research communications
and Hirshfeld surface analysis of 2-aminopyridinium hydrogen phthalate
aDepartment of Physics, School of Advanced Sciences, Kalasalingam Academy of Research and Education, Krishnankoil - 626 126, India, bCondensed Matter Physics Laboratory, International Research Centre, Kalasalingam Academy of Research and Education, Krishnankoil - 626 126, India, cDepartment of Physics, Er. Perumal Manimekalai College of Engineering, Hosur 635 117, India, and dDepartment of Physics, University College of Engineering, Anna University, Nagercoil 629 004, India
*Correspondence e-mail: athi81s@yahoo.co.in
Aminopyridine and phthalic acid are well known synthons for supramolecular architectures for the synthesis of new materials for optical applications. The 2-aminopyridinium hydrogen phthalate title salt, C5H7N2+·C8H5O4−, crystallizes in the non-centrosymmetric P21. The nitrogen atom of the –NH2 group in the cation deviates from the fitted pyridine plane by 0.035 (7) Å. The plane of the pyridinium ring and phenyl ring of the anion are oriented at an angle of 80.5 (3)° to each other in the The anion features a strong intramolecular O—H⋯O hydrogen bond, forming a self-associated S(7) ring motif. The crystal packing is dominated by intermolecular N—H⋯O hydrogen bonds leading to the formation of 21 helices, with a C(11) chain motif. They propagate along the b axis and enclose R22(8) ring motifs. The helices are linked by C—H⋯O hydrogen bonds, forming layers parallel to the ab plane. Hirshfeld surface analysis and two-dimensional fingerprint plots were used to investigate and quantify the intermolecular interactions in the crystal.
Keywords: crystal structure; organic salt; hetero-synthon; NLO; hydrogen bonding; Hirshfeld surface analysis.
CCDC reference: 1954730
1. Chemical context
Crystal engineering and the design of supramolecular architectures are of significant interest owing to the technological applications of the resulting materials in the electronics and optical industries. Supramolecular interactions such as charge-assisted hydrogen bonds and π–π interactions play an important role in crystal engineering as they lead to directional molecular recognition events between molecules or ions, and therefore mediate self-assembly of well-defined supramolecular networks (Guelmami et al., 2007; Prakash et al., 2018; Siva et al., 2017). Amine-based materials are particularly important as they are synthesized by the condensation of the corresponding and and exhibit strong intermolecular hydrogen bonds between the electronegative acceptor and the N atom of the imine moiety. Pyridinium families are now considered to be potential materials for optical applications because of their flexibility in molecular design, strength and thermal stability, which are derived from delocalized clouds of electrons. Another electronic field of research related to 2-aminopyridinium salts is focused on their optical limiting and frequency-conversion applications (Liu et al., 2015; Siva et al., 2019). The present work is a part of a structural study of new proton-transfer compounds of 2-aminopyridine with phthalic acid and the corresponding hydrogen-bonding interactions. The hydrogen bonding present in the crystal of the title salt was substantiated by Hirshfeld surface analysis.
2. Structural commentary
The molecular structure of the title salt is shown in Fig. 1. Protonation on the N-atom site of the pyridine ring, atom N11, is confirmed by the elongated C—N bond distances [C11—N11 = 1.341 (8) Å and C15—N11 = 1.357 (9) Å] and the enlarged C11—N11—C15 bond angle of 122.3 (6)°. The nitrogen atom of the –NH2 group in the cation deviates from the pyridine ring plane (r.m.s. deviation = 0.0062 Å) by 0.035 (7) Å. The planes of the pyridinium ring of the cation and the phenyl ring of the anion are oriented at a dihedral angle of 80.5 (3)° in the In the anion the twisting of the carboxyl planes out of the benzene ring is negligible [planes O21/O22/C27 and O23/O24/C28 are inclined to the benzene ring (C21–C26) by 1.3 (8) and 0.7 (7)°, respectively], because of the strong O22—H22A⋯O23 intramolecular hydrogen bond (Fig. 1 and Table 1), which makes a self-associated S(7) ring motif.
3. Supramolecular features
2-Aminopyridine and phthalic acid are known materials for structure-extension properties, which connect the molecules in the supramolecular assembly. These supramolecular synthons are crystallized together not only to study the molecular structure but also the crystal packing via intermolecular interactions. This structure-extension property of the synthon molecules is generally exploited for possible non-centrosymmetric materials, which are desired as they possess many applications. The structure extension of the molecules is possible by linear (chain C motifs) and cyclic (ring R motifs) hydrogen-bonding associations. This was accomplished in the title compound, which exhibits non-linear optical (NLO) properties, because of the extensive intermolecular interactions.
The packing of the ions in the crystal is dominated by N—H⋯O and C—H⋯O hydrogen bonds (Table 1). A cation–anion hetero-synthon is formed via two N—H⋯O hydrogen bonds (N11—H1N⋯O24i and N12—H12A⋯O23i), that enclose an R22(8) ring motif (Fig. 2 and Table 1). These hetero-synthons are linked by a further N—H⋯O hydrogen bond (N12—H12B⋯O22ii), to form 21 helices, with a C(11) chain motif, that propagate along the b-axis direction. The helices are linked by C—H⋯O hydrogen bonds, forming layers lying parallel to the ab plane (Fig. 3 and Table 1). There are no significant C—H⋯π or π–π contacts present in the crystal (PLATON; Spek, 2009).
4. Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were performed with CrystalExplorer17 (Turner et al., 2017). The Hirshfeld surface is colour-mapped with the normalized contact distance, dnorm, from red (distances shorter than the sum of the van der Waals radii) through white to blue (distances longer than the sum of the van der Waals radii).
The Hirshfeld surface (HS) of the title salt, mapped over dnorm in the colour range of −0.7098 to 1.1914 arbitrary units, is given in Fig. 4. The short interatomic contacts, i.e. the donors and acceptors of the hydrogen bonds (Table 1), are indicated by the red spots.
The two-dimensional fingerprint plots for the title salt, the cation and the anion are given in Fig. 5. The relative percentage contributions of close contacts to the Hirshfeld surfaces of the title salt (Fig. 5a), and the cation (Fig. 5b) and anion (Fig. 5c), are compared in Table 2.
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For the title salt (Fig. 5a), the most significant contributions to the HS are from H⋯H (32.0%), O⋯H/H⋯O (31.0%), C⋯H/H⋯C (22.0%) and C⋯O (7.3%) contacts. On examination of the contributions to the HS of the cation (Fig. 5b) and anion (Fig. 5c) individually, it can be seen that the cation makes the largest contribution to the H⋯H contacts (40.4%), while the anion makes the largest contributions to the O⋯H/H⋯O (31.6%), C⋯H/H⋯C(24.0%) and C⋯O (8.8%) contacts (see also Table 2).
5. Database survey
A search of the Cambridge Structural Database (Version 5.40, last update May 2019; Groom et al., 2016) for 2-aminopyridinium salts indicated that the crystal structures of more than 220 structures have been reported. A search for 2-aminopyridinium benzoate salts gave 45 hits for 35 structures. The most significant in relation to the title salt are: 2-aminopyridinium benzoate (LUPZOL; Odabaşoğlu et al., 2003), 2-aminopyridinium 2′-carboxybiphenyl-4-carboxylate (DEZCOC; Wang et al., 2013), bis(2-aminopyridine) terephthalate (LAPMUL; Bis & Zaworotko), 2-aminopyridinium isophthalate (Bis & Zaworotko, 2005) and bis(2-aminopyridinium) 2,5-dicarboxybenzene-1,4-dicarboxylate (Rodrigues et al., 2012). In the crystals, the same hetero-synthon is formed via N—H⋯O hydrogen bonds. The CO2− groups in general lie close to the plane of the benzene ring in LUPZOL, LAQGOA and ZARHOR; the dihedral angle varies from 1.85–6.09°. However, the corresponding dihedral angles in DEZCOC and LAPMUL are considerably lager; ca 47.92 and 23.97° in DEZCOC and 17.37° in LAPMUK. While DEZCOC crystallizes in a P32, the other four compounds, LUPZOL, LAPMUL, LAQGOA and ZARHOR, crystallize in a centrosymmetric monoclinic (P21/c or P21/n) and hence do not exhibit NLO properties.
6. Synthesis and crystallization
A 1:1 mixture of 2-aminopyridine and phthalic acid was heated to 313 K and stirred for 1 h before being poured into a petri dish and kept undisturbed for 25 days. Colourless block-shaped single crystals were obtained by the slow evaporation of a methanol and water (v:v = 20:80%) solution.
7. Refinement
Crystal data, data collection and structure . The OH and NH H atoms were located in a difference-Fourier map and refined freely. The NH2 and C-bound H atoms were included in calculated positions and treated as riding atoms: N—H = 0.86 Å, C—H = 0.93 Å with Uiso(H) = 1.2Ueq(N, C).
details are summarized in Table 3
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Supporting information
CCDC reference: 1954730
https://doi.org/10.1107/S2056989019012957/ff2163sup1.cif
contains datablocks I, Global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019012957/ff2163Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989019012957/ff2163Isup3.cml
Data collection: SMART (Bruker, 2001); cell
SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2008) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015b) and PLATON (Spek, 2009).C5H7N2+·C8H5O4− | F(000) = 272 |
Mr = 260.25 | Dx = 1.444 Mg m−3 |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71073 Å |
a = 5.1593 (6) Å | Cell parameters from 2425 reflections |
b = 8.6124 (9) Å | θ = 2.2–24.7° |
c = 13.5745 (19) Å | µ = 0.11 mm−1 |
β = 97.087 (4)° | T = 293 K |
V = 598.56 (13) Å3 | Block, colourless |
Z = 2 | 0.26 × 0.24 × 0.20 mm |
Bruker SMART APEX CCD area-detector diffractometer | Rint = 0.023 |
Radiation source: fine-focus sealed tube | θmax = 25.0°, θmin = 1.5° |
ω scans | h = −6→6 |
6704 measured reflections | k = −10→10 |
2099 independent reflections | l = −16→14 |
1972 reflections with I > 2σ(I) |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: mixed |
R[F2 > 2σ(F2)] = 0.059 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.186 | w = 1/[σ2(Fo2) + (0.0796P)2 + 0.5949P] where P = (Fo2 + 2Fc2)/3 |
S = 1.24 | (Δ/σ)max < 0.001 |
2099 reflections | Δρmax = 0.35 e Å−3 |
180 parameters | Δρmin = −0.24 e Å−3 |
1 restraint | Absolute structure: Flack x determined using 880 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013) |
Primary atom site location: dual | Absolute structure parameter: 0.1 (4) |
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. |
x | y | z | Uiso*/Ueq | ||
C11 | 0.5973 (12) | 0.4659 (7) | 0.8983 (5) | 0.0401 (14) | |
C12 | 0.7974 (14) | 0.3719 (9) | 0.9463 (6) | 0.0545 (19) | |
H12 | 0.8233 | 0.3657 | 1.0152 | 0.065* | |
C13 | 0.9516 (13) | 0.2908 (8) | 0.8913 (7) | 0.056 (2) | |
H13 | 1.0809 | 0.2268 | 0.9232 | 0.067* | |
C14 | 0.9221 (15) | 0.3005 (8) | 0.7882 (7) | 0.057 (2) | |
H14 | 1.0323 | 0.2466 | 0.7510 | 0.069* | |
C15 | 0.7263 (13) | 0.3915 (8) | 0.7440 (5) | 0.0489 (16) | |
H15 | 0.7002 | 0.3992 | 0.6751 | 0.059* | |
N11 | 0.5683 (10) | 0.4714 (6) | 0.7988 (4) | 0.0370 (12) | |
N12 | 0.4392 (12) | 0.5509 (8) | 0.9461 (4) | 0.0532 (16) | |
H12A | 0.3216 | 0.6079 | 0.9134 | 0.064* | |
H12B | 0.4542 | 0.5492 | 1.0099 | 0.064* | |
H1N | 0.448 (13) | 0.538 (8) | 0.764 (5) | 0.031 (15)* | |
C21 | 0.1288 (10) | 0.3445 (6) | 0.3331 (4) | 0.0302 (12) | |
C22 | 0.0707 (13) | 0.3464 (8) | 0.4303 (4) | 0.0421 (15) | |
H22 | −0.0615 | 0.2820 | 0.4472 | 0.050* | |
C23 | 0.1998 (15) | 0.4394 (9) | 0.5026 (5) | 0.0534 (18) | |
H23 | 0.1531 | 0.4385 | 0.5666 | 0.064* | |
C24 | 0.3968 (15) | 0.5326 (9) | 0.4797 (5) | 0.0514 (17) | |
H24 | 0.4850 | 0.5969 | 0.5278 | 0.062* | |
C25 | 0.4648 (13) | 0.5309 (8) | 0.3840 (5) | 0.0465 (15) | |
H25 | 0.6035 | 0.5925 | 0.3697 | 0.056* | |
C26 | 0.3347 (10) | 0.4413 (7) | 0.3089 (4) | 0.0333 (13) | |
C27 | 0.4332 (12) | 0.4634 (9) | 0.2093 (5) | 0.0431 (15) | |
C28 | −0.0455 (11) | 0.2378 (7) | 0.2648 (4) | 0.0335 (13) | |
O21 | 0.6142 (12) | 0.5515 (7) | 0.2021 (4) | 0.0696 (16) | |
O22 | 0.3306 (11) | 0.3890 (8) | 0.1326 (4) | 0.0627 (15) | |
O23 | −0.0154 (9) | 0.2241 (6) | 0.1742 (3) | 0.0469 (11) | |
O24 | −0.2148 (10) | 0.1635 (6) | 0.3020 (3) | 0.0488 (12) | |
H22A | 0.17 (2) | 0.320 (11) | 0.149 (7) | 0.08 (3)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C11 | 0.039 (3) | 0.039 (3) | 0.043 (3) | −0.011 (3) | 0.004 (3) | 0.009 (3) |
C12 | 0.052 (4) | 0.052 (4) | 0.055 (4) | −0.006 (3) | −0.014 (3) | 0.020 (3) |
C13 | 0.034 (3) | 0.046 (4) | 0.083 (6) | 0.000 (3) | −0.008 (4) | 0.016 (4) |
C14 | 0.046 (4) | 0.044 (4) | 0.084 (6) | 0.009 (3) | 0.014 (4) | −0.003 (4) |
C15 | 0.046 (3) | 0.048 (4) | 0.052 (4) | 0.001 (3) | 0.002 (3) | −0.007 (3) |
N11 | 0.034 (2) | 0.038 (3) | 0.038 (3) | −0.002 (2) | 0.002 (2) | 0.006 (2) |
N12 | 0.059 (4) | 0.066 (4) | 0.036 (3) | 0.016 (3) | 0.010 (3) | 0.011 (3) |
C21 | 0.029 (3) | 0.031 (3) | 0.030 (3) | 0.004 (2) | 0.003 (2) | 0.001 (2) |
C22 | 0.046 (3) | 0.048 (4) | 0.032 (3) | −0.006 (3) | 0.006 (3) | −0.003 (3) |
C23 | 0.068 (4) | 0.058 (4) | 0.033 (3) | 0.000 (4) | 0.001 (3) | −0.009 (3) |
C24 | 0.056 (4) | 0.053 (4) | 0.042 (4) | −0.003 (3) | −0.006 (3) | −0.016 (3) |
C25 | 0.039 (3) | 0.047 (4) | 0.051 (4) | −0.006 (3) | −0.001 (3) | −0.001 (3) |
C26 | 0.031 (3) | 0.032 (3) | 0.036 (3) | 0.004 (2) | 0.003 (2) | 0.002 (2) |
C27 | 0.040 (3) | 0.046 (3) | 0.044 (4) | −0.001 (3) | 0.007 (3) | 0.011 (3) |
C28 | 0.038 (3) | 0.031 (3) | 0.031 (3) | 0.003 (3) | 0.001 (2) | 0.003 (2) |
O21 | 0.067 (3) | 0.073 (4) | 0.075 (4) | −0.023 (3) | 0.033 (3) | −0.001 (3) |
O22 | 0.065 (3) | 0.093 (4) | 0.033 (2) | −0.016 (3) | 0.015 (2) | 0.001 (3) |
O23 | 0.056 (3) | 0.056 (3) | 0.028 (2) | −0.009 (2) | 0.0030 (19) | −0.006 (2) |
O24 | 0.056 (3) | 0.055 (3) | 0.035 (2) | −0.021 (2) | 0.002 (2) | −0.004 (2) |
C11—N12 | 1.325 (9) | C21—C28 | 1.519 (8) |
C11—N11 | 1.341 (8) | C22—C23 | 1.374 (10) |
C11—C12 | 1.407 (9) | C22—H22 | 0.9300 |
C12—C13 | 1.351 (11) | C23—C24 | 1.361 (11) |
C12—H12 | 0.9300 | C23—H23 | 0.9300 |
C13—C14 | 1.391 (12) | C24—C25 | 1.387 (10) |
C13—H13 | 0.9300 | C24—H24 | 0.9300 |
C14—C15 | 1.359 (10) | C25—C26 | 1.385 (9) |
C14—H14 | 0.9300 | C25—H25 | 0.9300 |
C15—N11 | 1.357 (9) | C26—C27 | 1.514 (9) |
C15—H15 | 0.9300 | C27—O21 | 1.216 (9) |
N11—H1N | 0.93 (7) | C27—O22 | 1.280 (9) |
N12—H12A | 0.8600 | C28—O24 | 1.239 (7) |
N12—H12B | 0.8600 | C28—O23 | 1.264 (7) |
C21—C22 | 1.389 (8) | O22—H22A | 1.08 (10) |
C21—C26 | 1.421 (8) | O23—H22A | 1.32 (11) |
N12—C11—N11 | 118.4 (6) | C23—C22—C21 | 122.9 (6) |
N12—C11—C12 | 123.5 (6) | C23—C22—H22 | 118.5 |
N11—C11—C12 | 118.1 (7) | C21—C22—H22 | 118.5 |
C13—C12—C11 | 119.3 (7) | C24—C23—C22 | 119.4 (7) |
C13—C12—H12 | 120.3 | C24—C23—H23 | 120.3 |
C11—C12—H12 | 120.3 | C22—C23—H23 | 120.3 |
C12—C13—C14 | 121.8 (7) | C23—C24—C25 | 119.3 (6) |
C12—C13—H13 | 119.1 | C23—C24—H24 | 120.3 |
C14—C13—H13 | 119.1 | C25—C24—H24 | 120.3 |
C15—C14—C13 | 117.5 (7) | C26—C25—C24 | 122.7 (7) |
C15—C14—H14 | 121.2 | C26—C25—H25 | 118.7 |
C13—C14—H14 | 121.2 | C24—C25—H25 | 118.7 |
N11—C15—C14 | 120.9 (7) | C25—C26—C21 | 117.8 (6) |
N11—C15—H15 | 119.5 | C25—C26—C27 | 113.7 (6) |
C14—C15—H15 | 119.5 | C21—C26—C27 | 128.5 (5) |
C11—N11—C15 | 122.3 (6) | O21—C27—O22 | 119.4 (6) |
C11—N11—H1N | 121 (4) | O21—C27—C26 | 119.7 (6) |
C15—N11—H1N | 117 (4) | O22—C27—C26 | 120.8 (6) |
C11—N12—H12A | 120.0 | O24—C28—O23 | 121.7 (5) |
C11—N12—H12B | 120.0 | O24—C28—C21 | 117.2 (5) |
H12A—N12—H12B | 120.0 | O23—C28—C21 | 121.1 (5) |
C22—C21—C26 | 117.9 (5) | C27—O22—H22A | 112 (5) |
C22—C21—C28 | 114.0 (5) | C28—O23—H22A | 112 (4) |
C26—C21—C28 | 128.1 (5) | ||
N12—C11—C12—C13 | −179.0 (6) | C24—C25—C26—C27 | 177.2 (7) |
N11—C11—C12—C13 | −0.2 (9) | C22—C21—C26—C25 | 0.2 (8) |
C11—C12—C13—C14 | 1.6 (11) | C28—C21—C26—C25 | 179.0 (6) |
C12—C13—C14—C15 | −1.9 (11) | C22—C21—C26—C27 | −178.7 (6) |
C13—C14—C15—N11 | 0.9 (10) | C28—C21—C26—C27 | 0.1 (9) |
N12—C11—N11—C15 | 178.1 (6) | C25—C26—C27—O21 | 1.4 (9) |
C12—C11—N11—C15 | −0.8 (9) | C21—C26—C27—O21 | −179.7 (6) |
C14—C15—N11—C11 | 0.5 (10) | C25—C26—C27—O22 | −179.5 (7) |
C26—C21—C22—C23 | 1.2 (10) | C21—C26—C27—O22 | −0.6 (10) |
C28—C21—C22—C23 | −177.7 (6) | C22—C21—C28—O24 | −1.0 (7) |
C21—C22—C23—C24 | −1.1 (11) | C26—C21—C28—O24 | −179.9 (6) |
C22—C23—C24—C25 | −0.6 (11) | C22—C21—C28—O23 | −179.9 (6) |
C23—C24—C25—C26 | 2.1 (11) | C26—C21—C28—O23 | 1.2 (8) |
C24—C25—C26—C21 | −1.9 (9) |
D—H···A | D—H | H···A | D···A | D—H···A |
O22—H22A···O23 | 1.08 (10) | 1.32 (10) | 2.402 (7) | 173 (9) |
N11—H1N···O24i | 0.93 (7) | 1.78 (7) | 2.705 (7) | 180 (7) |
N12—H12A···O23i | 0.86 | 2.11 | 2.965 (7) | 174 |
N12—H12B···O22ii | 0.86 | 2.31 | 3.003 (8) | 138 |
C12—H12···O23iii | 0.93 | 2.53 | 3.374 (8) | 151 |
C14—H14···O21iv | 0.93 | 2.50 | 3.203 (9) | 132 |
Symmetry codes: (i) −x, y+1/2, −z+1; (ii) x, y, z+1; (iii) x+1, y, z+1; (iv) −x+2, y−1/2, −z+1. |
Contact | cation+anion | cation | anion |
H···H | 32.0 | 40.4 | 30.6 |
O···H/H···O | 31.0 | 26.3 | 31.6 |
C···H/H···C | 22.0 | 18.2 | 24.0 |
C···O | 7.3 | 4.6 | 8.8 |
N···H/H···N | 2.5 | 5.1 | 0.4 |
C···C | 2.5 | 2.2 | 2.6 |
Acknowledgements
SAB and VS are thankful to the management, Kalasalingam Academy of Research and Education, Krishnankoil, for their support.
Funding information
Funding for this research was provided by: Council of Scientific and Industrial Research.
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