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
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.