Metamagnetism in Cobalt Phosphates with Pillared Layer Structures:  [Co3(pyz)(HPO4)2F2] and [Co3(4,4‘-bpy)(HPO4)2F2]·xH2O

Two new cobalt phosphates, [Co3(pyz)(HPO4)2F2] (1) and [Co3(4,4‘-bpy)(HPO4)2F2]·xH2O (x ≈ 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) Å, b = 7.370(1) Å, c = 7.395(1) Å, β = 103.753(3)°, and Z = 4. Crystal data for 2 are the same as those for 1 except a = 29.940(2) Å, b = 7.4421(5) Å, c = 7.4170(5) Å, and β = 93.444(1)°.