Multifrequency EPR and redox reactivity investigations of a bis(μ-thiolato)-dicopper(II, II) complex

From a new tripodal ligand [(NSS)-S-2'H] with mixed N, S(thioether), and S(thiolate) donor set, the corresponding bis(mu-thiolato) dicopper(II) complex has been prepared and characterized. X-ray crystallographic analysis of the complex [Cu-2(N2SS')(2)](ClO4)(2)center dot C4H10O (1) demonstrates that the two five-coordinated Cu atoms are bridged by two thiolates leading to a nearly planar Cu2S2 core with a Cu1 center dot center dot center dot Cu1* distance of 3.418(8) angstrom and a large bridging angle Cu1S1Cu1* of 94.92 degrees. X-band (10 GHz), Q-band (34 GHz), and F-Band (115 GHz) EPR spectra of 1 are consistent with a weakly coupled dicopper( II, II) center attributed to an S = 1 state. Simulations for the three frequencies are obtained with a unique set of electronic parameters. The mean values of the spin Hamiltonian parameters for 1 are vertical bar D vertical bar = 0.210(3) cm(-1), E = 0.0295(5) cm(-1), vertical bar E/D vertical bar = 0.140, g(x) = 2.030(2), g(y) = 2.032(2), g(z) = 2.128(2). The electrochemical one-electron reduction of 1 generates the mixed-valent (CuCuI)-Cu-II species. EPR and UV-vis spectra are consistent with a type I localized mixed-valent species, while dinuclear Cu-A centers of native cytochrome c oxidase (CcO)(1-3) or nitrous oxide reductase (N2OR)(4) have a delocalized (CuCuI)-Cu-II mixed-valent state. After reoxidation of the (CuCuI)-Cu-II species, the initial complex 1 is regenerated through a reversible interconversion process.