Rare earth metals are essential materials for many technological needs, and the increase in demand for those materials requires the development of sustainable methods their recycling and recovery. (salen) vanadium oxo (salen = N,N’-ethylenebis(salicylideneaminato)) and its derivatives have been previously reported to bind to group 14 and 15 Lewis acids through oxygen of the vanadyl. Since rare earth metals also act as Lewis acid, we hypothesize that (salen) vanadium oxo and its derivatives may also interact with rare earth metals. To investigate this phenomena, synthesized (salen) vanadium (IV) oxo and (salenOMe) vanadium (IV) oxo (salenOMe = N,N’-ethylenebis(3-methoxysalicylideneaminato)) were dissolved in acetonitrile, and La (OTf)3 and Nd(OTf)3 salts were titrated into each solution and their behaviors tracked through UV-visible spectroscopy and cyclic voltammetry. UV-visible spectroscopy revealed a change of adsorption intensity for the vanadium complexes with addition of rare earth metal salt. Moreover, cyclic voltammetry of both vanadium oxo complexes in the presence of rare earth metal resulted in the growth of an irreversible reduction peak at about -2 V vs. Fe(C5H5)2+/0. These findings are consistent with an interaction between the vanadium oxo and rare earth metals. Furthermore, the chemical reactivity of both (salen) vanadium (IV) oxo and (salenOMe) vanadium (IV) oxo complexes were explored through addition of solidum metal in THF, and the product of these reactions were characterized by 1H NMR spectroscopy. This reduced product and its interaction with rare earth metals was also investigated in X-ray crystallography. The result of this research will evaluate the binding ability of vanadium oxo complex and its derivatives to rare earth metals and aim to establish whether this platform can be used as a new method of separation of rare earth metals.

Understanding the interaction between rare earth metals and vanadium oxo complexes

ACS Spring 2022

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