1. What is the new discovery that you made?
In our research, we use transition metal cations and banana-shaped organic molecules as building blocks to form and functionalise nano-sized rings and cages. In this publication we have found that certain Palladium-based structures form only in a distinct solvent, whereas in other solvents the formation seems to be disfavoured. For the first time, we were now able to obtain a M8L16 metallo-supramolecular catenane (made by two entangled rings; M = metal, L = ligand). To elucidate its structure, we used nuclear magnetic resonance spectroscopy, mass spectrometry and X-ray diffraction techniques.
2. What is its significance?
The significance of our findings can be illuminated from two perspectives: On the one hand, intensive research conducted by groups around the world has collected a set of rules concerning the size, shape and topology of self-assembled structures of the MnL2n-type, but catenation has never been observed for Palladium-based assemblies of this size. On the other hand, mechanically interlocked nanostructures are raising considerable interest as components of artificial molecular machines, substantiated by the 2016 Nobel Prize in Chemistry that was awarded to Sauvage, Feringa and Stoddart. Such self-assembled structures with increasing complexity promise future application as selective receptors, enzyme-mimicking catalysts and stimuli-responsive materials.
3. Is this related to Solvation Science? If yes, how?
Aside from the metal coordination geometry and various non-covalent attractive and repulsive forces, the solvent plays a major role. The importance of solvation in the stepwise assembly, catenation and aggregation of hollow supramolecular structures from simple organic molecules and metal cations, serving as a glue to join the nano-sized architectures, has been disregarded for a long time. To improve the predictability of the molecular design approaches, a deeper understanding of the solution-based formation of these compounds is needed. RESOLV gives us the possibility to examine solvation effects by a joint effort between supramolecular synthesis, state-of-the-art spectroscopy and high-level theoretical methods.
W. M. Bloch, J. J. Holstein, B. Dittrich, W. Hiller, G. H. Clever, Hierarchical Assembly of an Interlocked M8L16 Container, Angew. Chem. Int. Ed. 2018