RESUMO
The nature of non-covalent interactions in self-assembling systems is a topic that has aroused great attention in literature. In this field, the 1,3,5-triazinane-2,4,6-trione or cyanuric acid (CA) is one of the most widely used molecules to formulate self-assembled materials or monolayers. In the present work, a variety of molecular aggregates of CA are examined using three different DFT functionals (B3LYP, B3LYP-D3, and ω-B97XD) in the framework of the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis. Herein, a step by step aggregation path is proposed and the origin of cooperative effects is also examined. It is shown that a greater cooperativity is not always associated with a greater binding energy, and the greatest cooperative effect occurs with highly directional hydrogen bonds. The intramolecular charge transfers play a key role in this effect. Graphical abstract The noncovalent interactions in cyanuric acid supramolecules were analyzed. The calculations provide insights into the self-assembly steps from dimers to rosette-like motif. The complexes with collinear hydrogen bonds show positive cooperativity, while in the arrangement with double hydrogen bonds the cooperative effect is essentially zero.
RESUMO
Density functional theory (DFT) and atoms in molecules theory (AIM) were used to study the characteristic of the noncovalent interactions in complexes formed between Lewis bases (NH(3), H(2)O, and H(2)S) and Lewis acids (ClF, BrF, IF, BrCl, ICl, and IBr). In order to compare halogen and hydrogen bonds interactions, this study included hydrogen complexes formed by some Lewis bases and HF, HCl, and HBr Lewis acids. Ab initio, wave functions were generated at B3LYP/6-311++G(d,p) level with optimized structures at the same level. Criteria based on a topological analysis of the electron density were used in order to characterize the nature of halogen interactions in Lewis complexes. The main purpose of the present work is to provide an answer to the following questions: (a) why can electronegative atoms such as halogens act as bridges between two other electronegative atoms? Can a study based on the electron charge density answer this question? Considering this, we had performed a profound study of halogen complexes in the framework of the AIM theory. A good correlation between the density at the intermolecular bond critical point and the energy interaction was found. We had also explored the concentration and depletion of the charge density, displayed by the Laplacian topology, in the interaction zone and in the X-Y halogen donor bond. From the atomic properties, it was generally observed that the two halogen atoms gain electron population in response to its own intrinsic nature. Because of this fact, both atoms are energetically stabilized.