On the Existence of Triglycine Acetate, Triglycine Phosphate, Triglycine Oxalate and Triglycine Formate

Abstract

The authors of a recent paper (Cryst. Res. Technol. 2022, 57, 2100130) report to have grown crystals of triglycine acetate (TGAc) by slow evaporation of an aqueous solution containing glycine and acetic acid in 3:1 molar ratio. The infrared spectrum and unit cell data of the so-called TGAc crystal confirm that it is, in fact, Alpha-glycine. The non-formation of any TGAc is due to no chemical reaction occurring between glycine and acetic acid. Another publication (Cryst. Res. Technol. 2022, 57, 2100262) describes the growth and characterization of a so-called triglycine oxalate (TGO) crystal. The unit cell data and infrared spectrum of the TGO crystal reveal that the crystal grown is, in fact, the well-known glycinium hydrogen oxalate. A critical analysis of the publications reporting on the growth of triglycine phosphate (TGP) and triglycine formate (TGF) crystals reveals that these are not what the authors claim them to be. Despite their names, the TGAc or TGP or TGO or TGF crystals are not analogs of the triglycine sulfate (TGS) crystal but serve as examples to highlight the importance of single-crystal structure refinement to avoid improper characterization.