BINUCLEAR COMPLEXES OF MACROCYCLIC LIGANDS - ELECTROCHEMICAL AND SPECTRAL PROPERTIES OF HOMOBINUCLEAR CUIICUII,CUIICUI, AND CUICUI SPECIES INCLUDING AN ESTIMATED INTRA-MOLECULAR ELECTRON-TRANSFER RATE

Electrochemical techniques were employed to study electron transfer properties of a binuclear copper-macrocyclic ligand complex and to prepare several reduced derivatives. The complex, CuIICuIIL(ClO4)2•2H2O, was prepared by condensing 1, 3-diaminopropane with 5-methyl-2-hydroxyisophthalaldehyde and Cu(C104)2-6H20. The CuIICuII complex was reduced in successive, quasi-reversible, one-electron steps at -0.52 and -0.91 V vs. NHE. Constant-potential electrolysis was employed to prepare the reduced species, CuIICuIL(ClO4) and CuICuIL, both of which were isolated and fully characterized. The mixed-valence species, CuICuIL+, is stable in oxygen-free solutions (conproportionation constant : 3.97 X 106) and reacts with carbon monoxide to form an adduct, CuIICuIL(CO)ClO4. The diamagnetic CuICuIL species was obtained as essentially insoluble black needles which, however, formed a soluble dicarbonyl adduct, CuICuIL(CO)2, on exposure to CO. The latter complex was not isolated. At the ambient temperature CuICuIL+ exhibits an isotropic seven-line solution EPR spectrum while an anisotropic pattern was observed in frozen solutions (77 K), with four lines for g∥ and unresolved g⊥. Variable-temperature experiments indicated coalescence at about 200 K suggesting an intramolecular electron transfer rate of about 1.7 X 1010 s-1 at 298 K. Electronic absorption spectral measurements revealed at least two absorptions for CuIICuIL(ClO4)2 at 1700 and 1200 nm (CH2Cl2), which are not present in CuIICuIIL(ClO4)2•2H2O, CuICuIL, or the carbonyl derivatives. The new spectral bands may be attributable to intramolecular electron transfer processes. © 1979, American Chemical Society. All rights reserved.