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, CS4[Tc6S8Br6]center dot CsBr (CS4[1]center dot CsBr) and (PPh4)(4)[Tc6S8Br6] {(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]center dot CsBr, [3], and [4]. Sulfide-capped octahedral hexatechnetium(III) clusters [1](4-) and [2](4-) are discrete complex anions, whereas the selenide- and 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 Tc-6(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 [Re6S8X6](4-) (X = Br, I), whereas that of the TC6(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 Re-6(23e).