Spin-crossover between high-spin (S=5/2) and low-spin (S=1/ 2) states in six-coordinate iron(III) porphyrin complexes having two pyridine-N oxide derivatives

In contrast to the general tendency that six coordinate iron( III) porphyrin complexes with neutral oxygen ligands adopt a high-spin state in a wide range of temperature, some complexes with substituted pyridine N-oxides have exhibited spin-crossover from high-spin to low-spin states with decreasing temperature both in solution and in the solid state.