Structure, stability and chemical bonding character of covalent boron azides BX(N3)2 (X=F, Cl, Br)

Geometrical structures and stability of covalent boron azides BX(N3)2 (X=F, Cl, Br), including a previously reported trans BCl(N3)2 structure 1 with Cs symmetry, were investigated at the B3LYP/6-311+G* level of theory. The optimized cis structures 2 with C2v symmetry are virtually degenerate to 1 and are more stable than the optimized structures 3 and 4. Analysis of the natural population for the BX(N3)2 (X=F, Cl, Br) systems indicates that the central N-N bond in azide groups is intermediate between a single and double bond, the terminal N-N bond trends to be intermediate between a double and triple bond, and the sp2 hybridization B atom donates an empty p orbital to form a large delocalization π46 bond, which make these covalent boron azides to be more stable.