Hydrothermal synthesis, structures, and luminescent properties of zinc(ii) and cadmium(ii) phosphonates with a 3D framework structure using terephthalate as second linkers

Abstract

By introduction of 1,4-benzenedicarboxylic acid as a second organic ligand, two new divalent metal(II) phosphonates with a 3D framework structure, namely, [Zn(HL1)(bdc)_0.5] (1) and [Cd_1.5(HL2)(bdc)_0.5] (2) (H₂L1 = H₂O₃PCH(NH₂)C₆H₅, H₃L2 = H₂O₃PCH₂–NC₅H₉–COOH, H₂bdc = HOOCC₆H₄COOH), have been synthesized under hydrothermal conditions. The two compounds show three-dimensional (3D) framework structure with infinite two-dimensional (2D) networks pillared by H₂bdc. For compound 1, the {ZnO₄} polyhedra are interconnected by phosphonate groups into a 2D layer, and the adjacent layers are further cross-linked via the bdc²⁻ anions to generate a three-dimensional framework structure with two types of channel system along the c-axis. A notable feature of compound 1 is the presence of alternate left- and right-handed helical chains in the structure. In compound 2, the inorganic chains, composed of {Cd(1)O₇}, {Cd(2)O₄} and {CPO₃} polyhedra, are linked by HL2²⁻ ligands to form a double layer structure in the ab plane, and the adjacent layers are further linked by the bdc²⁻ anions to form a 3D framework structure with one-dimensional channel systems along the a-axis. Luminescence properties of compounds 1 and 2 have also been studied.