Effect of Fluoro-containing Ligand and/or Fluoride on Photoredox Stability of Iron(III) Complexes

Jozef Šima, Mário Izakovič, Rastislav Šípoš, Jozef Švorec

Department of Inorganic Chemistry, Slovak Technical University, Radlinského 9, 812 37 Bratislava, Slovakia
E-mail: jozef.sima@stuba.sk

Photochemical behaviour of iron(III) complexes [Fe(4-R-benacen)X(CH3OH)] where X = Cl or F, and 4-R-benacen(2-) are N,N’-ethylenebis(4-R-benzoylacetoneiminato) ligands with R = H, Cl or F, was investigated in methanolic solutions by steady-state photolysis at four different wavelengths. The course of photoredox processes was followed by UV-VIS spectrophotometry and spin-trapping EPR. It was found that both the axial coordination of a fluoride anion to the iron(III) central atom and the presence of the fluorine atoms of the equatorial 4-F-benacen ligand increased the photoredox stability of the iron(III) central atom when compared with analogous chloro complexes with unsubstituted benacen or 4-Cl-benacen ligands. Quantum yield of Fe(II) formation decreased with increasing wavelength of the incident radiation. Spin-trapping EPR documented the presence of •CH2OH radicals in irradiated systems. 19F-NMR showed that fluorine atoms of 4-F-benacen ligand did not interact with the central atom. A mechanism of the photodeactivation processes is proposed.

Keywords: photoredox stabilization, iron(III) complexes, benacen, fluoroligand, mechanism.