Difference in spin crossover pathways among saddle-shaped six-coordinated iron(III) porphyrin complexes

Area of Science:

• Inorganic Chemistry
• Materials Science
• Physical Chemistry

Background:

• Iron porphyrin complexes exhibit diverse electronic states and spin behaviors.
• Understanding spin crossover phenomena in solution is crucial for molecular magnetism and materials design.
• Saddle-shaped porphyrin complexes offer unique structural and electronic properties.

Purpose of the Study:

• To investigate the electronic states and magnetic properties of saddle-shaped iron porphyrin complexes in solution.
• To elucidate the factors governing spin crossover behavior in these complexes.
• To compare the spin crossover pathways of OMTPP and TBTXP complexes with related porphyrins.

Main Methods:

• Solution-state spectroscopic analysis including 1H NMR, 13C NMR, and EPR spectroscopy.
• Magnetic measurements to determine spin states (low-spin S = 1/2, intermediate-spin S = 3/2).
• Comparative analysis of complexes with varying axial ligands (DMAP, THF, Py, 4-CNPy).

Main Results:

• [Fe(OMTPP)L(2)](+) and [Fe(TBTXP)L(2)](+) complexes exhibit distinct spin states depending on axial ligands and temperature.
• [Fe(OMTPP)(DMAP)(2)](+) and [Fe(TBTXP)(DMAP)(2)](+) maintain a low-spin state.
• [Fe(OMTPP)(THF)(2)](+) and [Fe(TBTXP)(THF)(2)](+) show an intermediate-spin state.
• Py and 4-CNPy complexes display a temperature-dependent spin transition (S = 3/2 to S = 1/2).
• Low-temperature spin crossover in OMTPP and TBTXP complexes involves a less common (d(xz), d(yz))(4)(d(xy))(1) electron configuration.

Conclusions:

• The flexibility of the OMTPP and TBTXP porphyrin cores allows for ring ruffling and adoption of unique electron configurations.
• Porphyrin core rigidity is a key determinant in controlling spin crossover pathways in iron porphyrin complexes.
• This study reveals a novel spin crossover phenomenon in solution, influenced by porphyrin core structure and axial ligation.