Crystal structure of 2-(azaniumylmethyl)pyridinium bis(hydrogen squarate)

Abstract

The asymmetric unit of the title compound, C6H10N22+center dot 2C(4)HO(4)(-), 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 center dot center dot center dot O hydrogen bonds and an N-H center dot center dot center dot O hydrogen bond links the 2-(azaniumylmethyl) pyridinium cation to one of the squaric acid anions. The crystal structure features additional N-H center dot center dot center dot O and O-H center dot center dot center dot O hydrogen bonds, pi-pi stacking and unusual weak C-O center dot center dot center dot pi (ring) interactions.