The spin coupling in the diiron complex [Fe2(hpdta)(H2O)3Cl]

Area of Science:

• Computational chemistry
• Inorganic chemistry
• Quantum chemistry

Background:

• Dinuclear iron complexes exhibit complex electronic structures and spin coupling phenomena.
• Understanding these properties is crucial for applications in catalysis and materials science.
• Accurate theoretical modeling of such systems remains a challenge.

Purpose of the Study:

• To investigate the electronic structure and spin coupling of the dinuclear [Fe(2)(hpdta)(H(2)O)(3)Cl] complex.
• To evaluate the performance of different computational methods, including Density Functional Theory (DFT) and Configuration Interaction (CI) approaches.
• To compare theoretical predictions with experimental magnetic susceptibility data.

Main Methods:

• Density Functional Theory (DFT) calculations with various functionals.
• Multireference Configuration Interaction (MRCI) calculations on a model complex.
• Modified Valence Configuration Interaction (MVCI) calculations to account for orbital relaxation effects.

Main Results:

• DFT calculations predict both high-spin and low-spin states for iron centers, with relative energies highly dependent on the chosen functional.
• The calculated spin-spin coupling between high-spin iron centers varied by over a factor of two across different DFT functionals.
• MRCI calculations, even when correlating key orbitals, underestimated the experimentally inferred spin splitting by a factor of approximately three.
• MVCI calculations improved the agreement with experimental data by increasing the exchange splitting, though it remained smaller than the experimental value.

Conclusions:

• The electronic structure and spin coupling of dinuclear iron complexes are sensitive to the computational method employed.
• Standard DFT functionals may not accurately capture the spin states and coupling in these systems.
• Advanced CI methods, like MRCI and MVCI, offer better insights but require careful consideration of electron correlation and orbital relaxation effects to match experimental magnetic properties.