Fig. 1
Relative energies of two isomers of pristine cages (BN)19 and of their Ti-doped complexes. a Isomer 1 is the lowest energy form of (BN)19, consisting of 7 squares, 13 hexagons, and 1 octagon, with no B–B or N–N bond present. Isomer 2 contains 3 squares, 6 pentagons, and 12 hexagons. The presence of two B–B and two N–N bonds makes the latter isomer lie significantly higher in energy than the former. b Conversely, when doped with a single Ti atom, cage 2 becomes much more stable than cage 1, and gives the global minimum structure of Ti(BN)19. For both cages, the exohedral complex, Ti \(\subset\) (BN)19, has substantially lower energy than the corresponding endohedral one, Ti@(BN)19. All relative energies (including zero-point energy correction) have been obtained from DFT calculations. Boron, nitrogen, and titanium atoms are indicated by pink, blue, and dark red circles, respectively. Squares, pentagons, hexagons, and octagons are shown in green, cyan, white, and magenta, respectively
