From Octahedral to Pseudo-Seven-Coordinate: Halogen Bonding Reshapes Pb²⁺ Geometry and Exciton Dynamics

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photophysics

Background:

• Limited understanding of Pb2+ coordination geometry's role in low-dimensional lead halide photoluminescence (PL).
• Need for precise control over coordination environment to tune optoelectronic properties.

Purpose of the Study:

• To investigate how Pb2+ coordination geometry influences photoluminescence in low-dimensional lead halides.
• To employ halogen bonding (XB) as a tool to systematically modify hybrid perovskite structures and their optoelectronic properties.

Main Methods:

• Single-crystal X-ray diffraction to determine structural changes.
• Density Functional Theory (DFT) calculations for theoretical insights.
• Low-temperature (77 K) photoluminescence spectroscopy to analyze emission properties.

Main Results:

• Halogen bonding induces a novel "5+2" pseudo-seven-coordinate structure in lead halides.
• XB-modified iodoplumbate shows enhanced self-trapped exciton (STE) emission near 600 nm.
• XB-modified chloroplumbate lacks the prominent long-wavelength STE emission, highlighting the role of specific coordination.

Conclusions:

• Precise control over coordination geometry via halogen bonding is a powerful strategy for tuning optoelectronic performance.
• The "5+2" coordination environment stabilizes STE formation, enhancing specific emission bands.
• This approach offers a pathway to engineer structural complexity and optoelectronic properties in low-dimensional perovskite materials.