Abstract
The synthesis of some thio-oxocrown ether ligands, B1 (1,4-dithio-12-crown-4), B2 (1,7-dithio-12-crown-4), B3 (1,7-dithio-15-Crown-5), B4 (1,7-dithio-18-crown-6), B5 (1,10-dithio-18-crown-6), B6 (1,10-dithio-21-crown-7), under mild conditions, were reported. The ligands were characterized by FT-IR, 1H NMR and GC-MS spectroscopy. The formation of 1:1 ligand complexes with a variety of metal salts (Ag+, Ca+2, K+, Na+, Mg+2, Zn+2 and Fe+2) were investigated by a conductometric method in a 1:1 dioxane–water system at 25 °C, and the complexation constants (Ke = (ΛMAm -Λ) / ((Λ-ΛMaLbAm) [L]) and free energy (∆Go= - RT lnKe) values are calculated. Details of the specific molecular interactions between the ligands and metals were proposed. We also performed DFT calculations to explain their geometrical properties, charges and frontier molecular orbitals.
Highlights
Synthetic macrocycles, in particular crown ethers, have been known for over three quarters of a century, a real spate of publications in this area was observed in the late 1960s [1,2]
Various macrocyclic hosts with diverse affinity towards the metal ions and other funtions have been readily synthesized by changing the combinations of the oxygen and sulfur atoms forming the ring framework
The effect of various synthesized thiocrown ethers on the transport ability of the studied metal cations was not investigated systematically, preliminary results show that thiocrown ethers may possess an advantage over crown ethers containing only oxygen atoms in the cyclic framework for metal binding, because the introduction of a sulfur atom into a crown ring gives rise to a favorable entropic change upon complexation with the metal ions
Summary
In particular crown ethers, have been known for over three quarters of a century, a real spate of publications in this area was observed in the late 1960s [1,2]. Crown ethers contains “hard” ether–oxygen-bridges and show a binding preference toward “hard” metals (such as alkali and alkaline earth metal cation). Selectivity can be tuned by combining different hard/soft donor atoms in one ring system. In this regard oxo-thiocrown ethers are prepared and used as potential heavy-metal receptors. Oxo-thiocrown ethers having different ring size or arrangement have been prepared and their complexation properties have been investigated with various metal cations by conductometry [4,5,6,7]
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