Probing covalency in halogen bonds through donor K-edge X-ray absorption spectroscopy: polyhalides as coordination...

Area of Science:

• Solid-state chemistry
• Supramolecular chemistry
• Spectroscopy

Background:

• Halogen bonds (XBs) are crucial non-covalent interactions.
• Understanding the covalent character of XBs is essential for materials design.

Purpose of the Study:

• To experimentally determine the charge transfer and covalency in solid-state I₂X^- and I₄X^- materials.
• To propose a new notation for strong halogen bonds based on their covalent nature.

Main Methods:

• Donor K-edge X-ray absorption spectroscopy (XAS) was employed.
• Analysis focused on I₂X^- and I₄X^- systems (X = Cl, Br).

Main Results:

• Substantial covalent contributions were observed in these halogen bonds.
• The degree of covalency rivals or exceeds that in transition metal coordinate bonds.
• Charge transfer was experimentally quantified.

Conclusions:

• Certain halogen bonds possess significant covalent character.
• A new notation (X → Y) is proposed for these strong, covalent halogen bonds.
• This distinguishes them from weaker, less covalent hydrogen bonds.