Anion-Assisted Formation of Discrete Homodimeric and

Article pubs.acs.org/crystal

Anion-Assisted Formation of Discrete Homodimeric and Heterotetrameric Assemblies by Benzene Based Protonated Heteroaryl Receptors M. Arunachalam, Sourav Chakraborty, S. Marivel, and Pradyut Ghosh* Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata 700032, India S Supporting Information *

ABSTRACT: Anion-assisted formation of discrete homodimeric and heterotetrameric assemblies by benzene based protonated heteroaryl receptors L1−L6 have been studied thoroughly by single crystal X-ray diffraction studies. Crystallographic results elucidate the fact that protonated tripodal receptor L1 formed staggered homodimeric capsular assemblies 2 and 3 with CF3COO− and ClO4− ions, respectively. Protonation of L3 with trimesic acid also showed the formation homodimeric assembly, 6. In all these cases the anions are hydrogen bonded to the receptor molecules and show remarkable influence on the outcome of the self-assembly process to form discrete capsules. The necessity of the alkyl substitution on the benzene platform has been established from complexes 8, 9, and 10, which were obtained upon protonation of L6 with HNO3, HI, and HClO4, respectively. Interestingly, when a 1:1 mixture of L1 (tripodal) and L5 (dipodal) were treated with HClO4 and HBF4, discrete heterotetrameric assemblies have been isolated as complexes 11 and 12. The detailed solid state structural analysis of these complexes revealed the formation of heterotetrameric assemblies assisted by anion−water clusters. Correlation of these solid state structural assemblies with our previously reported complexes 1, 4, 5, and 7 has also been described. The role of anionic templates in assisting the formation of discrete capsular assemblies from receptors possessing heteroaryl units and 1,3,5-methyl substituted benzene platform has been established.

■

INTRODUCTION An upsurge in research activities in developing supramolecular architectures through self-assembly of two or more molecular components via noncovalent interactions is witnessed in the last two decades due to their enormous potential in host−guest chemistry.1 Thus, chemists worldwide have employed diverse strategies to achieve various supramolecular architectures. The use of anionic templates for complicated organic synthesis and the development of supramolecular architectures is a comparatively less explored area than the conventional approaches that make use of metal coordination.2 A great deal of information has been accumulated in recent years about anion-assisted interlocked molecules and self-assemblies.3,4 Encapsulation of anions/hydrated anions in a homodimeric capsular assembly by tripodal4 and hexapodal5 amide/urea based receptors have been reported by us and others in the literature. It is necessary to organize, control, or foresee the © 2012 American Chemical Society

formation of organized assemblies by the host molecules upon guest inclusion/binding. Our preliminary results on triprotonated benzimidazole functionalized L1 (Chart 1) showed NO3− assisted homodimeric assembly, 1 (Chart 2a) and Cl− induced disassembly processes.4d In another communication, we have investigated NO3− assisted assemblies of triprotonated tripodal receptors L2 and L3 (Chart 1).4f The imidazole substituted receptor L2 showed the formation of a distorted capsule [H3L2·3NO3·H2O], 4 (Chart 2b), whereas triprotonated dimethyl pyrazole substituted receptor L3 yielded the formation of a NO3− ion bridged macrocyclic assembly, [H3L3·3NO3], 5 (Chart 2c). However, diprotonated dipodal benzimidazole receptor L4 formed a zigzag polymeric chain upon NO3− ion Received: January 23, 2012 Revised: February 27, 2012 Published: March 5, 2012 2097

dx.doi.org/10.1021/cg300099m | Cryst. Growth Des. 2012, 12, 2097−2108

Crystal Growth & Design

Article

Chart 1. Molecular Structures of L1−L6

procedures.10 Complexes 1, 4, 5, and 7 were prepared by following our recent literature procedure.4f Synthesis of 1,3,5-Tris(benzimidazolylmethyl)benzene, L6. Benzimidazole (0.66 g, 5.6 mmol) was added to the suspension of sodium hydride (60% suspension in mineral oil) (0.17 g, 7 mmol) in dry THF (50 mL) in a 250 mL single neck round-bottom flask and stirred for 30 min. 1,3,5-Tris(bromomethyl)benzene (0.5 g, 1.4 mmol) was dissolved in 60 mL of dry THF and then added very slowly to the reaction mixture from a 100 mL pressure equalizer funnel. The reaction mixture was continued to stir for 36 h at room temperature. Solvent was removed in vacuo and extracted with dichloromethane (50 × 3 mL). The organic layer was thoroughly washed with water, saturated sodium hydrogen carbonate solution, saturated sodium chloride solution, and then dried over Na2SO4. Analytically pure L6 was obtained as white solid upon evaporation of dichloromethane in vacuo. Yield 72%. 1H NMR (300 MHz, DMSO-d6, δ (ppm)): δ 5.38 (s, 6H), 7.06−7.13 (m, 6H), 7.28−7.31 (d, 6H), 7.63 (d, 3H), 8.30 (s, 3H). 13C NMR (75 MHz, DMSO-d6): δ 47.44, 110.59, 119.45, 121.57, 122.31, 126.59, 133.47, 137.92, 143.52, 144.04. HRMS (ESI+) data: 469.2675 [L6]+, 937.5996. [2L6]+. Synthesis of Complex [H3L6·3CF3COOH·CF3COOH·4H2O]2, 2. Complex 2 was obtained by adding 0.5 mL of CF3COOH to the methanolic suspension of L1 (511 mg, 1 mmol). After the addition of acid, the suspension became clear, and the solution was filtered and kept for crystallization at room temperature. Colorless crystals suitable for X-ray crystallography were obtained after 2 days. Yield of 2: 65− 70%. 1H NMR (D2O, 300 MHz): δ (ppm) 2.42 (s, 9H), 5.94 (s, 6H), 7.74−7.75 (m, 6H), 7.93 (m, 6H), 8.86 (s, 3H). 13C NMR (D2O, 75 MHz): δ (ppm) 15.68, 45.93, 112.74, 114.71, 126.78, 127.31, 128.95, 130.86, 131.08, 138.63, 138.77, 141.93. Synthesis of Complex [H3L1·3ClO4·HClO4·nH2O], 3. Complex 3 was obtained by adding 0.5 mL of HClO4 to the methanolic suspension of L1 (511 mg, 1 mmol). After the addition of acid, the suspension turned clear, and the solution was filtered and kept for crystallization at room temperature. Colorless crystals suitable for Xray crystallography were obtained after 5 days. Yield of 3: 72−76%. 1H NMR (CD3OD, 300 MHz): δ (ppm) 2.41 (s, 9H), 5.91 (s, 6H), 7.75 (m, 6H), 7.92−7.97 (m, 6H), 8.87 (s, 3H). 13C NMR (CD3OD, 75

binding (Chart 2e). These preliminary results clearly suggested the role of substituents and the geometry of the anion toward the formation of various assemblies. Herein, we have undertaken a detailed self-assembly and comparative studies on a series of benzene platform based protonated heteroaryls L1−L6 (Chart 1) to address the nature of assembly, the size of the aggregate, the effect of anion templates, and the role of alkyl substitutions on the benzene platform toward the formation of organized homodimeric (Chart 2a,d) and heterotetrameric (Chart 3) assemblies. To date, the most extensively studied capsular assembly is homodimeric assemblies,4 where both the self-assembling counter parts are identical. Few eminent examples of heterodimeric,6 tetrameric,7 and hexameric8 assemblies are also reported in the literature. However, very limited reports show the existence of heterotetrameric assemblies.9

■

EXPERIMENTAL SECTION

Materials and Methods. Hydroiodic acid and 1,3,5-tris(bromomethyl)benzene were purchased from Sigma Aldrich and were used without further purification. Benzimidazole, tetrahydrofuran (THF), dimethyl formamide (DMF), diethyl ether, dichloromethane (DCM), sodium sulfate, sodium hydrogen carbonate, nitric acid, and perchloric acid were purchased from Cyno-chem, India, and were directly used without any further purification. Solvents were dried by conventional methods and distilled under nitrogen atmosphere before being used. Physical Measurements. 1H NMR and 13C NMR spectra were recorded on Bruker 500 and 125 MHz FT-NMR spectrometers equipped with the appropriate decoupling accessories, respectively, using tetramethylsilane as an internal reference. Chemical shifts are reported in units of parts per million, and HRMS measurements were carried out on QTof-Micro YA 263 instruments. Synthesis. Syntheses of receptors L1−L5 are quite straightforward and can be synthesized in good yields following the literature 2098



Article

Chart 2. Schematic Diagram Showing Binding of Anions in Complexes 1−10

2−3 days with 67% yield. The crystals were used for further analysis. H NMR (DMSO-d6, 500 MHz): δ (ppm) 1.79 (s, 18H), 2.06 (s, 9H), 3.66 (s, 6H), 4.14 (b, 6H), 8.63 (s, 9H). 13C NMR (125 MHz, DMSO-d6): δ (ppm) 10.06, 16.41, 25.31, 111.31, 131.99, 133.33, 133.59, 134.10, 140.41, 165.92. Synthesis of Complex [H3L6·3NO3·H2O], 8. Complex 8 was obtained by adding 0.5 mL of conc. nitric acid to the aqueous suspension of L6 (80 mg, 1 mmol). A clear suspension was obtained upon the addition of acid; the solution was filtered and kept for crystallization at room temperature. Colorless crystals suitable for Xray crystallography were obtained after 3 weeks. Single crystals of 8 were isolated manually under an optical microscope and dried completely before doing the analysis. Yield of 8: 30%; 1H NMR (300 MHz, DMSO-d6, δ (ppm)): 5.67 (s, 3H), 7.37−7.40 (m, 3H), 7.52− 7.57 (m, 9H), 7.86 (t, 3H), 9.57 (s, 3H). 13C NMR (75 MHz, DMSOd6: δ 49.58, 113.39, 116.28, 126.05, 126.46, 128.23, 131.45. Synthesis of Complex [H2L6·2I·H2O·DMF], 9. Complex 9 was obtained by adding 0.5 mL of conc. HI to the DMF solution of L6 (80 mg, 1 mmol). A clear suspension was obtained upon the addition of acid; the solution was filtered and kept for crystallization at room temperature. Colorless crystals suitable for X-ray crystallography were obtained after 6 weeks from the brownish solution. Single crystals of 9 were isolated manually under optical microscope and dried completely before doing the analysis. Yield: 20%. 1H NMR (300 MHz, DMSO-d6, δ (ppm)): δ 5.50 (s, 6H), 7.20 (t, 3H), 7.34−7.40 (m, 9H), 7.69 (d, 3H), 9.13 (s, 3H). 13C NMR (75 MHz, DMSO-d6): δ 49.19, 112.89, 117.30, 125.27, 125.40, 128.00, 132.13, 137.14, 143.18.

Chart 3. Schematic Diagram of Heterotetrameric Assemblies in Complexes 11 and 12

1

MHz): δ (ppm) 18.73, 48.87, 115.64, 118.05, 129.78, 130.24, 132.19, 134.35, 134.67, 142.22, 144.91. Synthesis of Complex [H3L3·3TMA·2H2O], 6. L3 (90 mg, 0.2 mmol) was taken in a 50 mL beaker and dissolved by adding excess of CH3OH upon heating at 60 °C. To the clear solution was added a methanolic solution of trimesic acid (126 mg, 0.6 mmol) and stirred well. The resulting mixture was kept for slow evaporation at ambient conditions. The colorless trigonal shaped crystals were obtained after 2099



Article

Table 1. Crystallographic Parameters of Complexes 2, 3, 6, and 8 parameters

complex 2

complex 3

complex 6

complex 8

chemical formula formula weight crystal size (mm) crystal description crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) cell volume (Å3) Z diffractometer dcalcd (g/cm3) F(000) μMoKα (mm−1) T (K) theta max (deg) obs. reflections parameters refined GOF (F2) R1 wR2

C82H71F24N12O24 2064.51 0.12 × 0.14 × 0.16 block triclinic P1̅ 12.479(4) 12.888(4) 15.116(5) 93.634(7) 94.092(7) 105.305(7) 2330.2(13) 1 Smart CCD 1.480 1067 0.139 100 (2) 25.0 22 047 659 1.050 0.0879 0.2708

C33H38Cl4N6O18 943.45 0.10 × 0.14 × 0.16 block rhombohedral R3̅ 43.7719(13) 43.7719(13) 12.7427(8) 90 90 120 21144(5) 18 Smart CCD 1.334 8730 0.325 100 (2) 20.9 45 587 556 1.064 0.0702 0.1810

C99H100N12O31 1953.91 0.22 × 0.28 × 0.32 block trigonal P3221 19.6800(10) 19.6800(10) 21.610(2) 90 90 120 7248.3(8) 3 Smart CCD 1.364 3078 0.104 293 (2) 24.7 66 739 677 1.064 0.0904 0.2417

C30H29N9O10 675.62 0.08 × 0.12 × 0.14 block triclinic P1̅ 9.4606(7) 10.5273(8) 17.5009(12) 79.280(2) 76.871(2) 63.893(2) 1516.85(19) 2 Smart CCD 1.479 704 0.114 100 (2) 25.0 14 492 442 1.062 0.0508 0.1302

Table 2. Crystallographic Parameters of Complexes 9, 10, 11, and 12 parameters

complex 9

complex 10

complex 11

complex 12

chemical formula formula weight crystal size (mm) crystal description crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) cell volume (Å3) Z diffractometer dcalcd (g/cm3) F(000) μMoKα (mm−1) T (K) theta max obs. reflections parameters refined GOF (F2) R1 wR2

C33H34I2N7O2 814.47 0.08 × 0.12 × 0.16 block monoclinic P21/n 9.3543(6) 22.1377(15) 16.6022(11) 90 104.2280(10) 90.00 3332.6(4) 4 Smart CCD 1.621 1608 1.928 100 (2) 25.0 31 189 399 1.05 0.0253 0.0576

C33H34Cl2N7O9 742.57 0.10 × 0.14 × 0.16 block monoclinic P21/n 9.4032(14) 22.782(3) 16.298(3) 90 103.400(3) 90.00 3396.4(9) 4 Smart CCD 1.452 1544 0.257 100 (2) 25.0 31 062 462 1.07 0.0406 0.1130

C58H73Cl5N10O27 1519.51 0.08 × 0.10 × 0.16 block monoclinic P21/c 20.4226(15) 18.5996(14) 20.1705(15) 90 117.501(2) 90 6796.0(9) 4 Smart CCD 1.485 3168 0.305 100 (2) 21.01 43 490 949 1.03 0.0584 0.1479

C58H71B5F20N10O6 1438.30 0.80 × 1.00 × 1.20 block monoclinic P21/c 20.5849(12) 18.4162(10) 19.9691(11) 90 117.953(1) 90 6687.0(7) 4 Smart CCD 1.429 2968 0.130 100 (2) 25.0 62 673 961 1.07 0.0637 0.1853

Synthesis of Complex [H2L6·ClO4·DMF], 10. Complex 10 was obtained by adding 0.5 mL of conc. HClO4 to the DMF solution of L6 (80 mg, 1 mmol). The solution was warmed, filtered, and kept for crystallization at room temperature. Initially, the solution was colorless, and it attains brownish yellow color after some time. Colorless crystals suitable for X-ray crystallography were obtained after

6 weeks. Single crystals of 10 were isolated manually under optical microscope and dried completely before doing the analysis. Yield: 40%. 1H NMR (300 MHz, DMSO-d6, δ (ppm)): δ 5.57 (s, 6H), 7.29 (d, 3H), 7.39−7.47 (m, 9H), 7.77 (d, 3H), 9.09 (s, 3H). 13C NMR (75 MHz, DMSO-d6) δ 48.93, 112.47, 117.61, 124.81, 127.73, 132.35, 137.27, 143.32. 2100



Article

Figure 1. (a) MERCURY diagram showing the CF3COO− stitched capsular aggregate of [H3L1]3+ with encapsulated water molecules in complex 2; (b) space filling view of the staggered assembly along the benzene cap. Color code: C, orange and purple; H, cyan; N, blue; O, red. Nonbonded hydrogen atoms, lattice solvent, and TFA ion are omitted for clarity. Synthesis of Complex [H3L1·H2L5·5ClO4·4H2O], 11. Complex 11 was obtained by adding 0.5 mL of conc. HClO4 to the aqueous suspension containing a mixture of 51 mg (0.1 mmol) of L1 and 38 mg (0.1 mmol) of L5. After the addition of acid, the suspension becomes clear, and the solution was warmed, filtered, and kept for crystallization at room temperature. Colorless blocks of crystals suitable for X-ray crystallography were obtained after 5−6 days. Yield of 11: 83%. 1H NMR (CD3OD-D2O 50% v/v, 500 MHz): δ (ppm) 2.27 (s, 3H), 2.39 (s, 9H), 2.40 (s, 6H), 5.77 (s, 4H), 5.86 (s, 6H), 7.33 (s, 1H), 7.71− 7.77 (m, 10H), 7.87 (d, 5H), 8.04 (d, 2H), 8.15 (d, 3H), 8.84 (s, 2H), 8.94 (s, 3H). 13C NMR (125 MHz, CD3OD-D2O 50% v/v): δ (ppm) 17.83, 18.78, 21.96, 48.65, 115.74, 117.95, 129.92, 130.38, 130.62, 134.41, 135.05, 142.19, 143.96. Synthesis of Complex [H3L1·H2L5·5BF4·nH2O], 12. Complex 12 was obtained by adding 0.5 mL of conc. HBF4 to the aqueous suspension containing mixture of 51 mg (0.1 mmol) of L1 and 38 mg (0.1 mmol) of L5. A clear suspension was obtained upon the addition of acid; the solution was warmed, filtered, and kept for crystallization at room temperature. Colorless blocks of crystals suitable for X-ray crystallography were obtained after a week. Yield of 12: 85%. 1H NMR (DMSO-d6, 500 MHz): δ (ppm) 2.32 (s, 36H), 4.16 (b, 10H), 5.696 (s, 8H), 5.79 (s, 12H), 7.26 (s, 2H), 7.691−7.656 (m, 20H), 7.903−7.861 (m, 10H), 8.10−8.08 (m, 10H), 9.05 (s, 10H) 13C NMR (DMSO-d6,125 MHz,): δ (ppm) 15.65, 16.48, 19.61, 45.38, 45.78, 113.49, 113.57, 115.09, 126.47, 127.01, 127.90, 129.1, 131.27−131.71, 140.35−140.50, 141.82. X-ray Measurement and Structure Determination. A summary of the crystal data and structure refinements for complexes 2, 3, 6, and 8 are given in Table 1, and crystallographic data and details of data collection for complexes 9, 10, 11, and 12 are given in Table 2. In each case, a crystal of suitable size was selected from the mother liquor and immersed in partone oil, then mounted on the tip of a glass fiber and cemented using epoxy resin. Intensity data for all four crystals were collected using MoKα (λ = 0.7107 Å) radiation on a Bruker SMART APEX diffractometer equipped with a CCD area detector at 100 K. The data integration and reduction were processed with SAINT11a software. An empirical absorption correction was applied to the collected reflections with SADABS11b The structures were solved by direct methods using SHELXTL12 and were refined on F2 by the full-matrix least-squares technique using the SHELXL-9713 program package. Graphics are generated using PLATON14 and MERCURY 2.3.15 Wherever possible, the hydrogen atoms are located on a difference Fourier map and refined, and in other cases, the hydrogen atoms are geometrically fixed.

In complex 2, the occupancies of the disordered oxygen atoms and fluorine of CF3COO− ion and a molecule of CF3COOH are refined using PART and SADI command in SHELXTL during refinement. EADP command has been used for the refinement of Uiso values to be common for the two sites of the disordered atoms. Hydrogen atoms of a water molecule labeled O1 have been located on a difference Fourier map and refined, and the hydrogen atoms are not located or fixed for other water molecules. Moreover, in complex 2, all the N−H protons of the benzimidazolium rings were geometrically fixed and refined isotropically. In complex 3, the occupancies of the disordered oxygen atoms of a ClO4− have been refined using FVAR and SADI command in SHELXTL during refinement. EADP command has also been used for the refinement of Uiso values to be common for the two sites of the disordered oxygen atoms. In addition to the three water molecules located for the complex 3 from the difference Fourier map, a number of diffused scattered electron density peaks were observed, which can be attributed to disordered water molecules present in this complex. Attempts to model these peaks were unsuccessful since the residual electron density peaks obtained were diffused. PLATON/SQUEEZE16 was used to refine the structure further. In complex 6, the occupancies of the disordered oxygen and carbon atoms of a [H2TMA]− ion has been refined using PART and DFIX command in SHELXTL during refinement. EADP command has also been used for the refinement of Uiso values to be common for the two sites of the disordered oxygen and carbon atoms of [H2TMA]− ion. In complex 11, the occupancies of the disordered oxygen atoms of a ClO4− has been refined using FVAR command and SADI and DFIX commands were also used in SHELXTL during structure refinement. EADP command has also been used for the refinement of Uiso values to be common for the two sites of the disordered oxygen atoms. In complex 12, the occupancies of the disordered oxygen atoms of a BF4− have been refined using FVAR command in SHELXTL during refinement. In addition to the six water molecules located for the complex 12 from the difference Fourier map, a number of diffused scattered electron density peaks was observed, which can be attributed to disordered water molecules present in this complex. Attempts to model these peaks were unsuccessful since residual electron density peaks obtained were diffused. PLATON/SQUEEZE16 was used to refine the structure further. Single Crystal X-ray Crystallographic Results. The crystallization of the complexes was achieved by slow evaporation of aqueous solutions containing the receptor and appropriate quantities of the acids. These reactions were all straightforward, resulting in readily isolable products. Attempts were made to synthesize complexes of L1− L6 from various anions such as HCl, HBr, HI, HNO3, CF3COOH, 2101



Article

HClO4, H2SO4, H3PO4, HBF4, and trimesic acid. However, we are successful to isolate crystalline complexes 1, 2, and 3 using, respectively, HNO3, CF3COOH, and HClO4 from L1; complex 4 using HNO3 from L2; complexes 5 and 6 using HNO3 and trimesic acid from L3; complex 7 using HNO3 from L4; and complexes 8, 9, and 10 using HNO3, HI, and HClO4 from L6. Similarly, in our attempt to get protonated crystalline complexes from an equimolar mixture of L1 and L5, we are fortunate to obtain complexes 11 and 12 with HClO4 and HBF4, respectively. Crystal Structure of [H3L1·3CF3COO·CF3COOH·4H2O]2 (2). The reaction of L1 with trifluoroacetic acid in methanol gave complex [H3L1·3CF3COO·CF3COOH·4H2O]2 (2). Complex 2 crystallizes in triclinic space group P1̅. All the three benzimidazolium nitrogen atoms of L1 are protonated. Though there are six CF3COO− ions, two molecules of trifluoroacetate and eight molecules of water are available in the lattice, only four CF3COO− ions and two molecules of water share two [H3L1]3+ to form a discrete staggered cage-like assembly as shown in Figure 1. The water molecules are encapsulated inside the tripodal cavity via three C−H···O hydrogen bonding interactions. The distance between the centroids of two apical benzene caps is ∼11.5 Å. The detailed analysis of the structure shows that the water is encapsulated in the bowl via three C−H···O interactions with the hydrogen bonding parameters C14−H14···O1 (C14···O1 = 3.294 Å, ∠C14−H14···O1 = 146.42°), C27−H27···O1 (C27···O1 = 3.166 Å, ∠C27−H27···O1 = 158.07°), and C40−H40···O1 (C40···O1= 3.148 Å, ∠C40−H40···O1 = 131.69°). The CF3COO−anions stabilize the dimeric capsule via N−H···O hydrogen bonding interactions with the protonated nitrogen atoms of the benzimidazolium units with the hydrogen bonding parameters N13−H13···O41 (N13···O41 = 2.802 Å, ∠N13−H13···O41 = 144.09°), N39−H39···O48 (N39···O48 = 2.667 Å, ∠N39−H39···O48 = 150.39°), and N26−H26···O41 (N26···O41 = 2.739 Å, ∠N26− H26···O41 = 167.75°). Details of these hydrogen bonding interactions are given in Table 3. In addition, CF3COO− anions are hydrogen bonded with the encapsulated water molecule by strong O−H···O interactions. The encapsulated water molecules have strong hydrogen bonding interactions with two CF3COO− anions that are further hydrogen bonded to a water molecule encapsulated in the other bowl. Interactions of encapsulated water with CF3COO− anion hydrogen bonded to the other bowl help to bring two molecules of L1 and thus assist the formation of a dimeric assembly. The encapsulated water molecules are H-bonded with CF3COO− with O···O bond distances 2.705 and 2.863 Å. Crystal Structure of [H3L1·3ClO4·HClO4·nH2O], 3. Upon protonation of L1 with perchloric acid in a methanol−water binary solvent mixture, we isolated 3, [H3L1·3ClO4·HClO4·2H2O], which crystallize in the rhombohedral system in the R3̅ space group. Single crystal X-ray crystallographic results revealed that L1 is in its triprotonated state and formed a homodimeric capsule stitched by six ClO4− anions and encapsulated two water molecules as guests (Figure 2). Among the six bridging ClO4− ions, two are disordered. As observed in cases of complex 2, and in complex 3 also, the encapsulated water is located exactly at the center of the tripodal cleft via C−H···O interactions with benzimidazolium C−H protons and hydrogen bonded to the glued anions via O−H···O interactions. The distance between the centroids of two apical benzene caps is 11.0 Å, which is almost comparable to the distance observed in case of complex 2. Detailed structural analysis shows that the water is encapsulated in the bowl via three C−H···O interactions with the hydrogen bonding parameters C18−H18···O1 (C18···O1= 3.286 Å, ∠C18−H18···O1=154.16°), C35−H35···O1 (C35···O1=3.227 Å, ∠C35−H35···O1= 156.55°), and C48− H48···O1 (C48···O1=3.509 Å, ∠C48−H48···O1=163.39°). The ClO4− anions are stabilized in the dimer via N−H···O and O−H···O interactions. The ClO4− anions form strong hydrogen bonding interactions with the protonated nitrogen atoms of the benzimidazolium units with the hydrogen bonding parameters N34−H34···O4B (N34···O4B = 2.727 Å, ∠N34−H34···O4B = 169.65°), N34− H34···O4B (N34···O4B = 3.040 Å, ∠N34−H34···O4B = 152.22°), N47−H47···O20 (N47···O20=2.892 Å, ∠N47−H47···O20=164.27°), and N60−H60···O11 (N60···O11=3.040 Å, ∠N60− H60···O11=163.57°). Details of these hydrogen bonding interactions

Table 3. Details of Hydrogen Bonding Parameters of Complex 2, 3, and 6 complex 2a D−H···A

D−H (Å)

H···A (Å)

O1−H1A···O481 N39−H39···O481 O1−H1B···O502 N13−H13···O413 C14−H14···O433 C40−H40···O433 N26−H26···O414 C14−H14···O15 C27−H27···O15 C40−H40···O15

0.84(4) 0.86 0.85(4) 0.86 0.93 0.93 0.86 0.93 0.93 0.93

D−H···A

D−H (Å)

H···A (Å)

N34−H34···O4A1 N34−H34···O5A1 N47−H47···O202 N60−H60···O113 N60−H60···O123 C18−H18···O14 C35−H35···O14

0.86 0.86 0.86 0.86 0.86 0.93 0.93

2.47 2.25 2.06 2.20 2.46 2.42 2.35 complex 6c

2.14(5) 1.89 1.89(4) 2.06 2.57 2.54 1.89 2.48 2.28 2.45 complex 3b

D···A (Å)

∠D−H···A (deg)

2.863(6) 2.667(5) 2.705(6) 2.802(5) 2.989(6) 3.173(6) 2.739(4) 3.294(5) 3.166(6) 3.148(6)

144(4) 150 160(5) 144 108 126 167.8 146 158 132

D···A (Å)


3.220(9) 3.040(9) 2.892(6) 3.040(7) 3.119(7) 3.286(8) 3.227(7)

146 152 164 164 134 154 157

D−H···A

D−H (Å)

H···A (Å)

D···A (Å)


N1−H1···O31 O2−H2···O112 N2−H2A···O103 N3−H3···O14 O4−H4···O125 N4−H4···O76 O5−H5···O137 N5−H5A···O68 N6−H6···O146

0.86 0.82 0.86 0.86 0.82 0.86 0.82 0.86 0.86

1.82 1.81 1.74 1.82 1.72 1.79 1.71 1.85 1.84

2.676(6) 2.580(7) 2.594(8) 2.669(9) 2.496(7) 2.636(6) 2.504(12) 2.703(12) 2.664(10)

176 157 169 170 157 170 163 172 160

Symmetry codes: (1) −1 + x, −1 + y, z; (2) 1 − x, 1 − y, −z; (3) −x, 1 − y, −z; (4) x, −1 + y, z; (5) x, y, z. bSymmetry codes: (1) 1/3 + x, −1/3 + y, −1/3 + z; (2) 5/3 − x, 4/3 − y, 4/3 − z; (3) 4/3 − x, 5/3 − y, 2/3 − z; (4) 1/3 + x, −1/3 + y, 2/3 + z. cSymmetry codes: (1) − x + y, 1 − x, 1/3 + z; (2) 1 − x, 1 − x + y, 2/3 − z; (3) −x + y, 1 − x, 4/3 + z; (4) −x + y, 2 − x, 1/3 + z; (5) 1 − y, 1 + x − y, 2/3 + z; (6) 1 + x − y, 2 − y, 4/3 − z; (7) 2 − y, 1 + x − y, 2/3 + z; (8) 1 − x + y, 2 − x, 1/3 + z. a

are given in Table 3. These interactions make the anion to reside nearer to the benzimidazolium moieties. One of the stitching ClO4− is strongly hydrogen bonded to the encapsulated water molecule (O1) by strong O−H···O interactions (O1···O11) with a bond distance of 2.902 Å. Interactions of encapsulated water with ClO4− hydrogen bonded to the other bowl help to bring two molecules of L1 and thus assist the formation of a dimeric capsule. Crystal Structure of [(H3L3)2·H(TMA)2·2(H3TMA)·(H2TMA)·H2O], 6. Upon protonation of L3 with trimesic acid (H3TMA) in methanol, we have isolated complex 6, [(H3L3)2·H(TMA)2·2(H3TMA)·(H2TMA).H2O] where L3 is in its triprotonated state. The compound crystallizes in the P3221 space group, and the structural analysis showed the formation of dimeric cage-like assembly stitched by [H(TMA)2]5− ions, [H2TMA]− ions, and water molecules (Figure 3a−d). Upon triprotonation, the arms of the receptor L3 oriented in such a way that the [H3L3]3+ moiety forms a bowl shaped cleft. The dimeric assembly is formed by the N−H···O hydrogen bonding interaction of 2102



Article

Figure 2. (a) MERCURY diagram showing the ClO4− stitched capsular aggregate of [H3L1]3+ with encapsulated water molecules in complex 3; (b) space filling view of the staggered assembly along the benzene cap. Disordered oxygen atoms of the ClO4−ions are omitted for clarity. Color code: C, orange and purple; H, cyan; N, blue; O, red; Cl, green.

Figure 4. View showing the hydrogen bonding interactions between NO3− and L6 in complex 8. Color code: C, orange and purple; H, green; N, blue; O, red.

the protonated pyrazolium nitrogens with the oxygen atoms of the [H2TMA]− ion and [H(TMA)2]5− ions via strong N−H···O hydrogen bonding interactions. In addition, [H2TMA]− anion is hydrogen bonded with the water molecule and the TMA fragment of the [H(TMA)2]5− ion. The detailed hydrogen bonding interactions are given in Table 3. The hydrogen bonding interactions among the [H(TMA)2]5−, [H2TMA]−, and water molecules form the tubular assembly are shown in Figure 3d. The distance between the centroids of two apical benzene caps is ∼11.2 Å, which is almost comparable to the distances observed in cases of complexes 1, 2, and 3. It is noteworthy to mention that a similar metal assisted formation of cage like assembly using L3 have been reported Mukherjee et al.17 Description of the Crystal Structure of Complex [H3L6·3NO3·H2O], 8. Upon protonation of L6 with HNO3 in water, we isolated complex 8, [H3L6·3NO3·H2O], where L6 is found to be in triprotonated state. Complex 8 crystallized in triclinic P1̅ space group. In complex 8, all the three arms of the receptor are not projected in one direction, rather, all the arms are projected in different directions. It is observed from the solid state structural analysis that in complex 8, all the three counter NO3− ions are hydrogen bonded to the N−H protons of the benzimidazolium units via N−H···O hydrogen bonding interactions (Figure 4). Moreover, these NO3− ions are also participated in C− H···O hydrogen bonding interactions with the receptor. Among the three anions, two are further coordinated to water molecules via O− H···O hydrogen bonding interactions, and this assists the formation of an infinite hydrogen bonded network. Detailed hydrogen bonding interactions are given in Table 4. Description of the Crystal Structure of Complex [H2L6·2I·DMF·H2O], 9. Protonation of L6 with HI in DMF yielded complex 9 [H2 L 6 ·2I·DMF·H 2 O] as colorless crystals in its bisprotonated state. Two of the three benzimidazole rings were protonated and one of the benzimidazolium N−H protons labeled as N25 is hydrogen bonded with the nitrogen atom of benzimidazole (labeled as N43) of the other molecule to form an infinite hydrogen

bonded network via N−H···O hydrogen bonding interactions (Figure 5). Moreover, the other protonated nitrogen atom (N10) is hydrogen bonded to the oxygen atom of the trapped DMF molecule via N− H···O hydrogen bonding interactions. In addition, the trapped DMF molecules are also participated in hydrogen bonding interactions with the iodide ions via C−H···I− interactions. Iodide ions are coordinated with the receptors via C−H···O interactions and are also coordinated with a water molecule via O−H···I− interactions. Details of the hydrogen bonding interactions are provided in Table 4. Description of the Crystal Structure of Complex [H2L6·2ClO4·DMF], 10. Protonation of L6 with HClO4 in DMF yielded complex 10 [H2L6.2ClO4.DMF] as colorless crystals in its bisprotonated state. Complex 10 crystallize in monoclinic P21/n space group and is iso-structural with complex 9. In complex 10, the receptor is bisprotonated and one DMF is π-stacked in between the arms of two receptor units. One of the benzimidazolium N−H protons labeled as N32 is hydrogen bonded with the nitrogen atom of benzimidazole (labeled as N50) of the other molecule to form an infinite hydrogen bonded network via N−H···O hydrogen bonding interactions (Figure 6). Moreover, the other protonated nitrogen atom (N17) is hydrogen bonded to the oxygen atom of the trapped DMF molecule via N− H···O hydrogen bonding interactions. In addition, the trapped DMF molecules are also participated in hydrogen bonding interactions with the ClO4−ions via C−H···O interactions. Details of these interactions are given in Table 4. Description of the Structure of Complex [H3L1·H2L5·5ClO4·4H2O], 11. Upon protonation with HClO4 to the mixture of L1 and L5 in a methanol−water binary solvent mixture forms a new assembly L1.2L5.L1 as shown in Figure 7 by encapsulating 14 water molecules and eight ClO4− ions, and the remaining water molecules and ClO4− ions are located in the lattice in complex 11. L1 forms dimeric capsular assembly upon coordination with ClO4− ions similar to the structure observed in complex 3, and L5 also shares its ClO4− counterions with

Figure 3. (a) MERCURY diagram showing [H2TMA]− and [H(TMA)2]5− ions stitched capsular aggregate of [H3L3]3+ in complex 6; (b) space filling view of the dimeric assembly; (c) view of the dimeric assembly along the benzene cap; and (d) space filling view of the hydrogen bonded belt of [H2TMA]− and [H(TMA)2]5−. Color code: C, orange, purple, and green; N, blue; O, red. 2103



Article

Table 4. Details of Hydrogen Bonding Parameters of Complex 8, 9, and 10 complex 8a D−H···A

d(D−H) (Å)

N20−H20···O31 N20−H20···O41 N30−H30···O102 N30−H30···O132 N43−H43···O53 N43−H43···O83 C21−H21···O43 C25−H25···O43 C29−H29···O124 C29−H29···O134 C39−H39···O413 C40−H40B···O75 C42−H42···O16 C42−H42···O93 C48−H48···O75

0.8609 0.8609 0.8603 0.8603 0.8584 0.8584 0.9299 0.9298 0.9297 0.9297 0.9312 0.9708 0.9297 0.9297 0.9295

D−H···A

d(D−H) (Å)

N10−H10···O41 N25−H25···N432 C20−H20···I13 C32−H32···I14

0.86 0.86 0.983 0.93

D−H···A

d(D−H) (Å)

N17−H17···O111 N32−H32···N502 C12−H12···O93 C16−H16···O104 C19−H19···O95 C25−H25B···O46 C27−H27···O56 C29−H29B···O8 C41−H41···O106

0.8601 0.8607 0.9300 0.9293 0.9310 0.9705 0.9299 0.9700 0.9300

d(D···A) (Å)


3.165(3) 2.712(3) 3.179(3) 2.788(3) 2.663(3) 3.383(4) 3.188(4) 3.390(4) 3.200(3) 3.296(3) 2.838(3) 3.231(4) 3.166(4) 3.256(4) 3.200(4)

136.42 163.23 129.36 167.38 148.50 157.77 141.68 157.64 166.95 136.81 102.18 144.41 146.99 128.80 160.53

d(D···A) (Å)


2.643(3) 2.659(4) 3.892(3) 3.804(3)

156 176 167 146

d(H···A) (Å)

d(D···A) (Å)


1.8916 1.8373 2.3953 2.3330 2.5520 2.3512 2.5109 2.4835 2.4832

2.658(3) 2.692(3) 3.169(4) 3.136(3) 3.400(4) 3.298(3) 3.416(3) 3.143(3) 3.399(3)

147.54 171.85 140.56 144.48 151.52 164.85 164.37 125.07 168.13

d(H···A) (Å)

2.4850 1.8768 2.5632 1.9418 1.8932 2.5727 2.4064 2.5113 2.2878 2.5559 2.4917 2.3915 2.3459 2.5915 2.3089 complex 9b d(H···A) (Å)

1.83 1.80 2.98 3.00 complex 10c

Figure 5. (a) View showing the hydrogen bonding interactions between I− and L6 in complex 9 and (b) view showing the trapped DMF molecules (space-fill) in the clefts. Color code: C, orange and purple; H, green; N, blue; O, red. Nonbonded hydrogen atoms are omitted for clarity. bonding of water molecules and BF4− ions as shown in Figure 8, which is structurally similar to that of complex 11. Detailed hydrogen bonding interactions with bond parameters are given in Table 5. In complex 12, the protonated benzimidazolium units are hydrogen bonded with water molecules rather than BF4− ions. These water molecules are further hydrogen bonded with the counter perchlorate anions to hold them together in forming the extended tripodal− dipodal mixed dimeric assembly.

■

DISCUSSION The principal focus of this study is to find out the role of anions, heteroaryl moieties, alkyl substitutents on the platform, and the overall receptor topology toward various supramolecular assemblies like discrete capsule, macrocycle to polymeric architectures. Several semirigid podand receptors with proton acceptor moieties were synthesized, and their protonated complexes were studied for their nature of assemblies in the solid state. An initial question arises as to whether the topology of anions plays a role in the self-assembly process of this category of receptor(s). Single-crystal X-ray structural analyses of complexes 1−3 revealed interesting structural correlation of anion-assisted assemblies of the triprotonated L1. Two units of [H3L1]3+ assemble to form a dimeric capsule where oxyanions such as NO3−, CF3COO−, and ClO4− act as anionic belt. In cases of inorganic oxyanions NO3− and ClO4−, six anions participated in the belt formation, whereas four CF3COO− are involved in the anionic belt in complex 2. Though the planar and tetrahedral anions show dimeric assemblies of triprotonated L1, the spherical anion such as Cl− failed to form such an organized assembly.4f One of the most noticeable characteristic of complexes 1, 2, and 3 is that all these complexes showed the encapsulation of a molecule of water in each of the two tripodal clefts of the assembly. Thus, it seems that the encapsulated water is playing a vital role in bringing the receptors together along with the anionic belt. It is noteworthy to mention that the aggregates formed from HNO3, CF3COOH, and HClO4 are almost similar in size as observed from the distance between the centroids of the apical benzene caps ranging from 11.0 to 11.5 Å (Figure 9). However,

a Symmetry codes: (1) −x, 1 − y, 1 − z; (2) −1 + x, −1 + y, z; (3) x, y, z; (4) 1 − x, 1 − y, 1 − z; (5) x, −1 + y, z; (6) 1 + x, y, z. bSymmetry codes: (1) 1 − x,1 − y, 1 − z; (2) 5/2 − x, −1/2 + y, 1/2 − z; (3) 1 + x, y, z (4) 1/2 + x, 1/2 − y, −1/2 + z. cSymmetry codes: (1) 1 − x, − y, −z; (2) −1/2 − x, 1/2 + y, 1/2 − z; (3) 1 − x, −y, 1 − z (4) −1 + x, y, −1 + z; (5) x, y, −1 + z; (6) −1/2 + x, 1/2 − y, −1/2 + z.

L1 and forms the mixed dimeric assembly. Detailed hydrogen bonding interactions with bond parameters are given in the Table 5. The cooperative self-assembly of two molecules of L1 and two molecules of L5 in the presence of perchlorate anions thus form the near spherical assembly. Detailed structural analysis showed that protonated benzimidazolium units are hydrogen bonded with water molecules rather than perchlorate ions in contradictory to complex 3 where anions are directly hydrogen bonded to the protonated benzimidazolium subunits. These water molecules are further hydrogen bonded with the counter perchlorate anions to hold them together in forming the extended tripodal−dipodal mixed dimeric assembly. Description of the Structure of Complex [H3L1·H2L5·5BF4·nH2O], 12. Upon protonation with acid of another tetrahedral anion, HBF4, to the mixture of L1 and L5 in a methanol−water binary solvent mixture forms complex 12. The structure of complex 12 was confirmed by single crystal X-ray crystallography. The complex crystallized in P21/c space group, and the structural analysis revealed the formation of heterotetrameric assembly L1·2L5·L1 by the usage of hydrogen 2104



Article

Figure 6. View showing the hydrogen bonding interactions between ClO4− and L6 in complex 10 and trapped DMF molecules in the clefts. Color code: C, orange and purple; H, green; N, blue; O, red; Cl, light green. Nonbonded hydrogen atoms are omitted for clarity.

Figure 7. (a) Space-fill view showing the staggered heterotetrameric capsular assembly in complex 11; (b) view showing the hydrogen bonding interactions among ClO4− ions and water molecules; and (c) space-fill view of the heterotetrameric assembly. Color code: C, orange, purple, and green; N, blue; O, red; Cl, light green. Nonbonded hydrogen atoms are omitted for clarity.

Table 5. Details of Hydrogen Bonding Parameters of Complex 11 and 12 complex 11a D−H···A

d(D−H) (Å)

d(H···A) (Å)

d(D···A) (Å)

∠D-H···A (deg)

O3−H3A···O21 O6−H6A···O232 O6−H6B···O41 O6−H6A···O253 O7−H7A···O254 O7−H7B···O35 N71−H71···O63 N45−H45···O31 N58−H58···O41 O3−H3B···O212 N87−H87···O65 N100−H100···O71

0.86(5) 0.84(3) 0.85(9) 0.84(3) 0.84(5) 0.85(5) 0.86 0.86 0.86 0.85 (10) 0.86 0.86

1.87(4) 2.40(5) 1.82(8) 2.24(6) 2.13(6) 1.98(6) 1.89 1.95 1.88 2.06 (11) 1.86 1.85 complex 12b

2.703(8) 2.943(5) 2.660(8) 2.956(6) 2.945(6) 2.822(6) 2.739(5) 2.770(5) 2.722(9) 2.903 (6) 2.706(5) 2.705(5)

163(6) 123(5) 170(8) 142(5) 162(8) 170(7) 167.0 158.0 166.0 167 (11) 169.0 174.0

D−H···A

d(D−H) (Å)

d(H···A) (Å)

d(D···A) (Å)

∠D-H···A (deg)

N12−H12···O41 N25−H25···O2A2 N38−H38···O12 N54−H54···O42 N67−H67···O32

0.86 0.86 0.86 0.86 0.86

1.85 1.87 1.95 1.85 1.85

2.710(3) 2.730(6) 2.775(3) 2.698(3) 2.705(3)

174.0 174.0 161.0 171.0 174.0

Symmetry codes: (1) x, y, z; (2) 1 − x, −1/2 + y, 1/2 − z; (3) 1 − x, 1 − y, 1 − z; (4) x, 3/2 − y, 1/2 + z; (5) 1 − x, 1/2 + y, 3/2 − z. bSymmetry codes: (1) 1 − x, 1 − y, 1 − z; (2) x, y, z. a

findings indicate that the nature of assembly is not entirely dependent on the receptor but also the participating anion. To our surprise, a simple variation of the heteroaryl substituent from benzimidazole to imidazole in L2 occurred, where the planar anion NO3− (which showed a homodimeric capsule with L1) did not form homodimeric capsule, rather, it resulted in the formation of infinite distortedassemblies.4f Similarly, protonation with HNO3 caused the dimethyl pyrazole functionalized receptor L3 yielded complex 5 as the NO3− bridged macrocyclic sheet-like assembly. Protonating L3 with

apical benzene capped hexaprotonated cyclophane with encapsulated anions showed a slightly smaller size of ∼9.5 Å.18 Comparing the anion dependent aggregation behavior of L1 from planar oxyanions such as nitrate and trifluoroacetate to the tetrahedral oxyanion, it is evident that the shape of the oxyanions does not alter/disturb the assembly, but the spherical anion such as Cl− resulted in the formation of a noncapsular infinite hydrogen bonded network, and also, Cl− has the tendency to rupture/disassemble the capsular dimer upon doping as demonstrated in our preliminary report.4h These 2105



Article

Figure 8. (a) View showing the hydrogen bonding interactions among BF4− ions and water molecules and (b) space-fill view of the heterotetrameric capsular assembly in complex 12. Color code: C, orange, purple, and green; N, blue; O, red; B, pale pink; F, yellow. Nonbonded hydrogen atoms are omitted for clarity.

Figure 9. Space-fill view showing the length of the dimeric capsular assemblies of complexes (a) 1, (b) 2, and (c) 3. Color code: C, orange and purple; N, blue; O, red; F, yellow-green; Cl, green. Panel a is redrawn using coordinates that were originally published in ref 4d.

receptors to direct the arms unidirectional and hence dictate the formation of a homodimeric capsular assembly. To achieve an extended cage-like assembly, we have utilized the mixed ligand systems as building blocks. In this connection, we have moved forward our investigation in the direction to make anion-assisted heterotetrameric assemblies from a mixture of tripodal and dipodal receptors. Among L1−L6, we have chosen L1 and L5 as our choice of ligands to investigate the anion-assisted formation of heterotetrameric assemblies. In our attempt to obtain protonated crystalline complexes from an equimolar mixture of L1 and L5, we were able to obtain complexes 11 and 12 with HClO4 and HBF4, respectively. Single crystal X-ray structural analysis of 11 showed the formation of the heterotetrameric assembly as shown in Figure 7, where the distance between the centroids of apical benzene caps of triprotonated L1 units is 13.310 Å, which is ∼2 Å longer than the distance observed in the case of complex 1, 2, and 3. The distance between the centroids of apical benzene caps of bisprotonated L5 is ∼18 Å. By comparing the dimensions of the assemblies of the ClO4− complex of L1 (2) with complex 11, it is observed that the cavity size of the aggregate is increased. Similarly in complex 12 also, L 1 and L 5 form the heterotetrameric assembly upon coordination with BF4− ions as observed in complex 11. The distance between the centroids of apical benzene caps of triprotonated L1 units is 13.125 Å, and

trimesic acid resulted in the formation of complex 6 as a [H2TMA]− and [H(TMA)2]5− bridged dimeric assembly (Figure 3). It is interesting to observe that the ligand, which does not form organized assembly with NO3− in complex 5,4f self-assembles to form an anion bridged homodimeric cage-like assembly with organic acid such as trimesic acid in complex 6. This demonstrated the dependence of the complementary aspects between the receptor and the participating anion. In order to probe the role of substitution in the apical benzene platform, we have selected L6 as a representative receptor, which is homologous to L1 and studied the complexation behavior with anions of various geometries such as planar (NO3−), spherical (I−), and tetrahedral (ClO4−) from the crystalline complexes 8, 9, and 10, respectively. It has been observed from the crystal structures that in none of these complexes in the protonated receptors formed organized assemblies as observed in the cases of complexes 1, 2, and 3. Comparing the NO3− and ClO4− complexes of L 1 with corresponding NO3 − and ClO 4 − complexes of L6 revealed that though the heteroaryl subunit and the platform are the same in both L1 and L6, the absence of methyl group in the benzene platform has resulted in a completely different pattern of unorganized assemblies. Thus, it is clear from these observations that the alkyl groups in the apical benzene platform are essential for the rigidity of the 2106



Article

Dordrecht, The Netherlands, 1999; pp 45−60. (g) Rebek, J. Jr. Acc. Chem. Res. 1999, 32, 278−286. (2) (a) Supramolecular Chemistry of Anions; Bianchi, A., BowmanJames, K., García-España, E., Eds.; Wiley-VCH, New York, 1997. (b) Sessler, J. L.; Gale, P. A.; Cho, W. S. Anion Receptor Chemistry: Monographs in Supramolecular Chemistry; RSC Publishing: Cambridge, U.K., 2006. (c) Arunachalam, M.; Ghosh, P. Chem. Commun. 2011, 47, 8477−8492. (d) Themed issue: Gale, P. A.; Gunnalaugsson, T. Supramolecular Chemistry of Anionic Species. Chem. Soc. Rev. 2010, 10, 3595−3596. (3) (a) Vickers, M. S.; Beer, P. D. Chem. Soc. Rev. 2007, 36, 211−225. (b) Mullen, K .M.; Beer, P. D. Chem. Soc. Rev. 2009, 38, 1701−1713. (4) (a) Busschaert, N.; Wenzel, M.; Light, M. E.; Hernández, P. I.; Tomás, R. P.; Gale, P. A. J. Am. Chem. Soc. 2011, 133, 14136−14148. (b) Custelcean, R.; Remy, P.; Bonnesen, P. V.; Jiang, D.; Moyer, B. A. Angew. Chem., Int. Ed. 2008, 47, 1866−1870. (c) Arunachalam, M.; Ghosh, P. Chem. Commun. 2009, 5389−5391. (d) Arunachalam, M.; Ghosh, P. Chem. Commun. 2009, 3184−3186. (e) Ravikumar, I.; Lakshminarayanan, P. S.; Arunachalam, M.; Suresh, E.; Ghosh, P. Dalton Trans. 2009, 4160−4168. (f) Arunachalam, M.; Ghosh, P. CrystEngComm 2010, 12, 1621−1627. (g) Arunachalam, M.; Ghosh, P. Inorg. Chem. 2010, 49, 943−951. (h) Ravikumar, I.; Ghosh, P. Chem. Commun. 2010, 46, 1082−1084. (5) (a) Arunachalam, M.; Ghosh, P. Org. Lett. 2010, 12, 328−331. (b) Arunachalam, M.; Ghosh, P. Chem. Commun. 2011, 47, 6269− 6271. (6) (a) Alajarín, M.; Pastor, A.; Orenes, R.; Steed, J. W.; Arakawa, A. Chem. Eur. J. 2004, 10, 1383−1397. (b) Ballester, P.; Gil-Ramírez, G. Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 10455−10459. (c) Chas, M.; Gil-Ramírez, G.; Ballester, P. Org. Lett. 2011, 13, 3402−3405. (d) Verdejo, B.; Rodríguez-Llansola, F.; Escuder, B.; Miravet, J. F.; Ballester, P. Chem. Commun. 2011, 47, 2017−2019. (7) (a) Hof, F.; Nuckolls, C.; Rebek, J. Jr. J. Am. Chem. Soc. 2000, 122, 4251−4252. (b) Hof, F.; Nuckolls, C.; Craig, S. L.; Martι ́n, T.; Rebek, J. Jr. J. Am. Chem. Soc. 2000, 122, 10991−10996. (c) Johnson, D. W.; Hof, F.; Iovine, P. M.; Nuckolls, C.; Rebek, J. Jr. Angew. Chem., Int. Ed. 2002, 41, 3793−3796. (d) Lipstman, S.; Goldberg, I. CrystEngComm 2010, 12, 52−54. (8) (a) MacGillivray, L. R.; Atwood, J. L. Nature 1997, 389, 469− 472. (b) Shivanyuk, A.; Rebek, J. Jr. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 7662−7665. (c) Evan-Salem, T.; Baruch, I.; Avram, L.; Cohen, Y.; Palmer, L. C.; Rebek, J. Jr. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 12296−12300. (d) Beyeh, N. K.; Kogej, M.; Åhman, A.; Rissanen, K.; Schalley, C. A. Angew. Chem., Int. Ed. 2006, 45, 5214−5218. (e) Shimizu, S.; Kiuchi, T.; Pan, N. Angew. Chem., Int. Ed. 2007, 46, 6442−6445. (f) Slovak, S.; Evan-Salem, T.; Cohen, Y. Org. Lett. 2010, 12, 4864−4867. (g) Hamada, F.; Yamada, M.; Kondo, Y.; Itoa, S.; Akibaa, U. CrystEngComm 2011, 13, 6920−6922. (9) (a) Schalley, C. A.; Martín, T.; Obst, U.; Rebek, J. Jr. J. Am. Chem. Soc. 1999, 121, 2133−2138. (b) Ebenezer, S.; Muthiah, P. T.; Butcher, R. J. Cryst. Growth Des. 2011, 11, 3579−3592. (10) (a) Cai, Y.-P.; Kang, B.-S.; Su, C.-Y.; Zhang, H.-X.; Yang, X.-P.; Deng, L.-R.; Xu, A.-W.; Zhou, Z.-Y.; Chan, A. S. C. Chin. J. Struct. Chem. 2001, 262. (b) Liu, H.-K.; Sun, W.-Y.; Tang, W.-X.; Yamamoto, T.; Ueyama, N. Inorg. Chem. 1999, 38, 6313−6316. (c) Yu, S.-Y.; Jiao, Q.; Li, S.-H.; Huang, H.-P.; Li, Y.-Z.; Pan, Y.-J.; Sei, Y.; Yamaguchi, K. Org. Lett. 2007, 9, 1379−1382. (d) Chawla, S. K.; Gill, B. K. Polyhedron 1997, 16, 1315−1322. (11) (a) SAINT and XPREP, version 5.1; Siemens Industrial Automation Inc.: Madison, WI, 1995. (b) Sheldrick, G. M. SADABS, Empirical Absorption Correction Program; University of Göttingen: Göttingen, Germany, 1997. (12) Sheldrick, G. M. SHELXTL Reference Manual, version 5.1; Bruker AXS: Madison, WI, 1997. (13) Sheldrick, G. M. SHELXL-97: Program for Crystal Structure Refinement; University of Göttingen: Göttingen, Germany, 1997. (14) Spek, A. L. PLATON-97; University of Utrecht: Utrecht, The Netherlands, 1997.

the distance between the centroids of apical benzene caps of bisprotonated L5 is ∼18 Å, which is almost comparable to the distances observed in case of complex 11.

■

CONCLUSIONS In summary, the structural motifs we have elucidated highlight a number of features that are likely to make important contributions by the anions and the receptors in order to construct the capsular assemblies. We have shown the staggered homodimeric aggregates assisted by anions of different geometries such as CF3COO− and ClO4− with L1, and the solid state structural analysis showed that the assemblies are discrete and that involves all the counteranions as well as taking advantage of entrapped water guests in its formation as observed in our earlier report with NO3− ion. Upon changing the heterocyclic functionality from benzimidazole to dimethylpyrazole (L3), the triprotonated receptor is unable to form an organized aggregate with NO3−, rather, it generated dimeric assembly with trimesic acid. The necessity of the presence of a methyl group in the high profile ligand L1 has been established by comparing the NO3− and ClO4− complexes of L1 with NO3− and ClO4− complexes of L6, which do not have methyl groups in the benzene platform. Interestingly, we have established that a mixture of tripodal and dipodal receptors can yield heterotetrameric assemblies upon protonation by acids of tetrahedral anions such as HClO4 and HBF4 with increased capsular dimension. The examples of structurally characterized complexes that exhibit heterotetrameric assemblies described here should help to develop anion-assisted assemblies of higher dimension and expand the understanding of the crucial role of anions in the construction of supramolecular architectures and self-assemblies.

■

ASSOCIATED CONTENT

* Supporting Information S

1

H and 13C NMR of all the structures and ligand L6; CIF files of all the structures. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*Fax: (+91) 33-2473-2805. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS P.G. gratefully acknowledges the Department of Science and Technology (DST), New Delhi, India, for financial support. M.A. would like to acknowledge IACS, Kolkata, India, for SRF. S.C. would like to thank IACS, Kolkata, India, for JRF. X-ray crystallographic studies were performed at the DST-funded National Single-Crystal X-ray Diffraction Facility at the Department of Inorganic Chemistry, IACS.

■

REFERENCES

(1) (a) Varner, J. E., Ed. Self-Assembling Architecture; Wiley-Liss: New York, 1988. (b) Cram, D. J. Nature 1992, 356, 29−36. (c) Lehn, J.-M. Supramolecular Chemistry, Concepts and Perspectives; VCH: Weinheim, Germany, 1995. (d) Conn, M. M.; Rebek, J. Jr. Chem. Rev. 1997, 97, 1647−1668. (e) Jasat, A.; Sherman, J. C. Chem. Rev. 1999, 99, 931− 967. (f) Böhmer, V.; Mogck, O.; Pons, M.; Paulus, E. F. NMR in Supramolecular Chemistry; Pons, M., Ed.; Kluwer Academic: 2107



Article

(15) Mercury 2.3, Supplied with Cambridge Structural Database; CCDC: Cambridge, UK, 2009. (16) Sluis, P. V. D.; Spek, A. L. PLATON/SQUEEZE. Acta Crystallogr. 1990, A46, 194. (17) Bar, A. K.; Chakrabarty, R.; Mukherjee, P. S. Inorg. Chem. 2009, 48, 10880−10882. (18) Arunachalam, M.; Ravikumar, I.; Ghosh, P. J. Org. Chem. 2008, 73, 9144−9147.

2108


Anion-Assisted Formation of Discrete Homodimeric and

Recommend Documents