From Solid-State Structure and Dynamics to Crystal Engineering

The investigation of the factors responsible for the stability of the diverse crystal forms that a given molecule can adopt in the solid state (polymorphs, hydrates, cocrystals, etc.) requires an appreciation of the relationship between static and dynamic behavior of atoms and molecules about equilibrium and far from equilibrium positions in the crystal structure. This is particularly relevant when dealing with molecules that are structurally nonrigid at ambient conditions in other media (solution, gas phase). The ease of motion of molecules in molecular crystals depends on the distribution of first neighboring molecules and on the network of intermolecular interactions, which are, in turn, also responsible for the relative thermodynamic stability of solid phases. The knowledge of the intermolecular interactions and of their interplay with the ionic charges commonly present in inorganic, coordination polymers and organometallic compounds is indispensable the application of crystal engineering strategies in the inorganic chemistry area. This microreview article describes, with numerous examples coming mainly from the authors' work, the scientific route that has led from early studies on dynamical processes taking place in the solid state to the design and preparation of novel molecular aggregates involving, inter alia, hydrogen bonded organometallic molecules, charged coordination complexes and metal organic frameworks. The use of solvent-free mechanochemical mixing of reactants as a method of choice for preparing supramolecular aggregates and hybrid organic–inorganic cocrystals will be discussed.