Merging boron solid state and molecular chemistry: Energy landscapes in the exo/endo closo-borane complex Sc[B24H24]+

The crystal structure of ScB12 suggests the possible existence of the closo B24H242− borane and derived exo and endohedral complexes. The extraction of the B24 ‘perfect’ truncated octahedron from the ScB12 crystal structure and the minimization of the energy by means of quantum-chemical computations leads to a snub cube structure. The two found stable exohedral structures are energetically more favorable than the endohedral complex by only ∼1 and ∼9 kcal/mol. The optimized geometry of the B24H242− molecular structure can be derived from the crystal fragment through a shrinkage plus pseudo-rotation of the B24 cage. Analogous solid structures embedding truncated octahedra are also compared with the title structure.