sigma-hole interactions\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoSTRUCTURAL
CHEMISTRY
ISSN: 2053-2296

Pyridine-4-thiol as halo­gen-bond (HaB) acceptor: influence of the noncovalent inter­action in its reactivity

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aDepartment of Organic and Inorganic Chemistry, Institute of Chemical Research `Andrés M. del Río' (IQAR), Universidad de Alcalá, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain, and bDepartment of Analytical Chemistry, Physical Chemistry and Chemical Engineering, Institute of Chemical Research `Andrés M. del Río' (IQAR), Universidad de Alcalá, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
*Correspondence e-mail: martaeg.mosquera@uah.es

Edited by A. Peuronen, University of Sheffield, United Kingdom (Received 1 December 2022; accepted 3 March 2023; online 15 March 2023)

The study of pyri­dine-4-thiol as a halo­gen-bond (HaB) acceptor has allowed the isolation of its cocrystal with the HaB donor IC6F4I, namely, 1,2,4,5-tetra­fluoro-3,6-di­iodo­benzene bis­(pyri­din-1-ium-4-ylsul­fanide), C6F4I2·2C5H5NS (1), where the S atom is the HaB acceptor, while the pyri­dine position is blocked by the proton. Furthermore, the S atom acts a dual acceptor and also establishes an inter­action with the pyri­dinium proton from an adjacent mol­ecule. The presence of these inter­actions in 1 contributes to the stabilization of the zwitterionic form. This pre-organization seems to have an influence on the reactivity of the com­pound since when left in di­chloro­methane solution, an unusual activation of the C—Cl bond is observed that leads to the formation of the bis­[(pyri­din-1-ium-4-yl)sul­fan­yl]methane dication, while the Cl atoms are still present as chloride counter-ions, i.e. 4,4′-[methane­diyldi(sul­fanedi­yl)]dipyri­dinium dichloride, C11H12N2S22+·2Cl (2). In the crystal structure of 2 it is observed that the S atom is now acting as the donor part of a chalcogenide bond with the chloride anions.

1. Introduction

Halogen bonding (HaB) is a noncovalent inter­action that has attracted increasing attention during the last few decades, due to its role in crystal engineering, mol­ecular recognition pro­cesses, as a structure-directing tool and for the modulation of some physical properties (Politzer et al., 2007[Politzer, P., Lane, P., Concha, M. C., Ma, Y. & Murray, J. S. (2007). J. Mol. Model. 13, 305-311.]; Brammer et al., 2001[Brammer, L., Bruton, E. A. & Sherwood, P. (2001). Cryst. Growth Des. 1, 277-290.]; Aakeröy et al., 2013[Aakeröy, C. B., Baldrighi, M., Desper, J., Metrangolo, P. & Resnati, G. (2013). Chem. Eur. J. 19, 16240-16247.]; Cavallo et al., 2016[Cavallo, G., Metrangolo, P., Milani, R., Pilati, T., Priimagi, A., Resnati, G. & Terraneo, G. (2016). Chem. Rev. 116, 2478-2601.]). Also, its influence in reactivity and catalysis is increasingly acknowledged (Bulfield & Huber, 2016[Bulfield, D. & Huber, S. M. (2016). Chem. Eur. J. 22, 14434-14450.]; Bamberger et al., 2019[Bamberger, J., Ostler, F. & Mancheño, O. G. (2019). ChemCatChem, 11, 5198-5211.]; Jónsson et al., 2022[Jónsson, H. F., Sethio, D., Wolf, J., Huber, S. M., Fiksdahl, A. & Erdelyi, M. (2022). ACS Catal. 12, 7210-7220.]).

In our group, we have explored this inter­action in metallic com­plexes, both for main group and transition metals, and have observed the influence of HaB in the structural arrangement and reactivity (Dortéz et al., 2020[Dortéz, S., Fernández-Palacio, F., Damián, J., Gaiteiro, C., Ramos, J., Gómez-Sal, P. & Mosquera, M. E. G. (2020). CrystEngComm, 22, 870-877.]; Mosquera et al., 2016[Mosquera, M. E. G., Gomez-Sal, P., Díaz, I., Aguirre, L. M., Ienco, A., Manca, G. & Mealli, C. (2016). Inorg. Chem. 55, 283-291.], 2017[Mosquera, M. E. G., Egido, I., Hortelano, C., López-López, M. & Gómez-Sal, P. (2017). Faraday Discuss. 203, 257-283.]; Vidal et al., 2013[Vidal, F., Dávila, M. A., Torcuato, A. S., Gómez-Sal, P. & Mosquera, M. E. G. (2013). Dalton Trans. 42, 7074-7084.]). In this work, we are inter­ested in exploring pyri­dine-4-thiol as a HaB acceptor since there are two possible sites able to act as such, namely, the pyri­dine group and the S atom. Pyridines are one of the most popular types of HaB acceptor, a search in the Cambridge Structural Database (CSD; Version 5.42, with updates to September 2021; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]) for HaB inter­actions with C—X (X = Br or I) gives over 1000 hits. On the other hand, sulfur has two available lone pairs and can be a potent HaB acceptor since it can inter­act with more than one HaB donor, which can lead to inter­esting topologies. However, it has been less studied, although in a search in the CSD, there is a significant number of structures that display S atoms as a HaB acceptor; a search for C—X⋯S (X = Br or I) inter­actions in the angle range 160–180° gave 715 hits.

We have explored the inter­action of pyri­dine-4-thiol with the iconic IC6F4I mol­ecule as HaB donor. Inter­estingly, for this mol­ecule, it is not the pyri­dine group but the S atom that acts as the HaB acceptor, which is surprising since in the related com­pound Py–S–Py, it is the pyri­dine group that acts as the HaB acceptor (Arman et al., 2010[Arman, H. D., Kaulgud, T. & Tiekink, E. R. T. (2010). Acta Cryst. E66, o2683.]). Furthermore, the presence of C—S⋯I inter­actions in this cocrystal favours the stabilization of the zwitterionic form for pyri­dine-4-thiol (namely, pyri­din-1-ium-4-ylsul­fanide), which has important implications in the reactivity of the mol­ecule, and in fact an unusual C—Cl activation of the di­chloro­methane solvent is observed to give the bis­[(pyri­din-1-ium-4-yl)sul­fan­yl]methane dication.

The structures of 1,2,4,5-tetra­fluoro-3,6-di­iodo­benzene bis­(pyri­din-1-ium-4-ylsul­fanide), 1, and 4,4′-[methane­diyldi(sul­fanedi­yl)]dipyri­dinium dichloride, 2, are reported.

2. Experimental

2.1. General considerations

All manipulations were carried out under an inert atmos­phere of argon using standard Schlenk techniques. All sol­vents were dried prior to use following standard methods. All reagents were commercially obtained and were used without further purification.

2.2. Synthesis and crystallization

2.2.1. Synthesis of cocrystal 1

Pyridine-4-thiol (14 mg, 0.126 mmol) and 1,2,4,5-tetra­fluoro-3,6-di­iodo­benzene (50 mg, 0.126 mmol) were placed in a Schlenk flask. To this mixture, CH2Cl2 (25 ml) and tetra­hydro­furan (12 ml) were added. In order to com­pletely dissolve the solid, a brief reflux with a heat gun was performed. The solution was filtered and left to evaporate slowly. After three weeks, yellow crystals were isolated (yield: 63%, 40 mg).

2.2.2. Synthesis of (HPy–CH2–PyH)Cl2 (2)

To pyri­dine-4-thiol (50 mg, 0.45 mmol) in a Schlenk flask was added CH2Cl2 (10 ml). To this suspension, C6F4I2 (180 mg, 0.45 mmol) was added and, to dissolve the mixture com­pletely, tetra­hydro­furan (10 ml) were added. The solution was left to stir for 48 h. A clear solution was formed, to which a layer of hexane (16 ml) was added. After the solution had dif­fused into the hexane, brown crystals of 2 of good enough quality for analysis by X-ray dif­fraction were isolated (yield: 32%, 22 mg).

2.3. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1[link]. H atoms were placed geometrically and left riding on their parent atoms, except for the H atoms bonded to N1 in cocrystal 1, and C10 and N1 in salt 2, which were found in a Fourier map.

Table 1
Experimental details

Experiments were carried out at 200 K with Mo Kα radiation using a Nonius KappaCCD dif­fractometer. H atoms were treated by a mixture of independent and constrained refinement.

  1 2
Crystal data
Chemical formula C6F4I2·2C5H5NS C11H12N2S22+·2Cl
Mr 624.18 307.25
Crystal system, space group Monoclinic, P21/c Orthorhombic, F2dd
a, b, c (Å) 16.288 (8), 5.790 (4), 10.546 (9) 8.0815 (4), 17.2161 (5), 18.9254 (12)
α, β, γ (°) 90, 104.77 (3), 90 90, 90, 90
V3) 961.7 (12) 2633.1 (2)
Z 2 8
μ (mm−1) 3.53 0.79
Crystal size (mm) 0.21 × 0.18 × 0.15 0.4 × 0.3 × 0.25
 
Data collection
Absorption correction Multi-scan (Blessing, 1995[Blessing, R. H. (1995). Acta Cryst. A51, 33-38.])
Tmin, Tmax 0.371, 0.426
No. of measured, independent and observed [I > 2σ(I)] reflections 3983, 2181, 1458 4579, 1386, 1177
Rint 0.040 0.069
(sin θ/λ)max−1) 0.649 0.650
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.032, 0.069, 0.93 0.041, 0.101, 1.10
No. of reflections 2181 1386
No. of parameters 122 84
No. of restraints 0 1
Δρmax, Δρmin (e Å−3) 0.99, −1.09 0.35, −0.30
Absolute structure Flack x determined using 445 quotients [(I+) − (I)]/[(I+) + (I)] (Parsons et al., 2013[Parsons, S., Flack, H. D. & Wagner, T. (2013). Acta Cryst. B69, 249-259.])
Absolute structure parameter −0.01 (11)
Computer programs: COLLECT (Nonius, 2004[Nonius (2004). COLLECT. Nonius BV, Delft, The Netherlands.]), DIRAX/LSQ (Duisenberg et al., 2003[Duisenberg, A. J. M., Kroon-Batenburg, L. M. J. & Schreurs, A. M. M. (2003). J. Appl. Cryst. 36, 220-229.]), EVALCCD (Duisenberg et al., 2003[Duisenberg, A. J. M., Kroon-Batenburg, L. M. J. & Schreurs, A. M. M. (2003). J. Appl. Cryst. 36, 220-229.]), SHELXT2018 (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXS2013 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), SHELXL2014 and SHELXL2016 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]), ORTEP-3 for Windows (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]) and WinGX (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]).

3. Results and discussion

In order to achieve the crystallization of pyri­dine-4-thiol and IC6F4I, both com­pounds were dissolved in a mixture of CH2Cl2 and tetra­hydro­furan under argon. The suspension was heated briefly to obtain a clear solution (Fig. 2[link]). From this, orange crystals were isolated after three weeks by slow evaporation and the structure was determined by X-ray dif­fraction analysis.

[Figure 1]
Figure 1
The synthetic scheme for the preparation of cocrystal 1.

As shown in Fig. 2[link], a cocrystal has been formed incorporating two mol­ecules of pyri­dine-4-thiol and one of IC6F4I. This com­pound crystallized in the monoclinic space group P21/c. In this case, it is the S atom that acts as the HaB acceptor, which stabilizes the zwitterionic form of pyri­dine-4-thiol and, at the same time, the pyri­dine group is blocked by the proton. It should be noted that pyri­dine-4-thiol has been used frequently as a ligand for d- and f-block metals, and in those cases most often the zwitterionic form is the one present (CSD; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]).

[Figure 2]
Figure 2
Displacement ellipsoid plot (30% probability) of 1, showing (a) the C—I⋯S halo­gen bonding and (b) a view of the mol­ecular packing via halo­gen and hydro­gen bonding (dashed lines).

For the HaB established between the pyri­dine-4-thiol and the perfluorinated unit, the S⋯I distance is particularly short [3.158 (7) Å and C—I⋯S = 175.74 (5)°; Table 2[link]]; considering that the van der Waals radius sum is 3.78 Å (Bondi, 1964[Bondi, A. (1964). J. Phys. Chem. 68, 441-451.]), this inter­action implies a significant reduction of 16.4%. This short distance has also been observed in other com­pounds and, in all cases, the S atom has a negative charge, as in ours, as evidenced by a search in the CSD. As shown in Fig. 3[link](b), when the S atom is neutral, the majority of the inter­actions appear at S⋯I distances over 3.5 Å. For shorter distances [Fig. 3[link](a)], the majority of the examples imply the thyo­cyanate anion, SCN (Zuluaga et al., 2020[Zuluaga, A. R., Brock, A. J., Pfrunder, M. C., Phonsri, W., Murray, K. S., Harding, P., Micallef, A. S., Postnikov, P. S., Guselnikova, O. A., Yusubov, M. S., Yoshimura, A., Nemykin, V. N. & Zhdankin, V. V. (2015). J. Org. Chem. 80, 5783.]; Postnikov et al., 2015[Postnikov, P. S., Guselnikova, O. A., Yusubov, M. S., Yoshimura, A., Nemykin, V. N. & Zhdankin, V. V. (2015). J. Org. Chem. 80, 5783-5788.]; Bozopoulos & Rentzeperis, 1986[Bozopoulos, A. P. & Rentzeperis, P. J. (1986). Acta Cryst. C42, 1014-1016.]; Hirschberg et al., 2014[Hirschberg, M. E., Barthen, P., Frohn, H., Bläser, D., Tobey, B. & Jansen, G. (2014). J. Fluor. Chem. 163, 28-33.]).

Table 2
Selected inter­atomic distances (Å) and angles (°) for 1 and 2

1   2
I1⋯S2 3.158 (7) C10—S1 1.800 (4)
C1—S1 1.708 (5) C1—N1 1.344 (7)
C6—I1 2.107 (4) C5—S1 1.743 (5)
F2⋯H3 2.583 (7)    
       
C4—N1—C3 121.7 (4) S1—C10—S1i 116.3 (4)
F1—C7—C6 120.1 (4) N1—C1—C6 120.4 (5)
C7—C6—I1 121.0 (3) C5—S1—C10 104.89 (19)
Symmetry code: (i) x, −y + [{5\over 2}], −z + [{3\over 2}].
[Figure 3]
Figure 3
Histograms of the S⋯I distances for the S⋯I—C inter­action for (a) an S atom with a −1 charge (149 hits) and (b) an S atom with no charge (339 hits). In salt 2, the S⋯I distance is 3.158 (7) Å.

Sulfur can form bifurcated inter­actions and in this case behaves as such; on one side it inter­acts with the I atom and on the other side with the pyri­dinium N—H proton. This behaviour as a dual acceptor for both a halo­gen and a H atom has been observed previously; however, there are not many examples (Ding et al., 2020[Ding, X., Tuikka, M. & Haukka, M. (2020). Crystals, 10, 165.]).

The perfluorinated unit, p-C6F4I2, inter­acts from both sides to give discrete units formed by the inter­action of two mol­ecules of pyri­dine-4-thiol. These units are linked via weaker N—H⋯I and C—H⋯F inter­actions to give layers. As mentioned before, for the related Py–S–Py derivative, the inter­action is established between the pyri­dine group and the I atom to give an NPy⋯I—C contact (NPy⋯I = 2.838 Å and NPy⋯I—C = 177.93°) (Arman et al., 2010[Arman, H. D., Kaulgud, T. & Tiekink, E. R. T. (2010). Acta Cryst. E66, o2683.]). Hence, the preference for one group or the other is not very strong and may even be governed by kinetics and, if there is a com­peting aceptor, such is in the case of the proton, may direct the choice of the donor. In fact, for the thio­cyanate, which can also act as a dual donor, the formation of both HaB inter­actions with the N or the S atom has also been oberved for the same donors (Soldatova et al., 2020[Soldatova, N. S., Postnikov, P. S., Suslonov, V. V., Kissler, T. Yu., Ivanov, D. M., Yusubov, M. S., Galmés, B., Frontera, A. & Kukushkin, V. Yu. (2020). Org. Chem. Front. 7, 2230-2242.]).

When the reaction is performed on a larger scale and left stirring for 48 h, the solution changes colour to brown. It was possible to obtain crystals from this solution by dif­fusion into a hexane layer. The isolated brown crystals were of good enough quality to be determined by single-crystal X-ray dif­fraction. Inter­estingly, a methyl­ene-bridged sulfide resulting from the displacement of both Cl atoms from di­chloro­methane by two mol­ecules of pyri­dine-4-thiol, i.e. an [L2CH2]2+ dication, is formed. The displaced Cl atoms are still present as chloride counter-ions of the dication generated. The activation of the C—Cl bond has been observed previously, most often via a radical mechanism and less frequently via a nucleophilic mechanism. In fact, in our group, we have observed a similar reactivity when a zwitterionic betaine derivative com­posed of a nucleophilic carbene and a carbodimide (CDI-NHC) is left stirring for a long time in a di­chloro­methane solution (Sánchez-Roa et al., 2018[Sánchez-Roa, D., Santiago, T. G., Fernández-Millán, M., Cuenca, T., Palma, P., Cámpora, J. & Mosquera, M. E. G. (2018). Chem. Commun. 54, 12586-12589.]). As in this case, the activation of the C—Cl bond is promoted by the presence of zwitterionic species. As mentioned before, the zwitterionic form of pyri­dine-4-thiol is stabilized by the presence of the HaB inter­action, which implies a pre-organization that influences the outcome of the reaction. A similar behaviour has been described previously for isocyanates (Soldatova et al., 2020[Soldatova, N. S., Postnikov, P. S., Suslonov, V. V., Kissler, T. Yu., Ivanov, D. M., Yusubov, M. S., Galmés, B., Frontera, A. & Kukushkin, V. Yu. (2020). Org. Chem. Front. 7, 2230-2242.]).

Moreover, the evolution of pyri­dine-4-thiol in solution when it is left stirring in solution at 67 °C for 15 h gives the [HS–Py–Py]+ derivative, as has been reported previously (Ding et al., 2020[Ding, X., Tuikka, M. & Haukka, M. (2020). Crystals, 10, 165.]). In our case, the presence of IC6F4I favours the com­petitive reaction that implies the CH2Cl2 activation.

Compound 2 crystallized in an ortho­rhom­bic noncentrosymmetric spatial group Fdd2. The central C atom shows an angle slightly wider [116.3 (4)°] than that typical of sp3-hy­bridation, probably due to the presence of the S atoms; the value is similar to that previously reported for bis­[(pyri­din-4-yl)sul­fan­yl]methane (Carballo et al., 2007[Carballo, R., Covelo, B., García-Martínez, E., Lago, A. B. & Vázquez-López, E. M. (2007). Z. Anorg. Allg. Chem. 633, 780-782.], 2008a[Carballo, R., Covelo, B., Fernández-Hermida, N., García-Martinez, E., Lago, A. B. & Vázquez-López, E. M. (2008a). Cryst. Growth Des. 8, 995-1004.],b[Carballo, R., Covelo, B., Fernández-Hermida, N., García-Martínez, E., Lago, A. B. & Vázquez-López, E. M. (2008b). J. Mol. Struct. 892, 427-432.], 2009[Carballo, R., Covelo, B., Fernández-Hermida, N., Lago, A. B. & Vázquez-López, E. M. (2009). CrystEngComm, 11, 817.]; Lago et al., 2013[Lago, A. B., Carballo, R., Rodríguez-Hermida, S. & Vázquez-López, E. M. (2013). CrystEngComm, 15, 1563.], 2014[Lago, A. B., Carballo, R., Rodríguez-Hermida, S. & Vázquez-López, E. M. (2014). Cryst. Growth Des. 14, 3096.]). The S—CH2—S plane forms an angle of 78.66 (8)° with the planes of the pyri­dine rings, which are placed in opposite directions relative to the central CH2 unit; this arrangement is also observed in the reported derivatives where bis­[(pyri­din-4-yl)sul­fan­yl]methane behaves as a ligand (Carballo et al., 2007[Carballo, R., Covelo, B., García-Martínez, E., Lago, A. B. & Vázquez-López, E. M. (2007). Z. Anorg. Allg. Chem. 633, 780-782.], 2008a[Carballo, R., Covelo, B., Fernández-Hermida, N., García-Martinez, E., Lago, A. B. & Vázquez-López, E. M. (2008a). Cryst. Growth Des. 8, 995-1004.],b[Carballo, R., Covelo, B., Fernández-Hermida, N., García-Martínez, E., Lago, A. B. & Vázquez-López, E. M. (2008b). J. Mol. Struct. 892, 427-432.], 2009[Carballo, R., Covelo, B., Fernández-Hermida, N., Lago, A. B. & Vázquez-López, E. M. (2009). CrystEngComm, 11, 817.]; Lago et al., 2013[Lago, A. B., Carballo, R., Rodríguez-Hermida, S. & Vázquez-López, E. M. (2013). CrystEngComm, 15, 1563.], 2014[Lago, A. B., Carballo, R., Rodríguez-Hermida, S. & Vázquez-López, E. M. (2014). Cryst. Growth Des. 14, 3096.]). This arrangement is the origin of the conformational chirality shown by this com­pound (Fig. 4[link]). In our case, this disposition is also influenced by the presence of a hydro­gen bond involving one chloride anion and the proton bonded to atom C4 of the ring. This conformation is reinforced by a chalcogen bond established between the Cl and S atoms [S⋯Cl = 3.373 (4) Å and C—S⋯Cl = 156.94 (5)°], which is significantly shorter than the van der Waals radii radius sum (3.55 Å; Bondi, 1964[Bondi, A. (1964). J. Phys. Chem. 68, 441-451.]). Although the S atom can present two σ-holes, in this case, only one inter­action is observed with the chloride anion.

[Figure 4]
Figure 4
Displacement ellipsoid plot (30% probability) of 2, showing (a) a view along the bc plane, (b) a view along the a direction and (c) a view of the packing directed by hydro­gen and chalcogen bonds.

As mentioned before, the formation of the cation in 2 is an unusual reaction. Although similar substitution reactions have been reported for some secondary aliphatic (Souquet et al., 1993[Souquet, F., Martens, T. & Fleury, M. B. (1993). Synth. Commun. 23, 817-828.]), alicyclic (Matsumoto et al., 1984[Matsumoto, K., Hashimoto, S., Ikemi, Y. & Otani, S. (1984). Heterocycles, 22, 1417-1420.]) or heteroaromatic amines (Juliá et al., 1982[Juliá, S., Sala, P., Del Mazo, J., Sancho, M., Ochoa, C., Elguero, J., Fayet, J. & Vertut, M. (1982). J. Heterocycl. Chem. 19, 1141-1145.]; Zhao et al., 2011[Zhao, X., Wu, T., Bu, X. & Feng, P. (2011). Dalton Trans. 40, 8072-8074.]), the process usually takes place under special conditions, such as very high pressures or in highly polar solvent mixtures. Futhermore, it should be noted that the formation of the neutral equivalent bis­[(pyri­din-4-yl)sul­fan­yl]methane from pyri­dine-4-thiol in the presence of CH2Cl2 has been described previously in basic conditions, i.e. in an alcoholic solution with an excess of NaOH, the reaction taking several days to com­plete (Amoedo-Portela et al., 2005[Amoedo-Portela, A., Carballo, R., Casas, J. S., García-Martínez, E., Lago-Blanco, A. B., Sánchez-González, A., Sordo, J. & Vázquez-López, E. M. (2005). Z. Anorg. Allg. Chem. 631, 2241-2246.]). In our case, the mechanism is dif­ferent, as shown in the reaction pathway displayed in Fig. 5[link]. Taking into account our previous studies, we have detected that the first step that implies the substitution of the chloride is the rate-determining step, and it proceeds via an SN2 mechanism. This process leads to a reactive chloro­methyl inter­mediate –CH2Cl+ which evolves quickly to the final product where both Cl atoms have been displaced (Sánchez-Roa et al., 2018[Sánchez-Roa, D., Santiago, T. G., Fernández-Millán, M., Cuenca, T., Palma, P., Cámpora, J. & Mosquera, M. E. G. (2018). Chem. Commun. 54, 12586-12589.]). Hence, in this case, the IC6F4I role would be as a catalyst.

[Figure 5]
Figure 5
The proposed mechanism for the formation of salt 2.

4. Conclusions

The substituted pyri­dine pyri­dine-4-thiol can behave as a HaB acceptor, having a preference for the S atom as the acceptor. In the cocrystal obtained, the concomitant presence of a HaB and a hydro­gen bond contributes to the stabilization of the zwitterionic form of pyri­dine-4-thiol. This arrangement has an effect on the reactivity and the activation of CH2Cl2 is pro­moted to give the bis[­(4-pyri­din-1-ium-4-yl)sulfanyl]­methane dication, where two sulfide–pyri­dinium units are bonded to a –CH2 group. This moiety could only come from the activation of the di­chloro­methane present as a solvent. Inter­estingly, there are not many examples of this type of activity and the current study opens up the possibility of developing processes for the transformation of chorinated hydrocarbons.

Supporting information


Computing details top

For both structures, data collection: COLLECT (Nonius, 2004); cell refinement: DIRAX/LSQ (Duisenberg et al., 2003); data reduction: EVALCCD (Duisenberg et al., 2003). Program(s) used to solve structure: SHELXT2018 (Sheldrick, 2015a) for (1); SHELXS2013 (Sheldrick, 2008) for (2). Program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015b) for (1); SHELXL2014 (Sheldrick, 2015b) for (2). For both structures, molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

1,2,4,5-Tetrafluoro-3,6-diiodobenzene bis(pyridin-1-ium-4-ylsulfanide) (1) top
Crystal data top
C6F4I2·2C5H5NSF(000) = 588
Mr = 624.18Dx = 2.155 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 215 reflections
a = 16.288 (8) Åθ = 3.2–16.1°
b = 5.790 (4) ŵ = 3.53 mm1
c = 10.546 (9) ÅT = 200 K
β = 104.77 (3)°Prism, pale yellow
V = 961.7 (12) Å30.21 × 0.18 × 0.15 mm
Z = 2
Data collection top
Nonius KappaCCD
diffractometer
2181 independent reflections
Radiation source: Enraf Nonius FR5901458 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.040
Detector resolution: 9 pixels mm-1θmax = 27.5°, θmin = 3.8°
CCD rotation images, thick slices scansh = 021
Absorption correction: multi-scan
(Blessing, 1995)
k = 77
Tmin = 0.371, Tmax = 0.426l = 1313
3983 measured reflections
Refinement top
Refinement on F20 constraints
Least-squares matrix: fullHydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.032H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.069 w = 1/[σ2(Fo2) + (0.0226P)2]
where P = (Fo2 + 2Fc2)/3
S = 0.93(Δ/σ)max = 0.001
2181 reflectionsΔρmax = 0.99 e Å3
122 parametersΔρmin = 1.09 e Å3
0 restraints
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.

Refinement. Data collection was performed at 200 (2) K, with the crystals covered with perfluorinated ether oil. Single crystals were mounted on a Bruker-Nonius Kappa CCD single crystal diffractometer equipped with a graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å). Multiscan absorption correction procedures were applied to the data (Blessing, 1995). The structure was solved using the WINGX package, (Farrugia, 2012) by direct methods (SHELXS-2013) and refined using full-matrix least-squares against F2 (SHELXL-2016).(Sheldrick, 2015) All non-hydrogen atoms were anisotropically refined.

Full-matrix least-squares refinements were carried out by minimizing w(Fo2 - Fc2)2 with the SHELXL2014 weighting scheme and stopped at shift/err < 0.001. The final residual electron density maps showed no remarkable features. Crystallographic data for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-2222767 [1] and 2222766 [2].

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.8563 (3)0.0026 (8)0.2712 (4)0.0330 (10)
C20.7891 (3)0.1543 (8)0.2540 (5)0.0350 (11)
H20.748110.1361160.3032460.042*
C30.7815 (3)0.3326 (8)0.1679 (5)0.0397 (11)
H30.7359130.4390040.1580660.048*
C40.9026 (3)0.2109 (9)0.1069 (5)0.0400 (12)
H40.941340.2319380.0540240.048*
C50.9132 (3)0.0325 (9)0.1917 (4)0.0387 (11)
H50.9594310.0708320.1980360.046*
C60.5758 (3)0.4353 (8)0.4694 (4)0.0312 (10)
C70.5349 (3)0.6360 (8)0.4217 (5)0.0365 (11)
C80.4605 (3)0.7008 (8)0.4527 (5)0.0354 (11)
F10.56773 (17)0.7763 (5)0.3454 (3)0.0503 (8)
F20.42425 (16)0.8996 (4)0.4053 (3)0.0434 (7)
I10.69103 (2)0.34216 (5)0.42717 (3)0.03545 (12)
N10.8384 (3)0.3580 (7)0.0967 (4)0.0380 (9)
S10.87081 (7)0.2220 (2)0.38297 (12)0.0365 (3)
H10.831 (3)0.461 (8)0.043 (4)0.032 (14)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.032 (2)0.038 (3)0.030 (3)0.008 (2)0.008 (2)0.004 (2)
C20.035 (2)0.040 (3)0.036 (3)0.001 (2)0.018 (2)0.000 (2)
C30.045 (3)0.037 (3)0.041 (3)0.000 (2)0.018 (2)0.006 (2)
C40.032 (2)0.056 (3)0.036 (3)0.007 (2)0.014 (2)0.004 (2)
C50.033 (2)0.050 (3)0.035 (3)0.001 (2)0.013 (2)0.001 (2)
C60.027 (2)0.034 (3)0.034 (3)0.0017 (19)0.009 (2)0.004 (2)
C70.033 (2)0.041 (3)0.038 (3)0.005 (2)0.015 (2)0.003 (2)
C80.035 (2)0.030 (3)0.041 (3)0.004 (2)0.010 (2)0.002 (2)
F10.0504 (17)0.0465 (17)0.064 (2)0.0074 (13)0.0331 (16)0.0169 (15)
F20.0435 (15)0.0363 (16)0.0520 (18)0.0113 (12)0.0151 (14)0.0109 (13)
I10.03240 (17)0.03685 (19)0.0390 (2)0.00084 (13)0.01266 (13)0.00130 (15)
N10.046 (2)0.037 (2)0.032 (2)0.001 (2)0.0113 (19)0.003 (2)
S10.0339 (6)0.0380 (7)0.0417 (7)0.0022 (5)0.0170 (6)0.0026 (5)
Geometric parameters (Å, º) top
C1—C21.398 (6)C6—C71.370 (6)
C1—C51.415 (5)C6—C8i1.376 (6)
C1—S11.708 (5)C6—I12.107 (4)
C2—C31.360 (6)C7—F11.346 (5)
C3—N11.341 (6)C7—C81.385 (6)
C4—N11.332 (6)C8—F21.332 (5)
C4—C51.348 (6)
C2—C1—C5116.1 (4)C8i—C6—I1121.4 (3)
C2—C1—S1122.6 (3)F1—C7—C6120.1 (4)
C5—C1—S1121.3 (3)F1—C7—C8118.8 (4)
C3—C2—C1121.0 (4)C6—C7—C8121.1 (4)
N1—C3—C2120.0 (4)F2—C8—C6i120.1 (4)
N1—C4—C5120.6 (4)F2—C8—C7118.5 (4)
C4—C5—C1120.7 (4)C6i—C8—C7121.4 (4)
C7—C6—C8i117.6 (4)C4—N1—C3121.7 (4)
C7—C6—I1121.0 (3)
Symmetry code: (i) x+1, y+1, z+1.
4,4'-[Methanediyldi(sulfanediyl)]dipyridinium dichloride (2) top
Crystal data top
C11H12N2S22+·2ClF(000) = 1264
Mr = 307.25Dx = 1.55 Mg m3
Orthorhombic, F2ddMo Kα radiation, λ = 0.71073 Å
Hall symbol: F -2d 2Cell parameters from 211 reflections
a = 8.0815 (4) Åθ = 3.4–16.4°
b = 17.2161 (5) ŵ = 0.79 mm1
c = 18.9254 (12) ÅT = 200 K
V = 2633.1 (2) Å3Prism, brown
Z = 80.4 × 0.3 × 0.25 mm
Data collection top
Nonius KappaCCD
diffractometer
1177 reflections with I > 2σ(I)
Radiation source: Enraf Nonius FR590Rint = 0.069
Horizonally mounted graphite crystal monochromatorθmax = 27.5°, θmin = 3.2°
Detector resolution: 9 pixels mm-1h = 109
CCD rotation images, thick slices scansk = 2222
4579 measured reflectionsl = 2224
1386 independent reflections
Refinement top
Refinement on F2Hydrogen site location: mixed
Least-squares matrix: fullH atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.041 w = 1/[σ2(Fo2) + (0.0356P)2 + 12.059P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.101(Δ/σ)max = 0.001
S = 1.10Δρmax = 0.35 e Å3
1386 reflectionsΔρmin = 0.30 e Å3
84 parametersAbsolute structure: Flack x determined using 445 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013)
1 restraintAbsolute structure parameter: 0.01 (11)
0 constraints
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.

Refinement. Data collection was performed at 200 (2) K, with the crystals covered with perfluorinated ether oil. Single crystals were mounted on a Bruker-Nonius Kappa CCD single crystal diffractometer equipped with a graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å). Multiscan absorption correction procedures were applied to the data (Blessing, 1995). The structure was solved using the WINGX package, (Farrugia, 2012) by direct methods (SHELXS-2013) and refined using full-matrix least-squares against F2 (SHELXL-2016).(Sheldrick, 2015) All non-hydrogen atoms were anisotropically refined.

Full-matrix least-squares refinements were carried out by minimizing w(Fo2 - Fc2)2 with the SHELXL2014 weighting scheme and stopped at shift/err < 0.001. The final residual electron density maps showed no remarkable features. Crystallographic data for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-2222767 [1] and 2222766 [2].

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C101.9499 (10)1.250.750.0248 (15)
C11.6370 (7)1.0985 (3)0.9457 (3)0.0323 (13)
H11.58141.05460.96190.039*
C31.7388 (8)1.2237 (3)0.9678 (3)0.0300 (13)
H31.75411.26460.99920.036*
C41.7957 (7)1.2300 (3)0.8997 (3)0.0260 (12)
H41.84891.2750.88470.031*
C51.7723 (7)1.1679 (3)0.8535 (2)0.0212 (10)
C61.6931 (7)1.1010 (3)0.8784 (3)0.0268 (12)
H61.6791.05840.84870.032*
N11.6613 (6)1.1590 (3)0.9894 (2)0.0283 (11)
S11.83235 (15)1.16275 (8)0.76516 (6)0.0270 (4)
Cl1.25853 (17)1.16469 (7)0.86975 (6)0.0280 (3)
H10A2.014 (9)1.262 (3)0.793 (3)0.04*
H1N1.627 (9)1.153 (4)1.035 (4)0.05*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C100.025 (4)0.027 (4)0.023 (3)000.010 (3)
C10.034 (3)0.032 (3)0.031 (3)0.006 (2)0.000 (2)0.010 (2)
C30.043 (4)0.025 (3)0.021 (2)0.006 (3)0.001 (2)0.001 (2)
C40.035 (3)0.019 (3)0.024 (2)0.001 (2)0.000 (2)0.0028 (19)
C50.021 (2)0.024 (2)0.019 (2)0.000 (2)0.000 (2)0.0024 (18)
C60.031 (3)0.022 (2)0.027 (3)0.005 (2)0.002 (2)0.003 (2)
N10.036 (3)0.032 (3)0.017 (2)0.005 (2)0.0056 (19)0.0041 (18)
S10.0396 (8)0.0235 (6)0.0179 (6)0.0028 (6)0.0029 (6)0.0006 (5)
Cl0.0376 (7)0.0253 (6)0.0210 (6)0.0034 (5)0.0058 (6)0.0024 (5)
Geometric parameters (Å, º) top
C10—S11.800 (4)C3—C41.371 (7)
C10—S1i1.800 (4)C4—C51.394 (7)
C1—N11.344 (7)C5—C61.400 (7)
C1—C61.354 (7)C5—S11.743 (5)
C3—N11.342 (7)
S1—C10—S1i116.3 (4)C4—C5—S1127.1 (4)
N1—C1—C6120.4 (5)C6—C5—S1114.0 (4)
N1—C3—C4120.6 (5)C1—C6—C5119.7 (5)
C3—C4—C5118.9 (5)C3—N1—C1121.6 (5)
C4—C5—C6118.8 (4)C5—S1—C10104.89 (19)
Symmetry code: (i) x, y+5/2, z+3/2.
Selected interatomic distances (Å) and angles (°) for 1 and 2 top
12
I1···S23.158 (7)C10—S11.800 (4)
C1—S11.708 (5)C1—N11.344 (7)
C6—I12.107 (4)C5—S11.743 (5)
F2···H32.583 (7)
C4—N1—C3121.7 (4)S1—C10—S1i116.3 (4)
F1—C7—C6120.1 (4)N1—C1—C6120.4 (5)
C7—C6—I1121.0 (3)C5—S1—C10104.89 (19)
Symmetry code: (i) x, -y+5/2, -z+3/2.
 

Acknowledgements

The authors would like to acknowledge the support of Alcalá University, Spain, and the Madrid Regional Government.

Funding information

Funding for this research was provided by: Universidad de Alcala (grant No. PIUAH21/CC-028); Madrid Regional Government (grant No. EPUINV/2020/001).

References

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