Crystal structure and Raman spectra of rubidium hydrogen squarate

Rubidium hydrogen squarate (RbHC4O4, RbHSQ) crystallized in monoclinic space group P21/c. This compound form a short asymmetric intermolecular hydrogen bond whose O-O distance is 2.482(4) Å. The hydrogen squarate anions are forming head-to-tail infinite chain hydrogen-bonding motifs. A long interplanar separation (4.15 Å) indicates that a weak π interaction occurs between hydrogen squarate anions in RbHSQ. The hydrogen bond and cation-anion interactions are the predominant driving forces in the crystal packing. The Raman spectrum of RbHSQ shows an average behaviour between squaric acid and squarate dianion, however, the vibrational modes at ca. 1800 cm−1 (CO stretching mode) and in the region 1500-1700 cm−1 (CO+CC stretching modes) are the most affected by the presence of strong hydrogen bonding interactions.