MMCT energy change in cyanidometal-bridged trinuclear complexes by changing the ligand electron donating ability

Abstract

To investigate the effect of metal-to-metal charge transfer (MMCT) in the complexes of cyanidometal-bridges, we synthesized and fully characterized a series of trimetallic cyanidometal-bridged compounds with the formula trans-[CpMe_xFe–NC–Ru(L)₄–CN–FeCpMe_x][PF₆]₂, N²⁺[PF₆]₂ (L = i-PrPy, N = 1, x = 0; N = 2, x = 1; N = 3, x = 3; N = 4, x = 4; N = 5, x = 5), and their one-electron and two-electron oxidized products N³⁺[PF₆]₃ and N⁴⁺[PF₆]₄. Electrochemical measurements show the presence of electronic interactions between the two terminal Fe units. As methyl substituents on the Cp ligands increase, the change trend of the MMCT energy from the remote terminal Fe^II to Fe^III in complexes N³⁺ is not obvious, which may be due to the increase in the electron-donating ability of the Cp ligands on both the terminals, electron-donating Fe^II and electron-accepting Fe^III ions, while the MMCT energy from the neighboring Ru^II to the terminal Fe^III in complexes N⁴⁺ decreases, strongly supported by the TDDFT calculations. All the mixed-valence compounds N³⁺ and N⁴⁺ belong to Class II systems.