting canted anti-ferromagnetism†Electronic supplementary information (ESI) available: Cif files, atomic parameters, X-ray diffraction patterns, IR spectra, TG curves, and thermal ellipsoid plot and atomic label schemes of compound 1-4. See DOI: 10.1039/c4tc00290cClick here for additional data file.

Guangmei Wang,Anja-Verena Mudring,Martin Valldor,Bert Mallick

doi:10.1039/c4tc00290c

Abstract

Four open-framework transition-metal phosphates; (NH4)2Co3(HPO4)2F4 (1), (NH4)Co3(HPO4)2(H2PO4)F2 (2), KCo3(HPO4)2(H2PO4)F2 (3), and KFe3(HPO4)2(H2PO4)F2 (4); are prepared by ionothermal synthesis using pyridinium hexafluorophosphate as the ionic liquid. Single-crystal X-ray diffraction analyses reveal that the four compounds contain cobalt/iron-oxygen/fluoride layers with Kagomé topology composed of interlinked face-sharing MO3F3/MO4F2 octahedra. PO3OH pseudo-tetrahedral groups augment the [M3O6F4] (1)/[M3O8F2] layers on both sides to give M3(HPO4)2F4 (1) and M3(HPO4)2F2 (2-4) layers. These layers are stacked along the a axis in a sequence AA…, resulting in the formation of a layer structure for (NH4)2Co3(HPO4)2F4(1). In NH4Co3(HPO4)2(H2PO4)F2 and KM3(HPO4)2(H2PO4)F2, the M3(HPO4)2F2 layers are stacked along the a axis in a sequence AA i … and are connected by [PO3(OH)] tetrahedra, giving rise to a 3-D open framework structure with 10-ring channels along the [001] direction. The negative charges of the inorganic framework are balanced by K+/NH4+ ions located within the channels. The magnetic transition metal cations themselves form layers with stair-case Kagomé topology. Magnetic susceptibility and magnetization measurements reveal that all four compounds exhibit a canted anti-ferromagnetic ground state (Tc = 10 or 13 K for Co and Tc = 27 K for Fe) with different canting angles. The full orbital moment is observed for both Co2+ and Fe2+.

Highlights

Inorganic open-framework materials such as molecular sieves are extensively used in many industrial processes such as heterogeneous catalysis, adsorption, ion-exchange, and separation,[1] and the preparation of new inorganic open-framework materials is one of the most vibrant elds in materials science
Successful syntheses of open-framework iron phosphates opened the way to a new family of open-framework materials that combine the well-known features of molecular sieves with magnetic properties
By comparing susceptibility data from eld cooled (FC) and zero- eld cooled (ZFC) samples it is obvious that all four compounds form magnetic domain structures, as from eld cooled (FC) results in a higher c than ZFC (Fig. 7)

Summary

Introduction

Inorganic open-framework materials such as molecular sieves are extensively used in many industrial processes such as heterogeneous catalysis, adsorption, ion-exchange, and separation,[1] and the preparation of new inorganic open-framework materials is one of the most vibrant elds in materials science. Transition metal compounds with Kagome topology, featuring two dimensional corner-sharing triangles have attracted signi cant interest because of their fascinating magnetic properties such as spin frustration, long-range antiferrimagnetism at low temperature and spin-canting.[13] Most investigations of Kagome topological materials have focussed on the jarosite family, AM3(SO4)2(OH)[6] (A 1⁄4 alkali metal ion, M 1⁄4 Fe3+, Cr3+, V3+), and its analogues.[14] To our knowledge, no cobalt and iron phosphates containing a Kagome lattice have been reported.

Results

Conclusion