Computational studies of electron paramagnetic resonance parameters for paramagnetic molybdenum complexes. 1. Method...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Accurate computation of electronic g-tensors and hyperfine couplings is crucial for understanding molybdenum-containing compounds.
• Density functional theory (DFT) methods are widely used but require careful parameterization for specific systems.
• Electron paramagnetic resonance (EPR) spectroscopy provides experimental data for validating computational models.

Purpose of the Study:

• To evaluate various density functional methods for computing molybdenum electronic g-tensors and hyperfine couplings.
• To investigate the impact of basis sets and exchange-correlation functionals on EPR parameters.
• To identify optimal computational strategies for accurate predictions in molybdenum complexes.

Main Methods:

• Systematic evaluation of density functional theory (DFT) methods, including hybrid functionals with varying Hartree-Fock exchange.
• Basis set studies using a moderate-sized 12s6p5d all-electron basis for molybdenum.
• Inclusion of spin-orbit corrections and scalar relativistic effects in calculations.
• Two-component g-tensor calculations with variational spin-orbit coupling.

Main Results:

• A moderate-sized 12s6p5d molybdenum basis set yields hyperfine tensors in excellent agreement with larger basis sets.
• Hybrid functionals with 30-40% Hartree-Fock exchange provide the best agreement with experimental g- and hyperfine tensors.
• Spin-orbit corrections are significant and necessary for accurate hyperfine tensor calculations.
• Scalar relativistic effects enhance isotropic Mo hyperfine coupling by 15-20%.
• Computed tensor orientations for MoXLCl2 complexes show good agreement with single-crystal EPR experiments.

Conclusions:

• Optimized DFT methods, particularly hybrid functionals with specific Hartree-Fock exchange, accurately predict molybdenum EPR parameters.
• A carefully chosen basis set and inclusion of spin-orbit effects are essential for high accuracy.
• The study provides a reliable computational framework for investigating molybdenum complexes using EPR spectroscopy.