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Eco-friendly synthesis, crystal structures, photophysical properties and DFT studies of new N-arylthiazole-5-carboxamides
Journal of Molecular Structure 1184 (2019) 193e199
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Eco-friendly synthesis, crystal structures, photophysical properties and DFT studies of new N-arylthiazole-5-carboxamides Jeevanreddy Miryala a, Anuj Tripathi b, Chetti Prabhakar b, Debajit Sarma c, Someshwar Pola a, **, Battu Satyanarayana a, * a b c
Department of Chemistry, Osmania University, Hyderabad, 500001, India Department of Chemistry, National Institute of Technology, Kurukshetra, India Department of Chemistry, Indian Institute of Technology Patna, Patna, 801103, Bihar, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 November 2018 Received in revised form 27 January 2019 Accepted 6 February 2019 Available online 8 February 2019
In this communication, we account the synthesis, spectroscopic, crystal structure, and photophysical and DFT studies of N-phenylthiazole-5-carboxamide derivatives. Synthesis of N-arylthiazole-5carboxamideswas obtained using eco-friendly conditions. Two compounds were synthesized with high yield under eco-friendly conditions. The conformed spectral data were reliable with the chemical structures of 2-bromo-4-methyl-N-arylthiazole-5-carboxamides. The single crystal study additionally endorses its three-dimensional structure, molecular shape, hydrogen bonding and the nature of short contacts. The crystal structure reveals that arylthiazole-5-carboxamides retains a non-planar structure with two crystals have shifted packing within the crystal unit. Its computed photophysical properties also in good agreement with the experimental findings. Moreover, UVevisible and fluorescence spectral studies evidence that the compound exposes proper absorption and fluorescence properties. © 2019 Elsevier B.V. All rights reserved.
Keywords: Eco-friendly synthesis N-phenylthiazole-5-carboxamide Single crystal DFT studies
1. Introduction Thiazole moiety is a very useful structural unit that is frequently found in various pharmaceuticals and functional materials [1e6]. Thiazole derivatives also play a vital role in the biochemistry of life; for example nutrients like vitamin B1 (thiamine) [7] which contain thiazolium ring are essential for fundamental process. Compounds containing thiazole skeleton have also been developed as antimicrobial (e.g., sulfathiazole), antifungal (ritonavir), and abafungin (antineoplastic) (Fig. 1). Moreover, thiazoles have extensive usage in flavoring, perfume and agrochemical industries. Apart from the significant biological activity, thiazolic derivatives have interesting electronic and optical properties [8,9]. Thiazoles based materials are frequently used in inorganic chemistry for constructing polydentate ligands [10]. Thiazoles are excellent systems which contribute significantly towards supramolecular chemistry by exhibiting polymorphism [11e14], specific material properties in confined medium and flexible self-
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (S. Pola), [email protected] (B. Satyanarayana). https://doi.org/10.1016/j.molstruc.2019.02.025 0022-2860/© 2019 Elsevier B.V. All rights reserved.
assemblies. Natural as well as synthetic thiazole peptides have well-known pharmacological and metal binding properties [15]. Thiazole moiety turns out to be a relatively dependable scaffold for hydrogelation [16]. Thiazole containing colorimetric and ratiometric receptors are very common in excited-state intramolecular proton transfer (ESIPT), fluorescence resonance energy transfer (FRET) and internal charge transfer (ICT)mechanism [17e19]. Thiazole-based receptors can be utilized to sense several kinds of metal cations such as carbazoles included thiazole is a chemosensor for Zn2þ [20]. Thiazoles being exciting and stable n-type organic heterocyclic semiconductor system, has fascinated several researchers as a new conjugated small molecule system [21e26]. Even though, thiazole is a highly electron-deficient heterocycle, it communicates good electron transporting facility and carries excellent photosensitive properties when it exists in donor and acceptor (DA) type conjugated systems. Further, the area of thiazole has been immensely significant because of its high chemical as well as thermal stability. In conclusion, the presence of highly electron withdrawing amide substituent on the thiazole ring can help to promote its electron-transporting nature [27]. Given the practical fact that N-phenylthiazole-2-carboxamide scaffold is an attractive system for good photophysical properties, several derivatives of the same also exhibited good photochemical and thermal stability [28],
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Fig. 1. Biologically active Thiazoles.
high luminescence efficiency and novel optoelectronic properties [29]. Also, it was reported that insertion of an electron withdrawing N-phenylthiazole-2-carboxamide moiety in a DA type molecular network lowers its band gap [30]. Therefore, it is necessary to research further on novel thiazole derivatives under eco-friendly condition. It is well-known that polyethylene glycol (PEG), as one of the non-hazardous alternatives of currently used organic solvents, has some excellent characteristics. Given multiple applications of thiazole moiety, in this work N-arylthiazole-5-carboxamide has been synthesized under eco-friendly condition. 1.1. Experimental details 1.1.1. Materials and measurements All the chemicals are purchased from Sigma-Aldrich, India and without further purification directly used for the synthesis of new compounds. 1.2. Experimental procedure Synthetic procedure for N-phenylthiazole-5-carboxamide (3). To the solution of compound 1 (1.0eq, 0.001 mol) in PEG-400, HATU (1.2eq, 0.0012 mol) was added and stirred for 15 min. The aniline 2 (1.0eq) and DIPEA (3.0eq) were further added and the reaction continued for 10 h. TLC was used to monitor the reaction progress until the starting compounds completely disappeared. After completion, reaction mixture was diluted with water and the desired compound was extracted using ethyl acetate. The crude products were purified by using column chromatography technique with ethyl acetate and n-hexane (3:7). The organic fraction was concentrated by evaporating solvent under reduced pressure to obtain pure compounds 3a and 3b with 85 and 78% yield respectively (shown in Scheme 1). Crystals of the compound 3a and 3b were obtained from ethyl acetate by diffusion method.
Scheme 1. Synthesis of new N-phenylthiazole-5-carboxamides.
2-bromo-4-methyl-N-(p-tolyl) thiazole-5-carboxamide (Compound 3a). Off-white crystalline solid (85%); m. p 130e132 C; 1H NMR (400 MHz, CDCl3) d 7.40 (d, J ¼ 8.4 Hz, 2H), 7.16 (d, J ¼ 8.2 Hz, 2H), 2.72(s, thiazole-CH3), 2.34 (s, Ar- CH3), (s, 3H); 13C NMR (100.1 MHz, CDCl3) d 158.56, 155.20, 136.87, 135.17, 134.37, 129.74, 120.62, 20.96, 17.34; ESI-MS m/z 311 [Mþ1], 313 [Mþ3], 333 [MþNa]. 2-bromo-N-(3,5-dimethylphenyl)-4-methylthiazole-5carboxamide (Compound 3b). White solid (77%); m. p 143e147 C; 1H NMR (400 MHz, CDCl3) d 7.39(br, NH) 7.16 (s, 2H), 6.82 (s, 1H), 2.72(s, CH3), 2.31(s, 2CH3); 13C-NMR (100.1 MHz, CDCl3) d 159.53, 158.54, 155.19, 139.02, 136.88, 136.78, 130.68, 127.07, 118.21, 21.36, 17.31; ESI-MS m/z 325 [Mþ1], 327 [Mþ3], 347 [MþNa]. 1.3. Characterization of compounds Mass spectral data was collected by HR-EI systems on JMS-700 double focusing mass spectrometer (JEOL, Tokyo, Japan). NMR spectra was recorded on a Bruker AV400 MHz spectrometer with chemical shifts referenced using the 1H resonance of residual d6DMSO. Melting points were verified on a Cintex apparatus. The electronic spectra was obtained in various solvents on a JASCO V650 UVeVis spectrophotometer. FT-IR spectra were recorded using Shimadzu spectrometer in the form of KBr pellets with 4 cm1 resolution. 1.4. Single crystal structure determination A suitable single crystal of each compound was carefully selected under a polarizing microscope and glued to a crystal mounting loop with paratone oil. The single crystal data were collected on a BRUKER AXS (D8 Quest System) X-ray diffractometer equipped with PHOTON 100 CMOS detector at 293 (2) K. The X-ray generator was operated at 50 kV and 30 mA using Mo Ka (l ¼ 0.71073 Å) radiation. The unit cell measurement, data collection (4 and u scan), integration, scaling and absorption corrections for the crystals of both complexes was done using Bruker Apex II software [31]. The data was collected with u scan width of 0.5 . Sufficient numbers of frames were collected for different sets of 4 keeping the sample-to-detector distance fixed. The data was reduced using SAINTPLUS [32], and an empirical absorption correction was applied using the SADABS program [33]. The structure was solved and refined using SHELXL97 [34] present in the WinGx suit of programs (Version 1.63.04a) [35]. All the hydrogen positions were initially located in the difference Fourier maps, and for the final refinement, the hydrogen atoms were
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Table 1 Crystal and structure refinement data for compounds (3a & 3b). Identification code
P-01 (compound 3a)
P-02 (compound 3b)
Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
C12H11BrN2OS 311.20 293 K 0.71073 Å Orthorhombic pca21 a ¼ 16.1141 (10) Å a ¼ 90 b ¼ 8.3104 (5) Å b ¼ 90 c ¼ 20.0643 (14) Å g ¼ 90 2686.9 (3) Å3 8 1.539 Mg m3 0.088 mm1 1248 0.20 0.15 0.10 mm3 2.7 to 25.1 h ¼ 18 / 19, k ¼ 9/9, l ¼ 23 / 23 43282 4763 100% Semi-empirical from equivalents 0.9838 and 0.9788 Full-matrix least-squares on F2 0.082 R1 ¼ 0.028, wR2 ¼ 0.058 R1 ¼ 0.040, wR2 ¼ 0.082 0.00161 (17) 0.37 and 0.44 e Å3
C13H13BrN2OS 325.245 293 K 0.71076 Å Monoclinic P 21/C a ¼ 21.693 (4) Å a ¼ 90 b ¼ 8.007 (2) Å b ¼ 98.96 c ¼ 7.975 (2) Å g ¼ 90 1368.4 (5) Å3 1 1.579 Mg m3 0.091 mm1 656 0.24 0.16 0.13 mm3 2.7 to 25.1 h ¼ 24 / 24, k ¼ 8/8, l ¼ 8/8 17282 1997 100% Semi-empirical from equivalents 0.9182 and 0.9242 Full-matrix least-squares on F2 0.083 R1 ¼ 0.022, wR2 ¼ 0.053 R1 ¼ 0.036, wR2 ¼ 0.082 0.00182 (19) 0.43 and 0.45 e Å3
Volume Z Density (calculated) Absorption coefficient F (000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta ¼ 25.00 Absorption correction Max. and min. transmission Refinement method Goodness-of-fit on F2 Final R indices [I > 2 sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole
located in geometrically ideal positions and refined in the riding mode. Final refinement included atomic positions for all the atoms, anisotropic thermal parameters for all the non-hydrogen atoms, and isotropic thermal parameters for all the hydrogen atoms. Fullmatrix least-squares refinement against jF2j was carried out using the WinGx package of programs [35]. Details of the structure solution and final refinements for the compounds are given in Table 1 and S1-S6. CCDC: 1871377e1871378 contains the crystallographic data (compounds 3a and 3b) for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Center (CCDC) via www.ccdc.cam.ac.uk/data_request/cif.
carboxamide is illustrated in Scheme 1. N-phenylthiazole-5carboxamide (3) had a good yield when 2-bromo-4methylthiazole-5-carboxylicacid (1) was treated with aromatic aniline (2) at room temperature in the presence of HATU, DIPEA, and PEG-400 as a solvent. Further, its chemical structure was established by using mass, FTIR, and NMR spectral analysis. The three-dimensional structure was confirmed for the compounds 3a and 3b with the support of single crystal X-ray diffractometer. (CCDC 1871377e1871378).
1.5. Results and discussion
The structure of compound N-phenylthiazole-5-carboxamide was established by HRMS, FTIR, 1H and 13CNMRspectroscopic techniques. Its FTIR spectrum reveals two strong IR absorption
The synthetic route for the preparation of N-phenylthiazole-5-
1.6. Spectroscopic properties
Fig. 2. Packing cell units and crystal structures of Compound 3a and 3b
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Fig. 3. Molecular plane image of compound 3a and 3b
Table 2 Polarity, Absorption (labs), emission (lem) and Stoke shift values of compound 3a and 3b in different solvents. Solvent
Polarity
labs (nm)
lem (nm)
3a
3b
3a
3b
3a
3b
Hexane CHCl3 EA THF CH3OH CH3CN DMF DMSO
0.08 1.15 1.88 1.75 2.87 3.44 3.86 4.10
286.9 288.3 286.1 301.5 282.1 281.6 287.1 283.5
280.5 278.2 282.5 293.4 271.5 285.0 285.3 283.1
399.0 412.4 404.5 407.5 403.0 399.5 451.0 401.5
400.6 411.5 405.5 413.2 402.0 399.0 398.2 402.5
113.9 124.1 118.4 106.0 120.9 117.9 163.9 118.0
120.1 133.3 123.0 119.8 130.5 114.0 112.9 119.4
established by mass spectral analysis, and the experimentally obtained mass peaks at 309.977 (M)þ and 311.197 (Mþ2)þ coincided with that of the calculated mass (Fig. S3).
Stroke shift (nm)
bands at 2928 and 2851 cm1that indicates asymmetric and symmetric CeH stretching vibrations of methyl group compound 3b (Fig. S1). Additionally, an active IR absorption band at1644 cm1 indicates the presence of the amide group in its molecular structure. In compound 3a and 3b, in its 1H NMR spectra (Fig. S2) one proton exhibits unique resonances at 7.39, and 7.16 ppm for other protons of aromatic moieties. The appearance of a broad singlet at 7.41 ppm is for one proton of the amide group. Also, three types of singlet were observed with two singlets at 2.72 and 2.34 ppm for two magnetically different methyl groups. Finally, its structure was
1.6.1. Crystal structures of compound 3a and 3b The compound 3a crystalline in orthorhombic with space group pca21 with a ¼ 16.114 (10) Å, b ¼ 8.310 (5) Å, c ¼ 20.064 (14) Å and ֯a ¼ b ¼ g ¼ 90 and the compound 3b crystalline in monoclinic space group P21/C with a ¼ 21.693 (4) Å, b ¼ 8.007 (2) Å, c ¼ 7.975 (2) Å and b ¼ 98.96 (3) (Table 1). Fig. 2 reveals the characterized ORTEP diagram of the compound 3a and 3b. In Fig. 2, the two rings are well-known for tagging with alphabets ‘A’, and ‘B’. This tagging is valuable for describing the intermolecular interactions in the difficult steps. Nevertheless, from the X-ray analysis data, it is noticeable that the molecule is not planar but shifted. Interestingly, the 4-methylphenyl and thiazole ring bridging of amide group at the position-5 of the thiazole ring. Further, bond length and bond angle values were all within the range, as presented in Table S1-S6 [36]. From the data of Table S1, it is observed that CeC, CeN and CeO bond length values in the two-ring system are holding amide group and intermolecular hydrogen bonding, which indicates that the non-bonding electrons of amide group of compounds are involved in delocalization. When compared two crystal planes, in the case of compound 3a two molecular units are present whereas compound 3b is with a single molecule on the plane and shown in Fig. 3. The plane passing through the compound 3a indicates that
Fig. 4. Absorption spectra of compounds 3a and 3b in various solvents (105 M).
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Fig. 5. Emission spectra of compounds 3a and 3b in various solvents (106 M).
the packing arrangement.
of
molecules
are
in
anti-cofacial
molecular
1.6.2. Photophysical properties To study the photophysical properties of synthesized compounds UV visible absorption and emission spectra were collected. The absorption and emission spectra for compounds 3a and 3b were measured in different solvents n-hexane, chloroform (CHCl3), tetrahydrofuran (THF), methanol (MeOH), ethyl acetate (EA), acetonitrile (CH3CN), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) with dilute concentration of 105 M to study its photophysical properties. These solvents were designated on the basis of the enhanced order of their polarity not depends on the dielectric constant values due to the interaction between solvents compounds 3a and 3b. The solvent polarity, absorption, emission spectral data and stroke shifts are presented in Table 2. Figs. 4 and 5 shows the UVevisible absorption and emission spectra in different solvents, respectively. In its absorption spectra, the compound exhibited one strong absorption band in UV region both in polar and non-polar solvents. Both the compounds are showing a strong absorption band in the range of 275 nm and 300 nm and are recognized due to a p/p* electronic transition. From Table 2, with change of solvent from low polarity (hexane) to high polarity (DMSO) there is negligible change in spectral shift of few nm. For compound 3a, observed absorption is at 301 nm in THF while on increasing the polarity of the solvent it shows a small blue shift (~15 nm) in DMSO (283 nm). Similar is the case for compound 3b here 10 nm blue shift was observed on the increasing polarity of solvent from THF (293 nm) to DMSO (283 nm). In its emission spectra, an intense blue emission band appearing between 375 nm and 475 nm has been perceived under their excitation wavelengths. Akin to absorption spectra, the fluorescence spectra of compounds 3a and 3b revealed considerably higher solvatochromic effects. There is a substantial change in emission maxima with the deviation of solvent systems from non-polar (hexane) to highly polar (EA) solvent with a Stokes shift of 50 nm. Moreover, a significant red shift of emission was observed, which is recognized by the improved interaction between the fluorescent molecule and a nonpolar solvent. However, in the case of methanol, no such observation was made because of its weak interactions with the chromophore. Also, the material was originated to be blue fluorescent under a UV lamp (l ¼ 375 nm). The quantum yields for the compounds 3a and 3b were calculated in two different solvents by using anthracene as a standard reference (frMeOH ¼ 0.2 and frCHCl3 ¼ 0.11) [37]. The quantum yields of the compounds 3a and
3b are 0.22 and 0.33 in methanol, whereas in the chloroform the quantum yields are 0.12 and 0.18 respectively. Lifetime decay of the compounds 3a and 3b are shown in Fig. 6. 1.7. Theoretical studies The synthesized molecules have been optimized with the help of Gaussian 09 software [38,39] using B3LYP functional with 6311 þ G (d, p) basis set. Further, these optimized structures are without imaginary frequencies and hence are characterized as true minima on potential energy surface. To predict the absorption maxima of the molecules, the lowest five excitations were calculated using TDDFT methodology using a long-range CAM-B3LYP function with 6-311 þ G (d, p) basis set. Further, different functionals were considered (B3LYP, M06, and WB97XD) to calculate absorption maxima to check whether there is any change in absorption with functionals. While B3LYP and M06 overestimated the absorption maxima, but long-range functional CAM-B3LYP and WB97XD are in good agreement with the experimental result (Table S7). In addition to this, solvent effect for all the molecules was also carried out by using the IEFPCM method at the same level of theory. Here in computational calculations same solvents which are experimentally reported were used i.e. n-hexane, chloroform
Fig. 6. Life-time decay pattern of compound 3a and 3b in THF (106 M).
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Table 3 Comparison of bond lengths (BL) and bond angles (BA)for molecules 3a and 3b with their crystal structure and optimized geometry structure..
BL Br1eC13 C13eS2 C13eN4 N4eC11 C11eC14 C11eC24 C14eS2 C14eC12 C12eO3 C12eN5 N5eC21 C21eC9 C21eC15 C15eC22 C22eC6 C6eC7 C6eC17 C7eC9 BA C13S2C14 C14C12N5 C12N5C21 C14C12N5C21
Crystal structure
Optimized structure
1.851 1.681 1.279 1.309 1.388 1.490 1.744 1.456 1.215 1.327 1.360 1.442 1.401 1.452 1.321 1.343 1.568 1.364
1.891 1.742 1.285 1.383 1.376 1.496 1.759 1.490 1.221 1.376 1.414 1.401 1.399 1.393 1.397 1.399 1.509 1.388
88.5 117.9 132.8 176.5
88.1 114.5 128.8 177.5
Table 3 (continued ) C11eC10 C10eC8 C7eC8 C5eC7 C7eC13 C10eC17 BA C28S2C22 C22C21N29 C21N29C4 C22C21N29C4
1.379 1.370 1.370 1.374 1.505 1.507
1.301 1.393 1.398 1.401 1.510 1.510
88.4 115.2 125.6 176.6
88.1 114.5 129.1 177.4
(CHCl3), tetrahydrofuran (THF), methanol (MeOH), ethyl acetate (EA), acetonitrile, dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) and was observed no change in absorption maxima with the change in solvents (Table S8). For a better understanding of the geometries of molecules, the bond lengths and bond angles of the optimized structure were compared with their crystal structure which are tabulated in Table 3. As observed in Table 3, there is negligible difference in calculated and experimental parameters. The experimentally reported absorption maxima for molecule 3a is at 287 nm in CHCl3. From TDDFT calculations, observed absorption maxima for 3a is at 274 nm which is in good agreement with the experimentally measured absorption energy. The major transition, in this case, is from H/L and oscillator strength corresponding to this transition is 0.558. Beside this, there are some minor transitions which are arising from H-1/L and H3/L. For molecule 3b, observed absorption maximum is at 279 nm. TDDFT calculated results are in accordance with the experimental result (272 nm). Unlike 3a, molecule 3b shows one major transition which is from H/L and one minor transition from H-2/L with oscillator strength 0.510. In Table 4 the absorption maxima oscillator strength, major transitions and % contribution were tabulated. From pictures of frontier molecular orbitals (FMOs), it is observed that charge transfer is taking place from sixmembered benzene ring to five-membered thiazole ring (Table 5). In molecule 3a, HOMO is showing higher electron density localized at six-membered benzene ring while in LUMO electron density shifts to five-membered thiazole ring. Further, the non-covalent and supramolecular interaction studies of 3a and 3b co-crystals with carboxylic acid, selenic acid, and different anions are under progress.
2. Conclusion
BL Br1eC28 C28eS2 C28eN31 N31eC23 C23eC22 C23eC24 C22eS2 C22eC21 C21eO3 C21eN29 N29eC4 C4eC11 C4eC5
Crystal structure
Optimized structure
1.857 1.702 1.290 1377 1.349 1.487 1.719 1.484 1.218 1.330 1.421 1.373 1.376
1.892 1.742 1.285 1.383 1.376 1.496 1.759 1.490 1.221 1.376 1.414 1.394 1.404
Here in this article, eco-friendly synthesis of two new N-phenylthiazole-4-carboxamides 3a and 3b were successfully synthesized using a simple way and thoroughly characterized with spectral methods. Its single crystal and DFT study exposed the presence of the non-planar structure. Theoretically calculated UV absorption bands coincide with that of the experimental values.
Table 4 Experimental (lexpin nm) and theoretical absorption (lcalin nm), Oscillator strength (f), Major transitions (MT) and % contribution calculated at Cam-B3LYP/6-311 þ G (d, p) level of theory for B3LYP/6-311 þ G (d, p) optimized geometries. Name
lcal
lexp
f
MT
%Ci
3a
274
287
0.558
3b
272
279
0.510
H/L H-1/L H-3/L H/L H-2/L
70 17 3 65 20
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Table 5 Frontier molecular orbitals (FMOs) calculated at B3LYP/6-311 þ G (d, p) level.
Moreover, its photophysical properties specify that it is a suitable absorbent and fluorescent materials with positive solvatochromic performance in various solvents. From the outcomes, it can be determined that compound 3a and 3b are capable materials for their applications in small molecular electronic device applications. Acknowledgment Authors would like to thank DST - FIST schemes and CSIR, New Delhi. Mr. Jeevanreddy Miryala thanks, Council of Scientific & Industrial Research (CSIR), New Delhi for the award of Senior Research Fellowship. SP is expressly thankful for sanctioned UGCSERO, Hyderabad, India. CP thanks to CSIR - New Delhi, India for financial support. Authors also thank Dr. Avijit Kumar Paul, NIT Kurukshetra for helping in the refinement of crystal data. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.02.025.
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Eco-friendly synthesis, crystal structures, photophysical properties and DFT studies of new N-arylthiazole-5-carboxamides Jeevanreddy Miryala a, Anuj Tripathi b, Chetti Prabhakar b, Debajit Sarma c, Someshwar Pola a, **, Battu Satyanarayana a, * a b c
Department of Chemistry, Osmania University, Hyderabad, 500001, India Department of Chemistry, National Institute of Technology, Kurukshetra, India Department of Chemistry, Indian Institute of Technology Patna, Patna, 801103, Bihar, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 November 2018 Received in revised form 27 January 2019 Accepted 6 February 2019 Available online 8 February 2019
In this communication, we account the synthesis, spectroscopic, crystal structure, and photophysical and DFT studies of N-phenylthiazole-5-carboxamide derivatives. Synthesis of N-arylthiazole-5carboxamideswas obtained using eco-friendly conditions. Two compounds were synthesized with high yield under eco-friendly conditions. The conformed spectral data were reliable with the chemical structures of 2-bromo-4-methyl-N-arylthiazole-5-carboxamides. The single crystal study additionally endorses its three-dimensional structure, molecular shape, hydrogen bonding and the nature of short contacts. The crystal structure reveals that arylthiazole-5-carboxamides retains a non-planar structure with two crystals have shifted packing within the crystal unit. Its computed photophysical properties also in good agreement with the experimental findings. Moreover, UVevisible and fluorescence spectral studies evidence that the compound exposes proper absorption and fluorescence properties. © 2019 Elsevier B.V. All rights reserved.
Keywords: Eco-friendly synthesis N-phenylthiazole-5-carboxamide Single crystal DFT studies
1. Introduction Thiazole moiety is a very useful structural unit that is frequently found in various pharmaceuticals and functional materials [1e6]. Thiazole derivatives also play a vital role in the biochemistry of life; for example nutrients like vitamin B1 (thiamine) [7] which contain thiazolium ring are essential for fundamental process. Compounds containing thiazole skeleton have also been developed as antimicrobial (e.g., sulfathiazole), antifungal (ritonavir), and abafungin (antineoplastic) (Fig. 1). Moreover, thiazoles have extensive usage in flavoring, perfume and agrochemical industries. Apart from the significant biological activity, thiazolic derivatives have interesting electronic and optical properties [8,9]. Thiazoles based materials are frequently used in inorganic chemistry for constructing polydentate ligands [10]. Thiazoles are excellent systems which contribute significantly towards supramolecular chemistry by exhibiting polymorphism [11e14], specific material properties in confined medium and flexible self-
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (S. Pola), [email protected] (B. Satyanarayana). https://doi.org/10.1016/j.molstruc.2019.02.025 0022-2860/© 2019 Elsevier B.V. All rights reserved.
assemblies. Natural as well as synthetic thiazole peptides have well-known pharmacological and metal binding properties [15]. Thiazole moiety turns out to be a relatively dependable scaffold for hydrogelation [16]. Thiazole containing colorimetric and ratiometric receptors are very common in excited-state intramolecular proton transfer (ESIPT), fluorescence resonance energy transfer (FRET) and internal charge transfer (ICT)mechanism [17e19]. Thiazole-based receptors can be utilized to sense several kinds of metal cations such as carbazoles included thiazole is a chemosensor for Zn2þ [20]. Thiazoles being exciting and stable n-type organic heterocyclic semiconductor system, has fascinated several researchers as a new conjugated small molecule system [21e26]. Even though, thiazole is a highly electron-deficient heterocycle, it communicates good electron transporting facility and carries excellent photosensitive properties when it exists in donor and acceptor (DA) type conjugated systems. Further, the area of thiazole has been immensely significant because of its high chemical as well as thermal stability. In conclusion, the presence of highly electron withdrawing amide substituent on the thiazole ring can help to promote its electron-transporting nature [27]. Given the practical fact that N-phenylthiazole-2-carboxamide scaffold is an attractive system for good photophysical properties, several derivatives of the same also exhibited good photochemical and thermal stability [28],
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Fig. 1. Biologically active Thiazoles.
high luminescence efficiency and novel optoelectronic properties [29]. Also, it was reported that insertion of an electron withdrawing N-phenylthiazole-2-carboxamide moiety in a DA type molecular network lowers its band gap [30]. Therefore, it is necessary to research further on novel thiazole derivatives under eco-friendly condition. It is well-known that polyethylene glycol (PEG), as one of the non-hazardous alternatives of currently used organic solvents, has some excellent characteristics. Given multiple applications of thiazole moiety, in this work N-arylthiazole-5-carboxamide has been synthesized under eco-friendly condition. 1.1. Experimental details 1.1.1. Materials and measurements All the chemicals are purchased from Sigma-Aldrich, India and without further purification directly used for the synthesis of new compounds. 1.2. Experimental procedure Synthetic procedure for N-phenylthiazole-5-carboxamide (3). To the solution of compound 1 (1.0eq, 0.001 mol) in PEG-400, HATU (1.2eq, 0.0012 mol) was added and stirred for 15 min. The aniline 2 (1.0eq) and DIPEA (3.0eq) were further added and the reaction continued for 10 h. TLC was used to monitor the reaction progress until the starting compounds completely disappeared. After completion, reaction mixture was diluted with water and the desired compound was extracted using ethyl acetate. The crude products were purified by using column chromatography technique with ethyl acetate and n-hexane (3:7). The organic fraction was concentrated by evaporating solvent under reduced pressure to obtain pure compounds 3a and 3b with 85 and 78% yield respectively (shown in Scheme 1). Crystals of the compound 3a and 3b were obtained from ethyl acetate by diffusion method.
Scheme 1. Synthesis of new N-phenylthiazole-5-carboxamides.
2-bromo-4-methyl-N-(p-tolyl) thiazole-5-carboxamide (Compound 3a). Off-white crystalline solid (85%); m. p 130e132 C; 1H NMR (400 MHz, CDCl3) d 7.40 (d, J ¼ 8.4 Hz, 2H), 7.16 (d, J ¼ 8.2 Hz, 2H), 2.72(s, thiazole-CH3), 2.34 (s, Ar- CH3), (s, 3H); 13C NMR (100.1 MHz, CDCl3) d 158.56, 155.20, 136.87, 135.17, 134.37, 129.74, 120.62, 20.96, 17.34; ESI-MS m/z 311 [Mþ1], 313 [Mþ3], 333 [MþNa]. 2-bromo-N-(3,5-dimethylphenyl)-4-methylthiazole-5carboxamide (Compound 3b). White solid (77%); m. p 143e147 C; 1H NMR (400 MHz, CDCl3) d 7.39(br, NH) 7.16 (s, 2H), 6.82 (s, 1H), 2.72(s, CH3), 2.31(s, 2CH3); 13C-NMR (100.1 MHz, CDCl3) d 159.53, 158.54, 155.19, 139.02, 136.88, 136.78, 130.68, 127.07, 118.21, 21.36, 17.31; ESI-MS m/z 325 [Mþ1], 327 [Mþ3], 347 [MþNa]. 1.3. Characterization of compounds Mass spectral data was collected by HR-EI systems on JMS-700 double focusing mass spectrometer (JEOL, Tokyo, Japan). NMR spectra was recorded on a Bruker AV400 MHz spectrometer with chemical shifts referenced using the 1H resonance of residual d6DMSO. Melting points were verified on a Cintex apparatus. The electronic spectra was obtained in various solvents on a JASCO V650 UVeVis spectrophotometer. FT-IR spectra were recorded using Shimadzu spectrometer in the form of KBr pellets with 4 cm1 resolution. 1.4. Single crystal structure determination A suitable single crystal of each compound was carefully selected under a polarizing microscope and glued to a crystal mounting loop with paratone oil. The single crystal data were collected on a BRUKER AXS (D8 Quest System) X-ray diffractometer equipped with PHOTON 100 CMOS detector at 293 (2) K. The X-ray generator was operated at 50 kV and 30 mA using Mo Ka (l ¼ 0.71073 Å) radiation. The unit cell measurement, data collection (4 and u scan), integration, scaling and absorption corrections for the crystals of both complexes was done using Bruker Apex II software [31]. The data was collected with u scan width of 0.5 . Sufficient numbers of frames were collected for different sets of 4 keeping the sample-to-detector distance fixed. The data was reduced using SAINTPLUS [32], and an empirical absorption correction was applied using the SADABS program [33]. The structure was solved and refined using SHELXL97 [34] present in the WinGx suit of programs (Version 1.63.04a) [35]. All the hydrogen positions were initially located in the difference Fourier maps, and for the final refinement, the hydrogen atoms were
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Table 1 Crystal and structure refinement data for compounds (3a & 3b). Identification code
P-01 (compound 3a)
P-02 (compound 3b)
Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions
C12H11BrN2OS 311.20 293 K 0.71073 Å Orthorhombic pca21 a ¼ 16.1141 (10) Å a ¼ 90 b ¼ 8.3104 (5) Å b ¼ 90 c ¼ 20.0643 (14) Å g ¼ 90 2686.9 (3) Å3 8 1.539 Mg m3 0.088 mm1 1248 0.20 0.15 0.10 mm3 2.7 to 25.1 h ¼ 18 / 19, k ¼ 9/9, l ¼ 23 / 23 43282 4763 100% Semi-empirical from equivalents 0.9838 and 0.9788 Full-matrix least-squares on F2 0.082 R1 ¼ 0.028, wR2 ¼ 0.058 R1 ¼ 0.040, wR2 ¼ 0.082 0.00161 (17) 0.37 and 0.44 e Å3
C13H13BrN2OS 325.245 293 K 0.71076 Å Monoclinic P 21/C a ¼ 21.693 (4) Å a ¼ 90 b ¼ 8.007 (2) Å b ¼ 98.96 c ¼ 7.975 (2) Å g ¼ 90 1368.4 (5) Å3 1 1.579 Mg m3 0.091 mm1 656 0.24 0.16 0.13 mm3 2.7 to 25.1 h ¼ 24 / 24, k ¼ 8/8, l ¼ 8/8 17282 1997 100% Semi-empirical from equivalents 0.9182 and 0.9242 Full-matrix least-squares on F2 0.083 R1 ¼ 0.022, wR2 ¼ 0.053 R1 ¼ 0.036, wR2 ¼ 0.082 0.00182 (19) 0.43 and 0.45 e Å3
Volume Z Density (calculated) Absorption coefficient F (000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta ¼ 25.00 Absorption correction Max. and min. transmission Refinement method Goodness-of-fit on F2 Final R indices [I > 2 sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole
located in geometrically ideal positions and refined in the riding mode. Final refinement included atomic positions for all the atoms, anisotropic thermal parameters for all the non-hydrogen atoms, and isotropic thermal parameters for all the hydrogen atoms. Fullmatrix least-squares refinement against jF2j was carried out using the WinGx package of programs [35]. Details of the structure solution and final refinements for the compounds are given in Table 1 and S1-S6. CCDC: 1871377e1871378 contains the crystallographic data (compounds 3a and 3b) for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Center (CCDC) via www.ccdc.cam.ac.uk/data_request/cif.
carboxamide is illustrated in Scheme 1. N-phenylthiazole-5carboxamide (3) had a good yield when 2-bromo-4methylthiazole-5-carboxylicacid (1) was treated with aromatic aniline (2) at room temperature in the presence of HATU, DIPEA, and PEG-400 as a solvent. Further, its chemical structure was established by using mass, FTIR, and NMR spectral analysis. The three-dimensional structure was confirmed for the compounds 3a and 3b with the support of single crystal X-ray diffractometer. (CCDC 1871377e1871378).
1.5. Results and discussion
The structure of compound N-phenylthiazole-5-carboxamide was established by HRMS, FTIR, 1H and 13CNMRspectroscopic techniques. Its FTIR spectrum reveals two strong IR absorption
The synthetic route for the preparation of N-phenylthiazole-5-
1.6. Spectroscopic properties
Fig. 2. Packing cell units and crystal structures of Compound 3a and 3b
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Fig. 3. Molecular plane image of compound 3a and 3b
Table 2 Polarity, Absorption (labs), emission (lem) and Stoke shift values of compound 3a and 3b in different solvents. Solvent
Polarity
labs (nm)
lem (nm)
3a
3b
3a
3b
3a
3b
Hexane CHCl3 EA THF CH3OH CH3CN DMF DMSO
0.08 1.15 1.88 1.75 2.87 3.44 3.86 4.10
286.9 288.3 286.1 301.5 282.1 281.6 287.1 283.5
280.5 278.2 282.5 293.4 271.5 285.0 285.3 283.1
399.0 412.4 404.5 407.5 403.0 399.5 451.0 401.5
400.6 411.5 405.5 413.2 402.0 399.0 398.2 402.5
113.9 124.1 118.4 106.0 120.9 117.9 163.9 118.0
120.1 133.3 123.0 119.8 130.5 114.0 112.9 119.4
established by mass spectral analysis, and the experimentally obtained mass peaks at 309.977 (M)þ and 311.197 (Mþ2)þ coincided with that of the calculated mass (Fig. S3).
Stroke shift (nm)
bands at 2928 and 2851 cm1that indicates asymmetric and symmetric CeH stretching vibrations of methyl group compound 3b (Fig. S1). Additionally, an active IR absorption band at1644 cm1 indicates the presence of the amide group in its molecular structure. In compound 3a and 3b, in its 1H NMR spectra (Fig. S2) one proton exhibits unique resonances at 7.39, and 7.16 ppm for other protons of aromatic moieties. The appearance of a broad singlet at 7.41 ppm is for one proton of the amide group. Also, three types of singlet were observed with two singlets at 2.72 and 2.34 ppm for two magnetically different methyl groups. Finally, its structure was
1.6.1. Crystal structures of compound 3a and 3b The compound 3a crystalline in orthorhombic with space group pca21 with a ¼ 16.114 (10) Å, b ¼ 8.310 (5) Å, c ¼ 20.064 (14) Å and ֯a ¼ b ¼ g ¼ 90 and the compound 3b crystalline in monoclinic space group P21/C with a ¼ 21.693 (4) Å, b ¼ 8.007 (2) Å, c ¼ 7.975 (2) Å and b ¼ 98.96 (3) (Table 1). Fig. 2 reveals the characterized ORTEP diagram of the compound 3a and 3b. In Fig. 2, the two rings are well-known for tagging with alphabets ‘A’, and ‘B’. This tagging is valuable for describing the intermolecular interactions in the difficult steps. Nevertheless, from the X-ray analysis data, it is noticeable that the molecule is not planar but shifted. Interestingly, the 4-methylphenyl and thiazole ring bridging of amide group at the position-5 of the thiazole ring. Further, bond length and bond angle values were all within the range, as presented in Table S1-S6 [36]. From the data of Table S1, it is observed that CeC, CeN and CeO bond length values in the two-ring system are holding amide group and intermolecular hydrogen bonding, which indicates that the non-bonding electrons of amide group of compounds are involved in delocalization. When compared two crystal planes, in the case of compound 3a two molecular units are present whereas compound 3b is with a single molecule on the plane and shown in Fig. 3. The plane passing through the compound 3a indicates that
Fig. 4. Absorption spectra of compounds 3a and 3b in various solvents (105 M).
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197
Fig. 5. Emission spectra of compounds 3a and 3b in various solvents (106 M).
the packing arrangement.
of
molecules
are
in
anti-cofacial
molecular
1.6.2. Photophysical properties To study the photophysical properties of synthesized compounds UV visible absorption and emission spectra were collected. The absorption and emission spectra for compounds 3a and 3b were measured in different solvents n-hexane, chloroform (CHCl3), tetrahydrofuran (THF), methanol (MeOH), ethyl acetate (EA), acetonitrile (CH3CN), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) with dilute concentration of 105 M to study its photophysical properties. These solvents were designated on the basis of the enhanced order of their polarity not depends on the dielectric constant values due to the interaction between solvents compounds 3a and 3b. The solvent polarity, absorption, emission spectral data and stroke shifts are presented in Table 2. Figs. 4 and 5 shows the UVevisible absorption and emission spectra in different solvents, respectively. In its absorption spectra, the compound exhibited one strong absorption band in UV region both in polar and non-polar solvents. Both the compounds are showing a strong absorption band in the range of 275 nm and 300 nm and are recognized due to a p/p* electronic transition. From Table 2, with change of solvent from low polarity (hexane) to high polarity (DMSO) there is negligible change in spectral shift of few nm. For compound 3a, observed absorption is at 301 nm in THF while on increasing the polarity of the solvent it shows a small blue shift (~15 nm) in DMSO (283 nm). Similar is the case for compound 3b here 10 nm blue shift was observed on the increasing polarity of solvent from THF (293 nm) to DMSO (283 nm). In its emission spectra, an intense blue emission band appearing between 375 nm and 475 nm has been perceived under their excitation wavelengths. Akin to absorption spectra, the fluorescence spectra of compounds 3a and 3b revealed considerably higher solvatochromic effects. There is a substantial change in emission maxima with the deviation of solvent systems from non-polar (hexane) to highly polar (EA) solvent with a Stokes shift of 50 nm. Moreover, a significant red shift of emission was observed, which is recognized by the improved interaction between the fluorescent molecule and a nonpolar solvent. However, in the case of methanol, no such observation was made because of its weak interactions with the chromophore. Also, the material was originated to be blue fluorescent under a UV lamp (l ¼ 375 nm). The quantum yields for the compounds 3a and 3b were calculated in two different solvents by using anthracene as a standard reference (frMeOH ¼ 0.2 and frCHCl3 ¼ 0.11) [37]. The quantum yields of the compounds 3a and
3b are 0.22 and 0.33 in methanol, whereas in the chloroform the quantum yields are 0.12 and 0.18 respectively. Lifetime decay of the compounds 3a and 3b are shown in Fig. 6. 1.7. Theoretical studies The synthesized molecules have been optimized with the help of Gaussian 09 software [38,39] using B3LYP functional with 6311 þ G (d, p) basis set. Further, these optimized structures are without imaginary frequencies and hence are characterized as true minima on potential energy surface. To predict the absorption maxima of the molecules, the lowest five excitations were calculated using TDDFT methodology using a long-range CAM-B3LYP function with 6-311 þ G (d, p) basis set. Further, different functionals were considered (B3LYP, M06, and WB97XD) to calculate absorption maxima to check whether there is any change in absorption with functionals. While B3LYP and M06 overestimated the absorption maxima, but long-range functional CAM-B3LYP and WB97XD are in good agreement with the experimental result (Table S7). In addition to this, solvent effect for all the molecules was also carried out by using the IEFPCM method at the same level of theory. Here in computational calculations same solvents which are experimentally reported were used i.e. n-hexane, chloroform
Fig. 6. Life-time decay pattern of compound 3a and 3b in THF (106 M).
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Table 3 Comparison of bond lengths (BL) and bond angles (BA)for molecules 3a and 3b with their crystal structure and optimized geometry structure..
BL Br1eC13 C13eS2 C13eN4 N4eC11 C11eC14 C11eC24 C14eS2 C14eC12 C12eO3 C12eN5 N5eC21 C21eC9 C21eC15 C15eC22 C22eC6 C6eC7 C6eC17 C7eC9 BA C13S2C14 C14C12N5 C12N5C21 C14C12N5C21
Crystal structure
Optimized structure
1.851 1.681 1.279 1.309 1.388 1.490 1.744 1.456 1.215 1.327 1.360 1.442 1.401 1.452 1.321 1.343 1.568 1.364
1.891 1.742 1.285 1.383 1.376 1.496 1.759 1.490 1.221 1.376 1.414 1.401 1.399 1.393 1.397 1.399 1.509 1.388
88.5 117.9 132.8 176.5
88.1 114.5 128.8 177.5
Table 3 (continued ) C11eC10 C10eC8 C7eC8 C5eC7 C7eC13 C10eC17 BA C28S2C22 C22C21N29 C21N29C4 C22C21N29C4
1.379 1.370 1.370 1.374 1.505 1.507
1.301 1.393 1.398 1.401 1.510 1.510
88.4 115.2 125.6 176.6
88.1 114.5 129.1 177.4
(CHCl3), tetrahydrofuran (THF), methanol (MeOH), ethyl acetate (EA), acetonitrile, dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) and was observed no change in absorption maxima with the change in solvents (Table S8). For a better understanding of the geometries of molecules, the bond lengths and bond angles of the optimized structure were compared with their crystal structure which are tabulated in Table 3. As observed in Table 3, there is negligible difference in calculated and experimental parameters. The experimentally reported absorption maxima for molecule 3a is at 287 nm in CHCl3. From TDDFT calculations, observed absorption maxima for 3a is at 274 nm which is in good agreement with the experimentally measured absorption energy. The major transition, in this case, is from H/L and oscillator strength corresponding to this transition is 0.558. Beside this, there are some minor transitions which are arising from H-1/L and H3/L. For molecule 3b, observed absorption maximum is at 279 nm. TDDFT calculated results are in accordance with the experimental result (272 nm). Unlike 3a, molecule 3b shows one major transition which is from H/L and one minor transition from H-2/L with oscillator strength 0.510. In Table 4 the absorption maxima oscillator strength, major transitions and % contribution were tabulated. From pictures of frontier molecular orbitals (FMOs), it is observed that charge transfer is taking place from sixmembered benzene ring to five-membered thiazole ring (Table 5). In molecule 3a, HOMO is showing higher electron density localized at six-membered benzene ring while in LUMO electron density shifts to five-membered thiazole ring. Further, the non-covalent and supramolecular interaction studies of 3a and 3b co-crystals with carboxylic acid, selenic acid, and different anions are under progress.
2. Conclusion
BL Br1eC28 C28eS2 C28eN31 N31eC23 C23eC22 C23eC24 C22eS2 C22eC21 C21eO3 C21eN29 N29eC4 C4eC11 C4eC5
Crystal structure
Optimized structure
1.857 1.702 1.290 1377 1.349 1.487 1.719 1.484 1.218 1.330 1.421 1.373 1.376
1.892 1.742 1.285 1.383 1.376 1.496 1.759 1.490 1.221 1.376 1.414 1.394 1.404
Here in this article, eco-friendly synthesis of two new N-phenylthiazole-4-carboxamides 3a and 3b were successfully synthesized using a simple way and thoroughly characterized with spectral methods. Its single crystal and DFT study exposed the presence of the non-planar structure. Theoretically calculated UV absorption bands coincide with that of the experimental values.
Table 4 Experimental (lexpin nm) and theoretical absorption (lcalin nm), Oscillator strength (f), Major transitions (MT) and % contribution calculated at Cam-B3LYP/6-311 þ G (d, p) level of theory for B3LYP/6-311 þ G (d, p) optimized geometries. Name
lcal
lexp
f
MT
%Ci
3a
274
287
0.558
3b
272
279
0.510
H/L H-1/L H-3/L H/L H-2/L
70 17 3 65 20
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Table 5 Frontier molecular orbitals (FMOs) calculated at B3LYP/6-311 þ G (d, p) level.
Moreover, its photophysical properties specify that it is a suitable absorbent and fluorescent materials with positive solvatochromic performance in various solvents. From the outcomes, it can be determined that compound 3a and 3b are capable materials for their applications in small molecular electronic device applications. Acknowledgment Authors would like to thank DST - FIST schemes and CSIR, New Delhi. Mr. Jeevanreddy Miryala thanks, Council of Scientific & Industrial Research (CSIR), New Delhi for the award of Senior Research Fellowship. SP is expressly thankful for sanctioned UGCSERO, Hyderabad, India. CP thanks to CSIR - New Delhi, India for financial support. Authors also thank Dr. Avijit Kumar Paul, NIT Kurukshetra for helping in the refinement of crystal data. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2019.02.025.
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