Theoretical and experimental studies of some main group compounds : from closed shell interactions to singlet diradicals and stable radicals

Abstract

Acquiring knowledge of different interactions within and between molecules is a fascinating undertaking as it not only deepens our understanding of chemical bonding but also offers insight into electronic structures, molecular properties and the connections between these two. This dissertation combines together three main group chemistry related topics within the aforementioned theme. Research presented in the first third of this dissertation describes wave function and density functional theory studies of weak inter- and intramolecular interactions in pnictogen-based dimers X3Pn···PnX3 (Pn = N-Bi; X = F-I), dithallenes RTlTlR (R = H, Me, tBu, Ph) and octachalcogen dications Ch82+ (Ch = S, Se). The conducted theoretical work revealed that dynamic electron correlation effects play a key role in the bonding of all examined systems. Most importantly, the results showed that the investigated Pn···Pn interactions are sufficiently strong to be useful in crystal engineering and they also provided the first comprehensive picture of transannular bonding in Ch82+. The second third of this dissertation focuses on the analysis of bonding interactions in group 13 dimetallenes REER (E = Al-In; R = H, Me, tBu, Ph) and in tetrachalcogen tetranitrides Ch4N4 (Ch = S, Se). The use of highly accurate theoretical methods provided insight into bonding in these systems and demonstrated that their electronic structures contain an important multiconfigurational component which had not been recognized before. Consequently, the published results give valuable new information about diradical contributions to bonding and serve as an illustrative example of the important role computational and theoretical methods nowadays play in the characterization of molecular systems. The last third of this dissertation discusses the results from systematic computational and experimental efforts targeting new stable radicals based on the ubiquitous β-diketiminate ligand. Density functional theory calculations, together with the characterization of the first spirocyclic aluminum bis-β- diketiminate radical, proved that this ligand framework offers a potential building block for the synthesis of a wide variety of new paramagnetic metal- ligand architectures.