The title compound (C7H8N2O2), is monoclinic, space group P21/n, witha=9.552(2),b=5.677(2),c=13.586(3)A, β=92.68(2)0, andDx=1.374 g-cm−3 forZ=4. The refinement converged toR=0.043,wR=0.038. The molecule is approximately planar, with dihedral angles of 3.7(2.1)0 between the amino group and the aromatic ring, and 3.2(2)0 between the nitro group and the ring. According to the UV spectrum in solution, the molecular geometry indicates weak intramolecular charge transfer. The three-dimensional structure is stabilized by three intermolecular H bonds. A bifurcated one induces the formation of chains along$[10\bar 1]$, while the other two link molecules that belong to adjacent chains and are related by an inversion center.Facultad de Ciencias Exacta

Ellena, Javier Alcides

Punte, Graciela María del Carmen

Rivero, Blas Eduardo

Journal of Crystallographic and Spectroscopic Research

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Journal of Chemical Crystallography. Vol. 26, No. 5, 1996 Conformational studies of substituted nitroanilines: geometry of 2-methyl-5-nitroaniline J. El lena,  (1)* G. Punte ,  (~) and B. E. Rivero (1) Received January 10, 1995 The title compound (C7.HsN202), is monoclinic, space group P21/n, with a = 9.552(2), b = 5.677(2), c = 13.586(3)A, 13 = 92.68(2) ~ and D~ = 1.374 g-cm -3 for Z = 4. The refinement converged to R = 0.043, wR = 0.038. The molecule is approximately planar, with dihedral angles of 3.7(2.1) ~ between the amino group and the aromatic ring, and 3.2(2) ~ between the nitro group and the ring. According to the UV spectrum in solution, the molecular geometry indicates weak intramolecular charge transfer. The three-dimensional structure is stabilized by three intermolecular H bonds. A bifurcated one induces the formation of chains along [101], while the other two link molecules that belong to adjacent chains and are related by an inversion center. KEY WORDS: Nitroaniline derivatives; 2-methyl-5-nitroaniline; nonlinear optic; spectroscopic study; structure determination; hydrogen bonds. Introduction Tailoring materials with nonlinear optical response, e.g., second harmonic generation (SHG), has been the aim of several studies of nitroaniline deriva- tives. It has been found that weak hydrogen bonds seem to determine the molecular organization of these compounds. 1-3 The authors propose that N-H. - .O interactions, with specific geometries and lengths exceeding the sum of the Van der Waals radii, are responsible for the formation of polar chains not only in solid state but also in solution.~ Therefore, the appro- priate packing of these chains would lead to the acen- tric crystals required for SHG. The present study intends to add to the under- standing of  the parameters that govem the molecular aggregation and the macroscopic properties of nitroan- ilines. The 2-methyl-4-nitroaniline (MNA) is an isomer of the title compound (M5NA) that shows strong con- jugative effects. It also exhibits an exceptionally large ~t)PROFIMO, Depto. de Ffsica, Facultad de Ciencias Exactas, UNLP, C.C.67, (1900) La Plata, Argentina. * To whom correspondence should be addressed. 319 linear electro-optic effect 4 and second harmonic coeffi- cient. 5 Conjugative effects in M5NA are expected to be smaller than in MNA, but larger than in the meta -~ nitroaniline(m-NA), which presents a low efficiency for second harmonic generation (SHG). Because of the known structural results for both aforementioned anilines, MNA 4 and m-NA, 6 we expected that M5NA would crystallize in a noncentrosymmetric space group and SHG would be observed. Tests done on powder samples did not show nonlinear second order effects. 7 To rationalize this result, an X-ray single crystal struc- ture determination was undertaken and UV data for M5NA and MNA in solution were obtained. Experimental The UV spectra were recorded on a Shimadzu UV-240 Spectrophotometer with a band width of  2nm. A well-shaped crystal obtained by slow evaporation from acetone was chosen for X-ray study. Crystal data and data collection and refinement details are shown in Table 1. Atomic parameters are given in Table 2. The structure was solved by direct methods with SHELXS86.  s The  model obtained was refined by full- 1074-1542/96/0500-0319509.50/0 9 1996 Plenum Publishing Corporation 320 Ellena, Punte, and Rivero Table 1. Crystal data and structure refinement," esd's in parentheses Crystal data Compound: CTN202H s Mr = 152.15 Space group: Monoclinic, P21/n Cell costants: = 9.552(2) .A a b = 5.677(2) A c = 13.586(3) A. 13 = 92.68(2) ~ V = 735.7(11) ~3 Z = 4  D~ = 1.374 g-cm -3 Data collection Enraf-Nonius CAD-4 Diffractometer 0/20 Scans 1071 Measured reflections 1071 Independent reflections 602 Observed reflection 469 Unobserved reflection if 1 <:: 3.0 (r(/) Corrections: lorentz and polarization Refinement Refinement on F Final R = 0.043 wR : 0.038 S = 2.25 602 Reflections 119 parameters Mo Kc~ x = 0.71073 A = 0.64 mm -I T = 295 K Size: 0.125 • 0.15 • 0.25 mm Color: yellow Crystal source: purify from commercial product: Janssen Cell parameters from: 20 reflections with 0 = 0-25 ~ 0,,~., = 25 ~ h = - I1  ~ II k = 0 ~ 6  1 = 0 - - , 1 6  I Standard reflec. (T,3,2) Frequency: 100 min Intensity variation: 3% w = 1.8305/[~2(IF,,I) + 5 • 10-SlF,,12 l (A/O')m~ = 0.012 Apm~ = 0.15 e ,~-3 Apmi, = -0.16 e A -3 Atomic scattering factors from International Tables, Vol. IV, Table 2.2B Data collection: CAD-4 (Enraf Nonius/3 software 1990. Cell refinement: CAD-4 (Enraf-Nonius) software 1990. Data reduc- tion: MoLEN. s Calculations were carried out on a micro VAXII system using the programs: PLUTO, I~ ORTEP-H II and PARST) 2 matrix least-squares procedure by means o f  S H E L X 7 6 .  9 Discussion M o l e c u l a r  g e o m e t r y  The aromatic ring is essentially planar, showing a small value o f  The Total Puckering Amplitude, 14 QT = 0.014(4). Unlike M N A  and m-NA, where the amino groups are twisted out of  the phenyl ring, 21.5(1) and 32.0(1) ~ respectively, the amino group in M5NA is coplanar with the aromatic ring, 3.7(2.1) ~ within the experimental error. On the other hand, the nitro group Table 2. Atomic coordinates and equivalent isotropic displacement parameters, esd's in parentheses U,q = 1/3 ~,i ~j Uoa*'a]'a:aj Atom xla y/b z/c U~u C(l) 1 .0040(4)  0 .1869(7)  0.2932(2) 0.0386(15) c(2) 0 .9620(4)  -0.0205(7) 0.2425(3) 0.0396(14) c(3) 0 .8685(4)  -0.1707(7) 0.2854(3) 0.0455(15) c(4) 0.8136(4) -0.1272(7) 0.3755(3) 0.0449(16) c(5) 0.8542(4) 0 .0781(7)  0.4221(3) 0.0384(14) c(6) 0.9481(4) 0 .2350(7)  0.3842(3) 0.0386(15) c(7) 1.0164(4) -0.0718(7) 0.1425(3) 0.0585(16) N(I) 1 .0990(4)  0 .3380(7)  0.2548(3) 0.0631(16) N(2)  0.7932(4) 0 .1379(7)  0.5161(2) 0.0492(14) O(I) 0 .7059(3 )  0 .0083(6)  0.5485(2) 0.0831(15) 0(2) 0 .8321(3 )  0 .3167(6)  0.5594(2) 0.0701(14) displays a dihedral angle of  3.2(2) ~ with the mean ring plane. This value coincides with that observed in m- NA, but is larger than the one found in MNA,  1.04(15) ~ The bond length C( I ) -N(1) ,  1.369(6)A, is shorter than in m-NA, 1.391(3),~, 6, and larger than in MNA,  1.353(3)A, 4 and in other conjugated 4-nitroanilines like p-nitroaniline, 1.356(3).A, 15 and N,N-dimethyl-p-nitro-  aniline, 1.35(8),~. 16 This indicates that the degree o f  conjugation between the amino and the nitro groups in M5NA is smaller than in the mentioned 4-nitroanilines. The bond C(5)-N(2) ,  1.468(5)A, is larger than the C(4)-N(2)  bond presented for the MNA,  1.422(3),~, and similar to the value observed in m-Na, 1.467(4),~, and to the mean value, 1.471 (2),~, reported by Domeni-  cano et al.17 for the C - N  bond length in nitrobenzene derivatives for which the substituents were chosen to avoid the conjugation. The C - M e  bond length, C(2 ) -  C(7) = 1.505(6)A is in agreement with the value pre- sented for the MNA, 1.507(3)A. The N - O  bonds, N ( 2 ) - O ( I )  1.210(5)A and N(2) -  0 (2 )  1.222(5),~,, agree with the mean value, 1.218(1 l)]k, obtained from 334 nitrobenzene deriva- tives surveyed from the 1987 version o f  the CSD. 18 The bond angle O(1) -N(2) -O(2) ,  121.9(3) ~ is smaller than the mean values 123.7(9) ~ but larger than the average, 118.9 ~ obtained from 44 nitroanilines NO2 groups involved in hydrogen bonds. ~ The bond lengths corrected by thermal vibra- tion, t2 Table 3, do not show departure from the trends described above. In f luence  o f  the subs t i tuents  The additivity o f  the effect o f  the substituents on the ring geometry was analyzed using the angular Geometry of 2-methyl-5-nitroaniline 321 Table 3. Bond lengths (,4,), esd's in parentheses, thermal vibration corrections in brackets C( 1 )---C(2) 1,412(5)[ 1.414] C( 1 )-N( 1 ) 1.369(6)[ 1.397] C(2)--C(3) 1.383(6)[ 1.3881 C(2)--C(7) 1.505(6)[ 1.524] C(3)-C(4) 1.376(6)[I.3771 C(4)-C(5) 1.373(6)[1.381] C(5)-C(6) 1.380(6)[ 1.380] C(5)-N(2) 1.468(5)[1.4771 C(6)~(  I ) 1.396(5)[ 1.3961 N(2)-0( I ) 1.210(5)[ 1.257] N(2)-O(2) 1.222(5)[ 1.2531 Bond angles (% esd's in parentheses C(I)-C(2)-C(7) 119.9(3) C( 1 )-C(2)-C(3) 118.8(3) C(5)---C(6)--C( I ) 119.0(4) C(6)--C( I )-N( 1 ) 120. I (3) C(6)-C( 1 )-C(2) 118.8(3) C(2)-C(I)-N(I) 120.9(3) C(2)--C(3)-C(4) 123.0(4) C(3)-C(2)-C(7) 121.1(4) C(4)--C(5)--N(2) 118.8(3) C(5)--C(4)-C(3) 116.8(4) C(6)~(5)-N(2) 117.8(3) C(6)-C(5)~(4) 123.3(4) C(5)-N(2)-O(2) 119.1(3) C(5)-N(2)-O(1) 118.9(3) O(I)-N(2)-O(2) 121.9(3) parameters of Domenicano and Murray-Rust (DMR), 19 Table 4. To get a better understanding of the results obtained, the additivity of  the effect of  the substituents in MNA and m-NA was also analyzed and included in Table 4. It can be seen from the value of the nonadditivity parameters (NAP), 2~ that additivity is accomplished in m-NA. For both M5NA and MNA the NAP parameter is less than 3o-, NAP 3.0 (1.7) and 4.4 (1.52) respec- tively. This would indicate that the additivity of the effects of the substituents is also attained in both com- pounds, within experimental error. However, the valid- ity of this hypothesis is weaker for MNA. These results are consistent with the different degree of intramolecu- lar charge transfer between the donor and the acceptor groups expected from their relative location and con- firmed by UV data, shown below. UV spectra Highly conjugated nitroanilines exhibit an intense band at about 375 nm. It can be assigned to an intramo- lecular charge transfer (CT) band due to a transition accompanied with a partial electron transfer from the electron-donating amino group to the electron- accepting nitro group through the 7r system of the benzene ring. 21 Figure 1 and Table 5 show that MNA presents a strong band at 374 nm, while the intensity of this band, positioned at 370 nm, drops in M5NA. As mentioned above, these results agree with the relative location of the amino and nitro substituents in both compounds. The MNA spectrum shows a second band at 224 nm. This can be assjgned to the benzene w --. at* transition modified by the amino group. The third band at 204 nm, and the shoulder at 260 nm, display the bathocbromic effect of the alkyl substituent on the spectrum at benzene. 21 The spectrum at M5NA displays two intense bands at 251 and 229 rim. They can be interpreted as benzene 'rr ---, "rr* transition modified by the nitro and amine substituents respectively. Further analysis of the M5NA spectrum shows a weaker band at 286 nm, probably arising from an electronic transition involv- ing the methyl and nitro substituents. The comparison of the present UV results with that found in the literature for m-NA (Table 5) confirms our previous assumption on the relative magnitude of the conjugative effects in the three compounds. Crystal  packing The molecules of M5NA exhibit a centrosymmet- tic arrangement. Figure 2 displays the intermolecular 0i Table 4. Experimental and calculated endocyclic angles, and non-additivity parameter values, esd's in parentheses 2-Methyl-5-nitro m-Nitroaniline 2-Methyl-4-nitro ANGLES (o) D,M.R." Exper. D.M.R. Exper. D.M.R. Ex. per. 0~ C(6)-C( 1 )--C(2) 120. l(4) 118,8(3) 118.9(2) 119. I(3) 120.2f,5) 119.3(2) 02 C( l )-C(2)--C(3) 118.7(5) 118.8(3) 118.3(3) 118.3(2) 118.6(4) 119.0(2) 03 C(2)-C(3)-C(4) 122.3(3) 123.0(3) 124,0(3) 123.9(3) 120.1(3) 120.8(2) 04 C(3)-C(4)-C(5) I 17.2(4) 116.8(3) 116.9(2) 116.8(3) 122.0(5) 120.7(2) 05 C(4)-C(5)--C(6) 123.1 (5) 123.3(3) 121.0(3) 121.3(2) 118.3(4) 119.1 (2) 06 C(5)-C(6)--C( 1 ) 118.7(3) I 19.0(3) 120.9(3) 120,6(3) 120.9(3) 121.2(2) N.A.PJ' 3.0 (tr = 1.7) 1.0 (o" = 1.7) 4.4 (o" = 1.5) "Domenicano and Murray-Rust? 9. h N.A.E = ~EI0c~p. - 0c~lc I; 0: endocyclic angles, tr = [E((rcal~. + o'cxp) z]tr2. 322 Ellena, Punte, and Rivero 15 e xlO ~ l 10 5 A 2-METHYL-5-NITROANILINE B 2-METHYL-4-NITROANILINE / '~ B II A ,' i I / f ~X t t /I I x I /~ A \ 20o.0 300.0 4oo.0 5oo.o A [nml  Fig. 1. MNA and M5NA UV spectra. hydrogen bonding scheme and the atom labels. As expected after Panunto et al., ~ an amino proton is situated between both oxygens of the nitro group. This induces the formation of infinite chains with three center interactions along the [10T] direction. The sec- ond amino proton, not locked in the interactions that give rise to the chains, is involved in a two center (TC) bond with a molecule of a neighboring chain. This interaction induces centrosymmetric dimers. Molecular orbital modeling of monomeric p- and m-nitroaniline aggregates, using AM I semiempirical molecular orbital methods, has shown that TC hydro- gen bonds are the optimal interactions. 23 This seems to contradict the Panunto et al. finding I and our present T" c ( 3 ) ~  Fig. 2. Drawing of the crystal packing showing the intermolecular hydrogen bonds scheme and the atom labels. Geometry of 2-methyi-5-nitroaniline 323 First band Compound h,,~x* ~m~x Table 5. UV spectral bands of M5NA, MNA and m-Na Second band Third band Fourth band hmax Em~x hmax Emax ~-max Emax Fifth band hmax Emax 2-Me-5-NA ~ 370 1.775 2-Me-4-NA" 374 11.108 m-NA b 370 1.349 * h,,~ in nm; "This work; bPasseron et  al.  22 286 4.151 251 11.t47 229 11.372 202 7.685 260 2.337 242 3.565 224 4.821 204 9.508 275 3.981 235 17 .378  . . . .  results regarding the organization of the nitroaniline molecules in polar chains through three center hydro- gen bonds. The apparent dissent can be explained because the bifurcated structure leaves the second amino hydrogen more available for interactions with neighboring chains favoring more effective three dimensional packing. To help the analysis of the factors that govern the molecular organization, we further examined the hydrogen bonds scheme in MNA, m-NA and M5NA. Table 6 and Fig. 3 exhibit Panunto e t  al.  ~ N-H---O hydrogen bond depiction for MNA and M5NA. These data show that in MNA, which displays a parallel chain arrangement, the interactions between chains are weaker than the interactions that induce chain forma- tion. In M5NA, that displays an antiparallel chain arrangement, though the bond length of the intrachain interaction is of the same order as the one found in MNA, there are two interchain TC bonds. These bonds produce the centrosymmetric dimers and would cause interchain interactions stronger than the intrachain ones. MNA m.p., 132~ is higher than M5NA m.p., 106(1)~ Neither the analysis of MNA and M5NA packing forces, given above, nor Dannenmberg 23 find- ings, on optimal hydrogen bond interactions, explain the difference. The strong molecular conjugation in MNA allows one to assume the generation of coopera- tive effects, which would contribute with additional stabilizing forces to the chains and might explain the m.p. difference. However, recent experimental and the- oretical charge density studies of MNA 24 do not seem to support the hypothesis. It is worth mentioning that the parameters which characterize m-NA's, hydrogen bond were not included in the above discussion because our analysis, based in Ploug-Sorensen e t  al.  6 H's atoms positions retrieved from CSD, t8 indicates a hydrogen bond scheme differ- ent from Panunto e t  al.  description.t In fact, the polar chains in m-NA originate from two TC hydrogen bonds, the donor atom of each being one H of the amino group and one of the H's o r t h o  to it. Besides, interchain interactions are caused by short N-H.--N contacts. Conclusions The present study shows that the geometry of the molecules of M5NA in the crystalline state agrees with H ~ O. b Fig. 3. Hydrogen bond's scheme and bond parameters used in Table 6. Compound Space group R (%) Table 6. Geometry of the intermolecular contacts" Length Symmetry relation N(H)...O(,~,) a (A.) Angle . (~ b N-H. "-O N-O...H M5NA h P 2 t / n  4.3 Glide Inversion MNA c la  4.0 Glide Glide " After Panunto et  al.; I bThis paper; "Howard et  al. 23 3.151 2.34 2.79 147 154 3.239 2.43 4.02 153 173 3.117 2.07 2.73 167 117 3.234 2.23 4.22 152 220 324 Ellena, Punte, and Rivero the degree of conjugation expected from the relative loca- tion of the substituents. The centrosymmetric packing is in accordance with the lack of nonlinear second order effects. The organization of the molecules in chains, in spite of the double bonded dimers formation, reinforce the Panunto e t  al .  ~ assumption on the hydrogen bond driven polar chain structure formation in nitroanilines. However, it was found that the bifurcated character of those interactions proposed by the mentioned authors was not sustained in all the compounds. Acknowledgments The authors thank E. E. Castellano, J. A. K. How- ard L. Bruzzone, E Rivas, and S. Etcheverry for helpful discussions, the Instituto de Quimica e Ffsica de Sao Carlos, Brazil, for experimental facilities and CONI- CET for financial support. J. E. is a fellows of CONI- CET. G. P. is a member of Carrera del Investigador Cientiffco del CONICET. B. E. R. is a member of CICPBA. References 1. Panunto, T.W.; Urbhnczyk-Lipkowska, Z.; Johnson, R.; Etter, M.C. Z Am. Chem. Soc. 1987, 109, 7786. 2. Etter, M.C. Acc. Chem. Ress. 1990, 23, 120. 3. Etter, M.C.; Huang, K.S.; Frankenbach, G.M.; Adsmond, D.A. ACS Syrup. Ser. 1991, 455, 446. 4. Lipscomb, G.E; Garito, A.F; Narang, R.S.J. Chem. Phys. 1981, 1509. 5. Levine, B.E; Bethea, C.G.; Thurmond, C.D.; Lynch, R.T.; Bernstein, J.L.J. Appl. Phys. 1979, 50, 2523. 6. Ploug-Sorensen, G.; Andersen, E.K.Acta Crystallogr. C, Crys- tal Struct. Commun., 1986, C42, 1813. 7. Tocho, J., 1992. Private communication. 8. Sheldrick, G.M. SHELXS86. Program for the Solution of Crys- tal Structure, Univ. of Gtningen, Germany, 1985. 9. Sheldrick, G.M. SHELX76. Program for Crystal Structure Determination, Univ. of Cambridege, England, 1976. 10. Motherwell, W.D.S.; Clegg, W. PLUTO. Program for Plotting Molecular and Crystal Structures. Univ. of Cambridge, England, 1978. 1 I. Johnson, C.K. ORTEP-II. A Fortran Thermal Ellipsoid Plot Program for Crystal Structure Illustrations. ORNL-5138. Oak Ridge National Laboratory, Tennessee, 1976. 12. Nardelli, M. Computer & Chemistry 1983, 7, 95. 13. Fair, C.K. MoLEN. All Interactive Intelligent System for Crys- tal Structure Analysis. Enraf-Nonius, Delft, the Netherlands, 1990. 14. Creamer, D.; Pople, J.A.J. Am. Chem. Soc. 1975, 95, 1354. 15. Calopietro, M.; Domenicano, A.; Marciante, C.; Portalone, G. International Union of Crystallography. Supp. Acta Crys- tallogr. 1981, A37, C-199. 16. Mak, T.C.W.; Trotter, J. Acta Crystallogr. 1965, 18, 68. 17. Domenicano, A.; Schultz, G.; Hargittai, I.; Colapietro, M.; Portalone, G.; George, P.; Bock, C.W. Struct. Chem. 1989, 1, 107. 18. Allen, F.H.; Kennard, O.; Taylor, R. Acc. Chem. Res. 1983, 16, 146. 19. Domenicano, A.; Murray-Rust, P. Tetrahedron Lett. 1979, 24, 2283. 20. Krygowsky, T.M. Prog. Phys. Org. Chem. 1990, 17, 239. 21. Suzuki, H. Electronic Absorption Spectra and Geometry of Organic Molecules; Academic Press: New York, 1967; pp. 463~1.98. 22. Passeron, S.; Brieux, G.A. Bull. Soc. Chim. France. 1963, $5, 35. 23. Dannenmberg, J.J. ACS Symp. Ser. 1991, 455, 458. 24. Howard, S.T.; Hursthouse, M.B.; Lehmann, C.W.; Mallinson, P.R.; Frampton, C.S.J. Chem. Phys. 1992, 97, 5616. SUPPLEMENTARY MATERIAL. Crystallographic data (excluding structure factors) for the structure reported in this paper has been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-1003/5024. Copies of avail- able material can be obtained, free of charge, on application to the Director, CCDC, 12 Union Road, Cambridge CB2 IEZ, UK, (fax: +44-(0)1223-336033 or e-mail: teched@chemcrys.cam.ac.uk). 

Conformational studies of substituted nitroanilines : Geometry of 2-methyl-5-nitroaniline

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Conformational studies of substituted nitroanilines : Geometry of 2-methyl-5-nitroaniline

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