Metal Complexes with Macrocyclic Ligands. Part XL. Syntheses and silver(I) complexes of mono- and disubstituted dithiadiazamacrocycles

A series of N₂S₂-macrocycles with ring sizes varying between 12 and 16, as well as two 12-membered N₂S₂-rings with a pendant carboxylic and amino group, respectively, were synthesized. Their complexation properties towards Ag⁺ were studied by pH titrations and by potentiometry with a silver electrode. The observation that 1:1 ([AgLH₂]³⁺, [AgLH]²⁺, [AgL]⁺) and 1:2 species ([AgL₂H₂]³⁺, [AgL₂H]²⁺, [AgL₂]⁺) were formed is interpreted by postulating that Ag⁺ can bind either to the S-donors only, or to both the N- and S-atoms. The most stable complex [AgL]⁺ in the series of the nonfunctionalized macrocycles was found for the 12-membered N₂S₂-ring 3 . The stability of it increased when an additional donor group was introduced into the side chain. The highest formation constant (logβ₁₁₀ = 14.43(1)) was obtained with the 12-membered ring 12 carrying the ethanamine side chain. In view of a radiochemical application, all Ag⁺ complexes were tested in blood serum for their stability, but were not stable enough against transmetallation.