Scientific paper
Synthesis, Characterization and DFT Studies of Two New n-conjugated Pyridine-based Tetrathiafulvalene Derivatives
Zhi-Gang Niu,1 Li-Rong He,1 Lin Li,1 Wen-Feng Cheng,1 Xiao-Yan Li,1 Hao-Hua Chen1 and Gao-Nan Li1'2*
1 College of Chemistry and Chemical Engineering, Hainan Normal University, Haikou 571158, China
2 State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
* Corresponding author: E-mail: ligaonan2008@163.com
Received: 26-03-2014
Abstract
Two new n-conjugated pyridine-based tetrathiafulvalene derivatives, 2-(2- (4,5-bis(methylthio)-1,3-dithiol-2-ylidene)-6-phenyl-[ 1,3]dithiolo[4,5-b][ 1,4]dithiin-5-yl)pyridine (2a) and 3-(2-(4,5-bis(methylthio)-1,3-dithiol-2-ylidene)-6-(pyridin-2-yl) -[1,3]dithiolo[4,5-b][1,4]dithiin-5-yl)quinoline (2b), have been synthesized and characterized by 1H NMR, elemental analysis and mass spectroscopies. The compound 2a has also been studied by X-ray crystallography and theoretical calculations using density functional theory (DFT) framework with B3LYP/6-311+G(d,p) level of theory. Its crystal structure is triclinic system, space group P1. The unit cell dimensions are: a = 8.813(3) A, b = 11.082(3) Á, c = 12.620(4) A, a = 88.805(5)°, P = 80.440(5)°, y = 75.680(5)°, V = 1177.3(6) A3, Z = 2. The molecule exhibits one classical C-H—N intermolecular hydrogen bonds, two kinds of short intermolecular S---S interactions and two types of C-H—rc supramolecular interactions.
Keywords: Tetrathiafulvalenes; Pyridine; Synthesis; Crystal Structure; DFT calculations
1. Introduction
Tetrathiafulvalene (TTF) and its derivatives have attracted chemists' considerable interests during the past two decades, because of their unique n-electron donor properties and serving as useful building blocks for new advanced materials.1-2 One of the research trends in new TTF derivatives for functional materials is to search for molecules with more n-extended systems exhibiting unusual geometric and electronic properties.3-5 In general, n-extended tetrathiafulvalene framework (exTTF) can enhance the dimensionality in materials by increasing intermolecular n-n and/or S-S interactions.6 Moreover, these short intermolecular distances within a column, corresponding to an overlap of the n/p orbitals, allow the delocalisation of electrons and thus conduction along the stacking direction.7 Therefore, a large synthetic effort has also been devoted to the preparation of exTTF derivatives.8-10
In our previous paper, we have reported several classes of n-conjugated pyridine-based TTF derivatives,11-12 which are beneficial to intramolecular electron transfer and communications. Our longer term goal is develop a new class of exTTF derivatives. In the current report, two new n-conjugated pyridine-based TTF derivatives (2a-2b) have been synthesized and characterized. Optimized conformation and molecular orbital diagram of 2a has been calculated with density functional theory (DFT).
2. Experimental
2. 1. Materials and Instrumentations
The starting materials 1,3-dithiole-2,4,5-trithio-ne,13 2-(phenylethynyl)pyridine14 and 4-(pyridin-2-ylethynyl) isoquinoline14 were synthesized as described
Scheme 1. Synthetic route of compounds 2a-2b.
in the literature. All commercial chemicals were used without further purification unless otherwise stated. Solvents were dried and degassed following standard procedures. 1H NMR spectra were recorded on a Bruker AM 500 MHz instrument. Chemical shifts were reported in ppm relative to Me4Si as internal standard. Elemental Analyses for C, H, and N were performed on a Perkin-Elmer 240 C analyzer. ESIMS spectra were recorded on a LCQ Fleet instrument.
2. 2. Synthesis of 5-phenyl-6-(pyridine-2-yl)-[1,3]dithiolo[4,5-b][1,4]dithiine -2 -thione (1a)
A suspension of 2-(phenylethynyl)pyridine (273 mg, 1.53 mmol) and 1,3-dithiole-2,4,5-trithione (200 mg, 1.02 mmol) in toluene (15 mL) were stirred at reflux under a nitrogen atmosphere for 20 h. The mixture was cooled to room temperature, filtered and washed with chloroform. The filtrate was evaporated and the residue was purified by column chromatography on silica gel eluted with petroleum ether/ethyl acetate (30:1) to give compound 1a (125 mg, 32.7%) as a pale yellow solid. 1H NMR (500 MHz, CDCl3): 5 8.65 (d, J = 4.0 Hz, 1H), 7.48 (t, J = 7.5 Hz, 1H), 7.32-7.35 (m, 1H), 7.27-7.30 (m, 4H), 7.24 (t, J = 6.0 Hz, 1H), 6.75 (d, J = 8.0 Hz, 1H). Analysis calculated for C16H9NS5: C, 51.17; N, 3.73; S, 42.69%; found: C, 51.09; N, 3.77; S, 42.70%. EI-MS (m/z): 375.8 [M + 1]+.
2. 3. Synthesis of 5-(pyridin-2-yl)-6-(quinolin-3-yl)-[1,3]dithiolo [4,5-b][1,4]dithiine -2-thione (1b)
The procedure of compound 1b (pale yellow solid, 136 mg, 28.2%) used 3-(pyridin-2-ylethynyl)quinoline as starting material was similar to that of compound 1a. 1H
NMR (500 MHz, CDCl3): 5 8.59-8.64 (m, 2H), 8.36 (s, 1H), 8.22 (d, J = 6.0 Hz, 1H), 7.84 (t, J = 8.0 Hz, 2H), 7.66 (t, J = 7.0 Hz, 1H), 7.42 (t, J = 7.0 Hz, 1H), 7.16-7.18 (t, J = 6.0 Hz, 1H), 76.85 (d, J = 6.0 Hz, 1H). Analysis calculated for C19H10N2S5: C, 53.49; N, 6.57; S, 37.58%; found: C, 53.54; IN, 6.51; S, 37.56%. EI-MS (m/z): 426.9 [M + 1]+.
2. 4. Synthesis of 2-(2-(4,5-bis(methylthio)-1,3-dithiol-2-ylidene)-6-phenyl-[1,3]dithiolo[4,5-b][1,4]dithiin-5-yl) pyridine (2a)
A mixture of compound 1a (69 mg, 0.16 mmol) and 4,5-bis(methylthio)-1,3-dithiol-2-one (45 mg, 0.21 mmol) was stirred together in freshly distilled triethylphosphite (3 mL) at 110 °C under a nitrogen atmosphere. After 3 h, the reaction was concentrated and purified by chromato-graphy over silica eluting with chloroform/methanol (50:1) to afford 2a (21 mg, 21.3%) as a bright orange solid. 1H NMR (500 MHz, CDCl3): 5 8.54-8.56 (m, 2H), 7.64-7.68 (m, 2H), 7.41 (s, 1H), 7.21-7.28 (m, 4H), 2.39 (s, 3H), 2.38 (s, 3H). Analysis calculated for C21H15NS8: C, 46.89; N, 2.60; S, 47.69%; found: C, 46.74; N, 2.56; S, 47.72%. EI-MS (m/z): 538.0 [M + 1]+.
2. 5. Synthesis of 3-(2-(4,5-bis(methylthio)-1,3-dithiol-2-ylidene)-6-(pyridin-2-yl) -[1,3]dithiolo[4,5-b][1,4]dithiin-5-yl) quinoline (2b)
The procedure of 2b (bright orange solid, 29 mg, yield: 27.2%) was similar to that of 2a. 1H NMR (500 MHz, CDCl3): 5 8.60 (d, J = 4.5 Hz, 1H), 7.44-7.47 (m, 1H), 7.28-7.35 (m, 4H), 7.23-7.25 (m, 2H), 7.08-7.11 (m, 1H), 6.67 (d, J = 9.0 Hz, 1H), 2.44 (s, 3H), 2.43(s, 3H). Analysis calculated for C21H15NS8: C, 46.89; N,
2.60; S, 47.69%; found: C, 46.74; N, 2.56; S, 47.72%. EI-MS (m/z): 587.8 [M + 1]+.
2. 6. Crystallographic Studies
X-ray diffraction data were collected on a Bruker Smart Apex CCD diffractometer equipped with graphite-monochromated Mo Ka (X = 0.71073 À) radiation at 293 K. Absorption corrections were applied using SADABS program.15 The structure was solved and refined using full-matrix least-squares based on F2 with program SHELXS97 and SHELXL9716 within Olex2.17 All non-hydrogen atoms were found in alternating difference Fourier syntheses and least-squares refinement cycles and, during the final cycles, refined anisotropically. Particularly, the anisotropic displacement parameters of these atoms on the pyridine ring (C10, C11, C12, C13, C14 and N1) and the terminal group (C1, C1', C4, S7 and S7') were restrained using DFIX, SIMU and ISOR commands. Crystallographic details, selected interatomic distances and angles are provided in supporting information.
2. 7. Computational Method
The geometry of compound 2a was optimized starting from the X-ray data by the DFT (density functional theory) method with B3LYP (Becke three-parameter Lee-Yang-Parr) hybrid density functional theory and the 6-311+G(d,p) basis set. All calculations were carried out with Gaussian 09 software package.18
3. Results and Discussion
3. 1. Description of Crystal Structure of 2a
- Compound 2a crystallizes in the triclinic space group P1 and an ORTEP plot of the molecule with atomic num-
bering scheme is shown in Fig. 1. The crystallographic data are listed in Table S1; selected bond lengths and bond angles are collected in Table S2. In the structure, the TTF moiety adopts a boat-like conformation with the average deviation from a least-squares plane of 0.3295 Á19 and bond lengths and angles are in the range expected for neutral TTF derivatives.20 While the pyridine ring (C10-N1-C11-C12-C13-C14) and the phenyl ring (C16-C17-C18-C19-C20-C21) are twisted against the six-membered ring (C7-S2-C9-C15-S1-C8), with the dihedral angle being 65.53° and 35.60°, respectively. The distances of C=C double bond [C(3)=C(4), C(5)=C(6), C(7)=C(8) and C(9)=C(15)] are in the range of 1.328(3)1.347(3) Á (Table S2), as well as in good agreement with those found in related structures.21 Besides, the terminal methyl group of the compound 2a is disordered over two sites (C1 and S7 with 0.526 occupancy, C1' and S7' with 0.474 occupancy).
Perspective view of the crystal packing in the unit cell is presented in Figs. 2-3 and the details of the hydrogen bonds are summarized in Table 1. In the crystal structure, there are one classical C-H—N intermolecular hydrogen bonds, two kinds of short intermolecular S—S interactions and two types of C-H -n supramolecular interactions. The primary interactions are C1-H1C—N1 hydrogen bonds with distance H1C—N1 = 2.51 Á and angle C1-H1C—N1 = 130.3°, resulting in dimerization of the molecules within the lattice. These dimmers are further connected by another S—S interaction (S1—S61 = 3.843 Á, S6—ST = 3.843 Á, S4-S411 = 3.859 Á and S41—S4u1 = 3.859 Á; symmetry codes in Fig. 2), completing the two-dimensional array. It is noteworthy that the strengths of the S—S distances are slightly longer than those in previously reported examples, which may be attributed to the boat-like conformation of the TTF unit.22-24 Molecules are also linked in a head-to-tail fashion into chains running along c (Fig. 3), involving weak C-H-tc contacts (C2-H2B-C&51 and C1'-H1'C-C^511,
Fig. 1. Molecular structure of compound 2a. Selected bond length and angles: S(1)-C(8), 1.742(2); S(2)-C(9), 1.782(3); S(3)-C(6), 1.752(3); S(4)-C(8), 1.759(3); S(5)-C(5), 1.739(3); S(6)-C(3), 1.763(3); S(7)-C(1), 1.693(8); S(8)-C(3), 1.737(3); C(3)-C(4), 1.342(5); C(5)-C(6), 1.337(4); C(7)-C(8), 1.329(5); C(9)-C(15), 1.343(4); N(1)-C(11), 1.367(7); C(17)-C(18), 1.359(5); C(8)-S(1)-C(15), 100.83(11); C(7)-S(3)-C(6), 93.55(16); C(5)-S(5)-C(4), 93.95(15); C(10)-N(1)-C(11), 116.3(5); C(17)-C(16)-C(21), 118.9(3).
symmetry codes in Table 1) between hydrogen atoms of two terminal methyl groups and the plane of the phenyl group (C16-C17-C18-C19-C20-C21). Analyses of the data in Table 1 give C—centroid distances of 3.483 A and 3.689 A, with corresponding C-H-centroid angles of 142° and 152°, respectively. In the crystal lattice, all abo-
Table 1 Hydrogen bond lengths (A) and bond angles (°) for compound 2a
Fig. 2. Representation of part of the lattice contents of compound 2a, the dotted line representing the S---S nonbonded contacts (blue) and the hydrogen bonds (green). [symmetry code: (i) -x, -y+1, -z; (ii) -x+1, -y+1, -z; (iii) x+1, y, z]
D-H-A	d(D-H)	rf(H-A)	á(D-A)	<DHA
C1-H1C-N11	0.96	2.51	3.211	130.3
C2-H2B-Cg5'	0.96	2.67	3.483	142
Cr-H1'C-Cg5n	0.96	2.81	3.689	152
Fig. 3. Views of the three-dimensional network which makes up the structure of compound 2a. C-H—rc contacts are shown as dotted lines. Red sphere represents the centroid of the C16-C21 benzene ring.
Symmetry codes: (i) -x+1, -y+1, -z; (ii) -x, -y+1, -z. Cg5 is the centroid of the C16-C21 benzene ring.
ve hydrogen bonds and intermolecular interactions play a significant role in stabilizing the crystal structure. No obvious tc-'-tc interactions are found in the structure.
3. 2. Theoretical Calculations
A DFT calculation was carried out to predict the geometry of the molecule 2a. The actual and optimized bond lengths and angles, which were obtained by X-ray crystallographic study as well as by geometry optimization at B3LYP/6-311+G level of theory, are reported in Table S2. Considering the sulfur as the focal point, some main structural parameters differ slightly between the X-ray and the theoretical structure. It is seen from Table S2, most of the optimized S-C bond lengths are longer than experimental ones agreeing within 0.2138 A. And the deviations of C-S-C bond angles between optimized and measured structures are within 1.852°. In addition, the C-C distance in phenyl group and the pyridine C-C distance are calculated as of 1.3949-1.4072 and 1.39451.4023 A ranges, respectively.25 It should be noticed that slight differences in bond parameters are attributed to the fact that the experimental results belong to solid phase while theoretical calculations belong to gaseous phase.26
The highest occupied molecular orbital (HOMO) energies, the lowest unoccupied molecular orbital (LUMO) energies, and the energy gap for mentioned molecule in above have calculated. The calculated HOMO-LUMO gap of molecule is 3.21 eV. The molecu-
HOMO 5.33 eV
Fig. 4. Molecular orbital diagram of the HOMO and LUMO of compound 2a.
LUMO 2.12 eV
lar HOMO/LUMO orbital pictures are depicted in Fig. 4. In analogy to other TTF(donor)-Acceptor compounds,27-29 the HOMO is mainly located on the TTF moiety, whereas the LUMO is mostly located on electron acceptor fragment.
4. Conclusions
In this paper, two new n-conjugated pyridine-based tetrathiafulvalene derivatives (2a-2b) have been successfully prepared and characterized. The crystal structure of 2a has been determined by single-crystal X-ray diffraction. The DFT geometry optimization has been carried out using B3LYP/6-311+G(d,p) basis sets and the calculated geometrical parameters are consistent with X-ray diffraction data. In the crystal packing, few weak C-H—N and C-H -n interactions and short intermolecular S—S contacts have been observed, which result in the forming of 3D structure.
5. Acknowledgements
This work was supported by the Science and Research Project of Education Department of Hainan Province (No. Hjkj2013-25) and the National Innovation Experiment Program for University Students (The research of metal complexes involving tetrathiafulvalene with tria-zole and pyridine ligands: syntheses and optoelectronic properties).
6. Supplementary Material
Crystallographic data for the structural analyses have been deposited in the Cambridge Crystallographic Data Centre, CCDC reference number 955915. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
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Povzetek
Sintetizirali in karakterizirali NMR, elementna analiza in masna spektroskopija) smo dva nova n-konjugirana piri-dinska tetratiafulvalenska derivata, 2-(2- (4,5-bis(metiltio)-1,3-ditiol-2-iliden)-6-fenil-[1,3]ditiolo[4,5-fe][1,4]ditiin-5-il)piridin (2a) in 3-(2-(4,5-bis(metiltio)-1,3-ditiol-2-iliden)-6-(piridin-2-il) -[1,3]ditiolo[4,5-b][1,4]ditiin-5-il)kinolin (2b). Spojino 2a smo raziskali tudi z rentgensko kristalografijo in teoretičnimi izračuni z uporabo teorije gostotnih funk-cionalov (DFT) na nivoju B3LYP/6-311+G(d,p). Kristalna struktura je v triklinskem sistemu prostorske skupine P. Velikost osnovne celice je: a = 8.813(3) A, b = 11.082(3) A, c = 12.620(4) A, a = 88.805(5)°, P = 80.440(5)°, y = 75.680(5)°, V = 1177.3(6) A3, Z = 2. Molekule kažejo eno klasično C-H—N intermolekularno vodikovo vez, dve vrsti kratkih intermolekularnih S—S interakcij in dve vrsti C-H—rc supramolekularnih interakcij.