Hydrogen bonds and electrostatic interactions in the 1:1 complex of DABCO di-betaine with squaric acid: Crystallographic, theoretical and spectroscopic studies

► Hydrogen squarate anions are bonded to homoconjugated DABCO di-betaine cations. ► OH···O and CH···O hydrogen bonds and N+···O electrostatic interactions are present. ► CH···O hydrogen bonds are confirmed by the νCH···O vibrations in the IR spectrum. ► DABCO moiety has a propeller conformation. ► The crystal structure is more extended than optimized ones.