Exchange coupling in binuclear oxy-bridged iron(III) protoporphyrin IX dimethyl ester

μ-Oxo-bis[protoporphyrin IX dimethyl ester iorn(III)] gave magnetic susceptibility data from 1·5 to 293 K which fit a model dimer with strong anti-ferromagnctic exchange coupling (2J 380 K) between highspin iron(III) atoms.