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

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,O^1':O²:O⁴,O^4':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 Cd^II centre is coordinated by six O atoms from four different (1,2,4,5-btc)^4- tetraanions. Each Cd^II 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 Cd^II centres. Neighbouring Cd^II 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.