Selective nitrogen adsorption via backbonding in a metal–organic framework with exposed vanadium sites

Abstract

Selective nitrogen adsorption via backbonding in a metal-organic framework with exposed vanadium sites. # These authors contributed equally to this work Industrial processes prominently feature π-acidic gases, and an adsorbent capable of selectively interacting with these molecules could enable a number of important chemical separations 1-4 . In nature, enzymes, and correspondingly their synthetic analogues, use accessible, reducing metal centers to bind and even activate weakly π-acidic species such as N 2 through backbonding interactions 5-7 , and incorporation of similar moieties into a porous material should give rise to a new mechanism of adsorption for these gaseous substrates 8 .However, synthetic challenges have prevented realization of such a material. Here, we report a metal-organic framework featuring exposed vanadium(II) centers with an electronic configuration and 3d-orbital energies conducive to the back-donation of electron density to weak π-acids, thereby enabling highly selective adsorption. This new adsorption mechanism, together with the presence of a high concentration of available adsorption sites, results in record N 2 capacities and selectivities for the removal of N 2 from mixtures with CH 4 , while further enabling the separation of olefins from paraffins at elevated temperatures.Ultimately, incorporating such π-basic metal centers into tunable porous materials offers a new handle for capturing and activating key molecular species within next-generation adsorbents.The implementation of adsorbent-based technology stands as a promising route toward mitigating the high energy and emission costs associated with current industrial chemical The synthesis of V 2 Cl 2.8 (

Self-adjusting binding pockets enhance H2 and CH4 adsorption in a uranium-based metal–organic framework

“…Metal-organic frameworks are a class of chemically-robust, porous, and oen rigid materials, composed of metal ions or clusters connected by bridging organic linkers. [1][2][3][4] The physical and chemical properties of these materials are highly tunable based on choice of metal and linker, and thus metal-organic frameworks have been proposed for a wealth of applications, [5][6][7][8][9] including catalysis, [10][11][12][13][14][15] sensing, [16][17][18] carbon capture, [19][20][21][22][23] gas separations, [24][25][26] and gas storage. [27][28][29][30][31] Metal-organic frameworks have attracted particular interest as candidate gas storage materials for H 2 and CH 4 that could enable more efficient use of these energy carriers as cleaner fuel alternatives.…”

High‐Valent Metal–Oxo Species at the Nodes of Metal–Triazolate Frameworks: The Effects of Ligand Exchange and Two‐State Reactivity for C−H Bond Activation

“…[37,46,47] Perhaps most notably,like several of the aforementioned MAFs,t he M 2 X 2 (BBTA) family is highly tunable,both with regards to the metal identity as well as the bridging monovalent anions connecting each metal center. To date,M 2 Cl 2 (BBTA) ( [36,40,43,[47][48][49][50][51] Forr eference, the pores of these materials are quite large,with diameters of approximately 13 and 23 for M 2 X 2 (BBTA) and M 2 X 2 -(BTDD), respectively. [52] Using DFT,w einvestigate the effects of exchanging the metal cation (M = V, Cr, Mn, Fe,C o, Ni, Cu) and bridging ligand (X = F, Cl, Br, OH, SH, SeH) on the frameworks ability to form reactive metal-oxo motifs for the oxofunctionalization of strong CÀHb onds.W hile some of these combinations of metals and ligands may not yield frameworks capable of forming (meta-)stable metal-oxo motifs,w e include aw ide range of metals and ligands to aid in the identification of overarching structure-property relationships across this family of tunable materials.A sar esult of this study,weshow how the choice of linker and anions within the first coordination sphere can be used to increase the stability of high-valent metal-oxo sites that are reactive toward strong C À Hb onds in the M 2 X 2 (BBTA) family of metal-triazolate frameworks.W ealso use the M 2 X 2 (BBTA) family to demonstrate the important role of electron spin for C À Hb ond activation via terminal metal-oxo species,w hile simultaneously clarifying several questions about the radical-like character of the metal-oxo motif.…”

Transition‐Metal‐Containing Porphyrin Metal–Organic Frameworks as π‐Backbonding Adsorbents for NO2 Removal

“…The p-backbonding is formed by the backdonation of d orbital electrons of TMs to the p* orbital of p-acidity adsorbates. [13] The strength of p-backbonding is between that of physisorption and that of chemisorption, readily allowing for good adsorption capacity and reversibility. [13] Herein, we report an aluminum-based PMOF (Al-PMOF) as p-backbonding adsorbent, which engages p-acid gas NO 2 via inserted TMs (nickel (Ni II ), cobalt (Co II ), copper (Cu II ), and zinc (Zn II )) as active adsorption sites.…”

“…[13] The strength of p-backbonding is between that of physisorption and that of chemisorption, readily allowing for good adsorption capacity and reversibility. [13] Herein, we report an aluminum-based PMOF (Al-PMOF) as p-backbonding adsorbent, which engages p-acid gas NO 2 via inserted TMs (nickel (Ni II ), cobalt (Co II ), copper (Cu II ), and zinc (Zn II )) as active adsorption sites. The moderate interaction of p-backbonding and the ultrastable substrate allow the Al-PMOF(Ni) to exhibit a superior NO 2 adsorption capacity and regenerability at ambient conditions, qualifying it as a potential candidate for NO 2 removal.…”

“…[1,18] Those (Figure 4 a), clearly suggesting pbackbonding between Ni and NO 2 , in contrast to the blueshift observed in the MOFs via a Lewis acidic mechanism. [13,19] The depletion of bands representing the hydroxy (OH) group at 3708 and 3710 cm À1 (Supporting Information, Figure S6), respectively, was ascribed to the formation of hydrogen bonding between the Al-OH metal node and NO 2 .…”