The Intricate Structural Chemistry of MII2nLn-Type Assemblies

The reaction of cis-blocked, square-planar MII complexes with tetratopic N-donor ligands is known to give metallasupramolecular assemblies of the formula M2nLn. These assemblies typically adopt barrel-like structures, with the ligands paneling the sides of the barrels. However, alternative structures are possible, as demonstrated by the recent discovery of a Pt8L4 cage with unusual gyrobifastigium-like geometry. To date, the factors that govern the assembly of MII2nLn complexes are not well understood. Herein, we provide a geometric analysis of M2nLn complexes, and we discuss how size and geometry of the ligand is expected to influence the self-assembly process. The theoretical analysis is complemented by experimental studies using different cis-blocked PtII complexes and metalloligands with four divergent pyridyl groups. Mononuclear metalloligands gave mainly assemblies of type Pt8L4, which adopt barrel- or gyrobifastigium-like structures. Larger assemblies can also form, as evidenced by the crystallogra...