Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

Contents lists available at ScienceDirect

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

FT-IR and FT-Raman spectra, normal coordinate analysis and ab initio computations of Trimesic acid G. Mahalakshmi a,b, V. Balachandran c,⇑ a

Department of Physics, Karpagam University, Coimbatore 641021, India Department of Physics, Government Arts College (Autonomous), Karur 639005, India c Research Department of Physics, Arignar Anna Government Arts College, Musiri, Tiruchirapalli 621211, India b

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 FT-IR and FT-Raman spectra

Trimesic acid of have been recorded.  The conformational equilibrium of

Trimesic acid was examined.  The complete assignments are

performed on the basis of the total energy distribution (TED).  HOMO–LUMO energy gap, electrostatic potential and thermodynamic parameters were performed.

a r t i c l e

i n f o

Article history: Received 18 November 2013 Received in revised form 14 December 2013 Accepted 10 January 2014 Available online 23 January 2014 Keywords: Vibrational spectra UV spectra NBO analysis Monomer Dimer Thermodynamic functions

a b s t r a c t The FT-IR and FT-Raman spectra have been recorded of Trimesic acid (1,3,5-benzenetricarboxylic acid, H3BTC). The molecular structure, conformational stability, geometry optimization, vibrational frequencies have been investigated. The total energy calculations of H3BTC were tried for various possible conformers. The spectra were interpreted with the aid of normal coordinate analysis based on ab initio Hartree–Fock (HF) and density functional theory (DFT/B3LYP) methods and 6-31+G(d,p) basis set level and was scaled using scale factors yielding good agreement between observed and calculated frequencies. Vibrational assignments and Natural bonding orbital (NBO) calculations are performed on the stable monomer of H3BTC using the same level of theory. Intramolecular hydrogen bond exists via ACOOH group gives the evidence for the formation of dimer entities in the title molecule. UV–VIS spectral analyses of H3BTC have been researched by theoretical calculations. In order to understand electronic transitions of the compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvent (DMSO and Chloroform) were performed. The calculated frontier orbital energies, absorption wavelengths (k), oscillator strengths (f ) and excitation energies (E) for gas phase and solvent (DMSO and Chloroform) are also illustrated. The statistical thermodynamic functions were obtained for the range of temperature 1001000 K. Reliable vibrational modes associated with H3BTC are made on the basis of total energy distribution (TED) results obtained from scaled quantum mechanical (SQM) method. Crown Copyright Ó 2014 Published by Elsevier B.V. All rights reserved.

Introduction Benzene-1,3,5-tricarboxylic acid (H3BTC) is widely used as building blocks due to its versatile coordination modes, rigidity ⇑ Corresponding author. Tel.: +91 431 2591338; fax: +91 432 6262630. E-mail address: [email protected] (V. Balachandran).

and potential ability for the construction of hydrogen bonds [1]. The self-assembly of organic supramolecular nanostructures is based on non-covalent interactions such as hydrogen bonding, p-stacking and van der Waals forces or metal ion ligand coordination as found in proteins, nucleic acids, liquid crystals and molecular complexes [2]. The spontaneous generation of organized structures depends on the design of molecular components

1386-1425/$ - see front matter Crown Copyright Ó 2014 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2014.01.061

536

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

capable of self-assembling into supramolecular entities. The nature of the species obtained is determined by the information stored in the individual components. Self-assembly methods represent a unique potential to create well-defined functional structures with dimensions on the nanometer scale, and to control surface properties. The assembly of supramolecular structures via hydrogenbonding has developed into a central theme for constructing a wide variety of molecular nanostructures in solution, in liquid crystals, in solid state and on surfaces [3]. Hydrogen bonds are formed when a donor with an available acidic hydrogen atom is brought into direct contact with an acceptor. Hydrogen bonding is not random, but selective and controlled by the directional strength of intermolecular interactions [4]. It can be used to tune the spatial arrangement of functionalized molecules and ions in the solid state surfaces. The structural and energetic features of hydrogen-bonding interactions have been extensively studied [4]. Carboxylic acids are commonly used as motif-controlling functional elements in crystal engineering. They can form hydrogen bonding patterns that contain a center of symmetry, the dimer motif, and also aggregate in acentric one-dimensional chains, catemers, resulting from the formation of hydrogen bonds to two or more neighboring acids [5]. The dimer synthon has been used to assemble a variety of supermolecules due to its bidentate character, which increases the strengths of interactions considerably. For example, Terephthalic acid (1,4-benzene dicarboxylic acid, TA) [6] and isophthalicacid (1,4-benzene dicarboxylic acid, IA) [7] form one-dimensional tapes and ribbons, respectively. Trimesic acid (1,3,5-benzene tricarboxylic acid, H3BTC) with its threefold molecular symmetry forms a two-dimensional network composed of characteristic honeycomb units [7–9]. The 1.4 nm diameter cavities of the honeycombs are often employed to fabricate inclusion compounds [10,11]. H3BTC represents a prototype material for supramolecular self-assembly. The acid and some analogue structural motifs have been used as template patterns to create a variety of nanostructures [5,11–13]. Functionalized H3BTC, its protonated forms, and its metal complexes were employed as unique building blocks in crystal engineering [14]. Experimental Trimesic acid is obtained from Lancaster Chemical Company, UK and used as such without further purification for the spectral measurements. The Fourier transform infrared spectrum of the title compound was recorded in the region 4000–400 cm1, at a resolution ±1 cm1, using BRUKER IFS 66 V Vacuum Fourier transform spectrophotometer equipped with an MCT detector, a KBr beam splitter and globar source. The FT-Raman was recorded on the same instrument with an FRA-106 Raman accessory in the region 3500–100 cm1. The 1064 nm Nd:YAG laser was used as an excitation source, and the laser power was set to 200 mW. Computational methods The entire vibrational assignments of H3BTC are predicted by means of HF and B3LYP method with internally stored standard 6-31+G(d,p) basis set level in Gaussian 09W software package [15]. B3LYP represents Becke’s three parameter hybrid functional method [16] with Lee–Yang–Parr’s correlation functional (LYP) [17,18]. The Cartesian representation of the theoretical force constants have been computed at optimized geometry by assuming C1 point group symmetry, scaling of the force fields were performed by scaled quantum mechanical procedure. Vibrational mode assignments in this work are performed on the basis of total energy distribution (TED) results obtained from MOLVIB program (version V7.0–G77) written by Sundius [19–21]. The Optimized

geometrical parameters, true rotational constants, fundamental vibrational frequencies, IR and Raman intensity, Raman activity, atomic charges, dipole moment, and thermodynamic functions such as the heat capacity, entropy, and enthalpy were investigated for the different temperatures from the vibrational frequencies calculations of the title molecule. The electronic properties, such as HOMO–LUMO energies, absorption wavelengths and oscillator strengths were calculated using B3LYP method of the time dependent TD-DFT, basing on the optimized structure in solvent and gas phase. The natural bonding orbitals (NBO) calculations [22] have been performed using NBO 3.1 program as implemented in the Gaussian 09W [15] package at the B3LYP/6-31+G(d,p) level in order to understand various second-order interactions between the filled orbitals of one subsystem and vacant orbitals of another subsystem, which is a measure of the intermolecular delocalization or hyperconjugation. The Raman activities (Si) calculated with the Gaussian 09W program are converted to relative Raman intensities (Ii) using the following relationship derived from the basic theory of Raman scattering [23];

Ii ¼

vi

h

f ð v 0  v i Þ 4 si  i vi 1  exp hc k T b

where v0 is the exciting frequency (in cm1 units), vi is the vibrational wavenumbers of the ith normal mode, h, c, and kb are universal constants, T is the temperature, and f is the suitably chosen common scaling factor for all the peak intensities.

Results and discussion The present compound under investigation has become a greater interest because it has three equivalent substituents namely carboxyl groups (ACOOH) that are attached to the benzene ring. The molecular energies of eight possible conformers of the title molecule are calculated using HF and B3LYP methods with 6-31+G(d,p) basis set. From the calculations, the most stable conformer is identifiedas C2 (EC2 = 21593.96 eV) and it is also found that, the conformer C7 (EC7 = 21593.10 eV) is the least stable conformer among others as shown in Table 1. Intra-hydrogen bonds can be responsible for the geometry and the stability of predominant conformation: the formation of hydrogen bonding between a hydroxyl and ACOOH cause the structure of the conformer C2 to be most stable conformer. Therefore, the discussion below refers only to this C2 conformer. The stable conformer structure C2 is shown in Fig. 1.

Table 1 Calculated energies and energy difference for eight conformers of H3BTC by HF and B3LYP methods and 6-31+G(d,p)basis set. Conformers

C1 C2 C3 C4 C5 C6 C7 C8

Energy differencesa (eV)

Energy (eV) HF

B3LYP

HF

B3LYP

21714.36 21714.36 21714.00 21713.61 21713.99 21713.89 21713.49 21713.75

21593.96 21593.97 21593.62 21593.23 21593.61 21593.51 21593.10 21593.37

0.011 0.000 0.367 0.757 0.381 0.484 0.876 0.615

0.008 0.000 0.155 0.740 0.354 0.459 0.865 0.596

a Energies of the other seven conformers relative to the most stable C2 conformer.

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

537

Dimer entity The dimer entities in H3BTC can be proved by shaping the structure by joining high-frequency OAH stretching and low-frequency O  O stretching mode. The basic mechanism by coupling highfrequency OAH and low-frequency O  O band is known as anharmonic-type coupling [24]. The dimer structure is shown in Fig. 2 contains two intermolecular hydrogen bonds which are similar as in the model given by Boczar [24], Marechal and Witkowski [25]. The strong hydrogen bond type of interaction between O8  H31AO30 and O9AH10  O29 is observed, the distance between O8  H31 and H10  O29 is about 1.69210 and 1.68201 Å respectively. The energy of the dimer structure calculated at B3LYP/6-31+G(d,p) is about 43.425.3254 eV and it is also found that, the energy of H3BTC dimer is found to be almost twice that of its stable monomer structure. Geometrical parameters The most optimized geometrical parameters such as, bond lengths and bond angles for the most stable C2 conformer and the dimer of H3BTC calculated at B3LYP method with 6-31+G(d,p) basis set are presented in Table 2 in accordance with atom numbering schemes given in Figs. 1 and 2, respectively. The geometrical parameters obtained from DFT method are seen agreement with the experimental values of H3BTC. Therefore, the experimental values are compared only with the DFT method and they are presented in Table 2. For comparative purpose, the experimental X-ray diffraction data [26] of H3BTC is also presented. When comparing experimental values, the computed bond lengths and bond angles are slightly larger, because theoretical calculations are performed upon the isolated molecule in the gaseous state and the experimental results are performed on the solid phase of the molecule [27]. The experimental CAC bond lengths of aromatic ring fall in the range from 1.379 to 1.493 Å, while the results obtained from B3LYP/6-31+G(d,p) fall in the range 1.3987–1.4916 Å for the monomer structure and 1.3947–1.5400 Å for the dimer structure. In contrast, carbon atom C7, C12, C17 in carboxylic group attached to ring C1, C3, and C5 makes bond lengths C1AC7, C3AC12,

Fig. 2. Dimer structure of Trimesic acid.

C5AC17 longer than that of ring CAC. The experimentally observed bond lengths are approximately 0.1 Å greater than that of ring CAC which is in good agreement with the calculated value. According to international crystallography values [28] the C@O and CAO bond lengths in the aromatic carboxylic group conform to an average value of 1.2260 Å and 1.3050 Å respectively. The experimental C@O and CAO bond lengths of the title molecule are 1.205 and 1.306 Å [26] respectively. The calculated value of C@O (1.215 Å) and CAO (1.3561 Å) in B3LYP of H3BTC is reported in Table 2 is in good agreement with experimental data. In contrast, the calculated C@O bond length of dimer is slightly larger than that of experimental. This is because of the fact that, upon dimerization one can find that the electron density of atoms delocalized from a filled lone pair of lewis base to an unfilled lewis acid. Intermolecular (O8  H31, H10  O29) bond distances which causes stabilization of the dimer structure of H3BTC are also reported in Table 2. The C1AC2AC3, C2AC3AC4, C3AC4AC5, C4AC5AC6, C1AC6AC5 and C2AC1AC6 bond angles are observed 119.8°, 120.0°, 120.1°, 119.9°, 119.9° and 120.1°. The optimized hexagonal CACAC bond angles fall in the range 119–120° except C6AC1AC7, C4AC3AC12, C4AC5AC17 (118.06°) and C2AC1AC7,

Fig. 1. Various possible conformers of Trimesic acid.

538

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

Table 2 Optimized geometrical parameters of H3BTC at B3LYP/6-31+G(d,p) basis set. Bond length (Å)

X-raya (Å)

C1AC2 C1AC6 C1AC7 C2AC3 C2AH11 C3AC4 C3AC12 C4AC5 C4AH116 C5AC6 C5AC17 C6AH21 C7AO8 C7AO9 O9AH10 C12AO13 C12AO14 C14AH15 C17AO18 C17AO20 O18–H19

1.38 1.39 1.48 1.39 – 1.39 1.48 1.39 – 1.39 1.49 – 1.21 1.31 – 1.21 1.32 – 1.33 1.20 –

Calculated value (Å) Monomer

Dimer

1.38 1.39 1.48 1.39 – 1.39 1.48 1.39 – 1.39 1.49 – 1.21 1.31 – 1.21 1.32 – 1.33 1.20 –

1.40,1.40 1.40,1.40 1.54, 1.54 1.40, 1.40 1.07, 1.07 1.40, 1.40 1.54, 1.54 1.40, 1.40 1.07, 1.07 1.40, 1.40 1.54, 1.54 1.07, 1.07 1.23, 1.23 1.36, 1.36 0.96, 0.97 1.23,1.23 1.23, 1.36 0.97, 0.97 1.23, 1.23 1.36, 1.36 0.96, 0.97

Intermolecular H bond lengths and angles O8  H31 H10  O29 O9AH10  O29 O8AH31  O30 C7AO8  H31 C28AO29  H10

Bond angle (°)

X-raya (Å)

Calculated value (Å) Monomer

Dimer

C2AC1AC6 C2AC1AC7 C6AC1AC7 C1AC2AC3 C1AC2AH11 C3AC2AH11 C2AC3AC4 C2AC3AC12 C4AC3AC12 C3AC4AC5 C3AC4AH16 C5AC4AH16 C4AC5AC6 C4AC5AC17 C6AC5AC17 C1AC6AC5 C1AC6AH21 C5AC6AH21 C1AC7AO8 C1AC7AO9 O8AC7AO9 C7AO9AH10 C3AC12AO13 C3AC12AO14 O13AC12AO14 C12AO14AH15 C5AC17AO18 C5AC17AO20 O18AC17AO20 C17AO18AH19

– 121.0 119.4 119.7 120.4 – 119.8 – 116.5 – 120.5 – 119.8 118.9 121.9 – – 121.0 124.0 – 123.0 – 123.0 114.2 122.7 – 124.0 113.5 122.5 –

120.15 121.94 117.91 119.80 120.08 120.10 120.04 121.89 118.05 120.08 119.95 119.95 119.97 118.06 121.95 119.93 119.21 120.85 124.62 112.99 122.37 106.91 124.67 112.92 122.40 106.89 124.59 112.89 122.51 106.98

120.00, 120.01 119.99, 119.99 119.99, 119.99 119.99,119.99 120.00, 120.00 120.00, 120.00 119.99, 120.00 120.00, 119.99 120.00, 120.00 120.00, 120.00 119.99, 119.99 119.99, 119.99 119.99, 119.99 120.00, 120.00 120.00, 120.00 120.00, 119.99 119.99, 120.00 120.00, 120.00 130.07, 130.07 112.29, 112.29 117.63, 117.63 109.38, 110.60 130.07, 130.07 112.29, 112.29 117.63, 117.63 110.60, 110.60 130.07, 130.07 112.29, 112.29 117.63, 117.63 110.60, 130.08

1.69 1.68 164.48 164.23 139.85 139.03

Note: Bond lengths are in Å, bond angles are in degrees. a Taken from Ref [26].

C2AC3AC12, C6AC5AC17 (122°). Due to the intra hydrogen bonding, the actual structure is distorted. So the bond angle is varied ±2°. The hexagonal ring CACAH angles are found to be 120°. The CACAO bond angles of H3BTC are greatly affected by H-bonding interactions as shown in Table 2.The small difference between the computed values is due to the reason that calculation belongs to gaseous phase and experimental result belongs to solid phase. Intermolecular hydrogen bonds for dimeric structure are almost linear (the OAH  O angle equals 175.0°). NBO analysis NBO analysis provides the most accurate possible ‘natural Lewis structure’ picture of j, because all orbital details are mathematically chosen to include the highest possible percentage of the electron density. A useful aspect of the NBO method is that it gives information about interactions in both filled and virtual orbital spaces that could enhance the analysis of intra and intermolecular interactions. The second-order Fock matrix has been carried out to evaluate the donor–acceptor interactions in the NBO basis [29]. The interactions result is a loss of occupancy from the localized NBO of the idealized Lewis structure into an empty non-Lewis orbital. For each donor (i) and acceptor (j), the stabilization energy E(2) associated with the delocalization i ? j is estimated as

Eð2Þ ¼ DEij ¼ qi

F 2ði;jÞ

ej  ei

where qi is the ith donor orbital occupancy, ej and ei are diagonal elements (orbital energies) and F(i,j) is the off-diagonal NBO Fock matrix element. In hydrogen bonded systems, the stability of the molecule may cause several factors; hyperconjugative interactions, inter-intramolecular hydrogen bonding, intermolecular charge transfer (ICT), electron density transfer (EDT) and cooperative effect due to the delocalization of electron density from the filled lone pairs of Lewis base ‘n(y)’ into the unfilled antibonding of Lewis acid ‘r*(XAH)’. In the present work, NBO analysis has been performed on the monomer and dimer with the aid of NBO 3.1 program as implemented in the Gaussian 09W package. In the case of H3BTC, the intermolecular interactions are formed by the orbital overlap between n (O) and r*(OAH). {i.e.n1 (O8) ? r*(O30AH31), n1 (O29) ? r*(O9AH10)}. The NBO analysis of H3BTCdimer clearly gives theevidences of the formation of two strong H-bonded interactions between oxygen lone electron pairs and r*(OAH) antibonding orbitals. The occupancies and their respective energies of oxygen lone pairs and antibonding orbitals which are responsible for the stabilization of H-bonded monomer and dimer entities of H3BTC are given in Table 3. The stabilization energy E(2) associated with the hyperconjugative interactions viz. n1 (O8) ? r*(O30AH31) and n1 (O29) ? r*(O9AH10) are obtained 0.9150 and 2.1239 eV, respectively, as shown in Table 4. It is worth mentioning that, the differences in stabilization energies reported in Table 4 are reasonable. In the view of the fact that, the accumulation of electron density in the

539

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547 Table 3 Occupancies and energies of interacting Lewis base and Lewis acid sites. Parameters

n1(O8) n1(O8) n1(O9) n1(O9) n2(O29)a n2(O30) a r*(C1AC7) r*(C7AO8) r*(C7AO9) r*(O9AH10) a

Occupancy (e)

Table 5 Composition of hydrogen bonded NBO’s in terms of natural atomic hybrids.

Energy (eV)

NBO

Monomer

Dimer

Docc

Monomer

Dimer

DE

1.977 1.889 1.979 1.876 1.655 1.808 0.058 0.173 0.069 0.008

1.927 1.831 1.969 1.811 1.928 1.969 0.049 0.022 0.052 0.011

0.049 0.058 0.010 0.068 0.273 0.161 0.009 0.152 0.017 0.003

26.767 12.557 23.264 14.440 11.891 12.728 16.100 4.424 16.003 19.752

17.639 21.698 20.530 12.792 18.034 20.347 16.196 23.013 16.542 18.671

9.129 9.141 2.734 1.648 6.142 7.619 0.096 18.589 0.540 1.081

Monomer

n

sp (C7AO8) %s – char %p – char. of %p – char. of q(C7)/e q(O8)/e spn (C7–O9) %s – char %p – char. of %p – char. of q(C7)/e q(O9)/e

1.89

C7 O8

C7 O9

sp 34.56% 65.40% 34.60% 0.8621 0.5068 sp2.69 26.97% 69.33% 30.67% 0.8326 0.5538

Dimer 1.95

sp 33.82% 66.95% 33.05% 0.8182 0.5749 sp2.60 27.67% 68.44% 31.56% 0.8273 0.5618

DNBO +s 0.74 1.55 1.55 0.0439 0.0681 s 0.7% 0.89% 0.89% 0.0053 0.008

Values for monomer are taken from identical NBOs of other unit.

Table 4 The second order perturbation energies E(2) (kal/mol) corresponding to the most importantcharge transfer interactions (donor ? acceptor) of H3BTC. Donor (i)

Acceptor (j)

E(2) (eV)

E(j)  E(i) (eV)

F(i,j) (eV)

Within unit 1 n1(O8) r*(C7AO9) n1(O8) r*(C7AO9) n1(O9) r*(C7AO8) n1(O9) r*(C7AO8)

0.193 1.297 0.397 3.141

42.178 30.477 44.355 17.687

2.014 4.517 2.966 5.333

From unit 1 to unit 2 n1(O8) p*(C22AC28) n1(O9) p*(C28AO29) n1(O9) p*(C28AO29) n1(O8) r*(O30AH31)

0.003 0.005 0.010 0.915

29.933 44.355 41.906 24.218

0.191 0.354 0.490 3.619

From unit 2 to unit 1 n1(O30) p*(C7AO8) n1(O29) r*(O9AH10) n1(O29) r*(O9AH10)

0.016 1.246 2.124

42.178 35.103 26.939

0.626 5.197 5.823

Within unit 2 r*(C28AO30) n1(O29) n1(O29) r*(C28AO30) n1(O30) r*(C28AO29)

0.392 0.986 3.094

40.273 32.109 17.687

2.803 4.027 5.306

antibonding r*(OAH) is not only transferred from the lone electron pair n (O) butalso from the entire molecule. Unusually, rehybridization plays a negative effect in C7AO8 bond. It is observed in Table 5 that the s-character of (C7AO8) hybrid orbitals increases (0.74%) from sp1.89 to sp1.95 that leads to a conspicuous strengthening of (C7AO8) bond and its contraction. This shows the existence of a mesomeric structure characterized by delocalization of electron density from the r*(C7AO8) antibonding orbital to the remaining part of the molecule. This is quite possible because the energy of r*(C7AO8) antibonding orbital (23.0129 eV) is higher than the energy of r*(O9AH10) antibonding orbital (18.6711 eV) which supports the likelihood of the delocalization of ED from the CAO to the OAH region. This is clearly reflected in the geometry as bond (C7AO8) contracts to an amount of 0.1266 Å with respect to the monomer. Further, the second order perturbation theory analysis of Fock matrix in NBO basis shows that the n1 (O8) and n1 (O9) can readily interact with r*(H10) and r*(H31) antibonding orbitals. In addition, the s character of spn hybrid orbital for the (C7AO9) bond decreases from sp2.69 to sp2.60 upon dimerization, which substantiates the bond weakening. HOMO–LUMO energy gap An analysis of the electron density of highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of H3BTC can give us some idea about the ground and excited state proton transfer processes. Both HOMO and LUMO of

H3BTC monomer and dimer are of p type, but their phases are quite different as shown in Figs. 3 and 4, respectively. The energies corresponding to various HOMO and LUMO levels of H3BTC are performed by B3LYP/6-31+G(d,p) method. The HOMO–LUMO energy calculation reveals that, there are 54 occupied and 259 unoccupied molecular orbitals associated with H3BTC monomer. The energies corresponding to the highest occupied and lowest unoccupied molecular orbitals of H3BTC monomer are found to be 8.08777 and 2.46154 eV respectively as shown in Table 6. The energy gap between various occupied and unoccupied molecular orbitals of H3BTC was calculated at the B3LYP/6-31+G(d,p) level and is 5.6262 eV, reveals that the energy gap reflects the chemical activity of the molecule. LUMO as an electron acceptor represents the ability to obtainan electron. HOMO represents the ability to donate an electron. HOMO (8.08777 eV) orbital on the aromatic ring of H3BTC (Fig. 3a) is primarilyof anti-bonding character type over C1, C2, C3 and O20 atoms, whereas C4, C5, C6 and O8, O9 show bonding character. The HOMO1 (8.16369 eV) orbital (Fig. 3b) on the aromatic ring show that the atoms C2, C3, C4 having considerable bonding character, where as the atoms C1, C6, C5 having anti-bonding character. A HOMO2 (8.27199 eV) orbital shown in Fig. 3c has no amplitude over the aromatic ring, whereas the orbital overlap on the carbonyl oxygen of H3BTC shows considerable double bond character type. In contrast, all the three LUMO (2.46154 eV) surfaces shown in Fig. 3d, e and f are p* in nature. Because if we look into the electronic distributionof LUMO within the aromatic ring the C2, C3, C6, C5 position have bonding character whereas the C1, C4 position have antibonding character. The orbital overlapping on the H3BTC dimer is shown in Fig. 4. A HOMO1 (7.45375 eV) orbital shown in Fig. 4a has no amplitude [30] over the aromatic ring, whereas the orbital overlap on the only one carbonyl oxygen of dimer H3BTC shows considerable double bond character type. The left and right side of dimer HOMO2 (7.71824 eV) orbital on the aromatic ring show that the atoms C23, C22 and C2, C3, C4 having considerable bonding character, whereas the atoms C25, C26 and C1, C6, C5 having anti-bonding character, respectively. In contrast, all the LUMO (7.24776 eV) surfaces of dimmers are p* in nature. Because if we look into the electronic distribution of LUMO within the ring the C25, C22 and C2, C3, C6, C5 position have bonding character whereas the C24, C23, C26, C27 and C1, C4 position have antibonding character. In DFT the electro negativity is defined as negative of partial derivative of energy E of an atomic or molecular system with respect to the number of electron N for a constant external potential V(r)

g ¼ 1=2ð@ 2 E=@N2 ÞvðrÞ where E is the total energy, N is the number of electrons of the chemical species and g is the chemical potential, which is identified as the negative of the electronegativity (v) as defined by Iczkowski

540

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

(a) HOMO

(d) LUMO

(b) HOMO-1

(c) HOMO-2

(e) LUMO+1

(f) LUMO+2

Fig. 3. HOMO–LUMO structure of monomer of Trimesic acid.

(a) HOMO

(d) LUMO

(b) HOMO-1

(e) LUMO-1

(c) HOMO-2

(f) LUMO-2

Fig. 4. HOMO–LUMO structure of dimer of Trimesic acid.

541

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547 Table 6 Selected occupied and unoccupied molecular orbital energies and energy gap of H3BTC. Molecular orbitals

Monomer B3LYP/6-31+G(d,p)

Dimer B3LYP/6-31+G(d,p)

Energy E (eV)

Possible molecular orbital energy transition

Energy gap Gap DE (eV)

Energy E(eV)

Possible molecular orbital energy transition

Energy gap Gap DE (eV)

8.088 8.164 8.272

HOMO ? LUMO HOMO1 ? LUMO HOMO2 ? LUMO HOMO ? LUMO+1

5.626 5.702 5.810 5.641

7.248 7.454 7.718

HOMO ? LUMO HOMO1 ? LUMO HOMO2 ? LUMO HOMO ? LUMO+1

4.507 4.712 4.976 4.683

HOMO1 ? LUMO+1 HOMO2 ? LUMO+1 HOMO ? LUMO+2 HOMO1 ? LUMO+2 HOMO2 ? LUMO+2

5.717 5.825 6.978 7.053 7.162

HOMO1 ? LUMO+1 HOMO2 ? LUMO+1 HOMO ? LUMO+2 HOMO1 ? LUMO+2 HOMO2 ? LUMO+2

4.888 5.152 4.773 4.978 5.242

Occupied HOMO HOMO1 HOMO2 Unoccupied LUMO LUMO+1 LUMO+2

2.462 2.447 1.110

Table 7 Quantum chemical parameter of H3BTC. Chemical parameter

Monomer

Dimer

Ionization potential(I) (eV) Electron affinity(A) (eV) Global hardness(g) (eV) Global softness (S) (eV) Chemical potential (l) (eV) Electrophilicity (x) (eV) Electro negativity (v) (eV)

2.462 8.088 2.813 263.217 5.275 4.945 5.275

9.192 10.295 9.743 75.997 0.551 0.016 0.551

and Margrave [31]. According to Koopman’s theorem [32], the energies of the HOMO and the LUMO orbital’s of the molecule are related to the ionization potential, I, and the electron affinity, A, respectively, by the following relations: I = EHOMO and A = ELUMO. Absolute electro negativity v, and absolute hardness g of the molecule are given by [33], v = (I + A)/2 and g = (I  A)/2. The softness is the inverse of the hardness r = 1/g. Parr et al. [34] introduced the global electrophilicity index (x) in terms of chemical potential and hardness as x = l2/2g. The quantum chemical parameters of the molecule in both the monomer and dimer are presented in the Table 7.

2.724 2.548 2.458

are determined using the vibrational wave numbers and these results are presented in the Tables 8 and 9 for HF and B3LYP/631+G(d,p) methods, respectively. The correlation equations between these thermodynamic properties and temperatures were fitted by parabolic formula. All the thermodynamic data provide helpful information for the further study on the title compound. As observed from Tables 8 and 9 all the values of E, Cp, Svip, ðH0  E00 Þ=T and ðG0  E00 Þ=T are increasing with temperature range from 100 to 1000 K which attributed to the enhancement of the molecular vibration as the temperature increases [36]. The correlation equations between heat capacity, entropy, enthalpy, Gibb’s free energy and internal thermal energy were formulated by using fitting factors (R2) for these thermodynamic properties is 0.9990. For C2 conformer the following equations are used to predict thermodynamic parameters, like molar heat capacity at constant pressure, internal energy and entropy for other range of temperature. For HF

ðCp0 Þv ib ¼ 7:614 þ 0:168T  0:00008T 2 ðR2 ¼ 0:999Þ ðS0 Þv ib ¼ 59:47 þ 0:209T  0:00006T 2 ðR2 ¼ 0:999Þ ðEÞv ib ¼ 84:33 þ 0:026T þ 0:00004T 2 ðR2 ¼ 0:999Þ For B3LYP

ðCp0 Þv ib ¼ 7:994 þ 0:169T  0:000081T 2 ðR2 ¼ 0:999Þ

Thermodynamic function analysis The thermodynamic functions are determined from spectroscopic data by statistical methods [35]. The thermodynamic quantities such as entropy Svib, heat capacity at constant pressure (Cp), enthalpy ðH0  E00 Þ=T, Gibb’s free energy ðG0  E00 Þ=T and internal thermal energy (E) for various range (1001000 K) of temperatures

ðS0 Þv ib ¼ 59:89 þ 0:212T  0:000062T 2 ðR2 ¼ 0:999Þ ðEÞv ib ¼ 82:28 þ 0:027T þ 0:00004T 2 ðR2 ¼ 0:999Þ One of the important parameters of thermodynamics is the partition function. The partition function links thermodynamics, spectroscopy and quantum theory. The different types of partition

Table 8 Thermodynamic parameters for H3BTC in C2 conformer by B3LYP/6-31+G (d,p). Temperature (K)

E (kcal/ Mol)

CP (Cal/ MolKelvin)

Svib (Cal/ MolKelvin)

ðH0  E00 Þ=T (Cal/ MolKelvin)

ðG0  E00 Þ=T (Cal/ MolKelvin)

Vibrational partition function Vib (BOT)

Vib (v = 0)

100 200 300 400 500 600 700 800 900 1000

86.1163 89.0189 93.3694 98.9985 105.6865 113.2222 121.4310 130.1786 139.3630 148.9060

23.6614316 38.4936503 52.5098546 64.4183824 73.9611126 81.436603 87.3188667 92.0217299 95.8474753 99.0063474

79.6234 100.5313 118.7875 135.4725 150.8005 164.8811 177.8294 189.7685 200.8157 211.0767

15.8702 23.44196 30.79168 37.6634 43.9042 49.4774 54.4199 58.8003 62.6926 66.1651

63.7532 77.0893 87.9958 97.80908 106.8963 115.4037 123.4096 130.9682 138.1231 144.9116

2.6402D184 3.7171D90 1.1548D57 1.3024D40 9.0856D30 4.6252D22 3.5529D16 1.8776D11 1.5922D07 3.6161D04

1.9834D+01 1.0188D+03 4.8726D+04 2.1561D+06 8.5804D+07 3.0044D+09 9.1497D+10 2.4158D+12 5.5430D+13 1.1112D+15

542

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

Table 9 Thermodynamic parameters for H3BTC in C2 conformer by HF/6-31+G (d,p). E (kcal/ Mol)

CP (Cal/ MolKelvin)

Svib (Cal/ MolKelvin)

ðH0  E00 Þ=T (Cal/ MolKelvin)

ðG0  E00 Þ=T (Cal/ MolKelvin)

100 200 300 400 500 600 700 800 900 1000

88.1028 90.9544 95.2368 100.8014 107.4282 114.9036 123.0516 131.7076 140.8601 150.3416

23.3457 37.7774 51.5626 63.3211 72.8266 80.3598 86.3499 91.1756 95.1195 98.3835

78.9643 99.5329 117.5136 134.0125 149.2039 163.1747 176.0293 187.8861 198.5603 209.0565

15.6342 23.06874 30.3162 37.1453 43.3674 48.9296 53.8635 58.2364 62.1226 65.5905

63.3300 76.4642 87.1974 96.8671 105.8365 114.2450 122.1658 129.6496 136.7377 143.4659

Thermodynamical parameters (Kcal/mol)

Temperature (K)

Vib (BOT)

Vib (v = 0)

4.2864D189 1.2287D92 2.1277D59 5.4965D42 6.1934D31 4.2895D23 4.0708D17 2.5050D12 2.3796D8 5.8951D5

1.6358D+1 7.5903D+2 3.3249D+4 1.3662D+6 5.1081D+7 1.6957D+9 4.9291D+10 1.2489D+12 2.7614D+13 5.3537D+14

internal energy, enthalpy, and Gibb’s free energy with temperature are graphically represented in Fig. 5.

180

Hyperpolarizability

120 60

E CP Svib 0 0 (H -E0 )/T 0 0 (G -E0 )/T

0 -60 -120 0

Thermodynamical parameters (Kcal/mol)

Vibrational partition function

200

400

600

800

1000

180 120

The first hyperpolarizabilities (btotal) of this novel molecular system, and related properties (b, a0 and a) of H3BTC were calculated using B3LYP/6-31+G(d,p) basis set, based on the finite-field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field. Polarizabilities and hyperpolarizabilities characterize the response of a system in an applied electric field [37]. They determine not only the strength of molecular interactions (long-range inter induction, dispersion force, etc.) as well as the cross sections of different scattering and collision process and also the nonlinear optical properties (NLO) of the system [37,38]. First hyperpolarizability is a third rank tensor that can be described by 3  3  3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to the Kleinman symmetry [38]. The components of first hyperpolarizability (btotal) are defined as the coefficients in the Taylor series expansion of the energy in the external electric field. When the external electric field is weak and homogeneous, this expansion becomes:

E ¼ E0  la F a  1=2aab F a F b  1=6babc F a F b F c þ    60

where E0 is the energy of the unperturbed molecules, Fa the field at the origin la, aab and babc are the components of dipole moments, polarizability and the first hyperpolarizabilities, respectively. The total static dipole moments l, the mean polarizabilities a0, the anisotropy of the polarizabilities a and the mean first hyperpolarizabilities btotal, using the x, y and z components they are defined as: [39,40]. The total static dipole moment is

E CP Svib 0 0 (H -E0 )/T 0 0 (G -E0 )/T

0 -60 -120

0

200

400

600

800

1000

Fig. 5. Correlation graphs of thermodynamic parameters with termperature for Trimesic acid.

functions are (i) translational partition function, (ii) rotational partition function, (iii) vibrational partition function and (iv) electronic partition function. Partition functions can be used to calculate heat capacities, entropies, equilibrium constants and rate constants. There are two ways to calculate the partition function depending on the zero point energy to be either the bottom of the internuclear potential energy well, or the first vibrational level. The variation of the thermodynamic functions such as entropy, heat capacity,

l¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðl2x þ l2y þ l2z Þ

The isotropic polarizability is

ao ¼

axx þ ayy þ azz 3

The polarizability anisotropy invariant is

h







a ¼ 21=2 axx  ayy 2 þ ayy  azz 2 þ ðazz  axx Þ2 þ 6a2xx and the average hyperpolarizability is

btotal ¼ and

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðb2x þ b2y þ b2z Þ

i

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547 Table 10 Electric dipole moment l (Debye), mean polarizability a0 (1022 esu) anisotropy polarizability Da (1025 esu) and first hyperpolarizability btot(1031 esu) for Monomer and Dimer of H3BTC. Parameters

lx ly lz l axx ayy azz axy axz ayz ao

Values

Parameters

Monomer

Dimer

1.932 1.979 0.000 2.765 68.814 98.571 84.650 0.002 1.830 0.000 84.012

1.232 0.364 0.439 1.357 275.036 123.731 170.657 0.161 3.807 0.215 189.808

bxxx byyy bzzz bxyy bxxy bxxz bxzz byzz byyz bxyz btot Da

Values Monomer

Dimer

10.143 52.817 0.001 62.121 1.800 0.008 0.079 0.066 0.003 0.004 75.295 25.982

193.864 13.312 0.169 131.506 19.487 16.272 0.246 0.784 9.463 3.900 5656.672 18038.873

543

The different values of the electrostatic potential represented by different colors; red represents the regions of the most negative electrostatic potential, blue represents the regions of the most positive electrostatic potential and green represents the region of zero potential. Potential increases in the order red < orange < yellow < green < blue. Such mapped electrostatic potential surfaces have been plotted for title molecule in B3LYP/6-31+G(d,p) basis set using the computer software Gauss view [42]. Projections of these surfaces along the molecular plane and a perpendicular plane are given in Fig. 6. This figure provides a visual representation of the chemically active sites and comparative reactivity of atoms. It may see that, in both methods, a region of zero potential envelopes the p-system of the aromatic rings, leaving a more electrophilic region in the plane of hydrogen atoms in H3BTC molecule [43]. Vibrational spectra

Fig. 6. Electrostatic potential surface map of Trimesic acid.

bx ¼ bxxx þ bxyy þ bxzz by ¼ byyy þ bxxy þ byzz

In order to obtain the spectroscopic signature of H3BTC molecule, a frequency calculation is performed on the gaseous phase of the molecule, while experimental FT-IR and FT-Raman are performed on the solid phase of the molecule. Hence there are disagreements between calculated and observed vibrational wavenumbers. To overcome discrepancies between observed and calculated wavenumbers, the scale factor (1.0638) is used. For this purpose the scaling of the force field was performed according to the SQMFF procedure [44]. The present molecule H3BTC consists of 21 atoms, so it has 57 normal vibrational modes. Detailed description of vibrational modes can be given by means of normal coordinate analysis. For this purpose, the full set of 72 standard internal coordinates (containing 18 redundancies) was defined as given in Supplementary data (S1). From these, a non-redundant set of local symmetry coordinates was constructed (see Supplementary data (S2)). Fig. 7 presents the experimental IR and Raman spectra. The experimental wavenumbers are depicted in Table 11 together with the calculated wavenumbers of H3BTC molecule. The resulting vibrational wavenumbers for the optimized geometry and the proposed vibrational assignments as well as IR intensities (IIR) and Raman intensities (IRaman) are also given in Table 11. The complete vibrational assignments provided in this study are based on the total energy distribution (TED) results obtained from MOLVIB program [19–21]. It is observed that, in solid H3BTC the ACOOH groups are involved in intermolecular hydrogen bonding interactions.

bz ¼ bzzz þ bxxz þ byyz The B3LYP/6-31+G(d,p) method calculated the first hyperpolarizability for monomer and dimer of H3BTC is 75.2949  1031 and 656.672  1031 esu respectively. We conclude that the title compound is an attractive object for future studies of nonlinear optical properties [41]. The total molecular dipole moment (l), mean polarizability (a0) and anisotropy polarizability (Da) and first hyperpolarizability (btotal) of H3BTC monomer and dimer are computed and are depicted in Table 10. Molecular electrostatic potential (MEP) analysis Molecular electrostatic potential (MEP) at a point in the space around a molecule gives an indication of the net electrostatic effect produced at that point by the total charge distribution (electron + nuclei) of the molecule and correlates with dipole moments, electronegativity, partial charges and chemical reactivity of the molecules. It provides a visual method to understand the relative polarity of the molecule. An electron density isosurface mapped with electrostatic potential surface depicts the size, shape, charge density and site of chemical reactivity of the molecules.

CAH vibrations In the present study, the three adjacent hydrogen atoms left around the benzene ring of H3BTC give rise to three CAH stretching modes (v4,v5,v6), three CAH in-plane bending (v18, v20, v22) and three CAH out-of-plane bending (v26, v27, v28) modes. The heteroaromatic organic molecule shows the presence of the CAHstretching vibrations in the 3000–3100 cm1 range which is the characteristic region for the identification of CAH stretching vibrations [45]. Accordingly, the CAH stretching modes of H3BTC are assigned to 3100 and 3024 cm1 in FT-IR and 3071 cm1 in FT-Raman. These modes are calculated from the most stable C2 conformer. They are very pure modes since their TED contributions are almost 100%. In aromatic compounds, the CAH in-plane and out-of-plane bending vibrations appear in the range 1000–1300 cm1 and 750–1000 cm1 [46,47] respectively. Hence the CAH in-plane bending modes of H3BTC are assigned to 1276, and 1117 cm1 in FT-IR and 1163 cm1 in FT-Raman. The calculated values of this modes show better agreement with the experimental values. The TED contribution results at the last column of Table 11 show that, CAC stretching vibrations interacting considerably with CAH inplane bending mode. The CAH out-of-plane bending vibrations of

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

Tranmittance (%)

544

4000

3500

3000

2500

1500

2000

1000

400

427 355

572 452

660

946 862

1044

1163

1295

161

187

1584

3071

3483

3214

1428

1636

1781

124

741

Wavenumber (cm-1)

Wavenumbers (cm−1) Fig. 7. Observed FT-IR and FT-Raman spectra of Trimesic acid.

H3BTC are attributed to 966 and 946 cm1 in FT-IR and FT-Raman. In the present study, the scaled theoretical values of CAH out-of plane bending modes calculated at HF/6-31+G(d,p) and B3LYP/631+G(d,p) show good agreement with the experimental values of H3BTC as well as with that of similar kind of molecules [48]. The TED contribution to these modes indicates that, CAH out-of-plane bending modes are also highly pure modes like CAH stretching modes.

Carboxylic acid group vibrations Generally carboxylic acid group containing molecules possesses dimeric character. The carboxylic acid dimer is formed by strong hydrogen bonding in the solid and liquid state. Hence the derivatives of carboxylic acids are best characterized by the carbonyl and hydroxyl groups. The presence of carbonyl group is the most important in the infrared spectrum because of its strong intensity of absorption and high sensitivity towards relatively minor changes in its environment. Intra- and intermolecular hydrogen bonding factors affect the carbonyl and absorptions in common organic compounds due to inductive, mesomeric, field and conjugation effects [49]. The characteristic infrared absorption wavenumbers of C@O in acids are normally strong in intensity and found in the region 1690–1800 cm1 [43]. In the present study, the strong band at 1723 cm1 in FT-IR and the band at 1781, 1720 and 1673 cm1 in FT-Raman are assigned to C@O stretching. The band observed at 1404, 1340 cm1 in FT-IR and 1295 cm1 in FT-Raman are assigned to CAO stretching (v14, v16, v17) mode.

The wavenumbers of this mode calculated by DFT is in excellent agreement with the experimental FT-IR and FT-Raman wavenumbers. The OAH stretching vibrations are characterized by a very broad band appearing in the region 3400–3600 cm1 [50]. Hence the band observed at 3420 cm1 in FT-IR and 3483, 3214 cm1 in FT-Raman is assigned to OAH stretching of carboxylic acid group of H3BTC. The scaled theoretical values, by HF and B3LYP methods and 6-31+G(d,p) basis set are in good agreement with OAH stretching of similar kind of molecules [26]. In the case of carboxylic acid containing dimer structure, the OAH out-of-plane bending and CAO out-of-plane bending bands involve some interaction between them. Hence these are referred to as coupled OAH out-of-plane bending and CAO out-of-plane bending vibrations [50]. This is also confirmed by TED output results. The strong band observed at 1340 cm1 in FT-IR and 1295 cm1 in FT-Raman are assigned to OAH out-of-plane bending of carboxylic acid group. In this mode, the TED contribution of CAO stretching is significant. Ring vibrations In the present study of H3BTC, the benzene ring possesses six ring CAC stretching vibrations in the region 1460–1660 cm1 and 1070–1150 cm1. As revealed by TED, the ring CAC stretching modes are observed at 1468 and 1043 cm1 in FT-IR and 1636, 1428, 1354 and 1044 cm1 in FT-Raman for H3BTC. The in-plane and out-of-plane bending vibrations of the benzene ring are generally observed below 1000 cm1 [51] and these modes are not pure but contain a significant contribution from other modes and are substituent-sensitive. In the title molecule, ring in-plane and

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

545

Table 11 Comparison of the experimental (FT-IR, FT–Raman wavenumbers (cm1)) and theoretical harmonic scaled wavenumbers (cm1), Infrared intensities (IIR), Raman intensities (IRaman) of monomer and dimer of H3BTC calculated by HF and B3LYP methods and 6-31+G(d,p) basis set. No.

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 v43 v44 v45 v46 v47 v48 v49 v50 v51 v52 v53 v54 v55 v56 v57

Observed frequencies cm1

Theoretically calculated at HF/631+G⁄⁄ and B3LYP/631+G⁄⁄

FTIR

Unscaled

FT-Raman

3483 3420 3214 3100 3024

1723

1606 1468

3071 1781 1720 1673 1636 1584 1428

1404 1354 1340 1295 1276 1181 1163 1127 1117 1043

1066 1044

966 946 862 825 741 691 656

660 633

606 572

532 524 452 427 367 355 318 263 187 161 124

IIR

Scaled

Assignments/(%TED) IRaman

a

b

a

b

a

b

a

b

4127 4109 3900 3424 3390 3350 2001 1992 1985 1800 1794 1608 1591 1540 1493 1481 1424 1348 1333 1310 1284 1262 1226 1224 1125 1115 1090 1083 973 964 884 883 843 759 714 704 701 641 636 634 602 545 531 488 488 388 377 348 293 215 215 142 140 111 60 58 57

3766 3766 3600 3130 3123 3113 1808 1800 1794 1646 1641 1484 1471 1408 1376 1358 1351 1292 1237 1176 1174 1146 1127 1120 1016 996 984 963 902 891 795 794 756 689 678 643 639 618 611 591 578 505 492 451 450 360 350 326 271 195 194 131 129 103 53 53 51

3483 3468 3291 3124 3093 3056 1816 1753 1747 1684 1639 1515 1460 1435 1374 1353 1323 1286 1203 1188 1151 1121 1089 1047 990 981 959 903 856 848 778 752 742 668 628 620 617 564 560 558 530 480 467 429 429 341 332 306 258 189 189 125 123 98 53 51 50

3421 3421 3271 3130 3123 3113 1761 1624 1618 1595 1580 1439 1427 1370 1341 1325 1291 1266 1161 1152 1122 1105 1071 1040 987 965 940 895 864 824 770 746 682 662 622 608 576 557 551 533 521 466 454 427 366 355 326 320 264 176 165 138 126 93 48 48 46

26.69 173.61 135.43 3.49 5.34 7.14 511.19 396.09 189.09 38.51 4.77 4.00 9.21 52.08 33.90 251.92 87.23 11.32 42.36 357.37 539.71 104.56 42.90 15.71 0.40 0.61 1.04 11.45 0.01 6.97 0.18 0.04 162.73 10.47 35.43 102.72 85.08 0.08 0.01 13.16 246.65 12.78 32.63 0.11 0.75 1.48 0.48 1.76 2.41 0.00 0.00 0.58 1.19 0.02 0.02 2.15 1.49

2.48 1.70 2.14 0.01 1.31 0.79 0.00 0.00 3.21 2.01 0.59 2.71 0.03 0.52 30.19 16.82 319.82 0.11 6.42 0.08 121.21 135.65 16.78 15.93 247.82 0.00 0.04 1.18 0.02 8.21 0.12 0.21 0.13 9.25 22.08 66.61 152.79 455.23 259.65 87.42 5.92 125.88 416.20 81.19 23.22 6.18 5.39 76.71 221.34 523.99 880.20 7.17 4.95 2.85 220.35 326.78 9.36

31.53 5.20 13.09 10.41 9.49 8.78 49.89 30.54 16.21 53.45 32.16 2.93 2.99 22.64 2.32 5.51 0.53 32.53 4.27 8.92 4.76 1.53 0.34 1.78 0.02 0.02 100 0.23 3.51 9.59 3.15 2.45 1.01 51.82 0.09 1.76 0.92 17.19 0.76 12.01 0 2.34 1.98 25.16 27.68 34.76 26.84 75.91 1.32 30.88 43.84 20.95 5.24 2.63 88.45 50.56 13.09

34.06 10.76 14.16 8.04 7.53 7.23 100.29 46.73 32.03 59.74 36.05 6.94 3.26 41.34 0.21 1.80 7.22 0.42 47.55 9.93 14.41 1.54 0.54 3.40 77.72 0.05 0.02 0.04 2.80 10.80 0.65 0.12 0.28 50.39 0.16 0.99 2.17 17.22 11.70 0.36 0.04 1.69 1.76 4.02 5.49 24.82 23.25 54.10 0.12 23.43 31.00 18.05 13.87 0.71 82.93 100.00 17.26

mOH(98) mOH(98) mOH(98 mCH(98) mCH(97) mCH(98) mCO(66), dOH(21),dCC(12) mCO(68), dOH(19),dCC(10) mCO(67), dOH(19),dCC(11) mCC(72), dCH(20) dOH(37), mCC(28) mCC(37), dCH(21) mCC(61), dCH(12) mCO(75), dCC(12),dCO(24) mCC(60), dCH(18) mCO(68),mCC(33) mCO(64), mCC(38) dCH(45),mCC(32),dOH(15) dOH(36), mCC(13) dCH(52), mCC(30), dOH(13) dOH(40),mCC(18)dCH(12) dCH(47), mCO(25),dOH(11) mCC(43) mCC(45), dCH(12),dOH(12) mCC(48), dCH(13),dOH(10) cCH(89), cCH(89), cCH(88), cCC(36),dring (20),dOH(10) cCC(38),dring (22),dOH(11) dCO (56),dCC(22) dCO (55),dCC(22) dCO (50),dCC(26) dCC(33) cOH(36), cCH(11) dring (30),dOH(16) dring (35) cOH(38), cCH(16) cOH(36), cCH(14) dring (34) cCO(56), cCH(25) dCC(60),dCO (28) dCC(43),dCO (21) cring(35),cOH(10) cring(26),cOH(8) cCO(53) dCO (42) dCO (36) dCO (40) cCO(87) cCO (88) cCO (92) c ring (28) cCO(85) cCOOH(71) cCOOH(70) cCOOH(70)

a

HF/6-31+G(d,p), bB3LYP/6-31+G(d,p). v, Stretching, d, in-plane bending, c, out-of-plane bending, o, twisting.

out-of-plane bending modes are observed at 452, 355 cm1 in FTRaman and 187, 161 cm1 in FT-IR. From TED results, the bands at 427, 367, 124 cm1 in FT-Raman are assigned to ring out-of-plane bending vibrations. The peaks for these modes are not observed in FT-IR spectrum since these modes are possible to appear only in far IR spectrum. The scaled theoretical wavenumbers corresponding to ring vibrations are found to have a good correlation with the experimental observations.

UV–VIS spectra analysis Molecules allow strong pp⁄ and r–r⁄ transition in the UV–VIS region with high extinction coefficients. Ultraviolet spectra analyses of H3BTC monomer have been researched by theoretical calculation. In order to understand electronic transitions of compound, TD-DFT Calculations on electronic absorption spectra in gas phase and solvents (DMSO, Chloroform) were performed. The calculated frontier orbital energies, absorption wavelengths (k), oscillator

546

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547

Table 12 Theoretical electronic absorption spectra of TFMBP (absorption wavelength k (nm), excitation energies E (eV) and oscillator strengths (f)) using TDDFT/B3LYP/6-31+G(d,p) method in gas and solvent (water) phase. Gas

H1L H2L H3L

DMSO

DE (eV)

f

max (nm)

DE (eV)

f

max (nm)

DE (eV)

f

273.79 271.37 268.66

4.528 4.569 4.615

0.0001 0.0000 0.0000

265.98 265.63 263.29

4.661 4.668 4.709

0.0001 0.0002 0.0000

269.97 269.95 264.69

4.593 4.593 4.684

0.0000 0.0002 0.0001

14 12

Gas DMSO Choloroform

10

Intensity

Chloroform

max (nm)

8 6 4

owing to the intensities of the molecular vibrations increase with increasing temperature. Furthermore, the polarizability, the first hyperpolarizability and total dipole moment properties of title molecule have been calculated and the results are discussed. Lower in the HOMO and LUMO energy gap reveals the significant degree of charge transfer interactions taking place within the molecule. The absorption wavelengths (k), excitation energies and oscillator strengths (f) were calculated in gas phase and solvents (DMSO and Chloroform). Molecular coefficient analyses suggest that the electronic spectrum corresponds to the p ? p⁄ electronic transition.

2

Appendix A. Supplementary material

0

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2014.01.061. 150

200

250

300

350

400

Wavelength (nm) Fig. 8. Calculated UV–Visible spectra of Trimesic acid.

strengths (f ) and excitation energies (E) for gas phase and solvent are illustrated in Table 12 and the UV–VIS spectra of H3BTC monomer is shown in Fig. 8. The visible absorption maxima of this molecule from calculations of the molecular orbital geometry show that correspond to the electron transition between frontier orbitals such as translation from HOMO to LUMO. As can be seen from Table 12, the calculated absorption maximum values have been found to be 273.79, 271.37, 268.66 nm for gas phase, 265.98, 265.63, 263.29 nm for DMSO and 269.97, 269.95, 264.69 nm for chloroform solution of H3BTC monomer at DFT/B3LYP/631+G(d,p) method. Conclusions Molecular structure and vibrational wavenumbers of H3BTC is studied using vibrational spectra and density functional method. The most stable monomer conformer of compound ws determined, and according to the results the dimer conformations was analyzed with B3LYP/6-31+G(d,p) level of theory. Based on calculated energy differences, the C2 conformer is found to be most stable conformer. The hydrogen bonding between a hydroxyl group O@COH was determined as dimer structure. A complete vibrational analysis of H3BTC was performed on the basis of the SQM force field obtained by DFT calculation. The wavenumbers proposed by PED calculations are in fair agreement with the observed wavenumbers. The NBO analysis reveals the reasons for hyperconjugative interaction, ICT and stabilization of the molecule. The MEP map shows the negative potential sites are on oxygen atoms as well as the positive potential sites are around the hydrogen atoms. The correlations between the statistical thermodynamics and temperature are also obtained. It is seen that the heat capacities, entropies and enthalpies increase with the increasing temperature

References [1] T.R. Shattock, P. Vishweshwar, Z.Q. Wang, M.J. ZaworotkoCryst, Growth Des. 5 (2005) 2046. [2] J.M. Lehn, Supramolecular Chemistry, Wiley-VCH, Weinheim, 1995. pp. 271. [3] L.J. Atwood, J.E.D. Davies, D.D. MacNicols, F. Vögtle, J.M. Lehn (Eds.), Comprehensive Supramolecular Chemistry, Pergamon, New York, 1996. [4] M.C. Etter, Acc. Chem. Res. 23 (1990) 120–126. [5] R. Melendez, A.D. Hamilton, Top. Curr. Chem. 198 (1998) 97–129. [6] M. Bailey, C.J. Brown, Acta Crystallogr. 22 (1967) 325–387. [7] R. Alcala, S. Martinez-Carrera, Acta Crystallogr. B25 (1972) 1671–1677. [8] D.J. Duchamp, R.E. March, Acta Crystallogr. B25 (1969) 5–19. [9] M.J. Zaworotko, Chem. Commun. (2001) 1–9. [10] F.H. Herbstein, Top. Curr. Chem. 140 (1987) 107–129. [11] J.L. Atwood, D.D. MacNicol, F. Vögtle, J.M. Lehn (Eds.), Comprehensive Supramolecular Chemistry, Pergamon press, New York, 1996. vol. 6, p. 635. [12] F.H. Herbstein, M. Kapon, I. Maor, G.M. Reisner, In Compr. Supramol. Chem. Acta Crystallogr. B 37 (1981) 136. [13] S. De Feyter, A. Gasquiere, M. Klapper, K. Müllen, F.C. De Schryver, Nano Lett. 3 (2003) 1485–1488. [14] S.V. Kolotuchin, E.E. Fenlon, S.R. Wilson, C.J. Loweth, S.C. Zimmerman, Angew. Chem. Int. Ed. 34 (1996) 2654–2657. [15] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H.Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.Austn, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K.Morokuma, G.A. Voth, P.Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q.Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P.Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A.Nanayakkara, M. Challacombe, P.M.W. Gill, B.Johnson, W. Chen, M.W. Wong, C.Gonzalez, J.A. Pople, Gaussian Inc, Gaussian 03, Revision B.01, Pittsburgh, PA, New York, 2003. [16] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652. [17] C. Lee, W. Yang, G.R. Parr, Phys. Rev. B 37 (1998) 785–789. [18] B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 157 (1989) 200–206. [19] T. Sundius, J. Mol. Struct. 218 (1990) 321–326. [20] T. Sundius, Vib. Spectrosc. 29 (2002) 89–95. [21] Molvib (V.7.0), QCPE Program No. 807, 2002. [22] E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO version 3.1, TCI, University of Wisconsin, Madison, 1998. [23] J. Chocholousova, V. Vladimir, P. Hobza, Chem. Phys. 6 (2004) 37–41. [24] Marek Boczar, Lukasz Boda, Marek J. Wojcik, Spectrochim. Acta A 64 (2006) 757–760. [25] Y. Marechal, A. Witkowski, J. Chem. Phys. 48 (1968) 3697.

G. Mahalakshmi, V. Balachandran / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 535–547 [26] Z.H.U. Yulan, M.A. Feng, M.A. Kuirong, Licao, Lianhua Zhao, J. Chem. Sci. 123 (2011) 687–696. [27] Mehmet Karabacak, Mehmet Cinar, Sahin Ermec, Mustafa Kurt, J. Raman Spectrosc. 41 (2010) 98–105. [28] F.H. Allen, Acta Crystallogr. B58 (2002) 380–388. [29] A.E. Reed, L.A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988) 899–926. [30] T. Karthick, V. Balachandran, S. Perumal, A. Nataraj, J. Mol. Struct. 1005 (2011) 190–201. [31] L. Larabi, Y. Harek, O. Benali, S. Ghalam, Prog. Org. Coat. 54 (2005) 256–262. [32] I. Lukovits, I. Bako, A. Shaban, E. Kalman, Electrochim. Acta 43 (1998) 131–136. [33] R.G. Parr, L.V. Szentpaly, S. Liu, J. Am. Chem. Soc. 121 (1999) 1922–1924. [34] H.S. Randhawa, Modern Molecular Spectroscopy, First edition., Macmillan India Ltd., 2003. [35] J. Bevan Ott, J. Boerio-Goates, Calculations from Statistical Thermodynamics, Academic Press, 2000. [36] C.R. Zhang, H.S. Chen, G.H. Wang, Chem. Res. Chin. U20 (2004) 640–646. [37] Y. Sun, X. Chen, L. Sun, X. Guo, W. Lu, J. Chem. Phys. Lett. 381 (2003) 397–403. [38] O. Christiansen, J. Gauss, J.F. Stanton, J. Chem. Phys. Lett. 305 (1999) 147–155. [39] A. Kleinman, J. Phys. Rev. 126 (1962) 1977–1979.

547

[40] V.P. Gupta, A. Sharma, V. Virdi, V.J. Ram, Spectrochim. Acta Part A 64 (2006) 57–67. [41] K. Parimala, V. Balachandran, Spectrochim. Acta Part A 81 (2011) 711–723. [42] A. Frish, A.B. Neilson, A.J. Holder, GAUSSVIEW User Manual, Gaussian Inc., Pittsburgh, CY, 2009. [43] M. Silverstein, G. Clayton Basseler, C. Morill, Spectrometric Identification of Organic Compounds, Wiley, New York, 1981. [44] J. Baker, A.A. Jarzecki, P. Pllay, J. Phys. Chem. A 102 (1998) 1412–1424. [45] G. Socrates, Infrared Characteristic Group of Frequencies, Wiley, New York, 1980. [46] G. Varasanyi, Assignments of Vibrational Spectra of Seven Hundred Benzene Derivatives, Wiley, New York, 1974. [47] K. Akhbari, A. Morsali, J. Iran. Chem. Soc. 5 (2008) 48–56. [48] V. Krishnakumar, R. Mathamal, J. Raman Spectrosc. 40 (2009) 264–271. [49] M. Karabacak, J. Mol. Struct. 919 (2009) 215–222. [50] Y.R. Sharma, Elementary Organic Spectroscopy, ShobanLalNagin Chand & Company, Educational Publishers, New Delhi, 1980. [51] N.P.G. Roeges, A Guide to the Complete Interpretation of Infrared Spectra of Organic Structures, Wiley, New York, 1994.