Towards engineering of solid-state supramolecular rotors via halogen bonding

Halogen bonding (XB), namely any interaction involving halogen atoms as electrophilic species, is attracting an ever-increasing interest thanks to its unique physico-chemical properties, specifically its strength, directionality, and tunability. All these features make the halogen bond a precious structural tool for the design and synthesis of novel functional materials with new and exciting properties. My PhD project was devoted to study this rather peculiar non-covalent interaction and expand its frontiers from fundamental aspects towards engineering a new class of functional materials. Specifically my work has been focusing on the two following research strands: • Studying halogen bonding at a fundamental level by focusing on new tools for its identification and characterization. To reach this goal we built libraries of halogen-bonded complexes, and coupled standard characterization techniques (thermal analysis and XRD measurements) with new experimental approaches to characterize the complexes. In particular, we employed Attenuated Total Reflection Far-IR spectroscopy and solid-state NMR techniques (15N and 13C) to search for diagnostic features of the XB occurrence and geometrical features thereof. Furthermore, we complemented experimental data analysis with theoretical calculations to rationalize our findings. • Engineering amphidynamic cocrystals based on halogen bonding and studying the effect of the nature and strength of the XB on the dynamics of these systems. Firstly, we synthesized the molecular building blocks through conventional organic synthesis, then we obtained the crystalline supramolecular rotors by co-crystallization, and finally we fully characterized the obtained species, focusing on crystal structures and internal dynamics. To do so, we used variable temperature (VT) single crystal XRD and solid state NMR (1H spin- lattice relaxation and 2H quadrupolar echo) experiments. Finally, we compared the kinetics and thermodynamics related to the rotators motion in isostructural supramolecular rotors to see the effect of the XB strength on the rotators dynamic performances.

Il legame alogeno, ovverosia qualsiasi interazione che coinvolga un atomo alogeno come specie elettrofila, sta attirando un crescente interesse nella comunità scientifica, grazie alle sue proprietà chimico-fisiche uniche, che lo rendono un prezioso strumento per la sintesi e la progettazione di nuovi materiali funzionali. Il mio dottorato è stato dedicato allo studio di questa specifica interazione non covalente, sia dal punto di vista di studi fondamentali che per lo sviluppo di una innovativa strategia per l'ingegnerizzazione di rotori supramolecolari allo stato solido. In particolare mi sono dedicato a studi spettroscopici (spettroscopia vibrazionale e NMR allo stato solido) di cocristalli basati su legame alogeno per sviluppare nuove tecniche diagnostiche di questa interazione non covalente, laddove tecniche di routine non siano disponibili. Seconda parte del mio dottorato è stata dedicata allo sviluppo di una nuova classe di materiali dinamici basati sul legame alogeno.