Photoredox chemistry of iron(iii) oxalato complexes with n,n'-1,1-r_2-ethylenebis(r'-salicylideneiminato) l1gands

摘要

The complexes Na[Fe(R'-sal-R_2-en)(C_2O_4)],where R'-sal-R_2-en"~ are tetradentate open-chain N,N''-l,l-Rrethylenebis(R'-salicylideneiminato) N_2O_2-ligands (R = H orCH_3;R' = H,5-C1,5-Br,3,5-Br_2,3-OCH_3 or 4-OCH_3),are redox stable in methanolic solutions in the dark.Continuous irradiation of such solutions by ultraviolet and/or visible light leads to photophysical and photochemical deactivation processes yielding Fe(ll),CO_2 and CH_2O as final products.Using EPR spin trapping technique,carbon dioxide anion radicals CO_2~-were identified in methanolic solutions of the complexes irradiated at lambda_(irt) > 300 nm.Tetradentate ligands behave as innocent moiety not participating in redox processes of the complexes.The efficiency of the photoredox processes,expressed by the quantum yield of Fe(II) formation,PHI_(Fe(II)),slightly decreases with increased wavelength of the incident radiation,and is influenced by the peripheral groups R and R' of the tetradentate ligands.A mechanism of the primary photochemical and subsequent thermal reactions is proposed.