Manipulation of the heme electronic structure by external stimuli and ligand field

This review describes the switching behaviors of the electronic structure, which were observed in iron(III) porphyrinoids, by the addition of external stimuli. The combined analysis by various methods, such as EPR, Mossbauer, SQUID, single crystal X-ray structure analysis, revealed a wide variety of electronic structures of the heme related complexes. This paper focuses in particular on the spin-crossover phenomenon in the solid state. An overview of spin-crossover phenomena found in iron(III) porphyrinoids between (i) S = 5/2 and S = 1/2, (ii) S = 3/2 and S = 1/2, (iii) S = 5/2 and S = 3/2, will be described.