Ligand dynamics on the surface of zirconium oxo clusters

Abstract

The dynamics of carboxylate ligands on the surface of zirconium oxo clusters was investigated in two case studies. Zr₄O₂(methacrylate)₁₂ was investigated by one- and two dimensional NMR spectra both in the solid state and in solution. In solution, the cluster is C_2h symmetric; stepwise intramolecular exchange of the four non-equivalent ligands was observed when the temperature was raised from −80 °C to −50 °C. The individual exchange processes were assigned to different ligand positions. Ab initio molecular dynamics simulations were performed for Zr₆(OH)₄O₄(formate)₁₂ to study the trajectory for the rearrangement of three chelating ligands into bridging positions, i.e. the conversion of the C₃-symmetric into an O_h-symmetric cluster. The observation of a dip in the energy barrier along the reaction coordinate was related to the intermediate formation of hydrogen bonds between the moving oxygen atom of the rearranging ligand and a μ₃-OH group of the cluster. Thus, the motion of the ligand requires a concerted motion in three dimensions.