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. 2021 Nov 3;9(Pt 1):31-42.
doi: 10.1107/S2052252521009593. eCollection 2022 Jan 1.

Differences in thermal expansion and motion ability for herringbone and face-to-face π-stacked solids

Xiaodan Ding  1 , Ethan Zahid  1 , Daniel K Unruh  1 , Kristin M Hutchins  1
Affiliations

Differences in thermal expansion and motion ability for herringbone and face-to-face π-stacked solids

Xiaodan Ding et al. IUCrJ. .

Abstract

A series of aromatic organic molecules functionalized with different halogen atoms (I/ Br), motion-capable groups (olefin, azo or imine) and molecular length were designed and synthesized. The molecules self-assemble in the solid state through halogen bonding and exhibit molecular packing sustained by either herringbone or face-to-face π-stacking, two common motifs in organic semiconductor molecules. Interestingly, dynamic pedal motion is only achieved in solids with herringbone packing. On average, solids with herringbone packing exhibit larger thermal expansion within the halogen-bonded sheets due to motion occurrence and molecular twisting, whereas molecules with face-to-face π-stacking do not undergo motion or twisting. Thermal expansion along the π-stacked direction is surprisingly similar, but slightly larger for the face-to-face π-stacked solids due to larger changes in π-stacking distances with temperature changes. The results speak to the importance of crystal packing and intermolecular interaction strength when designing aromatic-based solids for organic electronics applications.

Keywords: crystal engineering; halogen bonding; intermolecular interactions; pedal motion; properties of solids; thermal expansion; π-stacking.

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Figures

Figure 1
Figure 1
Geometries of (a) type-I and type-II halogen⋯halogen interactions and (b) herringbone and offset face-to-face π-stacking. (c) Pedal motion in a di­phenyl molecule with a motion-capable group.
Figure 2
Figure 2
Structures and abbreviations of halogenated molecules in this work with (a) one motion group and (b) two motion groups. The compound abbreviations are shown in bold.
Figure 3
Figure 3
Images of each crystal with the corresponding molecular structure for (a) herringbone and (b) face-to-face π-stacked arrangements.
Figure 4
Figure 4
X-ray crystal structures at 290 and 190 K highlighting unresolved or resolved disorder within (a) imine-I, (b) azo-I, (c) diolefin-Br, (d) diolefin-I Br and (e) diazo-I. Disorder is only shown for the bridge groups for clarity.
Figure 5
Figure 5
Single-crystal X-ray structures showing 2D halogen-bonded sheets, layers and TE axes for (a) and (b) olefin-I, (c) and (d) olefin-Br, and (e) and (f) olefin-I Br. Type-II halogen bonds are shown with yellow dashed lines, type-I halogen bonds are shown with blue dashed lines and C—H⋯X forces are shown with green dashed lines. Structures are shown at 290 K for olefin-Br and olefin-I Br, and 270 K for olefin-I (due to poor data quality at 290 K).
Figure 6
Figure 6
Single-crystal X-ray structures at 290 K showing 2D halogen-bonded sheets, layers and TE axes for (a) and (b) imine-I, and (c) and (d) azo-I. Disorder in the aromatic rings and halogens has been omitted for clarity. Type-II halogen bonds are shown with yellow dashed lines, type-I halogen bonds are shown with blue dashed lines and C—H⋯I forces are shown with green dashed lines.
Figure 7
Figure 7
Single-crystal X-ray structures at 290 K showing 2D halogen-bonded sheets, layers and TE axes for (a) and (b) diolefin-I, (c) and (d) diolefin-Br, and (e) and (f) diolefin-I Br. Type-II halogen⋯halogen bonds are shown with yellow dashed lines, type-I bonds are shown with blue dashed lines and C—H⋯X forces are shown with green dashed lines.
Figure 8
Figure 8
Single-crystal X-ray structures at 290 K, highlighting the 2D halogen-bonded sheets, layers and TE axes for (a) and (b) di­imine-I, and (c) and (d) di­imine-Br. Type-II halogen⋯halogen bonds are shown with yellow dashed lines, type-I bonds are shown with blue dashed lines and C—H⋯X bonds are shown with green dashed lines.
Figure 9
Figure 9
(a) and (b) Single-crystal X-ray structures at 290 K showing 2D halogen-bonded sheets, herringbone packing and TE axes for diazo-I. Disorder in the aromatic rings has been omitted for clarity. Type-II halogen⋯halogen bonds are shown with yellow dashed lines, type-I bonds are shown with blue dashed lines and C—H⋯X bonds are shown with green dashed lines. (c) and (d) Conformational switch in major sites of diazo-I (bottom molecule) between 270 and 250 K. Only the major sites are shown for both molecules.
Figure 10
Figure 10
Single-crystal X-ray structures at 290 K highlighting the 2D halogen-bonded sheets, layered packing and TE axes for (a) and (b) imine-Br, (c) and (d) azo-Br(a), and (e) and (f) azo-I Br. Type-II halogen⋯halogen bonds are shown with yellow dashed lines.
Figure 11
Figure 11
Single-crystal X-ray structures at 290 K highlighting 2D halogen-bonded sheets, layered packing and TE axes for (a) and (b) diazo-Br, and (c) and (d) diazo-I Br. Type-II halogen⋯halogen bonds are shown with yellow dashed lines and C—H⋯X bonds are shown with green dashed lines.
Figure 12
Figure 12
Single-crystal X-ray structures highlighting X 2 axes for representative (a) and (b) herringbone structures (imine-I), and (c) and (d) face-to-face π-stacked structures (imine-Br). The X 2 planes are shown in red and going into the page.
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