SC–SC solvent-assisted linker exchange (SALE) in MOF materials is of high interest due to the potential applications. In this work, we reported an efficient transformation via SALE in a water-stable 3D MOF ({[Ni1.5(L)­(4,4′-azobpy)­(H2O)]·6.5H2O} n (1)) (H3L = 1-aminobenzene-3,4,5-tricarboxylic acid). The reaction progress of SALE was monitored and proved by single crystal XRD, PXRD and UV–vis absorption analyses, and the structural integrity of progeny MOFs {[Ni1.5(L)­(4,4′-bpy)­(H2O)]·6H2O} n (2), {[Ni1.5(L)­(bpe)­(H2O)]·8.5H2O} n (3), and {[Ni1.5(L)­(NH2-bpy)­(H2O)]·7.5H2O} n (4) were maintained very well, which is rarely in reported MOF materials. Theoretical calculations and the analyses of core–shell crystals give us better understanding of the exchange process. Interestingly, MOFs 2 and 3 obtained by SALE methods showed the different magnetic behavior comparing to parent MOF 1. Especially, because of the functional −NH2 group, progeny MOF 4 displayed the good capability to remove Hg2+ ions with an adsorption capacity of 93.693 mg/g. This work provides a new way to develop multifunctional MOF materials.

Direct propylene epoxidation with molecular oxygen is a dream reaction with 100% atom economy, but aerobic epoxidation is challenging because of the undesired over-oxidation and isomerization of epoxide products. Herein, we report the construction of uniform cobalt ions confined in faujasite zeolite, namely, Co@Y, which exhibits unprecedented catalytic performance in the aerobic epoxidation of propylene. Propylene conversion of 24.6% is achieved at propylene oxide selectivity of 57% at 773 K, giving a state-of-the-art propylene oxide production rate of 4.7 mmol/gcat/h. The catalytic performance of Co@Y is very stable, and no activity loss can be observed for over 200 h. Spectroscopic analyses reveal the details of molecular oxygen activation on isolated cobalt ions, followed by interaction with propylene to produce epoxide, in which the Co2+–Coδ+–Co2+ (2 < δ < 3) redox cycle is involved. The reaction pathway of propylene oxide and byproduct acrolein formation from propylene epoxidation is investigated by density functional theory calculations, and the unique catalytic performance of Co@Y is interpreted. This work presents an explicit example of constructing specific transition-metal ions within the zeolite matrix toward selective catalytic oxidations.

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A rare example of SC-SC triggered by Cu heterogeneous oxidation was demonstrated in a Fe(II)-based MOF {[Fe(L)(HO)]·3HO} (1), which occurred a slow conversion into an oxidized MOF 2 ({[Fe(L)(HO)]·3(OH)} ) with retention of single crystallinity. The Fe → Fe progress of the reaction oxidation was proved by single crystal XRD, PXRD, XPS, Fe Mössbauer spectroscopy, and UV-vis. We used 1 and 2 as catalysts to catalyze the tandem Nazarov cyclization, and the results show that acylation products were only harvested when 1 was a catalyst, while the oxidized transformer 2 lead mainly to the formation of cyclization products under identical conditions. Through the test of different substrates, 2 can be a good heterogeneous catalyst candidate for the formation of cyclopentenone[ b] benzenes. This work provides a new way to design efficient and hard-synthesized heterogeneous catalyst materials.