Defect-engineered indium-organic framework displays the higher CO adsorption and more excellent catalytic performance on the cycloaddition of CO with epoxides under mild conditions.

In order to achieve the high adsorption and catalytic performance of CO, the direct self-assembly of robust defect-engineered MOFs is a scarcely reported and challenging proposition. Herein, a highly robust nanoporous indium(III)-organic framework of {In(CPPDA)(HO)·2DMF·3HO} (NUC-107) consisting of two kinds of inorganic units of chain-shaped [In(COO)(HO)] and watery binuclear [In(COO)(HO)] was generated by regulating the growth environment. It is worth mentioning that [In(COO)(HO)] is very rare in terms of its richer associated water molecules, implying that defect-enriched metal ions in the activated host framework can serve as strong Lewis acid. Compared to reported skeleton of [In(CPPDA)(μ-OH)(DMF)(HO)] (NUC-66) with tetranuclear clusters of [In(μ-OH)(COO)(DMF)(HO)] as nodes, the void volume of NUC-107 (50.7%) is slightly lower than the one of NUC-66 (52.8%). However, each In ion in NUC-107 has an average of 1.5 coordinated small molecules (HO), which far exceeds the average of 0.75 in NUC-66 (HO and DMF). After thermal activation, NUC-107a characterizes the merits of unsaturated In sites, free pyridine moieties, solvent-free nanochannels (10.2 × 15.7 Å). Adsorption tests prove that the host framework of NUC-107a has a higher CO adsorption (113.2 cm/g at 273 K and 64.8 cm/g at 298 K) than NUC-66 (91.2 cm/g at 273 K and 53.0 cm/g at 298 K). Catalytic experiments confirmed that activated NUC-107a with the aid of n-BuNBr was capable of efficiently catalyzing the cycloaddition of CO with epoxides into corresponding cyclic carbonates under the mild conditions. Under the similar conditions of 0.10 mol% MOFs, 0.5 mol% n-BuNBr, 0.5 MP CO, 60 °C and 3 h, compared with NUC-66a, the conversion of SO to SC catalyzed by NUC-107a increased by 21%. Hence, this work offers a valuable perspective that the in situ creation of robust defect-engineered MOFs can be realized by regulating the growth environment.