Spectroscopic and Computational Studies on [PhTt[sup tBu][sub 2]Ni[sub 2](μ-O)[sub 2]]: Nature of the Bis-μ-oxo (Ni[sup 3+]) [sub 2] 'Diamond' Core.

Spectroscopic and density functional theory (DFT) electronic structure computational studies on a binuclear bis-µ-oxo bridged (Ni[sup 3+])[sub 2] complex, [(PhTt[sub Bu])[sub 2]Ni[sub 2](µ-O)[sub 2]] (1), where (PhT[sup Bu]) represents phenyltris((tert-butylthio)methyl)borate, are presented and discussed. These studies afford a detailed description of the Ni[sub 2]O[sub 2] core electronic structure in bis-µ-oxo (Ni[sup 3+])[sub 2] dimers and provide insight into the possible role of the (PhT[sup Bu]) thioether ligand in the formation of 1 from a Ni[sup 1+] precursor by O[sub 2] activation. From a normal coordinate analysis of resonance Raman data, a value of k[sub Ni-O] = 2.64 mdyn/Å is obtained for the Ni-O stretch force constant for 1. This value is smaller than k[sub Cu-o] = 2.82-2.90 mdyn/Å, obtained for bis-µ-oxo (Cu[sup 3+])[sub 2] dimers possessing nitrogen donor ligands, indicating a reduced metal-oxo bond strength in 1. Electronic absorption and magnetic circular dichroism spectroscopic techniques permit identification of several O→Ni and S→Ni charge transfer (CT) transitions that are assigned on the basis of DFT calculations. The dominant O→Ni CT transition of I occurs at 17 700 cm[sup -1], red-shifted by ∼7000 cm[sup -1] relative to the corresponding transition in bis-µ-oxo (Ni[sup 3+])[sub 2] dimers with nitrogen donor ligands. This red-shift along with the relatively low value of k[sub Ni-O] are due primarily to the presence of the thioether ligands in I that greatly affect the compositions of the Ni[sub 2]O[sub 2] core MOs. This unique property of the thioether ligand likely contributes to the reactivity of the Ni center in the precursor [(PhTt[sup tBu])Ni[sup 1+]CO] toward O[sub 2]. DFT computations reveal that conversion of a hypothetical side-on peroxo (Ni[sup 2+])[sub 2] dimer, [(PhT[sub tBu])[sub 2]Ni[sub 2](µ-η²:η²-O[sub 2])], to the bis-µ-oxo (Ni[sup... [ABSTRACT FROM AUTHOR]