Exploring the Programmable Assembly of a Polyoxometalate–Organic Hybrid via Metal Ion Coordination

The conformational flexibility and programmed assembly of a dumbbell-shaped polyoxometalate–organic hybrid molecule comprising two Dawson-type polyoxometalates linked by a 2,2′-bipyridine unit, which can be coordinate to metal ions, in this case of Zn²⁺, are described. SAXS, UV/vis, and NMR spectroscopic techniques confirm that the hybrid molecules exist as the <i>trans</i> dumbbell in metal-ion-free solutions and can be reversibly transformed into the <i>cis</i> dumbbell through coordination upon the addition of ZnCl₂ into a DMSO solution containing the hybrid. Subsequent addition of EDTA reverses the switching process by extracting the Zn²⁺ cations from the hybrid. During the interchange process between <i>trans</i> and <i>cis</i> dumbbells, a further reorganization of the hybrid molecules occurs through bond rotation to minimize steric clashes between the polyoxometalate subunits, in order to stabilize the corresponding dumbbell conformation. The Zn²⁺-controlled conformational transformation of the hybrid can be further utilized to manipulate the hybrid’s solvophobic interaction-driven self-assembly behavior in the metal-ion driven reversible formation of 140 nm sized vesicles, studied by laser light scattering techniques