Density Functional Theory Study. Hypervalent Iodine (iii) Alkyl Crown Ether Supramolecular Interaction

Hypervalent compounds have attracted a lot of attention recently. Self-assembly of molecular subunits into supramolecular structures via hydrogen bonding or a transition-metal coordination is a well-documented phenomenon of exceptional significance, but the self-assembly field of hypervalent compounds is studied scarcely. Secondary bonding between heavier main-group atoms has also been recognized as an important non-covalent interaction that can be exploited for the rational design of supramolecuar structures. Secondary I…O bonds represent an essential feature of structural chemistry of hypervalent iodine. Masahito Ochiai's team has studiedλ³ -iodane-crown-ether on experiment, but we haven't seen reports on theoretical studies of intermolecular interactions in these complexes. The present study has been undertaken in an attempt to find the differences of intermolecular interactions between hypervalent complexes and non-hypervalent complexes, the nature of intermolecular interactions, and the factors that effect the stability of the hypervalent-complexes.In this thesis, we use program ADF based on Density-Function theory to study the hypervalent-iodine-crown-ether and non-hypervalent-iodine-crown-ether dimmers exactly. The theoretical analysis and experimental results show that calculating at PBE/TZP level is the suitable method for these systems. The geometrical structures of complexes are optimized and the interaction energy is decomposed.In I₂(ICl)-18-crown-6, the iodine atom only contacts with single oxygen atom, and the angle of I(C1)—1…O is near to 180°. The form of the non-hypervalent-iodine complexes is the result of electrostatic interaction and orbital interaction together, and the percentage of the electrostatic interaction contributing to the total attraction interactions is 56%～57%. It reflects that electrostatic interaction is slightly dominant.Inλ³-iodane-crown-ether, the iodine atom contacts with more than two oxygen atoms, and the shape of C—I…O is near to linear. The form of the hypervalent-iodine complexes is also the result of electrostatic interaction and orbital interaction together, and the percentage of the electrostatic interaction contributing to the total attraction interactions is 60%～63%. It reflects that electrostatic interaction is dominant absolutely.In short, hypervalent-iodine complexes are very stable, but the non-hypervalent-iodine complexes are not. It will make us to enhance the stability of hypermolecular complexes. The form of the two kinds of complexes is the result of electrostatic interaction and orbital interaction together, and electrostatic interaction is dominant either. However, electrostatic interaction is less dominant in non-hypervalent-iodine complexes. Moreover, the stability of complexes is influenced by substituted groups on hypervalent atom, ring size in crown ethers, and electronegativity of hypervalent elements.