Multifrequency EPR and Redox Reactivity Investigations of a Bis(μ-thiolato)-dicopper(II,II) Complex

From a new tripodal ligand [N2SS‘H] with mixed N, S(thioether), and S(thiolate) donor set, the corresponding
bis(μ-thiolato)dicopper(II) complex has been prepared and characterized. X-ray crystallographic analysis of the
complex [Cu2(N2SS‘)2](ClO4)2·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···Cu1* distance of 3.418(8) Å and a large bridging
angle Cu1S1Cu1* of 94.92°. 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 |D| = 0.210(3) cm-1, E = 0.0295(5) cm-1, |E/D| = 0.140, gx = 2.030(2), gy = 2.032(2),
gz = 2.128(2). The electrochemical one-electron reduction of 1 generates the mixed-valent CuIICuI species. EPR
and UV−vis spectra are consistent with a type I localized mixed-valent species, while dinuclear CuA centers of
native cytochrome c oxidase (CcO)1-3 or nitrous oxide reductase (N2OR)4 have a delocalized CuIICuI mixed-valent
state. After reoxidation of the CuIICuI species, the initial complex 1 is regenerated through a reversible interconversion
process.