Preparation, characterization and crystal structures of three salts of the quaterpyridine ligand

As a result of a reaction between 6,6′′′-dimethyl-2,2′:6′,2′′:6′′,2′′′-quaterpyridine C22H18N4 and lanthanide(III) salts, compounds, [C22H20N4]2+·2(CF3SO3)− (1) and [C22H20N4]2+·2(ClO4)− (2), have been obtained. They were characterized by spectroscopic techniques (ESI-MS, NMR, IR), elemental analysis, and their formulae were confirmed on the basis of X-ray crystallography. It turned out that the perchlorate crystallizes as two solvates: with acetonitrile and disordered water molecules. These are the first structural characterization of a 6,6′″-dimethyl-2,2′:6′,2″:6″,2′″-quaterpyridinium dication. Due to the intramolecular hydrogen bond it adopts the previously unobserved cis/trans/cis conformation. In all three crystals the dications have Ci symmetry, they occupy the special positions in their respective space groups. In the crystal structures the π–π stacking and weak hydrogen bonds add directionality to the dominating electrostatic interactions between cations and anions.