Featuring I···N Halogen Bond and Weaker Interactions in Iodoperfluoroalkylimidazoles: An Experimental and Theoretical Charge Density Study

The experimental charge density distribution of two new iodoperfluoroalkylimidazole derivatives has been determined with the aspherical atom model against single-crystal X-ray diffracted intensities and analyzed by means of the Bader Quantum Theory of Atoms In Molecules. The compounds self-assemble in the solid state forming infinite chains through strong I···N halogen bonds. The topological and energetic features of these interactions have been determined and compared with those of a previously reported I···N interaction formed by an iodoperfluoroarene derivative, allowing elucidation of the role of hybridization of the carbon atom bonded to the halogen atom in the nature of the halogen bonding interaction. The weaker interactions present in the crystal structures have been investigated as well, with particular attention to F···F interactions. They have also been analyzed through the Interacting Quantum Atoms approach in order to elucidate their role in stabilizing the crystal structure

Experimental and Theoretical Charge Density Study of the I-N Halogen Bond and F-F Interactions in Iodoperfluoroalkylimidazoles

Halogen bonding (XB), namely any noncovalent interaction involving halogens as electrophilic sites, is a relatively new item in the supramolecular toolbox and shares numerous properties with the better known hydrogen bonding. The X 19 19 19N(O) halogen bond has been thoroughly investigated by means of several experimental and theoretical techniques, including the topological analysis of the X-ray multipole refined charge density [1]. Fluorine-Fluorine interactions [2] are much less explored intermolecular interactions, though F\u2022\u2022\u2022F contacts below or just above the sum of van der Waals radii of the fluorine atoms are ubiquitous in fluorinated organic structures. We present here the results obtained on two iodotetrafluoroethylimidazole derivatives, whose crystal structure is dominated by formation of I 19 19 19N halogen bonds between equivalent molecules, and stabilized by the presence of F 19 19 19F and other weak (C\u2013H 19 19 19F, C\u2013H 19 19 19\uf070 and \uf070 19 19 19\uf070) interactions. The experimental charge densities have been derived from X-ray data collected at 100 K, using the aspherical atom formalism of Stewart [3] as implemented in VALTOPO [4], as well as by accurate M062X/6-311++G(d,p) and MP2/6-311++G(d,p) calculations in gas phase, and M062X/6-311G(d,p) calculations in solid state [5]. The topological analysis of charge density and its Laplacian allowed to elucidate the role exerted on the XB properties by the alkyl/aryl moiety bonded to the iodine atom through comparison with previous results [1a]. Moreover, an Interacting Quantum Atoms (IQA) analysis [6] on the M062X/6-311++G(d,p) optimized halogen bonded dimer revealed the nature essentially electrostatic for this interaction, though the dispersive contribution resulted to be significant. Selected dimers extracted from the crystal structure were as well submitted to IQA analysis in order to investigate the nature of the F 19 19 19F interactions and in particular the relative electrostatic/exchange contributions. Both Type I (\u3b81 \uf040 \u3b82) and Type II (\u3b81 \uf040 180\ub0 and \u3b82 \uf040 90\ub0, where \u3b81=C\u2013X1\u2022\u2022\u2022X2 and \u3b82=X1\u2022\u2022\u2022X2\u2013C angles) geometries have been considered. All interactions in the presently investigated systems follow the relationship recently suggested by Spackman et al [7]

Unravelling the Nature of I-N Halogen Bond and F-F Interactions by Charge Density Studies on Iodoperfluoroalkylimidazoles

Halogen bonding (XB), namely any noncovalent interaction involving halogens as electrophilic sites, is a relatively new item in the supramolecular toolbox and shares numerous properties with the better known hydrogen bonding. The X 19 19 19N(O) halogen bond has been thoroughly investigated by means of several experimental and theoretical techniques. Fluorine-Fluorine interactions [1] are much less explored intermolecular interactions, though F 19 19 19F contacts below or just above the sum of van der Waals radii of the fluorine atoms are ubiquitous in fluorinated organic structures. We present here the results obtained by experimental and theoretical charge density studies on two iodotetrafluoroethylimidazoles, whose crystal structure is dominated by the formation of I 19 19 19N halogen bonds between equivalent molecules, and stabilized by the presence of F 19 19 19F and other weak (C-H 19 19 19F, C-H 19 19 19\u3c0 and \u3c0 19 19 19\u3c0) interactions. The charge density has been obtained by multipolar refinement against single-crystal X-ray diffracted intensities collected at 100 K [3] and by M06-2X/6-311++G(d,p) and MP2/6-311++G(d,p) calculations in gas phase, and M06-2X/6-311G(d,p) calculations in solid state [2]. An Interacting Quantum Atom (IQA) [4] analysis on the M06-2X/6-311++G(d,p) halogen bonded dimer at the experimental geometry has been carried out confirming the essentially electrostatic nature for this interaction, though the exchange-correlation contribution resulted to be significant. Moreover, the dispersion contribution into halogen bonding interaction energy has been estimated through the D2 version of Grimme\u2019s dispersion [5], as implemented in the \u3c9B97XD functional, and compared with the corresponding counterpoise-corrected interaction energy, revealing the importance of dispersion in this mainly electrostatic interaction. Selected dimers extracted from the crystal structure were as well submitted to IQA analysis in order to investigate the nature of F 19 19 19F interactions and in particular the relative electrostatic/exchange-correlation contribution