Abstract
By means of quantum-mechanical calculations, we study the influence of the charge, spin, substituents, and atom encapsulation on the volume of the cages in icosahedral boranes and carboranes B12H12 2–, CB11H12 –, o-C2B10H12, m- C2B10H12, p-C2B10H12 and 1,2-disubstituted o-C2B10H12.
Monoradicals derived from hydrogen abstraction in o-
C2B10H12, m-C2B10H12, p-C2B10H12 lead to slight cage contractions (|ΔV| < 0.1 Å3 ). On the other hand, 1,2-disubstitution in o-C2B10H12 and their dianions derived from double proton abstraction on the susbtituent, and {Li+, Be2+} atom encapsulation in B12H12 2–, CB11H12
–, o-C2B10H12, m-C2B10H12, p-C2B10H12 always leads to a cage expansion, to a larger extent for endohedral compounds (ΔV ≈ 2 Å3 ) as compared to dianions derived from 1,2-disubstituted o-C2B10H12 (ΔV ≈ 1 Å3 ) and 1,2-disubstituted o-C2B10H12 (ΔV < 0.14 Å3 ).

