Inorganic Molecular Electride Mg₄ O₃ : Structure, Bonding, and Nonlinear Optical Properties

Area of Science:

• Materials Science
• Quantum Chemistry
• Nonlinear Optics (NLO)

Background:

• Growing demand for advanced materials in nonlinear optics (NLO) necessitates exploration of highly polarizable molecules with excess electrons.
• Electrides, compounds with excess diffuse electrons, are promising but rarely synthesized, especially as molecular species.
• Previous studies observed electride-like features in MgO crystals with defect F-centers, inspiring new molecular designs.

Purpose of the Study:

• To theoretically design and characterize a novel molecular species exhibiting electride characteristics.
• To investigate the role of electride electron pairs in the nonlinear optical properties of the designed molecule.
• To assess the potential experimental observability of the designed molecular electride and its properties.

Main Methods:

• Theoretical design of a molecular species based on a Mg4O4 cube with one oxygen atom removed (Mg4O3).
• Computational analysis including first hyperpolarizability (β), vertical detachment energies (VDE), excitation energies (ΔE), polarizabilities (α), and IR spectra.
• Comparison of NLO properties between the designed electride-like cluster and related non-electride structures.

Main Results:

• A novel molecular electride (Mg4O3) was theoretically designed, featuring a diffuse electride multicentered bond formed by two extruded 3s electrons.
• The designed molecular electride exhibits a significantly large first hyperpolarizability (β = 5733 au), crucial for NLO applications.
• Complete Mg4O4 and Mg4O3^2+ structures without the electride electron pair showed substantially lower β values, highlighting the electron pair's importance.

Conclusions:

• The theoretical design demonstrates the feasibility of stable molecular electrides with significant NLO properties.
• The electride electron pair is identified as the key factor responsible for the enhanced first hyperpolarizability.
• Calculated properties (β, VDE, ΔE, α, IR spectra) are predicted to be experimentally verifiable, serving as evidence for stable molecular electride formation.