Do certain imidazolium-based ionic liquid ion pairs/mordenite capture H2S by conformational traps? An ONIOM-DFT study

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We present detailed ONIOM(ωB97X-D:PM6) calculations for the formation mechanism of novel composites combining protonic mordenites (H-MOR) with various ionic liquids: 1,3-dimethyl-imidazolium chloride [MMIm]Cl, 1-ethyl-3-methyl-imidazolium chloride [EMIm]Cl; 1-methyl-3-propyl-imidazolium chloride [PMIm]Cl; 1-butyl-3-methyl-imidazolium chloride [BMIm]Cl, 1-(2-hydroxyethyl)-3-methyl-imidazolium chloride [HEMIm]Cl, 1,3-dimethyl-1,3,2-diazasilolium chloride [MMSiN]Cl, and 1,3-dimethyl-1,3-diphospholium chloride [MMPP]Cl. The most feasible [M]-MOR formation mechanism ([M] + = [MMIm] + , [EMIm] + , [PMIm] + , [BMIm] + , [HEMIm] + , [MMSiN] + [MMPP] + ) involves an ion exchange at the T4O10 position favoring the isolation of a minimal number of [M] + isomers (i.e., conformational traps). The interaction of these [M]-MOR composites with pollutant gases has afterward been evaluated. Among the studied sytems, [EMIm]-MOR and [HEMIm]-MOR present electronic and steric conditions for potential applications in gas separation, capture, and storage (H 2 and H 2 S). The H-MOR framework exhibits two structural conformers with the [HEMIm] + cation in the confined space. Both, the MOR-T4O10-[HEMIm] and MOR-T4O10-[HEMIm] HB conformers, interconvert by a dynamic equilibrium with a transition state MOR-T4O10-TS1 acting as a conformational switch ( - ) that selectively recognizes and captures H 2 S through a plier-like conformation. • In silico design of novel composites combining Ionic Liquids with mordenite (MOR) was examined. • A composites formation mechanism that involves the ion exchange of H + by Imidazolium-based Ionic Liquid cation on T4O10 position in H-MOR. • The existence of conformational traps within the mordenite framework was demonstrated. • A new molecular H 2 S recognition/capture mechanism using [HEMIm]-MOR composite was proposed.