Experimental and Computational Study of Counterintuitive ClO₄^–···ClO₄^– Interactions and the Interplay between π⁺–π and Anion···π⁺ Interactions

The novel noncovalent interactions between the charged and neutral aromatic rings and with anions are utilized to design the solid-state assembly of triply protonated PTPH₃ (PTP = 4′-(4-pyridyl)-3,2′:6′,3″-terpyridine) with H₂O and three ClO₄^–, which is synthesized and characterized by single-crystal X-ray diffraction analysis. Crystallography reveals that the π⁺–π⁺, π⁺–π, and various anion···π interactions are the major driving forces in the stabilization of the self-assembled structure. In the title complex, a layered assembly is formed through the mutual influence of π⁺–π⁺ and π⁺–π interactions. The anions are interacting with the charged π-acceptors, which are again stabilized through π⁺–π interactions. Therefore, the overall stabilization is governed through π⁺–π/π–π⁺, (π⁺–π⁺)_n, and anion···π⁺/π⁺–π/π–π⁺ networks in the solid state. The interaction energies of the main driving forces observed in the crystal structure have been calculated using density functional theory. In addition, the short O···O contact between ClO₄^– anions has been analyzed in detail both computationally and exploring the Cambridge Structural Database.