Robust Anionic LnIII-Organic Frameworks: Chemical Fixation of CO2, Tunable Light Emission, and Fluorescence Recognition of Fe3.

Abstract

With the aim of exploring and enriching nanocaged functional platforms of lanthanide-organic frameworks, the subtle combination of [Ln2(CO2)8] secondary building units and [Ln(CO2)4] units by employing the hexacarboxylic acid of 4,4',4″-(pyridine-2,4,6-triyl)tris(1,3-benzenedicarboxylic acid) (H6PTTBA) successfully realized the self-assembly of highly robust multifunctional {LnIII2}LnIII-organic anionic skeletons of {(Me2NH2)[Ln3(PTTBA)2]·xDMF·yH2O}n (1-Ln), which had remarkable intrinsic nature of high thermal and water stability, large permanent porosity, interconnected nanocaged void volume, and high specific surface area. Here, only the Eu-based framework of 1-Eu was taken as one representative to discuss in detail. Gas-sorption experiments showed that the activated solvent-free 1-Eu framework possessed the outstanding ability to separate the mixed gases of CO2/CH4 (50:50, v/v) with an ideal adsorbed solution theory selectivity of 14. Furthermore, 1-Eu was an efficient and recycled catalyst for the chemical cycloaddition of CO2 and epoxides into their corresponding carbonates, which possessed a better catalytic performance than the documented unique Eu3+-organic framework of [Eu(BTB)(phen)] and could be widely applied in industry because of its simple synthetic conditions and high yield. In the meantime, adjustable emission colors devoted by the efficient Tb3+ → Eu3+ energy transfer confirmed that Eux/Tb1-x-organic framework could be taken as a good substitute for barcode materials by changing the ratio of Eu3+ and Tb3+. Moreover, quantitative luminescence titration experiments exhibited that 1-Eu possessed good selectivity for the identification of Fe3+ in aqueous solution by fluorescence quenching with a low limit of detection value of 6.32 × 10-6 M.