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.