Reaction-path calculations and crystal structures of 1,1′-(ethyl­ene-1,2-di­yl)dipyridinium dichloride dihydrate and 1,1′-(ethyl­ene-1,2-di­yl)dipyridinium dibromide

The design of new organic–inorganic hybrid ionic materials is of inter­est for various applications, particularly in the areas of crystal engineering, supra­molecular chemistry and materials science. The monohalogenated inter­mediates 1-(2-chloro­eth­yl)pyridinium chloride, C₅H₅NCH₂CH₂Cl⁺·Cl⁻, (I′), and 1-(2-bromo­eth­yl)pyridinium bromide, C₅H₅NCH₂CH₂Br⁺·Br⁻, (II′), and the ionic disubstituted products 1,1′-(ethyl­ene-1,2-di­yl)dipyridinium dichloride dihydrate, C₁₂H₁₄N₂²⁺·2Cl⁻·2H₂O, (I), and 1,1′-(ethyl­ene-1,2-di­yl)dipyridinium dibromide, C₁₂H₁₄N₂²⁺·2Br⁻, (II), have been isolated as powders from the reactions of pyridine with the appropriate 1,2-dihalo­ethanes. The monohalogenated inter­mediates (I′) and (II′) were characterized by multinuclear NMR spectroscopy, while (I) and (II) were structurally characterized using powder X-ray diffraction. Both (I) and (II) crystallize with half the empirical formula in the asymmetric unit in the triclinic space group P. The organic 1,1′-(ethyl­ene-1,2-di­yl)dipyridinium dications, which display approximate C2h symmetry in both structures, are situated on inversion centres. The components in (I) are linked via inter­molecular O—H...Cl, C—H...Cl and C—H...O hydrogen bonds into a three-dimensional framework, while for (II), they are connected via weak inter­molecular C—H...Br hydrogen bonds into one-dimensional chains in the [110] direction. The nucleophilic substitution reactions of 1,2-di­chloro­ethane and 1,2-di­bromo­ethane with pyridine have been investigated by ab initio quantum chemical calculations using the 6–31G** basis. In both cases, the reactions occur in two exothermic stages involving consecutive S_N2 nucleophilic substitutions. The isolation of the monosubstituted inter­mediate in each case is strong evidence that the second step is not fast relative to the first.

S1. Introduction

The design of new organic–inorganic hybrid ionic materials is of current inter­est for various applications, particularly in the areas of crystal engineering, supra­molecular chemistry and materials science (Kimizuka & Kunitake, 1996; Mitzi et al., 1999; Bonhomme & Kanatzidis, 1998; Wachhold & Kanatzidis, 2000) and also for optical semiconductor materials (Kagan et al., 1999; Li et al., 2008). We have previously reported the use of the 1,1'-methyl­enedipyridinium dication, i.e. [(C₅H₅N)₂CH₂]²⁺, in the syntheses of the organic–inorganic hybrid ionic complexes [(C₅H₅N)₂CH₂][MCl₄] (M = Zn, Cd; Al-Ktaifani & Rukiah, 2011), [(C₅H₅N)₂CH₂][PtCl_n] (n = 4 or 6; Al-Ktaifani & Rukiah, 2012a), [(C₅H₅N)₂CH₂][CuCl₄] and [(C₅H₅N)₂CH₂][AuCl₄]₂ (Al-Ktaifani & Rukiah, 2012b), whose molecular structures were confirmed by powder X-ray diffraction studies. Very recently, the organic–inorganic hybrid salts [(C₅H₅N)₂CH₂]₂[Fe(CN)₆]·8H₂O and [(C₅H₅N)₂CH₂][Fe(CN)₅NO]·5H₂O were synthesized and their nonlinear optical properties investigated (Zidan et al., 2015a,b). In a similar manner, the 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dication, i.e. [C₁₂H₁₄N₂]²⁺, was prepared for use in the syntheses of new organic–inorganic hybrid ionic complexes. During the course of these latter studies, we have isolated the monosubstituted inter­mediates 1-(2-chloro­ethyl)­pyridinium chloride and 1-(2-bromo­ethyl)­pyridinium bromide as pure compounds. The disubstituted 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dication was also isolated in a pure form with two different counter-ions, namely Cl^- and Br^-. While 1-(2-bromo­ethyl)­pyridinium bromide was reported recently as an inter­mediate in the preparation of chitosan-ethyl pyridinium bromide (Kathalikkattil et al., 2012) and 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide and bromo­ethyl­pyridinium bromide were reported previously as a mixture (Almarzoqi et al., 1986), to our knowledge, there is no report in the literature of the isolation of the pure monosubstituted inter­mediates [C₅H₅NCH₂CH₂Cl]Cl, (I'), and [C₅H₅NCH₂CH₂Br]Br, (II'), or of the molecular and crystal structures of [C₁₂H₁₄N₂]Cl₂.2H₂O, (I), and [C₁₂H₁₄N₂]Br₂, (II). The molecular structures of related salts of the 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dication have been reported, namely with iodate (Gholizadeh et al., 2011), dichromate(VI) (Gholizadeh et al., 2012), perchlorate, peroxodi­sulfate (Gholizadeh et al., 2014), bis­(1,2-di­cyano­ethene-1,2-di­thiol­ato-κ²S,S')cuprate(II) (Hu et al., 2013) and dibromidodichloridomercurate(II) (Wang et al., 2007).

We report here the NMR spectroscopic characterizations of 1-(2-chloro­ethyl)­pyridinium chloride and 1-(2-bromo­ethyl)­pyridinium bromide, the solid-state powder diffraction analyses of 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dichloride dihydrate, (I), and 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide, (II), and quantum chemical calculations of the reaction paths for the preparations of all four products.

S2. Experimental

All reactions and manipulations were carried out in air with reagent-grade solvents. ¹H and ¹³C{¹H} NMR spectra were recorded on a Bruker Bio spin 400 spectrometer. Microanalysis was performed using EURO EA. Powder X-ray diffraction measurements were performed using a Stoe STADI-P diffractometer.

S2.1. Synthesis and crystallization

S2.1.1. Preparation of 1-(2-chloro­ethyl)­pyridinium chloride, (I')

A mixture of ClCH₂CH₂Cl (3 ml, 38 mmol) and C₅H₅N (10 ml, 174 mmol) was heated to 333 K for 72 h to give a brown–orange precipitate, which was filtered off and washed with Et₂O. The volatiles were removed in a vacuum to afford a dark-beige powder (yield 4 g, 60%; m.p. 388 K). ¹H NMR (400 MHz, DMSO-d₆, 25): δ 4.32 (t, 2H, CH₂Cl, ³J = 5.6 Hz), 5.13 (t, 2H, CH₂, ³J = 5.6 Hz), 8.25 (m, 2H, py), 8.71 (m, 1H, py), 9.36 (m, 2H, py). ¹³C{¹H} NMR (DMSO-d₆): δ 44.24 (s, CH₂Cl), 61.51 (s, CH₂), 128.51 (s, py), 145.96 (s, py), 146.91 (s, py). Analysis calculated for C₇H₉Cl₂N: C 47.22, H 5.09, N 7.87%; found: C 47.22, H 4.90, N 8.07%.

S2.1.2. Preparation of 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dichloride dihydrate, (I)

A mixture of ClCH₂CH₂Cl (2 ml, 25 mmol) and C₅H₅N (10 ml, 124 mmol) was heated to 373 K for 72 h to give a brown precipitate, which was filtered off and washed with Et₂O. The volatiles were removed in a vacuum to afford a pale-brown powder [yield 5.25 g, 75%; m.p. 483 K (decomposition)]. ¹H NMR (400 MHz, DMSO-d₆, 25): δ 5.36 (s, 4H, CH₂), 8.21 (m, 4H, py), 8.40 (m, 2H, py), 8.66 (m, 4H, py). ¹³C{¹H} NMR (DMSO-d₆): δ 59.72 (s, CH₂), 128.79 (s, py), 145.95 (s, py), 147.04 (s, py).

S2.1.3. Preparation of 1-(2-bromo­ethyl)­pyridinium bromide, (II')

A mixture of BrCH₂CH₂Br (1 ml, 38 mmol) and C₅H₅N (10 ml, 116 mmol) was stirred at ambient temperature for 24 h to give a white precipitate, which was filtered off and washed with Et₂O. The volatiles were removed in a vacuum to afford a white powder (yield 1.4 g, 45%; m.p. 407 K). ¹H NMR (400 MHz, DMSO-d₆, 25): δ 4.14 (t, 2H, CH₂Br, ³J = 6 Hz), 5.10 (t, 2H, CH₂, ³J = 6 Hz), 8.24 (m, 2H, py), 8.71 (m, 1H, py), 9.18 (m, 2H, py). ¹³C{¹H} NMR (DMSO-d₆): δ 31.81 (s, CH₂Br), 60.94 (s, CH₂), 127.94 (s, py), 145.16 (s, py), 146.45 (s, py). Analysis calculated for C₇H₉Br₂N: C 31.49, H 3.40, N 5.25%; found: C 31.36, H 2.74, N 5.39%.

S2.1.4. Preparation of 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide, (II)

A mixture of BrCH₂CH₂Br (3 ml, 35 mmol) and C₅H₅N (10 ml, 174 mmol) was heated to 333 K for 72 h to give a white precipitate, which was filtered off and washed with Et₂O. The volatiles were removed in a vacuum to afford a white powder (yield 7 g, 60%; m.p. 398 K). ¹H NMR (400 MHz, D₂O, 25): δ 5.39 (s, 4H, CH₂), 8.18 (m, 4H, py), 8.71 (m, 2H, py), 8.90 (m, 4H, py). ¹³C{¹H} NMR (D₂O): δ 62.94 (s, CH₂), 132.02 (s, py), 147.56 (s, py), 150.37 (s, py).

S2.2. Refinement

The two ionic compounds 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dichloride dihydrate, (I), and 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide, (II), crystallize as very fine powders. Since no single crystal of sufficient size and quality could be obtained, the crystal structures were analyzed using powder X-ray diffraction. The powder samples of (I) and (II) were lightly ground in a mortar, loaded into two Mylar foils and fixed onto the sample holder with a mask of suitable inter­nal diameter (8.0 mm). Powder X-ray diffraction data were collected at room temperature with a Stoe STADI-P diffractometer using monochromatic Cu K_α1 radiation (λ = 1.54060 Å) selected with an incident beam curved-crystal germanium Ge(111) monochromator and using the Stoe transmission geometry (horizontal set-up) with a linear position sensitive detector (PSD). The patterns were scanned over the angular range 6.0–80.0° (2θ) for both (I) and (II). The peak positions were identified with the program WinPLOTR (Roisnel & Rodríguez-Carvajal, 2001). Pattern indexing was performed using the program DicVol6.0 (Boultif & Louër, 2004). The first 20 lines of the powder pattern were completely indexed on the basis of triclinic cells for both (I) and (II). The figures of merit were sufficiently high to support the indexing results obtained [M(20) = 53.4, F(20) = 100.4 (0.0071, 28) for (I); M(20) = 75.8, F(20) = 124.31 (0.0060, 27) for (II) (de Wolff et al., 1968; Smith & Snyder, 1979)]. The whole powder diffraction pattern for each case was subsequently refined with cell and resolution constraints (LeBail method; Le Bail et al., 1988) with triclinic space group P1 using the `profile matching' option of the program FullProf (Rodriguez-Carvajal, 1990). The number of formula units per unit cell for (I) and (II) was estimated to be Z = 1, or Z' = 0.5 for the space group P1. Both structures were solved using direct methods (EXPO2013; Altomare et al. 2013). The initial structures from EXPO2013 were used as input to GSAS (Larson & Von Dreele, 2004) implemented in EXPGUI (Toby, 2001) for Rietveld refinements. During refinement, the effect of the asymmetry of low-order peaks was corrected using a pseudo-Voigt description of the peak shape (Thompson et al., 1987), which allows for angle dependent asymmetry with axial divergence (Finger et al., 1994). Microstrain broadening by Stephens (1999). [included to include citation; please reword to make a readabel sentence] Both the asymmetry parameters of this function, S/L and D/L, were fixed at 0.024 during the Rietveld refinement. For the final refinement, H atoms were introduced at calculated positions for aromatic CH and methyl­ene CH₂ groups. The coordinates of these H atoms were fixed during refinement. In the case of salt (I), the water H atoms were located in a difference Fourier map and their coordinates were refined with soft restraints on the bond lengths and angle (O—H = 0.82±0.01 Å and H—O—H = 104.5±1°) until suitable hydrogen-bond geometry was attained, at which point these atoms were fixed for the final refinement. No other soft restraints were imposed for either structure. The final refinement used anisotropic atomic displacement parameters for Cl and water O atoms in (I) and for Br atoms in (II), isotropic atomic displacement parameters for C and N atoms, and a fixed global isotropic atomic displacement parameter (0.035 Ų) for H atoms. Intensities were corrected for absorption effects with a function for a plate sample in transmission geometry with a µ.d value of 0.56 for (I) and 1.70 for (II) (µ is the absorption coefficient and d is the sample thickness). The µ.d values were determined experimentally. A spherical-harmonic correction (Von Dreele, 1997) of intensities for preferred orientation was applied in the final refinement with two coefficients for (I) and eight coefficients for (II). This led to better molecular geometry with better agreement factors. The final Rietveld plots for (I) and (II) are given in Fig. 1. Crystal data and refinement details are provided in Table 1.

S2.3. Ab initio calculation of reaction pathway

Ab initio computational studies were performed for the reactions of 1,2-di­chloro­ethane and of 1,2-di­bromo­ethane with pyridine. Activation energies for these two reactions were calculated at several levels of theory. The geometries and the ground-state energies of the rea­cta­nts, transition states and products were fully optimized at the Hartree–Fock level of theory using different basis sets (from STO up to 6-31G**) as implemented in the Firefly quantum chemical package (A. Granovsky; https://classic.chem.msu.su/gran/firefly/index.html), which is partially based on the GAMESS (US) source code (Schmidt et al., 1993). Gabedit (Allouche, 2011), a graphical user inter­face for computational chemistry software, was used to build the structures of all starting molecules. The optimized geometries of the rea­ctant molecules were put into reaction and the full path of the reaction was found using the HF/6-31G** basis set. The optimization and frequency calculations for all of the transition states were carried out in order to determine accurately the shape of the transition state. Each of the transition state structures gave only one imaginary harmonic vibrational frequency, corresponding to the formation of the C—N bonds. The intrinsic reaction coordinates (IRCs) were also calculated to generate the paths of the reactions–rea­cta­nts to transition states to products (Gonzales & Schlegel, 1989; Ayala & Schlegel, 1997). These calculations were performed using the same conditions used for optimization and frequency.

S3. Results and discussion

The ionic disubstitution products 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dichloride dihydrate, (I), and 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide, (II), were prepared directly by treatment of the appropriate reagent XCH₂CH₂X (X = Cl, Br) with pyridine under atmospheric pressure and slightly elevated temperatures [373 K for (I) and 333 K for (II); Almarzoqi et al., 1986]. The monosubstituted inter­mediates 1-(2-chloro­ethyl)­pyridinium chloride, (I'), and 1-(2-bromo­ethyl)­pyridinium bromide, (II'), were isolated at 333 and 298 K, respectively. Each inter­mediate was obtained as a pure salt, viz. (I') as a very hygroscopic brown–orange powder and (II') as a white powder that was less hygroscopic than (I'). Although both (I') and (II') are insoluble in common organic solvents, they have good solubility in water and di­methyl sulfoxide.

The molecular structures of (I') and (II') were confirmed in solution by both ¹H and ¹³C{¹H} (DMSO-d₆) NMR spectroscopy. As expected, the ¹H and ¹³C{¹H} NMR spectra for (I') and (II') are similar, very informative and consistent with their molecular structures. The ¹H NMR spectrum of (I') gave the expected five resonances for five environmentally different proton groups in their expected chemical shift regions. It showed triplets at 4.32 and 5.13 p.p.m., which correspond to the CH₂Cl and NCH₂ groups, respectively. Three resonances at 8.25, 8.71 and 9.36 p.p.m. correspond to three environmentally different proton groups of pyridine. The ¹H NMR peaks of (I') are in their expected intensity ratios. The ¹³C{¹H} NMR spectrum of (I') also showed the expected five singlets for five different C-atom environments with the C of the CH₂Cl group at 44.24 p.p.m., the NCH₂ C atom at 61.51 p.p.m., and the three environmentally different C-atom centres of pyridine at 128.51, 145.96 and 146.91 p.p.m. In a similar manner, the ¹H NMR spectrum of (II') also showed the expected five resonances for five different proton environments, two triplets at 4.14 and 5.10 p.p.m. for the CH₂Cl and NCH₂ groups, respectively, with the pyridine ring resonances at 8.24, 8.71 and 9.18 p.p.m. The ¹³C{¹H} NMR spectrum of (II') gave five singlets for five environmentally different C centres at 31.81 (CH₂Br), 60.94 (NCH₂), and 127.94, 145.16 and 146.45 p.p.m. (pyridine).

The two salts (I) and (II) were isolated pure, and their molecular and crystal structures (Fig. 2) were determined by powder X-ray diffraction. Both ionic compounds crystallize with a half-formula in the asymmetric unit (Z' = 0.5) in space group P1. Salt (I) is a dihydrate, while (II) crystallizes in anhydrous form. The organic dications in both structures reside on inversion centres located at the mid-point of the C1—C1ⁱ bond [symmetry code: (i) -x+1, -y+1, -z+1]. They also display noncrystallographic C2h symmetry with bond distances and angles comparable to normal values (Tables 2 and 3; Allen et al., 1987). The crystal packing is characterized by weak inter­molecular O—H···Cl, C—H···Cl and C—H···O inter­actions for (I) (Table 4) and C—H···Br short contacts for (II) (Table 5). In (I), the Cl^- anions and water molecules are linked via O—H···Cl hydrogen bonds to form one-dimensional chains along the [100] direction. Furthermore, the dications and the Cl^- anions are also linked via weak C—H···Cl hydrogen bonds to form one-dimensional chains along [001]. These two chains are crosslinked via weak inter­molecular C—H···O and C—H···Cl hydrogen bonds to form a three-dimensional network (Fig. 3a). In (II), weak inter­molecular C—H···Br hydrogen bonds link the dications and Br^- anions into one-dimensional chains along the [110] direction (Fig. 3b).

Quantum chemical calculations of the reaction paths for the syntheses of (I) and (II) show that the reaction in each case occurs in two consecutive S_N2 steps (see Scheme 1). The details of geometries and ground state energies, in terms of all of the basis sets used for the ab initio calculation of the reaction pathways, are not the subject of this paper; so only the results of the HF/6-31G** basis set will be presented here. The geometries and energies of the rea­cta­nts, transition states and final product molecules, along with the energy profiles, are shown in Fig. 4 for the formation of (I) and in Fig. 5 for (II), including both steps of the reaction pathway in each case.

For the reaction of pyridine with 1,2-di­chloro­ethane, which gives (I') and (I), in the first step, as the N atom of the pyridine molecule approaches a C-atom centre of ClCH₂ClCH₂Cl to form the N—C bond, the Cl atom bonded to the same C-atom centre begins to depart from the opposite side of the C-atom environment to form a first transition state (Fig. 4a) in which a partial C···N bond (2.456 Å) is formed while the C—Cl bond starts to break (C···Cl = 2.776 Å). The N···C···Cl angle in the transition state is 82.3°. The energy difference between the rea­cta­nts and the transition state (the activation energy) is found to be 0.087334 Hartree. Next, the incoming pyridine molecule comes closer to the carbon centre forming a covalent C—N bond (1.494 Å), while at the same time the Cl completes its egress to form the monosubstituted product 1-(2-chloro­ethyl)­pyridinium chloride, (I'). The energy difference between (I') and the rea­cta­nts is negative (-0.009745 Hartree); that is, the reaction is exothermic. In (I'), the torsion angle Cl—C—C—N is gauche (68.3°), and there is a weak hydrogen bond between an ortho-H and the Cl^- anion. In the second step, another pyridine molecule attacks the second C-atom centre of (I') from the side opposite Cl, concomitant with C—Cl bond elongation, forming a second transition state (Fig. 4b). The calculated transition state has a partial C···N bond (2.077 Å), a partial C···Cl bond (2.461 Å) and a nearly linear N···C···Cl angle (159.5°). The activation energy of this step is calculated as 0.04204 Hartree. The final product (I) is obtained when the C—N bond is fully formed (1.49 Å) and the covalent C—Cl bond is completely ruptured. The dication geometry of (I) is in accord with the results obtained from the powder X-ray diffraction study (Table 2). The distances between the Cl^- anion and ortho-H atoms of the dication from the computational study (average H···Cl distance = 2.396 Å) are shorter than those obtained by X-ray diffraction (average 2.68 Å). Such discrepancies are not surprising, because the calculations apply to isolated molecules in the gas phase. The energy difference between the inter­mediate and the final product (I) is -0.03438 Hartree, indicating another exothermic reaction. It can be concluded, in addition, that the second substitution step is sufficiently slow, relative to the first (albeit not necessarily slower than the first step in absolute terms), to permit the isolation of the monosubstitution product (I').

A similar calculation has been carried out for the reaction of 1,2-di­bromo­ethane and pyridine. As expected the reaction is found to take place in two consecutive S_N2 steps. Fig. 5 shows the relevant geometrical parameters. In the first step, the monosubstituted product (II') is obtained via a transition state (Fig. 5a) in which the C···N and C···Br bonds are elongated, with distances 2.399 and 2.915 Å, respectively, and with N···C···Br = 82.8°. The activation energy of this step is 0.09152 Hartree. The enthalpy of formation for (II') is negative (-0.002366 Hartree). For the second step, the final product (II) is obtained via a transition state (Fig. 5b) in which the stretched C···N and C···Br bond lengths are 2.019 and 2.567 Å, respectively, with C···N···Br = 162.3°. This step is also exothermic (-0.023327 Hartree), with an activation energy of 0.0467 Hartree. The calculated geometry of the dication is also consistent with that obtained by X-ray diffraction (Table 3). Similarly to the case of the first product (I), the average Br-to-dication contact distances from the computation are also found to be shorter than those obtained experimentally (calculated 2.682 Å, experimental 2.79 Å). For both products (I) and (II), by comparing the geometries of the transition states of the two reaction paths, and through experimental isolation of (I') and (II'), it can be concluded that the reaction mechanisms consist of two consecutive S_N2 nucleophilic substitutions.

Structure description

The design of new organic–inorganic hybrid ionic materials is of current inter­est for various applications, particularly in the areas of crystal engineering, supra­molecular chemistry and materials science (Kimizuka & Kunitake, 1996; Mitzi et al., 1999; Bonhomme & Kanatzidis, 1998; Wachhold & Kanatzidis, 2000) and also for optical semiconductor materials (Kagan et al., 1999; Li et al., 2008). We have previously reported the use of the 1,1'-methyl­enedipyridinium dication, i.e. [(C₅H₅N)₂CH₂]²⁺, in the syntheses of the organic–inorganic hybrid ionic complexes [(C₅H₅N)₂CH₂][MCl₄] (M = Zn, Cd; Al-Ktaifani & Rukiah, 2011), [(C₅H₅N)₂CH₂][PtCl_n] (n = 4 or 6; Al-Ktaifani & Rukiah, 2012a), [(C₅H₅N)₂CH₂][CuCl₄] and [(C₅H₅N)₂CH₂][AuCl₄]₂ (Al-Ktaifani & Rukiah, 2012b), whose molecular structures were confirmed by powder X-ray diffraction studies. Very recently, the organic–inorganic hybrid salts [(C₅H₅N)₂CH₂]₂[Fe(CN)₆]·8H₂O and [(C₅H₅N)₂CH₂][Fe(CN)₅NO]·5H₂O were synthesized and their nonlinear optical properties investigated (Zidan et al., 2015a,b). In a similar manner, the 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dication, i.e. [C₁₂H₁₄N₂]²⁺, was prepared for use in the syntheses of new organic–inorganic hybrid ionic complexes. During the course of these latter studies, we have isolated the monosubstituted inter­mediates 1-(2-chloro­ethyl)­pyridinium chloride and 1-(2-bromo­ethyl)­pyridinium bromide as pure compounds. The disubstituted 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dication was also isolated in a pure form with two different counter-ions, namely Cl^- and Br^-. While 1-(2-bromo­ethyl)­pyridinium bromide was reported recently as an inter­mediate in the preparation of chitosan-ethyl pyridinium bromide (Kathalikkattil et al., 2012) and 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide and bromo­ethyl­pyridinium bromide were reported previously as a mixture (Almarzoqi et al., 1986), to our knowledge, there is no report in the literature of the isolation of the pure monosubstituted inter­mediates [C₅H₅NCH₂CH₂Cl]Cl, (I'), and [C₅H₅NCH₂CH₂Br]Br, (II'), or of the molecular and crystal structures of [C₁₂H₁₄N₂]Cl₂.2H₂O, (I), and [C₁₂H₁₄N₂]Br₂, (II). The molecular structures of related salts of the 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dication have been reported, namely with iodate (Gholizadeh et al., 2011), dichromate(VI) (Gholizadeh et al., 2012), perchlorate, peroxodi­sulfate (Gholizadeh et al., 2014), bis­(1,2-di­cyano­ethene-1,2-di­thiol­ato-κ²S,S')cuprate(II) (Hu et al., 2013) and dibromidodichloridomercurate(II) (Wang et al., 2007).

We report here the NMR spectroscopic characterizations of 1-(2-chloro­ethyl)­pyridinium chloride and 1-(2-bromo­ethyl)­pyridinium bromide, the solid-state powder diffraction analyses of 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dichloride dihydrate, (I), and 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide, (II), and quantum chemical calculations of the reaction paths for the preparations of all four products.

All reactions and manipulations were carried out in air with reagent-grade solvents. ¹H and ¹³C{¹H} NMR spectra were recorded on a Bruker Bio spin 400 spectrometer. Microanalysis was performed using EURO EA. Powder X-ray diffraction measurements were performed using a Stoe STADI-P diffractometer.

A mixture of ClCH₂CH₂Cl (3 ml, 38 mmol) and C₅H₅N (10 ml, 174 mmol) was heated to 333 K for 72 h to give a brown–orange precipitate, which was filtered off and washed with Et₂O. The volatiles were removed in a vacuum to afford a dark-beige powder (yield 4 g, 60%; m.p. 388 K). ¹H NMR (400 MHz, DMSO-d₆, 25): δ 4.32 (t, 2H, CH₂Cl, ³J = 5.6 Hz), 5.13 (t, 2H, CH₂, ³J = 5.6 Hz), 8.25 (m, 2H, py), 8.71 (m, 1H, py), 9.36 (m, 2H, py). ¹³C{¹H} NMR (DMSO-d₆): δ 44.24 (s, CH₂Cl), 61.51 (s, CH₂), 128.51 (s, py), 145.96 (s, py), 146.91 (s, py). Analysis calculated for C₇H₉Cl₂N: C 47.22, H 5.09, N 7.87%; found: C 47.22, H 4.90, N 8.07%.

A mixture of ClCH₂CH₂Cl (2 ml, 25 mmol) and C₅H₅N (10 ml, 124 mmol) was heated to 373 K for 72 h to give a brown precipitate, which was filtered off and washed with Et₂O. The volatiles were removed in a vacuum to afford a pale-brown powder [yield 5.25 g, 75%; m.p. 483 K (decomposition)]. ¹H NMR (400 MHz, DMSO-d₆, 25): δ 5.36 (s, 4H, CH₂), 8.21 (m, 4H, py), 8.40 (m, 2H, py), 8.66 (m, 4H, py). ¹³C{¹H} NMR (DMSO-d₆): δ 59.72 (s, CH₂), 128.79 (s, py), 145.95 (s, py), 147.04 (s, py).

A mixture of BrCH₂CH₂Br (1 ml, 38 mmol) and C₅H₅N (10 ml, 116 mmol) was stirred at ambient temperature for 24 h to give a white precipitate, which was filtered off and washed with Et₂O. The volatiles were removed in a vacuum to afford a white powder (yield 1.4 g, 45%; m.p. 407 K). ¹H NMR (400 MHz, DMSO-d₆, 25): δ 4.14 (t, 2H, CH₂Br, ³J = 6 Hz), 5.10 (t, 2H, CH₂, ³J = 6 Hz), 8.24 (m, 2H, py), 8.71 (m, 1H, py), 9.18 (m, 2H, py). ¹³C{¹H} NMR (DMSO-d₆): δ 31.81 (s, CH₂Br), 60.94 (s, CH₂), 127.94 (s, py), 145.16 (s, py), 146.45 (s, py). Analysis calculated for C₇H₉Br₂N: C 31.49, H 3.40, N 5.25%; found: C 31.36, H 2.74, N 5.39%.

A mixture of BrCH₂CH₂Br (3 ml, 35 mmol) and C₅H₅N (10 ml, 174 mmol) was heated to 333 K for 72 h to give a white precipitate, which was filtered off and washed with Et₂O. The volatiles were removed in a vacuum to afford a white powder (yield 7 g, 60%; m.p. 398 K). ¹H NMR (400 MHz, D₂O, 25): δ 5.39 (s, 4H, CH₂), 8.18 (m, 4H, py), 8.71 (m, 2H, py), 8.90 (m, 4H, py). ¹³C{¹H} NMR (D₂O): δ 62.94 (s, CH₂), 132.02 (s, py), 147.56 (s, py), 150.37 (s, py).

Ab initio computational studies were performed for the reactions of 1,2-di­chloro­ethane and of 1,2-di­bromo­ethane with pyridine. Activation energies for these two reactions were calculated at several levels of theory. The geometries and the ground-state energies of the rea­cta­nts, transition states and products were fully optimized at the Hartree–Fock level of theory using different basis sets (from STO up to 6-31G**) as implemented in the Firefly quantum chemical package (A. Granovsky; https://classic.chem.msu.su/gran/firefly/index.html), which is partially based on the GAMESS (US) source code (Schmidt et al., 1993). Gabedit (Allouche, 2011), a graphical user inter­face for computational chemistry software, was used to build the structures of all starting molecules. The optimized geometries of the rea­ctant molecules were put into reaction and the full path of the reaction was found using the HF/6-31G** basis set. The optimization and frequency calculations for all of the transition states were carried out in order to determine accurately the shape of the transition state. Each of the transition state structures gave only one imaginary harmonic vibrational frequency, corresponding to the formation of the C—N bonds. The intrinsic reaction coordinates (IRCs) were also calculated to generate the paths of the reactions–rea­cta­nts to transition states to products (Gonzales & Schlegel, 1989; Ayala & Schlegel, 1997). These calculations were performed using the same conditions used for optimization and frequency.

The ionic disubstitution products 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dichloride dihydrate, (I), and 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide, (II), were prepared directly by treatment of the appropriate reagent XCH₂CH₂X (X = Cl, Br) with pyridine under atmospheric pressure and slightly elevated temperatures [373 K for (I) and 333 K for (II); Almarzoqi et al., 1986]. The monosubstituted inter­mediates 1-(2-chloro­ethyl)­pyridinium chloride, (I'), and 1-(2-bromo­ethyl)­pyridinium bromide, (II'), were isolated at 333 and 298 K, respectively. Each inter­mediate was obtained as a pure salt, viz. (I') as a very hygroscopic brown–orange powder and (II') as a white powder that was less hygroscopic than (I'). Although both (I') and (II') are insoluble in common organic solvents, they have good solubility in water and di­methyl sulfoxide.

The molecular structures of (I') and (II') were confirmed in solution by both ¹H and ¹³C{¹H} (DMSO-d₆) NMR spectroscopy. As expected, the ¹H and ¹³C{¹H} NMR spectra for (I') and (II') are similar, very informative and consistent with their molecular structures. The ¹H NMR spectrum of (I') gave the expected five resonances for five environmentally different proton groups in their expected chemical shift regions. It showed triplets at 4.32 and 5.13 p.p.m., which correspond to the CH₂Cl and NCH₂ groups, respectively. Three resonances at 8.25, 8.71 and 9.36 p.p.m. correspond to three environmentally different proton groups of pyridine. The ¹H NMR peaks of (I') are in their expected intensity ratios. The ¹³C{¹H} NMR spectrum of (I') also showed the expected five singlets for five different C-atom environments with the C of the CH₂Cl group at 44.24 p.p.m., the NCH₂ C atom at 61.51 p.p.m., and the three environmentally different C-atom centres of pyridine at 128.51, 145.96 and 146.91 p.p.m. In a similar manner, the ¹H NMR spectrum of (II') also showed the expected five resonances for five different proton environments, two triplets at 4.14 and 5.10 p.p.m. for the CH₂Cl and NCH₂ groups, respectively, with the pyridine ring resonances at 8.24, 8.71 and 9.18 p.p.m. The ¹³C{¹H} NMR spectrum of (II') gave five singlets for five environmentally different C centres at 31.81 (CH₂Br), 60.94 (NCH₂), and 127.94, 145.16 and 146.45 p.p.m. (pyridine).

The two salts (I) and (II) were isolated pure, and their molecular and crystal structures (Fig. 2) were determined by powder X-ray diffraction. Both ionic compounds crystallize with a half-formula in the asymmetric unit (Z' = 0.5) in space group P1. Salt (I) is a dihydrate, while (II) crystallizes in anhydrous form. The organic dications in both structures reside on inversion centres located at the mid-point of the C1—C1ⁱ bond [symmetry code: (i) -x+1, -y+1, -z+1]. They also display noncrystallographic C2h symmetry with bond distances and angles comparable to normal values (Tables 2 and 3; Allen et al., 1987). The crystal packing is characterized by weak inter­molecular O—H···Cl, C—H···Cl and C—H···O inter­actions for (I) (Table 4) and C—H···Br short contacts for (II) (Table 5). In (I), the Cl^- anions and water molecules are linked via O—H···Cl hydrogen bonds to form one-dimensional chains along the [100] direction. Furthermore, the dications and the Cl^- anions are also linked via weak C—H···Cl hydrogen bonds to form one-dimensional chains along [001]. These two chains are crosslinked via weak inter­molecular C—H···O and C—H···Cl hydrogen bonds to form a three-dimensional network (Fig. 3a). In (II), weak inter­molecular C—H···Br hydrogen bonds link the dications and Br^- anions into one-dimensional chains along the [110] direction (Fig. 3b).

Quantum chemical calculations of the reaction paths for the syntheses of (I) and (II) show that the reaction in each case occurs in two consecutive S_N2 steps (see Scheme 1). The details of geometries and ground state energies, in terms of all of the basis sets used for the ab initio calculation of the reaction pathways, are not the subject of this paper; so only the results of the HF/6-31G** basis set will be presented here. The geometries and energies of the rea­cta­nts, transition states and final product molecules, along with the energy profiles, are shown in Fig. 4 for the formation of (I) and in Fig. 5 for (II), including both steps of the reaction pathway in each case.

For the reaction of pyridine with 1,2-di­chloro­ethane, which gives (I') and (I), in the first step, as the N atom of the pyridine molecule approaches a C-atom centre of ClCH₂ClCH₂Cl to form the N—C bond, the Cl atom bonded to the same C-atom centre begins to depart from the opposite side of the C-atom environment to form a first transition state (Fig. 4a) in which a partial C···N bond (2.456 Å) is formed while the C—Cl bond starts to break (C···Cl = 2.776 Å). The N···C···Cl angle in the transition state is 82.3°. The energy difference between the rea­cta­nts and the transition state (the activation energy) is found to be 0.087334 Hartree. Next, the incoming pyridine molecule comes closer to the carbon centre forming a covalent C—N bond (1.494 Å), while at the same time the Cl completes its egress to form the monosubstituted product 1-(2-chloro­ethyl)­pyridinium chloride, (I'). The energy difference between (I') and the rea­cta­nts is negative (-0.009745 Hartree); that is, the reaction is exothermic. In (I'), the torsion angle Cl—C—C—N is gauche (68.3°), and there is a weak hydrogen bond between an ortho-H and the Cl^- anion. In the second step, another pyridine molecule attacks the second C-atom centre of (I') from the side opposite Cl, concomitant with C—Cl bond elongation, forming a second transition state (Fig. 4b). The calculated transition state has a partial C···N bond (2.077 Å), a partial C···Cl bond (2.461 Å) and a nearly linear N···C···Cl angle (159.5°). The activation energy of this step is calculated as 0.04204 Hartree. The final product (I) is obtained when the C—N bond is fully formed (1.49 Å) and the covalent C—Cl bond is completely ruptured. The dication geometry of (I) is in accord with the results obtained from the powder X-ray diffraction study (Table 2). The distances between the Cl^- anion and ortho-H atoms of the dication from the computational study (average H···Cl distance = 2.396 Å) are shorter than those obtained by X-ray diffraction (average 2.68 Å). Such discrepancies are not surprising, because the calculations apply to isolated molecules in the gas phase. The energy difference between the inter­mediate and the final product (I) is -0.03438 Hartree, indicating another exothermic reaction. It can be concluded, in addition, that the second substitution step is sufficiently slow, relative to the first (albeit not necessarily slower than the first step in absolute terms), to permit the isolation of the monosubstitution product (I').

A similar calculation has been carried out for the reaction of 1,2-di­bromo­ethane and pyridine. As expected the reaction is found to take place in two consecutive S_N2 steps. Fig. 5 shows the relevant geometrical parameters. In the first step, the monosubstituted product (II') is obtained via a transition state (Fig. 5a) in which the C···N and C···Br bonds are elongated, with distances 2.399 and 2.915 Å, respectively, and with N···C···Br = 82.8°. The activation energy of this step is 0.09152 Hartree. The enthalpy of formation for (II') is negative (-0.002366 Hartree). For the second step, the final product (II) is obtained via a transition state (Fig. 5b) in which the stretched C···N and C···Br bond lengths are 2.019 and 2.567 Å, respectively, with C···N···Br = 162.3°. This step is also exothermic (-0.023327 Hartree), with an activation energy of 0.0467 Hartree. The calculated geometry of the dication is also consistent with that obtained by X-ray diffraction (Table 3). Similarly to the case of the first product (I), the average Br-to-dication contact distances from the computation are also found to be shorter than those obtained experimentally (calculated 2.682 Å, experimental 2.79 Å). For both products (I) and (II), by comparing the geometries of the transition states of the two reaction paths, and through experimental isolation of (I') and (II'), it can be concluded that the reaction mechanisms consist of two consecutive S_N2 nucleophilic substitutions.

Refinement details

The two ionic compounds 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dichloride dihydrate, (I), and 1,1'-(ethyl­ene-1,2-diyl)dipyridinium dibromide, (II), crystallize as very fine powders. Since no single crystal of sufficient size and quality could be obtained, the crystal structures were analyzed using powder X-ray diffraction. The powder samples of (I) and (II) were lightly ground in a mortar, loaded into two Mylar foils and fixed onto the sample holder with a mask of suitable inter­nal diameter (8.0 mm). Powder X-ray diffraction data were collected at room temperature with a Stoe STADI-P diffractometer using monochromatic Cu K_α1 radiation (λ = 1.54060 Å) selected with an incident beam curved-crystal germanium Ge(111) monochromator and using the Stoe transmission geometry (horizontal set-up) with a linear position sensitive detector (PSD). The patterns were scanned over the angular range 6.0–80.0° (2θ) for both (I) and (II). The peak positions were identified with the program WinPLOTR (Roisnel & Rodríguez-Carvajal, 2001). Pattern indexing was performed using the program DicVol6.0 (Boultif & Louër, 2004). The first 20 lines of the powder pattern were completely indexed on the basis of triclinic cells for both (I) and (II). The figures of merit were sufficiently high to support the indexing results obtained [M(20) = 53.4, F(20) = 100.4 (0.0071, 28) for (I); M(20) = 75.8, F(20) = 124.31 (0.0060, 27) for (II) (de Wolff et al., 1968; Smith & Snyder, 1979)]. The whole powder diffraction pattern for each case was subsequently refined with cell and resolution constraints (LeBail method; Le Bail et al., 1988) with triclinic space group P1 using the `profile matching' option of the program FullProf (Rodriguez-Carvajal, 1990). The number of formula units per unit cell for (I) and (II) was estimated to be Z = 1, or Z' = 0.5 for the space group P1. Both structures were solved using direct methods (EXPO2013; Altomare et al. 2013). The initial structures from EXPO2013 were used as input to GSAS (Larson & Von Dreele, 2004) implemented in EXPGUI (Toby, 2001) for Rietveld refinements. During refinement, the effect of the asymmetry of low-order peaks was corrected using a pseudo-Voigt description of the peak shape (Thompson et al., 1987), which allows for angle dependent asymmetry with axial divergence (Finger et al., 1994). Microstrain broadening by Stephens (1999). [included to include citation; please reword to make a readabel sentence] Both the asymmetry parameters of this function, S/L and D/L, were fixed at 0.024 during the Rietveld refinement. For the final refinement, H atoms were introduced at calculated positions for aromatic CH and methyl­ene CH₂ groups. The coordinates of these H atoms were fixed during refinement. In the case of salt (I), the water H atoms were located in a difference Fourier map and their coordinates were refined with soft restraints on the bond lengths and angle (O—H = 0.82±0.01 Å and H—O—H = 104.5±1°) until suitable hydrogen-bond geometry was attained, at which point these atoms were fixed for the final refinement. No other soft restraints were imposed for either structure. The final refinement used anisotropic atomic displacement parameters for Cl and water O atoms in (I) and for Br atoms in (II), isotropic atomic displacement parameters for C and N atoms, and a fixed global isotropic atomic displacement parameter (0.035 Ų) for H atoms. Intensities were corrected for absorption effects with a function for a plate sample in transmission geometry with a µ.d value of 0.56 for (I) and 1.70 for (II) (µ is the absorption coefficient and d is the sample thickness). The µ.d values were determined experimentally. A spherical-harmonic correction (Von Dreele, 1997) of intensities for preferred orientation was applied in the final refinement with two coefficients for (I) and eight coefficients for (II). This led to better molecular geometry with better agreement factors. The final Rietveld plots for (I) and (II) are given in Fig. 1. Crystal data and refinement details are provided in Table 1.

Computing details

For both compounds, data collection: WinXPOW (Stoe & Cie, 1999); data reduction: WinXPOW (Stoe & Cie, 1999); program(s) used to solve structure: EXPO2014 (Altomare et al., 2013); program(s) used to refine structure: GSAS (Larson & Von Dreele, 2004); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012).

Figures

	Fig. 1. The final Rietveld plots for (a) (I) and (b) (II). Observed data points are indicated by dots, the best-fit profile (upper trace) and the difference pattern (lower trace) are solid lines. The vertical bars indicate the positions of Bragg peaks.
	Fig. 2. The molecular structures of (a) (I) and (b) (II), showing the atom-labelling schemes. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as small spheres of arbitrary radii. [Symmetry code: (i) -x+1, -y+1, -z+1].
	Fig. 3. Crystal packing of salts (a) (I) and (b) (II). Hydrogen bonds are shown as dashed lines.
	Fig. 4. Energy profile of the reaction pathway leading to the formation of salt (I), showing (a) the first stage and (b) the econd stage reactions with optimized structures for the reactants, transition states and products. HF/6–31G** optimized selected bond lengths (Å) and angles (°) and the energies at 0 K for the reactants, transition states and products are given.
	Fig. 5. Energy profile of the reaction pathway leading to the formation of salt (II), showing (a) the first and (b) the second stage reactions, with optimized structures for the reactants, transition states and products. HF/6–31G** optimized selected bond lengths (Å) and angles (°) and the energies at 0 K for the reactants, transition states and products are given.

(I) 1,1'-(Ethylene-1,2-diyl)dipyridinium dichloride dihydrate

Crystal data

C12H14N2^2+·2Cl^−·2H2O	V = 359.24 (10) Å^3
Mr = 293.18	Z = 1
Triclinic, P1	F(000) = 154
Hall symbol: -P 1	Dx = 1.355 Mg m^−3
a = 5.3844 (5) Å	Cu Kα1 radiation, λ = 1.5406 Å
b = 7.3682 (7) Å	µ = 4.04 mm^−1
c = 9.7405 (9) Å	T = 298 K
α = 104.3951 (10)°	Particle morphology: fine powder
β = 102.234 (1)°	light brown
γ = 97.2263 (8)°	flat sheet, 8 × 8 mm

Data collection

Stoe transmission STADI-P diffractometer	Data collection mode: transmission
Radiation source: sealed X-ray tube	Scan method: step
Ge 111 monochromator	2θmin = 6.0°, 2θmax = 79.98°, 2θstep = 0.02°
Specimen mounting: Powder loaded into two Mylar foils

Refinement

Least-squares matrix: full	96 parameters
Rp = 0.030	0 restraints
Rwp = 0.040	H-atom parameters not refined
Rexp = 0.033	Weighting scheme based on measured s.u.'s
R(F^2) = 0.03813	(Δ/σ)max = 0.02
3700 data points	Background function: GSAS Background function number 1 with 20 terms. Shifted Chebyshev function of 1st kind 1: 746.182 2: -728.274 3: 262.549 4: -17.4620 5: -27.4982 6: 2.25918 7: 23.4441 8: -11.7577 9: -13.7218 10: 22.1644 11: -8.15113 12: -3.07390 13: 6.41738 14: -4.25520 15: 1.06054 16: 2.97031 17: 0.782776 18: -1.31641 19: 0.399884 20: 0.350968
Profile function: CW Profile function number 4 with 27 terms Pseudovoigt profile coefficients as parameterized in Thompson et al. (1987. Asymmetry correction of Finger et al. (1994). Microstrain broadening by Stephens (1999). #1(GU) = 0.000 #2(GV) = 0.000 #3(GW) = 10.752 #4(GP) = 0.000 #5(LX) = 0.000 #6(ptec) = 0.00 #7(trns) = 19.02 #8(shft) = -1.7005 #9(sfec) = 0.00 #10(S/L) = 0.0240 #11(H/L) = 0.0240 #12(eta) = 0.6000 Peak tails are ignored where the intensity is below 0.0010 times the peak Aniso. broadening axis 0.0 0.0 1.0

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
CL1	0.9544 (4)	0.7257 (3)	0.3268 (2)	0.03258
C1	0.5157 (16)	0.4052 (9)	0.4520 (8)	0.027 (3)*
H1A	0.49308	0.3111	0.50724	0.035*
H1B	0.68695	0.41206	0.4321	0.035*
N1	0.3156 (13)	0.3418 (9)	0.3118 (7)	0.017 (3)*
C2	0.0927 (19)	0.2342 (11)	0.3044 (8)	0.012 (3)*
H2	0.06585	0.19788	0.38678	0.035*
C3	−0.0991 (15)	0.1748 (11)	0.1736 (11)	0.023 (3)*
H3	−0.25261	0.09591	0.16601	0.035*
C4	−0.0500 (17)	0.2271 (11)	0.0549 (11)	0.024 (4)*
H4	−0.17775	0.18791	−0.03443	0.035*
C5	0.1805 (19)	0.3376 (12)	0.0670 (10)	0.028 (4)*
H5	0.21399	0.3765	−0.01388	0.035*
C6	0.3659 (15)	0.3986 (11)	0.1976 (10)	0.029 (4)*
H6	0.52197	0.47406	0.20547	0.035*
O1w	0.4693 (9)	0.9409 (7)	0.2825 (5)	0.04227
H1w	0.59945	0.89532	0.28436	0.075*
H2w	0.42167	0.92346	0.35258	0.075*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
CL1	0.031 (3)	0.038 (3)	0.036 (3)	0.008 (2)	0.015 (2)	0.017 (2)
O1w	0.026 (5)	0.051 (5)	0.075 (6)	0.020 (4)	0.028 (5)	0.045 (4)

Geometric parameters (Å, º)

C1—C1^i	1.527 (11)	C4—H4	0.941
C1—H1A	0.989	C4—C5	1.361 (10)
C1—H1B	0.979	C5—H5	0.946
C1—N1	1.475 (8)	C5—C6	1.371 (10)
N1—C2	1.331 (7)	C6—H6	0.925
C2—H2	0.939	C6—N1	1.347 (8)
C2—C3	1.391 (9)	O1w—H1w	0.813
C3—H3	0.927	O1w—H2w	0.811
C3—C4	1.372 (8)
C1^i—C1—H1A	106.1	C2—C3—C4	118.5 (8)
C1^i—C1—H1B	112.1	H3—C3—C4	121.1
C1^i—C1—N1	111.4 (8)	C3—C4—H4	119.5
H1A—C1—H1B	109.3	C3—C4—C5	120.2 (9)
H1A—C1—N1	108.6	H4—C4—C5	120.3
H1B—C1—N1	109.2	C4—C5—H5	120.5
C1—N1—C2	118.7 (9)	C4—C5—C6	120.7 (10)
C1—N1—C6	118.3 (8)	H5—C5—C6	118.8
C2—N1—C6	123.1 (7)	N1—C6—C5	118.1 (8)
N1—C2—H2	120.2	N1—C6—H6	121.5
N1—C2—C3	119.4 (8)	C5—C6—H6	120.4
H2—C2—C3	120.4	H1w—O1w—H2w	104.6
C2—C3—H3	120.2
C2—N1—C1—C1^i	−89.2 (9)	N1—C1—C1^i—N1^i	−180.0 (6)
C6—N1—C1—C1^i	89.6 (9)	N1—C2—C3—C4	1.0 (13)
C1—N1—C6—C5	179.3 (8)	C2—C3—C4—C5	−1.1 (13)
C1—N1—C2—C3	179.3 (7)	C3—C4—C5—C6	−0.2 (14)
C6—N1—C2—C3	0.5 (13)	C4—C5—C6—N1	1.7 (13)
C2—N1—C6—C5	−1.9 (13)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1W···Cl1	0.81	2.43	3.229 (6)	167
O1W—H2W···Cl1^ii	0.81	2.67	3.183 (6)	122
C2—H2···Cl1^i	0.94	2.73	3.596 (8)	153
C3—H3···O1W^iii	0.93	2.40	3.231 (10)	149
C4—H4···O1W^iv	0.94	2.47	3.400 (11)	172
C5—H5···Cl1^v	0.95	2.88	3.648 (8)	141
C6—H6···Cl1	0.92	2.63	3.509 (9)	159

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x−1, y, z; (iii) x−1, y−1, z; (iv) −x, −y+1, −z; (v) −x+1, −y+1, −z.

(II) 1,1'-(Ethylene-1,2-diyl)dipyridinium dibromide

Crystal data

C12H14N2^2+·2Br^−	V = 332.32 (4) Å^3
Mr = 346.05	Z = 1
Triclinic, P1	F(000) = 170
Hall symbol: -P 1	Dx = 1.729 Mg m^−3
a = 5.7608 (3) Å	Cu Kα1 radiation, λ = 1.5406 Å
b = 6.4257 (3) Å	µ = 7.53 mm^−1
c = 9.6848 (5) Å	T = 298 K
α = 80.7074 (11)°	Particle morphology: fine powder
β = 81.2351 (10)°	light brown
γ = 70.8554 (5)°	flat sheet, 8 × 8 mm

Data collection

Stoe transmission STADI-P diffractometer	Data collection mode: transmission
Radiation source: sealed X-ray tube	Scan method: step
Ge 111 monochromator	2θmin = 6.0°, 2θmax = 79.98°, 2θstep = 0.02°
Specimen mounting: Powder loaded into two Mylar foils

Refinement

Least-squares matrix: full	109 parameters
Rp = 0.029	0 restraints
Rwp = 0.037	H-atom parameters not refined
Rexp = 0.029	Weighting scheme based on measured s.u.'s
R(F^2) = 0.01768	(Δ/σ)max = 0.04
3700 data points	Background function: GSAS Background function number 1 with 20 terms. Shifted Chebyshev function of 1st kind 1: 586.651 2: -304.259 3: -7.34098 4: 54.3369 5: -21.2246 6: -22.1608 7: 53.9900 8: -29.1153 9: -21.3555 10: 36.6434 11: -11.5829 12: -8.12441 13: 9.00680 14: -7.25715 15: 6.53796 16: 4.23813 17: -5.01710 18: 0.343807 19: 3.94090 20: -2.41293
Profile function: CW Profile function number 4 with 27 terms Pseudovoigt profile coefficients as parameterized in Thompson et al. (1987. Asymmetry correction of Finger et al. (1994). Microstrain broadening by Stephens (1999). #1(GU) = 0.000 #2(GV) = 0.000 #3(GW) = 15.849 #4(GP) = 0.000 #5(LX) = 0.724 #6(ptec) = 0.00 #7(trns) = 3.13 #8(shft) = 0.0000 #9(sfec) = 0.00 #10(S/L) = 0.0240 #11(H/L) = 0.0240 #12(eta) = 0.6000 Peak tails are ignored where the intensity is below 0.0010 times the peak Aniso. broadening axis 0.0 0.0 1.0

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.1643 (2)	0.2256 (2)	0.30189 (14)	0.02332
C1	0.5795 (18)	0.3836 (13)	0.5328 (13)	0.015 (4)*
H1A	0.73999	0.37876	0.5509	0.035*
H1B	0.59314	0.27317	0.46758	0.035*
N1	0.4350 (14)	0.3274 (11)	0.6674 (9)	0.011 (3)*
C2	0.4682 (18)	0.3816 (16)	0.7878 (14)	0.021 (4)*
H2	0.57385	0.47144	0.78565	0.035*
C3	0.3475 (17)	0.3257 (14)	0.9165 (12)	0.028 (4)*
H3	0.37416	0.36025	0.99885	0.035*
C4	0.1914 (17)	0.1991 (16)	0.9125 (12)	0.028 (4)*
H4	0.11033	0.1524	0.99747	0.035*
C5	0.1578 (17)	0.1459 (13)	0.7893 (14)	0.015 (4)*
H5	0.05402	0.05897	0.7885	0.035*
C6	0.283 (2)	0.2042 (15)	0.6671 (11)	0.020 (4)*
H6	0.25644	0.17151	0.58182	0.035*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0312 (16)	0.0296 (14)	0.0181 (17)	−0.0204 (12)	0.0014 (14)	−0.0088 (16)

Geometric parameters (Å, º)

C1—C1^i	1.566 (17)	C3—C4	1.405 (11)
C1—H1A	0.957	C4—H4	0.938
C1—H1B	1.001	C4—C5	1.350 (13)
C1—N1	1.496 (10)	C5—H5	0.944
N1—C2	1.327 (13)	C5—C6	1.353 (14)
C2—H2	0.963	C6—N1	1.362 (9)
C2—C3	1.386 (12)	C6—H6	0.929
C3—H3	0.909
C1^i—C1—H1A	114.0	C2—C3—H3	122.8
C1^i—C1—H1B	107.8	C2—C3—C4	115.3 (11)
C1^i—C1—N1	106.2 (10)	H3—C3—C4	121.8
H1A—C1—H1B	110.5	C3—C4—H4	118.5
H1A—C1—N1	109.9	C3—C4—C5	120.9 (12)
H1B—C1—N1	108.1	H4—C4—C5	120.6
C1—N1—C2	120.7 (10)	C4—C5—H5	119.9
C1—N1—C6	119.2 (10)	C4—C5—C6	120.9 (9)
C2—N1—C6	120.0 (11)	H5—C5—C6	119.1
N1—C2—H2	118.7	N1—C6—C5	119.6 (11)
N1—C2—C3	123.3 (10)	N1—C6—H6	119.1
H2—C2—C3	117.9	C5—C6—H6	121.1
C2—N1—C1—C1^i	−91.5 (10)	N1—C1—C1^i—N1^i	−180.0 (7)
C6—N1—C1—C1^i	93.7 (9)	N1—C2—C3—C4	2.2 (14)
C1—N1—C6—C5	177.7 (8)	C2—C3—C4—C5	−2.5 (14)
C1—N1—C2—C3	−177.2 (9)	C3—C4—C5—C6	3.2 (15)
C6—N1—C2—C3	−2.4 (14)	C4—C5—C6—N1	−3.3 (15)
C2—N1—C6—C5	2.9 (14)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2···Br1^i	0.96	2.79	3.721 (11)	163
C5—H5···Br1^ii	0.94	2.84	3.743 (10)	161
C6—H6···Br1	0.93	2.79	3.676 (11)	160

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x, −y, −z+1.