Abstract
The electronic structure of the [Cu3S2](3+) core of [(LCu)(3)(S)(2)](3+) (L = N,N,N',N'-tetramethyl-2R,3R-cyclohexanediamine) is investigated using a combination of Cu and S K-edge X-ray absorption spectroscopy and calculations at the density functional and multireference second-order perturbation levels of theory. The results show that the [Cu3S2](3+) core is best described as having all copper centers close to but more oxidized than Cu2+, while the charge on the S-2 fragment is between that of a sulfide (S2-) and a subsulfide (S-2(3-)) species. The [Cu3S2](3+) core thus is different from a previously described, analogous [Cu3O2](3+) core, which has a localized [(Cu3+Cu2+Cu2+)(O2-)(2)](3+) electronic structure. The difference in electronic structure between the two analogues is attributed to increased covalent overlap between the Cu 3d and S 3p orbitals and the increased radial distribution function of the S 3p orbital (relative to O 2p). These features result in donation of electron density from the S-S sigma* to the Cu and result in some bonding interaction between the two S atoms at similar to 2.69 angstrom in [Cu3S2](3+), stabilizing a delocalized S = 1 ground state.