Binuclear complexes of macrocyclic ligands. Electrochemical and spectral properties of homobinuclear CuIICuII, CuIICuI, and CuICuI species including an estimated intramolecular 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, Cu/sup II/Cu/sup II/L(ClO/sub 4/)/sub 2/.2H/sub 2/O, was prepared by condensing 1,3-diaminopropane with 5-methyl-2-hydroxyisophthalaldehyde and Cu(ClO/sub 4/)/sub 2/.6H/sub 2/O. The Cu/sup II/Cu/sup II/ 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, Cu/sup II/Cu/sup I/L(ClO/sub 4/) and Cu/sup I/Cu/sup I/L, both of which were isolated and fully characterized. The mixed-valence species, Cu/sup II/Cu/sup I/L/sup +/, is stable in oxygen-free solutions (conproportionation constant: 3.97 x 10/sup 6/) and reacts with carbon monoxide to form an adduct, Cu/sup II/Cu/sup I/L(CO)ClO/sub 4/. The diamagnetic Cu/sup I/Cu/sup I/L species was obtained as essentially insoluble black needles which, however, formed a soluble dicarbonyl adduct, Cu/sup I/Cu/sup I/L(CO)/sub 2/, on exposure to CO. The latter complex was not isolated. At the ambient temperature Cu/sup II/Cu/sup I/L/sup +/ exhibits an isotropic seven-line solution EPR spectrum while an anisotropic pattern was observed in frozen solutions (77/sup 0/K), with four lines for g parallel to and unresolved g perpendicular to. Variable-temperature experiments indicated coalescence at about 200/sup 0/K suggesting anmore » intramolecular electron transfer rate of about 1.7 x 10/sup 10/ s/sup -1/ at 298/sup 0/K. Electronic absorption spectral measurements revealed at least two absorptions for Cu/sup II/Cu/sup I/L(ClO/sub 4/)/sub 2/ at 1700 and 1200 nm (CH/sub 2/Cl/sub 2/), which are not present in Cu/sup II/Cu/sup II/L(ClO/sub 4/)/sub 2/.2H/sub 2/O, Cu/sup I/Cu/sup I/L, or the carbonyl derivatives. The new spectral bands may be attributable to intramolecular electron transfer processes. 11 figures, 5 tables.« less