Reversible Electroactive Behavior in a Zn-Based Metal-Organic Framework via Mild Oxidation Potential

This work describes the synthesis and characterization of a Zn-based metal-organic framework, [Zn₂(TTPA)(SDB)₂·(DMF)(H₂O)] (1, TTPA = tris(4-(1H-1,2,4-triazol-1-yl)phenyl)amine, SDB = 4,4'-sulfonyldibenzoate). A newly designed strategy with a redox-active linker, TTPA, and mediated by a V-shaped carboxylic linker with Zn²⁺ metal ions resulted in an electroactive framework. The V-shaped carboxylic linker with Zn²⁺ metal ions forms linear struts interlinked by two of the side-arms of the TTPA ligands to form a square grid network. The interior of the grid is enough to accommodate the third side-arm of the TTPA ligands, acting as a confinement grid that provides steric protection when triarylamine radical cations were generated. In addition, modular packing of axially aligned TTPA ligand facilitates charge propagation. Optical switching studies confirmed that 1 is electrochemically reversible up to 48 cycles at a potential of 0.9 V vs Fc/Fc⁺. Framework 1 remained robust after annealing at 180 °C for 20 h as corroborated by the PXRD. These studies confirm the importance of crystal engineering design, where electron transfer is possible in a two-ligand approach.