April 8, 2003 12:2 WSPC/145-JNOPM 00127 ...

April 8, 2003 12:2 WSPC/145-JNOPM

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Journal of Nonlinear Optical Physics & Materials Vol. 12, No. 1 (2003) 113–121 c World Scientific Publishing Company

INFRARED SPECTRUM AND NONLINEAR OPTICAL PROPERTIES OF p-NITROANILINE-L-TARTARIC ACID (2:1) MOLECULAR COMPLEX

M. K. MARCHEWKA∗ and H. RATAJCZAK Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroclaw 2, P.O. Box 937, Poland ∗[email protected] S. DEBRUS Universite Pierre et Marie Curie, Laboratoire d’Optique des Solides, CNRS-UMR 7601, 4, place Jussieu, 75252 Paris Cedex 05, France Received 15 September 2002 The crystals of a new molecular complex, i.e. p-nitroaniline with L-tartaric acid were obtained by slow evaporation of an aqueous solution at room temperature. Room temperature powder infrared measurements were carried out. Tentative assignment for most bands was done. Very strong and broad absorption in the region of 3200–1800 cm −1 of infrared spectrum is observed. This notable vibrational effect suggests the presence of intense hydrogen-bonded network in the crystal structure of the complex. Second harmonic generation (SHG) efficiency deff = 3.85 deff (KDP). Some spectral features of this new crystal are referred to corresponding one for two other crystals comprising p-nitroaniline molecule i.e. p-nitroanilinium perchlorate and p-nitroanilinium-p-toluene-sulphonate. Keywords: p-nitroaniline; tartrates; hydrogen bond; Fourier transform infrared; second harmonic generation.

1. Introduction p-nitroaniline-L-tartaric acid compound has been chosen to study as a potential material for nonlinear optics due to its high second harmonic generation (SHG) efficiency, deff = 3.85 deff (KDP). The family of hydrogen-bonded crystals comprising tartaric acid molecule is quite wide. Stern1 and Okaya2 published the structure of tartaric acid. Different methods were used to study the salts of tartaric acid, including structural,3 – 15 optical16 – 20 and dielectric21,22 one. Infrared spectra can be useful in the clarification of the role of hydrogen bonds in the crystals exhibiting nonlinear optical properties. The complex of orthoarsenic acid with NH2 -C(CH2 OH)3 23 as well as 3-nitrobenzoic acid hydrazide24 are good examples of non-centrosymmetric crystals based on hydrogen bond interactions. Fuller25 and Row26 analyzed the role of tartaric acid molecule in the nonlinear optical activity of the crystals. The complex of 2-amino-5-nitro-pyridine with tartaric acid,27 and the 113


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number of salts of substituted pyridines with L-tartaric acid28 are representative among good generators. 2. Experimental 2.1. Preparation The starting compounds, p-nitroaniline (Aldrich, 99%) and L-tartaric acid (Aldrich, 99%) were used as supplied. After p-nitroaniline was added to dissolved acid, the solution was cooled to room temperature. Then, the solution was purified with the aid of active charcoal. The solution slowly evaporated during a few days till the crystals appeared. 2.2. Spectroscopic measurements Infrared spectra were taken at room temperature with a Bruker IFS-88 spectrometer in the region 4000–80 cm−1 . Resolution was set up to 2 cm−1 , signal/noise ratio was established by 32 scans, weak apodisation. The polycrystalline powders were achieved by grinding in agate mortar with pestle. Sample, as suspension in oil, was put between KBr windows. The powder infrared spectrum was taken in Nujol and Fluorolube to eliminate bands originating from oils. The measured spectra are shown on Figs. 1–4. The wave numbers of the bands and their relative intensities are provided in Table 1.

WAVENUMBERS (cm−1 ) Fig. 1. Room temperature powder FTIR spectrum of p-nitroaniline-L-tartrate crystal in Nujol oil (4000–380 cm−1 ).


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p-Nitroaniline-L-Tartaric Acid (2:1) Molecular Complex

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WAVENUMBERS (cm−1 ) Fig. 2. Room temperature powder FTIR spectrum of p-nitroaniline-L-tartrate crystal in Fluorolube oil (4000–1320 cm−1 ).

WAVENUMBERS (cm−1 ) Fig. 3.

Room temperature powder FTIR spectrum of p-nitroaniline in Nujol oil (4000–400 cm −1 ).

The elemental analysis performed on Perkin-Elmer 2400 CHN analyzer is consistent with the 2:1 composition of p-nitroaniline : tartaric acid. Found: C: 40.66%; H: 4.20%; N: 14.70%. Calculated for (C6 H6 N2 O2 )2 (C4 H6 O6 : C: 45.08%; H: 4.25%; N: 13.14%.


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2.3. Kurtz Perry powder test SHG experiment was carried out using Kurtz–Perry powder technique described in Ref. 29. The calibrated samples (studied and KDP) were irradiated at 1064 nm by an Nd+ :YAG laser (Quanta Ray DCR-11) and the second harmonic beam power diffused by the powder sample (at 532 nm) was measured as a function of the fundamental beam power. 3. Assignments of the Bands and Discussion The bands observed in the measured region 4000–80 cm−1 arise from the vibrations of protons in the hydrogen bonds, the internal vibrations of the p-nitroanilinium cations and the vibrations of L-tartaric acid anions. The bands below 300 cm−1 arise from the lattice vibrations of the crystal. Juxtaposition of the infrared spectrum of p-nitroanilinium-L-tartaric acid crystal (Figs. 1, 2 and 4) with spectrum of p-nitroaniline alone (Fig. 3) clearly shows, that many bands corresponding to e.g. aniline ring breath (at 1306 and 1301 cm−1 ) changed their position due to self-association with intermolecular interactions through hydrogen bonds existing in title crystal. Some new bands appeared, e.g. 3443 cm−1 (asymmetrical stretching −1 −1 of NH+ (symmetrical deformation of NH+ 3 group), 1605 cm 3 group), 1208 cm −1 (C–N stretch) or 795 cm (symmetrical ring breathing). 3.1. The vibrations of p-nitroanilinium cations The assignment for internal vibrations of p-nitroanilinium cation was done with the help of paper published by Evans30 and Gao.31 Most bands observed in infrared spectrum belong to benzene ring modes, only some of them may be assigned to the vibrations of NH+ 3 group. For assignment of phenyl ring modes the classical work of Herzberg32 as well as paper by Miller33 are helpful. Herzberg’s notation was used for numbering normal modes associated with the phenyl ring. The medium band corresponding to 6(A1 ) mode of benzene ring was found at 1016 cm−1 . In p-nitroanilinium perchlorate crystal at the same frequency strong infrared band is observed34 while in the case of p-nitroaniline p-toluenesulphonate a very strong infrared band is present at 1018 cm−1 .35 The very strong band located at 740 cm−1 was attributed to NO2 out-of-plane deformation type of vibration (wagging). In the case of p-nitroanilinium perchlorate, similar very strong band is observed at 739 cm−1 ,34 while in the case of p-nitroaniline p-toluenesulphonate a strong infrared band is present at 737 cm−1 .35 The in-plane ring deformations, 8(B1 ), give rise to infrared bands at 720, 677 and 633 cm−1 , which are close to those, observed in pnitroanilinium perchlorate,34 (722, 680 and 638 cm−1 ) and p-nitroaniline p-toluenesulphonate,35 (721, 674 and 633 cm−1 ). The reliable group vibrations of benzene ring are the stretching one.36 The bands at 1507 and 1470 cm−1 were attributed to ring stretching type of vibrations. Corresponding bands are observed at 1510


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Table 1. Wavenumbers (cm−1 ) and relative intensitiesa of the bands observed in the powder infrared spectrum of the p-nitroaniline-L-tartaric acid crystal. FTIR 3481w 3443w 3361m 3344w 3243w 3219w 3165wsh 3124m 3120w 3114m 3092m 3064m 3037m 3013m 2907msh 2847s 2772sb 2714s 2551sb 2448s 2385msh 2212w 1996vw 1964vw 1930vw 1798vw 1751w 1735m 1680vw 1636w 1605s 1588m 1564msh 1520vs 1507ssh 1494vs 1481vs 1470s 1444m 1426m 1421msh 1399wsh 1360vs 1349vs 1325s

Assignment asym stretch (NH2 and NH3 ) asym stretch (NH3 ) asym stretch (NH2 and NH3 ) asym stretch (NH2 and NH3 ) sym stretch (NH2 and NH3 ) sym stretch (NH2 and NH3 ) sym stretch (NH2 and NH3 ) C–H stretch C–H stretch C–H stretch C–H stretch C–H stretch C–H stretch C–H asym stretch O–H stretch, A component O–H stretch, B component

“benzene finger” “benzene finger” “benzene finger” “benzene finger” C=O stretch C=O stretch COO− asym stretch COO− asym stretch δNH+ 3 COO− asym stretch COO− asym stretch asym def (NH2 and NH3 ) ring stretch ring stretch ring stretch ring stretch CH2 sciss COO− sym stretch COO− sym stretch COO− sym stretch NO2 stretch NO2 stretch CH2 twist

FTIR 1306vs 1301vssh 1241w 1208m 1182w 1175w 1122msh 1116s 1109s 1092w 1080w 1016m 974vw 963vw 936vw 917vw 890vw 861vs 848s 844ssh 825vw 795m 756vw 740vs 720vw 700vw 696vw 677m 633w 623vw 590vwb 528vw 500vwsh 473m 434vw 419vw 389m 366w 358vw 303m 247vw 204m 150m 111w

Assignment aniline ring breath aniline ring breath NO2 stretch C–N stretch C–H in-plane def rock (NH2 and NH3 ) C–H in-plane def C–H in-plane def C–C and C–N stretch 6(A1 ) mode of benzene ring C–H out-of-plane def C–H out-of-plane def C–C and C–N stretch ring breath C–H out-of-plane def C–H out-of-plane def symm ring breath C–H out-of-plane def NO2 out-of-plane def (wagg) in-plane ring bend symm ring breath symm ring breath in-plane ring def in-plane ring def in-plane ring def COO− in-plane def out-of-plane C–N bend sciss – rock, (NH2 and NH3 ) sciss – rock, (NH2 and NH3 ) out-of-plane ring bend out-of-plane ring bend skeletal def skeletal def and COO− wagg and C–C twist

skeletal def COO− twist lattice lattice

Abbreviations: a s — strong, w — weak, v — very, sh — shoulder, b — broad, m — medium, t.w. — transmission window, stretch — stretching, bend — bending, sciss — scissoring, wagg — wagging, rock — rocking, symm — symmetrical, breath — breathing, def — deformation.

and 1468 cm−1 in the case of p-nitroanilinium perchlorate crystal34 and at 1508 and 1496 cm−1 for p-nitroaniline p-toluenesulphonate.35 For other assignment of internal vibrations of p-nitroanilinium cations see Table 1.


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3.2. Tartaric acid molecules vibrations In the region 1750–1550 cm−1 the bands originating from va COO− and vC = O type of vibrations are present. Thus, the weak and medium infrared bands at 1751 and 1735 cm−1 , respectively, were assigned to stretching vibrations of C = O bonds of L-tartaric acid moieties, while the bands located at 1680, 1636, 1588 and 1564 cm−1 correspond to asymmetric stretching vibrations of ionised (COO− ) groups of L-tartaric acid molecules. In the region of 1450–1400 cm−1 one should expect the bands corresponding to symmetric stretching type of vibrations of COO − groups. The infrared bands observed at 1426, 1421 and 1399 cm−1 were attributed to these vibrations. 3.3. The hydrogen bonds vibrations The presence of strong band at 1605 cm−1 indicates on the proton transfer from carboxylic group of L-tartaric acid to amino group of p-nitroaniline. In such a case −NH+ 3 group is formed and the vibrations of hydrogen bonds manifest themselves as −NH+ 3 group vibrations of the p-nitroanilinium cation. One can expect, that similarly like in the case of p-nitroanilinium perchlorate crystal34 all three protons of −NH+ 3 group are engaged in weak interactions. The broad and intense absorption located in the region of 3200–1800 cm−1 with two submaxima (see Fig. 2) at 2772 and 1551 cm−1 originates from the set of rather weak hydrogen bonds of N–H· · ·O, N–H· · ·N and O–H· · ·O type. For medium O–H· · ·O type of hydrogen bond, the “A, B” structure caused by a Fermi resonance is frequently observed.37 Then, the bands at 2772 and 2551 cm−1 can be assigned as A and B component, respectively. The bands at 1092, 936, 861 and 825 cm−1 , listed in Table 1 and not assigned, can originate from deformation type of vibrations of hydrogen bonds. 3.4. Far infrared region The far-infrared spectrum for title crystal is presented in Fig. 4. The greatest differences between infrared spectrum of the p-nitroaniline and studied crystal are observed for the wave numbers lower than 550 cm−1 . The band at 528 cm−1 corresponding to in-plane C–N bending type of vibrations is broadened and observed at lower wave numbers. In the infrared spectrum of p-nitroaniline this band is sharp and located at 536 cm−1 . Similarly, band at 473 cm−1 , assigned to out-of-plane ring bend is also broadened. In the spectrum of p-nitroaniline this band is sharp and located at 490 cm−1 . Such an effects are the consequence of molecular interactions. One can see from Fig. 4, that in the region below 450 cm−1 at least seven well pronounced bands are present. The tentative assignment for some of them is given in Table 1. 3.5. Second harmonic generation For the powder SHG efficiency we have obtained quite high value (relative to


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WAVENUMBERS (cm−1 ) Fig. 4.

Far-infrared spectrum for title crystal.

KDP): deff = 3.85 deff (KDP). This result suggests the non-centrosymmetric crystal structure. In such a case second harmonic light should be observed.38 4. Summary p-nitroaniline molecule is known as having high quadratic hyperpolarizability.39,40 From this reason it is an attractive molecular unit in the nonlinear crystal engineering.41 – 43 The title crystal is an example where the inherent property of p-nitroaniline molecule is expressed due to the absence of macroscopic centre of symmetry. Having relatively high SHG efficiency (comparable to KDP), p-nitroaniline-L-tartaric acid crystal can possess potential application as optically nonlinear material. Comparison of infrared spectrum for title crystal versus p-nitroaniline alone shows that many bands are shifted and a new bands appeared. This is an evidence for complex formation. Weak interactions of O–H· · ·O, N–H· · ·O and N–H· · ·N type manifest themselves as perturbed amino group vibrations of mono-protonated pnitroanilinium cations. The pronounced feature in infrared spectrum is an intense and broad absorption in the region of 3200–2800 cm−1 , suggesting the existence in the studied crystal a set of weak hydrogen bond type of interactions. In many crystals from the group of cation-tartaric acid type, the ferroelectric phase transition is observed. As the studied compound belongs to this group, such a transition is possible also. This will be the subject of our future investigations.


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Acknowledgment This work was financially supported by the KBN (project No. 7 T09A 014 20). References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36.

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