Pyridyl/Pyrimidyl-Containing Ligands Modulating Two Cd(II)-MOFs with Distinct Architectures and Al³⁺ Sensing...

It is a challenging task to develop metal-organic frameworks (MOFs) with fascinating architectures and outstanding performance. In this work, two novel Cd(II)-MOFs, [Cd₂(L1)(BDC)₂·1.5i-PrOH] (1) and [Cd(L2)_0.5(BDC)(H₂O)] (2), with distinct sensing performances are successfully synthesized by pyridyl/pyrimidyl-containing functional ligands 9,10-bis(di(pyridine-4-yl)methylene)-9,10-dihydroanthracene (L1) and 9,10-bis(di(pyrimidin-5-yl)methylene)-9,10-dihydroanthracene (L2). 1 exhibits a 3D (4,6,10)-connected multicylindrical framework with compartments, constructed by 4-connected L1 and BDC^2- in modes A and B, 6-connected Cd1, and 10-connected [Cd₂(COO)₂]²⁺. 2 is fabricated by 4-connected BDC^2-, 7-connected Cd, and L2 bridges to generate a 3D (4,7)-connected pillar-layered framework with uncoordinated pyrimidyl N active sites. More importantly, their topologies have not been reported thus far. 1 and 2 have excellent water, pH, and thermal stabilities. 1 can efficiently sense TNP and MDZ in H₂O, but its Al³⁺ sensing ability is relatively average. In sharp contrast, 2 has ultrahigh Al³⁺ sensitivity. Its limit of detection (LOD) toward Al³⁺ (2.93 × 10^-7 M) is nearly 2 orders of magnitude and 25 times lower than that of 1 (1.18 × 10^-5 M) and the WHO's maximum Al³⁺ limit (7.41 × 10^-6 M) in drinking water, respectively. Their sensing mechanisms and different sensing performances are explored in depth.