Four novel Zn(II)/Cd(II) metal–organic frameworks constructed from 4′-(4-pyridyl)-4,2′:6′,4″-terpyridine: hydrothermal synthesis, crystal structures, and luminescent properties

Abstract

Four novel polymeric frameworks, [Zn(pytpy)Cl₂]_n (1), [Zn₂(pytpy)₂(ox)₂]_n·n(H₂O) (2), [Cd(pytpy)(mal)]_n·n(H₂O) (3) and [Zn₂(pytpy)(btc)(OH)]_n (4), (pytpy = 4′-(4-pyridyl)-4,2′:6′,4″-terpyridine, H₂ox = oxalic acid, H₂mal = malic acid and H₃btc = 1,3,5-benzenetricarboxylic acid) have been hydrothermally synthesized and structurally characterized. Compound 1 shows infinite helical chains, which are extended into a 3D supramolecular network by intermolecular hydrogen bonds. In the structure of 2, there is coexistence of left- and right-handed helical chains arranged alternately to generate a 2D layer. In 3, an in-situ reaction occurred, maleic acid was converted to malate by the hydroxylation of the ethylene group to prepare the microporous architecture. Compound 4 is a two-fold interpenetrating 3D ploymeric network with an intriguing topological structure. The luminescence properties of 1–4 have been investigated with fluorescence emission spectra and the UV-vis diffuse reflectance spectra in the solid state. Additionally, these four compounds possess great thermal stabilities, especially for 2, the framework is stable up to 400 °C.