Polymeric, Molecular and Ionic Organotin Complexes Containing

Article pubs.acs.org/crystal

Polymeric, Molecular and Ionic Organotin Complexes Containing Hypoxanthine, Adenine and 2‑Aminopurine. Synthesis and Supramolecular Structures Subrata Kundu,† Balaram Mohapatra,† Chandrajeet Mohapatra,† Sandeep Verma,† and Vadapalli Chandrasekhar*,†,‡ †

Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur - 208016, India National Institute of Science Education and Research, Institute of Physics Campus, School of Chemical Sciences, Bhubaneshwar-751005, India

‡

S Supporting Information *

ABSTRACT: The reaction of L1H [L1H = 3-(N9-hypoxanthyl)propanoic acid] with Me3SnCl or (n-Bu3Sn)2O afforded the 1D coordination polymers [Me3Sn(L1)]n (1) and [n-Bu3Sn(L1)]n (2), respectively. A similar reaction between L2H [3-{N9-(2-aminopurinyl)}propanoic acid] with (Ph3Sn)2O in a 2:1 ratio afforded a dimer [(L2)(Ph3Sn)L2{Ph3Sn(H2O)}]· 3CH3OH·3H2O (3). The reactions of 2-(N9-adeninyl)acetic acid (L3H) and 3-(N9-adeninyl)propanoic acid (L4H) with (Ph3Sn)2O in a 2:1 ratio afforded insoluble intractable products, which, upon addition of dilute HCl in methanol, afforded [{Ph2SnCl3(H2O)}(HL3Me)2Cl]·H2O (4) and [(Ph2SnCl4)(HL4Me)2] (5). Complexes 1−5 show an extensive supramolecular organization in the solid state as a result of several intermolecular interactions, prominent among which are the interactions between the nucleobases.

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INTRODUCTION Investigation of supramolecular structures of biomolecules is important from several points of view.1−14 Molecular recognition in biological systems depends on specific interactions between two or more partner molecules.1−9 Structure-based drug design is based on recognizing and optimizing such interactions between drugs and target receptors to elicit a biological response.2 In addition, recent efforts have focused on selfassembly properties of biomolecules in general and nucleobases, in particular, for development of functional materials.15−19 We have been interested in this problem from a slightly different point of view. Our interest concerns how main-group element chemistry can aid in creating supramolecular architectures with nucleobases and how such interactions would influence crystal structures of such main-group element containing complexes. This interest emanates from our extensive experience in organostannoxane chemistry where we and others have described a large number of novel structural forms.20−27 Further, the crystal structures of many organostannoxanes have revealed the formation of novel supramolecular architectures that are mediated by several noncovalent interactions such as C−H···O, C−H···π, O−H···O, and π···π interactions.28−36 In many cases, it has been found that the oxide and the hydroxide groups of the organostannoxanes also participate in the supramolecular interactions.37−42 Among the interesting supramolecular architectures observed in these systems, the Rangoli pattern in the hexaferrocenyl derivative [n-BuSn(O)(O2CCH2C5H4FeC5H5)]633 © XXXX American Chemical Society

is one of the most aesthetically pleasing. In an another instance, Höpfl et al. have reported a two-dimensional polymeric network of a pseudorotaxane structure as a result of supramolecular interactions between the two trinuclear macrocycles [n-Bu2Sn{1,3-C6H4-(COO)2}]3.36 In view of the interesting structural and supramolecular chemistry of organostannoxanes, we have previously used these systems to support multiadenine43 and multiuracil assemblies.44 In one of these adenine compounds, [n-Bu3SnL·0.33H2O]n [where LH = 3-(N9-adeninyl)propanoic acid], we observed an unprecedented homotrimeric motif of adenine in the supramolecular structure of a 1D polymer.43 Similarly in [t-Bu2Sn(μ-OH)L]2 [where LH = 3-(N1-uracyl)propanoic acid], we observed an unprecedented tetrameric uracil motif.44 These results have spurred us to examine other nucleobases. Accordingly, herein, we report our findings on the synthesis and structural characterization of [Me3Sn(L1)]n(1), [n-Bu3Sn(L1)]n (2), [(L2)(Ph 3 Sn)L2{Ph 3 Sn(H 2 O)}]·3CH 3 OH·3H 2 O(3), [{Ph2SnCl3(H2O)}(HL3Me)2Cl]·H2O (4), and [(Ph2SnCl4)(HL4Me)2] (5) [where L1H = 3-(N9-hypoxanthyl)propanoic acid, L2H = 3-{N9-(2-aminopurine)}propanoic acid, L3H = 2-(N9-adeninyl)acetic acid, L4H = 3-(N9-adeninyl)propanoic acid]. Hypoxanthine is an important biomolecule, but its Received: September 4, 2014 Revised: October 30, 2014

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dx.doi.org/10.1021/cg501322w | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

(m, 30H, Ph); 8.29 (s, 2H, IsoAd); 8.48 (s, 2H, IsoAd). IR (KBr, ν/cm−1): 3440 (s, br), 3063 (m, br), 1619 (s), 1582 (s), 1429 (m), 1401 (m), 1352 (s), 1296 (w), 731 (s), 698 (m), 638 (s). ESI-MS: m/z (%) 745.0438 [(Ph3Sn)2HCOO]+ (5); 906.1014 [(Ph3Sn)2L2]+(2). [{Ph2SnCl3(H2O)}(HL3Me)2Cl]·H2O (4). (Ph3Sn)2O (0.20 g, 0.28 mmol), L2H (0.11 g, 0.56 mmol), dilute HCl (1 N, 1 mL, excess). Yield: 0.18g (37%). mp 136 °C. Anal. (%) Calcd for C28H32Cl4N10O6Sn: C, 38.87; H, 3.73; N, 16.19. Found: C, 38.59; H, 3.79; N, 16.05.1H NMR [500 MHz, (CD3)2SO, ppm]: δ = 3.68 (s, 6H, CH3), 5.07 (s, NH2), 5.20 (s, 4H, CH2); 7.19 (m, 2H, Ph); 7.26 (m, 4H, Ph); 7.91 (d, 4H, Ph); 8.43 (s, 2H, Ad); 8.46 (s, 2H, Ad).119Sn NMR (150 MHz): δ= −396 ppm (s). IR (KBr, ν/cm−1): 3293 (s, br), 3098 (m, br), 3067 (m), 2980 (m), 1883 (w), 1757 (s), 1693 (s), 1632 (m), 1422 (s), 1368 (m), 1231 (s), 789(m), 735(m), 721 (m), 642(m). ESI-MS: m/z (%) 208.0842 [H(L3)CH3]+(100) (+ve mode); 378.8827 [Ph2SnCl3]− (50) (-ve mode). [(Ph2SnCl4)(HL4Me)2] (5). (Ph3Sn)2O (0.20 g, 0.28 mmol), L3H (0.12 g, 0.56 mmol), dilute HCl (1 N, 1 mL, excess). Yield: 0.15 g (31%). mp 148 °C. Anal. (%) Calcd for C30H34Cl4N10O4Sn: C, 41.94; H, 3.99; N, 16.30. Found: C, 41.78; H, 4.11; N, 16.15. 1H NMR [500 MHz, (CD3)2SO, ppm]: δ = 2.87 (t, 4H, CH2), 3.52 (s, 6H, CH3), 4.39(t, 4H, CH2); 7.19−7.39 (m, 6H, Ph); 7.94 (d, 4H, Ph); 8.45 (s, 2H, Ad); 8.48 (s, 2H, Ad). IR (KBr, ν/cm−1): 3333 (m, br), 3066 (m, br), 1699 (s), 1613 (m), 1429(m), 1217 (m), 1075 (s), 996 (m), 729 (s) 695 (s). ESI-MS: m/z (%) 222.0998 [H(L4)CH3]+ (50) (+ve mode); 378.8898 [Ph2SnCl3]− (50) (−ve mode).

supramolecular chemistry is not well documented in the literature. Interestingly, we have observed hypoxanthine ribbon formations in the solid-state structure of the coordination polymers 1 and 2. Complex 3 is dimer and has a 3D supramolecular structure. Complexes 4 and 5 are ionic; extensive supramolecular interactions are seen in both of these complexes.

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EXPERIMENTAL SECTION

All the reactions were performed under a dry nitrogen atmosphere by employing standard Schlenk techniques. All the solvents were purified by adopting standard procedures. Me3SnCl (Aldrich), (Ph3Sn)2O and (n-Bu3Sn)2O (Aldrich) were used as such without any further purification. L1H, L2H, L3H, and L4H were synthesized according to literature procedures (Supporting Information).45−47 IR spectra were recorded as KBr pellets on a Bruker Vector 22 FT IR spectrophotometer operating from 400 to 4000 cm−1. Elemental analyses were carried out using a thermoquest CE instruments model EA/110 CHNS-O elemental analyzer. Melting points were recorded using a JSGW melting point apparatus and are uncorrected. Suitable crystals for single-crystal X-ray diffraction measurements were mounted on a CCD Bruker SMART APEX diffractometer. Data were collected at 100(2) K using graphite monochromated Mo Kα radiation (λα = 0.71073 Å). The structures were solved by direct methods and refined (SHELXL 97) by full-matrix least-squares procedures on F2.48,49 The hydrogen atoms were included in idealized positions and were refined according to the riding model. Non-hydrogen atoms were refined with anisotropic displacement parameters. The O−H and N−H protons were included from the electron density map and refined isotropically. Details of the data collection and refinement parameters of 1−5 are given in Table 1. The residual electron densities present near to the tin center ( 2σ(I)] R indices (all data) largest diff. peak and hole (e·Å−3)

volume (Å3) Z density (Mg/m3) absorption coefficient (mm−1) F(000) crystal size (mm3) θ range for data collection (deg) index ranges

empirical formula formula weight temperature (K) wavelength (Å) crystal system space group unit cell dimensions

C

1.043 R1 = 0.0780, wR2 = 0.1782 R1 = 0.0888, wR2 = 0.1858 2.556 and −3.050

R1 = 0.0208, wR2 = 0.0467

R1 = 0.0274, wR2 = 0.0488 0.48 and −0.49

empirical

empirical

1.068

97.0

100.0

7388/50/499

7388 [R(int) = 0.0365]

2603 [R(int) = 0.0255]

2603/0/179

12954

0.877 and 0.830

−7 ≤ h ≤12, −14 ≤ k ≤14, −20 ≤ l ≤20

−8 ≤ h ≤ 14, −12 ≤ k ≤ 12, −15 ≤ l ≤ 15 7630

0.769 and 0.982

1024.0 0.16 × 0.13 × 0.11 4.09−24.71

736.0 0.16 × 0.12 × 0.11 5.26−51

2 C40H68N8O6Sn2 994.44 100(2) 0.71073 triclinic P1̅ a = 10.4055(13) Å, b = 12.6484(16) Å, c = 17.386(2) Å, α = 77.482(2)°, β = 89.515(3)°, γ = 89.422(3)° 2233.7(5) 2 1.479 1.171

C11H16N4O3Sn 370.99 100(2) 0.71073 monoclinic P21/c a = 11.563(5) Å, b = 10.350(5) Å, c = 12.463(5) Å, α = 90°, β = 110.254(5)°, γ = 90° 1399.3(11) 4 1.761 1.827

1

Table 1. Crystal Data Collection and Refinement Parameters for 1−5 3

R1 = 0.0855, wR2 = 0.1557 2.300 and −1.838

R1 = 0.0526, wR2 = 0.1353

1.085

10684/12/716

0.861 and 0.837

empirical

99.9

10684 [R(int) = 0.0477]

−11 ≤ h ≤11, −17 ≤ k ≤17, −26 ≤ l ≤26 31943

1304.0 0.19 × 0.17 × 0.16 2.22−25.50

C55H64N10O11Sn2 1278.59 100(2) 0.71073 triclinic P1̅ a = 9.6511(4) Å, b = 14.2607(6) Å, c = 22.0464(10) Å, α = 6.4420(10)°, β = 100.3120(1)°, γ = 103.2150(1)° 2868.8(2) 2 1.480 0.937

4

R1 = 0.0702, wR2 = 0.1640 3.520 and −1.800

R1 = 0.0628, wR2 = 0.1599

1.274

3420/0/238

0.908 and 0.879

empirical

99.9

3420 [R(int) = 0.0374]

−15 ≤ h ≤15, −25 ≤ k ≤25, −15 ≤ l ≤10 24707

1736.0 0.11 × 0.10 × 0.09 2.21−25.50

C28H32Cl4N10O6Sn 865.15 100(2) 0.71073 orthorhombic Pnma a = 12.9349(5) Å, b = 21.0223(9) Å, c = 13.1337(6) Å, α = 90°, β = 90°, γ = 90° 3571.3(3) 4 1.605 1.070

5

R1 = 0.0570, wR2 = 0.1341 1.756 and −1.592

R1 = 0.0535, wR2 = 0.1309

1.100

2976/6/228

0.886 and 0.848

empirical

97.7

2976 [R(int) = 0.0252]

−8 ≤ h ≤8, −13 ≤ k ≤12, −14 ≤ l ≤14 4433

434.0 0.15 × 0.13 × 0.11 2.08−25.00

C30H34Cl4N10 O4Sn 859.18 100(2) 0.71069 triclinic P1̅ a = 7.073(5) Å, b = 11.034(5) Å, c = 12.475(5) Å, α = 114.821(5)°, β = 92.830(5)°, γ = 99.652(5)° 8375.2(6) 1 1.653 1.102

Crystal Growth & Design Article



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Chart 1. Triorganotin Carboxylates: (a) Coordination Polymer and (b) Discrete Monomer11

Scheme 1. Synthetic Procedure of Complexes 1−5

earlier.53 It is worth mentioning that, in the presence of dilute HCl, only protonation at the N1 position of adenine occurred and no esterification reaction of L4H was observed previously.57 However, in the present instance, esterification of L3H and L4H was observed; this is presumably because of the presence of organotinchlorides, which are well-known in the literature for catalyzing the esterification reactions.58−60 119 Sn {1H} NMR spectra of 1 and 2 show singlets at −30 (s) and −20 (s) ppm, respectively, consistent with their molecular structures. The ESI-MS of 1 and 2 reveals a breakdown of the coordination polymer and shows peaks at 242.9869

[Me3Sn(CH3SOCH3)]+ (100%) and 369.1269 [n-Bu3Sn(CH3SOCH3)]+ (100%) respectively. The ESI-MS of 3 reveals a breakdown of the structural integrity, and peaks at 745.0438 [(Ph3Sn)2HCOO]+ and 906.1014 [(Ph3Sn)2(L2)]+ were observed. Peaks due to [Ph2SnCl3]−and [H(L3)CH3]+ at 378.8827 and 208.0842 were observed in the ESI-MS of 4 in the −ve and +ve modes for the anionic and cationic counterparts, respectively. 119Sn {1H} NMR spectra of 4 shows a singlet at −396(s) ppm, which is consistent with that observed in a literature precedent.61 Complex 5 shows a peak at 208.0842 [H(L3)CH3]+ in the +ve mode of ESI-MS, whereas, in the −ve D



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distance between Sn and the CO unit is 3.277(2) Å, which is shorter than the sum of the van der Waals radii between the Sn and O atoms (3.7 Å).63 Several hydrogen bonding interactions are present in the solid-state structure of 1. A hypoxanthine ribbon is generated by intermolecular hydrogen bonding (N1−H1···N7, 2.118 Å and C2−H2···O6, 2.395 Å) involving every hypoxanthine unit (Figure 2). Such a ribbon formation in a coordination polymer appears to be unique, although it has been observed in molecular compounds.64−66 Each hydrogen-bonded hypoxanthine trimer of the ribbon affords a 25-membered macrocycle within the main polymer (Figure 2). The result of these interactions is a 2D coordination polymer where successive triorganotin chains are separated by hypoxanthine ribbons. Additional crystal stabilizing interactions arise from C−H···N interactions between methyl groups of the tin atom with the hypoxanthyl N7 (Figure S1, Supporting Information). The asymmetric unit of complex 2 is given in Figure 3a. The asymmetric unit of 2 contains two repeating units of the 1D polymer. A detailed description of 2 is not warranted because of its structural similarity with 1. Also, surprisingly, the supramolecular framework in 2 is similar to that found in 1 in spite of the variation of the nature of the organic groups attached to the tin center (Figures 2 and 3b). Previously, in many instances, the organic groups attached to the tin center have been known to play an important role in the supramolecular structure.30 In the current instance, the recognition of the hypoxanthine units appears to dominate and overcome other factors. The molecular structure of 3 is given in Figure 4a, and the selected bond parameters are summarized in the caption of Figure 4. This reveals that there are two tin centers that are attached via a carboxylate group. The essential difference between the two tin centers is that, in one case, a carboxylate is a terminal ligand, whereas, in the other case, it is a water molecule. Both the tin centers are five-coordinated in a distorted trigonal bipyramidal geometry with the oxygen atoms occupying the axial positions. The average Sn−C (2.119 Å for Sn1; 2.124 Å for Sn2) and Sn−O (2.249 Å for Sn1and 2.238 Å for Sn2) bond distances of both the tin centers are also

Figure 1. Asymmetric unit of 1 (hydrogen atoms of the methyl groups have been omitted for clarity). Distances (Å): Sn1−O1, 2.222(2); Sn1−O2, 2.338(2); Sn1−C14, 2.116(3); Sn1−C12, 2.115(3); Sn1− C13, 2.119(3); O1−C11, 1.268(3); O2−C11, 1.253(3). Angles (deg): O1−Sn1−O2, 176.91(6); C12−Sn1−C13, 124.13(11); C14−Sn1− C12, 117.95(1); C14−Sn1−C13, 117.90(1).

mode, the dianion gives a peak at 378.8827 [Ph2SnCl3]− by losing a chloride anion. However, we could not find any signal in the 119Sn NMR; this could be because of a very fast exchange between [Ph2SnCl4]2− and [Ph2SnCl3]2− in solution. The asymmetric unit of complex 1 is given in Figure 1. It is a 1D polymer formed as a result of anisobidentate carboxylate coordination to tin ions (η1:μ2 mode). Selected bond parameters are summarized in the caption of Figure 1. Each tin is fivecoordinate in a distorted trigonal bipyramidal geometry (τ = 0.88; cf. the τ values for the idealized geometries are τ = 0, rectangular pyramidal; τ = 1, trigonal bipyramidal),62 with oxygen atoms occupying the axial positions. The Sn−O distances are 2.222 (2) and 2.338(2) Å, while the average Sn−C distance is 2.117(3) Å. The O−Sn−O bond angle is 176.91(6)°. The average C−Sn−C bond angle is 120.96(2)°. The long bond

Figure 2. Hydrogen bonding of 1 (methyl groups on tin atom have been omitted for clarity). Inset shows the interaction between hypoxanthine moieties with the number scheme. Hydrogen bonding parameters. Distances (Å): N1−H1···N7, 2.118; C2−H2···O6, 2.395. Angles (deg): N1−H1− N7, 173.78(4); C2−H2−O6, 143.24(2). E



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Figure 3. (a) Asymmetric unit of 2 (hydrogen atoms of the butyl groups have been omitted for clarity). Distances (Å): Sn1−O2, 2.382(2); Sn1− O3A, 2.222(2); Sn1−C24, 2.116(3); Sn1−C32, 2.241(4); Sn1−C28, 2.149(3); O2−C11, 1.250(4); O1A−C11, 1.268(3). Angles (deg): O2−Sn1− O3A, 172.42(8); C24−Sn1−C28, 121.16(2); C24−Sn1−C32, 126.75(3); C28−Sn1−C32, 111.88(2). (b) Hydrogen bonding network of 2 (part of butyl groups have been omitted for clarity). Distances (Å): C2−H2···O6A, 2.382; N1−H1···N7A, 2.222. Angles (deg): C2−H2−O6A, 145.99(2); N1−H1−N7A, 172.35(2).

Figure 4. (a) Molecular structure of 3 (hydrogen atoms of C10 and phenyl groups have been omitted for clarity). Distances (Å): Sn1−C13, 2.110(6); Sn1−C25, 2.113(6); Sn1−C19, 2.135(6); Sn1−O1, 2.175(4); Sn1−O3, 2.324(4); Sn2−C37, 2.117(6); Sn2−C31, 2.127(6); Sn2−C43, 2.129(6); Sn2−O4, 2.209(4); Sn2−O5, 2.268(4); Sn(1)−O(2), 3.100(4); Sn(2)−O(3), 3.257 (3). Angles (deg): O1−Sn1−O3, 175.71(2); O4− Sn2−O5, 174.22(1). (b) A 32-membered macrocycle formed via intermolecular hydrogen bonding in 3. Bond parameters: Distance (Å): O5− H5B···N1, 1.945; Angle (deg): O5−H5B−N1, 145.181(4).

nearly equal. In addition, a weak interaction is present between the CO unit and the tin centers (3.001 Å for Sn1; 3.256 Å for Sn2). Several hydrogen bonding interactions along with other noncovalent interactions are present in the crystal structure of 3. The supramolecular structure of 3 can be understood in a stepwise manner. First, the hydrogen atoms of the coordinated water molecule interact with the N1 nitrogen of modified 2-aminopurine (O5−H5B···N1, 1.946 Å) to form a 32-membered macrocycle (Figure 4b). Further, the macrocycles are interconnected by hydrogen bonding via a lattice water molecule (O7−H7A···N7, 2.781 Å; N2−H2B···O7, 2.273 Å;

O5−H5A···O7, 1.835 Å) to form a one-dimensional structure (Supporting Information, Figure S2). Next, such one-dimensional structures are interlinked through a pair of hydrogen bonding interactions of 2-aminopurine (N2A−H2AB···N1A, 2.188 Å), affording a 2D structure (Figure 5). Finally, π···π stacking67 of 2-aminopurine culminates in a 3D structure (Supporting Information, Figure S3). The molecular structure of complex 4 is given in Figure 6a. It is an ionic complex containing two cationic methyl-2-(N9adeninyl) acetate [H(L3)Me]+ and two anions, chloride and [Ph2SnCl3(H2O)]−. The tin center has a near-octahedral geometry. F



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Figure 5. 2D supramolecular structure of 3 (phenyl groups have been omitted for clarity).

Figure 6. (a) Molecular structure of complex 4. Distances (Å): Sn(1)−Cl(1), 2.481(1); Sn(1)−Cl(2), 2.607(1); Sn(1)−Cl(3), 2.521(1); Sn(1)− O(4), 2.351(1); Sn(1)−C(12), 2.139(1). Angles (deg): Cl(1)−Sn(1)−O(4), 175.66(1); Cl(2)−Sn(1)−Cl(3), 179.52(1); C(12)−Sn(1)−C(12)*, 167.88(2). (b) [Ph2SnCl3(H2O)]− and Cl− interaction in 4 through hydrogen bonding. Distances (Å): O(4)−H(4A)···Cl(4), 2.397; O(4)− H(4B)···Cl(2), 2.427. Angles (deg): O(4)−H(4A)−Cl(4), 158.31(3); O(4)−H(4B)−Cl(2), 165.60(3). (c) Hydrogen bonding in 4 (part of phenyl groups and ester groups have been omitted). Distances (Å): N(6)−H(6A)···Cl(4), 2.421; N(6)−H(6B)···N(7), 2.081; N(1)−H(1)···Cl(4), 2.374; C(8)−H(8)···Cl(1), 2.984; C(9)−H(9A)···Cl(3), 2.701. Angles (deg):N(6)−H(6A)···Cl(4), 148.75(3); N(6)−H(6B)···N(7), 157.95(3); N(1)− H(1)···Cl(4), 152.82(6); C(8)−H(8)···Cl(1), 153.02(3); C(9)−H(9A)···Cl(3), 158.05(5).

The supramolecular structure of 4 can be understood in a stepwise manner. First, the cationic nucleobase and [Ph2SnCl3(H2O)]− interact via π···π (3.612 Å) stacking.67 A chloride ion is hydrogen bonded with two cationic nucleobases through the protonated Watson−Crick faces (Figure 6a). Further, chloride ions are hydrogen bonded to the coordinated water of [Ph2SnCl3(H2O)]− through O(4)−H(4A)···Cl(4) hydrogen bonding (Figure 6a,b). A 1D chain is formed as a result of the interconnection of [Ph2SnCl3(H2O)]− through O4−H4B···Cl2 hydrogen bonding (Figure 6b). Two cationic adenine moieties dimerize through their Hoogsteen sites by hydrogen bonding (Figure 6c), and then each dimer is connected through the

N−H···Cl [N(6)−H(6A)···Cl(4), N(6)−H(6B)···N(7), N(1)−H(1)···Cl(4), C(8)−H(8)···Cl(1), C(9)−H(9A)··· Cl(3)] hydrogen bonding to form a 1D supramolecular structure (Figure 6c). The cumulative result of these multiple secondary interactions is the formation of a 3D supramolecular structure (Figure S4, Supporting Information). The molecular structure of complex 5 containing the dianionic complex [Ph2SnCl4]2− is given in Figure 7. The tin(IV) ion has a near-octahedral geometry; four chloride ions are present in the equatorial positions [Sn−Cl distances of 2.561(2) and 2.591(2) Å], while the apical positions contain two phenyl groups [Sn−C distances 2.149(6) Å]. Analogous to G



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Figure 7. Molecular structure of complex 5. Distances (Å): Sn(1)−Cl(1), 2.561(2); Sn(1)−Cl(2), 2.591(2), Sn(1)−C(13), 2.150(6). Angles (deg): Cl(1)−Sn(1)−Cl(1)*, 180.0; Cl(2)−Sn(1)−Cl(2)*, 180.0; C(13)−Sn(1)−C(13)*, 180.0.

Figure 8. Supramolecular interactions in 5. Distances (Å): N(1)−H(1)···Cl(1), 2.877; N(6)−H(6A)···Cl(1), 2.630; N(6)−H(6A)···Cl(1), 2.629. Angles (deg): N(1)−H(1)−Cl(1), 129.70(7); N(6)−H(6A)−Cl(1), 129.16(4); N(6)−H(6A)−Cl(1), 141.64(4).

themselves. Thus, in [Me3Sn(L1)]n (1) and [n-Bu3Sn(L1)]n (2), we have observed the formation of hypoxanthine ribbons within the two-dimensional networks. Utilizing main-group element chemistry to explore the supramolecular chemistry of nucleobases and utilizing the latter to build functional molecules appears to be an area fraught with interesting possibilities.

the previous example, 5 also generates a cation by the protonation of the N1 position. The cations interact through their Hoogsteen sites [N6− H6B···N7, 2.125(4) Å] to form an adenine dimer (Figure 8, pointed out by red square). The protonated Watson−Crick sites interact with the chlorine atoms of the two different [Ph2SnCl4]2− by means of four sets of hydrogen bonding [two sets of N1−H1···Cl1, 2.584(8) Å and two sets of N6−H6A··· Cl2, 2.630 (2) Å] (Figure 8). A π−π stacking [3.590(3) Å]67 interaction occurs between the adenine and the phenyl groups of [Ph2SnCl4]2− (Figure 8). All of the above interactions of 5 culminate in a 3D supramolecular framework (Figure 8).

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ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data in CIF format, some structural diagrams, and bond parameters. This material is available free of charge via the Internet at http://pubs.acs.org.

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CONCLUSION We have shown the efficacy of using organotin platforms for constructing multinucleobase arrays. The supramolecular chemistry of such systems has been shown to be extremely rich, containing diverse noncovalent interactions, the most prominent of these being the interactions between the nucleobases

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected], [email protected]. Phone: (+91) 512-2597259. Fax: (+91) 521-259-0007/7436 (V.C.). Notes

The authors declare no competing financial interest. H



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ACKNOWLEDGMENTS S.K. and B.M. are thankful to the CSIR, New Delhi, and C.M. thanks UGC, India, for the award of a Senior Research Fellowship. S.V. thanks DST Thematic Unit of Excellence for facilities, Department of Science and Technology, New Delhi, for the award of the National J. C. Bose Fellowship and DAESRC Outstanding Investigator Award for financial support. V.C. is thankful to the Department of Science and Technology, New Delhi, for the award of the National J. C. Bose Fellowship.

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Polymeric, Molecular and Ionic Organotin Complexes Containing

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