B═N Bond Cleavage and BN Ring Expansion at the Surface of Boron Nitride Nanotubes by Iminoborane

Abstract

A new feature of reactivity of iminoborane (HBNH) at the surface of boron nitride nanotube has been revealed by this theoretical study. The HBNH molecule not only selectively breaks the B═N double bond of the BN nanotubes (BNNTs) but also expands the hexagonal network of the tube to larger cages at the surface. Such expanded structures are stabilizing by 30–50 kcal/mol depending on the chirality and reactive site of the tubes. Complexation energy decreases with diameter (because of the strain effect) of the tube and is lowest for a planar BN-sheet. However, a [2+2]-cycloaddition reaction that is common for iminoborane is also exhibited depending on the site and chirality. For zigzag tube, diagonal BN bonds, either at the edge or at the middle of the tube, are cleaved, but BN bonds parallel to the tube axis undergo cycloaddition reactions. In contrast, diagonal BN bonds of the armchair BN-tube prefer cycloaddition and bonds perpendicular to the tube axis follow this new reactivity pattern. Transition state...