Synthesis, structure and characterization of a new glycolate: sodium glycolate–glycolic acid (1/1)

Among various glycolates, potassium glycolate glycolic acid (PGGA), ammonium glycolate glycolic acid (AGGA) and rubidium glycolate glycolic acid (RGGA) are isostructural, with the general formula A(C₂H₃O₃)(C₂H₄O₃) (A = K, NH₄ and Rb). However, whether Na⁺ can occupy the A site and its effects on structure and properties remained unknown. This study synthesized sodium glycolate glycolic acid (SGGA), analyzed its composition, structure, vibrational spectra and thermal behaviour, and compared the results with PGGA. SGGA has the formula Na⁺·C₂H₃O₃^-·C₂H₄O₃ or Na(C₂H₃O₃)(C₂H₄O₃), with orthorhombic crystallinity. Although the salt lacks chiral C atoms, it crystallizes in the unique chiral space group P2₁2₁2₁. Among various glycolates, only PGGA and RGGA display relatively similar powder X-ray diffraction (PXRD) patterns, while those of other glycolates are distinctly different, providing a key basis for distinguishing A(C₂H₃O₃)(C₂H₄O₃) glycolates. Although SGGA and PGGA show closely related vibrational spectra and thermal behaviour due to structural similarities, differences are observed in certain spectral peaks. Moreover, PGGA decomposes into carbonates at a marginally higher temperature than SGGA. This work provides insight into glycolic acid bonding and the structural role of Na⁺ in glycolates, guiding new mineral discovery.