Self-assembly of nanostructures with high complexity based on metal⋯unsaturated-bond coordination

[Display omitted] •Focus on metal⋯unsaturated-bond coordination for self-assembly.•Concerted metal–acetylene π-coordination afforded highly-entangled polyhedra.•Collaboration of weak and strong coordinations is promising for higher molecular complexity. The coordinative self-assembly of relatively simple building blocks toward complex nanostructures is currently of high interest in the context of developing artificial nanomaterials that are comparable to biological systems. Even though a substantial body of research has already been assembled, only few classes of coordination donors, namely, nitrogen- or oxygen-containing donors, have historically been used, as research has focused predominantly on the robustness and designability of the coordinated structures. As an alternative approach, the use of the relatively weak but loosely directed π-coordination between metal ions and unsaturated carbon–carbon bonds has emerged; this strategy is expected to provide structurally flexible and highly tolerant bonding in complex nanoarchitectures. Most prominently, studies that combine metal–acetylene π-coordination with conventional coordination have recently realized the formation of very large discrete polyhedral complexes with unprecedented molecular entanglement based on trifurcate motifs, which represent the tip of the iceberg in terms of the potential advantages of this concept.