Halogen Bonding in Fluoroalkylhalides:  A Quantum Chemical Study of Increasing Fluorine Substitution

Abstract

We describe the results of quantum chemical calculations (DFT and MP2) on the intermolecular interactions involving ammonia and halofluoromethanes. The equilibrium C−X···N geometries are linear and the X···N distances are shorter than the sum of the van der Waals radii. The binding energies of CF3X···NH3 increase from 2 to 6 kcal/mol on following the sequence X = Cl, Br, I. Also, progressive introduction of F atoms in methyliodides raises the interaction energy from 2 kcal/mol for CH3I to 6 kcal/mol for CF3I. Therefore, halogen bonding involving perfluorinated alkylhalides and appropriate donors can be comparable in strength to strong hydrogen bonding. This agrees with recent experimental observations, that also the former can drive the construction of supramolecular edifices overcoming the low affinity between perfluorocarbons and hydrocarbons. Calculation of the atomic charges by the Atoms in Molecules method indicates that the charge-transfer contribution to the interaction energy is much less important for the present systems than for dihalogen−ammonia complexes.

Magnitude and Origin of the Attraction and Directionality of the Halogen Bonds of the Complexes of C6F5X and C6H5X (X=I, Br, Cl and F) with Pyridine

“…A similar enhancement of the attraction in the halogen bond by the introduction of fluorine atoms has been reported for 1,4-diiodobenzene and 1,4-diido-2,3-5,6-tetrafluorobenzene [12] and for CH 3 I and CF 3 I. [60] Interaction energy potentials for pyridine complexes with perfluoroalkyl iodides: The interaction energy potentials calculated for the R F I-pyridine complexes (R F = CF 3 , C 2 F 5 and C 3 F 7 ; 11-13) are compared with that of the C 6 F 5 I-pyridine complex (1) in Figure 4a. The R F I-pyridine complexes (11-13) have C s symmetry.…”

“…[52][53][54][55][56][57][58][59] Symmetry-adapted perturbation theory (SAPT), atoms-in-molecules (AIM) and natural bond orbital (NBO) calculations were applied to elucidate the nature of halogen bonds. [60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77] The structures and binding energies of small model complexes of the halogen bond have also been studied by ab initio molecular orbital calculations. Although the halogen bonds of aryl halide molecules have often been used for molecular recognition and crystal engineering, most of the calculations of interaction energies have been carried out for complexes of halogen molecules or alkyl halides with small donor molecules, such as NH 3 , H 2 O and H 2 CO.…”

σ‐Hole bonding and hydrogen bonding: Competitive interactions

“…Under these conditions, the hydrogen bonds are usually stronger, the primary exceptions being when the -hole bond involves bromine or in one instance selenium. (Iodine and tellurium would form even stronger -hole bonds [3,15,25].) However Table III shows that the situation is quite different when the -hole bond donor contains more than one electron-withdrawing group; note in particular the ⌬E min (0 K) of Ϫ12.2 kcal/mole for H 3 N----SeFOF and Ϫ9.7 kcal/mole for H 3 N----Se(CN)OCN.…”

Prediction of Hydrate and Solvate Formation Using Statistical Models

“…Quantum chemical calculations and electrostatic potential approaches [64][65] By looking at the capped sticks model, it can be seen that this structure possesses four hydrogen bond donors. Three of these donors are involved in intramolecular hydrogen bonding, which renders them unavailable for intermolecular bonding according to Etter's rules.…”