The endohedral heterofullerenes (B@C₅₉B)₂, (B@C₅₉N)₂, (N@C₅₉B)₂ and (B@C₅₉N–N@C₅₉B) are investigated using dispersion corrected density functional theory. Several spin states of these complexes are considered and their stable spin states are reported. For ¹[(B@C₅₉B)₂] and ¹[(B@C₅₉N–N@C₅₉B)], the encapsulated atoms are positioned near the surface of the host cages, in contrast to other spin states where they are positioned at the centre of the cages. In complexes ¹[(B@C₅₉N)₂], ³[(B@C₅₉N)₂] and ⁷[(N@C₅₉B)₂], the guest atoms are found to be at the centre of the host cages. The spin polarization and the transfer of spin density between the components of the complexes for different stable spin states are analyzed. Based on the spin states of the complexes, the spin–spin interaction is found to be either ferromagnetic or anti-ferromagnetic. Unlike other complexes, in ¹[(B@C₅₉B)₂] and ¹[(B@C₅₉N–N@C₅₉B)] the spin density is transferred from the guest to the host followed by anti-ferromagnetic coupling between the monomers. The thermodynamic feasibility of formation of the complexes is also examined. The electron affinity, ionization potential and dipole moment of the above systems are determined. The singlet state of the heterodimer (B@C₅₉N–N@C₅₉B) showed high polarity due to the slight rotation along the dihedral angle ϕ_NCCB.