Zinc triad metal ion complexes of NN′S ligand N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine

Abstract

The coordination chemistry of divalent zinc triad metal ions with N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine (L) was investigated by X-ray crystallography and proton NMR. Chloride salts yielded non-homologous M(L)Cl₂ complexes. Hg(L)Cl₂ and Zn(L)Cl₂ were five-coordinate monomers with distorted square pyramidal and trigonal bipyramidal geometries, respectively. Cd(L)Cl₂ formed a six-coordinate polymer with a distorted octahedral geometry. These complexes had similar nearly temperature independent proton NMR spectra suggesting structural differences between them were less extensive in solution due to fluxional processes. Although 1:1 metal to ligand complexes were most thermodynamically stable for the chloride salts at all [M²⁺]/[L], the thermodynamic stability of [M(L)(NCCH₃)_x]²⁺ only exceeded that of [M(L)₂]²⁺ when [M²⁺] ≥ [L] with perchlorate salts. Slow intramolecular and intermolecular exchange conditions for [M(L)₂]²⁺ and slow intermolecular exchange conditions for [M(L)(NCCH₃)_x]²⁺ were found on the proton chemical shift and in some cases J(M¹H) time scales. Strong interactions between divalent zinc triad metal ions and thioether ligand components at physiologically relevant temperatures suggest interactions with methionine should be considered in developing a more complete understanding of the bioactivities of these metal ions.