Static and Dynamic Crystal Engineering: Towards New Materials Based on Boronic Acids and Solid-state Molecular Motion

The ultimate goal of crystal engineering is making crystals with a purpose. This means designing de novo molecular solids possessing precise structural and physicochemical properties and inducing subtle modifications to conveniently modulate said properties. In the continuous quest for novel crystalline materials, it is of fundamental importance to search for new building blocks, explore new interaction modes and new strategies for the modification of the structural properties of solids, such as the formation of co-crystals, salts, complexes or solid solutions. The research activity performed in my PhD was mainly dedicated to two topics: 1. the design and synthesis of new single-component and multi-component assemblies based on hetero-aryl boronic acids and the investigation of their recognition features; 2. the study of molecular motion in some crystalline complexes and salts and the modification of those dynamics through the principles of crystal engineering. The first topic is addressed in the second chapter of this thesis. A number of different solid forms were obtained exploiting the various interaction modes of some simple and inexpensive boronic acids, including an exfoliable layered co-crystal, supramolecular zwitterions, a polymeric ternary co-crystal and covalent zwitterionic adducts. The third chapter is dedicated to the latter topic. Supramolecular crystalline complexes and salts possessing parts in rapid motion were synthesised and characterised by means of combined XRD and solid-state NMR analyses. The formation of solid solutions was successfully employed to fine-tune the dynamical properties of those compounds. Finally, the high-pressure behaviour of some supramolecular crystalline rotors was studied by using diamond anvils cells (DACs).