Conformational analysis, spectroscopic study (FT-IR, FT-Raman, UV, 1H and 13C NMR), molecular orbital energy and NLO properties of 5-iodosalicylic acid

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 295–305

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

Conformational analysis, spectroscopic study (FT-IR, FT-Raman, UV, H and 13C NMR), molecular orbital energy and NLO properties of 5-iodosalicylic acid 1

Caglar Karaca a, Ahmet Atac a, Mehmet Karabacak b,⇑ a b

Department of Physics, Celal Bayar University, Manisa, Turkey Department of Mechatronics Engineering, H.F.T. Technology Faculty, Celal Bayar University, Turgutlu, Manisa, Turkey

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

 Monomeric conformations of 5-iodo-

salicylic acid were investigated.  The compound was characterized by

FT-IR, FT-Raman, NMR and UV spectroscopy.  The vibrational frequencies, chemical shifts and electronic absorption wavelengths were calculated by DFT.  Density of state diagrams for 5-iodosalicylic acid were analyzed.

a r t i c l e

i n f o

Article history: Received 28 April 2014 Received in revised form 24 July 2014 Accepted 31 August 2014 Available online 29 October 2014 Keywords: 5-iodosalicylic acid DFT Infrared and Raman spectra UV and NMR spectra HOMO–LUMO and MEP Density of state

a b s t r a c t In this study, 5-iodosalicylic acid (5-ISA, C7H5IO3) is structurally characterized by FT-IR, FT-Raman, NMR and UV spectroscopies. There are eight conformers, Cn, n = 1–8 for this molecule therefore the molecular geometry for these eight conformers in the ground state are calculated by using the ab-initio density functional theory (DFT) B3LYP method approach with the aug-cc-pVDZ-PP basis set for iodine and the aug-cc-pVDZ basis set for the other elements. The computational results identified that the most stable conformer of 5-ISA is the C1 form. The vibrational spectra are calculated DFT method invoking the same basis sets and fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method with PQS program. Total density of state (TDOS) and partial density of state (PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis for C1 conformer were calculated using the same method. The energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT) results complement with the experimental findings. Besides, charge transfer occurring in the molecule between HOMO and LUMO energies, frontier energy gap, molecular electrostatic potential (MEP) are calculated and presented. The NMR chemical shifts (1H and 13C) spectra are recorded and calculated using the gauge independent atomic orbital (GIAO) method. Mulliken atomic charges of the title molecule are also calculated, interpreted and compared with salicylic acid. The optimized bond lengths, bond angles and calculated NMR and UV, vibrational wavenumbers showed the best agreement with the experimental results. Ó 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +90 236 314 10 10; fax: +90 236 314 20 20. E-mail address: [email protected] (M. Karabacak). http://dx.doi.org/10.1016/j.saa.2014.08.137 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

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Introduction

Experimental details

Salicylic acid (SA) is also known 2-hydroxybenzoic acid, is widely used as a preservative in food products, as plant growth regulators, antiseptic and in organic synthesis, as an ingredient in antimicrobial washes to inhibit the spoilage of fresh vegetable and anti-fungal agents. SA has shown to regulate a large variety of physiological processes in plants [1–4]. SA has recently become attractive to experimentalists so as to biological significance, especially in medical and enzyme chemistry [5–8]. Iodine is applied in the treatment of thyrotoxic crisis to produce a thyroid gland of firm texture suitable for operation; it avoids the increased vascularity and friability of the gland with increased risk of haemorrhage. Iodine has powerful bactericidal activity. It is used for disinfecting skin and for the treatment of minor wounds and abrasions. Iodine has been used in the purification of drinking water in case of as catalysts in amoebicidal and bactericidal emergencies. Iodo-benzene and its derivatives have many biologically active such as pesticides, pigment, and fluorescent brighteners and also useful in dye industry for the high bright colors as well as pharmaceutical industry. It is also used as analytical reagents and in the manufacture of disinfectants, antiseptics, deodorants, medicines and other iodine compounds and also they are of great importance in organic synthesis and used esterification [9]. Iodobenzoates are used as antiinfective, contraceptive agent and X-ray contrast medium for diagnostic radiology. SA and its derivatives have recently become attractive to spectroscopic researchers due to their dimeric nature. Experimentally, Raman spectra of salicylic acid and its derivatives are reported [10,11]. Boczar et al. [12] reported the optimized dimer geometry and vibrational assignments of salicylic acid. The salicylic acid NMR spectrum is obtained and its substituent effect on the spectral properties of salicylic acid derivatives was investigated [13,14]. Chen and Shyu [15] investigated conformers and intramolecular hydrogen bonding of SA monomer and its anions. Experimental FT-Raman, FT-IR and theoretical dimer conformer of 5-bromosalicylic acid [16] and 5-fluro, 5-chlorosalicylic acid [17] have been studied in our previous works. Spectroscopic studies of monomeric and dimeric structures of 5-nitrosalicylic acid and its theoretical calculation were carried out by Karthick et al. [18]. Amino-substituted salicylic acid was reported by experimental and theoretical study [7]. Nogueira [19] investigated of frequencies of 3-aminosalicylic acid and 2-mercaptonicotinic acid by the infrared and Raman spectra. Infrared and Raman spectra, ab initio calculations and vibrational assignment of 4-amino-salicylic acid are studied by Akkaya and Akyuz [20]. The molecular structures and intra-molecular hydrogen bonding affect for salicylic acid, 2-hydroxythiobenzoic acid, 2-hydroxythiono benzoic acid and 2-hydroxydithiobenzoic acid have been precisely investigated by using an ab-initio and DFT methods [21]. The crystal structure of SA were studied by X-ray [22,23] but no experimental geometric structure study on free 5-ISA. And literature survey reveals that to the best of our knowledge, no experimental and computational vibrational, NMR and UV spectroscopic study on free 5-ISA have been published in the literature, yet. This inadequacy observed in the literature encouraged us to make this theoretical and experimental vibrational, UV and NMR spectroscopic research based on the conformers of the molecule to give a correct assignments of the fundamental bands in experimental FT-IR, FT-Raman, UV and NMR spectra. Besides these, the dipole moment, nonlinear optical (NLO) properties (linear polarizability and first hyperpolarizability), chemical hardness, electronegativity, chemical potential, electrophilicity index and Mulliken atomic charge have also been studied by using the same method and basis set.

The compound 5-ISA in solid state was purchased from Sigma Aldrich Company with a stated purity of 98%. FT-IR spectrum of 5-ISA was recorded between 4000 and 400 cm1 on a Perkin– Elmer FT-IR System Spectrum BX spectrometer, which was calibrated using KBr disc technique. The spectrum was recorded at room temperature, with a scanning speed of 10 cm1 min1 and the spectral resolution of 4.0 cm1. FT-Raman spectrum of the studied sample was recorded at 3500–50 cm1 on a Bruker RFS 100/S FT-Raman instrument using 1064 nm excitation from an Nd: YAG laser. The detector is a liquid nitrogen cooled Ge detector. Five hundred scans were accumulated at 4 cm1 resolution using a laser power of 100 mW. 1H and 13C NMR spectra were performed in Varian Infinity Plus spectrometer at 300 K. The compound was dissolved in dimethyl sulfoxide (DMSO). Chemical shifts were reported in ppm relative to tetramethylsilane (TMS) for 1H and 13 C NMR spectra. 1H and 13C NMR spectra were obtained at a base frequency of 75 MHz for 13C and 400 MHz for 1H nuclei. The ultraviolet absorption spectrum of 5-ISA is examined in the range of 200–400 nm using Shimadzu UV2101PC, UV–VIS recording spectrometer. The UV pattern is solved in water and ethanol. Data are analyzed by UV PC personal spectroscopy software, version 3.91.

Computational details The molecular geometry, optimization energies, NMR chemical shifts, UV and vibrational frequencies calculations were carried out for 5-ISA with the GAUSSIAN09 software package [24] by using the B3LYP [25,26]. The geometrical parameters for eight conformers/ isomers of the title molecule in the ground state were optimized at DFT/B3LYP level of theory using the aug-cc-pVDZ-PP basis set [27,28] for iodine atom and the aug-cc-pVDZ basis set [29,30] for the other elements. The most stable conformation is C1 form, therefore we used this form for all calculations and compared with experimental results. After geometric optimization, the electronic properties were calculated using B3LYP method of the time-dependent DFT (TDDFT) [31–33]. TD-DFT is proved to be a powerful and effective computational tool for study of ground and excited state properties by comparison to the available experimental data. Hence, we used TD-DFT to obtain wavelengths kmax and compared with the experimental UV absorption of 5-ISA. The contribution of a group to a molecular orbital was calculated by using Mulliken population analysis. GAUSSSUM 2.2 [34] was used to calculate group contributions to the molecular orbitals and to prepare the PDOS and OPDOS spectra. The DOS and OPDOS spectra are created by convoluting the molecular orbital information with GAUSSIAN curves of unit height and FWHM (Full Width at Half Maximum) of 0.3 eV. Mayer bond orders and electron density map were calculated with use of QMFORGE and Multiwfn programs [35,36]. 1 H and 13C chemical shifts are calculated at the same level of theory in addition to pseudo potential for the iodine atom, basing on the optimized structure. This effective core potential basis set was mentioned by name as the aug-cc-pVDZ-PP [37]. The calculated 1H and 13C chemical shifts are referenced to tetramethylsilane (TMS). The vibrational frequencies, infrared and Raman intensities for the planar (Cs symmetry point group) structure of the molecule were calculated using DFT the same basis sets with pseudo potential for iodine atom. Computed harmonic frequencies were scaled in order to improve the agreement with the experimental results. The wavenumbers in the range from 4000 to 1700 cm1 and lower than 1700 cm1 are scaled with 0.954 and 0.960, respectively [38].

C. Karaca et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 295–305 Table 1 Calculated energies and energies differences for eight conformers of 5-ISA. Conformers

C1 C2 C3 C4 C5 C6 C7 C8

Energy

Energy differencesa

(Hartree)

(kcal/mol)

(Hartree)

(kcal/ mol)

7415.39507405 7415.38842782 7415.38559545 7415.37866378 7415.37795714 7415.37733487 7415.37140541 7415.36801230

4653230.85521958 4653226.68464711 4653224.90730803 4653220.55761926 4653220.11419594 4653219.72371561 4653216.00292313 4653213.87371437

0.000 0.007 0.009 0.016 0.017 0.018 0.024 0.027

0.000 4.171 5.948 10.298 10.741 11.132 14.852 16.982

a Energies of the other seven conformers relative to the most stable C1 conformer.

The TED was calculated by using the SQM method and PQS program [39,40] in order to characterize of fundamental vibrational modes. Result and discussion The title molecule 5-ISA (also known as 5-iodo-2-hydroxybenzoic acid) is of extreme importance in terms of three substituents such as iodine atom, hydroxyl group (OH) and carboxyl group (COOH) which are attached to a planar benzene ring. Calculated energies and energy differences [the relative energy of the other conformers was as: DE = E(Cn)  E(C1), the conformer C1 is the lowest energy as reference point] for all conformers of 5-ISA was determined and presented in Table 1 and their optimized geometries are shown in Fig. 1. Intra-hydrogen bonds can be responsible for the geometry and the stability of a predominant conformation; the formation hydrogen bonding between a hydroxyl group and O@COH cause the structure of the conformer C1 to be the most stable conformer of 5-ISA. Furthermore, our previous works [16,17] we have obtained the same geometry in terms of atom positions for all conformers of 5-fluorosalicylic acid (5-FSA), 5-chlorosalicylic acid (5-ClSA) and 5-bromosalicylic acid (5-BrSA). The calculations

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showed that the conformer C8 to be the least stable conformers while these is not enumerated according to the 5-FSA, 5-ClSA and 5-BrSA. From DFT calculations of conformers, the conformer C1 is predicted more stable from 4.171 to 16.982 kcal mol1 than the other conformers of the 5-ISA.

Geometrical structures The first task for the computational work was to determine the optimized geometry for eight positions of 5-ISA. The atomic numbering scheme of the most stable conformer and other conformers were shown with the front and lateral view of 5-ISA in Fig. 1. The calculated bond lengths and bond angles of the C1 conformer is given in Table 2. The molecular structure of 5-ISA has not been studied and no experimental data have been published yet. Therefore, we compared all results with the similar structures [16,41]. Several authors [42,43] have explained the changes in frequency or bond length of the CAH bond on substitution due to a change in the charge distribution on the carbon atom of the benzene ring. The substituents may be either of the electron withdrawing type (F, Cl, Br, I). The carbon atoms are bonded to the hydrogen atoms with a r bond in benzene and the substitution of a halogen for hydrogen reduces the electron density at the ring carbon atom. The ring carbon atoms in substituted benzenes exert a larger attraction on the valance electron cloud of the hydrogen atom resulting in an increase in the CAH force constant and a decrease in the corresponding bond length. The reverse holds well on substitution with electron donating groups. The actual change in the CAH bond length would be influenced by the combined effects of the inductive–mesomeric interaction and the electric dipole field of the polar substituent [16]. Since the large deviation from experimental CAH bond lengths may arise from the low scattering of hydrogen atoms in the X-ray diffraction experiment. The perceivable ones are for the bond distances of CAH among which the biggest difference is 0.123 Å. The CAX (X; F, Cl, Br, I) bond length indicates a considerable increase when substituted in place of CAH. This has been observed even in benzene derivatives [44]. The iodine atom is in the plane of the salicylic acid. The bond distance CAI is approximately 0.016 Å

Fig. 1. The optimized geometric structures (a) front and (b) lateral view of 5-ISA.

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Table 2 Comparison of geometric parameters, bond lengths (Å), and bond angles (0) for the C1 conformer of 5-iodo-salicylic acid. Bond lengths (Å) C1AC2 C1AC6 C1AC10 C2AC3 C2AO14 C3AC4 C3AH7 C4AC5 C4AH8 C5AC6 C5AI16 C6AH9 C10AO11 C10AO12 O11AH13 O12AH15 O14AH15

Calculated 1.419 1.411 1.468 1.406 1.343 1.388 1.089 1.407 1.089 1.387 2.116 1.087 1.350 1.231 0.971 1.736 0.986

p-IBAa

5-BrSAb

1.37 1.42 1.50 1.39 – 1.36 – 1.38 – 1.39 2.10 – 1.28 1.23 – – –

1.404 1.403 1.476 1.386 1.350 1.366 – 1.387 – 1.353 – – 1.309 1.227 0.850 – 0.850

Mayer bond order 1.229 1.332 0.993 1.292 0.967 1.455 0.829 1.315 0.839 1.388 0.982 0.840 1.000 1.419 0.701 0.144 0.633

0

Bond angles ( ) C2AC1AC6 C2AC1AC10 C6AC1AC10 C1AC2AC3 C1AC2AO14 C3AC2AO14 C2AC3AC4 C2AC3AH7 C4AC3AH7 C3AC4AC5 C3AC4AH8 C5AC4AH8 C4AC5AC6 C4AC5AI16 C6AC5AI16 C1AC6AC5 C1AC6AH9 C5AC6AH9 C1AC10AO11 C1AC10AO12 O11AC10AO12 C10AO11AH13 C2AO14AH15 a b

119.8 118.7 121.5 119.1 122.9 118.0 120.5 118.5 121.0 120.4 119.5 120.1 120.0 119.8 120.2 120.2 118.9 120.9 114.9 124.1 121.0 106.8 107.5

119 119 121 119 – – 120 – – 121 – – 120 119 120 120 – – 116 125 120 – –

118.7 120.5 120.9 119.5 122.5 118.0 121.0 – 119.8 119.2 – – 121.4 118.4 120.2 120.1 – – 115.3 122.0 122.6 108.8 109.7

Ref. [41]. Ref. [46].

greater than experimental value [41] which is in good agreement with calculated value. In international tables for crystallography [45] the CO bond lengths in the carboxylic acid group conform to the average values are tabulated for an aromatic carboxylic acid in which C@O is 1.226(20) Å and CAO is 1.305(20) Å. The corresponding bond lengths in the 5-BrSA are 1.227(6) and 1.309(6) Å [46] which are calculated at 1.225 and 1.347 Å [16]. In this study, the CAO bond value of the molecule which compared with all conformers, is good agreement with the experimental data for the C1 conformer. The C1 conformer of 5-ISA has the C10@O12 bond distance is 1.231 Å, this band is obtained at 1.230 Å with X-ray [41]. The other C10AO11 bond value is observed at 1.28 Å [41] which is calculated at 1.350 Å. The bond distance CACOOH is found to be 1.467 Å for 5-FSA crystal [47], 1.474 Å for 5-ClSA crystal [48] and 1.50 Å for p-iodobenzoic acid (p-IBA) crystal [41]. This bond length C1AC10 is calculated at 1.468 Å for 5-ISA. In the ring part the optimized geometry of the molecule shows very good agreement with experiment. The CC bond lengths of the benzene ring are observed in the range of 1.353–1.404 Å [46] which are calculated in the region 1.387–1.419 Å in the benzene ring. For salicylic acid these bond lengths are observed in the range of 1.383–1.416 Å in the benzene ring [49].

Substitution with hydroxyl group and carboxyl group leads to some changes of the bond angles in the benzene ring. The C2AC1AC6 and C1AC2AC3 angles at the position of the OH and COOH groups substituent is smaller (1190) and the others are equal typical hexagonal angle of 1200. This clearly shows that the substitution of the OH and COOH groups in place of hydrogen appreciably affects the CACAC bond angles. The torsional angles C2AC1AC10AO11 and C6AC1AC10AO12 are 179.30 and 178.80, respectively. The tilt angles are calculated at ca. 1800. The dihedral angles are nearly the same among the all conformers. Bond order is a useful tool for characterizing bond type and measuring bond strength. Mayer bond order (MBO) [50] is a natural extension of Wiberg bond order [51] for non-orthogonal basis. The MBO between atom A and B is defined as:

i XXh a BAB ¼ BaAB þ BbAB ¼ 2 ðP SÞab ðPa SÞba þ ðPb SÞab ðPb SÞba a2A b2B

For restricted close-shell circumstance, namely Pa = Pb = 1/2 P the formula can be simplified to

BAB ¼

XX ðPSÞab ðPSÞba a2A b2B

where P, Pa and Pb are total, alpha and beta density matrix respectively, S is overlap matrix. Total valence measures atomic bonding capacity, and the expression given by Mayer is as follows:

X XX V A ¼ 2 ðPSÞaa  ðPSÞab ðPSÞba a2A

a2A b2B

Free valence is defined as follows:

FA ¼ V A 

X XX s BAB ¼ ðP SÞab ðPs SÞba B–A

a2A b2B

s

where P is spin density matrix. This quantity displays remaining capacity of forming new bonds by sharing electron pairs. We used Multiwfn program to calculate MBO [36]. The calculated MBO is 0.633 for OH (O14AH15) while for OH (O11AH13) is 0.701, indicating that the bond OH is slightly stronger than the bond in carboxylic group. The other bond orders are presented in Table 2. Electronic structure and UV spectrum The most important application of the DOS plots is to demonstrate molecule orbital (MO) compositions and their contributions to chemical bonding through the OPDOS plots which are also referred in the literature as Crystal Orbital Overlap Population

Fig. 2. Calculated partial electronic density of states.

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Fig. 3. Density of states diagrams for 5-ISA molecule.

(COOP) diagrams. The COOP (or OPDOS) is similar to DOS because it results from multiplying DOS by the overlap population. DOS plot shows population analysis per orbital and shows a modest view of the character of the molecular orbitals in a prescribed energy range while OPDOS plot shows percentage contribution of a group to each molecular orbital. The OPDOS shows the bonding, anti-bonding and nonbonding interaction of the two orbital’s, atoms or groups. The interaction between the two groups can be visualized using a COOP or OPDOS diagram. A positive value of the COOP indicates a bonding interaction, whereas negative value means an anti-bonding interaction and zero value indicates nonbonding interactions [52]. The DOS and TDOS plots are shown in Figs. 2 and 3. Both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are the main orbital taking part in chemical reaction. The HOMO energy characterizes the ability of electron giving whereas LUMO energy characterizes the ability of electron accepting, and the gap between HOMO and LUMO characterizes the molecular chemical stability in Fig. S1. The energy gap between the HOMO and the LUMO is a critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity [53]. The result provides a pictorial representation of MOs compositions and their contributions to chemical bonding. The OPDOS diagram is shown in Fig. S2 and in the frontier occupied and virtual molecular orbitals, values of the interaction between iodine atom and benzene, COOH, and OH groups are selected. The benzene ring shows weakest bonding properties iodine atom in 5-ISA. As can be seen from OPDOS plot in the HOMO and LUMO molecular orbitals iodine atom and benzene have significant anti-bonding character while HOMO1 and LUMO+1 have bonding character. The interaction of the iodine atom with hydroxyl orbitals has almost all a nonbonding character according to the given energy regions. In the

LUMO+1 the bonding interaction (red line) of the iodine atomic orbital with the COOH is seen clearly in OPDOS diagram. The overlap population value of the HOMO for iodine atom with benzene are 0.07124 and for iodine and COOH + 0.00853 according to this diagram. As can be seen from OPDOS, LUMO overlap population value are 0.03240 for iodine atom with benzene, 0.07124 for iodine atom with COOH and 0.00024 for iodine atom and OH. Not only the energy levels of the five highest, the five lowest molecular orbitals and full energy levels of 5-ISA but also energy gaps of three possible transitions for the title molecule are shown in Fig. S3. The experimental absorption wavelengths (energies) and computed electronic values, such as absorption wavelengths (k), excitation energies (E), oscillator strengths (f), and major contributions of the transitions and assignments of electronic transitions are tabulated in Table 3 for ethanol and water solvents. The UV– Vis electronic absorption spectrum of 5-ISA were measured and calculated in water and ethanol solutions and both of them almost similar spectra as seen from Fig. 4 and Fig. S4. It is observed that the recorded absorption bands centered at 319, 236 and 213 nm in ethanol solution. The regarding transitions are recorded at 312, 236 and 213 nm in water solution. The full theoretical absorption spectrum was obtained from the calculation of the singlet excited states with TD-DFT at the B3LYP using afore-mentioned basis sets and solutions. The TD-DFT method predicted the maximum absorption peak at 326.83 and 326.41 nm with strong oscillator strength, while this peak was recorded at 319 and 312 nm experimentally in ethanol and water solutions, respectively. The other strong excitations were calculated at ca. 291 and 264 nm, were observed at 236 and 213 nm for water and ethanol and is also assigned from p to p* transition. The deviation between experiment and theory may be resulted from solvent effects. In view of the calculated absorption spectra, the maximum absorption wavelength corresponds to the electronic transition from the HOMO to LUMO with 97% contribution. The other electronic transition and their energy gaps were shown in Fig. S3. The value of chemical hardness is 2.19162 eV and 2.18972 eV in water and ethanol solvents. The values of electronegativity, chemical potential and electrophilicity index are given in Table 4. The DOS and PDOS in terms of Mulliken population analysis was calculated using Gausssum 2.2 program. The results provide a pictorial representation of MOs. The PDOS diagram may enable us to ascertain the orbital composition characteristics with respect to the particular fragments. The iodine atom plays significant role in the HOMOs. For instance, the orbitals of the iodine atom contribute at 40% [4pz ? 27% and 5pz ? 13%] in the HOMO, at 91% [4py ? 41%, 4px ? 23%, 5py ? 16% and 5px ? 11%] in the HOMO1, at 30% [4pz ? 22% and 5pz ? 8%] in the HOMO2 and at 23% [4pz ? 16% and 5pz ? 7%] in the HOMO3 molecular orbitals of 5-ISA. According to the Mulliken population analysis in the benzene ring play dominant role (50%), if it is compared with the other groups in the HOMO. The iodine atom orbital is contribute 61% [5px ? 19%, 5py ? 11%, 4px ? 11%, 3dxy ? 7%, 4py ? 6% and the others ? 7%] in the LUMO+1. In the present study, 3D plots of MEP of 5-ISA is illustrated in Fig. S5. The MEP is a useful property to study reactivity that an

Table 3 Experimental and calculated absorption wavelengths k (nm), excitation energies E (eV), absorbance values and oscillator strengths (f) of 5-ISA. Experimental

TD-DFT

Ethanol

Water

Ethanol

Water

(Water and ethanol)

k (nm)

E (eV)

Abs.

k (nm)

E (eV)

Abs.

k (nm)

E (eV)

f

k (nm)

E (eV)

f

Major contribution

Assignment

319 236 213

3.8890 5.2567 5.8243

0.071 0.255 0.750

312 236 213

3.9762 5.2567 5.8243

0.075 0.299 0.816

326.83 291.00 263.68

3.7935 4.2607 4.7021

0.0063 0.0002 0.0006

326.41 290.78 263.44

3.7984 4.2639 4.7064

0.0622 0.0002 0.0006

H ? L (97%) H ? L + 1 (99%) H–1 ? L (99%)

p–p* p–p* p–p*

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NMR details

Fig. 4. The experimental UV spectrum of the studied compound.

Table 4 Calculated energy values of 5-ISA in water and ethanol. TD-DFT/B3LYP/6-311++G(d,p)

Water

Ethanol

EHOMO (eV) ELUMO (eV) EHOMO1 (eV) ELUMO+1 (eV) DEHOMO–LUMO gap (eV) DEHOMO–LUMO+1 gap (eV) DEHOMO1–LUMO gap (eV) Chemical hardness (g) Electronegativity (v) Chemical potential (l) Electrophilicity index (x)

6.52425 2.14101 7.55258 1.24248 4.38324 5.28177 5.41157 2.19162 4.33263 4.33263 4.28260

6.52262 2.14319 7.55040 1.24357 4.37943 5.27905 5.40722 2.18972 4.33290 4.33290 4.28687

approaching electrophile will be attracted to negative regions (where the electron distribution effect is dominant). The importance of MEP lies in the fact that it simultaneously displays molecular size, shape as well as positive, negative and neutral electrostatic potential regions in terms of color grading and is very useful in research of molecular structure with its physiochemical property relationship. Some critical points (red and blue spheres correspond to maxima and minima respectively) within this surface are shown in Fig. S5 and the values of these points are presented in Table 5 by computing Monte Carlo method. The red point 6 which is global minimum on the surface is value 42.9170 kcal/mol whereas the blue point 3 is (+92.66594 kcal/ mol) global maximum arise from the abundant p electrons around the ring.

The theoretical and experimental 13C and 1H chemical shifts of 5-ISA are presented in Table 6, according to Fig. 1 atom positions were numbered. The first, full geometry optimization of 5-ISA is performed at the gradient corrected DFT using the hybrid B3LYP method based on Becke’s three parameters. Then, GIAO method [54] 1H and 13C chemical shift calculations of the compound were made by using the aug-cc-pVDZ-PP basis set and effective core potential for iodine atom and the aug-cc-pVDZ basis set for the other elements IEFPCM/DMSO solution [55]. Application of the GIAO approach to molecular systems was significantly improved by an efficient application of the method to the ab-initio SCF calculation, using techniques borrowed from analytic derivative methodologies. Relative chemical shifts were estimated by using the corresponding TMS shielding calculated in advance at the same theoretical level as the reference. The 1H and 13C chemical shifts are shown in Fig. 5(a) and their data collected in Table 6. One can deduce that the 13C and 1H NMR chemical shifts of 5-ISA are described fairly well by the selected DFT method combined with the basis set. There are seven carbon signals calculated theoretically while those signals are observed experimentally in 13C spectrum of the molecule. Aromatic carbons give signals in overlapped areas of the spectrum with chemical shift values ranging from 100 to 150 ppm [56,57]. The aromatic carbons were calculated at 109.61166.06 ppm, observed signals are in the range of 81.22161.30 ppm. All computations are in good agreement with experimental data. The carboxyl and hydroxyl groups which are an electronegative functional groups polarize the electron distribution, therefore the calculated 13C NMR chemical shift values of C10 bonded to carboxyl group and C2 bonded to hydroxyl group are too high, were observed at 171.11 and 161.30 ppm while which were calculated at 172.72 and 166.06 ppm, respectively. The carbon atom C5 is significantly observed in the up field with chemical shift value 81.22 ppm due to the influence of the electron density of iodine atom as can be seen from Fig. 5(b). The DFT calculations for the 13C nuclei calculate the orderings of the shifts at the C1, C2, C3, C4, C6 and C10 correctly, but fail to calculate the order for the C5, which is directly bonded to the halogen atom (iodine), regardless of the basis set. The aromatic protons were calculated in the region of 7.508.70 ppm, observed in 6.757.99 ppm. The carboxyl and hydroxyl proton chemical shifts would be more susceptible to intermolecular interactions as compared other heavier atoms. Therefore the OAH proton signal varies greatly with concentration and solvent effects and occasionally cannot be seen in the spectra. The correlation graphics between the experimental and calculated 13C NMR and 1H NMR chemical shifts of the title molecule are represented in Supplementary Fig. S6. The relations between the calculated and experimental chemical shifts (dexp) are usually linear and described by the following equation:

Table 5 Analysis of the molecular surface according to the Fig. S5. Point no

1 2 3 4 5 6

Minima

Point no

a.u.

eV

kcal/mol

0.02114 0.02114 0.05299 0.05301 0.05817 0.06840

0.57512 0.57519 1.44205 1.44256 1.58283 1.86120

13.2615 13.2632 33.2518 33.2636 36.4979 42.9170

1 2 3 4 5 6 7 8

Maximum a.u.

eV

kcal/mol

0.067196 0.039113 0.147684 0.043509 0.034854 0.034741 0.036048 0.036946

1.828509 1.064324 4.018692 1.183948 0.948421 0.945341 0.980906 1.00536

42.16309 24.54195 92.66594 27.30035 21.86938 21.79836 22.61844 23.18232

C. Karaca et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 295–305 Table 6 The experimental and calculated 13C and 1H isotropic chemical shifts (with respect to TMS, all values in ppm) for 5-ISA. Atom

Exp.

B3LYP

Atom

Exp.

B3LYP

C1 C2 C3 C4 C5 C6 C10

120.52 161.30 116.30 144.15 81.22 138.78 171.11

113.23 166.06 119.07 144.62 109.61 138.98 172.72

H7 H8 H9 H13 H15

6.75 7.72 7.99 – –

7.50 8.06 8.70 7.97 11.56

dcal: ðppmÞ ¼ 0:9942dexp: þ 3:8255 ðR2 ¼ 0:9799Þ

301

sign (k2)q peaks itself provides the information about the strength of interaction. Large, negative values of sign (k2)q are indicative of stronger attractive interactions and also we can identify different type regions by color as can be seen from Fig. 6(b). The bluer means the stronger interactive interaction, the partial half elliptical slab between oxygen and hydrogen shows blue color, therefore there was strong hydrogen bond between O12  H15. The interaction region marked by green can be identified as Van der Waals (VDW) interaction region and the regions in the center of ring and the others show strong steric effect. The RDG > 0.5 lines cross not only the attractive but also the repulsion spikes while the RDG = 0.2 line crosses the attractive interaction spikes. The low density, low-gradient spike for the sterically crowded remains at positive values of sign (k2)q.

Reduced density gradient (RDG)

Vibrational analysis

Johnson and co-workers [58] developed an approach to investigate the weak interactions in real space based on the electron density and its derivatives. The RDG is a fundamental dimensionless quantity coming from the density and its first derivative:

5-ISA molecule consists of 16 atoms, and therefore it has 42 normal vibrational modes. On the basis of Cs symmetry the 42 fundamental vibrations of the title molecule can be distributed as 29A0 + 13A00 . The vibrations of the A0 species are in plane and the A00 species vibrations are out-of-plane. All vibrations are active in both IR and Raman. But if the molecule has C1 symmetry point group, there would not be any relevant distribution. The correlation graphic describes harmony between the calculated and experimental wavenumbers (Fig. S7). The relations between the calculated and experimental wavenumbers are linear and described by the following equation:

RDGðrÞ ¼

jrqðrÞj

1 2ð3p2 Þ

1=3

qðrÞ4=3

The weak interactions can be isolated as regions with low electron density and low RDG value. The density values of the low-gradient spikes (the plot of RDG versus q) appear to be an indicator of the interaction strength. The sign of k2 is utilized to distinguish the bonded (k2 < 0) from non-bonded (k2 > 0) interactions. The plot of the RDG versus the electron density q multiplied by the sign of k2 can allow analysis and visualization of a wide range of interactions types. The results were calculated by Multiwfn and plotted by VMD program [36,59]. One or more spikes are found in the low-density, low gradient region as seen in Fig. 6(a), indicative of weak interactions in the system and the electron density value at the RDG versus

Fig. 5. The experimental (a) 1H and

13

mcal ¼ 0:8996mexp þ 79:694 ðR2 ¼ 0:9922Þ As a result, the performance of the B3LYP method with respect to the prediction of the wavenumbers within the molecule was quite close. The experimental and theoretical infrared and Raman spectra of 5-ISA are shown in Fig. 7, where the calculated intensity is plotted against the wavenumbers. The observed and calculated vibrational

C NMR spectra of 5-ISA in DMSO and (b) its electron density.

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Fig. 6. (a) Plots of the RDG versus the electron density q multiplied by the sign of k2 for 5-ISA. (b) The surfaces are colored on a blue–green–red scale according to values of sign k2. Blue indicates strong attractive interactions and red indicates strong non-bonded overlap. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

wavenumbers, proposed assignments and TED of 5-ISA are presented in Table 7. The last column contains a detailed description of the normal modes based on the TED. It should be noted that the calculations are made for a free molecule in vacuum, while experiments are performed for solid phase. Furthermore the anharmonicity is neglected in real system for calculated vibrations, and because of the low infrared and Raman intensity of some modes, it is difficult to observe them in IR and Raman spectra. Thus, there are disagreements between calculated and observed vibrational wavenumbers. The high frequency region above 3000 cm1 is the characteristic region for the ready identification of CAH and OAH stretching vibrations [60,61]. The OAH stretching is characterized by a very broad band appearing in the range of 3400–3600 cm1. The carboxylic acid OAH stretching bands are weak in Raman spectrum; therefore IR data are generally used. For salicylic acid, the OH vibration is observed at 3238 cm1 in FT-IR spectrum [13]. This band is calculated at 3610 and 3334 cm1 [13]. This frequency is

observed at 3221 cm1 in FT-IR and also calculated at 3687 and 3350 cm1 which modes are (m1, m2) of O11AH13, O14AH15 units, respectively. In the Raman spectrum this absorption is absent. As expected these two modes are pure stretching modes as it is evident from TED column, they are almost contributing 100%. As discussed in our previous papers [16,17] with the halogen (F, Cl, Br, .....etc.) substitution, OH stretching vibrations shifted to higher wavenumbers region [62]. This means that, the OH vibrations are sensitive due to halogen coordination. The OH in plane bending vibration occurs in the general of 1440–1395 cm1 [16,60]. In 5ISA, the OH in plane bending is assigned at 1440 and 1376 cm1 in FT-IR and 1412 cm1 in FT-Raman which are calculated 1418 and 1381 cm1. The OH in plane bending of a motion of a hydroxyl group is calculated at 1172 cm1 which is assigned at 1209 cm1. In this study, the OAH out-of-plane bending (m24, m25 and m31) is observed at 826 and 793 cm1 in FT-IR, at 829 and 794 cm1 in FT-Raman for O14–H15, at 552 cm1 in FT-IR for O11AH13. These bands are calculated at 820, 789 and 584 cm1, respectively. This

C. Karaca et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 295–305

303

Fig. 7. Theoretical and experimental infrared and Raman spectra of 5-ISA molecule.

vibration is observed at 554 cm1 in FT-Raman for 5-BrSA [16]. For 4-amino-salicylic acid, the OH out of bending is assigned to 625 cm1 by Akkaya and Akyüz [20]. The heteroaromatic structure shows the presence of the CH stretching vibrations in the 3000–3100 cm1 range which is the characteristic region for the ready identification of the CH stretching vibrations [60]. Accordingly, in the present study, the three adjacent hydrogen atoms left around the benzene ring, the 5-ISA give rise three CH stretching modes (m3–m5), three CH in plane bending (m13, m16, m18) and three CH out-of-plane bending (m19, m22, m27) vibrations which correspond to stretching modes of C4AH8, C6AH9 and C3AH7 units. The vibrations are assigned in the range of 3066–3144 cm1 for aromatic CH stretching [60] are in agreement with experimental values at 2980 and 2855 cm1 (FT-IR), 3083 cm1 (FT-Raman). These modes are calculated from 3177 to 3143 cm1. They are very pure modes since their TED contribution are 100%. In aromatic compounds, the CH in plane bending frequencies appear in the range of 1000–1300 cm1 and the CH out-of-plane bending vibration in the range of 750–1000 cm1 [63–65]. The CH in plane bending vibrations are assigned at 1236 cm1 in FT-IR and at 1351, 1236 and 1154 cm1 in FT-Raman. The calculated ones are 1335, 1241 and 1161 cm1 which shows well agreement with the experimental values. The CH out of-plane bend is assigned to FT-IR band at the 887 cm1 is observed at 870 in Raman spectrum. This band is calculated at 872 cm1 which are in good agreement with experimental value. The change in the frequencies of these deformations from the values in benzene is almost determined exclusively by the relative position of the

substituents and is almost independent of their nature. Both the in plane and out-of- plane bending vibrations are described as mixed modes. The TED contribution of the in plane and out-ofplane modes indicates that out-of-plane modes are also highly pure modes like the in plane bending fundamentals. The most characteristic feature of carboxylic group is a single band observed usually in the range of 1700–1800 cm1. This band is due to the C@O stretching vibration. In the solid state most of carboxylic acids form a dimeric structure that is due to the result of hydrogen bonding between two neighboring ACOOH groups. In such a case two m(C@O) are expected: one that is Raman active (in phase, symmetric stretching vibration) and the other one, out of phase (antisymmetric stretching vibration), is only IR active. The C@O stretching mode (m6, asymmetric stretching vibration) is observed at 1668 cm1 in FT-IR spectrum and observed at 1635 cm1 (symmetric stretching vibration) in FT-Raman spectrum The theoretical values of the C@O band show very good agreement with experimental results, which are predicted at 1699 and 1635 cm1. The TED values in Table 7 reveal that this antisymmetric stretching vibration is coupled with COH bending vibration. But this can be almost pure mode is evidenced from 72% of TED. The CAO stretching vibration is assigned at 1075 cm1 in FT-Raman and calculated at 1053 cm1 which has the TED value of 44%. The medium band in infrared (685 cm1) and in Raman (678 cm1) spectra is assigned to OACAO bending vibration and the scaled B3LYP predicted value at 664 cm1 shows good agreement with each other.

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Table 7 Comparison of the calculated harmonic frequencies and experimental (FT-IR and FT-Raman) wavenumbers (cm1). No

Experimental FT-IR

v1 v2 v3 v4 v5

v6 v7 v8 v9 v10 v11 v12 v13 v14 v15 v16 v17 v18 v19 v20 v21 v22 v23 v24 v25 v26 v27 v28 v29 v30 v31 v32 v33 v34 v35 v36 v37 v38 v39 v40 v41 v42 a

Theoretical Unscaled

Scaled

TED

3083

3751 3408 3232 3212 3197

3687 3350 3177 3158 3143

mO11AH13(100) mO14AH15(100) mCH(100) mCH(100) mCH(100)

1699 1635 1617 1508 1490 1418 1381 1335 1305 1282 1241 1172 1161 1140 1090 1053 872 826 820 789 764 735 664 625 615 584 542 460 436 370 368 312 230 173 151 142 84

Overtone + combination Overtone + combination mC = O(72) + dCOH(11) mCC(57) + dCCH(16) + mC = O(10) mCC(53) + dCCH(18) + dCOH(13) mCC(35) + dCCH(37) + dCOH(15) mCC(38) + dCCH(26) + dCCC(10) dCOH(45) + dCCH(22) + dOCO(19) mCC(40) + dCOH(32) + mCO(21) mCC(43) + mCO(20) + dCCH(14) sICCH(37) + sCCHH(24) + sCCCC(27) mC2  O(37) + mCC(29) + dCOH(10) dCCH(34) + mCC(27) + dCOH(24) dCOH(47) + mCC(23) + mC10  O(19) dCCH(58) + mCC(29) sCCCH(60) + sICCH(25) mCC(50) + dCCH(29) + mCI(10) mCO(44) + mCC(26) + dCCC(17) cCH(84) dCCC(49) + mCI(16) + dCCH(13) cO14H(57) + sCCCO(35) cO14H(44) + sCCCO(37) mCC(50) + dCCC(22) + mCO(16) sCCCH(47) + sCCCC(40) dOCO(33) + dCCO(31) + mCO(10) sCCOH13(49) + sCCCO(10) + sCCCH(22) dCCC(46) + mCI(28) cO11H(50) + sCCCH(18) dCCO(43) + dOCO(20) + dCCC(17) sCCCC(40) + sCCCH(19) + sCCOH(13) dCCO(48) + dCCC(15) + mCC(12) sCCCO(41) + sICCC(28) + sICCH(14) dCCO(28) + dCCC(27) + mCC(17) + dICC(11) dCCO(34) + dCC–COOH(27) + dICC(28) mCI(62) + dCCC(19) sCCCC(44) + sCCCO(26) + sICCC(14) dCCC(38) + dICC(34) + mCC(15) sCCCC(25) + sCCCO(40) + sICCC(11) sCCO11C10(47) + sCCO12C10(37)

A0 A0 A0 A0 A0 A0 A0 A0 A00 A0 A0 A0 A0 A00 A0 A0 A00 A0 A00 A00 A0 A00 A0 A00 A0 A00 A0 A00 A0 A00 A0 A0 A0 A00 A0 A00 A00

3221 2980 2855 2590 2360 1668 1631 1603 1565 1469 1440 1376 1316 1286 1236 1209 1147 1095 899 887 838 826 793

a

FT-Raman

0

A A0 A0 A0 A0

Assignments

1635 1578 1474 1412 1351 1311 1236 1154 1148 1094 1075 870 829 794 777

685

678

615 552 528 468 423

614 542 460 380 314 235 172 122 70

1729 1664 1645 1535 1515 1443 1405 1358 1328 1304 1263 1192 1181 1160 1109 1071 887 840 834 803 778 748 675 636 625 594 551 468 444 376 375 317 234 176 153 144 85

(P10%)

m; stretching, d; in-plane bending, c; out-of-plane (o.o.p.) bending, s; torsion.

The assignments of C–I (iodine atom) stretching and deformation vibrations have been made on the basis of the calculated TED and compared with similar molecules, tri-iodobenzoic acid [66] and the halogen substituted benzene derivatives [64]. Mathew et al. [67] assigned the C–I stretching vibration for p-iodonitrobenzene at 454 cm1. Mooney [68,69] assigned vibrations of C–X group (X = Cl, Br, I) in the frequency range of 1129–480 cm1. In the FT-IR spectrum of 5-ISA, the strong band at 615 cm1 is assigned to C–I stretching vibration. The low wavenumber prediction for this mode with our theoretical methods appears as a contradiction with the spectral region of 560 ± 100 cm1 reported [70] for other compounds with iodine. By contrast, the Raman band shows an appreciable intensity and it was detected at 235 cm1. As it is evident from TED, this is almost pure stretching vibration and it is almost contributing to 62%.

moment of 5-ISA is calculated at 0.4097 Debye with maximum contribution from lX. Polarizability is the quantity by which the induced dipole moment of a molecule is related to the external electric field that is providing the perturbative knock on the electron density. According to the present calculations, the mean polarizability of 5-ISA (as can be seen in Table S1) is found to 135.3353 a.u. The first static hyperpolarizability b value follows the same trend as mean polarizability and is found to be 231.7415 a.u. The hyperpolarizability is dominated by the longitudinal component bxxx, whereas the medium values of b are noticed for xxy, xyy and yyy directions. Our calculations clearly indicate that the hyperpolarizabilities are increased by the proton transfer.

Nonlinear optical properties

Mulliken atomic charge calculation has a significant role in the application of quantum chemical calculation to molecular system because of atomic charges effect electronic structure, dipole moment, molecular polarizability and other properties of molecular systems. The calculated Mulliken charge values of 5-ISA and salicylic acid are listed in Table S2. We plotted the graph of these values as shown in Fig. S8. The Mulliken atomic charges of salicylic

Dipole moment is one of the important quantities which are of fundamental importance in structural chemistry. It can be used as a descriptor to illustrate the charge movement across the molecule. The direction of the dipole moment vector in a molecule depends on the centers of positive and negative charges. The dipole

Mulliken atomic charges

C. Karaca et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 295–305

acid and 5-ISA are illustrated in Fig. S9. The charge distribution structure of 5-ISA is shown in the results show that substitution of the aromatic ring by iodine atom leads to a redistribution of electron density. The C5 atoms exhibit a negative charge, which are donor atoms, added iodine atom to C5, the values of Mulliken atomic charge atoms are bigger than others. Hydrogen atom which is an acceptor atom exhibits a positive charge.

[15] [16] [17] [18]

Conclusions

[25] [26]

The present study is off to aim the spectroscopic properties of derivative of salicylic acid. The FT-IR, FT-Raman UV–Vis, 1H and 13 C NMR techniques are used both experimentally and theoretically, to identify frequency assignments, magnetic and electronic properties of the 5-ISA molecule. Structure of 5-ISA is investigated using high-level quantum chemistry calculation. Hydrogen bond and Wan der walls force are explored using AIM (RDG) method. Between H15 and O12 have a strong hydrogen bond and between H9 and O11 possess Van der walls force as well. Results from experimental and theoretical study gave us a full description of the molecular geometry, NMR, UV and vibrational properties of this molecule. Based on calculated energy differences, the C1 conformer is found to be the most stable conformer. Molecular orbital coefficient analyses suggest that the electronic spectrum corresponds to the p ? p* electronic transition. The experimental NMR results good agreement with the calculated ones without halogen bonded to carbon atom since regardless of mixed basis set. The vibrational (FT-IR and FT-Raman) spectra of the 5-ISA are recorded with experimental and computed vibrational wavenumbers and TED. The molecular polarizability, anisotropy of polarizability and molecular first hyperpolarizability of 5-ISA molecule are presented. We hope the results of this study will help researchers to analysis and synthesis of new materials.

[27] [28] [29] [30]

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