The origin of the surprising stabilities of highly charged self-assembled polymetallic complexes in solution.

The thermodynamics of electrochemical and complexation reactions involving the heterobimetallic triple-stranded helicates [MA(L5)3]n+ (M=Ru(II), Cr(III) and A=Ca(II), Lu(III)) reveal that solvation processes mask intramolecular intermetallic repulsions in solution, a phenomenon at the origin of the surprising stabilities of highly charged self-assembled polymetallic complexes in solution. A judicious combination of Born-Haber cycles and the Born equation restores the expected electrostatic trend in the gas phase, in which intermetallic interactions can be simply modeled using a standard Coulombic approach. Semiquantitative estimation and prediction of the contribution of the intermetallic repulsion to the total free energy of the formation of discrete polymetallic assemblies in solution become thus accessible. This point is crucial for programming stable metallosupramolecular architectures in solution.