Design of a metal-organic framework with enhanced back bonding for the separation of N₂ and CH₄

Lee, K.; Isley, W. C., III; Dzubak, A. L.; Verma, P.; Stoneburner, S. J.; Lin, L.-C.; Howe, J. D.; Bloch, E. D.; Reed, D. A.; Hudson, M. R.; Brown, C. M.; Long, J. R.; Neaton, J. B.; Smit, B.; Cramer, C. J.; Truhlar, D. G.; Gagliardi, L.
J. Am. Chem. Soc. 2014, 136, 698 (doi:10.1021/ja4102979).

Gas separations with porous materials are economically important and provide a unique challenge to fundamental materials design, as adsorbent properties can be altered to achieve selective gas adsorption. Metal-organic frameworks represent a rapidly expanding new class of porous adsorbents with a large range of possibilities for designing materials with desired func-tionalities. Given the large number of possible frame-work structures, quantum mechanical computations can provide useful guidance in prioritizing the synthesis of the most useful materials for a given application. Here, we show that such calculations can predict a new metal-organic framework of potential utility for the separation of dinitrogen from methane, a particularly challenging separation of critical value for utilizing natural gas. An open V(II) site incorporated into a metal-organic frame-work can provide a material with a considerably higher enthalpy of adsorption for dinitrogen than for methane, based on strong selective back bonding with the former but not the latter.