Two three-dimensional mixed-ligated cobalt phosphonate coordination polymers: syntheses, crystal structures and magnetic properties

Abstract Two new mixed-ligated cobalt phosphonates, Co5(pbtc)2(4,4’-bpy)2(H2O)4•2H2O (1) and Co4.5(pbtcH0.5)2(bpm)(H2O)6•4H2O (2) (pbtcH5 = 5-phosphonatophenyl-1,2,4-tricarboxylic acid, 4,4’-bpy = 4,4′-bipyridine and bpm = 2,2’-bipyrimidine), are obtained by incorporating 4,4′-bipyridine and 2,2’-bipyrimidine co-ligands, respectively. Compound 1 has infinite chains constructed by the alternative arrangement of Co3 trimers and Co2 dimers, which are connected by pbtc5− and 4,4’-bpy to form a three-dimensional framework structure. For compound 2, zigzag-like pentamers of Co are connected by pbtc5− and bpm ligands achieving a different type of three-dimensional framework structure. The lattice water molecules fill in the void space in the framework structures of both compounds. Magnetic measurements show that the antiferromagnetic interactions are dominated in compound 1, while the weak ferromagnetic exchange couplings are observed in compound 2.