Nature of halogen‐centered intermolecular interactions in crystal growth and design: Fluorine‐centered interactions in dimers in crystalline hexafluoropropylene as a prototype (original) (raw)
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Crystal Growth & Design, 2020
Fluorination of compounds causes an increase in the proton-donating ability and a decrease in the proton-accepting capacity of groups in their vicinity. The formation of F ... F interactions is followed by the shift of the electron density in the area of F ... F contact, which creates a new region with a larger surface area, a higher negative potential, and, hence, the more pronounced accepting ability. The new region also has a greater ability to form multiple (simultaneous) interactions with species from the environment, thus compensating for the reduction of the accepting capacity of the groups in the vicinity. This phenomenon explains not only the abundance of F ... F interactions in crystal structures, but also a large number of structures with F ... O interactions. Only C-H ... F interactions are more numerous than F ... F interactions in crystal structures, which indicates a high affinity of fluorinated compounds for non-polar groups.
The nature, strength and directionality of C-FÁÁÁF interactions were theoretically evaluated on all symmetry unique dimers present in the CF 4 , C 2 F 4 and C 6 F 6 crystals and on CF 4 , CHF 3 , CH 2 F 2 and CH 3 F model dimers placed in two different geometries. On each dimer, the interaction energy was computed at the MP2/aug-cc-pVDZ level, and also an Atoms in Molecule analysis of the dimer electron density was done to find all intermolecular bonds. The characterization was completed by computing the energy components of the dimer interaction energy, using the SAPT method. The results show that in most dimers found in the CF 4 , C 2 F 4 and C 6 F 6 crystals, there are more than one C-FÁÁÁF intermolecular bond and sometimes even a C-FÁÁÁp intermolecular bond. By selecting dimers presenting one C-FÁÁÁF bond, the following strength can be estimated for a single C-FÁÁÁF bond: -0.21 kcal/mol in C(sp 3 ) atoms, -0.25 kcal/mol in C(non-aromatic sp 2 ), -0.41 kcal/mol in C(aromatic sp 2 ). The interaction energy of the dimer grows almost linearly with the number of C-FÁÁÁF bonds present. The relative orientation of the C-FÁÁÁF bond affects the bond strength. The SAPT calculations indicate that in collinear dimers, C-FÁÁÁF interactions are strongly dominated by the dispersion energetic component, while when in non-collinear conformations the electrostatic component can be as important as the dispersion one.
Journal of the American Chemical Society, 1991
High-resolution X-ray data were collected at low temperature (-151 (1) "C) to determine the crystal and molecular structure and the electron deformation density (EDD) of F4S=C(CH3)CF3. Crystal data is as follows: a = 1709.0 (7), b = 647.8 (6), c = 1698.0 (7) pm, @ = 136.96 (6)O, P 2 , / n , Z = 8. The sulfur, the two axial fluorine, and the carbon atoms exhibit a planar arrangement. The equatorial S-F bond distances are significantly shorter than the axial ones. Atomic valence deformations were analyzed in terms of static (SDD) and dynamic deformation densities (DDD) calculated from the fitted multipole populations and X-X Fourier synthesis. The EDD along the S-C bond does not show cylindrical symmetry, Le., the contours of constant electron density perpendicular to the bond reach out twice as far in the equatorial than in the axial direction. This feature can clearly be attributed to a double bond character. The axial S-F bond appears to be more polarized than the equatorial one. The charge loss at the sulfur atom is shared by the alkylidene and fluorine ligands in a ratio of about 1:2, leading to a polarized S-C bond. In the interpretation of the EDD along the bonds to the F atoms, the proper orientation of the reference density is shown to be useful. To emphasize these bond peaks, the electron density of the promolecule generated with the oriented atom model (OAM) proved itself to be superior to that of the promolecule calculated from spherical atoms.
The Journal of Physical Chemistry A, 2005
A bond path linking two saturated fluorine atoms is found to be ubiquitous in crowded difluorinated aromatic compounds. The bond path is shown to persist for a range of internuclear distances (2.3-2.8 Å) and a range of relative orientations of the two C-F internuclear axes. The F‚ ‚ ‚F bonding is shown to exhibit all the hallmarks of a closed-shell weak interaction. The presence of such a bond path can impart as much as 14 kcal/mol of local stabilization to the molecule in which it exists, a stabilization that can be offset or even overwhelmed by destabilization of other regions in the molecule. Several other weak closed-shell interactions were also found and characterized including F‚ ‚ ‚C, F‚ ‚ ‚O, and C‚ ‚ ‚C interactions, hydrogen bonding, dihydrogen bonding, and hydrogen-hydrogen bonding. This study represents another example of the usefulness and richness of the bond path concept and of the theory of atoms in molecules in general.
Can fluorine form triple bonds?
2022
A central dogma is that fluorine is the most electro negative element in the PSE and would thus act as a pure electron acceptor. However, to some chemists it is known, that fluorine can bond in duality. This means fluorine can act as a donor and an acceptor of bonds and thus electrons. The donor/acceptor properties of fluorine are known from the NF molecule, where a partial double bond character is present[1]. Up to now, however, chemists are not aware that fluorine may form even triple bonds, something that other elements from the second row of the PSE do as well. The subsequent work investigates theoretically the possibility of triple bonds between fluorine and Mn in a hetero dimer MnF. Moreover, mono fluorides isoelectronic to MnF and higher oxidation states of MnF are investigated. Furthermore, the tendency to form singlets and possibly multi-bonded states is investigated for higher transition metals and halogens as well. It is concluded that first the naive methodology of using Wigner-Witmer rules may find their limit in the case of MnF and isoelectronic compounds as well as higher homologues. Secondly, it is demonstrated that using ECP may lead to misleading results on higher transition metals when calculating heterodimers with halogens.
An Attractive Interaction between the π-Cloud of C6F6 and Electron-Donor Atoms
The Journal of Organic Chemistry, 1997
A theoretical study of the possible interaction of the π-cloud of hexafluorobenzene (C 6 F 6) with several small electron-donor molecules (FH, HLi, :CH 2 , NCH, and CNH) has been carried out. The calculations have been performed using HF, MP2, and hybrid HF/DFT methods (B3LYP) with the 6-31G** and 6-311++G** basis sets. The topology of the electron density of the complexes has been characterized using the AIM methodology. The characteristics of the electron density and molecular electrostatic potential maps of benzene and hexafluorobenzene have been compared. Finally, the results obtained from a search in the Cambridge Structural Database system of this kind of interaction are shown.