Two porous three-dimensional (3D) metal–organic frameworks based on diverse metal clusters: selective sensing of Fe3+ and Cr2O72−

Abstract

Two porous complexes, namely, {[H₂N(Me)₂]₂[Zn₅(L)₂(OH)₂]·3DMF·4H₂O}_n (1), and {[H₂N(Me)₂]₄[Cu₃(L)₂(H₂O)₂]·4DMF·3H₂O}_n (2) were solvothermally constructed based on a symmetrical V-shaped rigid multicarboxylic acid ligand H₅L (H₅L = 3,5-di(2′,5′-dicarboxylphenyl)benzoic acid). Complexes 1 and 2 display 3D frameworks with various metal clusters. Complex 1 is a 3D porous framework with a (4,8)-connected topology featuring a 1D pore structure in the a-axis direction with a penta-nuclear cluster [Zn₅(μ₂-COO)₆(μ₁-COO)₄(μ₃-O)₂]. By contrast, 2 displays a 3D (3,4)-connected net based on binuclear [Cu₂(COO)₄] paddlewheel SBUs. Complex 1 reveals solid-state luminescent properties at ambient temperature, and the maximum emission peak was observed at ∼443 nm (λ_ex = 339 nm). Meanwhile, 1 shows high selectivity and sensitivity not only for Fe³⁺ cations but also for Cr₂O₇²⁻ anions via the luminescence quenching effect with a low detection limit, which thus could be a potential crystalline material for detecting these substances. The mechanisms of the quenching effect and sensing properties of 1 were discussed in detail.