Crystal Structure of 2-(Azaniumylmethyl)pyridinium Bis(Hydrogen Squarate)

Abstract

The asymmetric unit of the title compound, C<inf>6</inf>H<inf>10</inf>N<inf>2</inf>2+·2C<inf>4</inf>HO<inf>4</inf>-, comprises two hydrogen squarate (Hsq-; systematic name: 2-hydroxy-3,4-dioxocyclobutanolate) anions and a 2-(azaniumylmethyl)pyridinium dication. The squaric acid molecules each donate an H atom to the N atoms of the pyridine ring and the aminomethyl units of a 2-(aminomethyl)pyridine molecule, forming the 1:2 salt. The Hsq- anions are linked by strong O-H⋯O hydrogen bonds and an N-H⋯O hydrogen bond links the 2-(azaniumylmethyl)pyridinium cation to one of the squaric acid anions. The crystal structure features additional N-H⋯O and O-H⋯O hydrogen bonds, π-π stacking and unusual weak C - O⋯π(ring) interactions.