CRYSTAL GROWTH & DESIGN
Preparation of Cocrystals of 2-Amino-3-nitropyridine with Benzenesulfonic Acids for Second-Order Nonlinear Optical Materials
2004 VOL. 4, NO. 4 807-811
Hideko Koshima,*,† Hironori Miyamoto,† Ichizo Yagi,‡ and Kohei Uosaki‡ Department of Applied Chemistry, Faculty of Engineering, Ehime University, Matsuyama 790-8577 Japan, and Graduate School of Science, Division of Chemistry, Hokkaido University, N10W8, Kita-ku, Sapporo, Hokkaido 060-0810 Japan Received October 9, 2003;
Revised Manuscript Received April 21, 2004
ABSTRACT: Noncentrosymmetic and chiral cocrystals were prepared from 2-amino-3-nitropyridine (2A3NP) and achiral benzenesulfonic acids (Ar-SO3H), which were designed for second-order nonlinear optical materials. Both components are commonly crystallized in 1:1 ionic forms of 2A3NPH+‚Ar-SO3-. The molecular packings of cocrystals are controlled by the aromatic-aromatic interactions as well as multidirectional ionic and hydrogen bonds between the 2A3NPH+ cations and the sulfonate anions. The crystal of 2A3NP with p-toluenesulfonic acid belongs to acentric space group Pna21, in which 2A3NPH+ cations and anions are alternately stacked with some dihedral angle due to the large sulfonate anions to form two independent column structures in a perpendicular direction to each other. The crystal of 2A3NP with p-nitrobenzenesulfonic acid crystallizes into chiral space group P212121. The 2A3NPH+ cations and the anions are also alternately stacked to give herringbone network of 2A3NPH+ cations. The crystal of 2A3NP with 2,5-dimethylbenzenesulfonic acid belongs to acentric space group Pn, in which two independent stacking structures are formed in perpendicular directions. Second-harmonic generation (SHG) power measured with an evanescent wave technique revealed the relatively high SHG efficiency of cocrystal of 2A3NP with p-toluenesulfonic acid, 2-fold larger than that of well-known m-nitroaniline. Noncentrosymmetric and chiral crystals formed from achiral organic compounds1,2 have inherently secondorder nonlinear optical (NLO) character.3-5 Our study of the preparation of noncentrosymmetric and chiral cocrystals by combining two different achiral molecules has revealed that the cocrystal approach provides higher possibilities for crystal structure design rather than a single-component approach.6-8 Organic-inorganic crystals of 2-amino-5-nitropyridine (2A5NP) with inorganic acids such as phosphoric acid were already reported by Masse and co-workers.9 Recently, we have prepared a series of cocrystals from 2A5NP and achiral benzenesulfonic acids (Ar-SO3H), and one of these cocrystals afforded high second-harmonic generation (SHG) power, larger by an order of magnitude than that of mnitroaniline.10 The organic-organic cocrystal approach confirmed the validity for crystal engineering of NLO materials. Hence, we tried to prepare a new series of cocrystals of 2-amino-3-nitropyridine (2A3NP) 1, which is an isomer of 2A5NP, by combining it with various benzenesulfonic acids to find three SHG cocrystals (Chart 1). The key molecule is 2A3NP 1, which has a nitro group as an electron donor and an amino group as an electron acceptor to induce NLO character. The nitrogen of pyridine moiety also acts as a cationic binding site, the nitro group as a hydrogen acceptor and the amino group as a hydrogen donor. The achiral benzenesulfonic acids a-c were used as strong anionic connectors. Both components (2 mmol:2 mmol) were dissolved in methanol (20 mL) and 2 M HCl (1 mL) with gentle heating * To whom correspondence should be addressed. Fax: +81-89-9279923. E-mail:
[email protected]. † Ehime University. ‡ Hokkaido University.
Chart 1
followed by evaporation to give cocrystals 1‚a-1‚c. Several millimeter sizes of single crystals were also obtained by slow evaporation at room temperature. The color of three crystals is light yellow. The melting points are 173-174, 200-203, and 185-186 °C, respectively, which are fairly high due to the ionic crystals. The crystals were submitted to X-ray crystallographic analysis to confirm their noncentrosymmetric (1‚a and 1‚c) and chiral (1‚b) nature in the space groups Pna21 and Pn, and P212121, respectively. The crystal data are summarized in Table 1. Both components are crystallized in a 1:1 ratio of 2A3NPH+ cation and Ar-SO3anion. The ionic species are formed by the transformation of the proton of sulfonic acid group of a-c to the pyridine nitrogen of 1. In the 2A3NPH+ cation, intramolecular hydrogen bond (N-Ha‚‚‚-Ob-N) is commonly formed between the amino group and the nitro
10.1021/cg034187s CCC: $27.50 © 2004 American Chemical Society Published on Web 06/17/2004
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Table 1. Crystal Data of the Cocrystals formula M cryst habit cryst syst space group a/Å b/Å c/Å β/deg cell vol/Å3 calcd density g cm-3 Z data/params R Rw
1‚a
1‚b
1‚c
C12H13O5N3S 311.31 platelet orthorhombic Pna21 (#33) 27.922(6) 7.4655(9) 13.315(2) 90.0 2775(2) 1.490
C11H10O7N4S 342.28 platelet orthorhombic P212121 (#19) 6.5727(7) 9.2129(8) 23.952(1) 90.0 1410.6(2) 1.612
C13H15O5N3S 325.34 block monoclinic Pn (#7) 8.2712(4) 13.0192(6) 13.9960(8) 87.313(2) 1505(1) 1.435
8 2516/381 0.045 0.102
4 1479/210 0.051 0.123
4 2722/392 0.070 0.169
Table 2. Intramolecular and Intermolecular Structural Parameters in the Cocrystalsa 1‚a interactions
a
Å
1‚b deg
Å
N-Ha‚‚‚-Ob-N N-Ha‚‚‚-Ob-N
2.15 (2.67) 2.27 (2.65)
Intramolecular Bonds 118 1.92 (2.67) 119
PyN+-H‚‚‚-Oa-S N-Ha‚‚‚-Ob-S N-Hb‚‚‚-Oc-S PyN+-H‚‚‚-Oa-S N-Ha‚‚‚-Ob-S N-Hb‚‚‚-Oc-S
1.84 (2.70) 1.92 (2.76) 1.93 (2.76) 1.94 (2.86) 2.36 (3.20) 2.10 (2.93)
Intermolecular Bonds 163 1.98 (2.79) 154 1.91 (2.73) 153 162 159 151
1‚c deg
Å
deg
133
2.08 (2.69) 2.01 (2.67)
119 124
165 172
1.73 (2.66) 2.34 (3.07) 1.93 (2.87) 1.72 (2.63) 1.93 (2.89) 2.14 (2.98)
168 133 172 155 170 144
The value in parentheses presents the distance between the N and O atom.
group. Three kinds of intermolecular bonding occur between the cation and anion in all three crystals. One is the pyridinium salt bridge (PyN+-H‚‚‚-Oa-S) between the pyridium cation and the Ar-SO3- anion. The other two interactions are the hydrogen bonds (N-Ha‚‚‚-Ob-S and N-Hb‚‚‚-Oc-S) between the NH2 group of 2A3NPH+ cation and the Ar-SO3- anion. The distances of the salt bridges and hydrogen bonds are in the range of 1.7-1.9 and 1.9-2.4 Å, respectively (Table 2). Figure 1 shows the molecular arrangement in the acentric crystal 1‚a. Two independent pairs A and B of 2A3NPH+ cations and p-toluenesulfonate anions exist in almost a perpendicular direction to each other. The 2A3NPH+ cations and the sulfonate anions of pair A are alternately stacked almost parallel with a dihedral angle of 5.4(7)°, and the pyridine and the phenyl moieties are considerably superimposed (Figure 1a) to form a 2-fold helical arrangement along the c axis (Figure 1b). The 2A3NPH+ and the anions of pair B are also alternately arranged in parallel with a dihedral angle of 2.3(7)°, but the pyridinium and phenyl moieties are partially superimposed (Figure 1b) to give nearly independent two columns along the b axis (Figure 1a). A pyridinium salt bridge (PyN+-H‚‚‚-O-S) and a hydrogen bond (N-H‚‚‚-O-S) are formed between the perpendicularly neighboring A and B stacks. A hydrogen bond (N-H‚‚‚-O-S) is also formed within each A and B stack. Figure 2 shows the molecular arrangement in the chiral crystal 1‚b. The 2A3NPH+ cation and the pnitrobenzenesulfonate anion are alternately stacked with some dihedral angle 21.1(2)° due to the large SO3anion. The pyridinium moiety of the cation and the
phenyl moiety of the anion are completely separated on the ac plane (Figure 2a). The 2A3NPH+ cations are arranged with the 2-fold screw axis to form a herringbone network along the b axis (Figure 2b). A 2A3NPH+ cation is connected to the neighboring anion through the pyridinium salt bridge (PyN+-H‚‚‚-Oa-S) and the hydrogen bond (N-Ha‚‚‚-Ob-S) in the same unit cell. However, the third sulfonate oxygen (-Oc-S) does not participate in any hydrogen bonding but interacts with neighboring nitro groups of 2A3NPH+ cation and the sulfonate anion. Figure 3 shows the molecular arrangements in the acentric crystal 1‚c. Two independent pairs A and B of 1 and c exist in the asymmetric unit (Figure 3a). The components 1 and c of pair A are alternately stacked with a dihedral angle of 7.1(5)° along the c axis. The 2A3NP+ cations and the sulfonate anions form independent zigzag arrangements along the diagonal axis on the ac plane as well as independent column structures along the a axis (Figure 3b). The components 1 and c of pair B are also alternately arranged with a dihedral angle of 5.2(5)° along the diagonal axis on the ac plane to form independent slanting layers of 2A3NP+ cations and sulfonate anions along the a axis (Figure 3c). A pyridinium salt bridge (PyN+-H‚‚‚-Oa-S) and a hydrogen bond (N-Ha‚‚‚-Ob-S) are formed between the perpendicularly neighboring A and B stacks. Another hydrogen bond (N-Hb‚‚‚-Ob-S) is formed within the each A and B stacks (Figure 3a). The intermolecular bindings and alternate stackings in 1‚c are similar to those in the crystals of 1‚a and 1‚b, but the different substituent groups, the methyl group of a, the nitro group of b, and two methyl groups of c, lead to the different packing arrangements among 1‚a, 1‚b, and
2-Amino-3-nitropyridine Cocrystals
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Figure 2. Molecular arrangements on the (a) bc plane and (b) ab plane in 1‚b. Yellow, red, blue, grey, and white atoms represent sulfur, oxygen, nitrogen, carbon, and hydrogen atoms, respectively. Figure 1. Molecular arrangements on the (a) ab plane and (b) ac plane in 1‚a. Yellow, red, blue, grey, and white atoms represent sulfur, oxygen, nitrogen, carbon, and hydrogen atoms, respectively.
1‚c. Namely, the organic-organic cocrystals give a variety of molecular arrangement. SHG powers of the crystals 1‚a-1‚c were measured in powder form by the total reflection method using a hemicylindrical BK7 glass prism, based on SHG with the evanescent wave (SHEW) technique.11 The fundamental wave (λ ) 1200 nm) was used with the fixed incident angle of 60°. Angle dependence of the SHG strength was not measured and parameter fitting was not applied because the refraction indices of 1‚a-1‚c are similar due to the analogous component molecules. The dependence of laser powers on the signals at 600 nm were measured and compared with well-known urea,12 m-nitroaniline,13 and 4-(N,N-dimethylamino)-3acetamidonitrobenzene (DAN)14 as standard SHG crystals. The results are summarized in Table 3. The relative SHG value of 1‚a was larger by an order of magnitude than that of urea, 2-fold larger than that of m-nitroaniline, and comparable to that of DAN. The SHG power of 1‚b was 2-fold larger than that of urea. The SHG power of 1‚c was the lowest of the three crystals. Absorption spectra of the powdered crystals were measured by the reflection method using barium sulfate as a reference. The cutoff wavelengths determined from the absorption edges were around 440 nm, favorable to SHG materials.
These SHG properties should reflect the molecular arrangements in the crystals. For instance, as we previously reported, the cocrystal of 2A5NP with pphenolsulfonic acid had very high SHG power by an order of magnitude of m-nitroaniline.10 The reason was elucidated that the herringbone arrangement of the 2A5NPH+ cations in the lattice induced the large charge-transfer enhancement to result in the high SHG efficiency. In the cocrystal 1‚b, the 2A3NPH+ cations form a similar herringbone network along the b axis (Figure 2b). However, the larger pitch (9.22 Å) of the 2A3NPH+ cations in 1‚b than that (6.36 Å) in the crystal of 2A5NP with p-phenolsulfonic acid cannot induce the large charge-transfer interaction to lead to the relatively low SHG value, 0.62 to that of m-nitroaniline (Table 3). In the case of cocrystal 1‚a, the columnar stacking of the 2A3NPH+ cations of the pair B along the b axis should induce the charge-transfer enhancement. However, the slightly large plane-to-plane distance (7.47 Å) of the 2A3NPH+ cations leads to the mild SHG efficiency, 2-fold larger than that of m-nitroaniline. On the other hand, the 2A3NPH+ cations and the ptoluenesulfonate anions of the pair A are alternately arranged in almost superimposed manner of the pyridinium ring and the benzene ring along the c axis (Figure 1a,b). The molecular arrangement in the pair A should disturb the charge-transfer interaction among the 2A3NPH+ chromophores to lead to the scarce enhancement of the SHG power. In the cocrystal 1‚c, the 2A3NPH+ cations of the pair A form a slanting column structure along the a axis
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Figure 3. Molecular arrangements on the (a) bc plane and ac plane of (b) A pairs and (c) B pairs in 1‚c. Yellow, red, blue, grey, and white atoms represent sulfur, oxygen, nitrogen, carbon, and hydrogen atoms, respectively. Table 3. SHG Powers of the Cocrystals cocrystal 1‚a 1‚b 1‚c
relative SHG power to urea m-nitroaniline DAN 7.78 2.33 0.49
2.06 0.62 0.13
0.86 0.26 0.05
cutoff wavelength (nm) 445 440 440
(Figure 3b). However, the large plane-to-plane distance (8.27 Å) hardly induces the charge-transfer enhancement among the 2A3NPH+ chromophores. In the pair B, the alternate arrangement of the 2A3NPH+ cations and the sulfonate anions along the diagonal axis on the ac plane, as well as the slanting layers of 2A3NP+ cations along the a axis, scarcely contribute to induce the SHG (Figure 3c). Such the molecular arrangements are the reason the cocrystal 1‚c has a very small SHG efficiency. In conclusion, the cocrystal approach using 2-amino3-nitropyridine and benzenesulfonic acids provided a new series of second-order NLO materials. The relation between the crystal structure and SHG power was elucidated. Acknowledgment. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology of Japan and Kurata Memorial Hitachi Science and Technology in Japan. Supporting Information Available: X-ray crystallographic information files (CIF) are available for 1‚a-1‚c. This material is available free of charge via the Internet at http:// pubs.acs.org.
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CG034187S
