Ag+ ion complexation properties of N-phenylpolythiazaalkane derivatives: synthesis, crystallography, 1H NMR spectroscopy, potentiometry and metal ion recognition properties

Abstract

A series of N-phenylpolythiazaalkane derivatives; the cyclic derivatives 4-phenyl-1-thia-4-azacyclohexane 1, 7-phenyl-1,4-dithia-7-azacyclononane 2, 10-phenyl-1,4,7-trithia-10-azacyclododecane 3 and 13-phenyl-1,4,7,10-tetrathia-13-azacyclopentadecane 4 and acyclic derivatives 6-phenyl-3,9-dithia-6-azaundecane 5 and 9-phenyl-3,6,12,15-tetrathia-9-azaheptadecane 6, have been studied towards complexation with Ag⁺ ion. Single crystals of two Ag(I) complexes, [Ag(2)₂][CF₃SO₃] and [Ag(4)][CF₃SO₃] were prepared and their structures were determined in the crystalline state by X-ray diffraction. In [Ag(2)₂][CF₃SO₃], two bidentate 2 ligands, in which two sulfur atoms act as coordination sites, sandwich Ag(I) to give a four-coordinate complex in near tetrahedral geometry. In [Ag(4)], Ag(I) enters into a cavity composed of four sulfur atoms to give a distorted tetrahedral geometry. The changes of the chemical shifts in ¹H NMR spectroscopy by the addition of CF₃SO₃Ag indicate that 1 and 2 exhibit small downfield shifts only for the protons of the thioether moiety, while 3, 4, 5 and 6 show drastic shifts for all protons. Ag⁺ ion complexation with N-phenylpolythiazaalkane and polythiaalkane derivatives, which were used for comparison, was studied in acetonitrile solution by potentiometry. Results show that the complex stability is governed primarily by the number of sulfur donor atoms, and the nitrogen atom of the N-phenylpolythiazaalkane derivatives scarcely contributes to the stability of the complexes. The extraction of transition metal ions with N-phenylpolythiazaalkane derivatives was examined and very high Ag⁺ ion selectivity was observed for most of them. The extraction equilibria of the Ag(I) complexes of N-phenylpolythiazaalkane derivatives were studied and the extraction constants of the extracted complexes determined. Results indicate that the extractability of 1∶1 complexes depends on their stability. In liquid membrane transport, all N-phenylpolythiazaalkane derivatives exhibited Ag⁺ ion selective transportability and the order for the Ag⁺ ion transport rate was 5 > 2 ≈ 3 > 4 ≈ 6  1.