Redox-active ligands as a challenge for electronic structure methods.

Area of Science:

• Computational Chemistry
• Materials Science
• Catalysis

Background:

• Redox-active ligands are key to enhancing 3d transition metal catalyst activity.
• These ligands complicate experimental determination of metal oxidation and spin states.
• First-principles calculations are essential for theoretical investigation.

Purpose of the Study:

• To evaluate common exchange-correlation (xc) functionals for density functional theory (DFT) calculations.
• To assess the impact of redox-active ligands on iron(II) tris(diimine) complexes.
• To identify and address computational artifacts in spin-state energy calculations.

Main Methods:

• Density functional theory (DFT) calculations.
• Systematic testing of various exchange-correlation (xc) functionals.
• Analysis of spin-state energy splittings in iron(II) tris(diimine) complexes.

Main Results:

• Spin-state energy splittings generally showed linear dependence on exact exchange admixture in xc functionals.
• The sensitivity of spin-state energetics to exact exchange was unexpectedly low despite significant electronic structure changes.
• Self-consistent field convergence to local minima, differing from the global minimum, was observed for certain complexes.

Conclusions:

• DFT with appropriate xc functionals is crucial for studying redox-active ligand effects in transition metal catalysis.
• Care must be taken to detect and correct for computational artifacts like convergence to local minima.
• Protocols for managing these artifacts are discussed for large-scale computational studies.