Influence of Changing the Remote Substituents on Charge Transfer Properties of Cyanide-Bridged Trinuclear Fe-Ru-Fe Complexes

To investigate the effect of ligand remote (>10 angstrom) substituents on the bridging metal center on the metal-to-metal charge transfer (MMCT) properties in cyanidometa-bridged complexes, a series of new cyanidometal-bridged complexes and their one-electron and two-electron oxidation products have been synthesized and well characterized (namely, trans-[Cp(dppe)Fe-NC-(L)Ru(PPh3)-CN-Fe(dppe)Cp][PF6](n) (n=2, 3, 4) (L=dmptpy, 1[PF6](n); L=meoptpy, 2[PF6](n); L=t-Buptpy, 3[PF6](n)) (Cp=1,3-cyclopentadiene, dppe=1,2-bis(diphenylphosphino)ethane, PPh3=triphenylphosphine, dmptpy=4 '-(4-dimethylaminophenyl)-2,2 ',6 ',2 ''-terpyridine, meoptpy=4 '-(4-methoxyphenyl)-2,2 ',6 ',2 ''-terpyridine, t-Buptpy=4 '-(4-tertbutylphenyl)-2,2 ',6 ',2 ''-terpyridine)). The investigations suggest that the cyanido-stretching (nu(CN)) vibration energy for the complexes is unsensitive to the electron-donating ability change of the remote substituents of the cyanidometal bridging auxiliary ligand from tertbutyl, methoxy to dimethylamino group. However, the MMCT energies of the one- and two-electron oxidation complexes are still sensitive to the remote substituents of the ligand on the bridging metal center, and decreases with the increase of the electron-donating ability of the remote substituents from tertbutyl, methoxy to dimethylamino group. All one-electron and two-electron oxidation products belong to Class II mixed valence compounds according to the classification of Robin and Day.