A series of metal–organic frameworks based on 5-(4-pyridyl)-isophthalic acid: selective sorption and fluorescence sensing

Abstract

Solvothermal reactions of 5-(4-pyridyl)-isophthalic acid (H₂pbdc) and transition-metal centers (Ni²⁺/Co²⁺/Zn²⁺) in the presence (or absence) of N-auxiliary 4,4′-bis(1-imidazolyl)biphenyl (bimb) ligand produce [Ni₂(pbdc)₂(μ²-H₂O)(H₂O)₂·(DMA)_2.7]_n (DMA = N,N′-dimethylacetamide, 1), [Ni₁₂(pbdc)₁₂(μ²-H₂O)₆(py)₂(H₂O)₈(DMA)₂·(H₂O)₅·(DMA)₉]_n (2), [Co₂(pbdc)₂(bimb)₂·(bimb)_0.5·(H₂O)₄·(DMF)_0.25]_n (3) and [Zn(pbdc)(bimb)·(H₂O)]_n (4), which exhibit structural diversity. Both compounds 1 and 2 display a uninodal 8-connected 3D tsi net, but feature different crystal systems and space groups from each other. Compound 3 adopts a 2-fold interpenetrating binodal (3,5)-connected 3D hms net and compound 4 features a rare 2-fold interpenetrating binodal (3,4)-connected 3D fsx architecture. In particular, activated 3 shows high-efficiency for the selective sorption of small molecules, including CO₂ over N₂ and CH₄, H₂ over N₂, as well as alcohols from water. More importantly, 4 represents the first report on a MOF as a promising luminescent probe for detecting pesticides, and also the very first example for detecting both pesticides and solvent molecules simultaneously.