PHOTOREDOX CHEMISTRY OF IRON(III) OXALATO COMPLEXES WITH N,N’-1,1-R₂-ETHYLENEBIS(R’-SALICYLIDENEIMINATO) LIGANDS

Mário Izakovič and Jozef Šima*
Department of Inorganic Chemistry,  Slovak Technical University ,
Radlinského 9, 81237 Bratislava,  Slovakia ; E-mail: jozef.sima@stuba.sk

Abstract 

The complexes Na[Fe(R’-sal-R₂-en)(C₂O₄)], where R’-sal-R₂-en^2- are tetradentate open-chain N,N'-1,1-R₂-ethylenebis(R’-salicylideneiminato) N₂O₂-ligands (R = H or CH₃; R’ = H, 5-Cl, 5-Br, 3,5-Br₂, 3-OCH₃ or 4-OCH₃), 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(II), CO₂ and CH₂O as final products. Using EPR spin trapping technique, carbon dioxide anion radicals CO₂^·- were identified in methanolic solutions of the complexes irradiated at l_irr > 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, F_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.

Key words: Iron(III) complexes, photochemistry, mechanism