Abstract
Metal–organic frameworks (MOFs) containing ZrIV‐based secondary building units (SBUs), as in the UiO‐66 series, are receiving widespread research interest due to their enhanced chemical and mechanical stabilities. We report the synthesis and extensive characterisation, as both bulk microcrystalline and single crystal forms, of extended UiO‐66 (Zr and Hf) series MOFs containing integral unsaturated alkene, alkyne and butadiyne units, which serve as reactive sites for postsynthetic modification (PSM) by halogenation. The water stability of a Zr–stilbene MOF allows the dual insertion of both −OH and −Br groups in a single, aqueous bromohydrination step. Quantitative bromination of alkyne‐ and butadiyne‐containing MOFs is demonstrated to be stereoselective, as a consequence of the linker geometry when bound in the MOFs, while the inherent change in hybridisation and geometry of integral linker atoms is facilitated by the high mechanical stabilities of the MOFs, allowing bromination to be characterised in a single‐crystal to single‐crystal (SCSC) manner. The facile addition of bromine across the unsaturated C−C bonds in the MOFs in solution is extended to irreversible iodine sequestration in the vapour phase. A large‐pore interpenetrated Zr MOF demonstrates an I2 storage capacity of 279 % w/w, through a combination of chemisorption and physisorption, which is comparable to the highest reported capacities of benchmark iodine storage materials for radioactive I2 sequestration. We expect this facile PSM process to not only allow trapping of toxic vapours, but also modulate the mechanical properties of the MOFs.
Highlights
Metal–organic frameworks (MOFs)[1] are multidimensional coordination networks comprised of metal nodes separated by organic linkers that have received widespread interest over the past 10-15 years,[2] mainly attributable to their permanent porosity, leading to potential application in areas such as gas capture and storage,[3] catalysis[4] and drug delivery.[5]
Bromination of a Zn–stilbene MOF has previously been reported, the forcing conditions required for quantitative conversion (100 8C) resulted in degradation of the MOF.[22a]. We recently communicated the quantitative bromination of the Zr–stilbene MOF [Zr6O4(OH)4(sdc)6]n (1) to [Zr6O4(OH)4(meso-sdc-Br2)6]n (1-Br2), as both bulk microcrystalline and single-crystal material (Figure 1 b and 1c).[23b]. Considering the harsh bromination conditions employed, we decided to investigate the use of N-bromosuccinimide (NBS) as a milder, alternative brominating agent (Table 1).[26]
We have demonstrated that the combined chemical and mechanical stabilities of Zr and Hf MOFs enable their postsynthetic halogenation across integral unsaturated linker functionalities
Summary
Metal–organic frameworks (MOFs)[1] are multidimensional coordination networks comprised of metal nodes separated by organic linkers that have received widespread interest over the past 10-15 years,[2] mainly attributable to their permanent porosity, leading to potential application in areas such as gas capture and storage,[3] catalysis[4] and drug delivery.[5]. Bulk microcrystalline and singlecrystal samples of [Zr6O4(OH)4(bdb)6]n (3) were synthesised in the presence of 30 equivalents of benzoic acid (see Supporting Information, Section S3).[33] SCXRD reveals that 3 adopts the typical UiO-66 topology, with Zr6O4(OH)4 clusters connected 12-fold by bdb2À ligands (Figure 2 a) in the Fm3 ̄ m space group with unit cell edge a = 33.3694(3) .
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