An orbital approach of electron transfer in multisite systems. Implications for carbon-rich spacers

International audienceA simple orbital approach is presented to treat electron transfer in mixed valence compounds with either organometallic (M(dppe)2Cl, M(dppe)Cp∗) or organic sites (triarylamine) and various bridges or spacers in particular carbon-rich ones. The orbital approach is based on the inspection of the HOMO of fragments constituting the complete system. The link is also made with solid-state concepts such as Holstein and Holstein-Peierls polarons. The HOMOs of different fragments are examined, in particular their decay along a conjugated chain starting from a donor group grafted at one extremity. Overlap considerations allow the qualitative prediction of the existence (or not) of an electronic interaction along a bridge. This approach is applied to a large variety of bridging systems with either an even or odd number of atoms: conjugated bridges, cross-conjugated systems, platinum bridges, aromatic bridges such as azulene or pyridine.The orbital approach allows also a discussion of the effect of oxidation on geometry changes (polaron formation), showing that the larger the fragment, the smaller the polaron energy. This is qualitatively applied to a series of mixed valence systems bridged by benzene, naphthalene or anthracene in the frame of a three-center model.(∗∗) in honor of Claude Lapinte, recognizing and appreciating a major actor of the chemistry developed in Renne