Ligand dynamics on the surface of zirconium oxo clusters.

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 C2h symmetric; stepwise intramolecular exchange of the four non-equivalent ligands was observed when the temperature was raised from -80 degrees C to -50 degrees 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 Oh-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 micro3-OH group of the cluster. Thus, the motion of the ligand requires a concerted motion in three dimensions.