PhD Johannes Kreutzer

Ligand Exchange Reactions of Transition Metal Oxo Clusters and their Application for the Synthesis of Inorganic-Organic Hybrid Materials

Abstract

Ligand exchange reactions of transition metal oxo clusters and the impact of modification of the ligand sphere of the clusters on properties of the hybrid materials was investigated.

Ligand binding energies of different ligands were calculated by means of DFT calculations. Different basis sets and functionals were evaluated with respect to a sufficiently accurate description of the geometry and the vibrational modes of the cluster Zr4O2(OMc)12 (OMc = methacrylate). Ligand binding energies of the methacrylate ligands with respect to different positions on the cluster and to electronic effects of different substituents on the ligands were also investigated.

The methacrylate ligands of Zr4O2(OMc)12 were completely exchanged with pivalic acid to verify that exchange reactions with carboxylic acids on Zr4O2(OMc)12 proceed under retention of the cluster core. Ligand exchange with different sterically demanding ligands was probed and the steric influence on the equilibrium reaction investigated.

Scrambling reactions between clusters with the same cluster core but different ligands were investigated by two - dimensional NMR spectroscopy and are a second preparative route to mixed - ligand clusters.

The question of site - selective ligand exchange was investigated by exchange of chelating carboxylate ligands with acetylacetonate. However, the stability of the cluster core seems to be of uttermost importance in this reaction. Besides successful site - selective ligand exchange, rearrangement of clusters and degradation was also observed.

The impact of ligand exchange reactions on properties of hybrid materials was investigated. Thereby different amounts of the methacrylate ligands of Zr4O2(OMc)12 was exchanged with pivalate ligands. Polymerization led to hybrid materials with different crosslinking densities. Mechanical and thermal properties of these hybrid materials were investigated. Furthermore, bifunctional clusters were synthesized by ligand exchange reactions and incorporated in a polymer network by STED lithography. After the lithographic process, it was shown that the second functionality remains active for chemical reactions.