Fabrication of new structures from a 3D cobalt phosphonate network: structural transformation and proton conductivity investigation

Abstract

Three cobalt-phosphonate networks with unique constructions, namely, [[Co₂(2,2′-bipy)₂(H₄L)(H₂O)₆]·6H₂O] (1), [Co₂(2,2′-bipy)₂(H₄L)(H₂O)₃] (2) and [Co₂(2,2′-bipy)₂(H₄L)(H₂O)₂]·H₂O (3), were successfully prepared from a 3D cobalt phosphonate network (Co318) utilizing a tetrahedral tetraphosphonic acid ligand. Compound 1 with a zero-dimensional structure was obtained by humidity stimulation of Co318 at room temperature. Furthermore, doubling the amount of 2,2-bipyridine in the reaction system of Co318 leads to a pink compound (2) and a purple compound (3). The structures of these three compounds were confirmed by single-crystal X-ray diffraction and characterized by PXRD, TGA, and IR spectroscopy. The structural transformations of these four compounds were investigated. The proton conductivities of compound 1, 2 and 3 were measured and the results proved that compound 1 displays a higher proton conductivity ability than the other two compounds.