Coordination of tridentate ligands to smi₂: Cooperativity and incremental effect on reduction potential and on reactivity

The effect of coordination of a series of tridentate ligands (TDLs) on various features of SmI₂ was determined. The TDLs used in this study were diethylene glycol (OOO), diethanolamine (ONO), 2-(2-Aminoethoxy) ethanol (OON), N-(2-Hydroxyethyl) ethylene diamine (ONN) and glycerol (GLY). Of special interest is the effect of these additives on the reduction potential of SmI₂. The cyclic voltammograms of the TDLs with nitrogen at the binding sites display simultaneously several peaks, each corresponding to a different coordination level of SmI₂, enabling determination of three equilibrium constants. The results are in concert with electronic spectra of SmI₂ complexes with these ligands. The second and third equilibrium constants were found to be larger than the first, demonstrating the cooperativity effect. Moreover, the incremental effect of each moiety on the reduction potential of SmI₂ was determined. Regarding reactivity of SmI₂, excessive coordination of some ligands is shown to have an adverse effect.