Electronic structure of the [tris(dithiolene)chromium](z) (z = 0, 1-, 2-, 3-) electron transfer series and their manganese(IV) analogues. An X-ray absorption spectroscopic and density functional theoretical study.

From the reaction mixture of 3,6-dichlorobenzene-1,2-dithiol, H(2)(Cl(2)-bdt), [CrCl(3)(thf)(3)], and NEt(3) in tetrahydrofuran (thf) in the presence of air, dark green crystals of N(n-Bu)(4)[Cr(Cl(2)-bdt)(3)] (S = 1) (1) were isolated upon addition of [N(n-Bu)(4)]Br. Oxidation of the AsPh(4)(+) salt of 1 with [Fc]PF(6) yielded microcrystals of [AsPh(4)][Cr(Cl(2)-bdt)(3)] (S = (1)/(2)) (2) whereas the reduction of 1 with sodium amalgam produced light green crystals of N-(n-Bu)(4)[Cr(Cl(2)-bdt)(3)].thf (S = (3)/(2)) (3). The corresponding maleonitriledithiolato complexes PPh(4)[Cr(mnt)(3)] (S = 1) (4) and PPh(4)[Cr(mnt)(3)] (S = (3)/(2)) (5) have been synthesized. Isoelectronic manganese complexes of 3 and 5, namely, NEt(4)[Mn(Cl(2)-bdt)(3)] (S = (3)/(2)) (6) and PPh(4)[Mn(mnt)(3)] (S = (3)/(2)) (7), have also been prepared. Complexes 1, 6, and 7 have been characterized by single crystal X-ray crystallography. Complexes 1-7 have been electrochemically studied and their UV-vis and electron paramagnetic resonance spectra (EPR) have been recorded; magnetic properties have been elucidated by temperature-dependent susceptibility measurements. It is shown by chromium K-edge and sulfur K-edge X-ray absorption spectroscopy (XAS) that the oxidation state of the central Cr ion in each compound is the same (+III, d(3)) and that all one-electron redox processes are ligand-based, involving one, two, or three ligand pi radical monoanions. Complexes 6 and 7 possess a Mn(IV) ion with three dianionic ligands. The results have been corroborated by broken symmetry (BS) density functional theoretical (DFT) calculations by using the B3LYP functional. Time-dependent DFT calculations have been performed to calculate the metal and sulfur K-pre-edges. It is suggested that the neutral complexes Cr(dithiolene)(3) S = 0 possess octahedral rather than trigonal prismatic CrS(6) polyhedra. Three ligand pi radicals (S(rad) = (1)/(2)) couple antiferromagnetically to the central Cr(III) ion (d(3)) yielding the observed diamagnetic ground state. It is established that the four members of the Cr(dithiolene)(3) (z = 0, 1-, 2-, 3-) electron transfer series are related by ligand-based one-electron transfer processes; for each of the four members it is shown that they contain a central Cr(III) (d(3)) ion, and the CrS(6) polyhedron is a (distorted) octahedron.