A new type of Lanthanide−sodium metalloring organic framework featuring high proton conduction in a wide temperature range and detection of Fe3+ ions

We present the design and synthesis of two novel isostructural metalloring organic frameworks (MROFs) {[(Me2NH2)1.25(H3O)4.25Na1.5X2(μ2-OH)(H2O)(SIP)4]n • x sol (FUT-2-X, X = Eu, Sm), which are composed of sulfonate-carboxylate ligand 5-sulfoisophthalic acid monosodium salt (NaH2SIP) and unprecedented Lanthanide - sodium metalloring [X4Na4(H2O)(SIP)2, X = Eu, Sm]. The two MROFs possess channel walls decorated with uncoordinated sulfonic acid groups and filled with abundant guest molecules residing within the framework, which support the proton conductivity of the materials by expanding the intermolecular hydrogen bonding network. FUT-2-Eu exhibits exceptional proton conductivity over a wide temperature range, achieving conductivity from 1.91×10-5 S cm-1 (-40 oC) to 2.65 × 10-3 S cm-1 (90 oC). Thanks to the dominant role of the additional guest H2O molecules in FUT-2-Eu's channels, which facilitate the formation of hydrogen-bonded networks for ultra-fast proton transfer with low energy barriers, FUT-2-Eu outperforms FUT-2-Sm in both operating temperature range and proton conductivity. It is worth noting that FUT-2-Eu has the widest operating temperature range among proton conduction materials of MROFs. Furthermore, FUT-2-Eu can be considered as an excellent luminescence sensor with high sensitivity (Ksv = 1.66 × 104 L·mol-1) and low detection limit (3.64 μM) for detecting Fe3+.