research communications
H-imidazol-3-ium
of 2-ethyl-4-methyl-1-(2-oxido-3,4-dioxocyclobut-1-en-1-yl)-1aOndokuz Mayis University, Faculty of Arts and Sciences, Department of Physics, Atakum, Samsun, Turkey, and bOndokuz Mayis University, Faculty of Arts and Sciences, Department of Chemistry, Atakum, Samsun, Turkey
*Correspondence e-mail: iclalb@omu.edu.tr
In the title inner salt molecule, C10H10N2O3, the four-membered cyclobutene ring is twisted by 7.1 (2)° with respect to the five-membered imidazole ring. The crystal packing exhibits an R22(9) hydrogen-bonding ring motif through N—H⋯O and C—H⋯O interactions. The potential non-linear optical properties were studied by a computational ab initio calculations performed at the DFT/B3LYP/6–31++G(d,p) level of theory.
Keywords: crystal structure; squarene; hydrogen bonding; quantum chemical calculations; non-linear optical properties.
CCDC reference: 945212
1. Chemical context
The study of the non-linear optical (NLO) properties of organic molecules and crystals are of great interest in physics, chemistry and applied technologies (Chemla et al., 1987). Certain classes of organic compounds exhibit very pronounced NLO and electro-optical (EO) effects. Their non-linearity is based on the presence of molecular units containing strongly delocalized π-electron systems with the donor and acceptor groups sited at opposite ends of the molecule (Bosshard et al., 1995; Kolev et al., 2008). The study of the development of new non-centrosymmetric single-crystal NLO materials to obtain efficient frequency doublers is the subject of crystal engineering. In this context, some squaric acid derivatives together with cyclobutenediones with proper substitution groups have been found to be of interest in terms of their high NLO responses (Kolev et al., 2008).
Squaric acid gives rise to two structurally different classes of derivatives, which can be described by the general molecular structures 1,3-N-squarenes and amine-containing molecule (Gsänger et al., 2014; Kolev et al., 2005). The squarenes shows photo-chemical, photo-conductive and NLO properties and can therefore be used as electron acceptors in photo-sensitive devices (Lindsay & Singer, 1995). On the other hand, substituted play an important role in NLO behavior due to their dipolar structures (Kolev et al., 2004). The conversion of the N2 atom of 2-ethyl-4-methylimidazole into the corresponding betaine squaric acid form provides a way of enhancing the charge-transfer transition at the molecular level.
This study reports a novel betain form of squaric acid with a 2-ethyl-4-methylimidazole molecule. The
together with its NLO properties, are reported here.2. Structural commentary
A view of the . The C1—C2—C3, C2—C1—C4 and C2—C3—C4 bond angles in the squarate ring system are almost 90°. The C1—C4—C3 bond angle is 95.0 (3)° due to the C4 atom bonding to the imidazole ring through N2 atom. The C—C distances in the planar squarate ring system of the compound reflect partial double-bond character for C1—C4 and C3—C4 [1.426 (4) and 1.440 (4) Å, respectively]. Single-bond character is observed for C1—C2 and C2—C3 [1.514 (5) and 1.516 (5) Å, respectively]. The observed bond lengths indicate a degree of delocalization in the squarate ring, as has been observed in previous studies (Kolev et al., 2005; Korkmaz et al., 2013). The C1—O1 and C3—O3 bond lengths are 1.234 (4) and 1.216 (4) Å, respectively. Conjugation of the squarate ring and the positively charged strong acceptor N2 result in a shortening of the carbonyl group C2=O2 bond [1.206 (4) Å]. A strong donor effect is observed for the 2-ethyl-4-methylimidazole group.
is given in Fig. 13. Supramolecular features
The structural properties of the molecule are the result of an extensive network of hydrogen-bonding interactions. The N—H⋯O and C—H⋯O heteronuclear hydrogen bonds that form an (9) ring motif contribute as both donor and acceptor to the crystal packing (Table 1, Fig. 2). The N⋯O distance should be in the region of 2.72–2.78 Å, The observed N1—H1⋯O1i D⋯A distance [2.680 (3) Å; Table 1] corresponds to a [(+/−)CAHB] interaction. Looking at the N⋯O distances in the symmetry-related hydrogen bonding between squarate ring systems, it can be seen that the interaction is slightly shorter than the relevant interval values and is symbolized as either N+—H⋯ O1\2− or N+—H⋯ O− (+/−)CAHB (Korkmaz & Bulut, 2013). The C—H⋯O (Table 1, Fig. 2) interactions correspond to weak hydrogen bonding with an electrostatic or dispersion character according to the classification of Jeffrey (1997). In the structure, the weak C—H⋯O interactions are responsible for the connection between the ribbons. Therefore it can be said that the hydrogen bonds form the molecular assembly, producing a uni-dimensional construction in the supramolecular view, while the C—H⋯O interactions extend this to bi-dimensionality.
4. Computational studies
We have applied computational methods to evaluate the compound in terms of NLO activity. The values of the μtot), linear polarizability (αtot) and first-order hyperpolarizability (βtot) of the molecule were calculated at the DFT/B3LYP method level of 6-31++G(d,p) by using Gaussian 03W program (Frisch et al., 2004). Urea is accepted as a prototype molecule for non-linear optical materials and results were compared with its values (Pu, 1991). The calculation results for μtot, αtot and βtot for urea at the same level are 3.8583 D, 4.9991 Å3 and 3.2637 x 10−31cm5/esu, respectively. The obtained values of μtot, αtot and βtot for the title compound are 14.8448 D, 22.2315 Å3 and 6.8664 × 10−30 cm5/esu, respectively. These values are comparable with those for some of the pyridinium-betains of squaric acid (Kolev et al., 2008). The value of βtot appears to be much greater than that of urea. This result clearly indicates that the title compound is a strong candidate to develop a non-linear optical material. This is a prerequisite for the design of efficient second- and third-order non-linear optical materials. It should be noted that the title compound crystallized in a centrosymmetric (P21/n).
(5. Synthesis and crystallization
The title compound was synthesized according to the procedure of Schmidt et al. (1984). Squaric acid (H2Sq; 1g, 8.7 mmol) and 2-ethyl-4-methylimidazole (0.96 g; 8.7 mmol) were dissolved in acetic anhydride (30 cm3) in the molar ratio 1:1 and the solution was heated to 323 K using a controlled bath and stirred for 1 h. The reaction mixture was then cooled slowly to room temperature. The crystals formed were filtered, washed with water and methanol, and dried in air. A few days later, well-formed crystals were selected for X-ray studies. Elemental analysis for the compound (green, yield 48%) C10H10N2O3: calculated: C, 58.00; H, 5.11; N, 13.56%. Found: C, 58.25; H, 4.89; N, 13.59%. M.p. 544 K.
6. Refinement
Crystal data, data collection and structure . The H atoms attached to C5 and N1 (H5 and H1, respectively) were located in Fourier difference maps and freely refined. The remaining H atoms were positioned geometrically (C—H = 0.96–0.97 Å) and refined using a riding model with Uiso(H) = 1.2 or 1.5Ueq(C).
details are summarized in Table 2Supporting information
CCDC reference: 945212
https://doi.org/10.1107/S2056989016009725/xu5888sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016009725/xu5888Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989016009725/xu5888Isup3.cml
Data collection: CrysAlis PRO (Agilent, 2011); cell
CrysAlis PRO (Agilent, 2011); data reduction: CrysAlis PRO (Agilent, 2011); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 2005); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015).C10H10N2O3 | Dx = 1.367 Mg m−3 |
Mr = 206.20 | Melting point: 544 K |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 4.7940 (4) Å | Cell parameters from 943 reflections |
b = 14.4120 (9) Å | θ = 4.0–30.4° |
c = 14.5360 (9) Å | µ = 0.10 mm−1 |
β = 93.848 (6)° | T = 293 K |
V = 1002.04 (12) Å3 | Prism, green |
Z = 4 | 0.34 × 0.22 × 0.22 mm |
F(000) = 432 |
Agilent SuperNova (single source at offset) Eos diffractometer | 3048 independent reflections |
Radiation source: SuperNova (Mo) X-ray Source | 1363 reflections with I > 2σ(I) |
Detector resolution: 16.0454 pixels mm-1 | Rint = 0.048 |
ω scans | θmax = 30.5°, θmin = 4.0° |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2011) | h = −6→6 |
Tmin = 0.708, Tmax = 1.000 | k = −16→20 |
5496 measured reflections | l = −20→11 |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Hydrogen site location: mixed |
R[F2 > 2σ(F2)] = 0.080 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.247 | w = 1/[σ2(Fo2) + (0.0793P)2 + 0.493P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
3048 reflections | Δρmax = 0.33 e Å−3 |
144 parameters | Δρmin = −0.35 e Å−3 |
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 | ||
H5 | 0.783 (8) | 0.546 (3) | 0.562 (2) | 0.060 (11)* | |
H1 | 0.312 (8) | 0.693 (3) | 0.724 (2) | 0.069 (12)* | |
O1 | 0.2719 (5) | 0.30379 (16) | 0.74162 (16) | 0.0548 (7) | |
N1 | 0.3883 (6) | 0.63979 (19) | 0.69274 (18) | 0.0419 (6) | |
N2 | 0.5210 (5) | 0.50284 (17) | 0.65685 (16) | 0.0382 (6) | |
O3 | 0.9453 (5) | 0.38166 (18) | 0.54799 (18) | 0.0614 (7) | |
C4 | 0.5674 (6) | 0.4072 (2) | 0.6522 (2) | 0.0375 (7) | |
C3 | 0.7687 (7) | 0.3595 (2) | 0.6001 (2) | 0.0432 (8) | |
O2 | 0.7096 (6) | 0.18740 (16) | 0.63047 (19) | 0.0675 (8) | |
C2 | 0.6603 (7) | 0.2691 (2) | 0.6374 (2) | 0.0454 (8) | |
C8 | 0.3574 (6) | 0.5506 (2) | 0.7126 (2) | 0.0393 (7) | |
C1 | 0.4553 (7) | 0.3249 (2) | 0.6897 (2) | 0.0409 (7) | |
C5 | 0.6580 (7) | 0.5660 (2) | 0.6024 (2) | 0.0415 (7) | |
C6 | 0.6446 (9) | 0.7446 (2) | 0.5893 (2) | 0.0590 (10) | |
H6A | 0.5446 | 0.7912 | 0.6210 | 0.089* | |
H6B | 0.8420 | 0.7551 | 0.5998 | 0.089* | |
H6C | 0.5932 | 0.7479 | 0.5244 | 0.089* | |
C9 | 0.1873 (8) | 0.5129 (2) | 0.7852 (2) | 0.0512 (9) | |
H9A | 0.1038 | 0.4547 | 0.7641 | 0.061* | |
H9B | 0.0369 | 0.5559 | 0.7955 | 0.061* | |
C7 | 0.5737 (7) | 0.6514 (2) | 0.6245 (2) | 0.0430 (8) | |
C10 | 0.3587 (12) | 0.4966 (3) | 0.8760 (3) | 0.0884 (16) | |
H10A | 0.2398 | 0.4723 | 0.9208 | 0.133* | |
H10B | 0.5056 | 0.4531 | 0.8665 | 0.133* | |
H10C | 0.4387 | 0.5543 | 0.8979 | 0.133* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0629 (16) | 0.0385 (13) | 0.0661 (15) | −0.0065 (11) | 0.0278 (13) | 0.0052 (11) |
N1 | 0.0482 (16) | 0.0340 (14) | 0.0439 (14) | 0.0004 (12) | 0.0053 (12) | −0.0031 (11) |
N2 | 0.0423 (15) | 0.0330 (13) | 0.0404 (12) | −0.0001 (11) | 0.0110 (11) | 0.0004 (10) |
O3 | 0.0610 (17) | 0.0521 (15) | 0.0753 (17) | 0.0066 (13) | 0.0351 (14) | 0.0089 (13) |
C4 | 0.0394 (16) | 0.0330 (16) | 0.0405 (15) | 0.0005 (13) | 0.0057 (13) | 0.0015 (12) |
C3 | 0.0439 (18) | 0.0396 (18) | 0.0474 (17) | 0.0035 (14) | 0.0118 (14) | 0.0021 (14) |
O2 | 0.0790 (19) | 0.0345 (14) | 0.0906 (19) | 0.0097 (13) | 0.0179 (15) | 0.0010 (13) |
C2 | 0.0479 (19) | 0.0380 (18) | 0.0511 (18) | 0.0041 (15) | 0.0089 (15) | 0.0028 (14) |
C8 | 0.0377 (16) | 0.0379 (17) | 0.0426 (15) | 0.0001 (13) | 0.0057 (13) | −0.0020 (13) |
C1 | 0.0448 (18) | 0.0337 (16) | 0.0447 (16) | −0.0004 (13) | 0.0074 (14) | 0.0013 (13) |
C5 | 0.0475 (19) | 0.0337 (17) | 0.0446 (16) | −0.0016 (14) | 0.0128 (15) | 0.0027 (13) |
C6 | 0.081 (3) | 0.038 (2) | 0.060 (2) | −0.0057 (18) | 0.018 (2) | 0.0014 (16) |
C9 | 0.055 (2) | 0.0435 (19) | 0.058 (2) | −0.0025 (16) | 0.0230 (17) | −0.0024 (16) |
C7 | 0.0524 (19) | 0.0368 (17) | 0.0403 (15) | −0.0042 (15) | 0.0062 (14) | 0.0006 (13) |
C10 | 0.128 (5) | 0.089 (3) | 0.049 (2) | −0.035 (3) | 0.012 (2) | 0.010 (2) |
C1—O1 | 1.234 (4) | C8—C9 | 1.479 (4) |
N1—C8 | 1.328 (4) | C5—C7 | 1.341 (4) |
N1—C7 | 1.386 (4) | C5—H5 | 0.91 (4) |
N1—H1 | 0.97 (4) | C6—C7 | 1.485 (5) |
C8—N2 | 1.353 (4) | C6—H6A | 0.9600 |
N2—C5 | 1.399 (4) | C6—H6B | 0.9600 |
C4—N2 | 1.399 (4) | C6—H6C | 0.9600 |
C3—O3 | 1.216 (4) | C9—C10 | 1.526 (5) |
C1—C4 | 1.426 (4) | C9—H9A | 0.9700 |
C3—C4 | 1.440 (4) | C9—H9B | 0.9700 |
C2—C3 | 1.516 (5) | C10—H10A | 0.9600 |
C2—O2 | 1.206 (4) | C10—H10B | 0.9600 |
C1—C2 | 1.514 (5) | C10—H10C | 0.9600 |
C8—N1—C7 | 111.0 (3) | N2—C5—H5 | 121 (2) |
C8—N1—H1 | 127 (2) | C7—C6—H6A | 109.5 |
C7—N1—H1 | 121 (2) | C7—C6—H6B | 109.5 |
C8—N2—C5 | 108.7 (3) | H6A—C6—H6B | 109.5 |
C8—N2—C4 | 129.1 (3) | C7—C6—H6C | 109.5 |
C5—N2—C4 | 122.1 (3) | H6A—C6—H6C | 109.5 |
N2—C4—C1 | 137.4 (3) | H6B—C6—H6C | 109.5 |
N2—C4—C3 | 127.6 (3) | C8—C9—C10 | 112.5 (3) |
C1—C4—C3 | 95.0 (3) | C8—C9—H9A | 109.1 |
O3—C3—C4 | 136.1 (3) | C10—C9—H9A | 109.1 |
O3—C3—C2 | 135.9 (3) | C8—C9—H9B | 109.1 |
C2—C3—C4 | 88.0 (2) | C10—C9—H9B | 109.1 |
O2—C2—C1 | 134.2 (3) | H9A—C9—H9B | 107.8 |
O2—C2—C3 | 137.3 (3) | C5—C7—N1 | 106.2 (3) |
C1—C2—C3 | 88.5 (2) | C5—C7—C6 | 131.9 (3) |
N1—C8—N2 | 106.5 (3) | N1—C7—C6 | 121.9 (3) |
N1—C8—C9 | 125.8 (3) | C9—C10—H10A | 109.5 |
N2—C8—C9 | 127.6 (3) | C9—C10—H10B | 109.5 |
O1—C1—C4 | 137.8 (3) | H10A—C10—H10B | 109.5 |
O1—C1—C2 | 133.6 (3) | C9—C10—H10C | 109.5 |
C2—C1—C4 | 88.6 (2) | H10A—C10—H10C | 109.5 |
C7—C5—N2 | 107.6 (3) | H10B—C10—H10C | 109.5 |
C7—C5—H5 | 132 (2) | ||
C8—N2—C4—C1 | 8.9 (6) | C4—N2—C8—C9 | 1.3 (5) |
C5—N2—C4—C1 | −173.9 (3) | N2—C4—C1—O1 | 0.0 (7) |
C8—N2—C4—C3 | −171.7 (3) | C3—C4—C1—O1 | −179.5 (4) |
C5—N2—C4—C3 | 5.6 (5) | N2—C4—C1—C2 | 179.6 (4) |
N2—C4—C3—O3 | −0.7 (6) | C3—C4—C1—C2 | 0.0 (3) |
C1—C4—C3—O3 | 178.9 (4) | O2—C2—C1—O1 | −0.6 (7) |
N2—C4—C3—C2 | −179.7 (3) | C3—C2—C1—O1 | 179.6 (4) |
C1—C4—C3—C2 | 0.0 (3) | O2—C2—C1—C4 | 179.8 (4) |
O3—C3—C2—O2 | 1.2 (7) | C3—C2—C1—C4 | 0.0 (2) |
C4—C3—C2—O2 | −179.8 (4) | C8—N2—C5—C7 | −0.9 (4) |
O3—C3—C2—C1 | −179.0 (4) | C4—N2—C5—C7 | −178.6 (3) |
C4—C3—C2—C1 | 0.0 (2) | N1—C8—C9—C10 | −93.9 (4) |
C7—N1—C8—N2 | −0.5 (3) | N2—C8—C9—C10 | 82.6 (4) |
C7—N1—C8—C9 | 176.7 (3) | N2—C5—C7—N1 | 0.5 (4) |
C5—N2—C8—N1 | 0.8 (3) | N2—C5—C7—C6 | −179.3 (3) |
C4—N2—C8—N1 | 178.3 (3) | C8—N1—C7—C5 | −0.1 (4) |
C5—N2—C8—C9 | −176.3 (3) | C8—N1—C7—C6 | 179.8 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O1i | 0.97 (4) | 1.73 (4) | 2.680 (3) | 164 (3) |
C6—H6A···O1i | 0.96 | 2.59 | 3.378 (4) | 139 |
C9—H9A···O1 | 0.97 | 2.35 | 3.112 (4) | 135 |
C9—H9B···O2i | 0.97 | 2.51 | 3.429 (5) | 158 |
Symmetry code: (i) −x+1/2, y+1/2, −z+3/2. |
Acknowledgements
We would like thank the Ondokuz Mayıs University Research Fund (PYO·FEN.1904.12.020) for financial support and also Dr Murat Taş for collecting the XRD data.
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