Spectroscopic and Computational Studies of a μ-η2:η2-Disulfido-Bridged Dinickel(II) Species, [{(PhTttBu)Ni}2(μ-η2:η2-S2)]: Comparison of Side-On Disulfido and Peroxo Bonding in (NiII)2 and (CuII)2 Species

In this study, a combined spectroscopic and computational approach has been employed to generate a detailed description of the electronic structure of a binuclear side-on disulfido (Ni-II)(2) complex, [{(PhTt(tBu))Ni}(2)(mu-eta(2):eta(2)-S-2)] (1, where PhTt(tBu) = phenyltris[(tert-butylthio)methyl]borate). The disulfido-to-Ni-II charge-transfer transitions that dominate the electronic absorption spectrum have been assigned on the basis of time-dependent density functional theory (DFT) calculations. Resonance Raman spectroscopic studies of 1 have revealed that the S-S stretching mode occurs at 446 cm(-1), indicating that the S-S bond is weaker in 1 than in the analogous mu-eta(2):eta(2)-S-2 dicopper species. DFT computational data indicate that the steric bulk of PhTt(tBu) stabilize the side-on core enough to prevent its conversion to the electronically preferred bis(mu-sulfido) (Ni-III)(2) structure. Hence, 1 provides an interesting contrast to its O-2-derived analogue, [{(PhTt(tBu))Ni}(2)(mu-O)(2)] which was shown previously to assume a bis(mu-oxo) (Ni-III)(2) "diamond core". By a comparison of 1 to analogous disulfidodicopper and peroxodinickel species, new insight has been obtained into the roles that the metal centers, bridging ligands, and supporting ligands play in determining the core structures and electronic properties of these dimers.