Synthesis and physical properties of hexakis(isothiocyanato)technetate(III) and -(IV) complexes. Structure of the [Tc(NCS)6]3- ion

Article abstract of DOI:10.1021/ic50207a001

The reaction between ammonium thiocyanate and (NH₄)₂TcX₆, X = Cl and Br, salts is shown to produce a mixture of red (λ 500 nm) [Tc(NCS)₆]^2- and air-sensitive yellow (λ 400 nm) [Tc(NCS)₆]^3- ions. These species were chromatographically separated and isolated as their ammonium, tetraphenylarsonium, or tetra-n-butylammonium salts. The technetium(IV) compound was also obtained through reduction of ammonium pertechnetate followed by treatment with ceric ion. Infrared, Raman, conductivity, and magnetic susceptibility data are reported for these complexes and shown to be consistent with octahedral structures. The detailed geometry of (n-Bu₄N)₃[Tc(NCS)₆] was determined in a single-crystal X-ray diffraction study. The compound crystallizes in the cubic system, space group Pa3, with a = 24.444 (6) A? and Z = 8. The technetium atom is situated on a crystallographic threefold rotation axis. The Tc-N bond lengths are 2.04 (2) and 2.05 (2) A?, and the N-Tc-N angles range from 88.0 (6) to 92.1 (7)°, indicative of nearly perfect octahedral symmetry. The average Tc-N-C and N-C-S bond angles are 173 (2) and 177 (2)°, respectively. Voltammetric studies in acetonitrile show a reversible one-electron transfer between [Tc(NCS)₆]^3- and [Tc(NCS)₆]^2- with E_1/2 of 0.18 V vs. SCE. Additional chemical redox reactions of these ions are reported.