A polar/ π model of interactions explains face-to-face stacked quinoid rings: a case study of the crystal of potassium hydrogen chloranilate dihydrate
Résumé
The nature of interactions between face-to face alternate stacked quinoid rings with π-systems, observed with short interring centroid•••centroid distance is analyzed by experimental and theoretical methods. Charge density studies based on X-ray diffraction and DFT calculations, complemented by impedance spectroscopy were employed to define the electronic and structural characteristics of the quinoid rings responsible for their interactions within the crystal packing. The crystal packing is mainly stabilized by several salt bridges between the K + cation and the hydrogen chloranilate anions. The proximity and orientation of the stacked quinoid rings in parallel roto-inversion arrangement is mainly governed by non-covalent interactions of unusual strength. Their estimated energy , more than 10 kcal mol-1 , as calculated by DFT methods, is comparable to medium-strong hydrogen bonding. It is the result of the unique electronic structure of 2,5-dihydroxyquinonate monoanion, which exhibits alternating electron-rich and electron-poor regions. Thus, the nature of interactions between π-systems of quinoid rings can be described by a polar/π model. These interactions have a great potential in crystal engineering and may be employed in design of functional materials.
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