Very strong hydrogen bonds in hydrated 1:1 adducts of an olefinic double betaine with perchloric and nitric acids: L·HClO4·H2O and L·HNO3·H2O [L=cis-(p-Me2N+C5H4N)2C2(COO−)2]

The hydrated 1:1 adducts of an olefinic double betaine with perchloric and nitric acids, L·HClO₄·H₂O I and L·HNO₃·N₂O2 [L=cis-(p-Me₂N⁺C₅H₄N)₂C₂(COO^–)₂], have been shown to be nearly isostructural by X-ray crystallography and infrared spectroscopy. The common cationic unit HL⁺ of both compounds exhibits significant semi-quinonoid character and possesses symmetrym, ist two coplanar carboxylate groups being linked by a very strong, nearly linear intramolecular O–H–O hydrogen bond [O...O 2.397(9)Å and O–H–O 167.1° for1; 2.388(7)Å and 167.4° for2]. The HL⁺ units are further connected by intermolecular O–H...O hydrogen bonds between the exocyclic carboxyl oxygen atoms and the water molecules to generate polymeric zigzag chains running parallel to thec axis, and the disordered ClO₄ or NO₃^– anions occupy channels running parallel to thea axis in the resulting host lattice.