Understanding the Nature of Weak Interactions Between Functionalized Boranes and N/O, Promising Functional Groups for Gas Separations.

The separation of nitrogen and oxygen gases is considered as a very challenging process, since both O-2 and N-2 are nonpolar molecules with similar kinetic diameters. Electronic structure theory can provide a fundamental understanding of effects that can lead to selective binding of nitrogen or oxygen gas for the development of novel separation processes. Boranes can bind dinitrogen through a dative bond, where the boron acts as a sigma acceptor and back-donates through pi orbitals. To better understand these interactions, we have performed highly accurate CCSD(F12)(T) and CCSDT(Q) computations for the BH3-N-2 and BH3-O-2 complexes. The coupled-cluster binding energies were used as reference for benchmarking different density functionals, and larger functionalized boranes were examined at the M05/def2-TZVPPD level. Symmetry adapted perturbation theory (SAPT) calculations were performed for the elucidation of the nature of the interaction between nitrogen and substituted boranes and how direct or distal functionalizations affect the strength of the weak dative bonds. By use of these methods, several boranes were found to bind N-2 over O-2. These molecular species are promising functional groups for incorporation into the next generation of advanced materials for efficient N-2/O-2 separations.