Resumen de Understanding the physical origin, topology and strength of noncovalent interactions by means of computational tools
Structure and stability of molecules, the formation of supramolecular aggregates in the solid state or in solution and, therefore, many chemical and biological processes in which they participate depend heavily on noncovalent interactions (NCIs). To fully exploit these weak interactions in order to reach specific chemical, biological and technological goals, a thorough understanding of their properties at the molecular level is crucial. In this doctoral thesis, different types of NCIs have been studied in detail in the gas phase using a combination of structural and computational methods. On one hand, searches in the Cambridge Structural Database (CSD) have revealed unnoticed intramolecular and intermolecular short contacts that dictate the structure of several families of molecules in their crystalline phases. Moreover, the analysis of the experimental structures has helped to identify the geometrical preferences that maximize the interaction strength. On the other hand, accurate density functional theory (DFT) calculations and other computational techniques have provided reliable information needed to unveil the energetics and physical nature of these interactions. The noncovalent interactions studied in this work are (1) Li···Li and X···X through-ring interactions in Li2X2 rings, (2) lone-pair-carbonyl interactions in acyl halides, (3) electrostatically disfavoured Br···C=O contacts, (4) sigma-hole interactions between lead(II) and sulphur or oxygen, (5) [N···I···N]+ halonium bonding, and (6) azido···azido contacts in metal complexes with different interaction topologies. The results indicate that, although the atoms or moieties involved are different, the origin of all these attractive interactions lies in the subtle interplay of the various contributions (Pauli exchange-repulsion, electrostatics, charge transfer, polarization, and dispersion forces) acting upon the formation of noncovalently-bonded systems, differing only in the relative weights of these forces in the overall interaction strength.
