New layered copper 1,3,5-benzenetriphosphonates pillared with N-donor ligands: their synthesis, crystal structures,...

The synthesis, crystal structures, and adsorption properties of a series of pillared layered copper phosphonates are reported herein. A hydrothermal reaction of copper oxide, 1,3,5-benzenetriphosphonic acid (BTP = H6bpt), and N-donor ligands with different lengths gives three new and one previously reported copper organophosphonates. X-ray crystal structural analyses revealed that compound 1, [Cu2(H4btp)2(pyr)] (pyr = pyrazine), forms a dense 3D network structure without open pores, and on the other hand, compounds 2-4, [Cu2(H2btp)(H2O)2(L)] (L = bipyridine for 2, 1,2-bis(4-pyridyl)ethylene for 3, and 1,3-bis(4-pyridyl)propane for 4), show topologically identical pillared layered frameworks with micropores. The framework structures are composed of copper phosphonate layers and N-donor ligands expanding the interlayer distances. Guest water molecules occupy the pores and are removable by drying treatment. Compounds 2-4 adsorb and desorb water vapor reversibly with structural transformation. Interestingly, compounds 2-4 adsorb ethanol vapor in spite of no adsorption of N2 molecules, indicating selective adsorption properties based not on the molecular size but on the molecular affinities to the surfaces.