[Back]

J. Kreutzer, U. Schubert:
"Ligand exchange reactions on transition metal oxo clusters and applications in materials chemistry";
Poster: International Symposium on Small Particles and Inorganic Clusters XVII, Fukuoka, Japan; 2014-09-07 - 2014-09-12; in: "ISSPIC XVII - Program & Abstract", (2014), 185 (B36).

Transition metal oxo clusters find increasing interest in material science as nanosized building blocks, especially for inorganic-organic hybrid materials. Clusters with polymerizable ligands attached to the cluster surface can act as co-monomers in polymer synthesis. Thereby the inorganic moiety is incorporated in a polymer matrix by covalent bonding. Numerous transition metal oxo clusters with polymerizable ligands were synthesized and used to obtain polymers with tailored properties.
Most of the clusters used as co-monomers so far have a high number of polymerizable groups of the same kind on their surface, resulting in highly crosslinked polymers. Ligand exchange on transition metal oxo clusters is one way to control the ratio of functionalized and non-functionalized ligands and can lead to less crosslinked polymers. Furthermore it is possible to obtain clusters with more than one functional group in the ligand sphere in an easy-to-adjust ratio by ligand exchange reactions.
In this work we will present a detailed NMR study of exchange reactions on carboxylate substituted Zr/Ti oxo clusters with different carboxylic acids. We will show that ligand exchange on the cluster proceeds under retention of the cluster core also in cases where all ligands have been exchanged. Steric and electronic effects of the incoming ligand towards exchange reactions will be discussed. Scrambling reactions between clusters with two different types of ligands are an additional way to easily adjust the ligand composition of transition metal oxo clusters. Complementary applications of ligand exchange reactions in material science will be presented. Polymer properties such as glass transition temper ature and storage modulus as well as mechanical properties of the polymer can be changed gradually by controlling the ligand sphere of transition metal oxo clusters.