The duals of the most spherical closo borane deltahedra having from 6 to 16 vertices form a series of homologous spherical trivalent polyhedra with even numbers of vertices from 8 to 28. This series of homologous polyhedra is found in endohedral clusters of the group 14 atoms such as the endohedral germanium cluster anions [M@Ge10]3- (M = Co, Fe) and [Ru@Ge12]3- The next members of this series have been predicted to be the lowest energy structures of the endohedral silicon clusters Cr@Si14 and M@Si16 (M = Zr, Hf). The largest members of this series correspond to the smallest fullerene polyhedra found in the endohedral fullerenes M@C28 (M = Zr, Hf, Th, U). The duals of the oblate (flattened) ellipsoidal deltahedra found in the dirhenaboranes Cp*2Re2Bn-2Hn-2 (Cp* = η5-Me5C5; 8 ≤ n ≤ 12) are prolate (elongated) trivalent polyhedra as exemplified experimentally by the germanium cluster [Co2@Ge16]4- containing an endohedral Co2 unit.

BACKGROUND: Synthesis, properties, structural peculiarities, and applications of nanobuds and related nanostructures are discussed. In addition, few relevant patents to the topic have been reviewed and cited. According to observed properties and those predicted by DFT calculations, the nanobuds are semiconducting and stable in normal conditions, can accept adatoms and molecules. They contain a relatively chemically inert carbon nanotubes and more active fullerene species and can be compatible with a variety of other materials, in particular polymers. In addition to nanobuds for SWCNTs, the nanobuds with graphene, small fullerenes or metal nanobud-like structures are also known.
METHODS: We have undertaken an extensive search of bibliographic databases for peer-reviewed research literature using a focused review question and inclusion/exclusion criteria. The characteristics of screened papers were described and critically compared.
RESULTS: Thirty-six papers were included in the review, mainly from high-impact international journals. The published articles correspond to the range 2006-2016; the term \"nanobuds\" appeared in 2006 after their discovery. The reports included approaches of the synthesis of carbon nanobuds, their formation mechanism, in situ engineering, different modes of attachment of fullerene on carbon nanotubes, DFT and MD calculations, nanobuds containing small fullerenes and graphene nanobuds, information about related noble metal nanobuds, and applications of carbon nanobuds.
CONCLUSIONS: The findings of this review confirm the importance of novel less-common nanostructures on the basis of carbon for fundamental science, their unusual properties and current and possible applications.