MANIFESTATIONS OF THE PERIPHERAL GROUP EFFECTS IN PHOTOOXIDATION OF 5-HYDROXY-4H-PYRAN-4-ONES COORDINATED TO THE IRON(III) CENTRAL ATOM

Anions of heterocyclic 5-hydroxy-4H-pyran-4-ones coordinate to the iro n(III) central atom forming tris( O,O-chelate)iron(III) complexes. The complexes are redox stable in the dark, their irradiation leads to th e photoreduction of Fe(III) to Fe(II) associated with oxidation of a l igand to its radical. The efficiency of the photoredox process is stro ngly wavelength dependent and influenced by the peripheral 2-CH2R and 6-CH3 groups of the ligands. The results on electrochemical properties of the free anions and the complexes are given also. Relations betwee n the electronic properties of the peripheral groups R, redox potentia l values and quantum yields of the photoreduction are reviewed. (C) 19 97 Elsevier Science S.A.