Stability of spherical molecular complexes: a theoretical study of self-assembled M12L24 nanoballs

Abstract

Supramolecular coordination complexes have become of great interest due to their broad spectrum of applicability, mainly in the area of biomedicine. Understanding the role played by the metal center and the weak interactions in the formation and stabilization of these compounds allow us to have a better design of these molecules and therefore a better guide for the examination of novel applications. In this work, we investigate the effect of noncovalent interactions and the presence of metal centers in the stabilization of Tominaga’s M12L24 nanoballs. We considered bis(4-pyridyl)-substituted bent frameworks involving two acetylenes spacers as the ligand (L), using –H, –CH3, and a cyanophenyl group as substituents, and two different metal cations: Pd2+ and Ni2+. We found that the bond distance between the metal and the ligand was smaller for the nickel complexes than for the palladium compounds. This is related to the dissociation energies (Ni2+ systems are more stable than Pd2+ compounds). Furthermore, nanoballs with the largest ligand’s substituent are significantly more stable than those with the smallest ligand’s substituents. Analyzing the frontier states and the Independent Gradient Model isosurfaces, we found that noncovalent interactions contribute to the stabilization of the complexes. Through the charge distribution, we observed that the metal also polarizes the density of the coordination bond. With these results we can conclude that metal centers and noncovalent interactions play an important role in the stabilization of nanoballs.