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 1-3 have been synthesized and characterized by 1H-NMR, 13C-NMR and mass spectrometry. A thermodynamic study of the complexation of compounds 1-5 with metal cations (Mn+); Pb2+ with 1, 2, 4, and 5; Ag+ with 1, 2, and 3 and Hg2+ with 2 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: 5 > 4 > 2 > 1 while the stability constants of Ag+ complexes vary as: 3 > 2 > 1. 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.