Synthesis, crystal growth, characterization and theoretical studies of 4-aminobenzophenonium picrate

Accepted Manuscript Synthesis, crystal growth, characterization and theoretical studies of 4-aminobenzophenonium picrate A. Aditya Prasad, K. Muthu, M. Rajasekar, V. Meenatchi, S.P. Meenakshisundaram PII: DOI: Reference:

S1386-1425(14)01053-1 http://dx.doi.org/10.1016/j.saa.2014.06.154 SAA 12413

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

25 April 2014 16 June 2014 29 June 2014

Please cite this article as: A. Aditya Prasad, K. Muthu, M. Rajasekar, V. Meenatchi, S.P. Meenakshisundaram, Synthesis, crystal growth, characterization and theoretical studies of 4-aminobenzophenonium picrate, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa. 2014.06.154

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Synthesis, crystal growth, characterization and theoretical studies of 4-aminobenzophenonium picrate A. Aditya Prasad, K. Muthu, M. Rajasekar, V. Meenatchi, SP. Meenakshisundaram* Department of Chemistry, Annamalai University, Annamalainagar-608 002, India. ABSTRACT Single crystals of 4-aminobenzophenonium picrate (4ABPP) were grown by slow evaporation of a mixed solvent system methanol-acetone (1:1,v/v) containing equimolar quantities of picric acid and 4-aminobenzophenone. The proton and carbon signals are confirmed by nuclear magnetic resonance spectroscopy. The various functional groups present in the molecule are identified by FT-IR analysis. Optimized geometry, first-order molecular hyperpolarizability (β), polarizability (α), bond length, bond angles and excited state energy from theoretical UV were derived by Hartree–Fock calculations. The complete assignment of the vibrational modes for 4-aminobenzophenonium picrate was performed by the scaled quantum mechanics force field (SQMFF) methodology using potential energy distribution. Natural bond orbital (NBO) calculations were employed to study the stabilities arising from charge delocalization and intermolecular interactions of 4ABPP. The atomic charge distributions of the various atoms present in 4ABPP are obtained by Mulliken charge population analysis. The as-grown crystal is further characterized by thermal and optical absorbance studies. Keywords: Crystal growth, FT-IR spectroscopy, NMR, HOMO – LUMO, Hyperpolarizability

*

Corresponding author Tel: 0091-4144-221670 E-mail: [email protected]

2

1. Introduction Mulliken’s theory of charge transfer interactions between an electron donor and electron acceptor has been successfully applied to many interesting studies. These complexes have attracted great attention for nonlinear optical materials and electrical conductivities [1–6]. The bond between the donor and acceptor is formed by the interaction between the electron poor ring of the picric acid and electron rich ring of benzophenone. Picric acid also forms charge transfer complexes with pyridine [7], piperidine [8] and amines [9, 10]. The organic materials with benzophenone, which are of great applications for second and third order nonlinear optical properties due to their high nonlinearity with good electronic response. According to the concepts of the molecular and crystal technology, the organic molecules offer many possibilities to tailoring the substances with desired properties through optimization of the microscopic hyperpolarizabilities and the incorporation of the molecules in a crystalline lattice [11-16]. In the present work, we report the synthesis, crystal growth, spectral and thermal studies of 4-aminobenzophenonium picrate single crystal. To support experimental studies the theoretical studies such as FT-IR, UV-vis, mulliken charge transfer, hyperpolarizability, NBO, molecular electrostatic potential (MEP) are done using Hartree – Fock (HF) method with GAUSSIAN 09W program [17]. 2. Experimental procedure 2.1. Synthesis and growth 4ABPP was synthesized by mixing stoichiometric amounts of 4-aminobenzophenone (Sigma-Aldrich) and picric acid (Sigma-Aldrich) in an equimolar ratio 1:1 using chloroform as solvent (Scheme 1). The mixture was stirred at room temperature (~30 °C) for 3 h and the picrate

3

was formed as reddish-yellow color precipitate. The precipitate was collected from the filter, dried and purified by recrystallization using mixed solvent, methanol and acetone (1:1, v/v). O -

O

O

N+

-

O N+

+ HO

O

O

O

NH2

N

CHCl3

O

O

O

O-

+

N

+

O-

N+

-

O NH3

O

N+ O

Scheme 1 Recrystallized 4ABPP was dissolved in mixed solvent system (methanol:acetone, 1:1, v/v) and the solution warmed with constant stirring for an hour to avoid co-precipitation of multiple phases. Reddish-yellow rod-like crystals were grown by slow evaporation solution growth technique and the crystals were harvested after a period of 8-10 days. Photographs of 4ABPP are shown in Fig. 1. 3. Results and discussion 3.1. FT-IR To analyze the presence of functional groups, Fourier transform infrared spectrum (FT-IR) was recorded using AVATAR 330 FT-IR spectrometer by KBr pellet technique in the spectral range of 400–4000 cm-1 and wavenumbers of vibrational modes calculated by HF level with the basis set 6-31G(d,p) using GAUSSIAN 09W [17]. The vibrations are assigned with potential energy distribution by using VEDA program [18]. Most of the observed vibrational patterns coincide with theoretically calculated vibrational modes. The molecular structure of 4ABPP consists of 43 atoms showing total 129 normal modes of vibrations and 31 vibrational modes are assigned by using PED. The molecular conformation yielded by geometry optimization exhibits

4

no special symmetries. So the molecule belongs to the C1 point group. In our study frequencies were scaled by using scaled quantum mechanics [19], with scaling factor 0.98. The deviation from the experiments is less than 10 cm-1 with few exceptions. The N–H stretch lies in the spectral range experimentally around ~3066 cm-1 but theoretically calculated frequency is ~3099 cm-1 showing high intense peak and ~3751cm-1, ~3678 cm-1 also show N–H stretching. The H-N-H bending of the ammonium group is observed at ~1866 cm-1 and the calculated frequency

is

~1848

cm-1.

Two

N–C

stretching

vibrations

were

observed

at

~1284 and 796 cm-1 showing sharp intense peaks and exactly suits with theoretical values at ~1284 and 795 cm-1. Other theoretical and experimental vibrational frequencies are given in Table 1. Both experimental and theoretical spectra are shown in Fig. 2. 3.2. NMR spectral analysis 1

H and

13

C NMR spectra were recorded on BRUCKER AVIII 400 MHz NMR

spectrometer operating at 400.13 MHz for 1H and 100.61 MHz for

13

C using standard

parameters. 4ABPP is dissolved in 0.5 ml of CDCl3 solvent and TMS (tetramethylsilane) was used as an internal standard. 1

H NMR spectrum of 4ABPP is shown in Fig. 3a. The signal at 9.20 ppm, corresponds to

NH3 proton of the 4-aminobenzopenonium group. The multiplet appeared in the range 6.86–7.73 ppm, corresponds to eleven protons, due to aromatic protons of the 4ABPP molecule. The signal at 2.18 ppm is due to solvent (acetone) peak. 13

C NMR spectrum of 4ABPP is shown in Fig. 3b. The signal at 195.3 ppm is due to the

carbonyl carbon. The weak signal at 153.2, 147.8, 138.4 and 137.21 ppm are due to ipso carbon of the 4ABPP molecule. The aromatic carbons signals are appeared in the range of

5

115.5 – 132.7 ppm. The signals at 207.1 ppm (C=O) and 30.9 ppm (CH3) are due to solvent (acetone) peak. 3.3. Optical absorbance studies UV–vis spectrum of 4ABPP was recorded using UV–1650PC UV–vis spectrophotometer. It shows minimum absorption in the visible region. Experimentally by using ethanol as a solvent, a peak is observed at the wavelength of ~344 nm (Fig. 4a). To support experimental observations, the theoretical electronic excitation energies and oscillator strengths were calculated by the TD-HF method using GAUSSIAN 09W [17] program with basis set 6–31G(d,p). TD-HF method produces oscillator strength (f, 0.2401) and excitation energy about ~291 nm (Fig. 4b). 3.4. Thermal analysis The thermal behavior of 4ABPP was studied by the thermo gravimetric and differential thermal analyses using a NETZSCH STA 449 F3 thermal analyzer in nitrogen atmosphere (Fig. 5). It is clear that there is no physically adsorbed water in the molecular structure of the crystal. TG curve shows a single stage weight loss at ~210 °C due to decomposition of 4ABPP into fragments and its subsequent volatilization. 3.5. First-order molecular hyperpolarizability Calculations were performed by using Hartree–Fock method, a program package on a personal computer without any constraints on the geometry using 6-31G (d, p) as the basis set with GAUSSIAN VIEW 5.0 molecular visualization [20]. The calculated and first-order molecular hyperpolarizability (β) and dipolemoment (µ) of the specimen are 6.089 x 10-30 esu (> 19 times of urea, 0.3728x10-30 esu obtained by HF/6-31G(d,p)) and 14 D respectively (Table 2). The maximum β is due to the behavior of nonzero µ values. High beta value is a required property of

6

an NLO material. It is possible to sustain nonlinearity at the macro level by crystal designing using proper substituents. 3.6. NBO analysis NBO calculations are performed using NBO 3.1 program as implemented in the GAUSSIAN 09W [17] package using HF/6-31G(d,p) method. In order to understand various second order interactions between the filled orbital of one subsystem is a measure of the intermolecular delocalization or hyper conjugation. Interaction between both filled and virtual orbital spaces, information is correctly explained by the NBO analysis should enhance intra and inter molecular interactions. The second order Fock matrix was carried out to evaluate donor (i)– acceptor (j) that is donor level bands to acceptor level bonds interaction in the NBO analysis [21]. For each donor (i) and acceptor (j), the stabilization energy E(2) associates with the delocalization i → j is estimated as E(2) = ∆Eij = qiF(i,j)2 /(εj - εi) where qi is the donor orbital occupancy, εj - εi are diagonal elements and F(i,j) is the off- diagonal NBO Fock Matrix element. NBO analysis provides a best method for interaction among bonds and also provides the convenient basis for investigating charge transfer molecular systems [22, 23]. The larger E2 value the more intensive is the more donation tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system [24]. Delocalization of electron density between occupied Lewis type (bond or lone pair) NBO orbital and formally unoccupied (anti bond or Ryd-berg) non-Lewis NBO orbital correspond to a stabilizing donor–acceptor interaction. NBO analysis has been performed on the 4ABPP molecule at the HF/6-31G(d,p) level in order to elucidate, the intra molecular hybridization and delocalization of electron density within the molecule. The intramolecular hyperconjugative

7

interactions of π (C21-N24) orbital to σ*(C20-C21), π*(C21-N24) lead to strong stabilization energies of 38.06 kJ/mol and 38.86 kJ/mol, respectively. In case of σ (C5-C6) orbital to σ*(C1-N7) shows the stabilization energy of 6.45 kJ/mol. The most important interaction energy in this molecule is electron donating from LP(O31) to the antibonding acceptor RY*(N24) resulting less stabilization energy of 3.56 kJ/mol. The same LP(O31) with π*(C21-N24) leads to moderate stabilization energy of 1.29 kJ/mol. The maximum energy delocalization takes part in the π–π* transition. The E(2)values and types of the transition are shown in Table 3. 3.7. Molecular electrostatic potential The MEP is a plot of electrostatic potential mapped on the constant electron density surface displaying electrostatic potential (electron+nuclei) distribution. The different values of the electrostatic potential at the surface are represented by different colors, red represents regions of most negative electrostatic potential (preferred site for electrophilic attack), blue represents regions of most positive electrostatic potential (preferred site for nucleophilic attack) and green represents regions of zero potential. To predict reactive sites for electrophilic and nucleophilic attack for 4ABPP, the MEP at the HF/6-31G(d,p) method was mapped with the total density of the molecule. As can be seen in Fig. 6, red indicates the more electron rich and blue the more electron poor area. Furthermore, the polarization effect is clearly visible. The colour code of this map is in the range between -0.125 to 0.125. Molecular shape, size and dipole moments of the molecule provide a visual method to understand the relative polarity [25]. As can be seen from the MEP map of the molecule, the negative region is mainly localized from nitro and carbonyl group whereas the positive region lies in the 6 membrane aromatic ring system. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of 4ABPP are shown in Fig. 7. The frontier orbital gap facilitates in characterizing the

8

chemical reactivity and kinetic stability of the molecule. The red and green colors represent the positive and negative values for the wave function. The HOMO is the orbital that primarily acts as an electron donor and the LUMO is the orbital that mainly acts as an electron acceptor [26, 27]. The energy gap between HOMO (–0.3114 eV) to LUMO (0.0634 eV) of the molecule is about 0.3749 eV. The HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. Mulliken [28] has derived the wave functions for the ground state and excited states of the complex and the charge distribution over the atoms thus produces a way of examining the proton transfer process. The proton transfer occurs from picric acid to pyridine. The charge distributions calculated by the Mulliken method [29] for the equilibrium geometry of 4ABPP is given in Table 4. The charge distribution on the molecule has an important influence on the vibrational spectra. Optimized molecular structure and Mulliken charge transfer of 4ABPP are shown in Fig. 8. 4. Conclusions Reddish-yellow color rod-like crystals of 4-aminobenzophenonium picrate were grown from methanol and acetone (v/v, 1:1) solution by conventional slow evaporation solution growth technique. The product formation was confirmed by FT-IR and NMR spectral analyses. TG/DTA reveals thermal stability of the as-grown material. HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. The NBO analysis revealed that the π to σ* and π to π* interactions give the strongest stabilization to the molecular system. Mulliken charge transfer indicates the charge distribution over the atoms and it well explains the proton transfer process. The excitation energy and oscillator strength are calculated by time-dependent Hartree–Fock theory. The crystal cohesion is achieved by intermolecular hydrogen bonds between picrate anions and amino groups of 4-aminobenzophenone. High β

9

value, a required property for an NLO material is observed. Further work is in progress to sustain nonlinearity at the macro level. Acknowledgments The authors thank the University Grant Commission (UGC), New Delhi, for financial support through research grant No. 41- 270/2012 (SR), and A. A is grateful to UGC for a project fellowship. K.M. is thankful to CSIR, New Delhi, for the award of a senior research fellowship. Reference [1]

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P. Pulay, G. Fogarasi, G. Pongor, J.E. Boggs, A. Vargha, J. Am. Chem. Soc.105(1983) 7037.

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Figure captions Fig. 1. Photographs of as-grown 4ABPP crystals. Fig. 2. FT-IR spectra of 4ABPP (a) Experimental and (b) Theoretical. Fig. 3. (a) 1H and (b) 13C NMR spectra of 4ABPP. Fig. 4. UV-vis spectra of 4ABPP (a) Experimental and (b) Theoretical. Fig. 5. TG/DTA curve of 4ABPP. Fig. 6. Molecular surfaces obtained using HF/6-31G(d,p) level of 4ABPP. Fig. 7. HOMO-LUMO energy gap of 4ABPP. Fig. 8. (a) Optimized molecular structure and (b) Mulliken charge transfer of 4ABPP indicated by color.

13

Fig. 1

14

(a)

(b)

Fig. 2

15

(a)

(b)

Fig. 3

16

Absorbance

(a)

Wavelength (nm)

(b)

Fig. 4

17

Fig. 5

18

Fig. 6

19

Fig. 7

20

(a)

(b)

Fig. 8

21

Table 1 Comparison of the experimental and calculated vibrational spectra and proposed assignments of 4ABPP. Experimental Mode Calculated wavenumbers(cm-1) Vibration assignments with PED wavenumbers no. Hf/6-31g(d,p) (≥10%) (cm-1) Frc FT-IR IIR Unscaled Scaled consts. 1 4.39334 3751.51 3676.48 9.0631 νNH (94) 2 6.81927 3678.34 3604.77 8.4223 νNH (38) 3 3543.3 0.826758 3438.17 3369.41 7.6149 νCH (51) + νCH(48) 4 0.626837 3430.12 3361.52 7.5826 νCH (48) + νCH(51) 5 3066 100 3099.46 3037.47 6.1456 νNH (56) 6 1983.96 12.5405 1956.76 1917.62 29.0615 νOC (89) 7 72.7327 1913.06 1874.8 26.2434 νOH (59) 8 1866.17 4.72335 1848.99 1812.01 2.2526 δHNH(57) 9 1629.05 9.81881 1645.34 1612.43 21.5001 νON(44) 10 36.4238 1609.8 1577.6 17.6506 νON(22) 11 4.5686 1606.77 1574.63 3.3323 δHCC(35)+νCC(17) 12 1597.71 1.61062 1580.22 1548.62 3.7871 δHCC(35) 13 1571.38 3.36856 1578.05 1546.49 7.4852 δHCC(34)+νCC(19) 14 1543.17 8.3809 1499.26 1469.27 4.5273 δHCC(16)+δHCC(18) 15 1506.59 42.5006 1496.58 1466.65 6.6362 νON(30) 16 1449.01 0.778937 1469.28 1439.89 1.7163 δHCC(58)+δHCC(15) 17 1362.51 0.675592 1348.03 1321.07 1.9411 δHCC(14)+δHCC(13) +δHCC(31)+νCC(15) 18 1324.26 1.1552 1337.82 1311.06 2.7476 δHCC(24)+νCC(23)+ νCC(12) 19 1284.91 0.506905 1284.3 1258.61 2.9031 δHCC(18)+ νCC(23)+ νCC(10)+νNC(36) 20 1202.9 4.7895 1202.35 1178.3 1.5381 δHCC(13)+δHCC(19)+ νCC(11)+ νCC(13) 21 1081.48 0.160873 1089.81 1068.01 4.0936 νCC(34)+νCC(23)+ νCCC(22) 22 975.88 1.34531 974.761 955.266 0.7655 τHCCC(18)+ τHCCC(19) +τHCCC(27) 23 959.57 0.934728 967.126 947.783 0.7414 τHCCC(14)+ τHCCC(43) 24 930.64 0.146519 938.433 919.664 0.8079 τHCCC(36)+ τHCCC(26)+ νON(10)+ δONO(59) 25 910.55 2.54593 912.861 894.604 5.2096 ϒOCON(34)+ϒOCCC(15) 26 844.13 1.60699 836.895 820.157 3.8408 ϒOCON(18)+ϒOCCC(40) 27 3.73457 818.54 802.169 0.777 τHCCC(10)+τCCCC(10)+ ϒOCCC(17) 28 796.38 2.60074 795.8 779.884 4.3813 νNC(12)+ δONO(40)+ δCCC(22) 29 740.66 0.948404 745.8 730.884 1.3856 τCCCC(11)+ ϒOCCC(40) 30 0.594829 730.059 715.458 2.2192 δOCC(16)+ δONC(11) +δNCC(12) 31 704.73 0.258192 694.909 681.011 1.8936 δCCC(38)+ δCCC(26)

22

ν –stretching, ϒ–out of plane bending, δ– in plane bending, τ– torsion IIR –IR intensity (K m mol–1)

Table 2 The calculated β components, βtot value (esu) and dipolemoment (µ , D) of 4ABPP. βxxx

586.386

βxxy

-422.923

βxyy

-341.94

βyyy

965.079

βxxz

289.464

βxyz

-184.04

βyyz

-30.766

βxzz

146.37

βyzz

-57.75

βzzz

64.316

βtot(×10-30)

6.089

µ

14.006

23

Table 3 Second-order perturbation theory analysis of Fock matrix in NBO basis for 4ABPP. Donor (i)

ED(i)(e)

Acceptor (j)

ED(j)(e)

σ (C1-C2) σ (C1-N7)

1.97763 1.98984

σ (C2-C3)

1.97623

σ (C4-C5)

1.97589

σ (C5-C6) σ (C10-C12)

1.97704 1.97467

σ (C17-C18)

1.97394

σ (C18-C19)

1.97531

σ (C19-N23)

1.98817

σ (C20-C21)

1.97375

π (C20-O22)

1.98384

σ (C21-N24)

1.98769

π (C21-N24)

1.63099

σ (N23-O26)

1.99526

LP (N7)

1.64296

LP (O29) LP (O30) LP (O31)

1.98169 1.96833 1.93289

σ*(C1-C6) RY*(C2) σ*(C5-C6) RY*(1)C1 σ*(C1-N7) RY*(C3) σ* (C3-C4) σ* (C1-N7) σ* (C10-C11) σ* (C12-C14) RY*(1)C16 σ* (C19-N23) σ* (N25-O28) RY*(1)C17 RY*(2)C17 σ*(N23-O26) RY*(C18) RY*(C20) RY*σ C 16 σ* (C20-O22) σ* (C21-N24) π*(C18-C19) π*(C21-N24) RY*(1)C16 σ* (C19-C20) σ* (C20-C21) π* (C21-N24) RY* (C19) RY* (C19) LP* (H36) RY*(H37) RY* (N25) RY* (N24) RY* (N24) π* (C21-N24)

0.02046 0.00563 0.01184 0.00513 0.02321 0.00634 0.0196 0.02321 0.02056 0.01304 0.00642 0.07008 0.04139 0.00806 0.00753 0.04838 0.00544 0.01695 0.00642 0.00627 0.05191 0.19784 0.66773 0.00526 0.05505 0.05826 0.66773 0.00714 0.00688 0.46645 0.0073 0.0176 0.01487 0.01487 0.66773

E(2)kJ mol 5.76 1.08 1.53 3.1 6.27 0.66 4.61 6.45 5.14 3.09 0.99 5.28 2.84 2.14 1.54 2.52 1.11 1.35 1.86 1.24 0.63 4.46 4.01 1.27 0.91 38.06 38.86 0.85 1.18 0.68 0.78 7.11 3.97 3.56 11.97

E(j)-E(i) a.u 1.79 2.46 1.89 2.15 1.46 2.39 1.77 1.47 1.75 1.78 1.97 1.5 1.66 2.42 2.4 1.71 1.92 1.74 1.92 1.78 1.52 0.68 0.45 2.55 1.84 0.6 0.36 2.78 2.71 3.19 3.12 2.47 2.21 2.27 1.13

F(i,j)a.u 0.091 0.046 0.048 0.073 0.085 0.036 0.081 0.087 0.085 0.066 0.04 0.08 0.062 0.064 0.054 0.059 0.041 0.044 0.054 0.042 0.028 0.052 0.046 0.051 0.037 0.138 0.114 0.044 0.05 0.046 0.048 0.118 0.084 0.081 0.104

24

a

ED is the occupation number. E is the energy of hyperconjugative interactions. c Energy difference between donor and acceptori andj NBO orbitals. d F(i, j) is the Fock matrix element betweeni andj NBO orbitals. b (2)

25

Table 4 Mulliken charge population [HF, 6-31G (d, p)] of 4ABPP. Atom number

Atom

Mulliken charge/e

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

C C C C C C N C O C C C C C C C C C C C C O N N N O O O O O O H H H H H H

0.114491 -0.13092 -0.13685 -0.11583 -0.11278 -0.15048 -0.74016 0.551734 -0.56666 -0.1387 -0.1446 -0.10792 -0.16613 -0.16197 -0.13078 0.01198 0.040515 0.00349 0.006782 0.622775 0.004239 -0.61811 0.491651 0.438588 0.490104 -0.44816 -0.46186 -0.47981 -0.46836 -0.54833 -0.48846 0.249994 0.219897 0.212777 0.173718 0.366879 0.370356

26

38 39 40 41 42 43 44 45

H H H H H H H H

0.498987 0.193015 0.191475 0.195407 0.158325 0.163421 0.27094 0.275346

27

Graphical abstract

28

Research highlights


Synthesis and characterization of a new organic picrate is reported
Picrate formation was confirmed by FT-IR and NMR spectral studies
HOMO and LUMO energy gap explains the eventual charge transfer interactions
First-order molecular hyperpolarizability is estimated.