Synthesis of thiadiamidocrown ethers and a thermodynamic study of their complexation with some metal ions using DFT calculations and conductometric method in acetonitrile

Three new thiadiamidocrown ethers <b>1-3</b> have been synthesized and characterized by ¹H-NMR, ¹³C-NMR and mass spectrometry. A thermodynamic study of the complexation of compounds <b>1-5</b> with metal cations (Mⁿ⁺); Pb²⁺ with <b>1</b>, <b>2</b>, <b>4</b>, and <b>5</b>; Ag⁺ with <b>1</b>, <b>2</b>, and <b>3</b> and Hg²⁺ with <b>2</b> in acetonitrile, has been carried out at 288-308 K using a conductometric technique. The observed molar conductivity of the metal salts solutions, ⋀, was found to decrease upon addition of crown ethers solutions and tend to level off near the mole ratios [L]_T/[M]_T of unity. The ΔH° and ΔS° values for the complexation reactions were evaluated from the slopes and intercepts of the van't Hoff plots, respectively. The results show that the stability constants of Pb²⁺ complexes at 25 °C vary as: <b>5</b> &gt; <b>4</b> &gt; <b>2</b> &gt; <b>1</b> while the stability constants of Ag⁺ complexes vary as: <b>3</b> &gt; <b>2</b> &gt; <b>1</b>. ΔG° values for all complexes have negative values indicating a spontaneous complex formation process. A theoretical calculations using DFT which was conducted on the above systems gave results that supported the experimental results in most of the cases.

本研究合成了3种新型硫二酰胺冠醚（thiadiamidocrown ethers）1~3，并通过氢核磁共振波谱法（¹H-NMR）、碳-13核磁共振波谱法（¹³C-NMR）以及质谱法（mass spectrometry）完成了结构表征。以乙腈为溶剂，采用电导测量技术（conductometric technique），在288~308 K的温度范围内，对化合物1~5与金属阳离子（Mⁿ⁺）的配位热力学开展了系统研究：其中Pb²⁺分别与化合物1、2、4、5配位，Ag⁺分别与化合物1、2、3配位，Hg²⁺与化合物2配位。实验测得金属盐溶液的摩尔电导率Λ会随着冠醚溶液的滴加而逐渐降低，并在配体总浓度与金属总浓度比[L]ₜ/[M]ₜ趋近于1:1时趋于平稳。配位反应的标准摩尔焓变（ΔH°）与标准摩尔熵变（ΔS°）可分别通过范特霍夫图（van't Hoff plots）的斜率与截距计算求得。实验结果表明，25 ℃下Pb²⁺配合物的稳定常数大小依次为：5 > 4 > 2 > 1；而Ag⁺配合物的稳定常数大小依次为：3 > 2 > 1。所有配合物的标准摩尔吉布斯自由能变（ΔG°）均为负值，表明配位反应为自发过程。本研究采用密度泛函理论（DFT）对上述体系开展了理论计算，所得结果在绝大多数情况下与实验结果吻合良好。