Reactant ratio-modulated entangled Cd(ii) coordination polymers based on rigid tripodal imidazoleligand and tetrabromoterephthalic acid: interpenetration, interdigitation and self-penetration

Abstract

By adjusting the molar ratio of the reactant metal salt and ligands, three new entangled coordination polymers, [Cd(tib)(tbta)(H₂O)]_n (1) and [Cd(Htib)(tbta)·Htbta·2CH₃OH]_n (2) and [Cd₂(tib)₂(tbta)₂(H₂O)·10H₂O]_n (3) (tib = 1,3,5-tris(1-imidazolyl)benzene and H₂tbta = tetrabromoterephthalic acid), have been prepared and structurally characterized by X-ray diffraction analyses. Complex 1 is a 2-fold interpenetrated three-dimensional (3D) 8-connected uninodal net with rare hex topology. Complex 2 presents a 2D 6³-hcb network, which is interdigitated with each other to form the 3D supramolecular framework stabilized hydrogen bonds and halogen bonds. Interestingly, an unprecedented hydrogen-bonded [(Htbta)₂(CH₃OH)₄] cluster was unmasked in the void of 2. Complex 3 is a complicated 3D self-penetrated framework with a point symbol of {4·6·8}{4·6⁵·8⁴}{6⁶}, which can be seen as a pair of 2-fold interpenetrated networks by breaking bidentate-bridging tib ligand. The comparative study revealed that 1–3 are particularly sensitive to the metal–ligand ratio in this system. The thermal stabilities and photoluminescence behaviors of 1 and 2 were also discussed.