Ionothermal synthesis of open-framework metal phosphates with a Kagomé lattice network exhibiting canted anti-ferromagnetism

Four open-framework transition-metal phosphates; (NH(4))(2)Co(3)(HPO(4))(2)F(4) (1), (NH(4))Co(3)(HPO(4))(2)(H(2)PO(4))F(2) (2), KCo(3)(HPO(4))(2)(H(2)PO(4))F(2) (3), and KFe(3)(HPO(4))(2)(H(2)PO(4))F(2) (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 MO(3)F(3)/MO(4)F(2) octahedra. PO(3)OH pseudo-tetrahedral groups augment the [M(3)O(6)F(4)] (1)/[M(3)O(8)F(2)] layers on both sides to give M(3)(HPO(4))(2)F(4) (1) and M(3)(HPO(4))(2)F(2) (2–4) layers. These layers are stacked along the a axis in a sequence AA…, resulting in the formation of a layer structure for (NH(4))(2)Co(3)(HPO(4))(2)F(4)(1). In NH(4)Co(3)(HPO(4))(2)(H(2)PO(4))F(2) and KM(3)(HPO(4))(2)(H(2)PO(4))F(2), the M(3)(HPO(4))(2)F(2) layers are stacked along the a axis in a sequence AA(i)… and are connected by [PO(3)(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(+)/NH(4) (+) 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 (T (c) = 10 or 13 K for Co and T (c) = 27 K for Fe) with different canting angles. The full orbital moment is observed for both Co(2+) and Fe(2+).