Applicability of the SQM Force Field Method to the Vibrational Spectra of Sodium Acetate

Abstract

The applicability of the scaled quantum mechanical force field (SQM FF) method to the prediction of the vibrational spectra of a charged molecule has been studied by the example of the acetate ion (CH3CO2-) in sodium acetate for which an efficient empirical valence force field (SVFF) based on observed IR spectra of six isotopomers of sodium acetate is available in the literature. Standard SQM FF calculations done on a free acetate ion at the B3LYP/6-31G level failed to give an acceptable estimation of even the most characteristic features of the observed spectra, which can be exemplified by the gross overestimation of the frequency separation of the nu(a)CO2- and nu(s)CO2- vibrations. In search for a better description, SQM calculations were done for three simple structural models of sodium acetate, testing different QM methods. The results indicate that in addition to taking into account the dielectric field effect of the surrounding medium, incorporation of a Na+ counterion is necessary to achieve a realistic simulation of the IR and Raman spectra. Satisfactory results were obtained with a bidentate Na-acetate complex by the SQM method coupled with a continuum model at the B3LYP/6-31+G level, whereas the use of the Onsager-type spherical cavity model and the polarizable continuum model (PCM) were found preferable over SCI-PCM.

B3LYP and in Situ ATR-SEIRAS Study of the Infrared Behavior and Bonding Mode of Adsorbed Acetate Anions on Silver Thin-Film Electrodes

“…The presence of solvent significantly modifies these frequency values. Keresztury et al 44 have obtained B3LYP theoretical frequencies of hydrated acetate using the SCRF model and the basis set 6-31+G**. These authors report values of 1622 and 1327 cm -1 respectively for the asymmetric and symmetric stretching modes of OCO for acetate in water.…”

The SPASIBA Force Field for Chondroitin Sulfate: Vibrational Analysis of d-Glucuronic and N-acetyl-d-Galactosamine 4-Sulfate Sodium Salts

“…Recently, Keresztury et al have shown that SQMFF-type calculations on the acetate ion at the B3LYP/6-31G* level were unable to explain the frequency splitting between the ν a and ν s modes of the carboxylate group. Furthermore, these authors pointed out the necessity to introduce a Na + counterion as a bidentate complex or as a water complex to obtain adequate vibrational descriptions of the antisymmetric and symmetric C−O stretching modes.…”

“…Addition of diffuse functions to the basis sets has been shown to be essential for accurate analyses of compounds containing lone pairs or anions or when dealing with transition structures, but it produces only a few changes when applied to molecules such as sugars. 28 Recently, Keresztury et al 29 have shown that SQMFF-type calculations on the acetate ion at the B3LYP/6-31G* level were unable to explain the frequency splitting between the ν a and ν s modes of the carboxylate group. Furthermore, these authors pointed out the necessity to introduce a Na + counterion as a bidentate complex or as a water complex to obtain adequate vibrational descriptions of the antisymmetric and symmetric C-O stretching modes.…”

Vibrational dynamics of acetate in D2O studied by infrared pump–probe spectroscopy

“…The solvation structures and anion-cation interactions of carboxylate salts have been extensively studied by steady-state infrared (IR) spectroscopy [2][3][4][5][6][7][8][9] and theoretical calculations based on density functional theory (DFT). [10][11][12][13] These studies suggest that the carboxylate anion forms hydrogen-bonded complexes with the solvent, although the static and dynamic hydrogen bonding interactions are not yet fully understood.…”