An Organic Receptor Isolated in an Unusual Intermediate Conformation: Computation, Crystallography, and Hirshfeld...

1,1″-1,4-Phenylene-bis(methylene)bis-4,4'-bipyridinium cation [C₂₈H₂₄N₄]²⁺ (c), an organic receptor that generally crystallizes in its anti conformation, has recently been shown to be isolated in its syn conformation in an ion-paired compound [C₂₈H₂₄N₄][Zn(dmit)₂]·2DMF (dmit^2- = 1,3-dithiole-2-thione-4,5-dithiolate; DMF = dimethylformamide). In this article, we demonstrated that the same receptor [C₂₈H₂₄N₄]²⁺ (c) can also be stabilized in an unusual intermediate conformation (neither syn nor anti) with PF₆^- anion in compound [C₂₈H₂₄N₄](PF₆)₂·(1,4-dioxane) (1·(1,4-dioxane)). The energetically favored anti conformation has been described in its nitrate salt [C₂₈H₂₄N₄](NO₃)₂·2H₂O (2·2H₂O). Compounds 1·(1,4-dioxane) and 2·2H₂O, crystallizing in triclinic and monoclinic systems with space groups P1̅ and P2₁/n, respectively, were additionally characterized by Hirshfeld surface analysis. The density functional theory calculations are performed to understand the internal mechanism of the stability of various conformers of cationic receptor c, compound 1, and compound 2. In conjunction with the electronic stability of the conformers, the natural bond orbital analysis and conformational equilibrium constants at different temperatures are also calculated to find out the sources of the different stability of the various conformers of experimentally synthesized compounds.