Synthesis, Crystal Structures, and Surface Photovoltage and Molecular Recognition Properties of Three Novel Metal Carboxyphosphonates with a 3D Pillared-Layered Structure

Three novel metal carboxyphosphonates with a 3D pillared-layered structure, namely, [Mn­(HL)] (<b>1</b>), [Co­(HL)]·H₂O (<b>2</b>), and [Cd₃(L₂)­(H₂O)₃] (<b>3</b>), (H₃L = 4-HOOCC₆H₄CH₂NHCH₂PO₃H₂), have been hydrothermally synthesized. Compounds <b>1</b>–<b>3</b> all feature three-dimensional (3D) framework structures with two-dimensional (2D) inorganic layers pillared by H₃L. In compounds <b>1</b> and <b>2</b>, each {MO₄} (M = Mn, Co) tetrahedron is linked via corner-sharing by three {CPO₃} tetrahedra to form a two-dimensional (2D) inorganic layer. The adjacent layers are further pillared by the organic backbone {−C₆H₄CH₂NHCH₂−} of the carboxyphosphonate ligand, generating a 3D pillared-layered structure. For compound <b>3</b>, interconnection of {Cd(1)­O₅N}, {Cd(2)­O₅N}, and {CPO₃} polyhedra via edge- and corner-sharing forms a two-dimensional (2D) inorganic layer. Such neighboring 2D inorganic layers are further cross-linked via the organic backbone {−C₆H₄CH₂NHCH₂−} of the carboxyphosphonate ligands and {Cd(3)­O₆} polyhedra, generating a 3D pillared-layered structure. Surface photovoltage properties of the compounds <b>1</b> and <b>2</b> have been studied. An interesting feature of compound <b>2</b> is the presence of dehydration/hydration properties. The molecular recognition properties of compound <b>3</b> in alkyl alcohol emulsions have also been studied