Undistorted linear Bi chains with hypervalent bonding in La₃TiBi₅ from single-crystal X-ray diffraction

Area of Science:

• Solid State Chemistry
• Materials Science
• Crystallography

Background:

• Lanthanum titanium bismuthide (La3TiBi5) is a complex pnictide with an intriguing crystal structure.
• Previous powder X-ray diffraction studies suggested anomalies in the Ti site's atomic displacement parameter.

Purpose of the Study:

• To accurately determine the crystal structure of La3TiBi5 using single-crystal X-ray diffraction.
• To analyze the electronic structure and bonding characteristics using first-principles calculations.
• To resolve discrepancies regarding the Ti site's atomic displacement parameter.

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• First-principles calculations for electronic structure analysis.
• Analysis of atomic displacement parameters and orbital mixing.

Main Results:

• The crystal structure of La3TiBi5 (Pearson code hP18) was established, revealing face-sharing TiBi6 octahedra and linear Bi chains.
• First-principles calculations showed significant La(5d)-Bi(6p) orbital mixing, leading to a 3D electronic structure instead of 1D Bi chains.
• The absence of anomalies in the Ti site's atomic displacement parameter was confirmed, contradicting prior powder diffraction results.

Conclusions:

• The 3D electronic structure stabilizes the polyanionic pnictide units against Peierls distortions.
• Hypervalent bonding in Bi chains is characterized by a long Bi-Bi distance (3.2264 Å) and specific bonding interactions.
• The study provides a comprehensive understanding of La3TiBi5's structure, bonding, and electronic properties.