Five water-stable luminescent CdII-based metal–organic frameworks as sensors for highly sensitive and selective detection of acetylacetone, Fe3+ and Cr2O72− ions

Abstract

Five new Cd^II-based ternary metal–organic frameworks (MOFs) constructed from structurally related ligands, namely, [Cd(L1)(DCTP)]_n (1), [Cd₂(L2)₂(DCTP)₂]_n (2), {[Cd₂(L3)(DCTP)₂]·3.75H₂O}_n (3), {[Cd(L4)(DCTP)]·0.85H₂O}_n (4) and [Cd_0.5(L5)_0.5(DCTP)_0.5]_n (5) (H₂DCTP = 2,5-dichloroterephthalic acid, L1 = 1,4-di(1H-benzo[d]imidazol-2-yl)butane, L2 = 1,5-di(1H-benzo[d]imidazol-2-yl)pentane, L3 = 1,3-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)propane, L4 = 1,4-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)butane and L5 = 1,6-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)hexane), have been hydrothermally synthesized and characterized. While 1 and 5 show the common 2D hcb and 3D sqc6 topologies, respectively, 2 exhibits a rare (4,4)-connected 2-node 2D 4,4L62 network, 3 reveals an unprecedented 3D (3,3,4,5)-connected framework with the point symbol {4·9²}₂{4²·8²·9²}{4²·8⁴·9³·10}₂{9³}₂ and 4 presents an unusual (3,5)-connected 3D gra topological framework. The results show that the coordination mode of dicarboxylate ligands and the auxiliary N-containing linkers have a crucial impact on the structural diversities of ternary Cd-MOFs. Further, 2 and 3 are favorable dual-functional fluorescent sensors for the detection of Fe³⁺/acetylacetone and Cr₂O₇²⁻ (pH = 4)/acetylacetone, respectively, with high sensitivity and selectivity.