Construction of a three-dimensional supramolecular framework based on an anionic cadmium(II) coordination network and protonated dipyridine organic cations.

Abstract

As a class of multifunctional materials, crystalline supramolecular complexes have attracted much attention because of their unique architectures, intriguing topologies and potential applications. In this article, a new supramolecular compound, namely catena-poly[4,4'-(buta-1,3-diene-1,4-diyl)dipyridin-1-ium [(μ4-benzene-1,2,4,5-tetracarboxylato-κ6O1,O1':O2:O4,O4':O5)cadmium(II)]], {(C14H14N2)[Cd(C10H2O8)]}n or {(1,4-H2bpbd)[Cd(1,2,4,5-btc)]}n, has been prepared by the self-assembly of Cd(NO3)2·4H2O, benzene-1,2,4,5-tetracarboxylic acid (1,2,4,5-H4btc) and 1,4-bis(pyridin-4-yl)buta-1,3-diene (1,4-bpbd) under hydrothermal conditions. The title compound has been structurally characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction and single-crystal X-ray diffraction analysis. Each CdII centre is coordinated by six O atoms from four different (1,2,4,5-btc)4- tetraanions. Each CdII cation, located on a site of twofold symmetry, binds to four carboxylate groups belonging to four separate (1,2,4,5-btc)4- ligands. Each (1,2,4,5-btc)4- anion, situated on a position of -1 symmetry, binds to four crystallographically equivalent CdII centres. Neighbouring CdII cations interconnect bridging (1,2,4,5-btc)4- anions to form a three-dimensional {[Cd(1,2,4,5-btc)]2-}n anionic coordination network with infinite tubular channels. The channels are visible in both the [1-10] and the [001] direction. Such a coordination network can be simplified as a (4,4)-connected framework with the point symbol (4284)(4284). To balance the negative charge of the metal-carboxylate coordination network, the cavities of the network are occupied by protonated (1,4-H2bpbd)2+ cations that are located on sites of twofold symmetry. In the crystal, there are strong hydrogen-bonding interactions between the anionic coordination network and the (1,4-H2bpbd)2+ cations. Considering the hydrogen-bonding interactions, the structure can be further regarded as a three-dimensional (4,6)-connected supramolecular architecture with the point symbol (4264)(42687·84). The thermal stability and photoluminescence properties of the title compound have been investigated.