Imposing control on self-assembly: rational design and synthesis of a mixed-metal, mixed-ligand coordination cage containing four types of component

Retrosynthetic analysis of a [M₁₆L₂₄]³²⁺ coordination cage shows how it can be assembled rationally, in a stepwise manner, using a combination of kinetically inert and kinetically labile components. Combination of the components of fac-[Ru(L^ph)₃](PF₆)₂, Cd(BF₄)₂ and L^naph in the necessary 4 : 12 : 12 stoichiometry afforded crystals of [Ru₄Cd₁₂(L^ph)₁₂(L^naph)₁₂]X₃₂ (X = a mono-anion) in which the location of the two types of metal ion [Ru(II) or Cd(II)] at specific vertices in the metal-ion array, and the two types of bridging ligand (L^ph and L^naph) along specific edges, is completely controlled by the synthetic strategy. The incorporation of four different types of component at pre-determined positions in a coordination cage superstructure represents a substantial advance in imposing control on the self-assembly of complex metallosupramolecular entities.