Chemical behavior of croconic acid coordinated to Co(II) adsorbed on silver surface

Abstract

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.

Probing ring contraction and decarboxylation of Rhodizonate and the influence of Cu (II) using surface‐enhanced Raman Scattering

“…The concomitant changes occurring in the 24 h SERS spectrum result in an overall spectrum that also differ from that expected for Cro. [30] The most intense bands are observed at 375, 426, 533, 556, 580, 641, 762, 1086, 1338, 1414, 1470 and 1522 cm -1 . Among the above cited bands, only those at 556 and 641 cm -1 occur at similar position in the SERS spectrum of Cro [30] (see Supporting Material).…”

“…This behavior was also seen for croconic acid and it was suggested that the deprotonated oxocarbon species may occur adsorbed on the metallic surface. [30] The pKa values of rhodizonic acid (H 2 C 6 O 6 ), the neutral conjugated basis of Rho containing two hydrogen bonded to two oxygen atoms, has been reported to be 4.37 and 4.66. [41] The SERS results indicate that, in despite of the presence of protonated and deprotonated species in solution, at different proportions in different pHs, there is a deprotonation of the acid in the process of adsorption on AgNP surfaces, even at pH 2, condition that would present ca.…”

“…Similar model was used in the case of Cro and the calculated spectrum matched well with the experimental one. [30] Table 1 includes the band position of the experimental and calculated spectra of Rho, as well as their assignments. The calculated Raman spectrum for the presented model showed a reasonably good agreement with the SERS spectra of Rho, as shown in Fig.…”

“…[18,[24][25][26][27][28][29][30][31] As part of that investigation, we have previously used SERS to study different oxocarbon molecules and its coordination with metal ions, specifically squaric and croconic acids. [28][29][30] In those studies, the SERS spectrum was proven sensitive to coordination of these molecules to metal ions. It was suggested that the interaction of both squaric and croconic acids with the Ag nanoparticle surface occurs through the C=O moieties.…”

“…The changes in the SERS spectral patterns of Cro as function of the concentration suggested that there is a decrease in the intermolecular plane-to-plane interactions with the decrease in the concentration. [30] In the present study, SERS spectroscopy was used in combination with DFT calculations to study the spontaneous thermal conversion of Rho to Cro in water. It has also been studied the catalytic effect of Cu (II) ions in this reaction.…”