Metal–organic frameworks based on the pyridine-2,3-dicarboxylate and a flexible bispyridyl ligand: syntheses, structures, and photoluminescence

Abstract

Three new metal–organic coordination polymers, [Cu(2,3-pydc)(bpp)]·2.5H₂O (1), [Zn(2,3-pydc)(bpp)]·2.5H₂O (2) and [Cd(2,3-pydc)(bpp)(H₂O)]·3H₂O (3) (2,3-pydcH₂ = pyridine-2,3-dicarboxylic acid, bpp = 1,3-bis(4-pyridyl)propane), have been synthesized at room temperature. All complexes have metal ions serving as 4-connected nodes but represent two quite different structural motifs. Complexes 1 and 2 are isomorphous, both of which feature 2D → 3D parallel interpenetration. Each two-dimensional (2D) layer with (4, 4) topology is interlocked by two nearest neighbours, one above and one below, thus leading to an unusual 3D motif. Complex 3 has a non-interpenetrating 3D CdSO₄ framework with cavities occupied by uncoordinated water molecules. The compounds have been characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis and X-ray crystallography. The photoluminescent studies of 2 and 3 show that both complexes exhibit intense fluorescent emissions at room temperature.