Aspects of NMR Characterization of Metallacrowns

Metallacrowns (MCs) are self-assembled metallamacrocycles that confine a significant number of metal ions and organic ligands in a small molecular volume. These assembled structures present a cavity that can selectively encapsulate specific metal ions which provide MCs with peculiar spectroscopic features and reactivity. Also, MCs can bind inorganic and organic anions allowing their use in strategies of molecular recognition. For these reasons, including remarkable stability and inertness toward disassembly and the presence of paramagnetic ions in their structure, MCs possibly are among the most interesting metallamacrocyclic complexes known to date. The elucidation of dynamic processes of ligand and solvent exchange in solution is pivotal in the study of MCs as potential probes in biological imaging, as nanoshuttles for drug delivery or in molecular recognition and sensing. In this chapter, we will present and discuss representative examples of NMR investigations of metallacrowns reactivity, dynamics of assembly, and cations/anions binding. The strategies and conditions employed in the 1D NMR characterization of MCs will be discussed along with the most recent PGSE approaches. Also, we will discuss how the paramagnetic nature of these complexes opens a window into the study of their structure in solution through NMR.