Nouveaux outils pour l'analyse de liaisons chimiques remarquables : caractérisation théorique de la nature des liens avec le béryllium

Abstract : The chemical bond is among the oldest and most important concepts in chemistry because it allows to describe chemical properties of a system, as well as to understand and predict chemical reactions. The main goal of this PhD thesis is to study new types of chemical interactions involving the beryllium atom. Be atom has a rich chemistry due to its low-lying pBe orbitals, but its high toxicity has limited the number of experimental studies, enhancing the importance of theory in the description of Be compounds. This thesis reports the theoretical analysis of three new types of Be bonds using high-level ab-initio and Density Functional Theory, and the applications of the Total Position Spread Tensor (TPS) to molecular systems. First, the non-covalent Beryllium Bonds (BerB). This type of bond is formed by an interaction between a Be moiety acting as a strong Lewis Acid (LA) and a Lewis Base (LB). The interaction between beryllium LA and fluorine derivatives (FR) generates a shole in the fluorine atom, otherwise not possible, opening the possibility to design new materials where fluorine binds through halogen bonds. This same interaction decreases the F-R bond energy, turning the F-R homolytic dissociation in an exothermic process, and suggesting BerBs can be used to produce spontaneously radical species. Moreover, in this thesis, Intramolecular Beryllium Bonds (IBerB) were studied in malonaldehyde- and tropolone-like systems. This interaction is stronger in unsaturated systems than in their saturated analogues due to the increase of the acidity and basicity of the LA and LB, respectively. Second, the intramolecular Be-Be bond in disubstituted naphthalene complexes. The anion species of 1,8-diBeY1-naphthalene derivatives show a very strong one-electron Be-Be bond. This bond is eight times stronger and 0.5 Å shorter than the one in the isolated dimer. These systems present high electron affinities, which give to them an exceptional property: the ability to behave as what we have named anion sponges. It was found that the interaction between anions and Be disubstituted naphthalene is among the highest anion affinities reported in the literature for neutral compounds. This property could lead to a wide range of applications as anions receptors and sensors. Third, the interaction between the Be2 molecule and Lewis bases, which has shown to en-hance the strength of the Be-Be bond compared with the isolated molecule. The non-covalent interaction in complexes of the type L : Be-Be : L decreases the distance and increases the strength of the Be-Be bond. The effect over the Be2 moiety depends on the nature of the Lewis bases. The most dramatic effect occurs when L are radical species. The Be-Be bond in this type of complexes is among the strongest reported in the literature due to an increase of the Be2 oxidation state from Be0 to Be2+. The same effect is found in ligands with pL orbitals, which conjugate with the pBe orbitals and increase the oxidation state of the Be2 moiety to +1. Therefore, the Be-Be interaction becomes stronger than the free Be2 molecule, although still weaker than that of complexes with radical species. At last, the complexes where the Be2 moiety remains neutral and interacts with the lone pairs of the LB show, to the best of our knowledge, the strongest Be-Be bond reported in the literature for the neutral Be dimer. Finally, the TPS is proposed as a new method for the description of chemical bonds. The TPS is quantity that describes the electron and spin fluctuation when a system is perturbed. In this PhD thesis the TPS is applied to diatomic molecules and to Be-carbonyl derivatives. The tensor shows a different behavior depending on the type of interaction, thus allowing the distinction between a covalent, ionic, charge-shift, and other types of bonds, and at the same time the tensor identifies the electron correlation nature of the system.
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Oriana Brea Noriega. Nouveaux outils pour l'analyse de liaisons chimiques remarquables : caractérisation théorique de la nature des liens avec le béryllium. Theoretical and/or physical chemistry. Université Paul Sabatier - Toulouse III, 2017. English. ⟨NNT : 2017TOU30039⟩. ⟨tel-01811168⟩

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