Abstract: The invention relates to a method for producing metal complexes of formula (2) [MaLxXn]Ym (2), where M is a metal from the group consisting of Mn(II), Mn(III), Mn(IV), Fe(II), Fe(III) or Fe(IV), X is a coordinating compound selected from mono-, bi- or tri-charged anions or neutral molecules which can coordinate to a metal in mono-, bi- or tri-dentate form, Y represents a non-coordinating counter-ion which ensures charge equalization of the complex, L represents a ligand of formula (1) or the protonized or de-protonized form thereof, and a, x, n, m, R, R1, R2, R3 and z have the meanings described in claim 1. Said method is characterized in that the reaction of one or more ligands of formula (1) with an iron salt or manganese salt is carried out in an acetone/water mixture in a temperature range from 0 to 50° C.