Ligand design for hollow spherical complexes

Coordination chemistry may be used to synthesise large molecules with a closed cavity of molecular dimensions and of roughly equal size in three dimensions. The systems discussed here will involve polytopic ligands linked into spherical shapes by metal coordination. After discussing general strategies for their synthesis using the coordinate bond, studies on systems possessing five-fold symmetry are discussed. This is particularly favourable for the formation of spherical molecules, and some of the problems of multicomponent self-assembly are discussed. After reviewing some recent work, it is suggested that either the combination of three-fold symmetry with four-fold or five-fold symmetry is particularly suitable for sphere formation.

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► Coordinate bonds can assemble large pseudo-spherical models of nanometric size.
► Self-assembly approaches allow combination of many components.
► Judicious incorporation of symmetry into ligands favours discrete cages over extended structures.