A density functional theory study of small base molecules and tetrahedral and cubane-like group V clusters encapsulated in B-80 shows that the boron buckyball is a hard acid and prefers hard bases like NH3 or N2H4 to form stable off-centered complexes. In contrast, tetrahedral and cubane-like clusters of this family are metastable in the cage. The most favorable clusters are the mixed tetrahedral and cubane clusters formed by nitrogen and phosphorus atoms such as P2N2@B-80, P3N@B-80, and P4N4@B-80. The boron cap atoms are electrophilic centers, and prefer mainly to react with electron rich nucleophilic sites. The stability of the complexes will be governed by the size and electron donating character of the encapsulated clusters. B-80 forms stable complexes with hard materials where a bidentate interaction of the encapsulated molecule with two boron cap atoms is preferred over a single direct complex toward a single endohedral boron.