Inverse CO2 /C2 H2 Separation with MFU-4 and Selectivity Reversal via Postsynthetic Ligand Exchange.

Although many porous materials, including metal-organic frameworks (MOFs), have been reported to selectively adsorb C2 H2 in C2 H2 /CO2 separation processes, CO2 -selective sorbents are much less common. Here, we report the remarkable performance of MFU-4 (Zn5 Cl4 (bbta)3 , bbta=benzo-1,2,4,5-bistriazolate) toward inverse CO2 /C2 H2 separation. The MOF facilitates kinetic separation of CO2 from C2 H2 , enabling the generation of high purity C2 H2 (>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C2 H2 is excluded from MFU-4 by narrow pore windows formed by Zn-Cl groups. Postsynthetic F- /Cl- ligand exchange was used to synthesize an analogue (MFU-4-F) with expanded pore apertures, resulting in equilibrium C2 H2 /CO2 separation with reversed selectivity compared to MFU-4. MFU-4-F also exhibits a remarkably high C2 H2 adsorption capacity (6.7 mmol g-1 ), allowing fuel grade C2 H2 (98 % purity) to be harvested from C2 H2 /CO2 mixtures by room temperature desorption.

Facile immobilization of PNNNP-Pd pincer complexes in MFU-4l-OH and the effects of guest loading on Lewis acid catalytic activity.

A palladium diphosphine pincer complex H3(PNNNP-PdI) has been encapsulated in the benzotriazolate metal-organic framework MFU-4l-OH ([Zn5(OH)4(btdd)3], btdd2- = bis(1,2,3-triazolo)dibenzodioxin), and the resulting materials were investigated as Lewis acid catalysts for cyclization of citronellal to isopulegol. Rapid catalyst immobilization is facilitated by a Brønsted acid-base reaction between the H3(PNNNP-PdI) benzoic acid substituents and Zn-OH groups at the framework nodes. Catalyst loading can be controlled up to a maximum of 0.5 pincer complexes per formula unit [PdI-x, Zn5(OH)4-nx(btdd)3(H3-nPNNNP-PdI)xx = 0.06-0.5, n ≈ 2.75]. Oxidative ligand exchange was used to replace I- with weakly coordinating BF4- anions at the Pd-I sites, generating the activated PdBF4-x catalysts (x = 0.06, 0.10, 0.18, 0.40). The Lewis acid catalytic activity of the PdBF4-x series decreases with increasing catalyst density as a result of the appearance of mass transport limitations. Initial catalytic rates show that the activity of PdBF4-0.06 approaches the intrinsic activity of a homogeneous PNNNP-PdBF4 catalyst analogue. In addition, PdBF4-0.06 exhibits better catalytic activity than the metallolinker-based MOF Zr-PdBF4 and was not subject to leaching or catalyst degradation processes observed for the homogeneous analogue.