Multiresponsive luminescent sensing behaviour of a tetraimidazole ligand and its 3D Cd(ii) metal–organic frameworks

Abstract

The detection of excess toxic anions or cations in an aqueous solution through various fluorescent materials such as organic or inorganic fluorescent materials has aroused significant interest recently. Herein, a new tetraimidazole ligand 1,3-bis(1-imidazolyl)-5-[3,5-bis(1-imidazolyl)-phenoxymethyl]-benzene (timpb) and its two Cd(II) metal–organic frameworks {[Cd₂(1,4-bdc)₂(timpb)]·5.5(H₂O)}_n (1) (1,4-benzenedicarboxylic acid = 1,4-H₂bdc) and {[Cd₂(4,4′-bpdb)₂(timpb)]·(MeCN)·2.5(H₂O)}_n (2) (4,4′-biphenyldicarboxylic acid = 4,4′-H₂bpdb) were synthesized. Through X-ray single crystal diffraction analysis, 1 can be considered as a 2-fold interpenetrating pillared-bilayer framework formed by linking [Cd₂(1,4-bdc)₄]_n layers with pairs of timpb ligands, whereas 2 exhibits a 2-fold interpenetrating 3D honeycombed framework formed by linking [Cd(4,4′-bpdb)]_n chains with timpb ligands. The solid-state luminescent properties of timpb, 1 and 2 at ambient temperature were also investigated. Moreover, timpb acted as a potential luminescent sensor for the detection of cations Fe³⁺ or Cu²⁺ and the anion Cr₂O₇²⁻, whereas 1 displayed high sensitivity toward the cation Fe³⁺ and anion Cr₂O₇²⁻.