Influence of electron-donating ability of ligand and pH value on MLCT properties of cyanido-bridged complexes

Abstract

In this work, one mononuclear complex CH3CNFeII(eq-Py4PzMe2) (1) and two binuclear complexes Cp(dppe)MIICNFeII(eq-Py4PzMe2) (M = Ru 2, Fe 3; Cp = cyclopentadiene, dppe = 1,2-bis(diphenylphosphino)ethane, eq-Py4PzMe2 = 2-(1-(6-(1,1-di(pyridin-2-yl)ethyl)pyridin-2-yl)-1-(pyridin-2-yl)ethyl)pyrazine) were synthesized. Combined with the TDDFT calculations, the metal-to-ligand charge transfer (MLCT) properties of all the compounds were investigated. The results show that for the mononuclear complex, the MLCT originates from FeII to the pyrazine (Pz) component of the eq-Py4PzMe2 ligand. After the substitution of CH3CN in complex 1 by the half-sandwich fragment Cp(dppe)MIICN, the binuclear complexes 2 and 3 exhibit the MLCT transition from the neighboring FeII atom to the Pz component of the eq-Py4PzMe2 together with some contributions from the remote MII. With the increase of the electron-donating ability from CH3CN, Cp(dppe)RuIICN to Cp(dppe)FeIICN, the MLCT transition energy decreases. Furthermore, with the decrease of pH value, all the MLCT absorption bands are significantly redshifted by 160 nm or more, and the extent of these red shifts increases from complex 1 to 2, to 3.