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

Removing dinitrogen, an omnipresent but noncombustible contaminant, from natural gas or other methane-rich gases is an extraordinarily difficult separation based on physical properties alone, as both gases lack a permanent dipole and have similar polarizabilities, boiling points, and kinetic diameters. In this work, by using dispersion-corrected density functionals and wavefunction approaches, we predict a new metal-organic framework (MOF) of potential utility for the highly selective and efficient separation of dinitrogen from methane, a particularly challenging separation of critical value for utilizing natural gas. Selective back bonding interactions from the vanadium(II) cation centers in V-MOF-74 to the unoccupied $\pi$* orbitals of N2 can be used to separate N2/CH4 mixtures. We compare our calculations with the experimentally characterized Fe-MOF-74.