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

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 (NAxSy-) 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. Group 12 complexes incorporating chelating mixed aromatic amine-alkylthiolate ligands have rarely been investigated; metal ion dependent differences in solid, solution, and gas phase aggregation are reported.