Metal-Metal Bridging Using the DPPP Dye System: Electronic Configurations within Multiple Redox Series

Redox series [LnRu(mu-DPPP)RuLn](k), H2DPPP = 2,5-dihydro-3,6-di-2-pyridylpyrrolo(3,4-c)pyrrole-1,4-dione and L = 2,4-pentanedionato (acac(-)), 2,2'-bipyridine (bpy), and 2-phenylazopyridine (pap), have been studied by voltammetry (CV, DPV), EPR, and UV-vis-NIR spectroelectrochemistry, supported by TD-DFT calculations. Crystal structure analysis and H-1 NMR revealed oxidation states [(acac)(2)Ru-III(mu-DPPP2-)Ru-III(acac)(2)] and [(bpy)(2)Ru-II(mu-DPPP2-)Ru-II(bpy)(2)](2+) for the corresponding precursors, isolated as rac diastereomers. Oxidation was observed to occur mainly at the bridging ligand (DPPP2(-) -> DPPP-), whereas the site of reduction (DPPP, Ru, or L) depends on effects from the ancillary ligands L. The metal coordination of a derivative of the pigment forming 2,5-dihydro-pyrrolo(3,4-c)pyrrole-1,4-dione (DPP) dyes and the analysis of corresponding multistep redox series add to the previously recognized coordinative and electron transfer potential of dye molecules of the azo, indigo, anthraquinone, and formazanate type.