The role of the Lewis acid-base properties in the supramolecular association of 1,2,5-chalcogenadiazoles

The secondary bonding interactions that link the supramolecular structures assembled by 1,2,5-chalcogenadiazoles were analyzed through explicit orthogonalization of molecular orbitals (NBO), topological analysis of the electron density (AIM), and the electron localization function (ELF). The results of these analyses are consistent with a bonding description that attributes important covalent and electrostatic character to these interactions. Application of these analyses to the individual molecules highlighted the structural features from which each of those contributions originates, namely the polarity and modest strength of the E-N bond. Both of these effects increase along the series S, Se, Te. Perturbations to the heterocycle electronic structure that result in a weaker and more polar E-N bond cause an increase in the Lewis acidity at the chalcogen centre, which in turn leads to stronger secondary bonding interactions with Lewis bases. Additionally, the contribution of dispersion forces is not negligible and is most important in the case of sulfur.