Controlled Reducibility of a Metal–Organic Framework with Coordinatively Unsaturated Sites for Preferential Gas Sorption

Abstract

The current interest in porous crystalline metal-organic frameworks (MOFs) [1] is largely due to their wide range of compositions and structure types with low framework densities, their tunability, and the possibility of accessible, coordinatively unsaturated metal sites (CUS). The existence of CUS can strongly modify interactions with gases [2] or liquid adsorbates, [3] and is thus of particular importance gas storage and separations.The redox properties of transition-metal-substituted zeolites and mesoporous materials have been extensively studied and used for selective catalysis in liquid-phase oxidation, [4] removal of nitrogen oxides, [5] and photocatalytic reactions.[6]These features are very rare for MOFs containing 3d metals, in particular with respect to the reducibility of the framework metal ions. [7] For this reason, we examine herein both the conditions of generation of iron CUS with mixed valence Fe II

Facile synthesis of size-controlled MIL-100(Fe) with excellent adsorption capacity for methylene blue

“…These porous materials are always composed of organic bridging ligands and metal ions to form three-dimensional extended networks with uniform pore diameter [11][12][13]. MIL-100(Fe) possesses two sets of mesoporous cages that are accessible through microporous windows and corresponding large Langmuir surface areas [14][15][16]. As reported previously, the Fe Lewis acid sites could be produced by the removal of the two terminal H 2 O molecules of iron octahedra and the partial departure of anions through vacuum activation.…”

Annulation of phenols with methylbutenol over MOFs: The role of catalyst structure and acid strength in producing 2,2-dimethylbenzopyran derivatives

“…Iron(III) trimesate MIL-100(Fe) and chromium(III) trimesate MIL-100(Cr) were synthesized according to the literature [50,51]. MIL-100(Fe) was prepared by mixing metallic iron (8. …”

A novel type of matrix for surface-assisted laser desorption–ionization mass spectrometric detection of biomolecules using metal-organic frameworks

“…Among the five cagetype MOFs, only iron (Fe) centered MIL-100 can produce coordinatively unsaturated metal sites (CUS) of mixed valence iron (Fe 2þ /Fe 3þ ) under thermal activation between 150 and 250 C [35], while only single valence CUS metal is produced for MOFs with Cr 3þ , Zr 4þ , and Al 3þ (for example, the presence of unique Cr 3þ in MIL-100(Cr) even at 400 C activation). Typically, during laser irradiation, which often raises the matrix temperature up to 200e250 C [36], the mixed valences of Fe 2þ /Fe 3þ CUS formed in MIL-100(Fe) can either act as a Lewis acid site (Fe 3þ ) to interact with carbohydrate molecules (an electron donor) [35] or a Lewis base site (Fe 2þ ) that stabilized the carbohydrate-alkali metal adduct formation. With the unique features of the unsaturated Fe 2þ /Fe 3þ sites, the iron centered MIL-100 formed a more stable complex with the analyte molecules that further enhanced the analyte intensity.…”