Metal-Metal Charge Transfer Properties of a Series of Trinuclear Fe₂Ru and Corresponding Pentanuclear Fe₂Ru₂Ag Cyanido-Bridged Complexes

A series of trimetallic cyanidometal-bridged compounds [MenCp(dppe)Fe-II-(mu-NC)-Ru-II(MeOpy)(4)-(mu-CN)-Fe-II(dppe)CpMen] [PF6] 2 (N[PF6](2), n= 0, N = 1; n= 1, N= 2; n= 3, N= 3; Cp= cyclopentadiene, dppe= 1,2-bis(diphenylphosphino)ethane, MeOpy= 4-methoxypyridine) and their one- and two-electron oxidized compounds N3+ and N4+ were synthesized and characterized. Meanwhile, a series of corresponding linear cyanido-bridged pentanuclear compounds [MenCp(dppe)Fe-III-(mu NC)-Ru-II(MeOpy)(4)-(mu-NC)-AgI-(mu-CN)-Ru-II(MeOpy)4-(mu-CN)-Fe-III- (dppe)CpMen][BF4](5) (M[BF4](5), n= 0, M= 4; n= 1, M= 5; n= 3, M= 6) were also obtained and well characterized. The investigations suggest that in the trinuclear system there exists remote interaction between the two Fe centers, but no significant interactions exist across the central silver unit between the metals on the two sides of the silver center in the pentanuclear system. In both the trinuclear N4+ and the pentanuclear M5+ complexes, there exists the neighboring Ru-II -> Fe-III MM'CT transitions, and the MM'CT energy in the corresponding trinuclear system is higher than those in the pentanuclear system in which no remote metal-metal interaction occurs. Meanwhile, as the substituted methyl groups on the cyclopentadiene increases, the redox potential of the ruthenium in the trinuclear N4+ series increases, but that in the pentanuclear M5+ complexes decreases.