Interaction of Boron Clusters with Aantisite Defective BNNTs: A DFT Study

Functionalization of the homonuclear nitrogen-nitrogen bonds of antisite defective (4, 4) BNNTs was investigated by quantum chemical calculations through their interaction with a B6 boron cluster. Two types of antisite defects were considered, exchange antisite defect produced by 180º rotation of a BN bond, and substitutional antisite defect produced by the substitution of a B atom with an N atom. Being able to stabilize an extra-added electron, the symmetric octahedral B6— ion shows magnetic and semiconductor behaviors which make the B6 particle a promising candidate for the search of novel nano-devices [1]. Six N-N bonds at the edges, near the edges, and in the middle of antisite defective BNNTs, lying diagonal or perpendicular to the tube axis, are considered for functionalization. The M06-2X functional in combination with 6-311+G (d, p) basis set is used for geometry optimizations to include correlation effects [2]. Based on our results, two-fold coordination together (double ring configuration of boron cluster) with the drastic structural changes and N-N bond cleavage (3.13-3.75 Å) occur between double ring B6 and BNNT surface. B-B bond lengths of adsorbed double ring B6 are obtained to be within 1.571–1.838 Å, shorter than those in a free B6 octahedron. The negative values of reaction energies indicate the exothermic character of the functionalization process. Functionalization of N-N bonds at the edge or near the edges of the narrower tubes is also found to be more favorable than those in the middle of the tubes. In the most stable complex antisite defective BNNT−B6, involving N-N bond at the edge, the B6 molecule pulls apart the N-N bond and becomes an integral part of the tube by expanding the original hexagonal ring. However, in other antisite defective BNNT-B6 clusters, involving N-N bonds at the middle of the tubes or near the edges, double ring B6 acts as a bridge at the top of the decagon of BNNTs [3].