Abstract The structure of aq. sodium acetate solution (CH3COONa, 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 CH3COO− were investigated separately and the OC shows a stronger hydration bonds comparing with OOC. With concentrations increasing, the hydration shell structures of CH3COO− are not affected by the presence of large number of ions, each CH3COO− group binds about 6.23 ± 2.01 to 7.35 ± 1.73 water molecules, which indicates a relatively strong interaction between CH3COO− 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 CH3COO− become effective only for the second hydration sphere of bulk water. The DFT calculations of CH3COONa (H2O)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.

中文翻译：

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通过 X 射线散射和密度泛函理论分析醋酸钠水溶液的结构

摘要 aq 的结构。通过 X 射线散射和密度函数理论 (DFT) 研究了醋酸钠溶液 (CH3COONa, NaOAc)。对于 Na+ 的第一水合层，Na+ 和 O(W, I) 之间的配位数 (CN) 从 0.976 mol/L 时的 5.02 ± 0.85 降低到 4.453 mol/L 时的 3.62 ± 1.21。分别研究了 CH3COO− 的羰基氧 (OC) 和羟基氧 (OOC) 的水合，与 OOC 相比，OC 显示出更强的水合键。随着浓度的增加，CH3COO-的水合壳层结构不受大量离子存在的影响，每个CH3COO-基团结合约6.23±2.01～7.35±1.73个水分子，表明CH3COO-与水的相互作用较强分子。Na+ 和 OC(OOC) 的 CN 的较大不确定性反映了水溶液中 Na-OC 和 Na-OOC 离子对的相对松散程度。NaOAc 溶液，即使在最高浓度 (4.453 mol/L) 下，也表明没有形成接触离子对 (CIP)。在 aq。NaOAc 溶液，即 Na+ 和 CH3COO− 的所谓“结构破坏”特性，仅对大量水的第二个水合球体有效。CH3COONa (H2O)n=5–7 簇的 DFT 计算表明溶剂共享离子对 (SIP) 结构出现在 n = 6 并在 n = 7 处成为主导，这与 X 射线的结果非常一致散射。Na+ 和 CH3COO− 的所谓“结构破坏”特性仅对大量水的第二水合球有效。CH3COONa (H2O)n=5-7 簇的 DFT 计算表明溶剂共享离子对 (SIP) 结构出现在 n = 6 并在 n = 7 处成为主导，这与 X 射线的结果非常一致散射。Na+ 和 CH3COO− 的所谓“结构破坏”特性仅对大量水的第二水合球有效。CH3COONa (H2O)n=5–7 簇的 DFT 计算表明溶剂共享离子对 (SIP) 结构出现在 n = 6 并在 n = 7 处成为主导，这与 X 射线的结果非常一致散射。