Theoretical investigation of geometric configurations and vibrational spectra in citric acid complexes

Abstract

The performance of advanced electronic ceramics is directly related to the synthesis route employed. Sol-gel methods are widely used for this purpose. However, the physicochemical intermediate steps are still not well understood. Better understanding and control of these processes can improve the final quality of samples. In this work, we studied theoretically the formation of metal complexes between citric acid and lithium or barium metal cations with different citric acid/metal proportions, using Density Functional Theory electronic structure calculations. Infrared and Raman scattering spectra were simulated for the more stable geometric configurations. Using this methodology, we identified some features of complexes formed in the synthesis process. Our results show that the complexes can be distinguished by changes in the bands assigned to C=O, COH-, and COO -group vibrations. An estimate of the most stable complexes is made based on total energy.

Eco-friendly Carboxymethyl Cellulose Nanofiber Hydrogels Prepared via Freeze Cross-Linking and Their Applications

“…The two peaks at 1688 and 1742 cm –1 observed in the CA spectrum are associated with strongly and weakly or non-hydrogen-bonded CO groups, respectively. ,, A single CO stretch mode was observed in the CMCF-F- x spectra, which indicated that almost all of the CO groups in the hydrogel were involved in hydrogen bonds with similar strength. Similar peak shifts have been observed in theoretical calculations for anhydrous CA and CA complexes − and in experimental results for the complex material of CMC and CA. , The CO stretching peak in the CMCF-F- x hydrogel spectra shifted to lower wavenumber with an increase in the CA concentration increased, i.e., from 1717 cm –1 for CMCF-F-0.05 to 1704 cm –1 for CMCF-F-2 (Figure b). The wavenumber of the CO stretching mode shifts downward owing to an increase in the hydrogen-bond strength. ,− Thus, the results indicate that the bond strength increased with an increase in the CA concentration.…”

“…Similar peak shifts have been observed in theoretical calculations for anhydrous CA and CA complexes − and in experimental results for the complex material of CMC and CA. , The CO stretching peak in the CMCF-F- x hydrogel spectra shifted to lower wavenumber with an increase in the CA concentration increased, i.e., from 1717 cm –1 for CMCF-F-0.05 to 1704 cm –1 for CMCF-F-2 (Figure b). The wavenumber of the CO stretching mode shifts downward owing to an increase in the hydrogen-bond strength. ,− Thus, the results indicate that the bond strength increased with an increase in the CA concentration.…”

“…All spectra had several peaks from the CO stretching vibrations in the 1500–1800 cm –1 range and the O–H stretching vibrations in the 3000–3800 cm –1 range. − The peak at 1717 cm –1 observed in the CMCF-F-0.05 spectrum is associated with CO groups involved in inter- and/or intramolecular interactions. − The peak position of CO stretching for CMCF-F- x hydrogels differed from those of CA and pure CMCF (1603 cm –1 ). The carboxylic CO stretching mode is usually observed in the range of 1600–1780 cm –1 , and the peak position changes depending on the bond length, which is significantly affected by the interaction with other molecules and/or formation of intra/intermolecular hydrogen bonds. − The peak change suggests that the CO groups in the CMCF-F- x hydrogels interact with CA and/or CMCF. The two peaks at 1688 and 1742 cm –1 observed in the CA spectrum are associated with strongly and weakly or non-hydrogen-bonded CO groups, respectively. ,, A single CO stretch mode was observed in the CMCF-F- x spectra, which indicated that almost all of the CO groups in the hydrogel were involved in hydrogen bonds with similar strength.…”

“…Figure a shows the IR spectra of CMCF-F- x ( x = 0.05, 0.1, 0.5, 1, and 2), pure CMCF, and CA. All spectra had several peaks from the CO stretching vibrations in the 1500–1800 cm –1 range and the O–H stretching vibrations in the 3000–3800 cm –1 range. − The peak at 1717 cm –1 observed in the CMCF-F-0.05 spectrum is associated with CO groups involved in inter- and/or intramolecular interactions. − The peak position of CO stretching for CMCF-F- x hydrogels differed from those of CA and pure CMCF (1603 cm –1 ). The carboxylic CO stretching mode is usually observed in the range of 1600–1780 cm –1 , and the peak position changes depending on the bond length, which is significantly affected by the interaction with other molecules and/or formation of intra/intermolecular hydrogen bonds. − The peak change suggests that the CO groups in the CMCF-F- x hydrogels interact with CA and/or CMCF.…”

New insights into UTSA-16

“…The vibrational spectrum of UTSA-16 is quite similar to that collected in the case of the reference compound and does not substantially change upon prolonged activation in a high vacuum till 363 K. By focusing the attention on the most relevant vibrational fingerprints, only IR spectra in the 1670-1500 cm À1 range clearly present the bands due to the n asym (COO À ) mode. 12,13 No bands ascribable to protonated -COOH groups are present, ruling out the presence of Hcit in the structure and all the citrate ligands being fully deprotonated in the material under study. In accordance with that, EDX analysis indicated a K : Co ratio of about 1 : 1.3, suggesting that a possible empirical formula of UTSA-16 here characterized would be K 2 Co 3 (cit) 2 .…”