Halogen bonds are not purely electrostatic
Relativistic DFT shows halogen and hydrogen bonds share HOMO–LUMO covalency; halogen bonds have weaker electrostatics but stronger orbital mixing.
Source
Halogen Bonding versus Hydrogen Bonding: A Molecular Orbital Perspective
Study at a glance
- Design
- Computational / modelling — ZORA-BP86/TZ2P energy decomposition of trihalide halogen bonds vs hydrogen bonds
- N
- Molecular orbital theory study — no sample N
- Population
- DX···A− and DH···A− model complexes (D, X, A = F–I)
- Outcome
- Electrostatic vs orbital contributions distinguishing halogen and hydrogen bonds
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
Authors computed trihalide DX···A− and hydrogen-bonded DH···A− complexes (D, X, A = F, Cl, Br, I) with ZORA-BP86/TZ2P and decomposed interaction energies into electrostatic and orbital terms.
What they found
Both bond types have a sizable covalent HOMO–LUMO piece. Halogen bonds are less electrostatic (DX less polar than DH) but often more orbital-stabilized. FH···F− to FH···I− weakens from −53 to −18 kcal mol−1; DF···A− fluorine bonds are partly inverted along Cl−–I−.
The limits
What it doesn't show
These are gas-phase model trihalides, not condensed-phase crystal engineering or protein halogen bonds with thermal sampling.
Key terms
- Halogen bond
- Attractive DX···A interaction where X is a halogen acting as an electrophile toward a Lewis base.
- HOMO–LUMO charge transfer
- Donation from the acceptor lone pair into the D–X or D–H σ* orbital.
- ZORA
- Zeroth-order regular approximation for relativistic effects in DFT, important for iodine.
- Energy decomposition
- Splitting ΔE into electrostatic, Pauli, and orbital-interaction terms.
- Fluorine bond
- DF···A− contact; here its strength trend along A− is partly inverted.
Flashcards
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
Halogen bonds in this DFT study are:
Common questions
Are halogen bonds purely electrostatic?
No—they have a sizable covalent HOMO–LUMO component, like hydrogen bonds.
How do they differ from H-bonds?
Weaker electrostatic attraction but often stronger orbital interaction.
What happens from F− to I− acceptors?
Bonds generally weaken as halide basicity falls.
What is unusual about DF···A−?
Strength can increase again from Cl− to I− (partial inversion).
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