Chromic behaviors and chemical fixation of CO2 without Co-catalysts of a cationic metal-organic framework

A cationic metal-organic framework (MOF) was constructed utilizing tetranuclear [Tb-4(mu (3)-OH)(4)(COO)6](2) second building unit (SBU) and a tri(pyridinium)pyridine derivative linker, resulting in a three-dimensional (3D) framework. The MOF exhibits reversible ionochromic behavior through ion exchange and hydrochromic property via electron transfer (ET). Importantly, the MOF incorporates nucleophilic anion in the channel, thereby facilitating the cyclization reaction between carbon dioxide (CO2) and epoxides to yield carbonates without necessitating additional co-catalysts. Furthermore, the MOF exhibits Lewis acidic sites, contributing to its enhanced catalytic activity under mild conditions. The MOF functions as a heterogeneous catalyst for CO2 epoxidation, operating without needing co-catalysts or solvents, and exhibits chromic properties. The work presents a strategy for designing MOFs that can directly participate in the chemical fixation of CO2 without adding additional nucleophilic anions, and can also serve as chromic materials.