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Outcomes of CSD searches for short C–I⋯C contacts to alkene, alkyne, 5-, 6- and 7-membered ring acceptors based on aromatic carbon and selected representative structures. (a) Distribution of the I⋯C contact lengths shorter than 4.68 Å across different acceptor types. For each XB acceptor type, the fraction of contacts with a linear geometry (C–I⋯C angle in the range from 140° to 180°) corresponding to halogen bonding, is indicated on the outer circle by a dotted pattern. Plots of the distribution of lengths and angles for C–I⋯C contacts to: (b) 6-membered ring and (c) alkyne (CC) acceptors. To guide the eye, contacts shorter than the van der Waals limit of 3.68 Å are shown in purple. Plots of the distribution of C–I⋯C contact lengths and angles for 5- and 7-membered ring, as well as alkene (CC) acceptors, are given in the ESI.† Fragment of the crystal structures⁶⁷ of: (d) (phenanthrene)(14tfib)2 and (e) (chrysene)(14tfib)3, illustrating the appearance of the C–I⋯πC ladder motif
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Carbon, although the central element in organic chemistry, has been traditionally neglected as a target for directional supramolecular interactions. The design of supramolecular structures involving carbon-rich molecules, such as arene...
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Citations
... Normally, these halogen bonds are classified as n-type, where the σ-hole is interacting with a lone pair on a heteroatom such as nitrogen or oxygen. In contrast, π-type halogen bonds are observed between an electrophilic halogen atom and a polycyclic aromatic surface and are considerably less common [5,6]. ...
The preference in the type of halogen bond accepted by anthraquinone (C14H8O2) from two isosteric donors, namely 1,4-diiodoperfluorobenzene (C6I2F4) and 1,4-diiodoperchlorobenzene (C6I2Cl4), is reported. The two co-crystals, (C6I2F4)·(C14H8O2) and (C6I2Cl4)·(C14H8O2), are sustained primarily by I···O rather than π-type halogen bonds to form these multicomponent solids. The ability for each component to engage in two divergent halogen-bonding interactions generates a one-dimensional chain structure for each co-crystal. The bias in the halogen-bonding type is due to the difference in electrostatic potential between the carbonyl oxygen and the aromatic surface on the anthraquinone. To support this observed preference, the binding energies of the I···O halogen bond were quantified for both co-crystals by using density functional theory calculations and then compared to the interaction energy for related π-type halogen bond from previously reported structures.
