Divergent Adsorption Behavior Controlled by Primary Coordination Sphere Anions in the Metal–Organic Framework Ni2X2BTDD

• Published in: Journal of the American Chemical Society 2021-10, Vol.143 (40), p.16343-16347
• Main Authors: Oppenheim, Julius J, Mancuso, Jenna L, Wright, Ashley M, Rieth, Adam J, Hendon, Christopher H, Dincǎ, Mircea
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.1c07449

CO, ethylene, and H2 demonstrate divergent adsorption enthalpies upon interaction with a series of anion-exchanged Ni2X2BTDD materials (X = OH, F, Cl, Br; H2BTDD = bis­(1H-1,2,3-triazolo­[4,5-b]­[4′,5′-i])­dibenzo­[1,4]­dioxin)). The dissimilar responses of these conventional π-acceptor gaseous ligands are in contrast with the typical behavior that may be expected for gas sorption in metal–organic frameworks (MOFs), which generally follows similar periodic trends for a given set of systematic changes to the host MOF structure. A combination of computational and spectroscopic data reveals that the divergent behavior, especially between CO and ethylene, stems from a predominantly σ-donor interaction between the former and Ni2+ and a π-acceptor interaction for the latter. These findings will facilitate further deliberate postsynthetic modifications of MOFs with open metal sites to control the equilibrium selectivity of gas sorption.