Nature of halogen‐centered intermolecular interactions in crystal growth and design: Fluorine‐centered interactions in dimers in crystalline hexafluoropropylene as a prototype

Abstract

The wide occurrence of halogen‐centered noncovalent interactions in crystal growth and design prompted this study, which includes a mini review of recent advances in the field. Particular emphasis is placed on providing compelling theoretical evidence of the formation of these interactions between sites of positive electrostatic potential, as well as between sites of negative electrostatic potential, localized on the electrostatic surfaces of the bound fluorine atoms in a prototypical system, hexafluoropropylene (C3F6), upon its interaction with another same molecule to form (C3F6)2 dimers. The existence of σ‐ and π‐hole interactions is shown for the stable dimers. Even so, weakly bound interactions locally responsible in holding the molecular fragments together cannot and should not be overlooked since they are partly responsible for determining the overall geometry of the crystal. The results of combined quantum theory of atoms in molecules, molecular electrostatic surface potential, and reduced density gradient noncovalent interaction analyses showed that these latter interactions do indeed play a role in the stability and growth of crystalline C3F6 itself and the (C3F6)2 dimers. A symmetry adapted perturbation theory energy decomposition analysis leads to the conclusion that a great majority of the (C3F6)2 dimers examined are the consequence of dispersion (and electrostatics), with nonnegligible contribution from polarization, which together competes with an exchange repulsion component to determine the equilibrium geometries. In a few structures of the (C3F6)2 dimer, the fluorine is found to serve as a six‐center five‐bond donor/acceptor, as found for carbon in other systems (Malischewski and Seppelt, Angew. Chem. Int. Ed. 2017, 56, 368). © 2019 Wiley Periodicals, Inc.

Does Oxygen Feature Chalcogen Bonding?

“…In the same time, it should not be presumed that dispersion dominant interactions are not chalcogen bonds. Similar conclusions were previously made for halogen-bonding interactions formed by the most electronegative fluorine atom in molecules [41,44,45].…”

“…In some cases, it is near either neutral or absent, and in other cases, it is either negative or positive (moderately weak or strong). This view is emerged from the sign and magnitude of V S,max being the measure of the nature and strength of the σ-hole, respectively [32,33,41,42,43,44]. As such, the σ-hole on the O atom is near neutral or absent on the N–O bond extensions of the –NO 2 fragment in FNO 3 (a).…”

“…This is a typical signature routinely employed by Politzer et al [30,32,42,43,70,72] to rationalize the presence of σ-hole-centered noncovalent interactions in complex systems. Such a feature is prevalent regardless of the nature of the interaction, such as chalcogen bonding, pnictogen bonding, tetrel bonding, halogen bonding, or hydrogen bonding [32,33,41,44,45,70,72].…”

“…The Molecular Electrostatic Surface Potential (MESP) [40] model was adopted to explore the local nature of electrostatic surface potential, and hence to provide insight into the nature of the reactive sites on the monomer molecules. Traditionally, the positive and negative signs of the local minimum and maximum of the electrostatic potential ( V S,min and V S,max , respectively) have been invoked to characterize the positive and negative sites on the molecular surfaces, respectively [33,41,42,43,44,45]. Note that the sign and magnitude of potential on the electrostatic surface of a main group atom M along the outer portion of the R–M bond extension is generally used to characterize the nature and quantify the strength and size of its σ-hole, respectively [42,43,44,45,46,47].…”

Does Chlorine in CH3Cl Behave as a Genuine Halogen Bond Donor?

“…Such a provocative view led to the suggestion that the MESP model is superior to other computational methods such as the second-order natural bonding orbital analysis (NBO) [30], the quantum theory of atoms in molecules in molecules (QTAIM) [31][32][33], and the density functional theory symmetry adapted perturbation theory energy decomposition analysis (DFT-SAPT-EDA) [34,35]. While the reliability of these latter methods has been questioned [36][37][38][39], such claims have been rebutted by others [40][41][42][43][44][45][46]. Some of these conflicting views have been briefly highlighted in one of our recent reviews [21].…”