Two luminescent lanthanide(iii) metal–organic frameworks as chemosensors for high-efficiency recognition of Cr(vi) anions in aqueous solution

Abstract

Two new lanthanide(III) metal–organic frameworks (MOFs) {[(CH₃)₂NH₂]₂[Ln₄(FDA)₇(DMF)₂]·0.5DMF}_n [Ln = Eu (1), and Tb (2)] based on furan-2,5-dicarboxylic acid (H₂FDA) have been successfully assembled and well characterized in detail. These MOFs are isostructural and demonstrate 12-connected sqc15 topologies, which are rarely observed in MOF chemistry, especially in lanthanide(III) MOFs. Moreover, these two MOFs could show a tolerance towards moisture and organic solvents and satisfactory chemical stabilities. More importantly, they exhibit sensitive and selective luminescence quenching response towards Cr₂O₇²⁻ and CrO₄²⁻ anions in aqueous solution with the average quenching K_sv values of 1.25 × 10⁴ L mol⁻¹ (Cr₂O₇²⁻) and 3.56 × 10³ L mol⁻¹ (CrO₄²⁻) for 1 and 1.46 × 10⁴ L mol⁻¹ (Cr₂O₇²⁻) and 4.35 × 10³ L mol⁻¹ (CrO₄²⁻) for 2 and the detection limits of 1.14 × 10⁻⁴ mol L⁻¹ (Cr₂O₇²⁻) and 1.12 × 10⁻⁴ mol L⁻¹ (CrO₄²⁻) for 1 and 7.42 × 10⁻⁵ mol L⁻¹ (Cr₂O₇²⁻) and 1.27 × 10⁻⁴ mol L⁻¹ (CrO₄²⁻) for 2. The high quenching K_sv values and low detection limits make them more feasible in sensing Cr(VI) anions in aqueous solution. The possible detection mechanism has been discussed in detail.