Solvent-induced framework interpenetration isomers and tuning of porosity of In-MOFs for efficient proton conduction and fluorescence sensing

Abstract

Tuning the porosity of MOFs can be achieved by varying the synthesis conditions, resulting in MOFs with distinct structures and connectivity. In this study, we have investigated the tuning of porosity and interpenetration by strategically varying the solvents employed during synthesis to modulate the MOF architectures. Two anionic In-MOFs obtained as structural isomers with distinct structures, topologies and interpenetration were synthesized through the synergistic assembly of oxalate (H₂ox) and 2,6-naphthalenedicarboxylic acid (H₂BNDC) with In³⁺ ions. Compound 1 is determined to have a 4-fold interpenetrated structure with a reported dia net, while compound 2 adopts an unprecedented self-penetrated topology that does not exist in the database of ToposPro. Both compounds 1 and 2 exhibit excellent proton conductivity under 98% relative humidity and at 100 °C, with proton conductivity (σ) values of 4.08 × 10⁻³ S cm⁻¹ and 7.00 × 10⁻⁴ S cm⁻¹, respectively. In addition, compound 2 was explored as a fluorescence sensor for detecting tetracycline (Tet) in water, with a quenching constant (K_sv) of 2.056 × 10⁴ M⁻¹ and a detection limit (LOD) of 0.145 μM.