Infrared Spectroscopy and Bonding of the B(NN) and B(NN) Cation Complexes.

The boron-dinitrogen cation complexes B(NN) and B(NN) are produced in the gas phase and are studied by infrared photodissociation spectroscopy in the N-N stretching vibrational frequency region. The geometric and electronic structures are determined by comparison of the experimental spectra with density functional theory calculations. The B(NN) cation is characterized to have a closed-shell singlet ground state with planar symmetry. The B(NN) cation is determined to have a B═B bonded (NN)BBNN structure with symmetry. Two isomers of the B(NN) cation contribute to the experimental spectrum. One is a N-tagged complex involving a B(NN) core ion. Another one is a B-B bonded B(NN) complex with a planar structure. Bonding analyses reveal that the B-NN interactions in these complexes come mainly from covalent orbital interactions, with the NN → B σ donation being stronger than the B → NN π back-donation.