Article pubs.acs.org/JPCB
Halogen Bonding and Chalcogen Bonding in 4,7-Dibromo-5, 6-dinitro-2,1,3-benzothiadiazole Mysore S. Pavan, Ajay Kumar Jana, S. Natarajan,* and Tayur N. Guru Row* Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India S Supporting Information *
ABSTRACT: An organic solid, 4,7-dibromo-5,6-dinitro-2,1,3-benzothiadiazole, has been designed to serve as an illustrative example to quantitatively evaluate the relative merits of halogen and chalcogen bonding in terms of charge density features. The compound displays two polymorphic modifications, one crystallizing in a non-centrosymmetric space group (Z′ = 1) and the other in a centrosymmetric space group with two molecules in the asymmetric unit (Z′ = 2). Topological analysis based on QTAIM clearly brings out the dominance of the chalcogen bond over the halogen bond along with an indication that halogen bonds are more directional compared to chalcogen bonds. The cohesive energies calculated with the absence of both strong and weak hydrogen bonds as well as stacking interaction are indicative of the stabilities associated with the polymorphic forms.
■
INTRODUCTION Intermolecular interactions have carved a niche in chemistry and biology mainly because they deal with how and why molecules come closer or repel each other.1 In this context, the interaction that has garnered much attention over the years is the hydrogen bond.2 The importance of the hydrogen bond and its utility encompasses the length and breadth of chemical, biological, and material science. The other interaction which is as significant as the hydrogen bond is the π···π stack, extensively found in biological molecules like DNA and proteins.3 Additionally, the presence of stacking plays a major role in several organic functional materials.4 In recent years, another class of interactions has gained significant attention, which involves the so-called “σ-hole” defined as the charge depleted region on an electronegative element belonging to groups IV−VII of the periodic table.5,6 In this context, the most commonly encountered σ-hole interaction involves the halogens and such interactions have been termed as “halogen bond”.7−9 One of the advantages this interaction possesses is the strength and directionality, which has prompted many researchers to take a critical look at other p-block elements such as chalcogens, pnicogens, and tetrels.10−21 Thus, today we have a whole gamut of intermolecular interactions that can be effectively utilized to construct supramolecular assemblies. There are, however, still some unanswered questions, as these interactions in many molecular crystals appear as surrogates to other strong and well-known interactions such as hydrogen bonds or π···π stacks. We envisioned a design strategy in generating a molecule devoid of protons, which may utilize the other noncovalent interactions such as the halogen and chalcogen bonding interactions. © XXXX American Chemical Society
Thus, we have synthesized the molecule, 4,7-dibromo-5,6dinitro-2,1,3-benzothiadiazole, using simple organic reactions. An experimental charge density analysis on this compound would reveal the relative importance/dominance of the halogen and chalcogen bonding interactions in this compound. Indeed, mapping of charge densities in intermolecular space in recent years using the multipole model22 followed by extracting the electron density information based on Bader’s QTAIM23 approach has not just provided a qualitative description of bonding features but has also yielded quantitative inputs of relevance to the properties exhibited in molecular crystalline substances.13,21,24−27 To aid in establishing the relative merits of chalcogen and halogen bonding interactions, we have also carried out a detailed computational analysis as well. The present compound, 4,7-dibromo-5,6-dinitro-2,1,3-benzothiadiazole, is an intermediate in our synthesis of a carboxylic acid derivative for a larger study toward the preparation of inorganic coordination polymers.
Special Issue: Biman Bagchi Festschrift Received: April 13, 2015 Revised: June 16, 2015
A
DOI: 10.1021/acs.jpcb.5b03533 J. Phys. Chem. B XXXX, XXX, XXX−XXX
The Journal of Physical Chemistry B
■
EXPERIMENTAL SECTION Materials and Methods. 2,1,3-Benzothiadizole was purchased from Sigma-Aldrich and HBr (48%), trifluoromethanesulfonic acid, H2SO4, HNO3, and NaHSO3 were obtained from SDfine (India). Synthesis of 4,7-dibromo-2,1,3-benzthiadiazole was carried out on the basis of an earlier report:28,29 HBr (48%, 40 mL) was added to 2,1,3-benzothiadizole (2.0 g, 14.687 mmol) and stirred for 10 min at RT followed by slow addition of Br2 solution (7.04 g, 44.06 mmol) in HBr (30 mL) through a pressure equalizer funnel. Then, the reaction mixture was heated at 85 °C for 6 h. The reaction mixture was cooled to room temperature and treated with 150 mL of saturated NaHSO3 solution to consume the excess Br2. The precipitate formed was filtered under a vacuum, washed with water, and finally washed with cold diethyl ether. Then, the product was dried under vacuum for 4 h to obtain a pale yellow color solid (5.34 g, 92%). 1H NMR (400Mz, CDCl3): δ = 7.73 (s, 2H) ppm. Synthesis of 4,7-dibromo-5,6-dinitro-2,1,3-benzthiadiazole: To a suspension of H2SO4 (12 mL) and 4,7-dibromo-2,1,3benzthiadiazole (1.0 g, 3.402 mmol) at 0 °C, trifluoromethanesulfonic acid (3.61 mL, 40.824 mmol) and HNO3 (4 mL) were sequentially added. The reaction mixture was kept at room temperature for 12 h and then poured into ice−water, and then, the precipitate was filtered, washed with water, and then dried under a vacuum. Finally, the crude product was purified through column chromatography (silica gel, 10% EtOAc/hexane) to obtain 4,7-dibromo-5,6-dinitro-2,1,3-benzthiadiazole (0.966g, 42%). 13C NMR (400Mz, CDCl3, ppm): δ = 110.78, 145.37, 151.79. After the purification, the compound was recrystallized by slow evaporation using chloroform as the solvent. During the crystallization, two different types of crystals of 4,7-dibromo5,6-dinitro-2,1,3-benzothiadiazole were found to grow concomitantly and were selected under a polarizing microscope. The two forms hereafter would be referred to as form I and form II.
Table 1. Crystallographic Details (Including Multipole Refinement Parameters for I) I CCDC no. mol. formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z, Z′ ρcalc (g/cm3) F(000) μ (mm−1) T (K) λ (Å) (sin θ/λ) max(Å−1) reflns. collected unique reflns. completeness (%) redundancy Rint
1058401 C6Br2N4O4S 383.98 orthorhombic P212121 6.5749(1) 10.2142(1) 15.2263(2) 90 90 90 1022.56(2) 4, 1 2.494 728 8.14 100(2) 0.71073 1.08 114524 12155 99.9 9.4 0.09 Spherical Atom Refinement R1 (F) 0.036 wR2 (F2) 0.060 goodness of fit 0.947 Δρmin, max (e Å−3) −0.88, 1.10 Flack parameter 0.004(4) Multipole Refinement reflns. used [I > 2σ(I)] 9242 no. of parameters 318 R1 (F2) 0.032 wR2 (F2) 0.051 goodness of fit 0.913 Δρmin, max (e Å−3) (sin θ/λ < 0.8) −0.31, 0.46
Article
II 1058402 C6Br2N4O4S 383.98 triclinic P-1 9.1670(5) 10.2561(5) 11.4773(6) 86.709(4) 77.084(4) 76.289(4) 1021.78(9) 4, 2 2.496 728 8.15 100(2) 0.71073 0.649 9337 4672 99.9 2 0.039 0.04 0.08 1.04 −0.84, 0.86
■
DATA COLLECTION AND STRUCTURE REFINEMENT DETAILS The high resolution charge density data on form I and routine data on form II were both collected on an Oxford Xcalibur
Figure 1. ORTEP diagram of the asymmetric unit in (a) form I and (b) form II. B
DOI: 10.1021/acs.jpcb.5b03533 J. Phys. Chem. B XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry B
Figure 2. Interaction motifs in I: (a) halogen bond between Br and N atoms; (b) chalcogen bond between S and O atoms; (c) type II Br···Br contact; (d and e) lone pair···π interactions involving oxygen atoms; (f) packing diagram of I.
XD2006.22,33 The function Σ w [|Fo|2 − |Fc|2]2 was minimized for all reflections with I > 2σ (I). Weights (w) were taken as 1/σ2 (Fo2), and the convergence criterion of the refinement was set to a maximal shift/esd of
