Crystal structure of bis­(3-carb­oxy-1-methyl­pyrid­inium) octa­bromide

Sirenko, V.Y.; Naumova, D.D.; Golenya, I.A.; Shova, S.; Gural'skiy, I.A.

doi:10.1107/S2056989023008460

research communications

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 79| Part 11| November 2023| Pages 977-981

https://doi.org/10.1107/S2056989023008460

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Crystal structure of bis(3-carboxy-1-methylpyridinium) octabromide

Valerii Y. Sirenko,^a ^* Dina D. Naumova,^a Irina A. Golenya,^a Sergiu Shova ^b and Il'ya A. Gural'skiy ^a

^aDepartment of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska St. 64/13, Kyiv 01601, Ukraine, and ^bDepartment of Inorganic Polymers, "Petru Poni" Institute of Macromolecular Chemistry, Romanian Academy of Science, Aleea Grigore Ghica Voda 41A, Iasi 700487, Romania
^*Correspondence e-mail: valerii_sirenko@knu.ua

Edited by M. Weil, Vienna University of Technology, Austria (Received 12 September 2023; accepted 26 September 2023; online 3 October 2023)

The crystal structure of the title salt, bis(3-carboxy-1-methylpyridinium) octabromide, 2C₇H₈NO₂⁺·Br₈²⁻, consists of 3-carboxy-1-methylpyridinium (N-methylnicotinic acid) cations, which are stacked between relatively rare [Br₈]^2– anions. The polybromide [Br₈]^2– anion has point group symmetry $[\overline{1}]$ and can be described as being composed of two [Br₃]⁻ anions connected with a Br₂ molecule in a Z-shaped manner. Contacts between neighboring octabromide anions ensure the creation of pseudo-polymeric chains propagating along [111]. The organic cations are located between anionic chains and are connected to each other through O—H⋯O hydrogen bonds and to the [Br₈]^2– anions through π⋯Br interactions that induce the creation of a supramolecular tri-periodic network. In addition, the presence of weak C—H⋯Br contacts leads to the creation of layers, which align parallel to (11 $[\overline{2}]$ ).

Keywords: crystal structure; octabromide anion; polyhalogen ions; N-methylnicotinic acid.

CCDC reference: 2297637

1. Chemical context

Polyhalide anions have been the subject of extensive studies within the past century, whereby polyiodides offer the greatest diversity of known compounds among all polyhalide anions. The first triiodide-containing crystal structure, (NH₄)[I₃], was determined and characterized by Mooney in 1935 (Mooney, 1935 ). The known anions range from the smallest possible unit, [I₃]⁻, through multiple discrete species of the types [I_2n+1]⁻, [I_2n+2]^2–, [I_2n+3]^3– and other types from [I₃]⁻ to [I₂₉]^3– (Svensson & Kloo, 2003 ) to infinite polymeric structures (Madhu et al., 2016 ). A significantly smaller number of polyhalide anions is known for lighter halogens. This fact is mostly associated with the higher volatility of bromine, chlorine and fluorine in comparison with iodine, and thus their tendency to loss of halogen. However, several polybromide mono- ([Br₃]⁻, [Br₅]⁻, [Br₇]⁻, [Br₉]⁻, [Br₁₁]⁻) and dianions ([Br₄]^2–, [Br₆]^2–, [Br₈]^2–, [Br₁₀]^2–) are also known so far (Sonnenberg et al., 2020 ).

One of the most common applications of polybromide anions is in halogenation reactions. They are typically accessible in stable solid bulk form or as liquids with no measurable vapor pressure, depending on the organic cation. Thus, they can be handled much more easily then elemental liquid bromine (Sonnenberg et al., 2020). Polybromides, for example [HMIM][Br₉] where HMIM = 1-hexyl-3-methylimidazolium, have also been shown to form room-temperature ionic liquids, which can potentially be applied as a liquid electrode (Haller et al., 2013 ). Moreover, the use of the tribromide anion in the [Br₃]⁻/Br⁻ redox pair as a mediator in dye-sensitized solar cells has been reported to be an efficient alternative to the frequently used [I₃]⁻/I⁻ system (Kakiage et al., 2013 ). Polybromides have also been applied in zinc/bromine redox-flow batteries (Naresh et al., 2022 ).

In the present communication, we report a new polybromide compound containing a Z-shaped octabromide anion, 2(C₇H₈NO₂)⁺ [Br₈]^2–, and report its synthesis, crystal structure and Hirshfeld surface analysis.

2. Structural commentary

The crystal structure of the title compound consists of 3-carboxy-1-methylpyridinium (or N-methylnicotinic acid) cations separated by [Br₈]^2– anions (Fig. 1). The polybromide [Br₈]^2– anion can be described as two [Br₃]⁻ moieties connected to a central Br₂ molecule in a Z-shaped manner (Fig. 2). The title salt has point group symmetry $[\overline{1}]$ , with the inversion center located at the midpoint of the central Br₂ molecule. The Br—Br distance in the latter is 2.4002 (15) Å, which is slightly higher than 2.308 Å observed in [(Bz)(Ph)₃P]⁺₂[Br₈]^2– where (Bz)(Ph)₃P⁺ = benzyltriphenylphosphonium (Wolff et al., 2011 ) and 2.354 Å in [Q⁺]₂[Br₈]^2– where Q⁺ = quinuclidinium (Robertson et al., 1997 ). The Br1—Br2—Br3 distances in the [Br₃]⁻ moiety of the title compound are 2.4095 (7) Å and 2.7303 (7) Å (Fig. 2). For comparison, while in [Q⁺]₂[Br₈]²⁻ these values are similar (2.432 and 2.663 Å), in [(Bz)(Ph)₃P]⁺₂[Br₈]²⁻ these bond lengths are rather equalized (2.518 and 2.498 Å). The angle between the [Br₃]⁻ and Br₂ fragment in the title compound is 90.37 (2)°, which lies in the range between 80° and 112° observed for the [Br₈]^2– anions in other octabromide compounds listed in the Database survey. The [Br₈]^2– anion in the title compound is planar with the mean deviation from the best plane through the eight atoms of 0.013 Å.

Figure 1
A fragment of the crystal structure of title compound showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry code: (i) −x, −y, -z.]

Figure 2
A fragment of the title compound showing the Z-shaped octabromide anion; numbers are bond lengths (in Å).

3. Supramolecular features

The Br1⋯Br1(−x + 1, −y + 1, −z + 1) distance between neighboring [Br₈]^2– anions is 3.1813 (12) Å, which is smaller than the sum of van der Waal radii of 3.7 Å. This interaction contributes to the formation of infinite supramolecular chains propagating along [111] (Fig. 3). The organic cations are located between anionic chains and are connected with [Br₈]^2– through π⋯Br interactions [with a centroid⋯Br distance of 3.5577 (18) Å] into a supramolecular tri-periodic framework (Fig. 4). Neighboring cations of N-methylnicotinic acid are hydrogen-bonded with each other (Fig. 3, Table 1). In addition, the organic cations show weak C—H⋯Br contacts with the polybromide anions (Table 1) that lead to the creation of layers extending parallel to (11 $[\overline{2}]$ ).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯O2ⁱ	0.80 (7)	1.89 (7)	2.668 (5)	164 (7)
C1—H1A⋯Br3ⁱⁱ	0.93	2.96	3.838 (5)	158
C5—H5⋯Br4ⁱⁱⁱ	0.93	2.99	3.881 (5)	160
C7—H7A⋯Br3ⁱⁱ	0.96	2.92	3.857 (6)	166
Symmetry codes: (i) ; (ii) x+1, y, z; (iii) .

Figure 3
The crystal structure of the title compound in a view along the b axis showing infinite chains of anions. Hydrogen bonds between organic cations are shown as black dashed lines. Br⋯Br contacts between [Br₈]^2– anions are shown as red dashed lines.

Figure 4
The π⋯anion interactions in the title compound.

4. Hirshfeld surface analysis

Hirshfeld surface analysis and two-dimensional fingerprint plots of the title compound were generated using Crystal Explorer (Spackman et al., 2021 ).

The graphical representation of the Hirshfeld surface of the 3-carboxy-1-methylpyridinium cation reveals the presence of a rather strong O—H⋯O hydrogen bond with a neighboring organic cation, as shown in bright red (d_norm plot, Fig. 5a), and the presence of weak C—H⋯Br contacts between the organic cation and the octabromide anion (d_norm plot, Fig. 5b-d) as well as π⋯Br interactions between the 3-carboxy-1-methylpyridinium and the fragment of polybromide anions located above the aromatic ring (shape-index plot, Fig. 5e). The contributions of selected weak interactions to the crystal packing are shown as two-dimensional Hirshfeld surface fingerprint plots in Fig. 6. The strongest contribution is from Br⋯H interactions (38.2%) with the next major contributions from O⋯H (20.4%) and Br⋯C (13.0%).

Figure 5
Hirshfeld surface of the 3-carboxy-1-methylpyridinium cation plotted over d_norm (a–d) or shape index (e). The neighboring atoms are shown in ball-and-stick mode for clarity. The surface regions with the strongest intermolecular interactions are shown in red.

Figure 6
Hirshfeld surface fingerprint plot for 3-carboxy-1-methylpyridinium showing overall (100%), Br⋯H, O⋯H and Br⋯C contributions. The d_e and d_i values are the distances to the closest external and internal atoms, respectively, from a given point to the Hirshfeld surface.

The graphical representation of the Hirshfeld surface of the octabromide anion is given in Fig. 7 (d_norm plot). The most prominent interaction is observed with a neighboring [Br₈]^2– anion and is shown in red. Observed contacts with the organic cation are significantly weaker and are shown in colors from light pink to white. The fingerprint plots for the octabromide anion are given in Fig. 8. Here the highest contributions are observed for Br⋯H (70.0%) and Br⋯C (15.3%) contacts. Other types of interaction make significantly smaller contribution to the crystal packing, viz. Br⋯O (7.7%), Br⋯Br (4.9%) and Br⋯N (2.2%).

Figure 7
Hirshfeld surface of the octabromide anion plotted over d_norm. The surface regions with the strongest intermolecular interactions are shown in red.

Figure 8
Hirshfeld surface fingerprint plot for octabromide anion showing overall (100%), Br⋯H, Br⋯C, Br⋯O, Br⋯Br and Br⋯N contributions.

5. Database survey

A search of the tribromide moiety in the Cambridge Crystal Database (CSD version 5.43, last update March 2022; Groom et al., 2016 ) revealed 327 crystal structures, while only 28 of them containing four Br atoms connected in a row. The closest analogues to the title compound containing Z-shaped octabromide anions were found to be REKBAK (Robertson et al., 1997), ICOVUS (Fromm et al., 2006 ), RAQGIB (Wolff et al., 2011) and PAQSAE (Sonnenberg et al., 2017 ).

6. Synthesis and crystallization

0.5 mmol of N-methylnicotinamide was mixed with 2 ml of HBr (48%_wt) and left to evaporate. After three days, red crystals appeared in the mixture. They were separated and kept in the mother solution prior to the diffraction measurement.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. Aromatic H atoms were positioned geometrically and refined with riding coordinates [U_iso(H) = 1.2U_eq(C)]. Methyl H atoms were positioned geometrically and were allowed to ride on C atoms and rotate around the N—C bond [U_iso(H) = 1.5U_eq(C)]. The H atom of the carboxyl group was found from a difference-Fourier map and was refined with a fixed distance of d(O—H) = 0.85 Å and with U_iso(H) = 1.5U_eq(O).

Table 2
Experimental details

Crystal data
Chemical formula	2C₇H₈NO₂⁺·Br₈²⁻
M_r	915.52
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	293
a, b, c (Å)	6.8537 (5), 7.0873 (6), 14.5145 (6)
α, β, γ (°)	95.746 (5), 91.156 (4), 115.002 (7)
V (Å³)	634.23 (8)
Z	1
Radiation type	Mo Kα
μ (mm⁻¹)	12.67
Crystal size (mm)	0.17 × 0.11 × 0.06

Data collection
Diffractometer	Xcalibur, Eos
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2021 $[Rigaku OD (2021). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ )
T_min, T_max	0.458, 1.000
No. of measured, independent and observed [I ≥ 2u(I)] reflections	9457, 3008, 1848
R_int	0.048
(sin θ/λ)_max (Å⁻¹)	0.689

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.047, 0.075, 1.02
No. of reflections	3008
No. of parameters	132
No. of restraints	1
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	1.38, −1.32
Computer programs: CrysAlis PRO (Rigaku OD, 2021 $[Rigaku OD (2021). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ ), SHELXT (Sheldrick, 2015 ), OLEX2.refine (Bourhis et al., 2015 ) and OLEX2 (Dolomanov et al., 2009 ).

Supporting information

CCDC reference: 2297637

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989023008460/wm5697sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989023008460/wm5697Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989023008460/wm5697Isup3.cml

checkCIF report

Computing details top

Data collection: CrysAlis PRO (Rigaku OD, 2021); cell refinement: CrysAlis PRO (Rigaku OD, 2021); data reduction: CrysAlis PRO (Rigaku OD, 2021); program(s) used to solve structure: SHELXT (Sheldrick, 2015); program(s) used to refine structure: olex2.refine (Bourhis et al., 2015); molecular graphics: Olex2 (Dolomanov et al., 2009); software used to prepare material for publication: Olex2 (Dolomanov et al., 2009).

Bis(3-carboxy-1-methylpyridinium) octabromide top

Crystal data top

2C₇H₈NO₂⁺·Br₈²⁻	Z = 1
M_r = 915.52	F(000) = 424.594
Triclinic, P1	D_x = 2.397 Mg m⁻³
a = 6.8537 (5) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.0873 (6) Å	Cell parameters from 2335 reflections
c = 14.5145 (6) Å	θ = 3.2–23.7°
α = 95.746 (5)°	µ = 12.67 mm⁻¹
β = 91.156 (4)°	T = 293 K
γ = 115.002 (7)°	Block, light red
V = 634.23 (8) Å³	0.17 × 0.11 × 0.06 mm

Data collection top

Xcalibur, Eos diffractometer	1848 reflections with I ≥ 2u(I)
Detector resolution: 16.1593 pixels mm^-1	R_int = 0.048
ω scans	θ_max = 29.3°, θ_min = 2.8°
Absorption correction: multi-scan (CrysAlisPro; Rigaku OD, 2021)	h = −8→9
T_min = 0.458, T_max = 1.000	k = −9→9
9457 measured reflections	l = −19→19
3008 independent reflections

Refinement top

Refinement on F²	13 constraints
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.047	w = 1/[σ²(F_o²) + (0.0186P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.075	(Δ/σ)_max = −0.001
S = 1.02	Δρ_max = 1.38 e Å⁻³
3008 reflections	Δρ_min = −1.32 e Å⁻³
132 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.0112 (5)

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

	x	y	z	U_iso*/U_eq
Br2	0.06745 (8)	0.45917 (8)	0.30515 (3)	0.05120 (19)
Br3	−0.18168 (9)	0.43980 (10)	0.15210 (3)	0.0628 (2)
Br1	0.29688 (10)	0.47662 (9)	0.43679 (4)	0.0673 (2)
Br4	−0.04755 (10)	0.12253 (10)	0.04613 (3)	0.0781 (3)
O1	0.9137 (6)	0.8874 (6)	0.3821 (2)	0.0564 (10)
O2	0.7895 (5)	1.0613 (5)	0.4839 (2)	0.0540 (10)
N1	0.4595 (6)	0.8218 (6)	0.1811 (2)	0.0420 (10)
C2	0.6297 (7)	0.9597 (7)	0.3314 (3)	0.0348 (12)
C6	0.7873 (8)	0.9736 (8)	0.4062 (3)	0.0430 (13)
C1	0.6035 (7)	0.8341 (7)	0.2488 (3)	0.0423 (13)
H1a	0.6851 (7)	0.7580 (7)	0.2398 (3)	0.0507 (15)*
C4	0.3646 (8)	1.0582 (8)	0.2730 (3)	0.0477 (13)
H4	0.2828 (8)	1.1345 (8)	0.2802 (3)	0.0572 (16)*
C5	0.3421 (8)	0.9306 (8)	0.1928 (3)	0.0497 (14)
H5	0.2430 (8)	0.9193 (8)	0.1454 (3)	0.0597 (17)*
C3	0.5093 (8)	1.0726 (8)	0.3430 (3)	0.0444 (13)
H3	0.5259 (8)	1.1585 (8)	0.3981 (3)	0.0533 (16)*
C7	0.4279 (8)	0.6816 (8)	0.0942 (3)	0.0660 (17)
H7a	0.508 (4)	0.600 (4)	0.1002 (9)	0.099 (3)*
H7b	0.2774 (10)	0.589 (4)	0.0823 (13)	0.099 (3)*
H7c	0.477 (5)	0.7640 (9)	0.0437 (5)	0.099 (3)*
H1	0.992 (7)	0.879 (9)	0.426 (3)	0.099 (3)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br2	0.0515 (4)	0.0417 (3)	0.0592 (3)	0.0185 (3)	0.0015 (2)	0.0076 (2)
Br3	0.0686 (4)	0.0771 (5)	0.0512 (3)	0.0412 (3)	−0.0081 (3)	0.0013 (3)
Br1	0.0787 (5)	0.0529 (4)	0.0661 (4)	0.0265 (3)	−0.0223 (3)	0.0019 (3)
Br4	0.0779 (5)	0.0717 (5)	0.0592 (4)	0.0069 (4)	−0.0200 (3)	0.0140 (3)
O1	0.057 (3)	0.077 (3)	0.047 (2)	0.042 (2)	−0.0104 (17)	−0.0010 (19)
O2	0.057 (2)	0.072 (3)	0.0359 (18)	0.036 (2)	−0.0069 (15)	−0.0123 (17)
N1	0.039 (3)	0.046 (3)	0.036 (2)	0.015 (2)	−0.0041 (18)	−0.0001 (19)
C2	0.029 (3)	0.040 (3)	0.032 (2)	0.012 (2)	−0.0030 (19)	0.006 (2)
C6	0.038 (3)	0.045 (3)	0.049 (3)	0.021 (3)	−0.002 (2)	0.005 (3)
C1	0.035 (3)	0.045 (3)	0.043 (3)	0.014 (2)	−0.002 (2)	0.004 (2)
C4	0.049 (3)	0.053 (3)	0.051 (3)	0.032 (3)	−0.002 (2)	0.004 (3)
C5	0.045 (3)	0.063 (4)	0.041 (3)	0.024 (3)	−0.007 (2)	0.009 (3)
C3	0.048 (3)	0.044 (3)	0.039 (3)	0.019 (3)	0.001 (2)	0.002 (2)
C7	0.074 (4)	0.078 (4)	0.041 (3)	0.034 (3)	−0.018 (3)	−0.020 (3)

Geometric parameters (Å, º) top

Br2—Br3	2.7307 (7)	C2—C1	1.380 (6)
Br2—Br1	2.4095 (7)	C2—C3	1.373 (6)
Br3—Br4	3.0625 (10)	C1—H1a	0.9300
Br1—Br1ⁱ	3.1813 (12)	C4—H4	0.9300
Br4—Br4ⁱⁱ	2.4002 (15)	C4—C5	1.365 (6)
O1—C6	1.290 (6)	C4—C3	1.370 (6)
O1—H1	0.845 (19)	C5—H5	0.9300
O2—C6	1.228 (5)	C3—H3	0.9300
N1—C1	1.348 (5)	C7—H7a	0.9600
N1—C5	1.332 (6)	C7—H7b	0.9600
N1—C7	1.476 (5)	C7—H7c	0.9600
C2—C6	1.483 (6)

Br1—Br2—Br3	178.04 (3)	H1a—C1—C2	120.0 (3)
Br4—Br3—Br2	90.37 (2)	C5—C4—H4	120.4 (3)
Br1ⁱ—Br1—Br2	162.42 (4)	C3—C4—H4	120.4 (3)
Br4ⁱⁱ—Br4—Br3	176.22 (3)	C3—C4—C5	119.2 (5)
H1—O1—C6	116 (4)	C4—C5—N1	121.2 (4)
C5—N1—C1	120.7 (4)	H5—C5—N1	119.4 (3)
C7—N1—C1	119.4 (4)	H5—C5—C4	119.4 (3)
C7—N1—C5	119.8 (4)	C4—C3—C2	119.8 (4)
C1—C2—C6	120.3 (5)	H3—C3—C2	120.1 (3)
C3—C2—C6	120.6 (4)	H3—C3—C4	120.1 (3)
C3—C2—C1	119.2 (4)	H7a—C7—N1	109.5
O2—C6—O1	125.2 (4)	H7b—C7—N1	109.5
C2—C6—O1	114.6 (4)	H7b—C7—H7a	109.5
C2—C6—O2	120.1 (5)	H7c—C7—N1	109.5
C2—C1—N1	120.0 (5)	H7c—C7—H7a	109.5
H1a—C1—N1	120.0 (3)	H7c—C7—H7b	109.5

O1—C6—C2—C1	9.9 (5)	N1—C1—C2—C6	179.8 (4)
O1—C6—C2—C3	−169.6 (4)	N1—C1—C2—C3	−0.6 (5)
O2—C6—C2—C1	−169.9 (4)	N1—C5—C4—C3	−0.7 (6)
O2—C6—C2—C3	10.6 (5)	C2—C3—C4—C5	0.3 (5)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2ⁱⁱⁱ	0.80 (7)	1.89 (7)	2.668 (5)	164 (7)
C1—H1A···Br3^iv	0.93	2.96	3.838 (5)	158
C5—H5···Br4^v	0.93	2.99	3.881 (5)	160
C7—H7A···Br3^iv	0.96	2.92	3.857 (6)	166

Symmetry codes: (iii) −x+2, −y+2, −z+1; (iv) x+1, y, z; (v) −x, −y+1, −z.

Funding information

This work was supported by the Ministry of Education and Science of Ukraine with grant for perspective development of a scientific direction `Mathematical Sciences and Natural Sciences' at Taras Shevchenko National University of Kyiv, No. 21BNN-06.

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