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Bromide and Tribromide 4-Cyanobenzene-EthylenedithioTTF Radical Salts, by chemical and electrochemical routes. Afonso Varatojo, Gonçalo Lopes, Vasco da Gama, Gonçalo Oliveira, Isabel C. Santos, Elsa B. Lopes, Dulce Simão, Manuel Almeida, and Sandra Rabaça Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.9b00790 • Publication Date (Web): 19 Aug 2019 Downloaded from pubs.acs.org on August 25, 2019

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Crystal Growth & Design

Bromide and Tribromide 4-CyanobenzeneEthylenedithio-TTF Radical Salts, by chemical and electrochemical routes Afonso Varatojo†, Gonçalo Lopes†, Vasco da Gama†, Gonçalo Oliveira†, Isabel C. Santos†, Elsa B. Lopes†, Dulce Simão‡, Manuel Almeida† and Sandra Rabaça†,*

† C2TN,

Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico,

Universidade de Lisboa, E.N. 10 ao km 139,7, 2695-066 Bobadela LRS, Portugal.

‡ Centro

de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, P-

1049-001 Lisboa, Portugal.

Keywords: Dissymmetric tetrathiafulvalene donor; Cyanobenzenetetrathiafulvalene; C−N… interactions; X-ray crystal structure, electrical properties.

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Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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ABSTRACT

Two

salts

of

the

dissymmetric

TTF-derivative

4-cyanobenzene-ethylenedithio-

tetrathiafulvalene (4-CNB-EDT-TTF) with bromide and tribromide anions and with different stoichiometries, namely (1:1) (4-CNB-EDT-TTF)Br3 (1) and (4:1) (4-CNB-EDTTTF)4Br (2) were obtained by electrocrystallisation and diffusion methods, respectively. The crystal structures of these compounds, as determined by single crystal X-ray diffraction, are based on head-to-tail donor dimers with ring over ring overlap and donor stack arrangement, interleaved by anions depending on (1:1) or (4:1) salt, respectively. The 4:1 salt behaves as a Mott insulator. In both salts the donors are connected to adjacent donors through C–N…H–C interactions which can be described as an modified R24 (10)* synthon for 1 and a combination of R22(10) and R24(10) synthons for 2.

1. INTRODUCTION


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The structure of molecular materials and as a consequence their physical properties, are determined by the dominant intermolecular interactions. Hydrogen bonding, besides its important role in biological systems, is one of the most resourced tools in crystal engineering,[1-7] successfully employed to achieve specific crystal structures in molecular materials with desired electrical, magnetic or optical properties.[8-15]

Although C-N…H-C interactions are usually considered weak they were found to play a significant role in crystal engineering of electrically conducting and superconducting molecular materials. This was the case of the salts of the electron donor 5cyanobenzene ethylenedithio-tetrathiafulvalene (5-CNB-EDT-TTF) with a 4:1 stoichiometry and two-dimensional metallic properties recently reported by us.[16] These salts are characterised by interesting metallic and superconducting properties associated with a unique bilayer structure of the donors, promoted by C-N…H-C interactions, arranged in a network of R22 (10) and R24 (10) synthons, leading to a headto-head arrangement of donor molecules in paired layers (bilayers). [16,17,18] The possible ways in which the C-N…H-C interactions can be organised in a crystal structure


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are critically dependent on the position of the nitrile group and therefore other isomers of this donor started to be also studied in this respect. The 4-cyanobenzeneethylenedithio-tetrathiafulvalene (4-CNB-EDT-TTF) isomer of this donor, was recently reported by us [19] together with its first radical cation salt, (4-CNB-EDT-TTF)I3. In this salt, (4-CNB-EDT-TTF)+ radical cations are connected to adjacent dimers through CN…H-C interactions described as an R22(10) synthon, however without the double layer arrangement of donors observed in the 5-CNB-EDT-TTF salts.

In this context, it appears as of obvious interest to investigate whether similar interactions can take place in salts with other anions. In this work we report the study of its bromide salts where these interactions and similar synthons are present, although in different arrangements.

Scheme 1. Molecular scheme for the 5-CNB-EDT-TTF and 4-CNB-EDT-TTF donors.


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2. EXPERIMENTAL SECTION

2.1 General Methods: Crystals of radical cation salt 1 were obtained by electrocrystallisation, at room temperature, from a dichloromethane solution of the 4CNB-EDT-TTF donor and n-Bu4N Br3. Crystals of radical cation salt 2 were obtained by slow diffusion of saturated dichloromethane and acetonitrile solutions of 4-CNB-EDTTTF and n-Bu4N Br3. 4-CNB-EDT-TTF was prepared following a previous described procedure.[19] Commercially available n-Bu4N Br3 (Aldrich) was also purified by recrystallisation in dichloromethane and diethyl ether. The solvents were purified using standard procedures [20] and freshly distilled immediately before its use. Electrocrystallisation was performed in H-shaped two-compartment cells separated by a glass frit with Pt electrodes and under galvanostatic conditions.


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2.2 Synthesis: (4-CNB-EDT-TTF)Br3 (1). A dichloromethane solution of the donor 4CNB-EDT-TTF (1.5 × 10−3 M) and the anion salt n-Bu4N Br3 (4.5 × 10−3 M) were added to H-shaped cell and sealed under nitrogen. Initially the current density applied was about 0.5 μA/cm2 and after the first crystals become apparent on the electrode (~5 days) it was slowly increased to 2 μA/cm2. After approximately a total of 4 weeks of applying the current, dark brown elongated platelet shaped crystals grown on the anode were collected and washed with dichloromethane.

(4-CNB-EDT-TTF)4Br (2). A solution of 4-CNB-EDT-TTF (0.005 g, 1.35 mmol) in dichloromethane (5 mL) was added to a test tube, layered with a small amount of pure acetonitrile, and finally, it was carefully added on the top a solution of n-Bu4N Br3 (0.019 g, 0.04 mmol) in acetonitrile (2 mL). The mixture was kept at dark and room temperature during 2 weeks. Black prism-shaped crystals were collected by filtering and washed with dichloromethane.

2.3 X-Ray crystallography: Selected single crystals were mounted on a loop with protective oil and X-ray data was collected on a Bruker APEX II CCD detector


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diffractometer using graphite monochromated MoKα radiation (λ = 0.71073 Å) and operating in a φ and ω scans mode. A semi empirical absorption correction was carried out using SADABS.[21] Data collection, cell refinement and data reduction were done with the SMART and SAINT programs.[22] The structures were solved by direct methods using SIR97[23] and refined by full-matrix least-squares methods using the program SHELXL97[24] using the winGX software package.[25] Non-hydrogen atoms were refined with anisotropic thermal parameters whereas H-atoms were placed in idealized positions and allowed to refine riding on the parent C atom. Molecular graphics were prepared using Mercury.[26] The crystallographic data for compounds 1 and 2 are listed in Table S1 in the Supplementary Material.

CCDC 1916523-1916524 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

2.4 Computational Details:


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The tight-binding band structure calculations [27] were of the extended Hückel type, as implemented in the Caesar 1.0 chain of programs [28], and a modified Wolfsberg– Helmholtz formula was used to calculate the non-diagonal H values [29]. All valence electrons were taken into account in the calculations and the basis set consisted of Slater-type orbitals of double- quality for C and N 2s and 2p, S 3s and 3p and of single quality for H1s. The ionization potentials, contraction coefficients and exponents were taken exactly as in our previous work for (CN-BEDT-TTF)4I3.[17]

3. RESULTS AND DISCUSSION

3.1 Synthesis: Trials on crystallisation procedure were made in order to find the best crystal growth conditions for the radical cation salts starting from tribromide salts. During different trials it became evident that the tribromide salt, n-Bu4N Br3, if in direct contact with the donor in solution, is readily reduced, leading to the production of an amorphous dark product, probably compound 2, this being a limitation for the electrocrystallisation, and making the chemical oxidation route more favorable. The ability of the tribromide to oxidize the donor is in agreement with the oxidation potentials previously reported for


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the reactions Br3-+2e-3Br- E1/2=+0.7 V vs S.C.E.[30] and (4-CNB-EDT-TTF)(4-CNBEDT-TTF)++1e- E1/2=+0.512 V vs Ag/AgNO3.[19]

Under diffusion control the reaction between the donor and the tribromide anion salt is controlled by the thickness of the diffusion layer of acetonitrile and crystals of the compound 2 (4-CNB-EDT-TTF)4+Br- could be obtained.

The electrocrystallisation was found however capable to lead to the tribromide salt 1 (4-CNB-EDT-TTF) +Br3- if a large excess of donor was used relatively to n-Bu4N Br3 which was only added to the donor solution when this one was already placed in the Hshaped cell. This procedure doesn’t totally prevent the formation of an amorphous compound on the electrocrystallisation cell but allowed the growth of well-formed radical salt 1 crystals on the electrode.

3.2 Crystal Studies: Radical cation salts 1 and 2 crystallised affording single crystals suitable for their structural refinement based on X-ray diffraction. The crystal data and refinement details are summarized in Table S1.


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Compounds 1 crystallise in the monoclinic system, space group P21/c, with the cell parameters:

a = 9.5528(3) Å;

b = 13.5403(3) Å;

c = 14.3250(4) Å;

α =  =90;

β = 101.691(2); V = 1814.47(9) Å3. Figure 1 shows ORTEP diagrams with the corresponding atomic numbering schemes. The asymmetric unit contains one independent 4-CNB-EDT-TTF molecule and one tribromide anion located in general positions. The donor geometry is almost planar with exception of the dihydrodithiin ring which presents the usual half-chair conformation. Their bond lengths (Table 2) are identical within the experimental uncertainty to those observed in others 1:1 salts with this donor, [19,31] namely the central C=C which is more sensitive to the degree of oxidation: C5-C6 = 1.387(4) Å, while in the neutral molecule this bond was found to be 1.334(4) Å, 1.353(5) Å and 1.315(6) Å in different polymorphs.[6]


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Figure 1. ORTEP diagram of compound 1 drawn at 60% probability level with the atomic numbering scheme. Hydrogen atoms labelling were omitted for clarity.

The crystal structure of 1 is made of head to tail dimers, with ring over ring overlap. These donor dimers are arranged zig-zag in layers parallel to b,c , alternating along a with the tribromide anions (Figure 2).

Figure 2. Crystal structure of 1: (a) view along the c axis; (b) partial view along a of one layer of dimers and surrounding tribromide anions; (c) partial view along b of donor dimers and surrounding tribromide anions.


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Table 2. Bond lengths (Å) of (4-CNB-EDT-TTF)+z donor in different compounds with different oxidation states z. Bonds are identified in the scheme below together with the HOMO diagram.

(4-CNB-EDT-TTF)nA

A

z

1

Br3- 1

2

Br-

0.25

-

0

α-1 (*) β-1 (*)

-

0

a

b1

b2

b1’

b2’

c1

c2

c1’

c2’

d1

d2

1.387(4) 1.722(3) 1.714(3) 1.730(3) 1.722(3) 1.739(3) 1.727(3) 1.745(3) 1.739(3) 1.386(4) 1.362(4) 1.348(7) 1.760(4) 1.756(5) 1.757(5) 1.754(4) 1.747(5) 1.742(4) 1.747(4) 1.766(5) 1.401(6) 1.332(6) 1.378(7) 1.742(4) 1.736(5) 1.747(5) 1.734(4) 1.752(5) 1.748(4) 1.743(4) 1.742(5) 1.395(6) 1.356(6) 1.334(4) 1.773(3) 1.757(3) 1.760(3) 1.757(3) 1.741(3) 1.771(3) 1.752(3) 1.760(3) 1.396(4) 1.324(4) 1.353(5) 1.712(3) 1.754(3) 1.753(3) 1.711(4) 1.773(4) 1.733(3) 1.726(4) 1.779(4) 1.363(6) 1.305(5) 1.315(6) 1.790(4) 1.756(4) 1.758(4) 1.793(4) 1.717(4) 1.752(4) 1.742(4) 1.720(4) 1.421(6) 1.365(6)

(*) in reference [19]


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The donors in the dimers are connected by S…S and C…H short contacts (S3…S6, S4…S5 and C11…H1B) listed in Table S2, with the overlap mode depicted in Figure 3. Each donor in the dimer shows also  interactions with two other donors through a partial overlap between the donors (See Figure S1-S2 and Table S3). Each donor in the dimer also presents strong interactions to one of the Br3- anions located side-by-side to the donors, as denoted by short S…Br contacts (Table S2).

Figure 3. Dimers overlap mode top and lateral views in 1 with short contacts depicted as thin doted lines. The mean plane distance between donors (excluding the CH2CH2 fragments) is 3.371Å.

Besides the intra-dimer short contacts this structure presents inter-dimer and dimeranion short contacts. These include CN mediated interactions (C13-N1…H2B-C2, C13-


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N1…H1B-C1, C13-N1…C1 and C13-N1…S1), C…S short contacts (C9…S1, C11…S3 and C12…S3) and also several short contacts with tribromide anions (Table S2). A slightly modify R24(10)*synthon in Etters’s notation[32,33,34] can be identified in this crystal structure, similar to those previously described in related compounds based on the isomer donor 5-CNB-EDT-TTF[16,17,18]. However the shortest contact does not involves a CN…H-C (the C13-N1…H1B-C1 is slightly above the sum of the Van der Walls radii (2.788 Å (+0.050)) but C13-N1…C1 and C13-N1…S1 (See Figure 4 and Table 3).


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Figure 4. Interdonor short contacts, depicted as blue and red thin dotted lines, associated with a R24(10)* modified synthon in 1.

Table 3

C-N…H-C, C-N1…S and S…H-C interactions in 1 and 2.

Contacts

Synthon

Symmetry

Length(Å)

operation 1 C13-N1…H2B*-C2* C13-N1…C1* C13-N1…H1B*-C1*

R2

4(10)*

C13-N1…S1* 2 C14-N2…H21*-C21* C1-N1… H26A*-C26* C1-N1… H20A*-C20*

R22(10)

R24(10)

Length∑VdW(Å)

-x,1-y,1-z

2.562

-0.188

x,-1+y,z

3.110

-0.140

x,-1+y,z

2.788

+(0.050)

x,-1+y,z

3.059

-0.291

-x,-y,-z

2.646

-0.104

-1+x,y,-1+z 2.559

-0.191

-x,-y,1-z

-0.006

2.744

Compound 2 crystallises in the triclinic system, space group P-1, with the cell parameters: a = 8.9438(3) Å; b = 11.6355(4) Å; c = 15.4189(4) Å; α = 107.5040(10);


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β = 100.1480(10),  = 95.1820(10); V = 1488.68(8) Å3. Figure 5 shows ORTEP diagrams with the corresponding atomic numbering schemes. The asymmetric unit contains two independent 4-CNB-EDT-TTF molecules (A and B) located on general positions and one bromide anion in a special position. The geometry of the donors is almost planar with exception of the dihydrodithiin ring which presents the usual half-chair conformation. Their bond lengths (Table 2) are in the range of those observed in others 4:1 salts with the isomer 5-CNB-EDT-TTF donor.[16,17,18,35] In molecules A and B the central C=C bond lengths are significantly different (C4-C5 = 1.348(7)Å, C17C18 = 1.378(7)Å) indicating that Molecule B is more oxidised, than molecule A. These results suggest that molecule A is partially oxidised (½+) while molecule B is neutral.


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Figure 5. ORTEP diagrams of compounds 2 drawn at 60% probability level with the atomic numbering scheme. Hydrogen atoms labelling were omitted for clarity. Molecule A is represented in blue and molecule B is represented in red.

The crystal structure consists in donor stacks along a-b with repeat BBAA (Figure 6(a) and overlap modes depicted in Figure 7). The donor stacks are packed in layers which alternate along c with the bromide anionic layers (Figure 6(b)).

Figure 6. Crystal structure of 2 viewed: along c (a); along a-b (b).


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Besides the  interactions, the donors in the stacks are connected by C…H, S…H and H…H short contacts (C2…H11B, C3…H11B, C9…H11B, S9…H7B and H7B…H26B) in 2 (see Figures S3-S5 and Tables S4-S7). Due to the two crystallographically independent donor molecules they present three different overlap modes, the AA and BB overlap modes with a head to tail configuration and the AB with a head to head configuration, all with ring over bond type (Figure 7(a1), (a2) and (a3)).

Figure 7. Donor dimers overlap mode top and lateral view of 2: (a1) AB donors; (a2) AA donors; (a3) BB donors. The intermolecular distance between the average plane of the central TTF moieties is 3.799Å for AA donors dimers and 3.569Å for BB donors dimers.


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The non coplanarity of AB donors dimers prevents the calculation of the distance between these average planes.

Besides the donors short contacts in the stack, there are other short contacts. Between adjacent stacks, molecules A and B are connected by S…S (S3…S10) short contact and molecule A presents short contacts to bromide (Table S4).

Figure 8. Interdonor contacts, as blue and red thin dotted lines, associated with the network of R22(10) and R24(10) synthons in compound 2.


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Donor molecules A in nearby stacks are connected by the C-N…H-C interaction (C14N2…H21-C21) as shown in Figure 8. Molecules A and B are connected by a bifurcate CN interaction (C1-N1…H26-C26 and C1-N1…H20A-C20). These interactions between CN nitrogen and hydrogens on carbons alpha to the CN groups or of a dithiin ring, are responsible for a network of R22(10) and a R24(10) synthons as shown in Figure 8.

3.3 Hirshfeld Surface Analysis: The evaluation of the intermolecular interactions in the two structures considered in this work was also made in a more quantitative way using the Hirshfeld surface.[36,37,38] The surface distances to the nearest atoms outside this surface are represented as de and those inside as di, and from these properties it is possible to determine the type (C-N…H-C, C-N…S, C-N…S, C-N…N-C, π…π, S…S, etc…) and the proximity of intermolecular contacts in a molecular crystal.[39,40] The function

dnorm, is a normalized contact distance and takes into account the van der Waals radius of the appropriate atom internal or external to the surface. These distances are mapped on the Hirshfeld surface providing a 3D picture of the intermolecular closer contacts and are used to generate fingerprint plots, a 2D summary of intermolecular interactions.


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Hirshfeld surfaces and 2D fingerprint plots were created from the Crystal Explorer 17[41] program on the basis of the CIF generated from single-crystal X-ray diffraction studies. The Hirshfeld surfaces mapped over dnorm[38] are shown in Figure 9. The dnorm surface shows dark-red spots essentially result of the strong S...C, S…S and C-N…H-C interactions. 1 also shows significant donor…Br interactions.

Figure 9. Hirshfeld surfaces of compounds 1 (a) and 2 (b) for molecule A and (c) molecule B mapped with dnorm. The colour scale describes the distances longer (blue), equal (white) or shorter (red) than the van der Waals radii.

The fingerprint plots (Figure S6, S7 and S8) were delineated into H...H, All...Br, C...H, S...H, N…N, S...C, S…S, C…N, N…S, N…H, C…C contacts, showing characteristic pseudo-


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symmetry wings in the de and di diagonal axes with different contributions for the various types of interactions. Here it can be seen that the most significant intermolecular interactions in 1 are the tribromide mediated interactions, corresponding to 27.2% of the total interactions. In 2 the bromide mediated interactions are significantly lower, only 2.8% (molecule A) and 1.7% (molecule B) of the total interactions of each molecule. This is in agreement with the number of bromide anion short contacts of these compounds (Table S2 and S4), where compound 1 presents eight bromide mediated short contacts, Br…S and Br…H, in contrast with only two Br…H short contacts in 2. The S…S interactions present in 2 a higher contribution, 23.2% (molecule A) and 24.8% (molecule B), than in 1, with only 11.3%, in spite of only one S…S short contact observed in 2 and two S…S short contacts in 1. It is also possible to evaluate the role of the synthons associated with the C-H…N-C interaction; Both compounds present similar contribution for this interaction, 1 11%, 2 10.1% (molecule A) and 16.2% (molecule B). It’s also worth noticing the π-π interactions which are easily quantified through the Hirshfeld surface analyses; The C…C interactions correspond to 5.5% of the interactions in 1, and to 7.6% and 8.4% in 2 (for


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molecules A and B respectively) despite none of the salts presenting C…C short contacts. For further details see Supplementary material.

3.4 Intermolecular Interaction Energies: The intermolecular electronic interactions in compound 2 are essentially between molecules in layers, and they were estimated by the extended Hückel approach using double zeta basis set.[27,28] Taking into account the fact that in the unit cell there are four donor molecules (2 inequivalent) there are 8 distinct intermolecular interactions as identified in Figure 10 and listed in Table 6. The largest interactions α are along the stacks, namely α1 and α3 between equivalent molecules AA and BB, while interstack contacts β are about one order of magnitude smaller. If the donor layers were regular with only one type of molecules equally spaced the 4:1 stoichiometry would lead to a metallic system with a single band derived from the HOMO, filled to 7/8. However the fact that there are 4 molecules by unit cell, the bands derived from HOMO are split into four with the upper one 1/2 filled, as depicted in Figure 11. Due to the


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relatively small bandwidth the ½ filled band is expected to behave as a Mott insulator, as it is invariably the case in molecular materials. Unfortunately the small size of the crystals which could be obtained prevented the direct measurement of the conductivity in the single crystals. A pressed pellet was made from the material available and the conductivity measured in the pellet was 1.7x10-3 S cm-1at 300K, this value for the conductivity at room temperature is compatible with the expected Mott insulating behavior.[42-53]


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Figure 10. Detail of donor packing in 2 view of one donor layer along the c axis with the identification of the distinct intralayer interactions α1, α2, α3, β1, β2, β3, β4, β5.

Table 6. Absolute Values of HOMO−HOMO Intermolecular Electronic Interaction Energies (eV) in (4-CNB-EDT-TTF)4Br Crystals.

Interaction Inter. Energy Hij (eV) Interaction Inter. Energy Hij (eV) α1 (A-A)

-0.2046

β2 (B-A)

0.0106

α2 (A-B)

-0.1058

β3 (B-A)

-0.0594

α3 (B-B)

0.2816

β4 (A-A)

-0.0312

β1 (A-B)

-0.0192

β5 (B-B)

0.0347


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Figure 11. Calculated electronic band structure for 2. The dashed line refers to the Fermi level. The reciprocal space points (a*,b*) indicated are Γ=(0, 0); X=(0.5, 0) M=(0.5, 0.5) Y=(0, 0.5).

4. CONCLUSIONS

We

have

successfully

synthetized

and

characterised

two

4-cyanobenzene-

ethylenedithio-TTF radical salts with bromide and tribromide anions, obtained from the same reagents by chemical and electrochemical synthesis, respectively. Under the chemical route the donor was oxidized by the reduction of tribomide anions to bromide in


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solution, with the crystallisation of (4-CNB-EDT-TTF)4Br radical salt crystals. By electrocrystallisation the partial oxidized donors crystallised with tribromide anions in the electrode as the (4-CNB-EDT-TTF)Br3 radical salt.

The donor bilayer structure previously described for many 5-CNB-EDT-TTF salts is not observed in the reported 4-CNB-EDT-TTF salts in spite the presence of several C-N…HC interactions. In 1, the donor cations are arranged head-to-tail in dimers related by an inversion centre, with ring over ring overlap and intradimer π–π interactions. In 2 the donor cations have a stack arrangement. In the stacks, the two independent asymmetric unit donors with a head to head overlap mode are related by inversion centres, giving rise to three overlap modes molecules with intradonors π–π interactions. The salt 2 behaves as a Mott insulator. In both salts the donors present several S-, C-, and N-mediated contacts and are connected to adjacent donors through C–N…H–C interactions which can be described as an modified R24 (10)* synthon for 1 and of R22(10), R24(10) synthons for 2. It can be concluded that the C–N…H–C interactions observed in the 5-CNB-EDT-TTF


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compounds are also present and play an important role in the structure of the compounds of this isomer, however with a different arrangement of synthons.

ASSOCIATED CONTENT

Supporting Information. The Supporting Information is available free of charge on the ACS Publication website at DOI:xxxxxx.

The Table with the crystallographic data, the short contact lists, the  interactions tables and figures, the perspectives of dnorm mapped on Hirshfeld surface and the corresponding Fingerprint plots of compounds 1 and 2 and a Hirshfeld surface detailed analyses. (PDF)

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected]. Tel: +351 21 9946216


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Present Addresses

Gonçalo Oliveira present address: Universidade do Porto Instituto de Física dos Materiais Instituto de Nanociência e Nanotecnologia, Rua do Campo Alegre Porto, PT 4169-007.

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Funding Sources This work was supported by FCT (Portugal) through contracts LISBOA-01-0145FEDER-029666 and UID/Multi/04349/2013.

Notes The authors declare no competing financial interest.

ORCID

Afonso Varatojo


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Gonçalo Lopes

Vasco da Gama 0000-0001-5741-3373

Gonçalo Oliveira 0000-0002-2162-1493

Isabel C. Santos 0000-0001-8350-480X

Elsa B. Lopes 0000-0003-1855-7758

Dulce Simão 0000-0001-5493-8158

Manuel Almeida 0000-0003-2222-5641

Sandra Rabaça 0000-0002-5324-8013

ACKNOWLEDGMENT We would like to thank to the Fundação para a Ciência e Tecnologia (FCT) for the financial support.

REFERENCES


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“For Table of Contents Use Only”

Manuscript title

Bromide and Tribromide 4-Cyanobenzene-Ethylenedithio-TTF Radical Salts, by chemical and electrochemical routes

Authors list

Afonso Varatojo, Gonçalo Lopes, Vasco da Gama, Gonçalo Oliveira, Isabel C. Santos, Elsa B. Lopes, Dulce Simão, Manuel Almeida and Sandra Rabaça

TOC graphic

Synopsis


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The [4-CNB-EDT-TTF]Br3 (1) and [4-CNB-EDT-TTF]4Br (2) salts were obtained by electrocrystallisation and diffusion methods, respectively. The crystal structures are based on donor dimers stack arrangement, interleaved by anions. The 4:1 salt is a Mott insulator. Donors are connected through C-N…H-C interactions described as an modified R24 (10)* synthon for 1 and a combination of R22(10) and R24(10) synthons for 2.


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Scheme 1. Molecular scheme for the 5-CNB-EDT-TTF and 4-CNB-EDT-TTF donors. 123x42mm (300 x 300 DPI)



Figure 1. ORTEP diagram of compound 1 drawn at 60% probability level with the atomic numbering scheme. Hydrogen atoms labelling were omitted for clarity. 1119x635mm (96 x 96 DPI)


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Figure 2. Crystal structure of 1: (a) view along the c axis; (b) partial view along a of one layer of dimers and surrounding tribromide anions; (c) partial view along b of donor dimers and surrounding tribromide anions. 227x111mm (96 x 96 DPI)



Figure 3. Dimers overlap mode top and lateral views in 1 with short contacts depicted as thin doted lines. The mean plane distance between donors (excluding the CH2CH2 fragments) is 3.371Å. 222x74mm (96 x 96 DPI)


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Figure 4. Interdonor short contacts, depicted as blue and red thin dotted lines, associated with a R24(10)* modified synthon in 1. 245x181mm (96 x 96 DPI)



Figure 5. ORTEP diagrams of compounds 2 drawn at 60% probability level with the atomic numbering scheme. Hydrogen atoms labelling were omitted for clarity. Molecule A is represented in blue and molecule B is represented in red. 1321x615mm (96 x 96 DPI)


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Figure 6. Crystal structure of 2 viewed: along c (a); along a-b (b). 164x169mm (96 x 96 DPI)



Figure 7. Donor dimers overlap mode top and lateral view of 2: (a1) AB donors; (a2) AA donors; (a3) BB donors. The intermolecular distance between the average plane of the central TTF moieties is 3.799Å for AA donors dimers and 3.569Å for BB donors dimers. The non coplanarity of AB donors dimers prevents the calculation of the distance between these average planes. 333x109mm (96 x 96 DPI)


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Figure 8. Interdonor contacts, as blue and red thin dotted lines, associated with the network of R22(10) and R24(10) synthons in compound 2. 338x190mm (96 x 96 DPI)



Figure 9. Hirshfeld surfaces of compounds 1 (a) and 2 (b) for molecule A and (c) molecule B mapped with dnorm. The colour scale describes the distances longer (blue), equal (white) or shorter (red) than the van der Waals radii. 232x152mm (96 x 96 DPI)


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Figure 10. Detail of donor packing in 2 view of one donor layer along the c axis with the identification of the distinct intralayer interactions α1, α2, α3, β1, β2, β3, β4, β5. 195x184mm (96 x 96 DPI)



Figure 11. Calculated electronic band structure for 2. The dashed line refers to the Fermi level. The reciprocal space points (a*,b*) indicated are Γ=(0, 0); X=(0.5, 0) M=(0.5, 0.5) Y=(0, 0.5). 338x190mm (96 x 96 DPI)


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Bromide and Tribromide 4-Cyanobenzene ... - ACS Publications

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