Synthesis and Characterization of Non‐Aqueous [TcXM‐PW11O39]n– with M = O, N: Comparing TcV and TcVI in Metal Oxide Matrices

Technetium‐99, a prevalent by‐product of the nuclear fuel cycle, is a transition metal with 9 accessible oxidation states and a half‐life of 2.1 × 105 years. 99TcVII has been found in the environment surrounding National Lab sites and fuel reprocessing centers, and its separation and long‐term storage is complicated by its extensive redox chemistry. In our prior work we have reported the synthesis and reduction of TcVO to TcIVO in α1‐ and α2‐Wells–Dawson P2W17O6110– polyoxometalates and reported on the polyoxometalate features that promote reduction and stabilization. In this work we report on the oxidation state stabilization of TcVO, TcVIO and TcVIN within the α‐Keggin PW11O397– polyoxometalate. Both Density Functional Theory and experimental results show that Tc in TBA4[TcVIN‐PW11O39] can be reduced to TcV, but any subsequent electrons reduce the tungsten framework of the polyoxometalate. TBA4[TcVO‐PW11O39] however, can be theoretically reduced down to TcI before reduction of the polyoxometalate occurs. We report on the oxidation state stabilization of technetium in α‐PW11O397– with O and N ancillary ligands. Our results suggest that Tc in the TcN complex generally favors higher oxidations states (TcV and above), while the Tc within the TcO complex can access a larger range of oxidation states, theoretically all the way down to the TcI.