Coordination chemistry of the methylmercury(II) ion in aqueous solution: a thermodynamic investigation

The reactions of the methylmercury(II) ion with a series of biologically relevant ligands have been investigated by potentiometry and calorimetry. The stability of the complexes is highly dependant on the type of donor atom involved in the formation of the coordinate bond. With ligands that contain more than one donor site a set of complexes was found in which methylmercury(II) ions replace the protons of a fully protonated ligand, one by one. The standard enthalpy and entropy changes of formation of a complex with a polydentate ligand are compared to the values for the corresponding monodentate ligand. This comparison has provided strong evidence for the existence of chelated species in solution, perhaps in equilibrium with non-chelated species.