Revision of the crystal structure of `bis(glycine) squaric acid'

Abstract

The crystal structure of `bis(glycine) squaric acid' [Tyagi et al. (2016). RSC Adv. 6, 24565–24576], is revised. Re-refinement of the structure against the original X-ray intensity data after correct placement of the donor H atoms proves that the compound is in fact the previously reported diglycinium squarate [systematic name: bis(carboxymethanaminium) 3,4-dioxocyclobut-1-ene-1,2-diolate; Anioła et al. (2014). New J. Chem. 38, 3556–3568]. The findings are consistent with the pKa rule.