Molecular structure of Fe(III) 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin perchlorate: a saddle-shaped porphyrin with an intermediate S=3/2 spin state

Recent crystallographic evidence of nonplanarity of several prosthetic grou ps in heme proteins has prompted the design of conformationally distorted s ynthetic porphyrins in order to assess the consequences of the nonplanarity observed in vivo. The crystal structure of the sterically crowded Fe(III) 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin perchlorate h as been determined and shows the macrocycle to be saddle-shaped with a smal l degree of ruffling. The combination of severe nonplanarity and of the wea k ligand-field counterion results in a nearly pure S = 3/2 intermediate spi n state of the Fe(III) as evidenced by its electron paramagnetic resonance spectrum in frozen solution at low temperatures. Published in 2001 by John Wiley & Sons, Ltd.