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)] (1), [Co­(HL)]·H2O (2), and [Cd3(L2)­(H2O)3] (3), (H3L = 4-HOOCC6H4CH2NHCH2PO3H2), have been hydrothermally synthesized. Compounds 1–3 all feature three-dimensional (3D) framework structures with two-dimensional (2D) inorganic layers pillared by H3L. In compounds 1 and 2, 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 3, 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 1 and 2 have been studied. An interesting feature of compound 2 is the presence of dehydration/hydration properties. The molecular recognition properties of compound 3 in alkyl alcohol emulsions have also been studied.