2D constraint modifies packing behaviour: a halobenzene monolayer with X₃ halogen-bonding motif

Jonathan A. Davidsona Department of Chemistry, University of Cambridge, Cambridge, UK

https://orcid.org/0000-0001-9242-3606

Stephen J. Jenkinsa Department of Chemistry, University of Cambridge, Cambridge, UK

https://orcid.org/0000-0001-9362-9665

Fabrice Gorrecb MRC Laboratory of Molecular Biology, Cambridge, UK

Stuart M. Clarkec BP Institute, University of Cambridge, Cambridge, UKCorrespondence[email protected]

https://orcid.org/0000-0001-5224-2368

Figures & data

Figure 1. (a) Schematic of the key parameters $θ_{1}$ and $θ_{2}$ used to characterise halogen–halogen contacts. If $θ_{1} \approx θ_{2}$ the contact is type I and not considered halogen bonded. Type II contacts typically exhibit $θ_{1} \geq 150^{\circ}$ and $θ_{2} \leq 120^{\circ}$ . For an ideal halogen bond $θ_{1} = 180^{\circ}$ and $θ_{2} = 90^{\circ}$ . (b) Schematic of the X $_{3}$ motif, which consists of three type II contacts in a trigonal geometry.

Figure 1. (a) Schematic of the key parameters θ1 and θ2 used to characterise halogen–halogen contacts. If θ1≈θ2 the contact is type I and not considered halogen bonded. Type II contacts typically exhibit θ1≥150∘ and θ2≤120∘. For an ideal halogen bond θ1=180∘ and θ2=90∘. (b) Schematic of the X3 motif, which consists of three type II contacts in a trigonal geometry.

Figure 2. (a) Chemical structure of triiodomesitylene, the first species shown to exhibit the X $_{3}$ halogen bonding motif. (b) Chemical structure of 1,3,5-triiodo-2,4,6-trifluorobenzene, the species considered in this work. Despite the structural similarity the fluorinated compound was found not to exhibit the X $_{3}$ bonding motif in the bulk [Citation38].

Figure 3. Collected diffractogram of papyex dosed with TITFB, the Graphite 002 peak is labelled. Below 5 $^{\circ}$ small-angle scattering is significant. In addition to the bulk graphite peak several additional ”sawtooth” peaks of much lower intensity can be seen.

$Figure 3. Collected diffractogram of papyex dosed with TITFB, the Graphite 002 peak is labelled. Below 5∘ small-angle scattering is significant. In addition to the bulk graphite peak several additional ”sawtooth” peaks of much lower intensity can be seen.$

Figure 4. Comparison between the collected (black) and modelled (blue) diffraction pattern for the TITFB monolayer structure shown in (a), (a) Optimised experimental structure for the TITFB monolayer. The unit mesh is hexagonal with lattice parameters $a = 9.28 (7)$ Å $γ = 60^{\circ}$ . (b) Background subtraction of the monolayer pattern (black) compared to the modelled pattern (blue).

$Figure 4. Comparison between the collected (black) and modelled (blue) diffraction pattern for the TITFB monolayer structure shown in (a), (a) Optimised experimental structure for the TITFB monolayer. The unit mesh is hexagonal with lattice parameters a=9.28(7) Å γ=60∘. (b) Background subtraction of the monolayer pattern (black) compared to the modelled pattern (blue).$

Table 1. Key geometric parameters for several relevant systems. $θ_{1}$ and $θ_{2}$ are defined in Figure (a).

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Figure 5. Maps of electron density accumulation (red) and depletion (green) for the condensed TITFB monolayer, relative to the electron density of isolated molecules constrained to the same local geometries but with doubled lateral lattice constant. Isosurface thresholds are set at (a) $\pm 2 \times 10^{- 3}$ electrons.Å $^{- 3}$ and (b) $\pm 4 \times 10^{- 3}$ electrons.Å $^{- 3}$ .

2D constraint modifies packing behaviour: a halobenzene monolayer with X₃ halogen-bonding motif

Table 1. Key geometric parameters for several relevant systems. $θ_{1}$ and $θ_{2}$ are defined in Figure (a).

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2D constraint modifies packing behaviour: a halobenzene monolayer with X3 halogen-bonding motif

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Table 1. Key geometric parameters for several relevant systems. θ1 and θ2 are defined in Figure 1(a).

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2D constraint modifies packing behaviour: a halobenzene monolayer with X₃ halogen-bonding motif

Table 1. Key geometric parameters for several relevant systems. $θ_{1}$ and $θ_{2}$ are defined in Figure (a).