Anion˗π and Intramolecular Hydrogen Bond Interactions in the Various Complexes of 1,3,5-Triamino-2,4,6-trinitrobenzene with H-, F-, Cl- and Br- Anions

The quantum chemical calculations were performed to investigate the interplay between the anion˗π and intramolecular hydrogen bond (IMHB) interactions in the various complexes of 1,3,5-triamino-2,4,6-trinitrobenzene (ANB) with Hˉ, Fˉ, Clˉ and Brˉ anions. For better understanding the cooperative effects, the parent molecules (ANB) and the corresponding complexes of 1,3,5˗trinitrobenzene with the mentioned anions are also considered, as a set of the reference points. In this regard, the IMHB and anion˗π interactions are comprehensively analyzed by energetic, geometrical, spectroscopic and topological descriptors. It was found that the coexistence of the anion˗π and IMHB increases the strength of both interactions. Furthermore, the influences of the anion-π and IMHB interactions on the significance of the π˗electron delocalization (π˗ED) of the resonance assisted hydrogen bond (RAHB) units and the aromaticity of the benzene ring are evaluated by the harmonic oscillator model of aromaticity (HOMA), as a geometry based index. According to the HOMA values, we concluded that the coexistence of the mentioned interactions decreases the aromaticity of benzene ring and increases the π˗ED of RAHB units. Finally, the strength of the non-covalent interactions and the significance of π˗ED and aromaticity strongly depend on type of the anion.