organic compounds
2-[(E)-2-(4-Chlorophenyl)ethenyl]-1-methylpyridinium iodide monohydrate†
aDepartment of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand, bCrystal Materials Research Unit, Department of Chemistry, Faculty of Science, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand, and cX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
*Correspondence e-mail: suchada.c@psu.ac.th
In the title compound, C14H13ClN+·I−·H2O, the cation is nearly planar and exists in an E configuration; the dihedral angle between the pyridinium and benzene rings is 0.98 (17)°. The cations stack in an anti-parallel manner along the a axis through two π–π interactions between the pyridinium and benzene rings [centroid–centroid distances 3.569 (2) and 3.6818 (13) Å, respectively]. The cation, anion and water molecule are linked into a chain along the a axis by weak C—H⋯O and C—H⋯I interactions together with O—H⋯I hydrogen bonds and the chains are further connected into a three-dimensional network.
Related literature
For bond-length data, see: Allen et al. (1987). For related structures, see, for example: Chantrapromma et al. (2007a,b,c). For background on non-linear optical properties, see, for example: Lakshmanaperumal et al. (2004); Marder et al. (1994); Qiu et al. (2007); Williams (1984); Zhai et al. (1999); Zhan et al. (2006).
Experimental
Crystal data
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Refinement
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Data collection: APEX2 (Bruker, 2005); cell APEX2; data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2003).
Supporting information
10.1107/S1600536808027724/is2329sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536808027724/is2329Isup2.hkl
The title compound was prepared by mixing solutions of 1,2-dimethylpyridinium iodide, 4-chlorobenzaldehyde and piperidine (1:1:1 molar ratio) in methanol. The resulting solution was refluxed for 12 hr under a nitrogen atmosphere. The solid which formed was filtered and washed with chloroform. Orange plate-like single-crystal suitable for X-ray
was obtained by recrystallization from methanol by slow evaporation of the solvent at ambient temperature after several days, Mp. 492–493 K.All H atoms were placed in calculated positions (O—H = 0.85–0.86 and C—H = 0.93–0.96 Å) and refined as riding, with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(O, methyl C), A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.76 Å from I1 and the deepest hole is located at 0.59 Å from I1.
Data collection: APEX2 (Bruker, 2005); cell
APEX2 (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2003).Fig. 1. The title compound showing 50% probability displacement ellipsoids and the atom-numbering scheme. The O—H···I hydrogen bond was drawn as dashed line. | |
Fig. 2. The packing diagram of the title structure viewed approximately along the c axis. Hydrogen bonds were drawn as dashed lines. |
C14H13ClN+·I−·H2O | F(000) = 736 |
Mr = 375.62 | Dx = 1.708 Mg m−3 |
Monoclinic, P21/c | Melting point: 492-493 K K |
Hall symbol: -P 2ybc | Mo Kα radiation, λ = 0.71073 Å |
a = 7.0876 (1) Å | Cell parameters from 4241 reflections |
b = 9.8096 (2) Å | θ = 1.9–30.0° |
c = 21.0940 (4) Å | µ = 2.36 mm−1 |
β = 95.147 (1)° | T = 100 K |
V = 1460.68 (5) Å3 | Plate, orange |
Z = 4 | 0.28 × 0.17 × 0.07 mm |
Bruker SMART APEXII CCD area-detector diffractometer | 4241 independent reflections |
Radiation source: fine-focus sealed tube | 3486 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.038 |
Detector resolution: 8.33 pixels mm-1 | θmax = 30.0°, θmin = 1.9° |
ω scans | h = −9→9 |
Absorption correction: multi-scan (SADABS; Bruker, 2005) | k = −13→12 |
Tmin = 0.561, Tmax = 0.845 | l = −26→29 |
18928 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.037 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.104 | H-atom parameters constrained |
S = 1.13 | w = 1/[σ2(Fo2) + (0.0483P)2 + 1.1431P] where P = (Fo2 + 2Fc2)/3 |
4241 reflections | (Δ/σ)max = 0.001 |
164 parameters | Δρmax = 2.13 e Å−3 |
0 restraints | Δρmin = −0.79 e Å−3 |
C14H13ClN+·I−·H2O | V = 1460.68 (5) Å3 |
Mr = 375.62 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 7.0876 (1) Å | µ = 2.36 mm−1 |
b = 9.8096 (2) Å | T = 100 K |
c = 21.0940 (4) Å | 0.28 × 0.17 × 0.07 mm |
β = 95.147 (1)° |
Bruker SMART APEXII CCD area-detector diffractometer | 4241 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2005) | 3486 reflections with I > 2σ(I) |
Tmin = 0.561, Tmax = 0.845 | Rint = 0.038 |
18928 measured reflections |
R[F2 > 2σ(F2)] = 0.037 | 0 restraints |
wR(F2) = 0.104 | H-atom parameters constrained |
S = 1.13 | Δρmax = 2.13 e Å−3 |
4241 reflections | Δρmin = −0.79 e Å−3 |
164 parameters |
Experimental. The data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
I1 | 0.96440 (3) | 0.30947 (2) | 0.374487 (10) | 0.02517 (9) | |
Cl1 | 0.65015 (14) | −0.33018 (11) | 0.25791 (5) | 0.0349 (2) | |
N1 | 0.7517 (4) | 0.2927 (3) | 0.58820 (14) | 0.0228 (6) | |
O1W | 0.4685 (5) | 0.3289 (4) | 0.39663 (18) | 0.0589 (10) | |
H1W1 | 0.5617 | 0.2949 | 0.3782 | 0.088* | |
H2W1 | 0.3691 | 0.2881 | 0.3808 | 0.088* | |
C1 | 0.7754 (5) | 0.3535 (4) | 0.64637 (17) | 0.0254 (7) | |
H1A | 0.7521 | 0.4464 | 0.6498 | 0.030* | |
C2 | 0.8329 (5) | 0.2805 (4) | 0.69966 (18) | 0.0277 (8) | |
H2A | 0.8473 | 0.3228 | 0.7393 | 0.033* | |
C3 | 0.8698 (5) | 0.1412 (4) | 0.69383 (17) | 0.0262 (7) | |
H3A | 0.9115 | 0.0900 | 0.7294 | 0.031* | |
C4 | 0.8440 (5) | 0.0817 (4) | 0.63559 (17) | 0.0264 (7) | |
H4A | 0.8674 | −0.0111 | 0.6318 | 0.032* | |
C5 | 0.7828 (5) | 0.1569 (4) | 0.58078 (17) | 0.0221 (7) | |
C6 | 0.7492 (5) | 0.0969 (4) | 0.51828 (17) | 0.0256 (7) | |
H6A | 0.7187 | 0.1548 | 0.4839 | 0.031* | |
C7 | 0.7592 (5) | −0.0353 (4) | 0.50694 (17) | 0.0268 (7) | |
H7A | 0.7883 | −0.0912 | 0.5421 | 0.032* | |
C8 | 0.7293 (5) | −0.1035 (4) | 0.44465 (16) | 0.0235 (7) | |
C9 | 0.7663 (5) | −0.2435 (4) | 0.44164 (18) | 0.0266 (7) | |
H9A | 0.8075 | −0.2903 | 0.4786 | 0.032* | |
C10 | 0.7425 (5) | −0.3135 (4) | 0.38414 (19) | 0.0271 (8) | |
H10A | 0.7680 | −0.4063 | 0.3824 | 0.033* | |
C11 | 0.6808 (5) | −0.2432 (4) | 0.33021 (17) | 0.0238 (7) | |
C12 | 0.6421 (5) | −0.1050 (4) | 0.33059 (17) | 0.0258 (7) | |
H12A | 0.6005 | −0.0596 | 0.2932 | 0.031* | |
C13 | 0.6668 (5) | −0.0354 (4) | 0.38847 (17) | 0.0250 (7) | |
H13A | 0.6414 | 0.0575 | 0.3896 | 0.030* | |
C14 | 0.6940 (5) | 0.3805 (4) | 0.53292 (18) | 0.0298 (8) | |
H14D | 0.6802 | 0.4727 | 0.5470 | 0.045* | |
H14A | 0.5754 | 0.3489 | 0.5126 | 0.045* | |
H14B | 0.7889 | 0.3769 | 0.5032 | 0.045* |
U11 | U22 | U33 | U12 | U13 | U23 | |
I1 | 0.02744 (14) | 0.02228 (14) | 0.02596 (14) | 0.00264 (9) | 0.00324 (9) | 0.00111 (9) |
Cl1 | 0.0368 (5) | 0.0385 (6) | 0.0293 (5) | −0.0051 (4) | 0.0027 (4) | −0.0126 (4) |
N1 | 0.0206 (13) | 0.0229 (16) | 0.0249 (15) | 0.0010 (11) | 0.0027 (11) | 0.0046 (12) |
O1W | 0.0347 (17) | 0.083 (3) | 0.058 (2) | 0.0104 (16) | −0.0028 (15) | −0.028 (2) |
C1 | 0.0246 (17) | 0.0238 (18) | 0.0278 (18) | 0.0003 (14) | 0.0028 (14) | 0.0000 (15) |
C2 | 0.0255 (17) | 0.032 (2) | 0.0261 (18) | −0.0004 (14) | 0.0028 (14) | −0.0020 (15) |
C3 | 0.0209 (16) | 0.031 (2) | 0.0263 (17) | 0.0017 (14) | −0.0021 (13) | 0.0030 (15) |
C4 | 0.0218 (16) | 0.0267 (19) | 0.0307 (18) | −0.0010 (14) | 0.0017 (14) | 0.0034 (15) |
C5 | 0.0175 (15) | 0.0230 (18) | 0.0265 (17) | −0.0009 (12) | 0.0050 (12) | −0.0007 (14) |
C6 | 0.0265 (17) | 0.0245 (19) | 0.0258 (17) | 0.0002 (14) | 0.0018 (14) | 0.0001 (14) |
C7 | 0.0272 (17) | 0.0261 (19) | 0.0268 (18) | 0.0021 (14) | 0.0002 (14) | −0.0019 (15) |
C8 | 0.0227 (16) | 0.0244 (19) | 0.0236 (16) | −0.0012 (13) | 0.0027 (13) | −0.0021 (14) |
C9 | 0.0288 (18) | 0.0231 (19) | 0.0272 (18) | 0.0000 (14) | −0.0009 (14) | 0.0014 (15) |
C10 | 0.0266 (17) | 0.0195 (18) | 0.035 (2) | −0.0016 (14) | 0.0038 (15) | 0.0009 (15) |
C11 | 0.0203 (16) | 0.0253 (19) | 0.0257 (17) | −0.0029 (13) | 0.0025 (13) | −0.0064 (14) |
C12 | 0.0233 (16) | 0.027 (2) | 0.0267 (17) | 0.0026 (14) | −0.0011 (13) | 0.0029 (14) |
C13 | 0.0246 (16) | 0.0172 (17) | 0.0329 (19) | 0.0022 (13) | 0.0013 (14) | 0.0009 (14) |
C14 | 0.037 (2) | 0.025 (2) | 0.0281 (18) | 0.0052 (15) | 0.0056 (15) | 0.0032 (15) |
Cl1—C11 | 1.744 (4) | C6—H6A | 0.9300 |
N1—C1 | 1.361 (5) | C7—C8 | 1.473 (5) |
N1—C5 | 1.361 (5) | C7—H7A | 0.9300 |
N1—C14 | 1.478 (5) | C8—C13 | 1.397 (5) |
O1W—H1W1 | 0.8628 | C8—C9 | 1.400 (5) |
O1W—H2W1 | 0.8523 | C9—C10 | 1.391 (5) |
C1—C2 | 1.364 (5) | C9—H9A | 0.9300 |
C1—H1A | 0.9300 | C10—C11 | 1.368 (5) |
C2—C3 | 1.399 (6) | C10—H10A | 0.9300 |
C2—H2A | 0.9300 | C11—C12 | 1.383 (5) |
C3—C4 | 1.358 (5) | C12—C13 | 1.396 (5) |
C3—H3A | 0.9300 | C12—H12A | 0.9300 |
C4—C5 | 1.407 (5) | C13—H13A | 0.9300 |
C4—H4A | 0.9300 | C14—H14D | 0.9600 |
C5—C6 | 1.444 (5) | C14—H14A | 0.9600 |
C6—C7 | 1.322 (5) | C14—H14B | 0.9600 |
C1—N1—C5 | 121.6 (3) | C13—C8—C9 | 118.5 (3) |
C1—N1—C14 | 117.3 (3) | C13—C8—C7 | 123.3 (3) |
C5—N1—C14 | 121.0 (3) | C9—C8—C7 | 118.2 (3) |
H1W1—O1W—H2W1 | 106.3 | C10—C9—C8 | 121.0 (3) |
N1—C1—C2 | 121.1 (4) | C10—C9—H9A | 119.5 |
N1—C1—H1A | 119.4 | C8—C9—H9A | 119.5 |
C2—C1—H1A | 119.4 | C11—C10—C9 | 118.8 (3) |
C1—C2—C3 | 119.0 (4) | C11—C10—H10A | 120.6 |
C1—C2—H2A | 120.5 | C9—C10—H10A | 120.6 |
C3—C2—H2A | 120.5 | C10—C11—C12 | 122.5 (3) |
C4—C3—C2 | 119.2 (3) | C10—C11—Cl1 | 119.1 (3) |
C4—C3—H3A | 120.4 | C12—C11—Cl1 | 118.4 (3) |
C2—C3—H3A | 120.4 | C11—C12—C13 | 118.4 (3) |
C3—C4—C5 | 121.7 (4) | C11—C12—H12A | 120.8 |
C3—C4—H4A | 119.2 | C13—C12—H12A | 120.8 |
C5—C4—H4A | 119.2 | C12—C13—C8 | 120.9 (3) |
N1—C5—C4 | 117.4 (3) | C12—C13—H13A | 119.6 |
N1—C5—C6 | 119.3 (3) | C8—C13—H13A | 119.6 |
C4—C5—C6 | 123.4 (3) | N1—C14—H14D | 109.5 |
C7—C6—C5 | 123.9 (3) | N1—C14—H14A | 109.5 |
C7—C6—H6A | 118.0 | H14D—C14—H14A | 109.5 |
C5—C6—H6A | 118.0 | N1—C14—H14B | 109.5 |
C6—C7—C8 | 127.0 (4) | H14D—C14—H14B | 109.5 |
C6—C7—H7A | 116.5 | H14A—C14—H14B | 109.5 |
C8—C7—H7A | 116.5 | ||
C5—N1—C1—C2 | 0.5 (5) | C5—C6—C7—C8 | −179.2 (3) |
C14—N1—C1—C2 | −178.4 (3) | C6—C7—C8—C13 | −6.4 (6) |
N1—C1—C2—C3 | 0.7 (5) | C6—C7—C8—C9 | 173.2 (4) |
C1—C2—C3—C4 | −1.3 (5) | C13—C8—C9—C10 | 0.3 (5) |
C2—C3—C4—C5 | 0.6 (5) | C7—C8—C9—C10 | −179.4 (3) |
C1—N1—C5—C4 | −1.1 (5) | C8—C9—C10—C11 | −0.4 (5) |
C14—N1—C5—C4 | 177.7 (3) | C9—C10—C11—C12 | 0.3 (5) |
C1—N1—C5—C6 | 177.9 (3) | C9—C10—C11—Cl1 | −179.9 (3) |
C14—N1—C5—C6 | −3.2 (5) | C10—C11—C12—C13 | −0.2 (5) |
C3—C4—C5—N1 | 0.6 (5) | Cl1—C11—C12—C13 | −179.9 (3) |
C3—C4—C5—C6 | −178.4 (3) | C11—C12—C13—C8 | 0.0 (5) |
N1—C5—C6—C7 | −173.9 (3) | C9—C8—C13—C12 | −0.1 (5) |
C4—C5—C6—C7 | 5.1 (6) | C7—C8—C13—C12 | 179.6 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1W1···I1 | 0.86 | 2.87 | 3.592 (4) | 143 |
O1W—H2W1···I1i | 0.85 | 2.87 | 3.567 (4) | 141 |
C14—H14A···O1W | 0.96 | 2.50 | 3.202 (5) | 130 |
C14—H14D···O1Wii | 0.96 | 2.56 | 3.460 (5) | 157 |
C1—H1A···I1iii | 0.93 | 3.20 | 3.830 (4) | 127 |
C2—H2A···I1iv | 0.93 | 3.18 | 3.825 (4) | 129 |
C3—H3A···I1iv | 0.93 | 3.21 | 3.840 (4) | 127 |
Symmetry codes: (i) x−1, y, z; (ii) −x+1, −y+1, −z+1; (iii) −x+2, −y+1, −z+1; (iv) x, −y+1/2, z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C14H13ClN+·I−·H2O |
Mr | 375.62 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 100 |
a, b, c (Å) | 7.0876 (1), 9.8096 (2), 21.0940 (4) |
β (°) | 95.147 (1) |
V (Å3) | 1460.68 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 2.36 |
Crystal size (mm) | 0.28 × 0.17 × 0.07 |
Data collection | |
Diffractometer | Bruker SMART APEXII CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 2005) |
Tmin, Tmax | 0.561, 0.845 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 18928, 4241, 3486 |
Rint | 0.038 |
(sin θ/λ)max (Å−1) | 0.703 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.037, 0.104, 1.13 |
No. of reflections | 4241 |
No. of parameters | 164 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 2.13, −0.79 |
Computer programs: APEX2 (Bruker, 2005), SAINT (Bruker, 2005), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2003).
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1W1···I1 | 0.86 | 2.8658 | 3.592 (4) | 143 |
O1W—H2W1···I1i | 0.85 | 2.8672 | 3.567 (4) | 141 |
C14—H14A···O1W | 0.96 | 2.5028 | 3.202 (5) | 130 |
C14—H14D···O1Wii | 0.96 | 2.5568 | 3.460 (5) | 157 |
C1—H1A···I1iii | 0.93 | 3.1968 | 3.830 (4) | 127 |
C2—H2A···I1iv | 0.93 | 3.1748 | 3.825 (4) | 129 |
C3—H3A···I1iv | 0.93 | 3.2053 | 3.840 (4) | 127 |
Symmetry codes: (i) x−1, y, z; (ii) −x+1, −y+1, −z+1; (iii) −x+2, −y+1, −z+1; (iv) x, −y+1/2, z+1/2. |
Acknowledgements
KC thanks the Development and Promotion of Science and Technology Talents Project (DPST) for a study grant. Financial support from the Center of Excellence for Innovation in Chemistry (PERCH-CIC), Commission on Higher Education, Ministry of Education, is gratefully acknowledged. The authors also thank Prince of Songkla University, the Malaysian Government and Universiti Sains Malaysia for the Research University Golden Goose grant No. 1001/PFIZIK/811012.
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In the last two decades, many efforts were focused on the discovery of new organic materials which exhibit large nonlinear optical (NLO) properties and would have applications in the fields of optoelectronics and photonics (Lakshmanaperumal et al., 2004; Marder et al., 1994; Qiu et al., 2007; Zhai et al., 1999; Zhan et al., 2006). In order to obtain second-order NLO single crystals, the main requirements should be the choice of molecules with large hyperpolarizability (β) and the alignment of these molecules with optimal orientation into a noncentrosymmetric space group in the crystal (Williams, 1984). Among the known organic NLO materials, ionic chromophores are of great interest because they exhibit large first hyperpolarizabilities (β) and have high melting points and hardness of their crystals. At the molecular level, a generally popular approach towards NLO materials is to design and synthesize compounds with extended conjugated π-systems with donor and acceptor groups because such compounds are likely to exhibit large values of molecular hyperpolarizability (β) and to possess polarization. Styryl pyridinium derivatives are considered to be good conjugated π-systems. In continuation of our on-going research on nonlinear optical materials (Chantrapromma et al., 2007a,b,c), the title compound, (I), was synthesized and the X-ray structure analysis was carried out in order to obtain detailed information about the molecular packing. However, compound (I) crystallizes in monoclinic space group P21/c and doesn't exhibit second-order nonlinear optic properties.
The asymmetric unit of the title compound consists of C14H13ClN+ cation, I- anion and one water molecule (Fig. 1). The conformation of the cation is essentially planar as indicated by the dihedral angle between the pyridinium (N1/C1—C5) and the benzene (C8—C13) rings, being 0.98 (17)°. The mean plane through C5/C6/C7/C8 plane makes dihedral angles of 6.1 (4)° and 6.4 (4)° with pyridinium and benzene rings, respectively. The cation exists in the E configuration and the torsion angle C5—C6—C7—C8 = -179.2 (3)°. The bond distances and angles in (I) have normal values (Allen et al., 1987) and comparable with closely related structures (Chantrapromma et al., 2007a,b,c).
The packing of the molecule down the c axis (Fig. 2), showing that the cation is linked with water molecule by weak C—H···O interactions (Table 1) and linked with I- anions by weak C—H···I interactions (Table 1) whereas the I- anion is linked with water molecule by O—H···I hydrogen bonds, forming one-dimensional chains along the a axis. These chains are further connected into a three-dimensional network (Fig. 2). π···π interactions involving pyridinium and benzene rings were also observed with Cg1···Cg2 distances of 3.662 (2) Å (symmetry code; 1 - x, -y, 1 - z) and 3.569 (2) Å (symmetry code; 2 - x, -y, 1 - z); Cg1 and Cg2 are the centroids of the N1/C1–C5 pyridinium and C8–C13 benzene rings, respectively. The crystal is stabilized by O—H···I hydrogen bond, weak C—H···O and C—H···I interactions.