What makes molecular iodine solid? Not London dispersion forces, but halogen bonds

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В журнале  Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy,   (IF 4.6) опубликована статья, соавторами которой являются  сотрудники  Лаборатории гетероциклических соединений НИОХ СО РАН:  к.х.н., снс Т.А. Ваганова  и д.х.н., гнс Е.В. Малыхин:

 

What makes molecular iodine solid? Not London dispersion forces, but halogen bonds

 

Haiyan Fanc, Tamara Vaganova, Evgenij Malykhin,  Enrico Benassi

 

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Volume 361, 5 February 2026, 126862
Available online 16 July 2022
doi: 10.1016/j.saa.2025.126862

 

Highlights

  • Halogen bonds (XB) dominate in solid iodine, not London dispersion forces.
  • I2 pair showing strongest XB indicates charge transfer
  • Raman spectra confirm XB by weakening of the I--I bonds.
  • Textbook descriptions of I2 solid-state interactions urge revision

Graphical abstract

 

 

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Abstract

The nature of intermolecular interactions in iodine (I₂) crystals has long been a subject of interest, traditionally attributed to London dispersion (LD) forces. Herein, we systematically investigate I₂⋯I₂ interactions through quantum mechanical calculations combined with spectroscopic and theoretical analyses. Focusing on three I₂⋯I₂ dimers extracted from the crystal structure, the nature of these interactions was further clarified using electron localization function (ELF) analysis and topological atoms-in-molecules (AIM). The results confirm XB is dominated in dimer 1, the most stable dimer. Comparisons of experimental Raman spectra with calculated spectra for dimer 1 and crystal fragments revealed frequency splitting of I---I stretching modes, directly linked to XB-induced weakening of specific I---I bonds. Collectively, these results provide the first systematic evidence that the intrinsic intermolecular interaction in I₂ crystals is halogen bonding, rather than LD forces. This work redefines our understanding of iodine's solid-state structure and the nature of the intermolecular interactions.

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