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. 2023 Oct 24;14(45):13031-13041.
doi: 10.1039/d3sc04191c. eCollection 2023 Nov 22.

Halogen bonding with carbon: directional assembly of non-derivatised aromatic carbon systems into robust supramolecular ladder architectures

Jogirdas Vainauskas  1   2 , Tristan H Borchers  1   2 , Mihails Arhangelskis  3 , Laura J McCormick McPherson  4 , Toni S Spilfogel  2 , Ehsan Hamzehpoor  2 , Filip Topić  2 , Simon J Coles  4 , Dmytro F Perepichka  2 , Christopher J Barrett  2 , Tomislav Friščić  1   2
Affiliations

Halogen bonding with carbon: directional assembly of non-derivatised aromatic carbon systems into robust supramolecular ladder architectures

Jogirdas Vainauskas et al. Chem Sci. .

Abstract

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 hydrocarbons, has been limited almost exclusively to non-directional π-stacking, or derivatisation with heteroatoms to introduce molecular assembly recognition sites. As a result, the predictable assembly of non-derivatised, carbon-only π-systems using directional non-covalent interactions remains an unsolved fundamental challenge of solid-state supramolecular chemistry. Here, we propose and validate a different paradigm for the reliable assembly of carbon-only aromatic systems into predictable supramolecular architectures: not through non-directional π-stacking, but via specific and directional halogen bonding. We present a systematic experimental, theoretical and database study of halogen bonds to carbon-only π-systems (C-I⋯πC bonds), focusing on the synthesis and structural analysis of cocrystals with diversely-sized and -shaped non-derivatised arenes, from one-ring (benzene) to 15-ring (dicoronylene) polycyclic atomatic hydrocarbons (PAHs), and fullerene C60, along with theoretical calculations and a systematic analysis of the Cambridge Structural Database. This study establishes C-I⋯πC bonds as directional interactions to arrange planar and curved carbon-only aromatic systems into predictable supramolecular motifs. In >90% of herein presented structures, the C-I⋯πC bonds to PAHs lead to a general ladder motif, in which the arenes act as the rungs and halogen bond donors as the rails, establishing a unique example of a supramolecular synthon based on carbon-only molecules. Besides fundamental importance in the solid-state and supramolecular chemistry of arenes, this synthon enables access to materials with exciting properties based on simple, non-derivatised aromatic systems, as seen from large red and blue shifts in solid-state luminescence and room-temperature phosphorescence upon cocrystallisation.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. (a) Halogen bond acceptor and donor molecules explored in this work, along with corresponding electrostatic surface potential (ESP) maps, with isosurfaces plotted at 0.01 a.u. Fragments of the halogen-bonded C–I⋯πC supramolecular ladder seen in the cocrystals of: (b) (azulene)(14tfib)2 and (c) (azulene)(ofiab)2 along with corresponding molecular diagrams.
Fig. 2
Fig. 2. Stick model representation of halogen-bonded fragments in explored 14tfib cocrystals, with extended motifs shown using space-filling models: (a) (benz)(14tfib) (CCDC code 2240199), (b) (anthra)(14tfib)2 (CCDC code 2249511, also CSD JEJXOP), (c) (tet)(14tfib) (CCDC code 2240203), (d) (pyr)(14tfib)2 (CCDC code 2240200), (e) (bant)2(14tfib)5 (CCDC code 2281269), (f) (pery)(14tfib)2 (CCDC code 2240202), (g) (cor)(14tfib)2 (CCDC code 2240204), (h) (dicor)(14tfib)3 (CCDC code 2240207). The I⋯Cπ intermolecular distances shorter than the sum of van der Waals radii for iodine and carbon atoms (3.68 Å) are shown as green dotted lines.
Fig. 3
Fig. 3. Structural motifs in (C60)(14tfib)2 and cocrystals of anthra and pyr with ofiab: (a) the C–I⋯C contact between iodine and C60 in (C60)(14tfib)2 (CCDC code 2240201); (b) interpenetration of two sql-grids in (C60)(14tfib)2; (c) space-filling representation of three distinct (C60)(14tfib)2sql-grids; (d) fragment of the supramolecular ladder in (anthra)(ofiab)2 (CCDC code 2240205) and (e) in (pyr)(ofiab)2 (CCDC code 2240206).
Fig. 4
Fig. 4. 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 structures of: (d) (phenanthrene)(14tfib)2 and (e) (chrysene)(14tfib)3, illustrating the appearance of the C–I⋯πC ladder motif.
Fig. 5
Fig. 5. Change in luminescence spectra upon the formation of halogen-bonded cocrystals with aromatic XB acceptors. (a) Solid-state luminescence spectra for pyr (blue) and (pyr)(14tfib)2 (red). (b) A sample of (top) pyr and (bottom) (pyr)(14tfib)2 excited with 365 nm LED light. (c) Solid-state luminescence spectra for cor (green) and (cor)(14tfib)2 (red). (d) A sample of (top) cor and (bottom) (cor)(14tfib)2 excited with 365 nm LED light. (e) Solid-state luminescence spectra for α-pery and (pery)(14tfib)2. (f) A sample of (top) α-pery and (bottom) (pery)(14tfib)2 excited with 365 nm LED light.
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