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The vibrational properties of croconic acid (CA), the associated anionic specie croconate (CR), and their complexes with the transition metals Co(II) were investigated through surface‐enhanced Raman scattering (SERS) spectroscopy. This is the first time the SERS spectra of CA and CR are reported. The normal Raman spectrum of CA after the addition of Co(II) was similar to the corresponding spectrum of CR in the presence of Co(II), suggesting the dissociative coordination of CA with Co(II) cation. Similar behavior occurs when CA and Co(II) coadsorb on silver nanoparticle surfaces as seen by SERS spectroscopy. In the same way, the SERS spectra of CA and CR have similar spectral patterns suggesting dissociative adsorption on the metallic nanoparticle surface. The SERS spectra of CR show changes with both concentration and pH values suggesting that according to the concentration of the oxocarbon, the structural arrangements of the adsorbates on the silver surfaces change, due to a decrease of intermolecular π–π interactions between neighboring rings.

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