Isolation and Characterization of Tb(IV) in Aqueous Media via Polyoxometalate Encapsulation

There has been a renaissance in high valent lanthanide chemistry, which has resulted in the first examples of tetravalent praseodymium (Pr) and terbium (Tb) in molecular systems. These feats have been achieved with tailored ligands that facilitate tetravalent lanthanide stability in non-aqueous conditions. The next step in realizing the potential of high valent lanthanide chemistry is moving towards complexes that are stable in ambient and aqueous conditions. In this investigation, we have advanced this paradigm by obtaining definitive evidence of the isolation of Tb(IV) in a molecular system under aqueous conditions utilizing the lacunary Wells-Dawson polyoxometalate, K10P2W17O61•20H2O. Herein we present the single crystal structure of K16Tb(IV)(P2W17O61)2•39.85H2O (Tb(IV)W34) as well as extensive spectroscopic evidence obtained via UV-Vis-NIR, X-ray absorption near edge spectroscopy, continuous wave X-band electron paramagnetic resonance spectroscopies and SQUID magnetometry measurements to confirm the oxidation state of Tb in W34 complexes as +4.