Triple Helicate—Tetrahedral Cluster Interconversion Controlled by Host–Guest Interactions

A unique ligand design allows the formation of both an M₂L₃ triple helicate and an M₄L₆ tetrahedron (M=Ti, Ga; L=ligand based on 2,6-diaminoanthracene). Although the tetrahedron is entropically disfavored, a strong host–guest interaction with Me₄N⁺ is enough to drive the equilibrium towards the tetrahedron. Remarkably, the helicate can be quantitatively converted into the tetrahedron simply by addition of Me₄N⁺ (shown schematically).