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Importance of hydrogen bonding for second harmonic generation effect: X-ray diffraction and DFT study on S-benzyl isothiouronium chloride
ARTICLE IN PRESS Journal of Physics and Chemistry of Solids 70 (2009) 322–325
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Importance of hydrogen bonding for second harmonic generation effect: X-ray diffraction and DFT study on S-benzyl isothiouronium chloride P. Hemalatha a, V. Veeravazhuthi b,, D. Velmurugan c, L. Senthilkumar a, J. Mallika d, D. Mangalaraj e a
Department of Physics, PSG College of Technology, Coimbatore-641 004, Tamil Nadu, India Department of Physics, PSG College of Arts and Science, Coimbatore-641 014, Tamil Nadu, India Department of Bio Physics and Crystallography, University of Madras, Chennai-600 025, Tamil Nadu, India d Department of Chemistry, PSG College of Arts and Science, Coimbatore-641 014, Tamil Nadu, India e Department of Nanotechnology, Bharathiar University, Coimbatore-641 046, Tamil Nadu, India b c
a r t i c l e in f o
a b s t r a c t
Article history: Received 5 July 2008 Received in revised form 6 September 2008 Accepted 31 October 2008
X-ray diffraction study of the nonlinear optical (NLO) material S-benzyl isothiouronium chloride (C8H11N2SCl) (SBTC) is reported for the first time. The single crystal of SBTC is orthorhombic with space group Pbca. SBTC exhibits second-order NLO susceptibility, and this study shows that hydrogen bonding is, in part, responsible for this. The present work shows that C–H?Cl and N–H?Cl hydrogen bonds direct the nature of the three-dimensional lattice. Such intermolecular interactions help to extend the molecular charge transfer into the supramolecular realm, the charge transfer originating as a consequence of the high level of molecular planarity and strong donor-to-acceptor interactions. Density functional theory (DFT) calculation and atom-in-molecule (AIM) analysis has been carried out to study the nature of hydrogen involved in the SBTC complex. & 2008 Elsevier Ltd. All rights reserved.
Keywords: A. Organic compound B. Crystal growth C. X-ray diffraction D. Crystal structure
1. Introduction Organic compounds are often formed by weak van der Waals bonds and hydrogen bonds and hence possess high degree of delocalization. Thus they are expected to be optically more nonlinear than inorganic compounds. Some of the advantages of organic materials include ease of varied synthesis, scope for altering the properties by functional substitutions, inherently high nonlinearity, high damage resistance, etc. The prototype organic nonlinear optical (NLO) material contains one or more delocalized bonds, typically a ring structure like benzene. Owing to the high polar nature of the molecules, organic NLO materials often tend to crystallize as long needles or thin platelets. New NLO frequency conversion materials can have a significant impact on laser technology, [1] optical communication, [2] and optical data storage technology [3]. These applications have unique and often competing material requirements and illustrate that no single nonlinear material will be suitable for all uses. The high optical thresholds and much versatility in the molecular design of organic materials provide many more opportunities for improving the SHG response [4]. SHG is one of the most important aspects to NLO research since it leads itself to a myriad of applications: from telecommunications to visible light
Corresponding author. Tel.: +91 422 2573386; fax: +91 422 2575622.
E-mail address: [email protected] (V. Veeravazhuthi). 0022-3697/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2008.10.023
lasers, through to surface-enhanced Raman spectroscopy [5–7]. The level of SHG response of a given material is inherently dependent upon its structural attributes. On a molecular scale, the extent of charge transfer (CT) across the NLO chromophore determines the level of SHG output [8–12]: the greater the CT, the larger the SHG output. The presence of strong intermolecular interactions, such as hydrogen bonds can extend this level of CT into the supramolecular realm, owing to their electrostatic and directed nature, thereby enhancing the SHG response. The structural characteristic of SBTC, on the molecular scale, reveals that they are: extremely p-conjugated, good planarity and strong electron donor and acceptor groups at opposite ends of the molecule. Density functional theory (DFT) is a cost-effective ab initio quantum chemistry procedure for studying physical properties of the molecules. DFT calculations have shown promising conformity with experimental results [13–15]. Therefore, in this present investigation DFT is used to study the geometry and characterization of hydrogen bond in the SBTC complexes.
2. Experimental and computational details Nonius CAD–4/MACII 3 diffractometer with MoKa (0.71073 A˚) radiation was employed for this study. Experimental details are given in Table 1. Density functional theory-based method has been used to investigate the electronic structure of the SBTC systems.
ARTICLE IN PRESS P. Hemalatha et al. / Journal of Physics and Chemistry of Solids 70 (2009) 322–325
Table 1 Crystallographic data of SBTC. Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density Absorption coefficient F(0 0 0) Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to y ¼ 25.001 Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I42sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole
323
S1 C8H11N2SCl 202.7 g 293(2) K 0.71073 A Orthorhombic Pbca a ¼ 8.4188 A˚, b ¼ 11.3642 A˚, c ¼ 20.5225 A˚ a ¼ b ¼ g ¼ 901 1963.5 A˚3 8 1.376 kg/m3 0.551 mm1 843 1.99–28.011 14php14; 10pkp10; 26plp6 20752 2337 [R(int) ¼ 0.0243] 99.9% Full-matrix least square on F2 2337/0/110 1.0332 R1 ¼ 0.02884, wR2 ¼ 0.0838 R1 ¼ 0.0309, wR2 ¼ 0.0862 0.0200(16) 0.230 and 0.208 A˚3
We have carried out geometry optimization for all the structures of the SBTC complexes using DFT with B3LYP exchange-correlation functional [16–18] and 6-311+G(d,p) basis set. The vibrational frequencies computed using the analytical second derivatives at the B3LYP/6-311+G(d,p) [Becke 3-parameters (Exchange), Lee, Yang and Pau (Correlation) level of theory for all complexes indicate no imaginary frequency, which implies that all the complexes are stationary states. The topological parameter electronic charge density has been calculated using atoms-inmolecule (AIM) analysis. All the calculations have been performed using the Gaussian 03 program [19].
3. Results and discussion An ORTEP (Oak Ridge Thermal Ellipsoid Plot) of SBTC crystal structure is shown in Fig. 1. Bond lengths and bond angles are given in Tables 2 and 3, respectively. The complete delocalization of p electrons of the ring systems makes them wholly aromatic in character. In case of phenyl ring, the delocalization of p electrons is caused by side–side overlapping of available p orbital present on the carbons constituting the ring. The ample delocalization of the p electrons is possible only if the ring is flat or planar, so as to allow cyclic overlap of p orbital [20]. From the crystallographic data, the angle of phenyl ring relative to the mean plane of the molecule is obtained as 0.8(1)1 [C(1)–C(6)]. The deviation of nitrogen group from the mean plane (i.e., 9.44(1)1) is large enough for the molecule. This, in turn, enhances the nitrogen–chloride donor–acceptor interactions across the molecule and hence, the degree of molecular CT. Significant molecular CT effects might be expected to cause a perturbation of aromatic ring towards a more quinoidal electronic configuration since provides more extended level of p-conjugation in the system [19]. Five intermolecular interactions were located within the threedimensional lattice of SBTC. Among these one interaction was weak interaction of the type C–H?Cl and four were strong interactions of the type N–H?Cl. Hydrogen bonding geometry details are given in Table 4. The weak intermolecular interaction C7-H1A?Cl [3.793 (1) A˚, 1731; Symmetry code: x+1, y, z+1], involves either p or Cl hydrogen bond acceptor. This type of acceptor is very common and C–H?p interactions are rare.
C8
C2
C7 N1
C3
C1
C6 C4 N2
C5 CL1
Fig. 1. ORTEP plot of SBTC crystal.
Table 2 Bond lengths (A˚). S(1)–C(8) S(1)–C(7) C(8)–N(2) C(8)–N(1) C(4)–C(3) C(4)–C(5) C(4)–C(7) C(5)–C(6) C(3)–C(2) C(6)–C(1)
1.740(1) 1.816(1) 1.309(2) 1.309(2) 1.384(2) 1.389(2) 1.506(2) 1.379(2) 1.392(2) 1.380(2)
Table 3 Bond angles (1). C(8)–S(1)–C(7) N(2)–C(8)–N(1) N(2)–C(8)–S(1) N(1)–C(8)–S(1) C(3)–C(4)–C(5) C(3)–C(4)–C(7) C(5)–C(4)–C(7) C(6)–C(5)–C(4) C(4)–C(3)–C(2) C(2)–C(1)–C(6) C(1)–C(2)–C(3)
104.2(1) 121.9(1) 115.5(1) 122.7(1) 118.9(1) 120.5(1) 120.6(1) 114.9(1) 120.6(1) 119.9(2) 119.9(2)
Table 4 Hydrogen bonding geometry (A˚). D–H?A
d(D?H)
d(H?A)
d(D?A)
o(DHA)
N2–H2B?CL1 N1–H1A?CL1a N1–H1B?CL1b C7–H7A?CL1b N2–H2A?CL1c
0.86 0.86 0.86 0.97 0.86
2.55 2.32 2.68 2.83 2.39
3.273(1) 3.157(1) 3.307(1) 3.793(1) 3.183(1)
143 164 131 173 153
Symmetry transformations used to generate equivalent atoms: a x1/2, y1/2, z+1. b x+1, y, z+1. c x+3/2, y1/2, z.
Moreover, although C–H?p interactions are generally fairly weak, they can be structurally significant. Since CH2 group in SBTC is an electron releasing group, it increases the overall electron density in the ring. Therefore C(7) donates less number of electrons to Cl(1), causing weak interaction.
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The hydrogen bonds concerned may be classified as weak, but are evidently highly influential especially since they appear to form at the expense of any classical O–H?X or N–H?X hydrogen bonds, despite the presence of such strong hydrogen bond donors. The systematic asymmetry of the S–C–N angle is 115.5(1)1 for the smaller and 122.7(1)1 for the larger, the latter involving the N atom participating in the stronger N–H–Cl interactions. The four strong interactions N1–H1Ay. CL1 [3.157(1)1, 1641; Symmetry code: x1/2, y1/2, z+1], N1-H1B. CL1 [3.307(1)1, 1311; Symmetry code: x+1, y, z+1], N2H2A. CL1 [3.183(1)1, 1531; Symmetry code: (x+3/2, y1/2, z] and N2-H2B..CL1 [3.273(1)1, 1431] Cl hydrogen bond acceptor.
Table 5 The optimized bond length, bond angle and electron density (r) (at bond critical point) in (a.u) of the SBTC complexes calculated using B3LYP methods with 6-311+G(d,p) basis set. System
Bond
Bond length (A˚)
Bond angle (1)
r (a.u)
SBTC-1
N–H?Cl C–H?Cl N–H?Cl N–H?Cl N–H?Cl
1.767 2.428 1.958 2.050 1.666
174.7 162.9 154.2 150.9 177.1
0.07361 0.01704 0.04429 0.03790 0.09393
SBTC-2 SBTC-3
0.10
3.1. DFT calculations
0.9512
0.09 0.08 0.07 ρ (au)
The three structures of hydrogen-bonded SBTC systems considered in the present work are shown in Fig. 2. The structures have been labeled as SBTC1, SBTC2 and SBTC3. Table 5 lists the bond lengths and bond angles of the three structures of SBTC complexes calculated using B3LYP method with 6-311+(d,p) basis set. In all the cases chlorine acts as the proton acceptor and S-benzylisothiouronium as proton donor. Of all the complexes, SBTC2 and SBTC3 have two and one N–H?Cl hydrogen bonds, respectively. But complex SBTC1 has one N–H?Cl and one C–H?Cl hydrogen bond. The hydrogen bond angles for SBTC1, SBTC2, and SBTC3 complexes are 174.71 and 162.91, 154.21 and 150.91, and 177.11, respectively. The complex SBTC3 is found to have smaller N–H?Cl hydrogen bond length (1.666 A˚) when compared with the SBTC1 (1.767 A˚) and SBTC2 (2.050 A˚, 1.958 A˚). On correlating both the bond lengths with respective bond angle
0.06 0.05 0.04 0.03 0.02 0.01 1.6
1.7
1.8
1.9
2.0 2.1 R (Å)
2.2
2.3
2.4
2.5
Fig. 3. Correlation between the electron density at bond critical point and the hydrogen bond distance for all the complexes considered in this work calculated using B3LYP method.
Fig. 2. The optimized structures of SBTC complexes.
values in all the complexes, it is evident that SBTC3 complex has strong N–H?Cl hydrogen bond due to linear bond angle value. Similarly the SBTC1, which has the second stronger hydrogen bond (1.767 A˚), has a bond angle value of 174.71; furthermore, if the geometrical parameters of SBTC1 and SBTC2 are compared, both complexes have two hydrogen bonds each but complex SBTC1 has one C–H?Cl, which is not a conventional hydrogen bond. The bond length of C–H?Cl is found to be large (2.42 A˚) of all bond lengths, but lies well within definition of hydrogen bond distance. The comparison of bond length and bond angle values with experimental data given in Table 4 reveals that the nature of hydrogen bond in both cases are same but the magnitude is different. An understanding of the nature of a hydrogen bond can be analyzed through the study of electron density at the bond critical point (BCP) of the various hydrogen bonds involved in the complexes. The value of electron density (r) (in atomic units) at BCP of N–H?Cl and C–H?Cl bonds calculated using AIM approach are presented in Table 5. The electron density values indicate the presence of hydrogen bond in all complexes in accordance with Popelier’s criteria [21,22]. It is expected that the strong bonds are usually associated with higher electron density values, indicating higher structural stability, as is observed for the N–H?Cl bond in the SBTC3 complex, which has higher electron density (0.09393 a.u) and strong hydrogen bond (1.66 A˚). This trend of order is found for all hydrogen bond lengths calculated at the bond critical points in all complexes. In this context, it should be noted that in the SBTC1 complex, apart from the N–H?Cl
ARTICLE IN PRESS P. Hemalatha et al. / Journal of Physics and Chemistry of Solids 70 (2009) 322–325
hydrogen bond, BCP also exists for the C–H?Cl bond. The electron density at the C–H?Cl BCP is 0.01704 indicating the presence of hydrogen bond in accordance with Popelier’s criteria [22,23]. The lines corresponding to the correlation fit are shown in Fig. 3. The correlation between the hydrogen bond length and electron density is inverse, that is, an increase in bond length corresponds to a decrease in the electron density, which is expected, since increase in distance results in reduced orbital overlap and hence low electron density along the bond. The correlation coefficient for the electron density with hydrogen-bond distance for B3LYP method is found to be 0.9512.
4. Conclusion The single crystal of SBTC is orthorhombic with space group Pbca and it exhibits second-order NLO susceptibility due to intermolecular hydrogen bonding. The electro negativity of nitrogen is higher compared to that of carbon. Since N(1) and N(2) have strong interaction with Cl(1), the N–H?Cl and C–H?Cl hydrogen bonding present in SBTC helps to create the delicate balance between competing molecular and supramolecular CT effects, thus to create SHG active material. DFT calculations predict N–H?Cl to be the strong hydrogen bond present in complex SBTC3 in accordance with experimental study. The AIM analysis augments the former result indicating a large electron density value for this hydrogen bond. References [1] R.F. Belt, G. Gashurov, Y.S. Liu, Laser Focus 10 (1985) 110–114. [2] R.S. Clark, Photonics Spectra 22 (1988) 135–140.
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[3] Gambino, Bull. Mater. Res. Soc. 15 (1990) 20–24. [4] S.P. Velsko, L.E. Davis, E. Wang, S. Monaco, D. Eimerl, Proc. Soc. Photo-Opt. Instrum. Eng. 824 (1988) 178–182. [5] N.J. Long, Chem. Int. Ed. Engl. 34 (1995) 21–25. [6] M.M. Fejer, Phys. Today 25 (1994) 57–61. [7] D.M. Burland, Chem. Rev. 94 (1994) 1–2. [8] B.L. Davydov, L.D. Derkacheva, V.V. Dunina, L.G. Koreneva, M.A. Samokhina, M.E. Zhabotinskii, V.F. Zolin, JEPT Lett. 12 (1970) 16–19. [9] J.L. Oudar, J. Zyss, Phys. Rev. A 26 (1982) 2028–2033. [10] J.L. Oudar, J. Chem. Phys. 67 (1977) 446–449. [11] S.J. Lalama, A.F. Garito, Phys. Rev. A 20 (1979) 1179–1184. [12] A.C. Albrecht, A. Morell, Chem. Phys. Lett. 64 (1979) 46–51. [13] V. Zavodnik, A. Stash, V. Tsirelson, R. de Vries, D. Feil, Acta Crystallogr. B 55 (1999) 45–54. [14] L.J. Farrugia, P.R. Mallinson, B. Stewart, Acta Crystallogr. B 59 (2003) 234–247. [15] V. Langer, D. Gyepesova´, E. Scholtzova´, J. Luston, J. Kronek, M. Koo´s, Acta Crystallogr. C 62 (2006) 416–418. [16] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–790. [17] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652. [18] P.J. Stephens, F.J. Devlin, C.F. Chabalowski, M.J. Frisch, J. Phys. Chem. 98 (1994) 1623–1626. [19] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, Jr., J.A. Montgomery, 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, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, 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 03, 2004, Gaussian Inc, Wallingford CTPA, 2001. [20] Requeline M. Cole, A.K. Adith Howard, J. Garry McIntyre, Acta Crystallogr. B 57 (2001) 410–415. [21] S.R. Marder, J.W. Perry, Adv. Mater. 5 (1993) 804–809. [22] U. Kock, P.L.A. Popelier, J. Phys. Chem. A 99 (1995) 9747–9750. [23] P.L.A. Popelier, J. Phys. Chem. A 102 (1998) 1873–1876.
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Importance of hydrogen bonding for second harmonic generation effect: X-ray diffraction and DFT study on S-benzyl isothiouronium chloride P. Hemalatha a, V. Veeravazhuthi b,, D. Velmurugan c, L. Senthilkumar a, J. Mallika d, D. Mangalaraj e a
Department of Physics, PSG College of Technology, Coimbatore-641 004, Tamil Nadu, India Department of Physics, PSG College of Arts and Science, Coimbatore-641 014, Tamil Nadu, India Department of Bio Physics and Crystallography, University of Madras, Chennai-600 025, Tamil Nadu, India d Department of Chemistry, PSG College of Arts and Science, Coimbatore-641 014, Tamil Nadu, India e Department of Nanotechnology, Bharathiar University, Coimbatore-641 046, Tamil Nadu, India b c
a r t i c l e in f o
a b s t r a c t
Article history: Received 5 July 2008 Received in revised form 6 September 2008 Accepted 31 October 2008
X-ray diffraction study of the nonlinear optical (NLO) material S-benzyl isothiouronium chloride (C8H11N2SCl) (SBTC) is reported for the first time. The single crystal of SBTC is orthorhombic with space group Pbca. SBTC exhibits second-order NLO susceptibility, and this study shows that hydrogen bonding is, in part, responsible for this. The present work shows that C–H?Cl and N–H?Cl hydrogen bonds direct the nature of the three-dimensional lattice. Such intermolecular interactions help to extend the molecular charge transfer into the supramolecular realm, the charge transfer originating as a consequence of the high level of molecular planarity and strong donor-to-acceptor interactions. Density functional theory (DFT) calculation and atom-in-molecule (AIM) analysis has been carried out to study the nature of hydrogen involved in the SBTC complex. & 2008 Elsevier Ltd. All rights reserved.
Keywords: A. Organic compound B. Crystal growth C. X-ray diffraction D. Crystal structure
1. Introduction Organic compounds are often formed by weak van der Waals bonds and hydrogen bonds and hence possess high degree of delocalization. Thus they are expected to be optically more nonlinear than inorganic compounds. Some of the advantages of organic materials include ease of varied synthesis, scope for altering the properties by functional substitutions, inherently high nonlinearity, high damage resistance, etc. The prototype organic nonlinear optical (NLO) material contains one or more delocalized bonds, typically a ring structure like benzene. Owing to the high polar nature of the molecules, organic NLO materials often tend to crystallize as long needles or thin platelets. New NLO frequency conversion materials can have a significant impact on laser technology, [1] optical communication, [2] and optical data storage technology [3]. These applications have unique and often competing material requirements and illustrate that no single nonlinear material will be suitable for all uses. The high optical thresholds and much versatility in the molecular design of organic materials provide many more opportunities for improving the SHG response [4]. SHG is one of the most important aspects to NLO research since it leads itself to a myriad of applications: from telecommunications to visible light
Corresponding author. Tel.: +91 422 2573386; fax: +91 422 2575622.
E-mail address: [email protected] (V. Veeravazhuthi). 0022-3697/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2008.10.023
lasers, through to surface-enhanced Raman spectroscopy [5–7]. The level of SHG response of a given material is inherently dependent upon its structural attributes. On a molecular scale, the extent of charge transfer (CT) across the NLO chromophore determines the level of SHG output [8–12]: the greater the CT, the larger the SHG output. The presence of strong intermolecular interactions, such as hydrogen bonds can extend this level of CT into the supramolecular realm, owing to their electrostatic and directed nature, thereby enhancing the SHG response. The structural characteristic of SBTC, on the molecular scale, reveals that they are: extremely p-conjugated, good planarity and strong electron donor and acceptor groups at opposite ends of the molecule. Density functional theory (DFT) is a cost-effective ab initio quantum chemistry procedure for studying physical properties of the molecules. DFT calculations have shown promising conformity with experimental results [13–15]. Therefore, in this present investigation DFT is used to study the geometry and characterization of hydrogen bond in the SBTC complexes.
2. Experimental and computational details Nonius CAD–4/MACII 3 diffractometer with MoKa (0.71073 A˚) radiation was employed for this study. Experimental details are given in Table 1. Density functional theory-based method has been used to investigate the electronic structure of the SBTC systems.
ARTICLE IN PRESS P. Hemalatha et al. / Journal of Physics and Chemistry of Solids 70 (2009) 322–325
Table 1 Crystallographic data of SBTC. Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density Absorption coefficient F(0 0 0) Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to y ¼ 25.001 Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I42sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole
323
S1 C8H11N2SCl 202.7 g 293(2) K 0.71073 A Orthorhombic Pbca a ¼ 8.4188 A˚, b ¼ 11.3642 A˚, c ¼ 20.5225 A˚ a ¼ b ¼ g ¼ 901 1963.5 A˚3 8 1.376 kg/m3 0.551 mm1 843 1.99–28.011 14php14; 10pkp10; 26plp6 20752 2337 [R(int) ¼ 0.0243] 99.9% Full-matrix least square on F2 2337/0/110 1.0332 R1 ¼ 0.02884, wR2 ¼ 0.0838 R1 ¼ 0.0309, wR2 ¼ 0.0862 0.0200(16) 0.230 and 0.208 A˚3
We have carried out geometry optimization for all the structures of the SBTC complexes using DFT with B3LYP exchange-correlation functional [16–18] and 6-311+G(d,p) basis set. The vibrational frequencies computed using the analytical second derivatives at the B3LYP/6-311+G(d,p) [Becke 3-parameters (Exchange), Lee, Yang and Pau (Correlation) level of theory for all complexes indicate no imaginary frequency, which implies that all the complexes are stationary states. The topological parameter electronic charge density has been calculated using atoms-inmolecule (AIM) analysis. All the calculations have been performed using the Gaussian 03 program [19].
3. Results and discussion An ORTEP (Oak Ridge Thermal Ellipsoid Plot) of SBTC crystal structure is shown in Fig. 1. Bond lengths and bond angles are given in Tables 2 and 3, respectively. The complete delocalization of p electrons of the ring systems makes them wholly aromatic in character. In case of phenyl ring, the delocalization of p electrons is caused by side–side overlapping of available p orbital present on the carbons constituting the ring. The ample delocalization of the p electrons is possible only if the ring is flat or planar, so as to allow cyclic overlap of p orbital [20]. From the crystallographic data, the angle of phenyl ring relative to the mean plane of the molecule is obtained as 0.8(1)1 [C(1)–C(6)]. The deviation of nitrogen group from the mean plane (i.e., 9.44(1)1) is large enough for the molecule. This, in turn, enhances the nitrogen–chloride donor–acceptor interactions across the molecule and hence, the degree of molecular CT. Significant molecular CT effects might be expected to cause a perturbation of aromatic ring towards a more quinoidal electronic configuration since provides more extended level of p-conjugation in the system [19]. Five intermolecular interactions were located within the threedimensional lattice of SBTC. Among these one interaction was weak interaction of the type C–H?Cl and four were strong interactions of the type N–H?Cl. Hydrogen bonding geometry details are given in Table 4. The weak intermolecular interaction C7-H1A?Cl [3.793 (1) A˚, 1731; Symmetry code: x+1, y, z+1], involves either p or Cl hydrogen bond acceptor. This type of acceptor is very common and C–H?p interactions are rare.
C8
C2
C7 N1
C3
C1
C6 C4 N2
C5 CL1
Fig. 1. ORTEP plot of SBTC crystal.
Table 2 Bond lengths (A˚). S(1)–C(8) S(1)–C(7) C(8)–N(2) C(8)–N(1) C(4)–C(3) C(4)–C(5) C(4)–C(7) C(5)–C(6) C(3)–C(2) C(6)–C(1)
1.740(1) 1.816(1) 1.309(2) 1.309(2) 1.384(2) 1.389(2) 1.506(2) 1.379(2) 1.392(2) 1.380(2)
Table 3 Bond angles (1). C(8)–S(1)–C(7) N(2)–C(8)–N(1) N(2)–C(8)–S(1) N(1)–C(8)–S(1) C(3)–C(4)–C(5) C(3)–C(4)–C(7) C(5)–C(4)–C(7) C(6)–C(5)–C(4) C(4)–C(3)–C(2) C(2)–C(1)–C(6) C(1)–C(2)–C(3)
104.2(1) 121.9(1) 115.5(1) 122.7(1) 118.9(1) 120.5(1) 120.6(1) 114.9(1) 120.6(1) 119.9(2) 119.9(2)
Table 4 Hydrogen bonding geometry (A˚). D–H?A
d(D?H)
d(H?A)
d(D?A)
o(DHA)
N2–H2B?CL1 N1–H1A?CL1a N1–H1B?CL1b C7–H7A?CL1b N2–H2A?CL1c
0.86 0.86 0.86 0.97 0.86
2.55 2.32 2.68 2.83 2.39
3.273(1) 3.157(1) 3.307(1) 3.793(1) 3.183(1)
143 164 131 173 153
Symmetry transformations used to generate equivalent atoms: a x1/2, y1/2, z+1. b x+1, y, z+1. c x+3/2, y1/2, z.
Moreover, although C–H?p interactions are generally fairly weak, they can be structurally significant. Since CH2 group in SBTC is an electron releasing group, it increases the overall electron density in the ring. Therefore C(7) donates less number of electrons to Cl(1), causing weak interaction.
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The hydrogen bonds concerned may be classified as weak, but are evidently highly influential especially since they appear to form at the expense of any classical O–H?X or N–H?X hydrogen bonds, despite the presence of such strong hydrogen bond donors. The systematic asymmetry of the S–C–N angle is 115.5(1)1 for the smaller and 122.7(1)1 for the larger, the latter involving the N atom participating in the stronger N–H–Cl interactions. The four strong interactions N1–H1Ay. CL1 [3.157(1)1, 1641; Symmetry code: x1/2, y1/2, z+1], N1-H1B. CL1 [3.307(1)1, 1311; Symmetry code: x+1, y, z+1], N2H2A. CL1 [3.183(1)1, 1531; Symmetry code: (x+3/2, y1/2, z] and N2-H2B..CL1 [3.273(1)1, 1431] Cl hydrogen bond acceptor.
Table 5 The optimized bond length, bond angle and electron density (r) (at bond critical point) in (a.u) of the SBTC complexes calculated using B3LYP methods with 6-311+G(d,p) basis set. System
Bond
Bond length (A˚)
Bond angle (1)
r (a.u)
SBTC-1
N–H?Cl C–H?Cl N–H?Cl N–H?Cl N–H?Cl
1.767 2.428 1.958 2.050 1.666
174.7 162.9 154.2 150.9 177.1
0.07361 0.01704 0.04429 0.03790 0.09393
SBTC-2 SBTC-3
0.10
3.1. DFT calculations
0.9512
0.09 0.08 0.07 ρ (au)
The three structures of hydrogen-bonded SBTC systems considered in the present work are shown in Fig. 2. The structures have been labeled as SBTC1, SBTC2 and SBTC3. Table 5 lists the bond lengths and bond angles of the three structures of SBTC complexes calculated using B3LYP method with 6-311+(d,p) basis set. In all the cases chlorine acts as the proton acceptor and S-benzylisothiouronium as proton donor. Of all the complexes, SBTC2 and SBTC3 have two and one N–H?Cl hydrogen bonds, respectively. But complex SBTC1 has one N–H?Cl and one C–H?Cl hydrogen bond. The hydrogen bond angles for SBTC1, SBTC2, and SBTC3 complexes are 174.71 and 162.91, 154.21 and 150.91, and 177.11, respectively. The complex SBTC3 is found to have smaller N–H?Cl hydrogen bond length (1.666 A˚) when compared with the SBTC1 (1.767 A˚) and SBTC2 (2.050 A˚, 1.958 A˚). On correlating both the bond lengths with respective bond angle
0.06 0.05 0.04 0.03 0.02 0.01 1.6
1.7
1.8
1.9
2.0 2.1 R (Å)
2.2
2.3
2.4
2.5
Fig. 3. Correlation between the electron density at bond critical point and the hydrogen bond distance for all the complexes considered in this work calculated using B3LYP method.
Fig. 2. The optimized structures of SBTC complexes.
values in all the complexes, it is evident that SBTC3 complex has strong N–H?Cl hydrogen bond due to linear bond angle value. Similarly the SBTC1, which has the second stronger hydrogen bond (1.767 A˚), has a bond angle value of 174.71; furthermore, if the geometrical parameters of SBTC1 and SBTC2 are compared, both complexes have two hydrogen bonds each but complex SBTC1 has one C–H?Cl, which is not a conventional hydrogen bond. The bond length of C–H?Cl is found to be large (2.42 A˚) of all bond lengths, but lies well within definition of hydrogen bond distance. The comparison of bond length and bond angle values with experimental data given in Table 4 reveals that the nature of hydrogen bond in both cases are same but the magnitude is different. An understanding of the nature of a hydrogen bond can be analyzed through the study of electron density at the bond critical point (BCP) of the various hydrogen bonds involved in the complexes. The value of electron density (r) (in atomic units) at BCP of N–H?Cl and C–H?Cl bonds calculated using AIM approach are presented in Table 5. The electron density values indicate the presence of hydrogen bond in all complexes in accordance with Popelier’s criteria [21,22]. It is expected that the strong bonds are usually associated with higher electron density values, indicating higher structural stability, as is observed for the N–H?Cl bond in the SBTC3 complex, which has higher electron density (0.09393 a.u) and strong hydrogen bond (1.66 A˚). This trend of order is found for all hydrogen bond lengths calculated at the bond critical points in all complexes. In this context, it should be noted that in the SBTC1 complex, apart from the N–H?Cl
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hydrogen bond, BCP also exists for the C–H?Cl bond. The electron density at the C–H?Cl BCP is 0.01704 indicating the presence of hydrogen bond in accordance with Popelier’s criteria [22,23]. The lines corresponding to the correlation fit are shown in Fig. 3. The correlation between the hydrogen bond length and electron density is inverse, that is, an increase in bond length corresponds to a decrease in the electron density, which is expected, since increase in distance results in reduced orbital overlap and hence low electron density along the bond. The correlation coefficient for the electron density with hydrogen-bond distance for B3LYP method is found to be 0.9512.
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