Metamagnetism in cobalt phosphates with pillared layer structures:: [Co3(pyz)(HPO4)2F2] and [CO3(4,4′-bpy)(HPO4)2F2]•XH2O

Two new cobalt phosphates, [Co-3(pyz)(HPO4)(2)F-2] (1) and [Co-3(4,4'-bpy)(HPO4)(2)F-2].xH(2)O (x approximate to 0.7) (2), have been synthesized by hydrothermal methods in the presence of aromatic amines, and characterized by single-crystal X-ray diffraction and magnetic susceptibility. Their structures consist of neutral sheets of fluorinated cobalt phosphate which are pillared through pyrazine and 4,4'-bipyridine molecules to form 3D frameworks. The structures are related to that of the mineral lazulite. Both compounds show long-range antiferromagnetic ordering below 15 K and metamagnetic behaviors. Compound 1 reveals a two-step magnetic phase transition. Crystal data for 1: monoclinic, space group C2/c (No. 15), a = 21.809(4) Angstrom, b = 7.370(1) Angstrom, c = 7.395(1) Angstrom, beta = 103.753(3)degrees, and Z = 4. Crystal data for 2 are the same as those for 1 except a = 29.940(2) Angstrom, b = 7.4421(5) Angstrom, c = 7.4170(5) Angstrom, and beta = 93.444(1)degrees.