Electronic Structure and Bonding Situation in M₂O₂ (M = Be, Mg, Ca) Rhombic Clusters

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Materials Science

Background:

• Understanding the electronic structure and bonding in metal oxide clusters is crucial for catalysis and materials design.
• Previous studies on diatomic metal oxides (MO) provide a basis for comparison.

Purpose of the Study:

• To investigate the electronic structure and bonding characteristics of M₂O₂ rhombic clusters (M = Be, Mg, Ca).
• To determine the nature of metal-metal interactions and metal-oxygen bonds within these clusters.

Main Methods:

• Ab initio coupled cluster with singles, doubles, and perturbative triples (CCSD(T)) calculations.
• Density functional theory (DFT) for electronic structure analysis.
• Charge and energy decomposition analyses.

Main Results:

• Equilibrium geometries show very short transannular metal-metal distances in M₂O₂ clusters, but no direct M-M bonds.
• Metal atoms (M) exhibit large positive partial charges, with valence electrons significantly shifted towards oxygen.
• Metal-oxygen bonds in M₂O₂ clusters are shorter and stronger than in diatomic MO.
• Bond dissociation energies for M₂O₂ fragmentation into 2 MO are very large.

Conclusions:

• The electronic structure of M₂O₂ rhombic clusters is characterized by strong metal-oxygen bonding and weak three-center M-O-M interactions, rather than direct M-M bonding.
• Despite short M-M distances, the bonding is primarily ionic, with minimal electron density between the metal atoms.