Halides with Fifteen Aliphatic C–H···Anion Interaction Sites

Since the aliphatic C–H···anion interaction is relatively weak, anion binding using hydrophobic aliphatic C–H (Cali–H) groups has generally been considered not possible without the presence of additional binding sites that contain stronger interactions to the anion. Herein, we report X-ray structures of organic crystals that feature a chloride anion bound exclusively by hydrophobic Cali–H groups. An X-ray structure of imidazolium-based scaffolds using Cali–H···A− interactions (A− = anion) shows that a halide anion is directly interacting with fifteen Cali–H groups (involving eleven hydrogen bonds, two bidentate hydrogen-bond-type binding interactions and two weakly hydrogen-bonding-like binding interactions). Additional supporting interactions and/or other binding sites are not observed. We note that such types of complexes may not be rare since such high numbers of binding sites for an anion are also found in analogous tetraalkylammonium complexes. The Cali–H···A− interactions are driven by the formation of a near-spherical dipole layer shell structure around the anion. The alternating layers of electrostatic charge around the anion arise because the repulsions between weakly positively charged H atoms are reduced by the presence of the weakly negatively charged C atoms connected to H atoms.


Crystallographic Information (1) Crystallographic data collection and refinement of the structure
Crystal [1](Cl)2 were coated with paratone oil and the diffraction data were measured at 173 K with Mo K radiation on an X-ray diffraction camera system using an imaging plate equipped with a graphite crystal incident beam monochromater. The RapidAuto software 1 was used for data collection and data processing. Structure was solved by direct method and refined by full-matrix least-squares calculation with the SHELXTL software package. 2 For [1](Cl)2, one bis-imidazolium cation and two chloride anions are observed as an asymmetric unit.
All non-hydrogen atoms are refined anisotropically; The hydrogen atoms of respective atom were found in the difference Fourier map and refined with isotropic displacement coefficients U(H) = 1.2U.
Refinement of the structure converged at a final R1 = 0.0406 and wR2 = 0.0801 for 2333 reflections with I > 2(I); R1 = 0.1020 and wR2 = 0.1201 for all 3842 reflections. The largest difference peak and hole were 0.569 and 0.579 e·Å 3 , respectively.
A summary of the crystals and some crystallography data are given in

Crystallographic Information (1) Crystallographic data collection and refinement of the structure
Crystal [1](Cl)2 were coated with paratone oil and the diffraction data were measured at 173 K with Mo K radiation on an X-ray diffraction camera system using an imaging plate equipped with a graphite crystal incident beam monochromater. The RapidAuto software 3 was used for data collection and data processing. Structure was solved by direct method and refined by full-matrix least-squares calculation with the SHELXTL software package. 4 For [1](Cl)2, one bis-imidazolium cation and two chloride anions are observed as an asymmetric unit.
All non-hydrogen atoms are refined anisotropically; The hydrogen atoms of respective atom were found in the difference Fourier map and refined with isotropic displacement coefficients U(H) = 1.2U.
Refinement of the structure converged at a final R1 = 0.0406 and wR2 = 0.0801 for 2333 reflections with I > 2(I); R1 = 0.1020 and wR2 = 0.1201 for all 3842 reflections. The largest difference peak and hole were 0.569 and 0.579 e·Å 3 , respectively.
A summary of the crystals and some crystallography data are given in (2) Detailed crystallographic data of [1](Cl)2 _____________________________________________________________ Symmetry transformations used to generate equivalent atoms:

DFT-SAPT results
The symmetry adapted perturbation theory calculations using density functional theory (DFT-SAPT) were For investigating the angle-dependence of long range H-bonding-like interactions, we also conducted calculations for CH4···Clˉ with different Clˉ···Hx-C angles (θ). For each system, only the interaction angle was fixed, while other parameters were optimized at the B97D/aVDZ level. The Clˉ ···Hx and Hx-C distances are shown in Table S3-2.

QTAIM results
The The relating distances and angles and QTAIM topological parameters for Clˉ···Hx interaction of the CH4-Clˉ and NH3CH3 + ···Cl models are shown in Table S3-4. All the QTAIM computations were performed with AIMALL package 10 with .wfx and .fchk files generated in Gaussian 3 used as the input. As can be seen from Table S3-4 results, all of Clˉ···Hx H-bonding-like interactions in models systems are non-covalent (from the The computed electron density (ρ(r)), the ratio of Laplacian of electron density (∇ 2 ρ(r)) or kinetic energy density (G(r)) to potential energy density (V(r)), and the electronic energy density (H(r)) at C-H..  Tables S3-4 and. S3-5 in the Supporting Information).
Therefore, as can be seen from Tables S3-4

Plot of noncovalent interaction (NCI) regions (NCIPLOT)
The NCI regions 14,15 can provide the information about the extent of the interaction (with non-bonded attractive or repulsive interactions) in real space. The NCI surface for intermolecular interactions around Clˉ in crystal structure of [1](Cl)2 is shown in Figure S3