Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 50–60

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Synthesis, structural and computational characterization of 2-amino3,5-diiodobenzoic acid and 2-amino-3,5-dibromobenzoic acid M. Hakkı Yıldırım a,⇑, Hümeyra Pasßaog˘lu b, Hakkı Yasin Odabasßog˘lu c, Mustafa Odabasßog˘lu d, Arzu Özek Yıldırım e a

Department of Property Protection and Security, Dereli Vocational School, Giresun University, 28950 Giresun, Turkey Department of Physics, Faculty of Arts and Science, Ondokuz Mayıs University, 55139 Samsun, Turkey Department of Textile Engineering, Faculty of Engineering, Pamukkale University, 20070 Denizli, Turkey d Department of Chemistry and Chemical Processing Technology, Denizli Vocational School of Tech. Sci., Pamukkale Univ., 20070 Denizli, Turkey e Department of Physics, Faculty of Arts and Science, Giresun University, 28200 Giresun, Turkey b c

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 The titled compounds were studied

Molecular electrostatic potential maps of 2A35Br (left) and 2A35I (right).

with XRD, FT-IR and UV–Vis methods.  Molecular geometries and all possible positional isomers were determined using DFT.  NLO calculations reveal the nonlinear optical material characters of the compounds.  Electrophilic attack regions were determined by MEP maps and Fukui functions.  Natural atomic charges of the compounds were determined by NPA method.

a r t i c l e

i n f o

Article history: Received 17 November 2014 Received in revised form 26 January 2015 Accepted 5 March 2015 Available online 11 March 2015 Keywords: Aminobenzoic acids 2-Amino-3,5-dibromobenzoic 2-Amino-3,5-diiodobenzoic Crystal structures DFT

a b s t r a c t The benzoic acid compounds 2-amino-3,5-dibromobenzoic acid (2A35Br) and 2-amino-3,5-diiodobenzoic (2A35I) acid have been synthesized and characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, UV–Vis spectroscopy and computational methods. Molecular geometry, intra- and inter-molecular interactions have been investigated by using X-ray diffraction technique. Fundamental vibrational bands of the title compounds were founded by FT-IR and UV–Vis method was used to obtain electronic bands. Geometry optimizations and the calculation of IR frequencies were performed both Gaussian type orbitals at Gaussian 09W and Slater type orbitals at ADF2009.01 software. The calculations are compatible with the experiment results. In addition, geometrical parameters, energies, HOMO–LUMO gaps and electrophilicity indexes have been calculated for thirty possible positional isomers of 2A35Br and 2A35I. Calculations show that 2A35Br and 2A35I isomers have the lowest energy, the narrowest HOMO–LUMO gap and the highest electrophilicity index values. Molecular electrostatic potential maps, Fukui indices, natural bond orbital analysis, thermodynamic parameters and non-linear optical properties of the 2A35Br and 2A35I were also investigated by theoretical calculations. Ó 2015 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +90 454 383 00 12x102. E-mail address: [email protected] (M.H. Yıldırım). http://dx.doi.org/10.1016/j.saa.2015.03.072 1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

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Introduction Aminobenzoic acid (ABA) is a member of the aromatic amino acids. It is also known as Vitamin L which is a biologically active substances. Their antimutagenic capacity decreases in the order of 2-ABA > 3ABA > 4ABA. Antimutagenic property is mainly attributed to the decomposition of N-methyl-N0 -nitro-N-nitrosoguanidine induced by the ABA isomers outside or inside the bacterial cells [1]. Experimental and theoretical IR, Raman, NMR spectra of 2-, 3- and 4-aminobenzoic acids were reported by Samsonowicz et al. [2]. Syahrani et al. investigated the Toxicity of 4- and 2aminobenzoic acids toward cell suspension cultures of Solanum mammosum [3]. Antibacterial activity of 4-amino benzoic acid and its effect on bacterial DNA synthesis were investigated by Richards and Xing [4]. Due to its wide applications, not only ABAs but also its halogenated derivatives have been extensively investigated [5–7]. Rzacynska et al. reported crystal structures of ammonium and sodium 2-amino-3,5-dichlorobenzoates [8]. Sundaraganesan et al. recorded FT-IR and FT-Raman spectra of 2amino-4,5-difluorobenzoic acid and reported a detailed interpretations of infrared, Raman spectra by support with HF and DFT calculations [9]. Karabacak et al. performed detailed investigation of IR and Raman spectra of 2-amino-5-bromobenzoic [10], 2, 3-difluorobenzoic and 2,4-difluorobenzoic acid [11] by both theoretical and computational methods. In the literature, there are a lot more publications on ABA derivatives [12–16]. To the best of our knowledge, there are no study that involved theoretical or experimental study of 2A35I and 2A35Br in the literature. In this study, we report the synthesis, characterization, crystal structure and computational analysis of 2A35Br and 2A35I. Also influences of halogen atoms’ positions to the energetic parameters and geometry are discussed. Non-linear optical properties, NBO analysis, thermodynamic parameters, Fukui indices and molecular electrostatic potential maps are investigated by theoretically.

non-hydrogen atoms were refined anisotropically by full matrix least-squares methods in SHELXL-97 [19]. Aromatic hydrogens of both compounds were positioned geometrically and refined by a riding model with Uiso 1.2 times that of attached atoms and remaining hydrogen atoms were found on Fourier difference map. WinGX [20], ORTEP-3 [21] for Windows and PLUTON [22] softwares were used for molecular drawings and other materials. Table 1 presents the data collection conditions and parameters of refinement process of title compounds. Computational procedures X-ray geometries of compounds were selected for the initial molecular geometries. Geometry optimizations and vibrational spectra calculations were performed by Gaussian and Slater type orbitals for comparison. Because one can expect different results when considered their different functional behaviors. Gaussian type calculations with a hybrid functional B3LYP [23] at 6311++G(d,p) basis set were performed with the Gaussian 09W [24] software package. Slater type calculations were performed by using the Amsterdam Density Functional package (ADF) 2009.01 [25–27] program. Geometry optimization in the ground state was carried out using B3LYP density functional calculations, with the TZP basis sets (all-electron triple zeta plus polarization function). The harmonic vibrational frequencies were calculated at the same level of theory for the optimized structures in both types of software. Each of 2A35I and 2A35Br have thirty positional isomers. These isomers were obtained from changing positions of halogens and carboxyl groups. These isomers were drafted by GaussView 5 [28] software and optimized by Gaussian 09W software with a hybrid functional B3LYP at 6-311+G(d,p) basis set. In all Gaussian type calculations, Midi! basis sets that developed by Truhlar and coworkers [29] were used for I atoms. Results and discussion

Material and methods

Crystal structure and optimized geometry

Synthesis

The molecular structures of compounds are given in Figs. 1 and 2 with the atom numbering scheme and selected geometrical parameters are listed in Table 3. 2A35Br crystallizes in the

The 2-amino-3,5-dibromobenzoic acid (Alfa Aesar, 0.5 g) was added to an ethyl alcohol (%95, 25 mL) and water (25 mL) solution and the mixture was heated at boiling temperature. The suitable crystals for X-ray analysis were obtained from clear solution by slow evaporation (m.p. 503–505 K). The 2-amino-3,5-diiodobenzoic acid (Alfa Aesar, 0.5 g) was added to an ethyl alcohol (%95, 25 mL) and water (25 mL) solution and the mixture was heated at boiling temperature. The crystals suitable for X-ray analysis were obtained from clear solution by slow evaporation (m.p. 507–509 K). Instrumentation FT-IR spectra of the compounds were recorded in the 4000– 400 cm1 region with a Bruker Vertex 80 V spectrometer using KBr pellet. Absorption spectra were determined on Unicam UV– Vis spectrometer. Crystal structure determination XRD data collections of compounds were performed on a STOE IPDS II diffractometer by the w scan technique using graphite monochromated Mo Ka radiation (k = 0.71073 Å) at 296 K. Cell parameters were determined using X-AREA software [17]. The crystal structures of compounds were solved by SIR92 [18]. All

Table 1 Crystallographic details of the titled compounds.

Chemical formula Color/shape Formula weight Cell setting Space group a (Å) b (Å) c (Å) a, b, c (°) Volume (Å3) Formula Z Density (calculated) (Mg m3) Absorption coefficient (mm1) Tmin, Tmax hmin, hmax kmin, kmax lmin, lmax R(int) Goodness of fit on F2 Final R1, wR2 (observed data) Final R1, wR2 (all data) Largest difference in peak and hole (e Å3)

2A35I

2A35Br

C7H5I2NO2 Pale yellow/prism 388.92 Monoclinic C2/c 23.7187(11) 4.7259(2) 17.8444(8) 90, 107.797(4), 90 1904.50(15) 8 2.713 6.57 0.180, 0.635 30, 30 6, 6 22, 22 0.0271 1.0970 0.031, 0.073 0.034, 0.075 0.721, 0.824

C7H5Br2NO2 Colorless /Prism 294.94 Monoclinic P21/c 13.4579(14) 3.9456(3) 16.3417(14) 90, 99.368(8), 90 856.16(13) 4 2.288 9.42 0.203, 0.817 16, 17 4, 4 20, 20 0.0656 1.150 0.048, 0.090 0.064, 0.095 0.495, 0.513

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Fig. 1. Perspective view down the crystallographic a axis to demonstrate a partial packing diagram and molecular structure for 2A35Br with hydrogen bonds are shown as dashed lines [Symmetry codes: (i) 1  x, 2  y, 1  z, (ii) x, 1 + y, z, (iii) x, y  1, z].

Fig. 2. A partial packing diagram and molecular structure for 2A35I with hydrogen bonds are shown as dashed lines [Symmetry codes: (i) 1  x, 3  y, 1  z, (ii) x, 2  y, 1/2 + z, (iii) x, 2  y, 1/2 + z].

monoclinic space group P21/c and 2A35I is in the monoclinic space group C2/c. Both of molecules are almost planar with maximum deviation from planarity via O2 with 0.1072 (44) Å and N1 with 0.1922 (41) Å for 2A35Br and 2A35I respectively. There are no significant differences between bond lengths of these molecules and they are close to the values found in other 2-amino-

3,5dichlorobenzoic acid [8] and 2-amino-3-bromobenzoic acid [30] compounds. Crystal structures are stabilized by both intra and intermolecular N–H  O and O–H  O type hydrogen bonds. There is a strong intramolecular N1–H1A  O1 hydrogen bond which generates an S (6) ring motif supporting the planarity of the molecule in both

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0.06 Å for STO. O1–C7–C1 bond angle deviation that 2.8° for both GTO and STO is the biggest. Discrepancies mainly arise from bond length and angle involved in hydrogen bonds. The reason is that the experimental values obtained from crystal structure and theoretical values obtained from the in vacuum phase. In the crystal structure, the experimental values are affected from molecular packing.

Table 2 Details of hydrogen bonding and short interactions in titled compounds. D–H  A

D–H (Å)

H  A (Å)

D  A (Å)

D–H  A (°)

2A35I N1–H1A  O1 N1–H2A  I1 N1–H1A  I2i O2–H2  O1ii

0.96 0.98 0.96 0.81

2.03 2.69 3.05 1.87

2.681 3.219 3.913 2.663

124 115 151 167

2A35Br N1–H1A  O1 N1–H1B  Br1 O2–H2  O1iii

0.87 (8) 0.83 (7) 0.79 (8)

2.11 (8) 2.70 (7) 1.86 (8)

2.714 (7) 3.059 (6) 2.645 (6)

126 (7) 107 (6) 173 (9)

Cg1

Cg2

p  p (Å)

a (°)

c (°)

2A35Br C1/C6

C1/C6iv

3.946 (3)

0

27.2

(2) (2) (2) (2)

(7) (8) (4) (3)

(6) (5) (5) (5)

(6) (6) (6) (9)

Vibrational spectra

Symmetry codes: (i) x, y + 2, z  1/2, (ii) x + 1, y + 3, z + 1, (iii) x + 1, y, z + 1, (iv) x, 1 + y, z.

of molecules. Strong intermolecular O2–H2  O1 hydrogen bonds generate R22 ð8Þ dimeric aggregates in both compounds (Figs. 1 and 2). These aggregates are linked via weak intermolecular N–H  I type hydrogen bonds and p  p stacking interactions for the 2A35I and 2A35Br compounds, respectively. Geometrical details of the hydrogen bonds are summarized in Table 2. Optimized molecular structures were obtained by energy minimization algorithm in Gaussian 09W and ADF 2009.01b software with the 6-311++G(d,p) and the TZP basis set, respectively. Some selected experimental and theoretical geometric parameters of title compounds are given in Table 3. As shown in the table, agreement between them are satisfactory. In order to estimate deviation from experimental values, RMS errors were calculated. RMSE calculations for 2A35Br show that RMSE between X-ray and GTO parameters are 0.117 Å in bond length, 1.15° in bond angles and 2.77° in dihedral angles. These errors slightly decrease in X-ray and STO comparisons with 0.101 Å, 0.835° and 2.22° for bond length, bond angle and dihedral angle, respectively. The greatest differences for the bond lengths are found for C3–Br1 and C5–Br2 bonds with the difference being 0.22 Å, 0.21 Å for GTO and 0.05 Å, 0.04 Å for STO, respectively. For the bond angles, the biggest deviations occur at C1–C2–N1 bond angle with 2.2° for GTO and 1.9° for STO. For 2A35I, RMSE values are obtained from comparison of X-ray and GTO are 0.06 Å for bond length, 1.7° for bond angles and 3.9° for dihedral angles. In addition, these values are 0.06 Å, 1.7° and 3.2° for X-ray and STO comparison. The greatest deviation of the bond length occurs at C7–O2 bond with 0.05 Å for GTO and

The experimental and calculated vibrational frequencies with their most characteristic band assignments of the studied 2A35I and 2A35Br are presented in Table 4. The calculated wavenumbers are usually higher than the corresponding experimental values. The major reason of that the experimental value is an anharmonic frequency while the calculated value is a harmonic frequency [31]. In addition, the combination of electron correlation effects, basis set deficiencies and calculated frequencies obtained from in vacuum give higher frequencies. To avoid this systematic error, the calculated wavenumbers are usually scaled by scaling factor. The scaling factors are taken as 0.983 for frequencies less than 1700 cm1 and 0.958 for frequencies above 1700 cm1 for B3LYP/ 6-311++G(d,p) level [32] in gaussian type calculations. In the slater type calculations, scaling factor is taken as 0.9648 for all frequencies [33]. The NH2 asymmetric and symmetric stretching bands are obtained at 3468, 3363 cm1 for 2A35Br and 3461, 3348 cm1 for 2A35I, respectively. For 2-aminobenzoic acid, these bands were reported at 3382 and 3495 cm1, respectively by Samsonowicz et al. [2]. Most of amino acids in the crystalline state exist as ‘zwitterions’, where the proton migrates from the acidic –COOH group to the basic –NH2 group to form the ionic groups [2]. Presence in IR spectra of both compounds asymmetrical and symmetrical stretching vibration bands of NH2 group shows that ionic state in these compounds is little or no apparent. In dimeric forms of amino benzoic acids, the very broad band in the 2500–3000 cm1 are attributed to OH stretching vibration involved in strong hydrogen bonds. This band is found about at 3615 and 3605 cm1 for GTO and STO type basis sets in theoretical calculations which performed at one molecule in vacuum form. The band observed at the 1700–1800 cm1 region due to the C@O stretching vibration is one of the characteristic features of the carboxylic group. Carboxylic acids in dimeric structure give symmetric and asymmetric C@O vibrations. The asymmetric stretch is usually seen at a higher wavenumber than the symmetric stretch and only asymmetric stretch is IR active [10]. On this basis, the asymmetric C@O stretch is observed in FT-IR as very strong band at 1679, 1672 cm1 for

Table 3 Experimental and calculated geometrical parameters of 2A35I and 2A35Br. Parameter

XRD (2A35I)

XRD (2A35Br)

GTO (2A35I)

STO (2A35I)

GTO (2A35Br)

STO (2A35Br)

C1–C2 C1–C6 C1–C7 C2–N1 C2–C3 C3–X1 C5–X2 C7–O1 C7–O2 O2–C7–O1 C1–C2–N1 C2–C3–X1 C2–C1–C7–O1 N1–C2–C3–X1

1.418 (6) 1.402 (6) 1.474 (6) 1.378 (6) 1.404 (6) 2.100 (4) 2.092 (4) 1.235 (5) 1.300 (6) 121.9 (4) 122.7 (4) 120.1 (3) 0.6 (6) 7.3 (6)

1.427 (6) 1.387 (7) 1.484 (7) 1.336 (7) 1.426 (7) 1.889 (5) 1.888 (6) 1.221 (7) 1.313 (6) 122.6 (5) 123.9 (5) 118.3 (4) 6.2 (9) 1.3 (7)

1.427 1.403 1.470 1.353 1.419 2.111 2.103 1.220 1.356 120.4 120.1 120.0 0.01 0.01

1.427 1.401 1.472 1.350 1.418 2.135 2.129 1.222 1.358 120.3 121.4 120.3 0.7 1.2

1.428 1.405 1.472 1.352 1.419 1.920 1.915 1.220 1.354 120.6 122.4 119.0 0 0

1.427 1.403 1.473 1.350 1.427 1.937 1.934 1.222 1.357 120.4 121.9 119.3 0.9 1.4

Bond lengths and angles are in units of Å and °, respectively.

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Table 4 Experimental and calculated characteristic IR bands for the titled compounds. Assignment

2-ABAa

masym (NH2) msym (NH2) m (O–H) m (C@O) q (NH2) m (C–C)

3495 3382 3060–2530 1670 1609 1586 1486

d (O–H) m (C–NH2) m (C–OH) c (C–H) Ring breathing masym (C–X)

1418 1326 1253 921 867

2A35Br

2A35I b

Exp.

Scaled GTO

Scaled STO

3468 3363 3000–2500 1679 1600 1564 1535 1452 1420 1326 1225 900 880 670

3540 3393 3615 1669 1614 1530 1447 1405 1166 1316 1070 913 793 681

3554 3393 3603 1671 1578 1542 1415 1332 1144 1290 1049 892 774 661

c

Exp.

Scaled GTO

Scaled STO

3461 3348 3000–2500 1672 1594 1562 1521 1440 1417 1316 1226 899 882

3527 3385 3617 1668 1611 1529 1445 1398 1169 1318 1072 874 789 267

3546 3388 3607 1671 1574 1537 1489 1413 1143 1289 1047 873 767 259

m, stretching; d, in plane bending; c, out of plane bending; q, scissoring; r, rocking; x, wagging; t, twisting. a b c

Ref. [2]. GTO: DFT/B3LYP/6-311++g(d,p). STO: DFT/B3LYP/TZP.

Table 5 Experimental and calculated electronic bands of 2A35Br and 2A35I. kobs (nm)

kcalc (nm)

Eex. (eV)

f

Major contribution

Ass.

2A35Br 243 357

254 349

4.88 3.55

0.008 0.134

H  1 ? L (68%), H ? L + 2 (30%) H ? L (97%)

p ? p⁄ p ? p⁄

2A35I 229 357

276 358

4.49 3.46

0.021 0.123

H  1 ? L (93%) H ? L (98%)

p ? p⁄ p ? p⁄

2A35Br and 2A35I, respectively. Due to the dimeric effects not counted in theoretical calculations this bands found in higher frequencies both compounds. The NH2 scissoring deformation appears in the 1638–1575 cm1 region with strong IR intensity. We assigned NH2 scissoring bands at 1600 cm1 for 2A35Br and 1594 cm1 for 2A35I in experimental IR spectrum. Corresponding frequencies were found at 1614 cm1 (GTO), 1578 cm1 (STO) for 2A35Br and 1611 cm1 (GTO), 1574 cm1 (STO) in the calculated spectrum. One of the most important vibrations in the FT-IR spectrum of benzene and its derivatives is the ring stretching vibrations. They are important due to very sensitive for substituents. Vibrations between 1400 and 1650 cm1 in benzene derivatives were assigned to ring C–C stretching modes by Varsanyi [34]. The C–C stretching frequencies obtained by experimental spectrum are well matched with both theoretical spectrum as seen in the Table 4. C–NH2 stretching vibrations were predicted at 1326 cm1 and 1316 cm1 and calculated values were founded close to these values. According to Mooney’s paper on infrared spectra of chloro- and bromobenzene derivatives, vibrations of the C–X group have been found (X = F, Cl, Br and I) in the wavenumber range of 1129–480 cm1 [35] while Varsanyi reported C–Br stretching mode to appear at longer wavelength region (200–480 cm1) [34]. Therefore, the band at 670 cm1 can be attributed to C–Br stretching mode. Because of the heavier mass of iodine, the C–I stretching vibration is predicted at under 400 cm1 where out of our spectral range (4000–400 cm1). The remainder of the experimental/calculated wavenumbers and their assignments are shown in Table 4. Electronic spectra The UV–Vis electronic absorption spectra of the compounds in methanol solvent were recorded within 200–800 nm range. The

electronic absorption maxima are observed at 243 and 357 nm in 2A35Br; 229 and 357 nm in 2A35I. These values are similar to those found in 2ABA compound (247 nm and 332 nm) [36]. The bands observed at 243 and 247 nm were ascribed to p–p⁄ transition of the aromatic ring, however the other bands can be attributed to p–p⁄ transition within the intramolecular hydrogen bonded ring (C1/C2/N1/H1A/O1/C7) for both molecules. In order to estimate excitation energies and oscillator strengths of the compounds in methanol solvent, TD-DFT calculations were performed by using PCM method at B3LYP/6-311G++(d,p) level. Major contributions to the electronic transitions were specified with the aid of Gaussum [37] program. These results are summarized in Table 5. As shown in table, the bands found at 243 and 229 nm are formed mainly HOMO  1 ? LUMO transitions while the bands at 357 are HOMO ? LUMO transitions for both compound. Experimental and calculated UV–Vis spectra of compounds are shown in Fig. 3 and it is seen that there is a good agreement between experimental and calculated spectra of compounds. Isomers of 2A35Br and 2A35I 2A35Br have thirty positional isomers with respect to changing three different functional groups; Br atom, NH2 and COOH group. Isomers were drafted by GaussView and optimized by Gaussian 09W with B3LYP method at 6-311G++(d,p) basis sets. Total energies, energies of frontier molecular orbitals (FMOs) and optimize geometries were obtained from mentioned calculations. 2A35Br has the lowest total energy in all isomers. Intra molecular hydrogen bonding between amino and carboxyl group can cause the isomer 2A35Br to be the most stable one. Total energy difference that is the relative energy of the other conformers with respect to 2A35Br are presented in Table S1 (supporting information) and the optimized possible geometric parameters are gathered in

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Fig. 3. Experimental and calculated UV–Vis spectra in methanol solution for the 2A35Br and 2A35I.

Table S2 (supporting information). FMOs that is the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are very informative computational parameters. The HOMO energy characterizes the capability of electron giving; LUMO characterizes the capability of electron accepting. The ionization energy and electron affinity can be expressed through HOMO and LUMO orbital energies as I = E(HOMO) and A = E(LUMO). Chemical potential was calculated from combination of I and A, l = 1/2(I + A). The gap between HOMO and LUMO orbital energies corresponds to the global hardness, g = 1/2(I  A), has been associated with the stability of chemical system. The global electrophilicity index x = l2/2g and softness f = 1/g were also calculated [38]. These parameters are given in Table S1. These

calculations show that 2A35Br has the most softness value and electrophilicity index. The same calculations performed for 2A35I isomers and the results are given Tables S3 and S4. Similarly to Br isomers 2A35I has minimum energy and the most softness and electrophilicity index. Non-linear optical properties Non-linear optical (NLO) effects arise from the interactions of electromagnetic fields in various media to produce new fields altered in phase, frequency, amplitude or other propagation characteristics from the incident fields [39]. NLO is at the forefront of current research because of its importance in providing the key

Table 6 NBO analysis of 2A35Br and 2A35I. Bond orbital (i)–(j)

2A35Br r(C1–C2) r(C1–C7) r(C2–N1) r(C3–Br1) p(C3–C4) r(C5–Br2) p(C5–C6) r(C7–O1) p(C7–O1) r(C7–O2)

Occupancy

Electron density (%)

Polarization coefficient of bond orbit

Hybrids (%p character)

(i)

(j)

(i)

(j)

(i)

(j)

1.95955 1.97360 1.98995 1.98276 1.74732 1.98374 1.71350 1.99501 1.98377 1.99500

49.56 51.70 41.14 49.27 56.87 49.88 56.76 35.19 28.30 32.12

50.44 48.30 58.86 50.73 43.13 50.12 43.24 64.81 71.70 67.88

0.7040 0.7190 0.6414 0.7019 0.7541 0.7062 0.7534 0.5932 0.5319 0.5668

0.7102 0.6950 0.7672 0.7123 0.6568 0.7080 0.6576 0.8051 0.8468 0.8239

sp1.94(65.91) sp2.33(69.92) sp2.37(70.28) sp3.65(78.41) sp1.00(99.99) sp3.45(77.41) sp1.00(99.97) sp2.00(66.56) sp1.00(99.49) sp2.71(72.89)

sp1.84(64.76) sp1.52(60.23) sp1.60(61.55) sp6.59(86.49) sp1.00(99.94) sp6.53(86.38) sp1.00(99.94) sp1.50(59.98) sp1.00(99.89) sp1.99(66.53)

1.95881 1.97344 1.99027 1.97562 1.74710 1.97707 1.71266 1.99504 1.98399 1.99487

49.61 51.67 41.01 55.91 57.32 56.58 57.24 35.17 28.21 32.11

50.39 48.33 58.99 44.09 42.68 43.42 42.76 64.83 71.79 67.89

0.7043 0.7188 0.6404 0.7477 0.7571 0.7522 0.7566 0.5930 0.5312 0.5667

0.7099 0.6952 0.7680 0.6640 0.6533 0.6589 0.6539 0.8052 0.8473 0.8239

sp1.93(65.87) sp2.33(69.96) sp2.41(70.64) sp3.55(77.95) sp1.00(99.99) sp3.34(76.90) sp1.00(99.99) sp2.00(66.60) sp1.00(99.49) sp2.73(73.01)

sp1.85(64.95) sp1.51(60.10) sp1.60(61.49) sp7.87(88.24) sp1.00(99.94) sp7.61(88.06) sp1.00(99.95) sp1.50(59.97) sp1.00(99.89) sp1.99(66.51)

2A35I

r(C1–C2) r(C1–C7) r(C2–N1) r(C3–I1) p(C3–C4) r(C5–I2) p(C5–C6) r(C7–O1) p(C7–O1) r(C7–O2)

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Table 7 Second order perturbation theory analysis of Fock matrix in NBO basis for 2A35Br and 2A35I. Donor NBO (i)

Acceptor NBO (j)

E(2) kcal/mol 2A35Br

2A35I

2A35Br

2A35I

2A35Br

2A35I

p(C5–C6) p(C7–O1) p(C3–C4) p(C5–C6) p(C7–O1)

n(LP1C1) n(LP1C1) p⁄(C5–C6) p⁄(C3–C4) p⁄(C7–O1) r⁄(C7–O1) r⁄(C1–C7) r⁄(N1–H1A) r⁄(C5–C6) r⁄(C4–C5) r⁄(C3–C4) r⁄(C2–C3) r⁄(C7–O2) p⁄(C7–O1) p⁄(C5–C6) n(LP1C1) r⁄(C7–O2) r⁄(C1–C7) r⁄(N1–H1A) r⁄(C2–C3) r⁄(C4–C5) r⁄(C5–C6) r⁄(C3–C4) r⁄(N1–H1B) p⁄(C7–O1) p⁄(C5–C6) p⁄(C3–C4)

33.65 5.68 12.83 24.35 0.89 6.35 2.89 1.98 1.69 1.38 1.22 1.17 0.58 79.94 78.67 1.13 31.7 14.82 5.53 3.49 3.46 3.22 3.09 1.63 43.44 9.13 8.77

33.58 5.64 12.29 25.16 0.89 6.26 2.94 2.07 1.56 1.37 1.07 1.1 0.6 81.56 80.19 1.05 31.66 14.64 5.81 2.79 2.83 2.64 2.49 2.38 43.21 7.58 7.18

0.15 0.26 0.3 0.28 0.39 1.21 1.15 1.16 1.57 1.53 1.56 1.51 1.05 0.12 0.15 0.13 0.62 0.72 0.73 0.82 0.84 0.88 0.88 0.73 0.34 0.3 0.31

0.14 0.26 0.3 0.28 0.39 1.21 1.15 1.16 1.45 1.42 1.45 1.39 1.05 0.12 0.15 0.13 0.62 0.72 0.73 0.79 0.81 0.85 0.85 0.7 0.34 0.28 0.28

0.083 0.052 0.057 0.075 0.018 0.078 0.052 0.043 0.046 0.041 0.039 0.038 0.022 0.105 0.111 0.014 0.127 0.094 0.059 0.048 0.048 0.047 0.047 0.031 0.112 0.051 0.05

0.082 0.052 0.056 0.076 0.014 0.078 0.052 0.044 0.043 0.04 0.035 0.035 0.023 0.106 0.112 0.014 0.127 0.094 0.06 0.042 0.043 0.042 0.04 0.037 0.111 0.044 0.043

n(LP1O2) n(LP1O1) n(LP1O1) n(LP1X2) n(LP1X2) n(LP1X1) n(LP1X1) n(LP1O1) n(LP1C1) n(LP1C1) n(LP1N1) n(LP2O1) n(LP2O1) n(LP2O1) n(LP2X1) n(LP2X2) n(LP2X2) n(LP2X1) n(LP2X1) n(LP2O2) n(LP3X2) n(LP3X1)

E(j)  E(i) a.u.

functions of frequency shifting, optical modulation, optical switching, optical logic, and optical memory for the emerging technologies in areas such as telecommunications, signal processing, and optical interconnections [40–43]. Organic molecules that exhibit extended p conjugation, in particular, show enhanced second order NLO properties [44]. The total static dipole moment (l), the mean linear polarizability (atot) and the first order hyperpolarizability (btot) using the x, y, z components are defined as [45]:

l¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi l2x þ l2y þ l2z

atot ¼

axx þ ayy þ azz 3

F(i,j) a.u.

NBO analysis Natural bond orbital (NBO) analysis is a useful method for studying intra and intermolecular bonding and provides a convenient basis for investigating hybridization and charge transfer in the molecular systems [47]. The bonding–anti bonding interaction can be quantitatively described in terms of the NBO approach that is expressed by means of second-order perturbation interaction energy E(2) [48]. This energy represents the estimate of the offdiagonal NBO Fock matrix element. The two electron stabilization energy E(2) associated with i(donor) ? j(acceptor) delocalization is

ð1Þ

ð2Þ

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi btot ¼ ðbxxx þ bxyy þ bxzz Þ2 þ ðbyyy þ bxxy þ byzz Þ2 þ ðbzzz þ bxxz þ byyz Þ2 ð3Þ The dipole moment (l), linear polarizability (atot) and the first hyperpolarizability (btot) were calculated at the B3LYP/6311++G(d,p) level using Gaussian 09W program package. The calculated dipole moment (l), polarizability (atot) and first hyperpolarizability (btot) for 2A35Br are 1.1871 D, 21.13 Å3, 3.59  1030 cm5/esu while 2A35I has 0.7545 D, 24.188 Å3, 5.27  1030 cm5/esu, respectively. Urea is one of the prototypical molecules used in the study of the NLO properties of molecular systems [46]. Therefore, it has been used frequently as a threshold value for comparative purposes. The values of atot and btot of urea are 5.042 Å3 and 0.765  1030 cm5/esu obtained at the same level. Theoretically, the first-order hyperpolarizability of both compounds is approximately six times the magnitude of urea. According to these results, both compounds are a good candidate of NLO material.

Table 8 Calculated thermodynamic parameters of the titled molecules at B3LYP/6311++G(d,p) level. T(°K)

100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500 525 550 575 600

C 0p;m

S0m

H0m

2A35Br

2A35I

2A35Br

2A35I

2A35Br

2A35I

19.09 22.33 25.46 28.48 31.40 34.22 36.94 39.56 42.07 44.47 46.76 48.94 51.01 52.97 54.81 56.55 58.19 59.73 61.18 62.55 63.83

19.16 22.28 25.26 28.14 30.94 33.67 36.32 38.90 41.39 43.78 46.08 48.27 50.36 52.34 54.21 55.98 57.64 59.21 60.69 62.08 63.38

78.11 83.17 87.88 92.34 96.60 100.69 104.65 108.48 112.20 115.83 119.35 122.79 126.15 129.42 132.61 135.73 138.78 141.75 144.65 147.49 150.27

79.21 84.26 88.95 93.37 97.58 101.61 105.51 109.28 112.95 116.51 119.99 123.38 126.69 129.92 133.08 136.17 139.19 142.13 145.02 147.83 150.59

1.40 1.97 2.62 3.34 4.14 5.01 5.95 6.96 8.03 9.16 10.35 11.60 12.90 14.25 15.64 17.08 18.57 20.09 21.65 23.25 24.88

1.39 1.96 2.60 3.32 4.11 4.97 5.89 6.88 7.93 9.05 10.22 11.45 12.73 14.07 15.45 16.88 18.35 19.86 21.41 22.99 24.61

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M.H. Yıldırım et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 50–60

Fig. 4. Molecular electrostatic potential maps of 2A35Br (left) and 2A35I (right).

Thermodynamic parameters

Table 9 Condensed Fukui functions of the titled molecules (X: Br or I). 

þ

C1 C2 C3 C4 C5 C6 C7 H1A H1B H2 H4 H6 N1 O1 O2 X1 X2

0

fk

fk

fk

2A35Br

2A35I

2A35Br

2A35I

2A35Br

2A35I

0.0505 0.0201 0.0504 0.1778 0.0240 0.1183 0.1042 0.0058 0.0204 0.0253 0.0277 0.0237 0.0437 0.1191 0.0482 0.1011 0.0878

0.0488 0.0188 0.0356 0.1782 0.0336 0.1221 0.1056 0.0050 0.0209 0.0250 0.0263 0.0226 0.0421 0.1180 0.0472 0.1163 0.1011

0.0740 0.0162 0.0628 0.0107 0.0979 0.0286 0.0061 0.0204 0.0227 0.0211 0.0284 0.0295 0.1965 0.0513 0.0229 0.1362 0.2083

0.0610 0.0211 0.0433 0.0140 0.0687 0.0297 0.0045 0.0185 0.0201 0.0196 0.0231 0.0256 0.1681 0.0481 0.0193 0.1726 0.2799

0.0623 0.0181 0.0566 0.0835 0.0369 0.0735 0.0491 0.0131 0.0215 0.0232 0.0280 0.0266 0.1201 0.0852 0.0355 0.1186 0.1480

0.0549 0.0199 0.0394 0.0821 0.0176 0.0759 0.0505 0.0117 0.0205 0.0223 0.0247 0.0241 0.1051 0.0831 0.0332 0.1444 0.1905

Thermodynamic parameters are helpful for understanding the chemical processes. The DFT is a well-established and efficient tool to predict these parameters [54]. Based on harmonic vibrational analysis and statistical thermodynamics, the thermodynamic parameters at B3LYP/6-311G++(d,p) level: entropy (S0m ), enthalpy (H0m ) and heat capacity (C 0p;m ) for the molecules were obtained in the temperature range, 100–600 K and listed in Table 8. The table shows that these thermodynamic parameters are increasing with temperature ranging from 200 to 600 K due to the fact that the vibrational intensities increase with the increasing temperature [55]. The correlation equations between heat capacity, entropy, enthalpy changes and temperatures are as follows and can be used for analyzing heat capacities, entropies and enthalpies in different temperatures fitted by quadratic formulas. For 2A35Br, the equations are:

S0m ¼ 59:67604 þ 0:19921T  8:13708x105 T 2 ; R2 ¼ 0:99985 C 0p;m ¼ 5:04243 þ 0:14887T  8:49913  105 T 2 ; R2 ¼ 1 estimated from the second-order perturbation theory using equation:

H0m ¼ 0:82233 þ 0:01628T þ 4:46746  105 T 2 ; R2 ¼ 0:99987

2

Eð2Þ ¼ DEij ¼

qi Fði; jÞ ð2j  2i Þ

ð4Þ

where qi is the donor orbital occupancy, ei and ej are diagonal elements and F(i, j) is the off-diagonal elements of Fock matrix [49]. The large value of E(2) indicates the more concentrated is the interaction between donors and acceptors. NBO analysis were performed at the DFT/B3LYP/6-311G+(d,p) level computation using NBO 3.1 program [49–53] implemented in the Gaussian 09W. NBO analysis transforms the delocalized molecular orbitals into localized molecular orbitals that are closely related to chemical bonding concepts. The hybridization of NBOs is shown in Table 6. The second order perturbation energy values E(2) and their important interactions between the electron donors and acceptors, are presented in Table 7. The NBO for a localized bond rij between atoms i and j is formed from orthonormal hybrids, hi and hj, using the relation, rij = cihi + cjhj where ci and cj are polarization coefficients [47]. The larger value of polarization coefficients indicates larger electron density value (%) of NBO which shows higher electronegativity (Table 6). The larger the E(2) value, the more intensive is the interaction between electron donors and electron acceptors (Table 7).

For 2A35I, the equations are:

S0m

¼ 61:1004 þ 0:19653T  8:00347  105 T 2 ; R2 ¼ 0:99982

C 0p;m ¼ 5:60092 þ 0:14243T  7:6767  105 T 2 ; R2 ¼ 0:99998 H0m ¼ 0:77406 þ 0:01587T þ 4:44528  105 T 2 ; R2 ¼ 0:9999 These equations will be helpful for the further studies of the compounds. Molecular electrostatic potential maps and Fukui indices The molecular electrostatic potential (MEP) V(r) that is created in the space around a molecule by its nuclei and electrons is well established as a guide to molecular reactive behavior. It is defined by Eq. (5),

VðrÞ ¼

Z X ZA qðr0 Þ 0  dr r0  r RA  r A

ð5Þ

in which ZA is the charge of nucleus A, located at RA, qðr0 Þ is the electronic density function of the molecule, and r 0 is the dummy

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M.H. Yıldırım et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 50–60

0.9

C7

0.7 0.5

H1A H1B

0.3

C2

X1

X2

H2 H4

H6

0.1 -0.1 -0.3

C1

C3

C4

C6 C5

2A35Br

-0.5

2A35I O1

-0.7 N1

-0.9

O2

Fig. 5. Plots of NPA charges on molecules. (X = Br or I).

integration variable [56,57]. MEP is related to the electronic density and is a very useful descriptor in determining sites for electrophilic and nucleophilic reactions as well as hydrogen bonding interactions [58]. As a real physical property, V(r) can be determined experimentally by diffraction or by computational methods [59]. MEP maps of 2A35Br and 2A35I at the B3LYP/6-311G++(d,p) optimized geometry were calculated and they are shown in Fig. 4. The negative (red) and the positive (blue) regions in the MEP are related to electrophilic reactivity and nucleophilic reactivity, respectively. As can be seen in Fig. 4, the negative region of the compounds is observed around the carboxyl O1 atom. The most negative V(r) value is 0.030 a.u. around the O1 in 2A35Br molecule while this value 0.032 a.u. for 2A35Br molecule, indicating a possible site for nucleophilic attack. These sites give the information about the region from where the compound can have intermolecular interactions. The frontier-electron theory of chemical reactivity by Fukui recognizes the key role of the valence electrons in forming molecules and considers therefore the distribution of the highest energy orbital electron density as being most important for electrophilic attack and the lowest energy vacant orbitals in nucleophilic substitution reactions. In reactions with radicals both orbitals become important. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are in this way considered as the principal factors governing the easiness of chemical reactions and the stereo selective path. Parr and Yang [60] have demonstrated that most of the frontier-electron density theory of chemical reactivity can be rationalized from the DFT. Parr and Yang defined a Fukui function (fk) to describe electrophilic attack (fk), nucleophilic attack (fk+) and neutral (radical) attack (fk0). Yang and Mortier proposed a finite difference approach to calculate Fukui function indices [61]. In a finite difference approximation, the condensed Fukui function values are given Yang et al. as þ

f k ¼ qk ðN þ 1Þ  qk ðNÞ for nucleophilic attack 

f k ¼ qk ðNÞ  qk ðN  1Þ 0

for electrophilic attack

f k ¼ ð1=2Þ½qk ðN þ 1Þ  qk ðN  1Þ

for neutralðradicalÞattack

where qk is the gross charge of the kth atom in the neutral (N), anionic (N + 1) and cationic (N  1) molecule, respectively, all with the ground state geometry of the N electron molecule. Gross charges may be determined by Mulliken, Hirshfeld and Natural charge

analysis. In a molecular system, the atomic site, which possesses the highest condensed Fukui function, favors the higher reactivity. Lee et al. [62] have calculated the condensed Fukui function of CO, SCN and H2CO molecules and reported that the most reactive site during the chemical reaction has the higher fk value. In this study, gross charges were calculated by natural population analysis (NPA) in order to calculate the condensed Fukui function. The condensed Fukui functions (fk) for the atoms of 2A35Br and 2A35I compounds are given in Table 9. This table shows that the C4, O1 and C6 atoms most reactive site for the nucleophilic attack and the X2, N1 and X1 (X = Br or I) atoms most reactive site for both electrophilic and radical attack. Atomic charges Atomic charges have an important role in the application of quantum chemical calculation to molecular system because they are effect dipole moment, molecular polarizability, electronic structure and other electronic properties of molecules. Natural atomic charges of 2A35Br and 2A35I, in terms of Natural Population Analysis [52], were obtained at B3LYP/6-311G++(d,p)/ level of theory. The plots of NPA charges on atoms for the molecules are shown in Fig. 5. Among all carbon atoms, the C7 atom has more positive charge in both molecules. These may be arising from attached electronwithdrawing nature of the O atoms. The most negative charges in both molecules are found on N1 atoms due to their electron withdrawing nature. In addition, it’s found the most positive charges are localized on H2 and H1A because they are involved in hydrogen bonding. Conclusion In this study, 2A35Br and 2A35I have been synthesized and characterized by IR, X-ray single-crystal diffraction and computational methods. The X-ray studies show that very broad band in IR spectrum at 2500–3000 cm1 of both compound arise from dimeric structure. The comparisons between the experimental and corresponding calculated geometric parameters (from GTOs and STOs) together with scaled vibrational frequencies show a good agreement between them. Isomer calculations show us that 2A35Br and 2A35I have minimum energy and highest electrophilicity index as compared with the other isomers. According to results of the MEP map, the negative potential site is on oxygen

M.H. Yıldırım et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 50–60

atom as well as the positive potential sites are around the hydrogen atoms. These sites may provide information about the possible reaction regions for the title structure. This study also demonstrates that the title compounds can be used as good nonlinear optical materials.

Acknowledgements Authors thank to Professor Orhan Büyükgüngör for his guidance in thus study. This study was founded by Ondokuz Mayıs University (PYO.FEN.1901.10) and Giresun University (FEN-BAPA-250414-75).

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