Supramolecular assemblies involving anion-pi and lone pair-pi interactions: experimental observation and theoretical analysis

Abstract

[eng] 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 ¼ protonated 2-aminopyridine, C3H4O4 ¼ malonic acid, ClO4 ¼ perchlorate, PF6 ¼ 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-p, p-p and anion-p interactions, play a key role in stabilizing the self-assembly process observed for both compounds. Intricate combinations of lone pair-p, p-p and anion-p interactions of the type lone pair-p/p-p/p-anion-p/p-lone pair and lone pair-p/p-p/p-anion are observed that are fully described, including by computational methods. The theoretical calculations allow estimating the strength of these p contacts.