Chemical bonding between thorium and novel BN nanomaterials

Abstract

We study the nature of chemical bonding of the thorium atom with novel BN-based nanomaterials: fullerenes B[Formula: see text]N[Formula: see text], B[Formula: see text]N[Formula: see text], B[Formula: see text]N[Formula: see text], and the BN analog of coronene—B[Formula: see text]N[Formula: see text]H[Formula: see text], used as a representative molecular fragment of the two dimensional hexagonal BN-sheet. Our ab initio calculations are performed within the dispersion-corrected density functional approach with a hybrid exchange-correlation potential. The smallest 20-atom BN-fullerenes B[Formula: see text]N[Formula: see text], B[Formula: see text]N[Formula: see text] proposed by us are shown to be stable and should be observable experimentally. Thorium is found at the center of these structures pushing the outer shell of atoms farther away. The shape of the B[Formula: see text]N[Formula: see text]-cage in Th@B[Formula: see text]N[Formula: see text] is conserved, while the shape of the B[Formula: see text]N[Formula: see text] molecule in Th@B[Formula: see text]N[Formula: see text] is largely deformed. The initially planar structure of B[Formula: see text]N[Formula: see text]H[Formula: see text] in the presence of thorium becomes corrugated, demonstrating pronounced off-plane displacements under the thorium atom. Other four-valent metals (Ti, Zr, and Hf) also cause off-plane displacements of B and N atoms albeit to a much smaller scale. In the 60-atom fullerene B[Formula: see text]N[Formula: see text], which is the BN analog of C[Formula: see text], two conformations of Th@B[Formula: see text]N[Formula: see text] are found: one is with thorium facing the hexagon with one B–B and one N–N covalent bonds and a second, lying 0.79 eV higher, with thorium close to the center of pentagon with one B–B covalent bond.