Coupling HOMO-LUMO

A first group of compounds Ce Cg2, Gd Cg2, Y Cg2, and the major [C2v] and minor [Cs] isomers of La Cg2 and Pr Cg2 showed two oxidation steps, the first reversible and the second irreversible, even at scan rates up to 1 V/s. The low potential of the first oxidation step, close to that of the ferrocene/ferrocenium couple (see Table 8.3 and Fig. 8.4), made these compounds rather good electron donors. These compounds could also be reduced in four to six distinct steps, most of them reversible, and their reducing ability was found even higher than that of and similar to that of the major isomer of Cg2 (C2). Noticeably, all these compounds had a very low electrochemical HOMO-LUMO gap (A ,gap<0.50 V). In addition, similar UV/Visible spectra were obtained for all of them,28 suggesting also similar electronic structures. ESR showed that Y Cg229 and both isomers of La CX249 52 are radical species and consequently that the formal oxidation state of the metal in these structures is probably + 3. Therefore, their low HOMO-LUMO gap is probably a consequence of their open-shell electronic structure. 

---