The coordination chemistry of divalent zinc triad metal ions is complicated by coordination number and geometry plasticity. A series of symmetric and asymmetric tridentate N and N,S donor ligands have been used to explore the intramolecular isomerization of bis-tridentate chelates under conditions of slow intermolecular exchange. There are nine regular polyhedral forms of bis-tridentate chelates, eight of which have been observed crystallographically for divalent zinc triad metal ions. Unfortunately, crystallization can selectively remove minor solution species with lower solubility. Variable temperature solution-state proton NMR has been used to evaluate the contribution of crystallized forms to solution equilibria. Rapid intramolecular exchange is commonly considered de rigueur for complexes of d¹⁰ metal ions. Surprisingly, bis-tridentate chelates of N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine exhibited slow exchange on the chemical shift time scale between several regular polyhedral forms at cryogenic temperatures. Isolated complexes of type [M(L)₂](ClO₄)₂ had trans facial coordination geometry, however proton chemical shift trends suggested the cis geometry was more thermodynamically stable. Although intramolecular exchange was rapid at ambient temperature, intermolecular exchange was slow on the J(¹⁹⁹Hg¹H) time scale for [Hg(L)₃]²⁺ and all three bis tridentate chelates exchange slowly on the chemical shift time scale with species of type [M(L)(NCCH₃)_x]²⁺. 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.