A novel cobalt sodium phosphate hydroxide with the ellenbergerite topology: crystal structure and physical properties
The novel phase Na2−xCo6(OH)3[HPO4][Hx/3PO4]3 (x ≈ 1.1) was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data and refined against F2 to R = 0.052, including positions of all hydrogen atoms. The compound crystallizes in the hexagonal space group P63mc, with unit-cell parameters a = 12.630(3) Å, c = 5.017(1) Å, V = 693.1(3) Å3, and Z = 2. The crystal structure is based on a 3D framework built from CoO6 octahedra and PO4 tetrahedra. Channels in the  direction accommodate columns of Na-centered octahedra sharing faces. The compound is a new structural representative of the topology shown by aluminosilicate mineral ellenbergerite and its numerous natural and synthetic varieties. Magnetic susceptibility measurements revealed a strong antiferromagnetic interaction and magnetic transition to low temperature spin-canted phase at TN = 44 K. The physical properties of the title compound are found to be very similar to those of the structurally related arsenate Co1−xCo6(OH)3[H2x/3AsO4]3[HAsO4] and vanadate Co7(OH)2(H2O)[VO4]4.