物理化学学报 >> 1986, Vol. 2 >> Issue (02): 133-140.doi: 10.3866/PKU.WHXB19860206

研究论文 上一篇    下一篇

NMR 法研究Na+在二元混合溶剂中的溶剂化

黄忆宁; 李芝芬; 刘瑞麟   

  1. 北京大学物理化学研究所
  • 收稿日期:1984-12-17 修回日期:1985-09-28 发布日期:1986-04-15

A STUDY ON THE SOLVATION OF Na IN BINARY MIXTURE OF SOLVENTS BY Na-23 NMR

Huang Yining; Li Zhifen; Liu Ruilin   

  1. Institute of Physical Chemistry, Peking University
  • Received:1984-12-17 Revised:1985-09-28 Published:1986-04-15

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摘要： 本文测定了NaClO_4在水-丙酮, 水-乙腈,水-乙醇以及NaBPh_4在甲醇-DMF, 甲醇-苯, 甲醇-二氧六圜混合溶剂体系中~(23)Na~+的化学位移随溶剂组成的变化规律。利用等溶剂化点比较了各溶剂对Na~+的溶剂化能力: H_2O>(CH_3)_2CO≥CH_3CN≥C_2H_5OH; DMF>CH_3OH。对于甲醇-DMF和水-丙酮体系, 估算出DMF对甲醇, 丙酮对水的Na~+优先溶剂化自由能分别为-2.7 kJmol~(-1)和+4.6 kJmol~(-1)。
在甲醇-苯混合溶剂体系中, ~(23)Na~+的化学位移独立于苯的含量。它支持了甲醇-惰性溶剂混合体系的单一溶剂化模型。而在甲醇-二氧六圜体系中~(23)Na~+的化学位移随混合溶剂组成而发生变化。~(23)Na~+磁共振的峰宽随二氧六圜的加入急剧增加, 这表明二氧六圜分子可能进入了在甲醇中的Na~+原溶剂化层, 导致了Na~+化学环境不对称。

Abstract: ~(23)Na~+ chemical shift of NaClO_4 in mixed solvents of water-acetone,water- acetonitrile, and water-ethanol and of NaBPh_4 in methanol-DMF, methanol-benzene, and methanol-dioxane were measured. By means of iso-solvation point the sol- rating abilities were compared as water>acetone≥acetonitile≥ethanol and DMF> methanol. The preferential solvation free energies of Na~+ for the pairs solvenst, methanol-DMF and water-acetone, were evaluated as -2.7 kJmol~(-1) for DMF to methanol and 4.6 kJmol~(-1) for acetone to water.
~(23)Na~+ chmical shift in methanol-benzene is independent of the content of benzene. It verified the simple solvation modle for ion in methanol-inert solvent mixture. However the chemical shift of ~(23)Na~+ in methanol-dioxane mixture varies with the composition of solvent. The linewidth of Na-23 resonance peak increases dramtically with the increasing of dioxane. It seems that the dioxane molecules disturb the primary solvation shell of Na~+ in methanol and result a unsymmetrical immediate surrounding for Na~+ cation.