Aggregation behavior of group 12 complexes of a tripodal mixed NS(thiolato) donor ligand

Abstract

Despite the concurrence of histidine and cysteine in the active sites of proteins associated with Zn²⁺, Cd²⁺ and Hg²⁺, coordination studies of these metal ions with chelating ligands containing a combination of aromatic amine and alkylthiolate (N^A_xS_y⁻) donors have been rare. The potentially tetradentate ligand 2-[bis(2-pyridinylmethyl)amino]ethanethiol (LH) and chloride salts were used to prepare new complexes of Cd²⁺ and Hg²⁺ for comparison with the known Zn²⁺ complex. Solution NMR studies revealed concentration-dependent equilibria between aggregate forms of the new complexes in CD₃CN. Trends in homonuclear and heteronuclear coupling provided additional insight regarding solution equilibria. ESI-MS from acetonitrile solutions supported differences in preferred aggregation states consistent with the solution NMR studies.