Facilitated reduction and oxidation of {[Ru(NH3)5]4(μ4-TCNX)}8+ by changing from TCNX = TCNQ to TCNQF4

The new tetraruthenium compound {[Ru(NH3)5]4(μ4-TCNQF4)}(PF6)8, TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyano-p-benzoquinodimethane, was studied by cyclic voltammetry, IR, UV–Vis–NIR and EPR spectroelectrochemistry. The better π acceptor qualities of TCNQF4 in comparison to TCNQ cause more accessible reduction to produce {[Ru(NH3)5]4(μ4-TCNQF4)}7+ with enhanced metal contribution to the singly occupied MO and low-energy shifted IR vibrational and NIR electronic absorptions. However, the two-electron oxidation to the (10+) ion is also facilitated. The reason is seen in a more metal-centered oxidation for the TCNQF4 complex while the previously studied TCNQ analogue is assumed to undergo a higher degree of oxidation at the bridging ligand. As a result, the title species has a redox potential range of only 0.52 V, indicating a significantly diminished HOMO–LUMO gap.

The fluorine substitution in the TCNQF4 bridge of [1]8+ results in a diminished HOMO-LUMO gap, originating from a lowered p∗ MO and a decreased oxidation potential.Figure optionsDownload as PowerPoint slide