Hydrogen-bonding, π-stacking and Cl−-anion–π interactions of linear bipyridinium cations with phosphate, chloride and [CoCl4]2− anions

Abstract

A series of protonated bipyridinium compounds has been synthesized and their crystal packing is discussed in terms of N–H⋯X contacts (X = O, Cl) together with π–π and Cl⁻⋯π interactions of the positively charged aromatic nitrogen heterocycles. The bipyridinium-anion combinations are diprotonated 4,4′-bipyridin-1,1′-ium bis(dihydrogenphosphate) dihydrate (3), 4,4′-bipyridin-1,1′-ium bis(1,1′-binaphthalene-2,2′-diyl phosphate)·2.5H₂O (4), 6,6′-diisoquinolin-2,2′-ium dichloride dihydrate (5), 2,2′-bi-1,6-naphthyridin-6,6′-ium dichloride dihydrate (6) and triprotonated 2,2′-bi-1,6-naphthyridin-1,6,6′-ium-tetrachlorocobaltate(II)-chloride (7). In all structures N⁺–H hydrogen bonding occurs only to the anion and not to water of crystallization. The packing in 3–6 can be rationalized by a separation of the hydrophobic C–H backbone of the bipyridines from the hydrophilic N–H, phosphate or chloride and water part. N⁺–H⋯⁻Cl/O hydrogen bonding and π–π-stacking are identified as the major packing interactions in 3–6. In 7 the π-stacking is replaced by remarkably short Cl⁻-anion–π interactions.