title: Unique interactions between diborane and pi orbitals: blue- or red-shifted hydrogen bonding?
abstract: A new type of hydrogen-bonding interaction in the diborane (B 2H 6)...pi (benzene C 6H 6, 1,3-cyclopentadiene C 5H 6, and cyclobutadiene C 4H 4) system is identified with the natural bond orbital and atoms-in-molecules analyses based on ab initio calculations. In comparison with the symmetric and asymmetric stretching vibrational modes of the bridging hydrogen atoms in free B 2H 6, the frequencies of the symmetric mode are red-shifted for B 2H 6...C 6H 6 and B 2H 6...C 5H 6 but blue-shifted for B 2H 6...C 4H 4. The frequency blue shifts of the asymmetric mode are found for all three complexes; the most significant blue shift is 14.73 cm (-1) for the asymmetric mode in B 2H 6...C 4H 4. In these complexes, the electron-deficient three-center two-electron bond B-H 1-B facing the pi orbital is shortened, while the opposite B-H 2-B bond is elongated.
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui, 230026, China. sxtian@ustc.edu.cn
authors.forename: Shan Xi
authors.initials: SX
authors.lastname: Tian
authors.forename: Hai-Bei
authors.initials: HB
authors.lastname: Li
authors.forename: Yubin
authors.initials: Y
authors.lastname: Bai
authors.forename: Jinlong
authors.initials: J
authors.lastname: Yang