Cr(I)-Cr(I) Terphenyl Bridged Complexes: A Broken-Symmetry DFT and Multideterminant CASSCF/NEVPT2 Handshake

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• Revisiting a chromium(I)-chromium(I) system stabilized by terphenyl ligands.
• Understanding the electronic structure and bonding in low-valent transition metal complexes.

Purpose of the Study:

• To evaluate the performance of various multideterminant ab initio and DFT methods for describing a Cr(I)-Cr(I) system.
• To consistently determine spin state ordering, magnetic interactions, and optimized geometry.

Main Methods:

• Multideterminant ab initio calculations: Complete Active Space Self-Consistent Field (CASSCF) and N-Electron Valence Perturbation Theory 2 (NEVPT2).
• Density Functional Theory (DFT) calculations: Including BLYP, B3LYP, ωB97X-D, M06-2X, and B3LYP-GD3 functionals.
• Broken-Symmetry (BS) DFT for singlet ground state analysis.

Main Results:

• All methods consistently identify a singlet ground state with antiferromagnetic coupling within the Cr(I)-Cr(I) moiety.
• CASSCF and BS singlet BLYP methods accurately predict the Cr-Cr bond order and experimental geometry (dCr-Cr ~ 1.7 Å).
• Singlet CASSCF and BS singlet B3LYP yield longer Cr-Cr bond lengths (> 2.5 Å), while restricted singlet B3LYP/BLYP show instability.

Conclusions:

• Multideterminant ab initio and DFT methods offer consistent insights into the Cr(I)-Cr(I) system's electronic and geometric properties.
• The choice of computational method significantly impacts the predicted Cr-Cr bond length and electronic delocalization.
• BS singlet DFT and NEVPT2 are recommended for accurately describing the experimental geometry of such low-valent chromium systems.