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Magnitude and Origin of the Attraction and Directionality of the Halogen Bonds of the Complexes of C 6 F 5 X and C 6 H 5 X (X=I, Br, Cl and F) with Pyridine
Author(s) -
Tsuzuki Seiji,
Wakisaka Akihiro,
Ono Taizo,
Sonoda Takaaki
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102562
Subject(s) - pyridine , halogen , chemistry , halogen bond , crystallography , attraction , ab initio , basis set , stereochemistry , computational chemistry , density functional theory , medicinal chemistry , organic chemistry , linguistics , alkyl , philosophy
The geometries and interaction energies of complexes of pyridine with C 6 F 5 X, C 6 H 5 X (X=I, Br, Cl, F and H) and R F I (R F =CF 3 , C 2 F 5 and C 3 F 7 ) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies ( E int ) for the C 6 F 5 X–pyridine (X=I, Br, Cl, F and H) complexes at the basis set limit were estimated to be −5.59, −4.06, −2.78, −0.19 and −4.37 kcal mol −1 , respectively, whereas the E int values for the C 6 H 5 X–pyridine (X=I, Br, Cl and H) complexes were estimated to be −3.27, −2.17, −1.23 and −1.78 kcal mol −1 , respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C 6 F 5 X. The values of E int estimated for the R F I–pyridine (R F =CF 3 , C 2 F 5 and C 3 F 7 ) complexes (−5.14, −5.38 and −5.44 kcal mol −1 , respectively) are close to that for the C 6 F 5 I–pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short‐range (charge‐transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C 6 F 5 I– and C 2 F 5 I–pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water–formaldehyde complex. The calculations suggest that the CI and CBr halogen bonds play an important role in controlling the structures of molecular assemblies, that the CCl bonds play a less important role and that CF bonds have a negligible impact.