Halogen Bonding Interactions in Halopyridine–Iodine Monochloride Complexes

• Published in: Crystal growth & design 2020-02, Vol.20 (2), p.543-551
• Main Authors: Awwadi, Firas F, Taher, Deeb, Kailani, Mohammed H, Alwahsh, Manal I, Odeh, Fadwa, Rüffer, Tobias, Schaarschmidt, Dieter, Lang, Heinrich
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.9b00408

Halogen bond interactions are investigated in four halopyridine iodine monochloride complexes nXPy­(N)–ICl in the solid state, solution and in silico, where nXPy = n-halopyridine, X = I or Br and n = 2 or 3. Two types of halogen bonding interactions were observed: stronger three-center Py­(N)–ICl halogen bonds and weaker two-center Py­(C)–X···Cl halogen bonds. Theoretical calculations (thermodynamic data and optimized bond distances) and solution NMR studies indicated that Py­(N)–ICl halogen bonding interactions are stronger in 3XPy­(N)–ICl complexes than in 2XPy­(N)–ICl complexes. In the solid state, relying on bond distances, nBrPy­(N)–ICl complexes show the same behavior to that in solution and in silico. In contrast, nIPy­(N)–ICl halogen bonding interactions are stronger in 2IPy­(N)–ICl than in 3IPy­(N)–ICl. The ionic and covalent characters of I–Cl and N–I bonds were studied by the analysis of electron density topology using Quantum Theory of Atoms in Molecules (QTAIM), and Natural Population Analysis (NPA)/Natural Bond Orbital (NBO) analysis. According to the NBO analysis of the solid state structure, the ionic character of the I–Cl bond is higher in 2IPy­(N)–ICl than in 3IPy­(N)–ICl.