Two cobalt monophosphonates: Syntheses, structures and magnetic properties

Hydrolysis of diethyl 6-chloro-2-pyridinephosphonate in HCl solution affords 6-hydroxy-2-pyridinephosphonic acid (H2hppa 1). In the structure, extensive hydrogen bonding interactions link the phosphonic acid molecules into a two-dimensional network. Reactions of H2hppa and cobalt acetate under hydrothermal conditions result in a new cobalt phosphonate Co(hppa)(H2O) (2). Compound 2 shows a layer structure, in which {Co2O2} dimers are connected through the corner-sharing of {CoO5N} octahedra and {PO3C} tetrahedra, forming an inorganic double-layer. Introduction of a second ligand (1,4-bis(imidazol-1-ylmethyl)benzene, L) in the reaction system, compound [Co(hppa)(L)0.5(H2O)]·H2O (3) was obtained. In this structure, Co2+ ions are bridged by O–P–O bridges into an inorganic layer and the layers are pillared up by 1,4-bis(imidazol-1-ylmethyl)benzene. Magnetic study suggests that the existence of weak ferromagnetic coupling between Co2+ ions in the {Co2O2} unit for 2. For compound 3, O–P–O bridges mediate very weak antiferromagnetic interactions.