Hypercoordinated PN₄ with Nonclassical N-N Bonds: An sp²⁺ Hybridized Framework Stabilized by d-Orbital Activation

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Chemistry

Background:

• Nitrogen's unique electronic structure limits non-integer hybridizations, posing challenges for nitride material development.
• Understanding nitride bonding modes is crucial for advancing classical bonding theory and discovering novel materials.

Purpose of the Study:

• To predict and characterize a novel hypercoordinated nitride phase.
• To investigate the bonding characteristics and properties of the predicted phase.
• To explore the role of nitrogen ligand fields and d-orbital activation in hypercoordinated systems.

Main Methods:

• Particle swarm optimization methods were employed for predicting new material phases.
• Density Functional Theory calculations were used to analyze structural, electronic, and mechanical properties.
• Comparative studies were performed on related MN4 compounds (M = P, As, Sb).

Main Results:

• A hypercoordinated phase, P3̅1c-PN4, was predicted, featuring PN6 octahedra and N4 units.
• The N4 units exhibit nonclassical bonding with sp2+ hybridization and intermediate N-N bond lengths.
• The predicted P3̅1c-PN4 demonstrates superhardness (45.26 GPa), high energy density (5.42 kJ/g), and pressure-induced blue-shifted absorption.

Conclusions:

• The strong nitrogen ligand field activates phosphorus 3d orbitals, stabilizing the six-coordinate framework.
• Nitrogen's ability to form nonclassical bonding and sp2+ hybridization provides a balance of rigidity and flexibility.
• This work provides a blueprint for designing tunable, multifunctional nitrides via orbital engineering under high pressure.