Chelation of ThIV, EuIII and NdIII by dianionic N,N′-bis(pyridoxylideneiminato)ethylene, (Pyr2en)2−. On the search of feasible modelings for heavy metals damage inhibition in living beings

The neutral Schiff base N,N′-bis(pyridoxylideneiminato)ethylene {H2pyr2en} reacts with Th(NO3)4 · 4H2O, NdCl3 · 6H2O and EuCl3 · 6H2O to give [Th(pyr2en)2(H2O)] (1), [Nd(pyr2en)(Hpyr2en)] · 12H2O (2) and [Eu(pyr2en)(Hpyr2en)] (3). In the three not yet reported bimolecular chelate systems the endo hydroxyl groups of the rings undergo deprotonation confirming the remarkable ability of the pyridoxal-containing ligand H2pyr2en to yield stable heavy metal chelates with unusual coordination polyhedra. Complexes 2 and 3 show a coordination number 8 for Nd and Eu, achieving a distorted quadratic antiprism. In complex 1 the additional water molecule increases the coordination number of Th to 9 producing a capped square antiprism. The synthesis and structural elucidation of the title complexes starting from a probably non-toxic metabolite like H2pyr2en should represent a useful contribution to the research on models of prevention and therapy of damage caused by radioactive and heavy elements.