Electronic properties of hydroquinone-containing ruthenium complexes in different oxidation states

Abstract

Some novel bis(2,2′-bipyridyl)ruthenium(II) complexes based on the ligands 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)benzene (H ₂ L ^p ) and 1,4-dihydroxy-2,3-bis(pyrazol-1-yl)benzene (H ₂ L ^o ) have been prepared and characterized. The spectroscopic properties of the analogous H ₂ L ^p complex containing deuteriated 2,2′-bipyridyl were also studied. The compounds have been oxidized and the electronic properties associated with both oxidation states examined in detail using resonance-Raman and UV/VIS/NIR spectroscopy. In the parent compounds the first redox process is hydroquinone based and the lowest-energy absorption is assigned to a hydroquinone to 2,2′-bipyridyl interligand transition. The products obtained upon oxidation are best described as ruthenium(II)–quinone complexes and their lowest-energy transition is assigned to a Ru ^II to quinone charge transfer.