Synthesis, structures, and properties of new chalcogenide-capped octahedral hexatechnetium(III) complexes [Tc₆S₈X₆] ^4- (X = Br, I), [Tc₆Se₈I₂], and [Tc₆Te₁₅]

Chalcogenide-capped octahedral hexatechnetium(III) complexes, Cs ₄[Tc₆S₈Br₆]·CsBr (Cs ₄[1]·CsBr) and (PPh₄)₄[Tc ₆S₈Br₆] {(PPh₄)₄[1]}, (PPh₄)₄[Tc₆S₈I₆] ((PPh₄)₄[2]}, [Tc₆Se₈I₂] ([3]), and [Tc₆Te₁₅] ([4]) were synthesized. Single-crystal X-ray structural studies were carried out for Cs ₄[1]·CsBr, [3], and [4], Sulfide-capped octahedral hexatechnetium(III) clusters [1]^4- and. [2]^4- are discrete complex anions, whereas the selenideand telluride-capped hexatechnetium(III) complexes adopt extended polymeric structures. A cyclic voltammogram of [1] ^4- in CH₃CN showed two one-electron redox waves: Tc ₆(24e/23e) and Tc₆(23e/22e). The potential of the Tc ₆(24e/ 23e) process is more positive than that of the Re ₆(24e/23e) process for the hexarhenium analog [Re₆S ₈X₆]^4- (X = Br, I), whereas that of the Tc ₆(23e/22e) process shifts to negative values compared, to the potential, of the Re₆(23e/22e) process. Thus, the Tc₆(23e) mixed-valence state is thermodynamically less stable than Re₆(23e).