Tetrathiaoxa Macrocycles with Dibenzo-subunits: A Search for New Tl(I)- and Ag(I)-Selective Ionophores

Novel S⁴O ⁿ mixed donor macrocycles (1, n=1; 2, n=2) were synthesized by the coupling reactions of corresponding dichlorides with dithiols under high dilution conditions. Synthesis and crystal structures of Tl⁺ and Ag⁺ complexes, Tl(2)⁺ and Ag(2)⁺], with macrocycle 2 are described. The electrode based on macrocycle 2 showed excellent potentiometric sensing ability for Tl⁺ and Ag⁺ ions. This remarkable sensing of the proposed electrode can be understood in terms of the synergy effect of a soft–soft acid–base interaction and π-coordination, especially for the Tl⁺ ion, which was observed from the crystal structure of the corresponding complex.