Nature of the Three-Electron Bond

Area of Science:

• Chemical Bonding Theory
• Quantum Chemistry

Background:

• Three-electron bonds (3e-bonds) are prevalent in various chemical species.
• Understanding the nature of these bonds is crucial for predicting molecular properties.

Purpose of the Study:

• To analyze the fundamental properties of 3-electron bonds.
• To determine if 3e-bonds exhibit charge shift bonding (CSB) characteristics.
• To compare 3e-bonds with established two-electron CSBs.

Main Methods:

• Utilized the breathing-orbital valence-bond (BOVB) method to analyze 15 diverse 3e-bonds.
• Quantified charge shift resonance energy (RE_CS) and bond dissociation energies (D_e).
• Employed the Laplacian (L) of the 3e-bond to probe CSB character, validated against MRCI calculations.

Main Results:

• All analyzed 3e-bonds, including σ and π types, were found to be charge shift bonds (CSBs).
• Bonding energy originates from resonance and charge shift, not individual valence bond structures, overcoming Pauli repulsion.
• Laplacian (L) values are positive, indicating excess kinetic energy, consistent with CSBs.

Conclusions:

• σ- and π-3-electron bonds are integral members of the charge shift bond family.
• 3e-CSBs share energetic and topological features with 2-electron CSBs.
• Proposed experimental tests to validate the existence and properties of 3e-CSBs.