Electronic Structures of Tris(dioxolene)chromium and Tris(dithiolene)chromium Complexes of the Electron-Transfer Series [Cr(dioxolene)<sub>3</sub>]<i><sup>z</sup></i><sup></sup> and [Cr(dithiolene)<sub>3</sub>]<i><sup>z</sup></i><sup></sup> (<i>z</i> = 0, 1−, 2−, 3−). A Combined Experimental and Density Functional Theoretical Study

From the reaction mixture of 3,6-di-<i>tert</i>-butylcatechol, H<sub>2</sub>[<sup>3,6</sup>L<sub>cat</sub>], [CrCl<sub>3</sub>(thf)<sub>3</sub>], and NEt<sub>3</sub> in CH<sub>3</sub>CN in the presence of air, the neutral complex [Cr<sup>III</sup>(<sup>3,6</sup>L<sup>•</sup><sub>sq</sub>)<sub>3</sub>] (<i>S</i> = 0) (<b>1</b>) was isolated. Reduction of <b>1</b> with [Co(Cp)<sub>2</sub>] in CH<sub>2</sub>Cl<sub>2</sub> yielded microcrystals of [Co(Cp)<sub>2</sub>][Cr<sup>III</sup>(<sup>3,6</sup>L<sup>•</sup><sub>sq</sub>)<sub>2</sub>(<sup>3,6</sup>L<sub>cat</sub>)] (<i>S</i> = <sup>1</sup>/<sub>2</sub>) (<b>2</b>) where (<sup>3,6</sup>L<sup>•</sup><sub>sq</sub>)<sup>1-</sup> is the π-radical monoanionic <i>o</i>-semiquinonate of the catecholate dianion (<sup>3,6</sup>L<sub>cat</sub>)<sup>2-</sup>. Electrochemistry demonstrated that both species are members of the electron-transfer series [Cr(<sup>3,6</sup>L<sub>O,O</sub>)]<i><sup>z</sup></i><sup></sup> (<i>z</i> = 0, 1−, 2−, 3−). The corresponding tris(benzo-1,2-dithiolato)chromium complex [N(<i>n</i>-Bu)<sub>4</sub>][Cr<sup>III</sup>(<sup>3,5</sup>L<sup>•</sup><sub>S,S</sub>)<sub>2</sub>(<sup>3,5</sup>L<sub>S,S</sub>)] (<i>S</i> = <sup>1</sup>/<sub>2</sub>) (<b>3</b>) has also been isolated; (<sup>3,5</sup>L<sub>S,S</sub>)<sup>2-</sup> represents the closed-shell dianion 3,5-di-<i>tert</i>-butylbenzene-1,2-dithiolate(2−), and (<sup>3,5</sup>L<sup>•</sup><sub>S,S</sub>)<sup>1-</sup> is its monoanionic π radical. Complex <b>3</b> is a member of the electron-transfer series [Cr(<sup>3,5</sup>L<sub>S,S</sub>)<sub>3</sub>]<i><sup>z</sup></i><sup></sup> (<i>z</i> = 0, 1−, 2−, 3−). It is shown by Cr K-edge and S K-edge X-ray absorption, UV−vis, and EPR spectroscopies, as well as X-ray crystallography, of <b>1</b> and <b>3</b> that the oxidation state of the central Cr ion in each member of both electron-transfer series remains the same (+III) and that all redox processes are ligand-based. These experimental results have been corroborated by broken symmetry density functional theoretical calculations by using the B3LYP functional.