Ruthenium Metal–Organic Frameworks with Different Defect Types: Influence on Porosity, Sorption, and Catalytic Properties

Abstract

By employing the mixed-component, solid-solution approach, various functionalized ditopic isophthalate (ip) defect-generating linkers denoted 5-X-ipH(2), where X = OH (1), H (2), NH2 (3), Br (4), were introduced into the mixed-valent ruthenium analogue of [Cu-3(btc)(2)](n) (HKUST-1, btc = benzene-1,3,5-tricarboxylate) to yield Ru-DEMOFs (defect-engineered metal-organic frameworks) of the general empirical formula [Ru-3(btc)(2-x)(5-X-ip)(x)Y-y](n). Framework incorporation of 5-X-ip was confirmed by powder XRD, FTIR spectroscopy, ultrahigh-vacuum IR spectroscopy, thermogravimetric analysis, H-1 NMR spectroscopy, N-2 sorption, and X-ray absorption near edge structure. Interestingly, Ru-DEMOF 1c with 32% framework incorporation of 5-OH-ip shows the highest BET surface area (approximate to 1300 m(2) g(-1), N-2 adsorption, 77 K) among all materials (including the parent framework [Ru-3(btc)(2)Y-y](n)). The characterization data are consistent with two kinds of structural defects induced by framework incorporation of 5-X-ip: modified paddlewheel nodes featuring reduced ruthenium sites (Ru delta+, 0 < delta < 2, type A) and missing nodes leading to enhanced porosity (type B). Their relative abundances depend on the choice of the functional group X in the defect linkers. Defects A and B also appeared to play a key role in sorption of small molecules (i.e., CO2, CO, H-2) and the catalytic properties of the materials (i.e., ethylene dimerization and the Paal-Knorr reaction).