Figure - available from: Journal of Solution Chemistry
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Overview Raman spectrum of a 0.479 mol·L⁻¹ La(CH3CO2)3 solution at 22 °C. Upper panel: wavenumber range from 100 to 2400 cm⁻¹ and lower panel from 2500 to 4200 cm⁻¹. The acetate bands dominate in the upper panel, where the water deformation mode appears at 1639 cm⁻¹ and a weaker water combination at 2145 cm⁻¹. Both bands are broad. The very broad O–H stretching band profile with bands at 3246 and 3400 cm⁻¹ dominate the lower spectrum. The narrow band at 2935.5 cm⁻¹ is the strongest acetate band. In each panel the IVV scattering profile is above the IVH scattering
Source publication
Aqueous solutions of La(CH3CO2)3, NaCH3CO2 and La(ClO4)3 were studied using Raman spectroscopy. In dilute NaCH3CO2 solution, acetate is fully hydrated and forms only minor amounts of ion pairs. The characteristic Raman bands are discussed and assigned. In fairly dilute La(ClO4)3 solutions, the La³⁺(aq) ion occurs as the nonahydrate. The separation...
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Citations
... These prior studies also concluded that the carboxylate COO − stretch band (near 1400 cm −1 ) was less quantitatively useful, presumably because of its overlap with to a CH 3 deformation mode, 29 although the apparent splitting between the symmetric and antisymmetric carboxylate stretch sub-bands has been interpreted as providing some information regarding the presence of unbound (free acetate), monodentate, bidentate, and bridging complexes. [19][20][21] Page 4 of 42 Physical Chemistry Chemical Physics ...
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In spite of the biological importance of the binding of Zn2+, Ca2+, and Mg2+ to the carboxylate group, cation-acetate binding affinities and binding modes remain actively debated. Here, we report the first use of Raman multivariate curve resolution (Raman-MCR) vibrational spectroscopy to obtain self-consistent free and bound metal acetate spectra and one-to-one binding constants, without the need to invoke any a priori assumptions regarding the shapes of the corresponding vibrational bands. The experimental results, combined with classical molecular dynamics simulations with a force field effectively accounting for electronic polarization via charge scaling and ab initio simulations, indicate that the measured binding constants pertain to direct (as opposed to water separated) ion pairing. The resulting binding constants do not scale with cation size, as
the binding constant to Zn2+ is significantly larger than that to either Mg2+ or Ca2+, although Zn2+ and Mg2+ have similar radii that are about 25% smaller than Ca2+. Remaining uncertainties in the metal acetate binding free energies are linked to fundamental ambiguities associated with identifying the range of structures pertaining to non-covalently bound species.
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... These prior studies also concluded that the carboxylate COO − stretch band (near 1400 cm −1 ) was less quantitatively useful, presumably because of its overlap with to a CH 3 deformation mode, 29 although the apparent splitting between the symmetric and antisymmetric carboxylate stretch sub-bands has been interpreted as providing some information regarding the presence of unbound (free acetate), monodentate, bidentate, and bridging complexes. [19][20][21] Page 4 of 42 Physical Chemistry Chemical Physics ...
The structure of aq. sodium acetate solution (CH 3 COONa, NaOAc) was studied by X-ray scattering and density function theory (DFT). For the first hydrated layer of Na ⁺ , coordination number ( CN ) between Na ⁺ and O(W, I) decreases from 5.02 ± 0.85 at 0.976 mol/L to 3.62 ± 1.21 at 4.453 mol/L. The hydration of carbonyl oxygen (OC) and hydroxyl oxygen (OOC) of CH 3 COO ⁻ were investigated separately and the OC shows a stronger hydration bonds comparing with OOC. With concentrations increasing, the hydration shell structures of CH 3 COO ⁻ are not affected by the presence of large number of ions, each CH 3 COO ⁻ group binds about 6.23 ± 2.01 to 7.35 ± 1.73 water molecules, which indicates a relatively strong interaction between CH 3 COO ⁻ and water molecules. The larger uncertainty of the CN of Na ⁺ and OC(OOC) reflects the relative looseness of Na-OC and Na-OOC ion pairs in aq. NaOAc solutions, even at the highest concentration (4.453 mol/L), suggesting the lack of contact ion pair (CIP) formation. In aq. NaOAc solutions, the so called “structure breaking” property of Na ⁺ and CH 3 COO ⁻ become effective only for the second hydration sphere of bulk water. The DFT calculations of CH 3 COONa (H 2 O) n=5–7 clusters suggest that the solvent-shared ion pair (SIP) structures appear at n = 6 and become dominant at n = 7, which is well consistent with the result from X-ray scattering.
