Mg_29-Pt₄₊: Chemical Bonding Inhomogeneity and Structural Complexity.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Complex metallic alloys (CMAs) are intermetallic compounds with intricate crystal structures.
• Understanding the atomic arrangement and bonding in CMAs is crucial for predicting their properties.
• Mg29-Pt4+ is a complex intermetallic compound with a large unit cell.

Purpose of the Study:

• To elucidate the crystal structure and local atomic arrangement of Mg29-Pt4+.
• To investigate the nature of chemical bonding and charge distribution within Mg29-Pt4+.
• To identify unique bonding features distinguishing Mg29-Pt4+ from other CMAs.

Main Methods:

• Single-crystal X-ray diffraction for crystallographic analysis.
• Atomic-resolution transmission electron microscopy (TEM) for local structure determination.
• Quantum theory of atoms in molecules (QTAIM) for charge and bonding analysis.

Main Results:

• Mg29-Pt4+ crystallizes in a cubic, non-centrosymmetric space group (F4̅3m) with a large unit cell containing approximately 400 atoms.
• Local disorder at the unit cell origin was resolved, attributed to charge equilibration.
• Distinct, spatially separated regions of heteroatomic and homoatomic bonding were identified, a novel feature for CMAs.

Conclusions:

• Mg29-Pt4+ exhibits an unusual bonding inhomogeneity, with Pt-containing units forming super-tetrahedrons linked by Mg-Mg bonds.
• The spatial separation of bonding regions is a key differentiator from other CMAs with homogeneous bonding.
• This structural complexity offers new insights into the design principles of complex metallic alloys.