Control of Iron(III) Spin-State in the Model Complexes of Azide Hemoprotein by Porphycene, Corrphycene, and Hemiporphycene Macrocycles

Spin states of the iron(III) complexes of porphyrin, porphycene, hemiporphycene, and corrphycene bearing both 1-methylimidazole and azide as axial ligands were analyzed with infrared (IR) spectroscopy at 20 °C. The IR stretching band of coordinating azide split into two peaks around 2047 and 2017 cm-1 reflecting an equilibrium between the high- (S = 5/2) and low- (S = 1/2) spin states. The high-spin fraction changed over a 0−90% range among the macrocycles, demonstrating that the tetrapyrrole array is essential to control the equilibrium.