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

Abstract

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.