Synthesis of 1,10-dithia-4,7,13,16-tetra-azacyclo-octadecane, 1-aza-4,7-dithiacyclononane, and N,N′-1,2-bis(1-aza-4,7-dithia-cyclononyl)ethane. Structural and solution studies of their silver complexes

The synthesis of the ligands 1-aza-4,7-dithiacyclononane, N,N′-1,2-bis(1-aza-4,7-dithiacyclo-nonyl)ethane, and 1,10-dithia-4,7,13,16-tetra-azacyclo-octadecane and their silver(I) complexes are reported. Stability constants in water and methanol have been determined using pH-metric methods, and enthalpies of complexation measured calorimetrically in methanol. The N-alkyl derivatives show enhanced enthalpies of complexation, but exhibit unfavourable entropies of complexation. Crystal structures of the [18]-N4S2 and bis[9]-NS2 silver complexes reveal distorted octahedral co-ordination geometry, although in aqueous solution the bis[9]-NS2 silver complex does not adopt the sandwich structure revealed in the crystallographic analysis.