Insight from electron density and energy framework analysis on the structural features of Fx-TCNQ (x = 0, 2, 4) family of molecules

Shukla, R.; Ruzié, C.; Schweicher, G.; Kennedy, A.R.; Geerts, Y.H.; Chopra, D.; Chattopadhyay, B.

doi:10.1107/S2052520618017109

research papers

STRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS

ISSN: 2052-5206

Volume 75| Part 1| February 2019| Pages 71-78

https://doi.org/10.1107/S2052520618017109

Insight from electron density and energy framework analysis on the structural features of F_x-TCNQ (x = 0, 2, 4) family of molecules

Rahul Shukla,^a Christian Ruzié,^b Guillaume Schweicher,^c Alan R. Kennedy,^d Yves H. Geerts,^b Deepak Chopra ^a and Basab Chattopadhyay ^b,^e ^*

^aCrystallography and Crystal Chemistry Laboratory, Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal By-Pass Road, Bhopal, Madhya Pradesh, India 462066, ^bLaboratoire de Chimie des Polymères, CP 206/01, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, 1050 Brussels, Belgium, ^cOptoelectronics Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, CB3 0HE, UK, ^dDepartment of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, UK, and ^eDepartment of Physics, Norwegian University of Science and Technology (NTNU), Høgskoleringen 5, 7491 Trondheim, Norway
^*Correspondence e-mail: basab.chattopadhyay@ntnu.no

Edited by A. Nangia, CSIR–National Chemical Laboratory, India (Received 6 October 2018; accepted 2 December 2018; online 24 January 2019)

In this study, the nature and characteristics of the intramolecular and intermolecular interactions in crystal structures of the fluoro-substituted 7,7,8,8-tetracyanoquinodimethane (TCNQ) family of molecules, i.e. F_x-TCNQ (x = 0, 2, 4), are explored. The molecular geometry of the reported crystal structures is directly dependent on the degree of fluorination in the molecule, which consequently also results in the presence of an intramolecular N≡C⋯F—C π-hole tetrel bond. Apart from this, the energy framework analysis performed along the respective transport planes provides new insights into the energetic distribution in this class of molecules.

Keywords: fluorination; tetracyanoquinodimethane; π-hole interaction; tetrel bond; electron density; energy framework; TCNQ; intermolecular interactions; charge density analysis.

CCDC references: 1818662; 1818663; 1818664; 1818665

1. Introduction

In the past decade, organic electronics have been the focus of intense scientific interest based on the possibility that they will provide a viable alternative to Si-based devices for large area electronics (Myers & Xue, 2012 ; Root et al., 2017 ; Wang et al., 2018 ). Several attempts has been made to design a highly efficient organic semiconductor (OSC) molecule with high charge carrier mobility (Dou et al., 2015 ; Horowitz, 1998 ; Tsutsui et al., 2016 ; Yang et al., 2018 ). One of the most important factors that affects the charge carrier mobility of an OSC molecule is the final crystal structure that it adopts in the solid state. High mobilities are observed in compounds having strong π-overlap between molecules in the crystalline state (Wang et al., 2018; Yassar, 2014 ). In this regard, one of the molecular systems which has garnered significant attention is the fluorinated tetracyanoquinodimethane (F_x-TCNQ: x = 0, 2, 4) family of molecules. Among the different derivatives, it is reported that F₂-TCNQ shows much higher electron mobility in Organic Field Effect Transistors (OFETs) than TCNQ or F₄-TCNQ, up to 25 cm² V⁻¹ s⁻¹ compared with ∼ 0.1 cm² V⁻¹ s⁻¹. High band-like electron mobility observed in F₂-TCNQ was attributed to the presence of planar molecular packing and one molecule in the primitive unit cell (Chernyshov et al., 2017 ; Krupskaya et al., 2015 ; Sosorev, 2017 ). While the molecular packing of these molecules has been discussed previously, the aim of this study was to perform an in-depth quantitative and qualitative investigation into the unique structural and molecular features in this class of molecules.

Hence, we present a detailed structural analyses of F_x-TCNQ (x = 0, 2, 4) (Scheme 1) family of molecules. We are also reporting for the first time, the crystal structure of another difluoride derivative i.e. 2,6-difluoro-7,7,8,8-tetracyanoquinodimethane (F₂′-TCNQ) (Scheme 1) in this study. We have investigated how the position and extent of fluorination affects the molecular geometry of different TCNQ derivatives. The intramolecular N≡C⋯F—C π-hole tetrel bond is present as a consequence of fluorination was explored through theoretical X-ray electron density analysis (Hansen & Coppens, 1978 ). To the best of our knowledge, the analysis of the π-hole tetrel bonds in these molecules is the first of its kind. The overall molecular packing in these molecules was explored by means of energy framework analysis (Turner et al., 2015 ) and the important intermolecular contacts such as C—H⋯N and π⋯π stacking were analysed quantitatively via calculation of the interaction energy (Turner et al., 2014 ) and topological analysis of the electron density (Bader, 1985 . 1991 ).

2. Methods

2.1. Materials and crystallization

TCNQ was purchased from Sigma-Aldrich; F₂-TCNQ and F₄-TCNQ were obtained from TCI Europe. All three compounds were used without further purification. F₂′-TCNQ was synthesized by the method reported in the literature (Mochida et al., 1997 , 1999 ). All the compounds were crystallized via the sublimation method.

2.2. X-ray data collection

Single-crystal X-ray diffraction data were collected using a Bruker APEX II diffractometer equipped with a CCD detector using monochromated Mo Kα radiation (λ = 0.71073 Å) and φ and ω scans. The data collection for all compounds was carried out at 100 (2) K. The unit-cell measurement, data collection, integration, scaling and absorption corrections for each compound were performed using APEX3 (Bruker, 2012a ) software. The intensity data were processed using the SAINT (Bruker, 2012b ) suite of programs. The crystal structures were solved by direct methods using SIR92 (Altomare et al., 1994 ) and refined using the full-matrix least-squares method in SHELXL2014 (Sheldrick, 2015 ) present in the program suite WinGX (Version 2014.1; Farrugia, 2012 ). Empirical absorption correction was applied using SADABS (Bruker, 2001 ). The non-hydrogen atoms were refined anisotropically and the hydrogen atoms bonded to C were set at 1.082 Å for Csp²—H which corresponds to neutron diffraction data and were refined isotropically. The molecular connectivity and the crystal packing diagrams were generated using Mercury3.9 (Macrae et al., 2008 ). Geometrical calculations were performed using PARST (Nardelli, 1995 ) and PLATON (Spek, 2009 ). The detailed crystallographic data are summarized in Table S1.

2.3. Multipolar modelling

Single-point periodic quantum mechanical calculations were carried out using CRYSTAL09 (Dovesi et al., 2005 ; 2009 ) at TZVP level of theory (Peintinger et al., 2013 ), the geometry obtained from the experimental structure determination was used as input data. The shrinking factors (IS1–IS3) along with the reciprocal lattice vectors were set to 4 (27 k-points in the irreducible Brillouin zone). The bielectronic Coulomb and exchange series values for the truncation parameter were set as ITOL1–ITOL4 = 7 and ITOL5 = 14, respectively. The level shifter was set to 0.7 Hartree per cycle for a better convergence. Upon convergence of energy (∼10⁻⁶ Hartree), the periodic wavefunctions were obtained. Static theoretical structure factors were derived at sin(θ/λ) = 1.41 Å⁻¹ resolution using the XFAC module of CRYSTAL09. The theoretical multipolar refinements along with topological analysis were performed with the MoPro (Jelsch et al., 2005 ; Guillot et al., 2014 ) software package using the Hansen and Coppens (1978) multipole formalism. The atomic positions were held fixed to the values obtained from the experimental structure determination during the spherical atom model refinements. All theoretical structure factors were assigned unit weights during the refinements. The displacement parameters were set to zero to consider a static model and multipolar refinements of the theoretical data were carried out up to the octupole level for non-H atoms and to the dipole level for H atoms. The crystallographic parameters obtained after multipolar refinement confirm the good quality of the model (Table S1). Fig. S1 shows the residual electron density maps [Figs. S1(a)–S1(d)], 2D deformation density map [Figs. S1(e)–S1(h)], 2D Laplacian map [Figs. S1(i)–S1(l)]. Fig. S2 shows the fractal dimensional plots of the respective molecules.

2.4. Topological analysis

The topological analysis was based on Quantum Theory of Atoms In Molecule (QTAIM) developed by Bader (Bader, 1985, 1991). Topological parameters such as the electron density (ρ) and Laplacian (∇²ρ) were evaluated at the bond critical point (BCP). At the BCP, the first derivative of the electron density vanishes, i.e. ∇ρ = 0. The Laplacian signifies whether the interaction is a shared interaction (∇²ρ < 0) or a closed-shell interaction (∇²ρ > 0). Intermolecular/intramolecular interactions are closed-shell interactions with a positive value for both ρ and Laplacian at the BCP (Bader, 1985, 1991).

2.5. Energy framework analysis

We have performed an energy framework analysis (Turner et al., 2015) using CrystalExplorer (Version 17.5; Turner et al., 2017 ) on the important intermolecular interactions present along the transport plane in each of the molecules (Fig. 1c). Energy framework analysis has emerged as a useful tool in crystal engineering for correlating different phenomena such as mechanical properties (Turner et al., 2015), polymorphism (Dey et al., 2016 ) and host–guest interaction (Shi et al., 2015 ) with three-dimensional topology of interaction energies based on different intermolecular interactions present in molecular crystals. In this analysis, the interaction energies between different molecular pairs are represented via cylindrical tubes connecting the centres of mass of the interacting molecules. The radius of the cylindrical tube is directly proportional to the interaction energies. Further insights can be gained when the energy topology, which is represented by cylindrical tubes, is disintegrated into electrostatic and dispersive components.

Figure 1
(a) Molecular view of the reported crystal structures drawn with 50% ellipsoidal probability along with the numbering scheme and important bond angles. (b) Cell parameters. (c) Molecular packing along the transport plane: TCNQ (ab-plane), F₂-TCNQ ( $[{\bar 2} 0 0]$ ), F₂′-TCNQ (100) and F₄-TCNQ (ac-plane).

2.6. Molecular electrostatic potential map

Molecular electrostatic potential maps for the four molecules were plotted on the Hirshfeld isosurface at the MP2/6-311G** level using CrystalExplorer 17 (Turner et al., 2017).

3. Result and discussion

3.1. Molecular geometry and intramolecular N≡C⋯F—C π-hole tetrel bond

Molecular views of all the compounds along with cell parameters and molecular packing are shown in Fig. 1. Complete crystallographic details of all the structures are reported in Table S1. Similar to previously reported structures (Table S2) in the Cambridge Structural Database (Version 5.39; Groom et al., 2016 ), TCNQ crystallizes in the monoclinic space group C2/c with Z′ (number of molecules in the asymmetric unit) = 0.5. F₂-TCNQ crystallizes in the monoclinic space group C2/m with Z′ = 0.25, F₄-TCNQ crystallizes in the orthorhombic Pbca space group with Z′ = 0.5. We also report, for the first time, the crystal structure of 2,6-difluoro-7,7,8,8-tetracyanoquinodimethane (F₂′-TCNQ), which crystallizes in the monoclinic space group P2₁/c with Z′ = 1. The effect of fluorination is evident from the analysis of the molecular geometry of the four crystal structures (Fig. 1a). In the case of TCNQ, the magnitude of ∠A (C—C—N) and ∠A′ is ∼180° (Table 1). As hydrogen is replaced by fluorine, the magnitude of ∠A′ decreases to 177.9 (2)° in the case of F₂-TCNQ whereas ∠A largely remains unaffected. In the case of F₂′-TCNQ and F₄-TCNQ, the magnitudes of ∠A and ∠A′ decrease to 175.94 (15)° and 176.18 (15)°, and 174.6 (3)° and 175.9 (2)°, respectively (Table 1). Except for F₂′-TCNQ, ∠A = ∠B and ∠A′ = ∠B′ due to the presence of crystallographically imposed symmetry. The magnitudes of ∠B and ∠B′ in F₂′-TCNQ are 176.76 (16)° and 178.64 (16)°, respectively.

Table 1
Magnitudes of important bond angles present in the reported crystal structures

Molecule	∠A (°)	∠A′ (°)	∠B (°)	∠B′ (°)	∠C (°)	∠C′ (°)
TCNQ	179.92 (14)	179.33 (12)	179.92 (14)	179.33 (12)	118.59 (10)	118.59 (10)
F₂-TCNQ	179.8 (2)	177.9 (2)	179.8 (2)	177.9 (2)	115.71 (16)	115.71 (16)
F₂′-TCNQ	175.94 (15)	176.18 (15)	176.76 (16)	178.64 (16)	112.99 (12)	118.68 (13)
F₄-TCNQ	174.6 (3)	175.9 (2)	174.6 (3)	175.9 (2)	113.60 (19)	113.60 (19)

The presence of an intramolecular π-hole interaction, where the lone pair (lp) of F interacts with the electron-deficient region (π-hole) of the CN bond resulting in the formation of an intramolecular lp⋯π interaction [Figs. 2(a)–2(d)]. It was also substantiated via quantitative inputs from the topological parameters characterized by the finite positive values of the electron density and the Laplacian at the (3, −1) F⋯C(π) bond critical point between the fluorine and the carbon atom [Figs. 2(a)–2(d)]. The magnitude of ρ ranges from 0.089 to 0.108 e Å⁻³ while the magnitude of ∇²ρ ranges from 1.53 to 1.78 e Å⁻⁵. The relatively small value of ρ and the positive value of ∇²ρ establishes the closed-shell nature of the interaction (Bader, 1985, 1991). The large magnitude of these topological parameters indicates the highly stabilizing nature of these intramolecular interactions (Table 2). The π-hole tetrel bonding nature of this intramolecular interaction is further supported by 2D deformation density maps where the charge-concentrated (CC) region on fluorine is clearly directed towards the charge-depleted (CD) region on the carbon atom of the C≡N bond [Figs. 2(e)–2(h)]. It is important here to note that N≡C⋯F—C π-hole tetrel bonds are uncommon and their presence might lead to new possibilities for understanding chemical reactivity in such classes of compounds.

Table 2
Geometrical and topological parameters at intramolecular F⋯C bond critical point

Interaction	d_F⋯C (Å)	C—F⋯C (°)	R_ij (Å)	ρ (e Å⁻³)	∇²ρ (e Å⁻⁵)
F₂-TCNQ
F1⋯C2	2.647 (2)	92	2.658	0.089	1.53
F₂′-TCNQ
F1⋯C2	2.563 (1)	94	2.582	0.108	1.78
F2⋯C1	2.598 (2)	93	2.617	0.096	1.62
F₄-TCNQ
F1⋯C2	2.607 (2)	91	2.616	0.094	1.63
F2⋯C1	2.599 (2)	92	2.604	0.099	1.65

Figure 2
(a–d) Molecular plots depicting the presence of F⋯C (π) (3,−1) bond critical point. (e–h) 2D deformation density plots showing the presence of charge-concentrated (blue) and charge-depleted (red) regions between the interacting atoms.

Apart from the deviation in the C—C≡N bond, the angular deviation was also observed in the hexadiene ring. ∠C (Fig. 1) was observed to be 118.59 (10)°, 115.71 (16)° and 113.60 (19)° for TCNQ, F₂-TCNQ and F₄-TCNQ, respectively (Table 1). The corresponding ∠C and ∠C′ angles in F₂′-TCNQ were calculated to be 112.99 (12)° and 118.68 (13)°, respectively, which clearly shows the effect of fluorination on the alteration in the observed molecular geometry from the ideal value of 120°.

3.2. Molecular packing along the transport plane

In this study, we have performed the packing analysis exclusively along the transport plane. The transport plane corresponds to the surfaces where the accumulation of electrons takes place in the FET devices. The transport planes for TCNQ (ab-plane), F₂-TCNQ ( $[{\bar 2} 0 0]$ ) and F₄-TCNQ (ac-plane) molecules were reported recently (Krupskaya et al., 2015) and we have utilized the same planes for this analysis. Since the transport plane for F₂′-TCNQ is not known, the crystal morphology [using BFDH morphology (Donnay & Harker, 1937 ) module in Mercury3.9] was obtained and (100) emerges as a potential transport plane due to the presence of well-defined molecular layers similar to those observed for the other three structures (Fig. S3). In addition to this, we have performed topological analysis along the transport plane in order to analyse the features of different interactions such as hydrogen bonds and π–π stacking interactions.

3.2.1. Packing analysis of TCNQ and F₂-TCNQ

In both TCNQ and F₂-TCNQ, the significant electrostatic contribution is present along the transport plane due to the presence of short and moderately strong C—H⋯N interactions [motif I in TCNQ and motif II in F₂-TCNQ; Table S6; Figs. 3(a) and 3(e)], which forms a 1D molecular chain [Figs. 4(a)–4(f)]. The value of ρ has magnitudes of 0.057 e Å⁻³ (TCNQ) and 0.051 e Å⁻³ (F₂-TCNQ), while ∇²ρ has magnitudes of 1.10 e Å⁻⁵ (TCNQ) and 0.72 e Å⁻⁵ (F₂-TCNQ) at the (3,−1) BCP of the C—H⋯N interaction. Both structures are also supported by the presence of type I N⋯N contacts as confirmed by the topological analysis [Figs. 3(a) and 3(e), Table S7]. This is in accordance with the observation made in a previous study (Chernyshov et al., 2017). Also in both structures, the similar chain formed by C—H⋯N interactions are interconnected to each other via two different molecular stacking motifs (motifs II and III in TCNQ; motifs I and III in F₂-TCNQ; Fig. 3).

Figure 3
Different molecular motifs present along the transport plane of (a–c) TCNQ, (d–f) F₂-TCNQ, (g–i) F₂′-TCNQ and (j–k) F₄-TCNQ

Figure 4
Total energy contribution in (a) TCNQ, (e) F₂-TCNQ (i) F₄-TCNQ, (m) F₂′-TCNQ. Electrostatic energy contribution in (b) TCNQ, (f) F₂-TCNQ, (j) F₄-TCNQ, (n) F₂′-TCNQ. Dispersion energy contribution in (c) TCNQ, (g) F₂-TCNQ, (k) F₄-TCNQ, (o) F₂′-TCNQ. Overlay of the dominant contributor along the transport plane in (d) TCNQ, (h) F₂-TCNQ, (l) F₄-TCNQ, (p) F₂′-TCNQ. ES stands for electrostatic and D stands for the dispersive component.

In the case of TCNQ, the similar chains formed by C—H⋯N interaction are interconnected to each other via two dispersion dominant stacking interactions [motif II, −23.2 kJ mol⁻¹; motif III, −17.4 kJ mol⁻¹; Fig. 4(a)]. These stacking interactions are oriented along a and b axes while the electrostatically driven motif I is oriented in between the stacking motif. Because of this, the tube representing the dominant electrostatic component roughly makes an angle of ∼45° with the dominant dispersive component (Fig. 4d).

In the case of F₂-TCNQ, the similar chains formed by C—H⋯N interaction along the a axis (motif II, −26.2 kJ mol⁻¹) are interconnected to each other by two stacking motifs along the b axis (motif I, −28.8 kJ mol⁻¹; motif III, −17.9 kJ mol⁻¹). Thus the total interaction energy (IE) along the b axis is −46.8 kJ mol⁻¹, whereas along the a axis the magnitude is −23.2 kJ mol⁻¹. Of the two stacking motifs, one is highly dispersive in nature (∼68%) whilst the other has a significant electrostatic contribution (∼49%) (Table S7) also. However, the magnitudes of the electrostatic (−13.7 kJ mol⁻¹) and dispersive (−14.1 kJ mol⁻¹) contributions in motif III are significantly lower than the dominant electrostatic (−32.9 kJ mol⁻¹) contribution in motif II and dispersion (−28.7 kJ mol⁻¹) contribution in motif I. Interestingly, topological analysis of motif I of F₂-TCNQ reveals the presence of a C—F⋯F—C interaction (Fig. 3d). This shows that π⋯π interactions in stacking motifs are also assisted by other types of intermolecular interactions. Only in the case of F₂-TCNQ are the tubes representing the dominant electrostatic and dispersion are approximately orthogonal to each other (Fig. 4h). In a recent review, it was reported that electron conductivity is typically high in the direction of the strong intermolecular interactions (Wang et al., 2018). In the case of F₂-TCNQ also, the total interaction strength was found to be significantly higher in the π-stacking direction. Another important observation is that the overall contribution of electrostatic energy (−59.8 kJ mol⁻¹) was more than dispersion energy (−53.3 kJ mol⁻¹) along the transport plane in the case of F₂-TCNQ, while dispersion was more dominant in the structures of the other three species (Table S7).

3.2.2. Packing analysis of F₄-TCNQ

While the molecular packings of TCNQ, F₂-TCNQ, and F₄-TCNQ along the transport plane are uniform [Figs. 4(a)–4(i)] wherein a specific arrangement of molecule is present in two dimensions, the differences arising on account of the role played by the combination of electrostatic and dispersive forces acting between the molecules. The molecular packing along the c axis in F₄-TCNQ [Fig. 4(i)] is governed by molecular stacking [motif I, IE = −34.0 kJ mol⁻¹; Fig. 3(j)] with significant contribution from both electrostatic (∼54%) and dispersion components (∼46%) (Table S7). This stacking layer is interconnected to another similar layer down the a axis via dispersive (∼67%) F⋯F and F⋯N interactions [motif II, −22.5 kJ mol⁻¹; Fig. 3(k)]. The absence of a significantly electrostatic dominant interaction (where the contribution of the electrostatic component is significantly greater than the dispersive component towards stabilization) (Table S6) causes both the electrostatic and dispersion components (Fig. 4l) to be orientated in a non-orthogonal manner along the c axis.

3.2.3. Packing analysis of F₂′-TCNQ

The energy framework analysis of F₂′-TCNQ reveals that it has non-uniform packing [Figs. 4(m)–4(o)] along the expected transport plane compared with the other three molecules which have uniform packing [Figs. 4(a)–4(i)]. In the case of F₂′-TCNQ, the molecular layer present along the b axis is formed by a molecular stacking interaction (motif I, −24.2 kJ⁻¹, Table S7) with 81% contribution from the dispersion component towards stabilization, The topological analysis reveals the presence of multiple π⋯π and lp⋯π interactions in motif I (Fig. 3g). This molecular layer is then connected to another similar layer along the c axis via the electrostatic-dominant (62%) moderately strong C—H⋯N (d_H⋯N = 2.49 Å; ∠C—H⋯N = 166°) and N4⋯C12 lp⋯π interactions (motif II, IE = −22.3 kJ mol⁻¹) giving rise to a T-shaped dimer (Fig. 4m).The molecular packing is then further extended along the c axis via another stacking interaction (motif III, −20.3 kJ mol⁻¹). Interestingly, the topological analysis revealed the presence of a hydrogen bond due to the presence of a (3,−1) BCP between H8 and N3 [d_H⋯N = 2.82 Å; ∠C—H⋯N = 105°; Fig. 3(i)]. This also explains the origin of a substantial electrostatic component in this stacking motif (Table S6). Hence, the molecular packing along the expected transport plane of F₂′-TCNQ is stabilized by two alternate types of molecular layers which results in non-uniform packing.

3.3. Electrostatic potential maps

In all four molecules (see Fig. 5) the positive electrostatic region (in blue) belongs to the quinodimethane region and the hydrogen atoms present in the molecule while the negative electrostatic region belonged to the cyano region (in red). Despite its high electronegativity, the negative electrostatic region on fluorine was significantly less than that of the cyano group. This observation is consistent with the observation made in a previous study (Ji et al., 2018 ). However, the most important aspect of these MESP maps is how the electrostatic potential distribution exists in these molecules. In the case of TCNQ and F₄-TCNQ (Fig. 5), the electrostatic distributions for both sides of the molecules are the same but are oriented in opposite directions. In the case of F₂-TCNQ, the front and back sides of the molecule are connected by a mirror image which is responsible for the similar distribution of the electrostatic potential above and below the plane. This unique distribution of electrostatic potential exclusively in F₂-TCNQ separates it from the other molecules investigated in this study. In the case of F₂′-TCNQ, the electrostatic potential distribution on both sides of the molecule is completely different with no relation between the electrostatic potential distributions on both sides.

Figure 5
Molecular electrostatic potential (MESP) maps of the four crystal structures drawn on Hirshfeld isosurface at ± 0.03 contour level. Red represents negative and blue represents positive electrostatic potentials (both front and back view). The arrows between the front and back of a given molecule in TCNQ and F4-TCNQ show that the electrostatic potential distribution of the two faces are similar but are oriented in the opposite direction. The cross between the front and back of F2′-TCNQ shows that the electrostatic potential distribution in the front and back of the molecule is not similar with respect to each other. The dotted lines shown in the front view of F2-TCNQ represent the existence of a mirror plane due to which the electrostatic potential distribution on the front and back of F2-TCNQ is same.

4. Summary

In this study it is observed that the degree of fluorination in the F_x-TCNQ (x = 0, 2, 4) family of molecules affects the geometry in the molecules. Fluorination also results in the presence of an intramolecular N≡C⋯F—C interaction which acts as a conformational lock. The theoretical charge density analysis confirms this interaction to be a proper donor–acceptor interaction where the lone pairs of fluorine interact with the electron-deficient region of the C≡N bond. Topological analysis establishes the presence of a (3,−1) F⋯C bond critical point and hence this interaction can be categorized as a π-hole tetrel bond. The energy framework analysis revealed the energetic distribution along the transport plane in the reported molecules. The analysis showed that F₂-TCNQ, which has exceptionally high charge carrier mobility compared with other derivatives, also has unique structural features. All the molecules have significant contribution from electrostatic and dispersion components towards the stabilization of the molecular packing. However, only in the case of F₂-TCNQ were the tubes representing the dominant electrostatic and dispersion contributions orthogonal to each other. The molecular electrostatic potential map also reveals that F₂-TCNQ has a unique electrostatic distribution compared with other molecules.

Supporting information

CCDC references: 1818662; 1818663; 1818664; 1818665

Crystal structure: contains datablocks global, TCNQ, F2'-TCNQ, F2-TCNQ, F4-TCNQ. DOI: https://doi.org/10.1107/S2052520618017109/aw5018sup1.cif

Tables S1-S7, Figs S1-S3. DOI: https://doi.org/10.1107/S2052520618017109/aw5018sup2.pdf

Structure factors: contains datablock TCNQ. DOI: https://doi.org/10.1107/S2052520618017109/aw5018TCNQsup3.hkl

Structure factors: contains datablock F2-TCNQ. DOI: https://doi.org/10.1107/S2052520618017109/aw5018F2-TCNQsup4.hkl

Structure factors: contains datablock F2prime-TCNQ. DOI: https://doi.org/10.1107/S2052520618017109/aw5018F2prime-TCNQsup5.hkl

Structure factors: contains datablock F4-TCNQ. DOI: https://doi.org/10.1107/S2052520618017109/aw5018F4-TCNQsup6.hkl

Computing details top

Data collection: Bruker APEX2 for TCNQ, F2'-TCNQ, F2-TCNQ. Cell refinement: Bruker SAINT for TCNQ, F2'-TCNQ, F2-TCNQ. Data reduction: Bruker SAINT for TCNQ, F2'-TCNQ, F2-TCNQ. Program(s) used to solve structure: SHELXS97 (Sheldrick 2008) for TCNQ, F2'-TCNQ, F2-TCNQ. Program(s) used to refine structure: SHELXL2014 (Sheldrick 2014) for TCNQ, F2'-TCNQ, F2-TCNQ; SHELXL2014/7 (Sheldrick, 2014) for F4-TCNQ. Molecular graphics: Bruker SHELXTL for TCNQ, F2'-TCNQ, F2-TCNQ. Software used to prepare material for publication: Bruker SHELXTL for TCNQ, F2'-TCNQ, F2-TCNQ.

(TCNQ) top

Crystal data top

C₁₂H₄N₄	F(000) = 416
M_r = 204.19	D_x = 1.362 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.8782 (13) Å	Cell parameters from 4041 reflections
b = 6.9117 (10) Å	θ = 2.5–30.6°
c = 16.398 (2) Å	µ = 0.09 mm⁻¹
β = 98.288 (6)°	T = 100 K
V = 995.8 (3) Å³	Block, yellow
Z = 4	0.61 × 0.35 × 0.19 mm

Data collection top

Bruker APEX-II CCD diffractometer	R_int = 0.103
φ and ω scans	θ_max = 30.6°, θ_min = 2.5°
11008 measured reflections	h = −11→12
1519 independent reflections	k = −9→9
1097 reflections with I > 2σ(I)	l = −23→23

Refinement top

Refinement on F²	2 restraints
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.046	All H-atom parameters refined
wR(F²) = 0.118	w = 1/[σ²(F_o²) + (0.064P)² + 0.058P] where P = (F_o² + 2F_c²)/3
S = 1.06	(Δ/σ)_max = 0.001
1519 reflections	Δρ_max = 0.31 e Å⁻³
81 parameters	Δρ_min = −0.26 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
N1	0.80648 (12)	0.74384 (16)	0.23996 (6)	0.0237 (3)
N2	0.47985 (11)	0.93410 (14)	0.40007 (7)	0.0235 (3)
C1	0.78636 (12)	0.80879 (15)	0.30193 (7)	0.0164 (3)
C3	0.76099 (12)	0.88998 (14)	0.37933 (7)	0.0143 (3)
C4	0.87937 (12)	0.94389 (14)	0.43884 (7)	0.0132 (3)
C6	0.84897 (12)	1.02605 (15)	0.51607 (7)	0.0148 (3)
C5	1.03554 (12)	0.92036 (15)	0.42576 (7)	0.0143 (3)
C2	0.60472 (13)	0.91479 (15)	0.39040 (7)	0.0161 (3)
H6	0.7321 (5)	1.0408 (18)	0.5269 (8)	0.023 (3)*
H5	1.0566 (16)	0.8616 (19)	0.3673 (4)	0.031 (4)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0249 (6)	0.0263 (5)	0.0199 (6)	−0.0007 (4)	0.0028 (4)	−0.0035 (4)
N2	0.0191 (5)	0.0287 (6)	0.0223 (6)	0.0000 (4)	0.0020 (4)	0.0005 (4)
C1	0.0136 (5)	0.0171 (5)	0.0182 (6)	−0.0009 (4)	0.0012 (4)	0.0004 (4)
C3	0.0153 (5)	0.0136 (5)	0.0142 (6)	0.0006 (4)	0.0029 (4)	0.0015 (4)
C4	0.0141 (5)	0.0110 (5)	0.0151 (6)	0.0011 (4)	0.0041 (4)	0.0026 (4)
C6	0.0156 (5)	0.0150 (5)	0.0146 (6)	0.0017 (4)	0.0043 (4)	0.0022 (4)
C5	0.0148 (5)	0.0147 (5)	0.0142 (6)	0.0016 (4)	0.0048 (4)	0.0007 (4)
C2	0.0171 (6)	0.0164 (5)	0.0142 (6)	−0.0005 (4)	0.0001 (4)	0.0002 (4)

Geometric parameters (Å, º) top

N1—C1	1.1482 (15)	C4—C6	1.4484 (16)
N2—C2	1.1501 (14)	C6—C5ⁱ	1.3477 (16)
C1—C3	1.4349 (16)	C6—H6	1.0823 (10)
C3—C4	1.3785 (15)	C5—C6ⁱ	1.3477 (16)
C3—C2	1.4352 (16)	C5—H5	1.0824 (10)
C4—C5	1.4424 (15)

N1—C1—C3	179.92 (14)	C5ⁱ—C6—C4	120.52 (10)
C4—C3—C1	122.08 (10)	C5ⁱ—C6—H6	120.5 (7)
C4—C3—C2	122.03 (10)	C4—C6—H6	118.9 (7)
C1—C3—C2	115.88 (10)	C6ⁱ—C5—C4	120.89 (10)
C3—C4—C5	121.02 (10)	C6ⁱ—C5—H5	121.3 (8)
C3—C4—C6	120.39 (10)	C4—C5—H5	117.8 (8)
C5—C4—C6	118.59 (10)	N2—C2—C3	179.33 (12)

C1—C3—C4—C5	−0.12 (16)	C3—C4—C6—C5ⁱ	−179.72 (10)
C2—C3—C4—C5	−179.00 (10)	C5—C4—C6—C5ⁱ	0.17 (17)
C1—C3—C4—C6	179.76 (10)	C3—C4—C5—C6ⁱ	179.72 (10)
C2—C3—C4—C6	0.88 (15)	C6—C4—C5—C6ⁱ	−0.17 (17)

Symmetry code: (i) −x+2, −y+2, −z+1.

(F2'-TCNQ) top

Crystal data top

C₁₂H₂F₂N₄	F(000) = 480
M_r = 240.18	D_x = 1.579 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.8303 (9) Å	Cell parameters from 7666 reflections
b = 5.4679 (5) Å	θ = 3.3–30.5°
c = 19.2479 (17) Å	µ = 0.13 mm⁻¹
β = 102.417 (5)°	T = 100 K
V = 1010.39 (16) Å³	Block, yellow
Z = 4	0.31 × 0.20 × 0.14 mm

Data collection top

Bruker APEX-II CCD diffractometer	R_int = 0.084
φ and ω scans	θ_max = 30.7°, θ_min = 2.7°
23312 measured reflections	h = −14→14
3100 independent reflections	k = −7→7
2273 reflections with I > 2σ(I)	l = −27→27

Refinement top

Refinement on F²	2 restraints
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.051	All H-atom parameters refined
wR(F²) = 0.124	w = 1/[σ²(F_o²) + (0.0539P)² + 0.4801P] where P = (F_o² + 2F_c²)/3
S = 1.05	(Δ/σ)_max < 0.001
3100 reflections	Δρ_max = 0.40 e Å⁻³
171 parameters	Δρ_min = −0.37 e Å⁻³

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
F2	0.92048 (9)	−0.26958 (17)	0.20358 (5)	0.0224 (2)
F1	0.94270 (9)	0.36736 (17)	0.04012 (5)	0.0222 (2)
N3	0.44424 (15)	0.6836 (3)	0.07372 (7)	0.0250 (3)
N2	1.21929 (13)	0.1565 (2)	0.03203 (7)	0.0202 (3)
N4	0.39781 (13)	0.0763 (3)	0.21822 (7)	0.0205 (3)
N1	1.18901 (15)	−0.4399 (3)	0.16696 (7)	0.0252 (3)
C11	0.48390 (15)	0.5039 (3)	0.10193 (8)	0.0172 (3)
C10	0.54116 (15)	0.2852 (3)	0.13753 (7)	0.0153 (3)
C9	0.67055 (14)	0.2031 (3)	0.13152 (7)	0.0141 (3)
C8	0.74731 (14)	0.3314 (3)	0.08731 (7)	0.0148 (3)
C6	0.87415 (15)	0.2514 (3)	0.08335 (7)	0.0149 (3)
C4	0.94325 (14)	0.0414 (3)	0.12087 (7)	0.0135 (3)
C3	1.07141 (14)	−0.0400 (3)	0.11296 (7)	0.0145 (3)
C2	1.15158 (15)	0.0761 (3)	0.06789 (7)	0.0159 (3)
C12	0.46158 (15)	0.1669 (3)	0.18191 (7)	0.0161 (3)
C1	1.13504 (15)	−0.2612 (3)	0.14495 (7)	0.0172 (3)
C5	0.86132 (15)	−0.0777 (3)	0.16526 (7)	0.0148 (3)
C7	0.73298 (15)	−0.0084 (3)	0.17031 (7)	0.0156 (3)
H7	0.6795 (16)	−0.112 (3)	0.2043 (7)	0.025 (5)*
H8	0.7060 (17)	0.4937 (18)	0.0580 (8)	0.022 (5)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F2	0.0217 (5)	0.0212 (5)	0.0258 (5)	0.0069 (4)	0.0085 (4)	0.0122 (4)
F1	0.0187 (4)	0.0230 (5)	0.0280 (5)	0.0035 (4)	0.0119 (4)	0.0135 (4)
N3	0.0239 (7)	0.0228 (7)	0.0290 (7)	0.0051 (6)	0.0072 (6)	0.0024 (6)
N2	0.0185 (6)	0.0215 (6)	0.0211 (6)	0.0016 (5)	0.0057 (5)	0.0014 (5)
N4	0.0184 (6)	0.0224 (7)	0.0218 (6)	0.0032 (5)	0.0069 (5)	0.0017 (5)
N1	0.0272 (7)	0.0252 (7)	0.0242 (7)	0.0089 (6)	0.0078 (6)	0.0055 (6)
C11	0.0141 (6)	0.0201 (7)	0.0188 (6)	0.0007 (5)	0.0066 (5)	−0.0020 (6)
C10	0.0158 (7)	0.0162 (7)	0.0140 (6)	−0.0002 (5)	0.0030 (5)	−0.0016 (5)
C9	0.0150 (6)	0.0144 (6)	0.0128 (6)	−0.0003 (5)	0.0029 (5)	−0.0022 (5)
C8	0.0163 (7)	0.0139 (6)	0.0144 (6)	0.0013 (5)	0.0036 (5)	0.0019 (5)
C6	0.0163 (7)	0.0148 (7)	0.0147 (6)	−0.0013 (5)	0.0056 (5)	0.0029 (5)
C4	0.0148 (6)	0.0135 (6)	0.0124 (6)	−0.0004 (5)	0.0035 (5)	−0.0002 (5)
C3	0.0154 (6)	0.0141 (6)	0.0136 (6)	0.0003 (5)	0.0026 (5)	0.0011 (5)
C2	0.0139 (6)	0.0180 (7)	0.0151 (6)	0.0036 (5)	0.0018 (5)	0.0003 (5)
C12	0.0144 (6)	0.0170 (7)	0.0168 (6)	0.0032 (5)	0.0028 (5)	−0.0016 (5)
C1	0.0166 (7)	0.0207 (7)	0.0154 (6)	0.0015 (6)	0.0058 (5)	−0.0001 (6)
C5	0.0177 (7)	0.0128 (6)	0.0136 (6)	0.0008 (5)	0.0026 (5)	0.0040 (5)
C7	0.0177 (7)	0.0156 (6)	0.0141 (6)	0.0004 (5)	0.0047 (5)	0.0014 (5)

Geometric parameters (Å, º) top

F2—C5	1.3410 (16)	C9—C7	1.440 (2)
F1—C6	1.3377 (16)	C8—C6	1.339 (2)
N3—C11	1.149 (2)	C8—H8	1.0827 (10)
N2—C2	1.1446 (19)	C6—C4	1.4461 (19)
N4—C12	1.1469 (19)	C4—C3	1.3750 (19)
N1—C1	1.149 (2)	C4—C5	1.4488 (19)
C11—C10	1.432 (2)	C3—C1	1.438 (2)
C10—C9	1.377 (2)	C3—C2	1.439 (2)
C10—C12	1.431 (2)	C5—C7	1.341 (2)
C9—C8	1.436 (2)	C7—H7	1.0827 (10)

N3—C11—C10	176.76 (16)	C3—C4—C5	123.95 (13)
C9—C10—C12	122.41 (13)	C6—C4—C5	112.99 (12)
C9—C10—C11	120.49 (13)	C4—C3—C1	123.34 (13)
C12—C10—C11	117.01 (13)	C4—C3—C2	123.87 (13)
C10—C9—C8	120.19 (13)	C1—C3—C2	112.65 (12)
C10—C9—C7	121.11 (13)	N2—C2—C3	176.18 (15)
C8—C9—C7	118.68 (13)	N4—C12—C10	178.64 (16)
C6—C8—C9	119.25 (13)	N1—C1—C3	175.94 (15)
C6—C8—H8	119.2 (9)	F2—C5—C7	119.00 (12)
C9—C8—H8	121.6 (9)	F2—C5—C4	116.47 (12)
F1—C6—C8	118.72 (12)	C7—C5—C4	124.53 (13)
F1—C6—C4	116.21 (12)	C5—C7—C9	119.48 (13)
C8—C6—C4	125.04 (13)	C5—C7—H7	118.9 (9)
C3—C4—C6	123.03 (12)	C9—C7—H7	121.7 (10)

C12—C10—C9—C8	−178.77 (13)	C6—C4—C3—C1	−174.12 (13)
C11—C10—C9—C8	−2.3 (2)	C5—C4—C3—C1	3.6 (2)
C12—C10—C9—C7	−0.2 (2)	C6—C4—C3—C2	1.2 (2)
C11—C10—C9—C7	176.33 (13)	C5—C4—C3—C2	178.89 (13)
C10—C9—C8—C6	178.64 (13)	C3—C4—C5—F2	4.2 (2)
C7—C9—C8—C6	0.0 (2)	C6—C4—C5—F2	−177.90 (11)
C9—C8—C6—F1	177.74 (12)	C3—C4—C5—C7	−176.06 (14)
C9—C8—C6—C4	−0.2 (2)	C6—C4—C5—C7	1.9 (2)
F1—C6—C4—C3	−0.7 (2)	F2—C5—C7—C9	177.61 (12)
C8—C6—C4—C3	177.30 (14)	C4—C5—C7—C9	−2.1 (2)
F1—C6—C4—C5	−178.62 (12)	C10—C9—C7—C5	−177.50 (14)
C8—C6—C4—C5	−0.6 (2)	C8—C9—C7—C5	1.1 (2)

(F2-TCNQ) top

Crystal data top

C₁₂H₂F₂N₄	F(000) = 240
M_r = 240.18	D_x = 1.579 Mg m⁻³
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
a = 10.1713 (19) Å	Cell parameters from 3976 reflections
b = 5.8670 (12) Å	θ = 2.4–30.4°
c = 8.8512 (17) Å	µ = 0.13 mm⁻¹
β = 106.969 (7)°	T = 100 K
V = 505.20 (17) Å³	Block, yellow
Z = 2	0.23 × 0.18 × 0.13 mm

Data collection top

Bruker APEX-II CCD diffractometer	R_int = 0.059
φ and ω scans	θ_max = 30.6°, θ_min = 2.4°
8822 measured reflections	h = −11→14
849 independent reflections	k = −8→8
688 reflections with I > 2σ(I)	l = −12→12

Refinement top

Refinement on F²	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F² > 2σ(F²)] = 0.047	w = 1/[σ²(F_o²) + (0.0384P)² + 0.6736P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.109	(Δ/σ)_max < 0.001
S = 1.10	Δρ_max = 0.45 e Å⁻³
849 reflections	Δρ_min = −0.28 e Å⁻³
59 parameters	Extinction correction: SHELXL-2014/7 (Sheldrick 2014, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.027 (5)

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
F1	0.76125 (11)	0.5000	0.97938 (13)	0.0191 (3)
N1	0.33218 (17)	0.5000	0.44923 (19)	0.0196 (4)
N2	0.02227 (18)	0.5000	0.6963 (2)	0.0235 (4)
C5	0.52791 (19)	0.5000	0.8524 (2)	0.0143 (4)
C6	0.63140 (17)	0.5000	0.9873 (2)	0.0138 (4)
C2	0.13778 (19)	0.5000	0.7091 (2)	0.0163 (4)
C4	0.38735 (18)	0.5000	0.8568 (2)	0.0135 (4)
C1	0.30968 (19)	0.5000	0.5689 (2)	0.0155 (4)
C3	0.28096 (19)	0.5000	0.7187 (2)	0.0148 (4)
H5	0.549 (2)	0.5000	0.7394 (12)	0.017 (6)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F1	0.0144 (5)	0.0297 (6)	0.0156 (5)	0.000	0.0083 (4)	0.000
N1	0.0196 (8)	0.0248 (8)	0.0153 (8)	0.000	0.0066 (6)	0.000
N2	0.0209 (8)	0.0297 (9)	0.0193 (8)	0.000	0.0048 (6)	0.000
C5	0.0176 (8)	0.0151 (8)	0.0121 (8)	0.000	0.0073 (6)	0.000
C6	0.0142 (8)	0.0153 (8)	0.0137 (8)	0.000	0.0072 (6)	0.000
C2	0.0197 (9)	0.0185 (9)	0.0114 (8)	0.000	0.0058 (6)	0.000
C4	0.0174 (8)	0.0116 (8)	0.0125 (8)	0.000	0.0060 (6)	0.000
C1	0.0152 (8)	0.0177 (8)	0.0128 (8)	0.000	0.0028 (6)	0.000
C3	0.0176 (8)	0.0146 (8)	0.0136 (8)	0.000	0.0066 (6)	0.000

Geometric parameters (Å, º) top

F1—C6	1.3430 (19)	C6—C4ⁱ	1.447 (2)
N1—C1	1.147 (2)	C2—C3	1.434 (3)
N2—C2	1.147 (3)	C4—C3	1.376 (3)
C5—C6	1.342 (2)	C4—C6ⁱ	1.447 (2)
C5—C4	1.442 (2)	C1—C3	1.439 (3)
C5—H5	1.0828 (11)

C6—C5—C4	120.14 (15)	C3—C4—C5	120.32 (16)
C6—C5—H5	120.4 (11)	C3—C4—C6ⁱ	123.97 (16)
C4—C5—H5	119.4 (11)	C5—C4—C6ⁱ	115.71 (16)
C5—C6—F1	118.77 (15)	N1—C1—C3	179.8 (2)
C5—C6—C4ⁱ	124.14 (16)	C4—C3—C2	125.10 (16)
F1—C6—C4ⁱ	117.08 (15)	C4—C3—C1	120.01 (16)
N2—C2—C3	177.9 (2)	C2—C3—C1	114.89 (16)

Symmetry code: (i) −x+1, −y+1, −z+2.

(F4-TCNQ) top

Crystal data top

C₁₂F₄N₄	D_x = 1.701 Mg m⁻³
M_r = 276.16	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 4348 reflections
a = 9.1905 (18) Å	θ = 2.8–29.8°
b = 8.0558 (17) Å	µ = 0.16 mm⁻¹
c = 14.564 (3) Å	T = 100 K
V = 1078.3 (4) Å³	Block, yellow
Z = 4	0.33 × 0.12 × 0.11 mm
F(000) = 544

Data collection top

Bruker APEX-II CCD diffractometer	R_int = 0.182
φ and ω scans	θ_max = 30.6°, θ_min = 2.8°
24791 measured reflections	h = −13→13
1658 independent reflections	k = −11→11
1024 reflections with I > 2σ(I)	l = −20→20

Refinement top

Refinement on F²	91 parameters
Least-squares matrix: full	0 restraints
R[F² > 2σ(F²)] = 0.071	w = 1/[σ²(F_o²) + (0.0424P)² + 0.8314P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.133	(Δ/σ)_max < 0.001
S = 1.12	Δρ_max = 0.36 e Å⁻³
1658 reflections	Δρ_min = −0.37 e Å⁻³

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
F2	0.34968 (13)	0.99415 (17)	0.33988 (8)	0.0213 (3)
F1	0.34137 (13)	1.26315 (16)	0.44053 (9)	0.0204 (3)
N1	0.3887 (2)	0.6728 (3)	0.23144 (14)	0.0282 (5)
N2	0.6559 (2)	0.4467 (3)	0.42763 (14)	0.0238 (5)
C1	0.4446 (2)	0.6989 (3)	0.30024 (16)	0.0190 (5)
C3	0.5166 (2)	0.7150 (3)	0.38750 (15)	0.0159 (5)
C4	0.5081 (2)	0.8521 (3)	0.44267 (14)	0.0150 (5)
C6	0.4200 (2)	1.1343 (3)	0.47016 (15)	0.0158 (5)
C5	0.4255 (2)	0.9975 (3)	0.41807 (14)	0.0147 (5)
C2	0.5975 (2)	0.5685 (3)	0.41154 (15)	0.0180 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F2	0.0203 (6)	0.0229 (7)	0.0205 (7)	−0.0010 (6)	−0.0101 (5)	0.0038 (6)
F1	0.0191 (7)	0.0171 (7)	0.0251 (7)	0.0051 (6)	−0.0058 (6)	0.0045 (6)
N1	0.0291 (11)	0.0327 (13)	0.0229 (11)	0.0025 (10)	−0.0016 (9)	−0.0005 (10)
N2	0.0203 (10)	0.0250 (11)	0.0261 (11)	0.0017 (9)	−0.0004 (9)	−0.0027 (9)
C1	0.0183 (11)	0.0186 (12)	0.0200 (12)	0.0005 (10)	0.0043 (9)	0.0007 (10)
C3	0.0110 (9)	0.0188 (12)	0.0179 (11)	−0.0014 (9)	0.0019 (8)	0.0033 (9)
C4	0.0099 (9)	0.0190 (12)	0.0160 (11)	−0.0012 (9)	0.0021 (8)	0.0047 (9)
C6	0.0098 (10)	0.0179 (12)	0.0198 (11)	−0.0002 (9)	−0.0005 (8)	0.0076 (9)
C5	0.0107 (9)	0.0197 (12)	0.0137 (10)	−0.0022 (9)	−0.0028 (8)	0.0037 (9)
C2	0.0138 (10)	0.0214 (13)	0.0187 (11)	−0.0015 (10)	0.0031 (9)	−0.0025 (10)

Geometric parameters (Å, º) top

F2—C5	1.335 (2)	C3—C2	1.438 (3)
F1—C6	1.337 (2)	C4—C6ⁱ	1.436 (3)
N1—C1	1.146 (3)	C4—C5	1.441 (3)
N2—C2	1.143 (3)	C6—C5	1.338 (3)
C1—C3	1.439 (3)	C6—C4ⁱ	1.436 (3)
C3—C4	1.368 (3)

N1—C1—C3	174.6 (3)	F1—C6—C5	118.47 (19)
C4—C3—C2	123.3 (2)	F1—C6—C4ⁱ	118.4 (2)
C4—C3—C1	124.4 (2)	C5—C6—C4ⁱ	123.2 (2)
C2—C3—C1	112.3 (2)	F2—C5—C6	118.7 (2)
C3—C4—C6ⁱ	123.7 (2)	F2—C5—C4	118.1 (2)
C3—C4—C5	122.71 (19)	C6—C5—C4	123.21 (19)
C6ⁱ—C4—C5	113.60 (19)	N2—C2—C3	175.9 (2)

C2—C3—C4—C6ⁱ	0.7 (3)	F1—C6—C5—C4	179.24 (18)
C1—C3—C4—C6ⁱ	179.6 (2)	C4ⁱ—C6—C5—C4	−2.2 (4)
C2—C3—C4—C5	−179.41 (19)	C3—C4—C5—F2	2.8 (3)
C1—C3—C4—C5	−0.5 (3)	C6ⁱ—C4—C5—F2	−177.26 (18)
F1—C6—C5—F2	−1.5 (3)	C3—C4—C5—C6	−177.9 (2)
C4ⁱ—C6—C5—F2	177.06 (19)	C6ⁱ—C4—C5—C6	2.0 (3)

Symmetry code: (i) −x+1, −y+2, −z+1.

Acknowledgements

DC thanks IISER Bhopal for infrastructural and research facilities.

Funding information

Funding for this research was provided by: Fonds De La Recherche Scientifique–FNRS (POLYGRAD Project 22333186 to Basab Chattopadhyay); DST-INSPIRE (award to Rahul Shukla); The Leverhulme Trust (Early Career Fellowship supported by the Isaac Newton Trust – award to Guillaume Schweicher).

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Volume 75| Part 1| February 2019| Pages 71-78

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