Electronic structure of the [MNH2]+ (M = Sc-Cu) complexes

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Inorganic Chemistry

Background:

• Transition metal complexes are crucial in catalysis and materials science.
• Understanding the electronic structure of metal-ligand interactions is key to predicting reactivity.
• Amide ligands offer unique bonding possibilities due to their electronic configuration.

Purpose of the Study:

• To investigate the ground-state geometries and electronic structures of first-row transition metal amide complexes ([MNH2]+).
• To elucidate the factors governing electronic structure differences across the transition metal series.
• To analyze the nature and relative strengths of sigma and pi bonding interactions in these complexes.

Main Methods:

• Density Functional Theory (DFT) using B3LYP for geometry optimizations.
• Complete Active Space Perturbation Theory (CASPT2) for accurate binding energy calculations.
• Inclusion of zero-point energies and relativistic effects for precise results.

Main Results:

• All first-row transition metal amide complexes ([MNH2]+) were found to have planar ground-state geometries.
• Electronic structures differ between early/middle (Sc+-Co+) and late (Ni+, Cu+) transition metals, influencing electron transfer.
• Pi-type interactions were consistently stronger than sigma-type interactions across the series, an unusual finding.

Conclusions:

• The planar geometry and unique electronic structure of [MNH2]+ complexes are robust across the first-row transition metals.
• Electron transfer dynamics are dictated by the relative energy levels of metal 3d orbitals and the NH2 ligand's HOMO.
• The dominance of pi-type interactions stems from the low-lying sp2 lone pair orbital of the NH2 ligand relative to the metal's 3d orbitals.