Complexation of dimethylphenylphosphonite to (5,10,15,20-tetraphenylporphyrinato)iron(III) yields a low-spin derivative [Fe(tpp){P(OMe)(2)Ph}(2)]ClO4, showing NMR and EPR properties consistent with an iron(III) ion in the unusual ground-state configuration (d(xz),d(yz))(4) (d(xy))(1).