Synthesis, Crystal Structure, and Optical Properties of the Barium -Pertechnetate Ba[TcO].

High-quality single crystals of the colorless title compound Ba[TcO] were prepared from radioactive, isotope-pure TcO by oxidation with HO in an aqueous ammonia solution and subsequent cation metathesis using an ion-exchange column. Single-crystal X-ray diffraction revealed Ba[TcO] to crystallize isotopically to Ba[MnO] in the orthorhombic space group with the lattice parameters = 747.34(5) pm, = 1244.08(7) pm, and = 1511.23(9) pm for = 8. Its crystal structure features [BaO] icosahedra surrounded by ten [TcO] tetrahedra connected via two edges and eight corners. The optical properties of Ba[TcO] investigated by UV-vis spectroscopy show the broad O → Tc ligand-to-metal charge transfer (2p → 4d) process within these discrete [TcO] anions at an absorption maximum of around 350 nm.