Geometric and electronic structures of B12C6N6 fullerene

An electron deficient fullerene B12C6N6 is studied by using ab initio calculations. The structure is generated by replacing N with C in the B12N12 cage to ensure only B–C and B–N bonds are formed. All the possible isomers are optimized and the low energy structures are determined. C and N atoms in the low energy isomers are inclined to segregate and form B2C2 and B2N2 squares. Natural bond analysis shows that the atomic orbitals of B, C and N in this cage hybrid approximately in sp2.3 and then form B–C and B–N bonds. The 2p orbitals perpendicular to the cage surface are partially occupied and the molecular orbitals formed by these orbitals are highly delocalized. The natural charge on N is about −1.17 in both B12N12 and B12C6N6, and the charge on C is −0.72 to −0.60. The molecular orbital compositions show that the B–N bonds are the same in B12N12 and B12C6N6, and the B–C bonds possess stronger covalent character. The HOMO of B12C6N6 is formed by 2p of B and C, and the LUMO is formed by 2p of C. The energy gap of C24, B12N12 and B12C6N6 is 2.52, 6.84 and 3.22 eV, respectively.