Prediction of endohedral borafullerenes X@B32C36

Context Inspired by the newly synthesized endohedral fullerene T CH₄@C₆₀ (1) and based on extensive density functional  theory calculations, we predict herein a series of endohedral borafullerenes C₃ CH₄@B₃₂C₃₆ (4), T BH₄@B₃₂C₃₆^– (5), C₁ H₂O@B₃₂C₃₆ (6), C₃ NH₃@B₃₂C₃₆ (7), and T C₈@B₃₂C₃₆^2– (8) which possess a B₃₂C₃₆ (3) shell isovalent with C₆₀, with  the neutral D₂ C₈@B₂₄C₄₄ (9) obtained from C₈@B₃₂C₃₆^2– (8) by symmetric C─B substitutions. Detailed adaptive natural  density partitioning (AdNDP) bonding analyses and iso-chemical shielding surfaces (ICSSs) calculations indicate that these  core–shell species are spherically aromatic in nature, rendering high stability to the systems. More interestingly, based on  the calculated efective donor–acceptor interaction between LP(O)→LV(B@B₃C₃) in H₂O@B₃₂C₃₆ (6), we propose the  concept of boron bond (BB) in chemistry which is defned as the in-phase orbital overlap between an electronegative atom A  as lone-pair (LP) donor and an electron-defcient boron atom with a lone vacant (LV) orbital as LP acceptor. A boron bond  appears to possess about 20~30% of the bond dissociation energy of a typical A-B covalent bond.