Synthesis, spectroscopic and electrochemical properties, and electronic structures of octahedral hexatechnetium(III) clusters [Tc6Q8(CN)6]4- (Q = S, Se).

Chalcogenide-capped molecular octahedral hexatechnetium(III) clusters [Tc(6)Q(8)(CN)(6)](4-) {Q = S ([1](4-)), Se ([2](4-))} were prepared by the substitution of axial ligands with cyanide. The structures of the new complexes were determined by single-crystal X-ray analysis. The IR spectra of [1](4-) and [2](4-) showed a C[triple bond]N stretching band at 2114 and 2105 cm(-1), respectively. In cyclic voltammetry, [1](4-) and [2](4-) in CH(3)CN showed reversible one-electron-oxidation waves assignable to the Tc(6)(24e/23e) process at +0.99 and +0.74 V, respectively. Density functional theory (DFT) calculations on the hexatechnetium complexes showed that the highest occupied molecular orbital (HOMO) was primarily localized on a Tc(6)Q(8) core and the lowest unoccupied molecular orbital (LUMO) was completely localized on the metal orbitals. The energy level of HOMO and the redox potential of the M(6)(24e/23e) process (M = Tc, Re) were found to have a good linear relationship. Time-dependent DFT calculations showed that the substantially allowed transitions with the lowest energy were Tc(6)Q(8) core-centered transitions. The electronic structures and electronic transition features of the hexatechnetium complexes were similar to those of the hexarhenium analogues [Re(6)Q(8)(CN)(6)](4-) (Q = S, Se); however, the energy gap between the HOMO and LUMO was smaller in the hexatechnetium complexes.