Low-Valent Metal Ions as MOF Pillars: A New Route Toward Stable and Multifunctional MOFs

Abstract

PCM-102 is a new organophosphine metal–organic framework (MOF) featuring diphosphine pockets that consist of pairs of offset trans-oriented P­(III) donors. Postsynthetic addition of M­(I) salts (M = Cu, Ag, Au) to PCM-102 induces single-crystal to single-crystal transformations and the formation of trans-[P2M]+ solid-state complexes (where P = framework-based triarylphosphines). While the unmetalated PCM-102 has low porosity, the addition of secondary Lewis acids to install rigid P–M–P pillars is shown to dramatically increase both stability and selective gas uptake properties, with N2 Brunauer–Emmett–Teller surface areas >1500 m2 g–1. The Ag­(I) analogue can also be obtained via a simple, one-pot peri-synthetic route and is an ideal sacrificial precursor for materials with mixed bimetallic MA/MB pillars via postsynthetic, solvent-assisted metal exchange. Notably, the M-PCM-102 family of MOFs contain periodic trans-[P2M]+ sites that are free of counter anions, unlike traditional analogous molecular complexes, since the precursor PCM-102 MOF is monoanionic, enabling access to charge-neutral metal-pillared materials. Four M-PCM-102 materials were evaluated for the separation of C2 hydrocarbons. The separation performance was found to be tunable based on the metal(s) incorporated, and density functional theory was employed to elucidate the nature of the unusual observed sorption preference, C2H2 > C2H6 > C2H4.

Synergistic binding sites in a hybrid ultramicroporous material for one-step ethylene purification from ternary C 2 hydrocarbon mixtures

“…Another important dimension is that the altering of anion pillars (e.g., SiF 6 ) can induce the distortion of pore shapes and the rotation of organic ligands (14,15), thus anionpillared HUMs have emerged as the promising C 2 light hydrocarbon adsorbents for binary separations such as C 2 H 2 /C 2 H 4 (16), C 2 H 2 / CO 2 (17), and C 2 H 4 /C 2 H 6 (18). However, the single-step C 2 H 4 purification from ternary C 2 mixtures has never been achieved in adsorptive separations using anion-pillared HUMs, because the quadrupole moment and kinetic diameter of C 2 H 4 [1.5 × 10 −26 (5,(20)(21)(22)(23)(24)(25)(26)(27).…”

Recent advances in microporous metal–organic frameworks as promising adsorbents for gas separation

“…By incorporating metal salts into PCM-102 via post-synthetic metal exchange, Sikma et al realized a series of MOFs (M-PCM-102, M = Cu, Ag, Au) for C 2 hydrocarbon separation. 99 Amongst them, Ag-PCM-102 exhibits the optimal separation performance with the ideal adsorption capacities in the order of C 2 H 2 > C 2 H 6 > C 2 H 4 . The IAST selectivities for 50/50 and 1/99 C 2 H 2 /C 2 H 4 are both 1.5 at 303 K and 1 bar.…”

Two isostructural metal–organic frameworks with unique nickel clusters for C2H2/C2H6/C2H4 mixture separation

“…28 Incorporation of open metal sites could potentially enhance the acetylene adsorption to promote the C 2 H 2 /C 2 H 4 selectivity, and subsequently maximize the overall separation performance, which has rarely been reported. 29 Herein, we report two isostructural MOFs with unique open nickel sites, BUT-150 (Ni 2 (m 2 -OH 2 )DiBP 4 , DiBP ¼ 5,5ʹ-([2,2 0bipyridine]-5,5 0 -diyl)diisophthalate) and BUT-151 (Ni 2 (m 2 -OH 2 ) DiPhen 4 , DiPhen ¼ 5,5ʹ-(1,10-phenanthroline-3,8-diyl) diisophthalate). These two MOFs were constructed using carboxylate linkers containing chelating 2,2 0 -bipyridine and o-phenanthroline units, respectively.…”

“…MOFs for olefin separation from paraffin through π complexation 10–12 at open metal sites or sieving effect 13–15 have been extensively explored due to the promise of tremendous energy saving through adsorptive separation as compared with cryogenic distillation. Recently, ethane selective sorbents including MOFs and HOFs (hydrogen bonded organic frameworks) have emerged and yield high purity ethylene in a one-step separation from C 2 H 6 /C 2 H 4 , 16–25 C 2 H 2 /C 2 H 6 /C 2 H 4 , 26–32 and C 2 H 2 /C 2 H 6 /C 2 H 4 /CO 2 (ref. 33 and 34) mixtures.…”

“…28 Incorporation of open metal sites could potentially enhance the acetylene adsorption to promote the C 2 H 2 /C 2 H 4 selectivity, and subsequently maximize the overall separation performance, which has rarely been reported. 29…”