A solid-state complex utilizing non-covalent interactions between two aromatic cations is synthesized and characterized. The X-ray study of the structure shows that the anion templated π⁺–π⁺ interactions are the major driving force in the crystal packing, while π⁺–π, π–π, π–anion and π⁺–anion interactions assist the overall stabilization of self-assembly. In addition, we also identify the cation-mediated non-covalent interaction between two π anions (π⁻–π⁻ interaction). The interaction energies of the important driving forces (π⁺–π⁺, π⁺–π, π–anion, π⁺–anion, and π⁻–π⁻ interactions) observed in the crystal structure are calculated using dispersion-corrected density functional theory (DFT-D).

The solid-state complex [PTPH₃](NO₃)₃·2(HNO₃) (1) has been synthesized and characterized by X-ray studies, where PTPH₃ is the triply protonated form of 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine (PTP). The solid-state structure of the complex reveals that the π⁺–π⁺ interactions are the major driving force in the crystal packing while π⁺–π, π–π and π–anion interactions assist the overall stabilization of self-assembly. Complex 1 exhibits two different π-stack layers, where layer 1 is generated through π⁺–π⁺ interactions and the mutual forces of π⁺–π⁺ and π⁺–π form layer 2. The interaction energies of the main driving forces (π⁺–π⁺, π⁺–π and π–anion interactions) observed in the crystal structure have been calculated using dispersion-corrected density functional theory (DFT-D). An analysis of the Hirshfeld surface of complex 1 shows the intermolecular interactions involved within the crystal structure and corresponding quantitative information are presented by fingerprint plots.

Two nickel(II) malonate coordination compounds, namely (C₅H₇N₂)₄[Ni(C₃H₂O₄)₂(H₂O)₂](ClO₄)₂ (1) and (C₅H₇N₂)₄[Ni(C₃H₂O₄)₂(H₂O)₂](PF₆)₂ (2) [where C₅H₇N₂ = protonated 2-aminopyridine, C₃H₄O₄ = malonic acid, ClO₄ ⁻ = perchlorate, PF₆ ⁻ = hexafluoridophosphate], have been synthesized from purely aqueous media, and their single-crystal structures have been determined by X-ray diffraction. As anticipated, various weak forces, i.e. lone pair–π, π–π and anion–π interactions, play a key role in stabilizing the self-assembly process observed for both compounds. Intricate combinations of lone pair–π, π–π and anion–π interactions of the type lone pair–π/π–π/π–anion–π/π–lone pair and lone pair–π/π–π/π–anion are observed that are fully described, including by computational methods. The theoretical calculations allow estimating the strength of these π contacts.