Heterohexanuclear (Cu₃Fe₃) complexes of substituted hexaazatrinaphthylene (HATN) ligands: twofold BF₄- association in the solid and stepwise oxidation (3e) or reduction (2e) to spectroelectrochemically characterized Species

Abstract

New tris(ferrocenylcopper) compounds [(μ₃-dqp){Cu(dppf)}₃][X]₃ (dppf=1,1'-bis(diphenylphosphinoferrocene), dqp=hexamethyl-, hexachloro- or un-substituted diquinoxalino[2,3-a:2',3'-c]phenazine=hexaazatrinaphthylene (HATN), X^-=BF₄^- or PF₆^-) undergo at least two different, reversible one-electron reductions and three very closely spaced one-electron oxidations. While the latter are attributed to the stepwise ferrocene→ferrocenium conversions, the first electron addition occurs in the ligand bridge to yield EPR detectable radical complexes. X-band EPR measurements at 9.5 GHz showed a partially resolved hyperfine structure, while high-frequency EPR measurements at 95 or 115 GHz revealed a small but variable axial g tensor anisotropy. All reversible steps were investigated by optically transparent thin-layer electrode (OTTLE) spectroelectrochemistry (UV/Vis/NIR regions), revealing very low energy transitions for the reduced forms in agreement with the frontier MO arrangement. A crystal structure of the compound with unsubstituted dqp shows notable deviation from the trigonal symmetry and the close association of two tetrafluoroborate anions with the complex trication along the quasi-trigonal axis to yield [(μ₃-dqp){Cu(dppf)}₃(BF₄)₂]BF₄.