Crystal and molecular structure of N-(4-nitrophenyl)-β-alanine—Its vibrational spectra and theoretical calculations

Spectrochimica Acta Part A 79 (2011) 758–766

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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

Crystal and molecular structure of N-(4-nitrophenyl)-␤-alanine—Its vibrational spectra and theoretical calculations M.K. Marchewka ∗ , M. Drozd, J. Janczak Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wrocław, 2, P.O. Box 937, Poland

a r t i c l e

i n f o

Article history: Received 22 October 2009 Received in revised form 7 June 2010 Accepted 26 August 2010 Keywords: ␤-Alanine derivative Crystal structure Gas phase structure DFT calculations Hydrogen bond Fourier transform infrared Fourier transform Raman

a b s t r a c t The N-(4-nitrophenyl)-␤-alanine in crystalline form directly by the addition of 4-nitroaniline to the acrylic acid in aqueous solution has been obtained. The title ␤-alanine derivative crystallizes in the P21 /c space group of monoclinic system with four molecules per unit cell. The X-ray geometry of ␤-alanine derivative molecule has been compared with those obtained by molecular orbital calculations corresponding to the gas phase. In the crystal the molecules related by an inversion center interact via symmetrically equivalent O–H· · ·O hydrogen bonds with O· · ·O distance of 2.656(2) A˚ forming a dimeric structure. The dimers of ␤-alanine derivative weakly interact via N–H· · ·O hydrogen bonds between the H atom of ␤amine groups and one of O atom of nitro groups. The room temperature powder vibrational (infrared and Raman) measurements are in accordance with the X-ray analysis. In aqueous solution of 4-nitroaniline and acrylic acid, the double C C bond of vinyl group of acrylic acid breaks as result of 4-nitroaniline addition. © 2010 Elsevier B.V. All rights reserved.

1. Introduction

2. Experimental

4-Nitroaniline molecule is known as having high quadratic hyperpolarizability [1,2]. From this reason it is an attractive molecular unit in the nonlinear crystal engineering [3–5]. However, the crystalline structure of 4-nitroaniline is known to be centrosymmetric [6]. Therefore, the crystal of 4-nitroaniline does not show SHG effect. One can expect that its compounds, or derivatives with optically active compounds may crystallize in the polar space groups. It is known that optically active forms (L or D) of amino acids [7] or/and their complexes or salts, are usually known to form non-centrosymmetric crystals [8]. For example, several l-alanine derivatives are used as materials for nonlinear optics [9–14]. During our search for new crystals exhibiting second harmonic generation, the title crystals were grown. In contrary to N-(4-nitrophenyl)-l-prolinol [15,16], the our compound of N(4-nitrophenyl)-␤-alanine crystallizes in centrosymmetric space group therefore second harmonic generation should not be observed [17]. Nevertheless, the title compound seemed to be interested according to extensive and different N–H· · ·O, O–H· · ·O and N–H· · ·N hydrogen bonding system that has been characterized by X-ray crystallography and vibrational spectroscopy.

2.1. Preparation

∗ Corresponding author. Tel.: +48 668976921. E-mail addresses: [email protected], [email protected] (M.K. Marchewka). 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2010.08.050

The starting compounds, 4-nitroaniline (Aldrich, 99%) and acrylic acid (Aldrich, 94%) was used as supplied and prepared in the ratio of 1:1. The dissolved acid was added to the hot solution of 4-nitroaniline. Next the solution was cooled to room temperature and it remained clear. The solution slowly evaporated during a few days till the crystals appeared. 2.2. X-ray data collection A colourless single crystal of the title compound having the edges of 0.40 mm × 0.34 mm × 0.28 mm was used for data collection on a four circle KUMA KM-4 diffractometer equipped with a two-dimensional area CCD detector. The graphite monochroma˚ and ω-scan technique with ω = 0.75◦ tized Mo K␣ ( = 0.71073 A) for one image were used for data collection. The 960 images for six different runs covering over 90% of the Ewald sphere were performed. Initially the lattice parameters were refined on 153 reflections obtained from 40 images for 8 runs with different orientation in the reciprocal space. Finally they were refined by least-squares methods based on all measured reflections. One image was monitored as a standard for controlling the stability of the crystal after every 40 images. Integration of the intensities, correction for Lorenz and polarization effects were performed using a KUMA KM-4 CCD software [18]. The face-indexed analyti-

M.K. Marchewka et al. / Spectrochimica Acta Part A 79 (2011) 758–766 Table 1 Crystal data and structure refinement parameters for N-(4-nitrophenyl)-␤-alanine crystal. Formula Formula weight (g/mol) Crystal system, space group ˚ a (A) ˚ b (A) ˚ c (A) ˇ (◦ ) V (A˚ 3 ) Z ˚ Mo K␣ (A) Dcalc (g/cm3 ) Dm (g/cm3 ), flotation  (mm−1 ) Crystal size (mm3 ) Crystal colour/habit 2max (◦ ) h k l ranges Reflections collected Independent reflections Observed reflections (F2 > 2(I)) Rint Refinement on F2 R1 wR2 (all data) Goodness-of-fit, S Extinction correction Largest difference peak and hole (e A˚ −3 )

C9 H10 N2 O4 210.19 Monoclinic, P21 /c 8.304 (2) 7.900 (2) 15.263 (3) 98.91 (3) 989.2 (4) 4 0.71073 1.411 1.41 2.488 0.40 × 0.34 × 0.28 Colourless/parallelepiped 58.96 −11, 9; −10, 10; −19, 21 6846 2415 826 0.0162 0.0395 0.0652 1.014 None +0.245, −0.183

cal absorption was calculated using the SHELXTL program [19], the maximum and minimum transmission factors being 0.6106 and 0.5426. A total of 7086 reflections were integrated (5279 independent reflections, Rint = 0.0362) were used for structure solution and refinement. 2.3. Structure solution and refinement The structure was solved by direct methods by use of SHELXS97 program [20]. Fourier map that calculated using the E ≥ 1.7 gave the positions of oxygen, nitrogen and most of the carbon atoms. The remaining non-hydrogen atoms were located from difference Fourier syntheses. Initially the structure was refined with isotropic thermal parameters. The hydrogen atoms were located from the difference Fourier maps, but in final refinement their positions were constrained using HFIX 43 with isotropic thermal parameters of 1.2Ueq of the nitrogen atoms joined directly hydrogen atoms (for H atoms of water molecules Uiso = 1.5Ueq of oxygen). In final refinement all non-hydrogen atoms were refined with anisotropic thermal parameters by full-matrix least-squares methods using the SHELXL97 program [20]. Scattering factors for neutral atoms and calculations for anomalous dispersion were as in SHELXL97 program [20]. Details of the data collection parameters, crystallographic data and final agreement factors are collected in Table 1. 2.4. Spectroscopic measurements The vibrational measurements were carried out at room temperature. Infrared spectra were taken with a Bruker IFS-88 spectrometer in the region 4000–80 cm−1 region. Resolution was set at 2 cm−1 , signal/noise ratio was established by 32 scans, weak apodization. Powder Fourier Transform Raman (FT-Raman) spectra were taken with an FRA-106 attachment to the Bruker IFS-88 spectrometer equipped with Ge detector cooled to liquid nitrogen temperature. Nd3+ :YAG air-cooled diode pumped laser of power ca. 200 mW was used as an exciting source. The incident laser excitation is 1064 nm. The scattered light was collected at the angle of 180◦ , in the region 3600–80 cm−1 , resolution 2 cm−1 , 256 scans.

759

Due to the poor detector response, the Raman counterparts of the infrared bands located above 3200 cm−1 are not observed in the spectrum. The polycrystalline powders were achieved by grinding in agate mortar with pestle. Samples, as suspensions in Nujol or Fluorolube, were put between KBr windows and the powder infrared spectra were taken in the region of 1320–400 cm−1 for suspension in Nujol and in the region of 4000–1320 cm−1 for suspension in Fluorolube. This procedure allows obtaining the spectrum free of bands originating either from Nujol or Fluorolube. Far-infrared spectra were taken in Nujol between polyethylene plates. For elimination of the side lobes that result after truncating the interferogram with a boxcar function the Norton–Beer weak apodization function was used.

2.5. Theoretical calculations The optimized equilibrium structure has been calculated by seven different ways [21]. The DFT/B3LYP method was used with 3-21G, 6-31G and 6-311G basis sets. Additional calculations were performed with RHF level of theory with three different basis sets (6-311G, 6-31G and TZV). The calculation of equilibrium structure was performed with using MP2 perturbation theory, also. In two cases of DFT method the values of calculated energy for investigated molecule were minimal (see Table 3) and in all DFT calculations the equilibrium structure was slightly different than in real crystal. The differences originate from the fact that calculations were performed for free molecule, only. The same result was obtained for calculation with MP2 method. For calculation of the harmonic frequencies, infrared intensities and potential energy distribution (PED) the data corresponding to minimal energy reached with HF 6-311G basis set was used. Next, the calculation was continued with the density functional triply-parameter hybrid model (B3LYP). The 6-311++G(d,p) basis set was used. Strictly speaking we used the optimized structural parameters of the HF calculation as starting data in the DFT calculations. During this calculations one negative frequency was achieved. A single negative frequency means a saddle point, which indicates a first order transition state. As is depicted in Fig. 1b, the nitro group seems to be perpendicular to the benzene ring in contrary to result of X-ray investigations. However, it should be remembered here, that all calculations were performed for free molecule, only. Unfortunately, all reasons why the orientation of nitro group followed from theoretical calculations is distinctly different from that observed in the crystal (X-ray data) remain not clear. On the basis of PED calculation the assignments of bands observed in IR spectra were proposed in Table 6. Calculated IR spectrum is presented in Fig. 4. The normal coordinate analysis has been carried out according to the procedure described and recommended by Fogarasi and Pulay [32]. The frequencies of stretching and bending vibrations were not scaled. Calculations were performed with the PC GAMESS [33] program, version 7.1 (Tornado), build number 4630 performed under Linux operating system. This job was executed on PC Cluster consisting three nodes.

3. Results and discussion During crystallization from the hot solution of 4-nitroaniline with the acrylic acid used in the molar proportion of 1:1 the one hydrogen atom is transferred from amine group to the ␣-carbon atom of vinyl group of acrylic acid (see for example [34]) and as an addition result the ␤-alanine derivative crystals are formed according to the reaction.

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M.K. Marchewka et al. / Spectrochimica Acta Part A 79 (2011) 758–766 Table 2 ˚ ◦ ). X-ray and calculated geometric parameters (A,

Fig. 1. View of the molecular structure of N-(4-nitrophenyl)-␤-alanine in crystal (a) and gas-phase (b) for a comparison. The displacement ellipsoids are drawn at the 50% probability level. H atoms are shown as spheres with arbitrary radii.

3.1. Description of the structure The molecular structure of obtained ␤-alanine derivative with the labeling of the atoms is shown in Fig. 1a. Selected X-ray geometrical parameters together with those corresponding to gas phase structure are collected in Table 2. As revealed by X-ray structure analysis the six-membered aromatic ring is planar, but shows distortions from the ideal hexagonal symmetry. The distortions are entirely consistent with those found in the similar 1,4-disubstituted benzene derivatives, especially with the p-substituted nitrobenzene derivatives [8]. The optimized geometry of the aromatic ring gives values similar to those found in the crystal. Thus, the ring distortion results mainly from the 1,4-substitution effect and, to a smaller degree from the crystal packing forces. In the crystal the planar NO2 group is slightly rotated along the C1–N1 bond. The inter-planar angle between the planes of nitro group and the phenyl ring equals to 5.2(1)◦ . The conformation of the ␤-alanine fragment (N2C7C8C9OOH) with respect to the phenyl ring is well described by the torsion angles of C3–C4–N2–C7, C4–N2–C7–C8 and C7–C8–C9–O3. In the

Bond

˚ X-ray [A]

˚ RHF [A]

Angle

X-ray [◦ ]

RHF [◦ ]

C1–C6 C2–C1 C3–C2 C4–C3 C4–C5 C6–C5 C1–N1 N1–O1 N1–O2 C4–N2 N2–C7 C7–C8 C8–C9 C9–O3 C9–O4

1.376(3) 1.380(3) 1.372(3) 1.401(3) 1.397(3) 1.375(3) 1.447(3) 1.228(3) 1.226(3) 1.369(3) 1.454(3) 1.518(3) 1.484(3) 1.267(3) 1.241(3)

1.426 1.420 1.359 1.469 1.472 1.358 1.456 1.213 1.207 1.299 1.456 1.559 1.514 1.294 1.241

C2–C1–N1 C2–C1–C6 C6–C1–N1 C3–C2–C1 C4–C3–C2 N2–C4–C5 C3–C4–N2 C5–C4–C3 C6–C5–C4 C1–C6–C5 O2–N1–O1 C1–N1–O2 C1–N1–O1 C4–N2–C7 N2–C7–C8 O4–C9–O3 C8–C9–O4 C8–C9–O3 C7–C8–C9

120.0(2) 120.6(2) 119.3(2) 119.4(2) 121.1(2) 122.2(2) 119.7(2) 118.1(2) 120.4(2) 120.2(2) 121.7(3) 119.1(3) 119.2(2) 124.6(2) 112.6(2) 121.6(3) 120.5(3) 117.9(3) 111.7(2)

117.7 124.3 117.9 118.0 120.2 123.9 116.8 119.2 119.7 118.4 130.2 116.3 113.5 131.0 108.9 123.8 121.0 115.1 111.7

crystal, these torsion angles are equal to −175.3(2)◦ , 83.3(2)◦ and −134.1(2)◦ , respectively. The equivalent torsion angles in the gas phase structure are equal to 179.0◦ , 134.9◦ and 151.9◦ , respectively. The carboxyl groups COOH and C8 atom lie exactly on the plane in X-ray and is almost planar in ab initio gas phase structures. However, the carboxyl group, as is illustrated by the values of the torsion angle of C7–C8–C9–O3, is different oriented in relation to the rest of molecule as is shown in Fig. 1b. In the gas phase, the interaction of the H atom of the ␤-alanine group with the carbonyl oxygen and formation weak intramolecular N2–H2a· · ·O4 hydrogen bond is the driving force for the change of the orientation of the COOH group. The C1–N1 bond joined the nitro group is equal ˚ This value is comparable to that found in several to 1.444(2) A. nitrobenzene derivatives in which the distance of Car –NO2 bond ranging from 1.446(3) to 1.476(3) A˚ [22] as well as to those found ˚ The C4–N2 bond length of in the gas phase structure (1.447(3) A). 1.361(2) A˚ is quite similar to that found in several crystals containing the Car –Nsp2 bond [22] indicating slightly delocalization of the ␲ electrons over this bond. The C7–C8 and C8–C9 bond distances correlate well with the distance of Csp3 –Csp3 and Csp3 –Csp2 bonds, respectively [22]. The differences between the X-ray and calculated values of the double C O and single C–OH bond lengths of the carboxyl group [1.241(3) and 1.267(3) A˚ in the crystal and 1.241 and 1.294 A˚ in the gas phase, respectively] arise from the interactions between the carboxyl groups of two molecules related by an inversion center that form the hydrogen bonded dimeric structure. The almost planar hydrogen bonded fragment of the dimer is typical for the RCOOH acids in solids, in which the charge is slightly delocalized over the ring, and well explain the X-ray intermediate C–O distances of the carboxyl group. The ab initio molecular orbital calculation shows the greater angles of O–C–O of carboxyl and O–N–O of nitro groups than corresponding angles in the crystal and can be explained by the steric Table 3 Comparison of values of equilibrium geometries calculated by different methods. Method

Energy of equilibrium geometry

DFT 321 DFT 631 DFT 6311 HF 6311 HF 631 TZV MP2

−754.4066451 −758.1886920 −758.3759346 −754.3564597 −754.1934543 −754.0294778 −755.672314

M.K. Marchewka et al. / Spectrochimica Acta Part A 79 (2011) 758–766

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Fig. 2. Packing of the molecules in N-(4-nitrophenyl)-␤-alanine crystal.

Table 4 Geometry of the hydrogen bonds. D–H· · ·A

˚ D–H (A)

˚ H· · ·A (A)

˚ D· · ·A (A)

Angle D–H· · ·A (◦ )

O(3)–H(31)· · ·O(4)a N(2)–H(2A)· · ·O(2)b

0.820(15) 0.86

1.85(2) 2.29

2.652(2) 3.113(2)

164(2) 160

Symmetry codes: (a) x − 1, y, z, (b) x − 1, y, z.

Table 5 Analysis of the fundamental modes for N-(4-nitrophenyl)-␤-alanine crystal. C2h

Acoustic

Translational

Librational

Internal

Selection rules

Ag Bg Au Bu

0 0 1 2

3 3 2 1

3 3 3 3

69 69 69 69

xx, yy, zz, xz xy, zy (Y) (X, Z)

Fig. 3. Room temperature powder FTIR and FT Raman spectra of title crystal.

effect of a lone-pair of electrons on the oxygen atoms predicted by the valence-shell electron pair repulsion theory (VSEPR) [23]. In the crystal the two molecules of N-(4-nitrophenyl)-␤alanine related by inversion center form hydrogen bonded dimeric structure via the pair of symmetrically equivalent O3–H31· · ·O4i relatively strong hydrogen bonds (see Fig. 2) with ˚ Additionally, the the donor–acceptor (O· · ·O) distance of 2.652(2) A. dimers are weakly interconnected by the N2–H2A· · ·O2ii hydrogen bond (cf. Table 4) forming chains that are aligned along the z-axis. 3.2. Assignments of the bands Fig. 4. Calculated IR spectrum of N-(4-nitrophenyl)-␤-alanine.

For monoclinic system and P21 /c space group with Z = 4, each N-(4-nitrophenyl)-␤-alanine molecule occupy C1 symmetry site. Total number (297) of optical modes may be divided into 21 lattice (9 translational and 12 librational) and 276 internal modes. Each normal vibration of a molecule is splitted into four unit cell modes (Ag + Bg + Au + Bu ) as shown in Table 5. The bands observed in the measured region 4000–80 cm−1 arise from the vibrations of protons in the intermolecular hydrogen bonds, the internal vibrations of the 4-nitroaniline moieties, acrylic acid (␤-alanine) moieties and from the vibrations of the lattice. The most pronounced feature of infrared spectrum is the very strong band at 3346 cm−1 with its very weak Raman counter-

part observed at 3348 cm−1 . The presence of only one band in this region corroborates the fact, that C C bond was broken with following C–N bond formation (see Scheme 1). As a consequence, instead of –NH2 group, which gives commonly two bands (␯a NH2 and ␯s NH2 ), the one N–H bond is present in the studied system. The above mentioned very strong infrared band at 3346 cm−1 correspond to the stretching vibration of N–H bond. Additionally, the absence of very strong infrared bands at 1636 and 1616 cm−1 with very strong Raman counterpart at 1639 cm−1 (the strongest band in the whole spectrum presented in Fig. 3) derived from the stretching vibrations of C C bond

Scheme 1.

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M.K. Marchewka et al. / Spectrochimica Acta Part A 79 (2011) 758–766

Table 6 The theoretical and experimental frequencies, intensities, PED, and tentative assignment for N-(4-nitrophenyl)-␤-alanine. FTIR

3487w 3346vs 3183m 3131m 3109m

3084m 3070m

FT Raman

Calc. int. [km/mol]

PED %

Assignment

354 22

O3–H31 100 O3–H31 100

O–H stretch O–H stretch N–H stretch, N–H· · ·O 3.113 A˚

3348vw 3313 3293

36 56

3094vw

3281

19

3086vw

3256 3237

3 12

3155

5

3058

37

3034m 3021m 2976m 2962m

Calc. freq. 3715 3344

2969vw

C6–H6 96 C2–H2 57, C3–H3 42 C3–H3 57, C2–H2 42 C7–H71 96 C8–H81 88, C8–H82 11 C8–H82 88, C8–H81 12

C–H stretch C–H stretch

C7–H72 98, C7–H71 2

C–H asym stretch

C–H stretch C–H stretch C–H stretch C–H stretch

␯O–H (A component) d(O· · ·O) = 2.652 A˚ C–H sym stretch C–H stretch

2960mb 2925vw 2907m 2875m 2773m 2752m 2725m 2663m 2650mb 2604m

␯O–H (B component) d(O· · ·O) = 2.652 A˚ 2591vw

2577m 2524m 2501m 2428m 2415m 2390m 2323m 2220w 2001vw

2430vw

Overtone Overtone Overtone

2066

301

C4–N2–H2a 71, N2–H2a 24

Overtone Overtone

1965vw 1919vw 1749vw 1705vs

1802

324

1694ssh

1774

88

1713

460

1627

33

1656

46

1595w

1615

131

1590w

1585

35

1541s 1502s

1541vw 1505w

1632

624

1463vs

1468vw 1453vw

C9–O4 44, C4–N2 14 C6–C5 21, C9–O4 15, C4–N2 13

1672vw 1636w 1609vw

1600vs

1592vssh

1446ssh

1395w

1396vw

N–H stretch

1574

16

1537

51

C4–N2 43, C3–C2 14 C9–O3 21, C8–C9 11, N2–C7–H71 11, C8–C9–O4 10 C6–C5 30, C3–C2 27, C2–C3–H3 14, C4–C3 12 C4–N2–C7–H71 21, C4–N2–C7–H72 21, N2–C7–H72 18, N2–C7–H71 12 N2–C7–C8–H82 33, N2–C7–C8–H81 27, C7–C8–H81 20, C7–C8–H82 13 N1–O2 62, N1–O1 37

C1–C2–H2 19, C6–C5–H5 17, C2–C3–H3 14, C1–C6–H6 10 C1–C6–H6 32, C1–C2–H2 21

C O stretch out-of-phase Aromatic ring C C stretch C O stretch in-phase C–N stretch C–O stretch out-of-plane

Aromatic ring C C stretch

C–H stretch

C–H stretch

C–N stretch NO2 asym stretch Ring stretch Ring stretch C–H in-plane bend (ring)

C–H in-plane bend (ring)

M.K. Marchewka et al. / Spectrochimica Acta Part A 79 (2011) 758–766

763

Table 6 (Continued) FTIR

FT Raman

1377m 1365m

1376vw

1351s 1334vs

Calc. freq.

Calc. int. [km/mol]

PED %

1532

138

N1–O1 35, C1–N1 15, N1–O2 15

1512

199

1503

66

1482

181

1466

17

1395

20

1373

262

1355

175

N2–C7–H71 27, C4–N2–C7–H71 17, C4–N2–C7–H72 16, N2–C7–H72 10 C3–C4–N2–H2a 21, C1–C6 15, C4–C3 12 C3–C4–N2–H2a 39, N2–C7–H72 10 C7–C8–H82 29, C9–O3–H31 20, C7–C8–H81 11 N2–C7–H71 18, N2–C7–H72 15, C7–C8–H81 12 C2–C1 17, C9–O3–H31 15, C2–C3–H3 10 C9–O3–H31 30, C9–O3 16 C7–C8–H81 25, C7–C8–H82 20, N2–C7–H72 16, N2–C7–C8–H81 11 C6–C5–H5 23, C2–C3–H3 20, C3–C2 16, C1–C6–H6 12, C1–C2–H2 12, C6–C5 12

1356vw 1351vw

1426vw 1409w

1320vs

1319m

1329

29

1305vs

1300vs

1321

16

1286vs 1274vs 1236s

1282m 1269m 1236w 1251

7

1226

123

1179

12

1145

1

1140

1

1106m

1121

23

N2–C7 29, N2–C7–C8 12, N2–C7–C8–H81 11

1093s 1039w

1039vw

1061

86

999m

999vw

1041

5

C1–C6–C5 32, C4–C3–C2 21, C3–C2–C1 14 C7–C8 29, C3–C2–C1 18, C1–C6–C5 17, C8–C9 13

1189s

1184s

1183w

1134m

C2–C3–H3 13, C1–C2–H2 12, C1–C6–H6 12, C3–C2 11, C6–C5–H5 11, C6–C5 11 C1–N1 24, C1–C6–C5 15, N1–O1 13, N1–O2 13, C1–C6 12, C3–C2–C1 10, C2–C1 10 C4–N2–C7–H71 14, N2–C7–C8–C9 14, C4–N2–C7–H72 12, N2–C7 11 C1–C2–C3–H3 35, C6–C1–C2–H2 26, C1–C6–C5–H5 11 C2–C1–C6–H6 37, C1–C6–C5–H5 25, C2–C1–C6–C5 13, C6–C1–C2–H2 12

1112vs

Assignment C–H in-plane bend (ring) NO2 stretch

NO2 sym stretch C–H in-plane bend

Ring stretch

C–H in-plane bend C–H in-plane bend

C–H in-plane bend

C–C stretch and C–H bend

C–H out-of-plane bend C–O bend C–H out-of-plane bend

C–H out-of-plane bend

O–H bend out-of-phase, O–H· · ·O 2.652 A˚ O–H bend in-phase, O–H· · ·O 2.652 A˚ NO2 stretch and C–C stretch C–H out-of-plane bend

Out-of-plane ring def

C–H out-of-plane bend

C–H out-of-plane bend

Out-of-plane ring def

C–H in-plane bend C–N stretch

C–N stretch and C–H bend Out-of-plane ring def

6(A1 ) mode of benzene ring

764

M.K. Marchewka et al. / Spectrochimica Acta Part A 79 (2011) 758–766

Table 6 (Continued) FTIR

FT Raman

Calc. freq.

Calc. int. [km/mol]

PED %

Assignment

979w

982vw

1004

93

C3–C2–C1–C6 46, C1–C2–C3–H3 17, C6–C1–C2–H2 17, C1–C6–C5–H5 15, C2–C1–C6–H6 11

In-plane ring def

915 930

106 20

C8–C9–O3–H31 46 C7–C8–C9 21, C8–C9 13, C8–C9–O3 11 C7–C8 21, N2–C7 14, C2–C1–C6 11 C1–C6–C5–H5 14, C6–C1–C2–H2 13, C1–N1–O2 12, C1–C2–C3–H3 12, C2–C1–C6–H6 10 C8–C9–O3–H31 16, C1–C6–C5–H5 11 C4–C3–C2–C1 59, C2–C1–C6–C5 44 C2–C1–N1–O2 25, C4–C3–C2–C1 10 C2–C1–N1–O1 26, C2–C1–N1–O2 16 C2–C1–C6 68, C8–C9–O4 20

964vw 949m

904w

904vw

971

19

856wsh

857m

910

44

906

127

845

15

850w

837s

835vw

867

97

806vw

803vw

857

62

788vw

776

3

716

185

C7–C8–C9 15, C4–C3–C2 14, C3–C2–C1 10

651

50

C8–C9–O4 37, C8–C9 21

618w

635

10

601w

614

22

579vw

563

7

539vw

548

48

C3–C2–C1–C6 33, C2–C3–C4–N2 15, C4–N2–C7–C8 12, C2–C1–C6–H6 10 C3–C2–C1 71, C1–C6–C5 16, C2–C1 12 C7–C8–C9 22, N2–C7–C8 10 C8–C9–O3 29, C4–N2–C7 11

753s 721w

755vw

699m 637w

695vw

628vw

542m

C–H out-of-plane bend O–H out-of-plane def, O–H· · ·O 2.652 A˚ C–C stretch

C–C stretch NO2 in-plane def

C–H out-of-plane bend, out-of-plane ring bend

NO2 rock and CCO bend NO2 rock and CH rock CO2 wag C–H out-of-plane bend, 4(B1 ) type C–C def

Out-of-plane ring def 8(B1 ) mode C O out-of-plane def Out-of-plane ring def, 8(B1 ) mode Out-of-plane ring def

Out-of-plane ring bend

C–N bend, C–C def C–O def

523wb

489m 416w

517vw 497vw 485vw 418vw

459

7

421

15

408

2

380

5

329

6

289vw

291

18

281vw

245

4

411wsh

394vw 349w

331w 295vw

289vwsh

CO2 wag

C7–C8–C9 23, C4–C3–C2–C1 18, C2–C3–C4–N2 11, C3–C4–N2–C7 10 C7–C8–C9 34, C8–C9–O3 23, C3–C4–N2 14 C3–C2–C1–C6 29, C2–C1–C6–C5 23 C2–C1–C6–C5 44, C1–N1–O1 18, C2–C1–C6 15

Out-of-plane ring bend C–C def

C–C def, C–N def

Out-of-plane ring bend Out-of-plane ring bend

341vw 331vw C3–C2–C1–C6 31, N2–C7–C8–C9 18, C1–N1–O2 18, C1–N1–O1 17 C2–C1–N1 19, C1–N1–O2 17, C4–C3–C2 13, C3–C2–C1–C6 11 C2–C1–N1 35, N2–C7–C8–C9 34

Out-of-plane ring bend

C–O def C–N def

CCN def.

M.K. Marchewka et al. / Spectrochimica Acta Part A 79 (2011) 758–766

765

Table 6 (Continued) FTIR

FT Raman

Calc. freq.

Calc. int. [km/mol]

PED %

237vw 192w

240vw 229

9

186vw

195

0

155vw

177

4

160

3

121vw

122

3

98vw

105

3

82

4

C3–C2–C1–N1 34, C3–C2–C1 14, N2–C7–C8 13, C1–N1–O1 12, C4–C3–C2 11 C7–C8–C9–O3 43, C7–C8–C9–O4 30, C3–C2–C1–N1 16 C3–C4–N2–C7 37, C2–C1–N1–O1 26, C2–C1–N1–O2 22, N2–C7–C8–C9 11, C4–C3–C2–C1 11 C2–C1–N1–O2 28, C2–C1–N1–O1 19, C3–C2–C1–N1 19, C4–N2–C7–C8 19 C4–N2–C7 18, C3–C2–C1–C6 17, C3–C4–N2 17, N2–C7–C8–C9 12, C3–C2–C1–N1 11, N2–C7–C8 10 C3–C4–N2–C7 38, C4–C3–C2–C1 15, C4–N2–C7 12, C3–C4–N2 11 C2–C3–C4–N2 41, C4–N2–C7–C8 41, C3–C2–C1–N1 11

−1179

7205

147w

Assignment O· · ·O stretch, N· · ·O stretch CCN def

COOH def

CCN def

CNO def

CNC def

CNC def

CNC def out of plane

Abbreviations: s—strong, w—weak, v—very, sh—shoulder, b—broad, m—medium, stretch—stretching, bend—bending, wag—wagging, rock—rocking, symm—symmetrical, breath—breathing, def—deformation.

corroborates the breaking of this bond in the case of studied crystal. 3.3. The vibrations of 4-nitrophenyl moiety The assignment for internal vibrations of 4-nitrophenyl moiety was done with the help of paper published by Evans [24] and Gao et al. [25]. Most bands observed in infrared and Raman spectra belongs to benzene ring modes. Only some of them may be assigned to the vibrations of N–H bond. For assignment of phenyl ring modes the classical work of Herzberg [26] as well as paper by Miller [27] are helpful. Herzberg’s notation was used for numbering normal modes associated with the phenyl ring. The bands corresponding to 6(A1 ) mode of benzene ring were found at 999 cm−1 in the infrared and Raman spectrum, respectively. The strong infrared band located at 753 cm−1 with very weak Raman counterpart at 755 cm−1 was attributed to out-of-plane C–H deformation, 4(B1 ), type of vibration of benzene ring. The out-ofplane ring deformations, 8(B1 ), give the infrared bands at 721, 699 and 628 cm−1 . The good group vibrations of benzene ring are the stretching one [28]. The very strong infrared bands at 1463 and 1453 cm−1 were assigned to ring stretching type of vibrations. For other assignment of internal vibrations of 4-nitrophenyl residue see Table 6. 3.4. Internal vibrations of ˇ-alanine moiety Two very weak bands observed in Raman spectrum at 2969 and 2925 cm−1 corresponds to the presence of coupled C–H bonds. They were assigned to the stretching vibrations of asymmetric and symmetric type, respectively. Similar bands were observed at 2958 and 2912 cm−1 in the infrared and Raman spectrum of 2,4,6-triamino1,3,5-triazin-1,3-ium tartrate monohydrate [29].

3.5. The hydrogen bonds vibrations The determination of the arrangement of hydrogen bonds from X-ray data is useful for the interpretation of vibrational spectra. According to crystallographic data there are two kinds of hydrogen bonds (Table 4). The position of infrared band originating from the absorption of particular hydrogen bond depends mainly on their length [30]. According to such a correlation for hydro˚ one can gen bond of O–H· · ·O type with the length of 2.652 A, expect the deformation vibrations in the ranges of 1300–1100 cm−1 and 1000–800 cm−1 , for in-plane and out-of-plane types, respectively. Therefore, two infrared bands at 1286 and 1274 cm−1 with Raman counterparts at 1282 and 1269 cm−1 were attributed to coupled in-plane vibrations of O–H bonds, out-of-phase and in-phase, respectively. The medium infrared band located at 949 cm−1 was assigned to the O–H out-of-plane type of vibration. The broad absorption in the region of 3300–1800 cm−1 can be divided into two components with maxima at ca. 2960 and 2650 cm−1 , for A and B component, respectively. These bands originate from the O–H stretching vibrations. The origin of such absorption was discussed by El-Amine Benmalti et al. [31].

4. Conclusions The reaction of 4-nitroaniline with acrylic acid yielded N(4-nitrophenyl)-␤-alanine in the crystalline form, as a result of addition of 4-nitroaniline molecule by its amine group to the double band of acrylic acid. Most bands of internal vibrations and vibrations of hydrogen bonds have been identified. The vibrational characteristics corroborates structural data which show that C C bond of vinyl part of acrylic acid was broken with following formation of C–C bond. Strands as open dimers are present in the

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structure, joined by medium O–H· · ·O type of hydrogen bond interactions in which the protons of carboxylic groups are engaged. Supplementary material Additional material comprising full details of the X-ray data collection and final refinement parameters including anisotropic thermal parameters and full list of the bond lengths and angles have been deposited with the Cambridge Crystallographic Data Center in the CIF format as supplementary publication No. CCDC 665406. Copies of the data can be obtained free of charge on the application to CCDC, 12 Union Road, Cambridge, CB21EZ, UK (Fax: +44 1223 336 033; email: [email protected]). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

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