6-Methyl-2-pyridyl - American Chemical Society

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N‑(6-Methyl-2-pyridyl)mesitylenesulfonamide: An Efficient Template for Polyiodides Fangfang Pan and Ulli Englert* Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen, Germany S Supporting Information *

ABSTRACT: A series of (poly-)iodides featuring I−, I3−, I5−, and I7− anions and even the challenging I42− dianion have been synthesized and structurally characterized by X-ray diffraction. The V-shaped sulfapyridine derivative N-(6methyl-2-pyridyl)mesitylenesulfonamide acts as the countercation in all compounds. Depending on stoichiometry and solvent, the different products are reproducibly accessible as phase-pure solids. N−H···I hydrogen bonds connect cations and iodide or triiodide anions to salts with related packing features. The same interactions allow for the stabilization of the much less popular tetraiodide, subtending this linear species between two cations. Monocationic pairs of (formally hemiprotonated) sulfonamides pack according to a common pattern and exert a pronounced templating effect on the formation of penta- and heptaiodides; their influence is based on charge, size, and shape matching. The higher polyiodides can readily be discerned by their Raman spectra.

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with respect to size, shape, charge, or space filling. Successful templating refers, however, to the overall iodide substructure rather than to the formation of certain discrete polyiodide anions. Quaternary diammonium13 and bipyridinium14 ions of well-defined dimensions have recently been identified as appropriate crystallization partners for I−···I−I···I− (I42−). Following the same strategy, Metrangolo et al. synthesized the I−···I−I···I−···I−I···I− (I73−) species with triammonium cations.15 The rational access to polyiodides is limited, however, by facile charge transfer between I−/I3− anions and I2 and by the often pronounced dependency on crystallization conditions, particularly in the case of polyiodides with high negative charges and low stability. Exceptions have therefore been reported in the original articles, together with rational syntheses.14,15 Despite these challenges, polyiodides have been a focus of scientific interest not only because of their structural diversity but also with applications in mind, for example in solar cells and in electronic or optical devices.7 In this contribution, we report polyiodide formation based on the templating effect of a V-shaped sulfapyridinium derivative, which may stabilize I−, I3−, and I42− by hydrogen bonds. In addition, the shape of the cation and its charge distribution closely matches those in our penta- and heptaiodides, making it a particularly well-suited template. Scheme 1 summarizes the structurally characterized compounds. They comprise a wide range of interiodine distances, but we did not encounter any I···I contacts in the range from 3.4 to 3.7 Å. We

INTRODUCTION Iodine plays a special role among the halides: the simultaneous presence of diiodine molecules and iodide anions often results in the formation of polyiodides. Interatomic distances in these anionic residues cover a wide range, from the classical single bond of less than 2.8 Å in I21 via elongated bonds of 2.9−3.2 Å in I3− moieties2 up to considerably longer contacts corresponding to halogen bonds; the upper limit for significant interactions may be associated with twice the van der Waals radius for iodine (i.e., ca. 4 Å).3 The numerical values for these distance ranges and their interpretation have been repeatedly discussed: Alcock established a limit between primary and secondary I−I bonds4 in order to determine the connectivity in polyiodides. Coppens suggested an empirically convenient cutoff at 3.3 Å for I−I bonds.5 In the same context, Kloo et al. proposed the range between 3 and 4 Å for secondary bonds based on theoretical calculations and structural statistics.6 In a later review, the same group considered I−I contacts of 3.4−3.7 Å as secondary bonds and 3.9 Å as the lower limit for van der Waals interactions.7 Not surprisingly, energy differences between such less clear-cut structure types are comparatively small, making the rational synthesis of higher polyiodides challenging. The unavoidable countercations often play a pivotal role and act as templates. Examples include alkali cations coordinated by suitable crown ethers, which were systematically investigated by the groups of Tebbe8 and Schröder.9 The latter authors also reviewed the self-assembly of polyiodide networks templated by a series of thioether macrocyclic complexes10 and pointed out the shape influence of the cation. Alternative complex cations comprise M(phen)32+11 and M(Cp)2+.12 All of these approaches make use of the complementary nature of cations and polyiodides © 2014 American Chemical Society

Received: October 17, 2013 Revised: January 15, 2014 Published: January 24, 2014 1057

dx.doi.org/10.1021/cg4015477 | Cryst. Growth Des. 2014, 14, 1057−1066

Crystal Growth & Design

Article

Scheme 1. Formation and Chemical Composition of the (Poly-)Iodides Which Have Been Structurally Characterized in This Work

trimethylphenyl)sulfonyl chloride (1:1) in dichloromethane, as described in the literature.19 For the synthesis of the polyiodides, a suitably diluted solution of HI (around 0.1 mmol/mL) was prepared by mixing 0.5 mL 57% (7.6 mol/L) HI with 37.4 mL methanol. Unless indicated otherwise, this diluted HI solution was used in the following syntheses. Reactions of 1 with aqueous HI afforded the products compiled in Scheme 1. The I2 content of the anions may be controlled by stoichiometry and reaction conditions. The diverse polyiodide anions may be understood as adducts of I− with different stoichiometries of I2. This molecular I2 is either contained in the hydriodic acid or explicitly added as a reactant; the alternative formation via oxidation of iodide ions requires much longer reaction times. The kinetics and the mechanism of the oxidation of I− in the presence of molecular oxygen in acidic solution have been studied by Kimura et al.20 Route A. 2 is accessible as an essentially phase pure powder by direct grinding of 1 (e.g., 145.0 mg) with concentrated hydriodic acid (e.g., one drop). Single crystals suitable for X-ray diffraction were obtained by reaction of an equimolar solution of 1 (145.0 mg, 0.5 mmol) and hydriodic acid (0.5 mmol) in methanol. Route B. 0.145 g (0.5 mmol) of 1, a slight excess of hydriodic acid (6.0 mL, 0.6 mmol) and 0.064 g of diiodine (0.25 mmol, HI:I2 ≈ 2:1) were dissolved in methanol and stirred for 30 min at room temperature. Fast concentration of the solvent under vacuum with a rotary evaporator yielded crystals of 3, suitable for X-ray diffraction and an oily residue. We have been able to further characterize this residue: it was redissolved in 15 mL of benzene and the solvent was allowed to evaporate slowly at ambient temperature; after complete evaporation, crystals corresponding to the tetraiodide 4, a benzene solvate, were obtained, together with a brown noncrystalline solid. This solvate was not sufficiently stable to obtain a satisfactory powder pattern and Raman spectrum. Route C. 0.145 g (0.5 mmol) of 1, a slight excess of hydriodic acid (6.0 mL, 0.6 mmol) and 0.127 g of diiodine (0.5 mmol, HI:I2 ≈ 1:1) were dissolved in methanol and stirred for 30 min at room temperature. Upon fast partial evaporation of the solvent under vacuum, crystalline 6α precipitated. When this precipitate was

therefore consider distances below 3.4 Å (i.e., slightly longer than the Coppens limit) as I−I bonds, and we will discuss contacts shorter than 4 Å as relevant. The results of our Raman spectrascopic studies also support this partitioning.

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EXPERIMENTAL SECTION

Structural Studies. X-ray diffraction data for all compounds have been collected at 100 K on a Bruker D8 goniometer equipped with an APEX CCD detector using Mo Kα radiation (λ = 0.71073 Å). The radiation source was an INCOATEC I-μS microsource. An Oxford Cryosystems 700 low temperature controller was used to ensure temperature stability during data collection. Intensity data were integrated with SAINT16 and corrected for absorption following the multiscan approach with SADABS.17 The structures were solved with direct methods (SHELXS97) and refined by full-matrix least-squares on F2 (SHELXL97).18 Anisotropic displacement parameters were assigned to non-H atoms. H atoms bonded to sulfapyridine N were localized in difference Fourier maps; their positions were refined freely in 2, 4, and 7, restrained to N−H distances of 0.88 Å in 5 and 6α, and constrained in 3 and 6β. During refinement, the crystal of 6β was found to be twinned by inversion; the occupancy of the smaller domain converged to 0.31(3). The two sulfapyridine moieties in this noncentrosymmetric structure are arranged about a noncrystallographic pseudocenter of inversion; anisotropic displacement parameters for C7, C27 and C12, C32 were constrained to be equal within pairs related by pseudo symmetry. Crystal data, information concerning data collection and reduction and convergence results have been compiled in Table S1 of the Supporting Information. Powder diffraction diagrams, difference Fourier maps displaying the reasonable assignment of the extra H in penta- and hepta-iodides, and details concerning intermolecular interactions are also available in the Supporting Information. Raman Spectroscopy. Raman spectra in the range 70−250 cm−1 were obtained with a Horiba LABRAM HR instrument equipped with a 633 nm HeNe excitation laser. Syntheses. N-(6-methyl-2-pyridyl)mesitylene-sulfonamide 1 was synthesized by reaction of 2-aminopyridine and (2,4,61058



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The reaction of I− and I2 to I3− implies the formation of an additional bond and is exothermic; it is carried out in acidic solution. The triiodide anion in 3 (Figure 2) is asymmetric,

redissolved, different solids formed as a function of the solvent used. From benzene, crystals of the hemisolvate 5 were obtained. In addition, two polymorphic ansolvates were encountered: 6α crystallized from methanol and 6β from ethanol. The powder diffractogram of 6α shows the presence of a small amount of the alternative polymorph 6β. Route D. Alternatively, both polymorphs 6α and 6β are accessible via direct reaction between 1 and a large excess of hydroiodic acid in methanol (6α) or ethanol (6β) by slow solvent evaporation over a period of 4 days. In a typical experiment, 0.145 g (0.5 mmol) of 1 were reacted with 20.0 mmol of HI. Route E. A slight excess of hydriodic acid (6.0 mL, 0.6 mmol), 0.254 g of diiodine (1.0 mmol, HI:I2 ≈ 1:2), and 0.145 g (0.5 mmol) of 1 were dissolved in methanol and stirred for 30 min at room temperature. Fast partial evaporation of the solvent under vacuum resulted in a crystalline precipitate of 7. Similar as in route C above, redissolution of the solid in methanol or ethanol gave 6α or 6β, respectively. Attempts to synthesize yet higher polyiodides by further increasing the amount of diiodine in the reaction have not been successful; they still led to the heptaiodide, the most iodine-rich compound in our system. All crystals investigated in this work are brown and platelet-shaped. The melting points of the compounds are closely related to their iodine content and to their packing efficiency. Crystals of the triiodide species 3 show the lowest melting point in the range of 111.0−113.0 °C; the melting point of the heptaiodide 7 is only slightly higher (112.3−114.0 °C), in agreement with its more efficient packing (67.1% for 7 vs 65.8% for 3). The melting points for the three pentaiodides all range from 128.5 to 132.0 °C; crystals of the polymorphs 6α and 6β cannot be reliably distingished based on this physical property (mp 128.5−130.5 °C for both). For these solventfree polymorphs, the melting point is slightly lower than for the benzene solvate: 5 undergoes visible changes over a wider temperature range and liquefies completely at 132.0 °C. These observations may well correspond to a gradual release of the cocrystallized benzene molecule immediately before the phase transition. Interestingly, crystals of the benzene solvate slowly change their color from brown to colorless when kept at ambient environment for two months. This phenomenon is probably associated with the release of iodine and results in an amorphous solid. The monoiodide is the most stable in this series of compounds, indicated by its significantly higher melting point of 192.0−194.0 °C.

Figure 2. The asymmetric unit of the triiodide 3.

with bond lengths I1−I2 = 3.0696(4) and I2−I3 = 2.7961(5) Å. Even the shorter I2−I3 bond is significantly elongated with respect to the I−I bond in diiodine because I− donates electron density into the antibonding LUMO σ* of the I2 molecule.22 Such asymmetric I3− species are energetically less favorable and hence less popular, but they may be stabilized in the solid by charge effects.23 The asymmetry in the triiodide is reflected in the Raman spectrum of 3, in which three intensities are detectable (Figure S3 of the Supporting Information). The one at 106 cm−1 corresponds to the typical symmetry stretching vibration ν1 of I3− species, while the appearance of a stronger asymmetric stretch of triiodide at 163 and the shoulder at around 75 cm−1 are ascribed to the asymmetric ν3 and bending ν2 vibrations, respectively. Their appearance is a consequence of the decrease in symmetry of the triiodide.24 In line with these arguments, the asymmetry in the triiodide anion in 3 can be attributed to the close neighborhood between the terminal atom I1 and the countercation. Although the triiodide anion is sterically more demanding than a monatomic iodide, the replacement of the latter by the former has only minor influence on the packing mode. The close relationship between the crystal structures of 2 and 3 can be perceived in their projections along the [100] direction (Figure 3). Closer inspection reveals, however, that the larger anion pushes neighboring sulfonamide cations apart and thus modifies the weak intermolecular contacts. Figure 4 displays these differences in packing: C−H···π interactions corresponding to contact A and π···π interactions between parallel aromatic rings (contact B) dominate in 2, whereas in 3 the C− H···π interactions (contact A) are weaker and the π···π stacking is replaced by lone-pair···π contacts between the sulfonyl-O and the aminopyridine group (contact B). Sulfonamide cations also stabilize the less common I42− anion, which has been synthesized previously with precise control under the viewpoint of crystal engineering.14,15,25 Only a very low barrier prevents this species from fragmentation.25 In accordance with route B in Scheme 1, the tetraiodide 4 is obtained as a solvate from benzene. Its formation agrees well with the mechanism of the I−/I3− redox couple proposed by Watanabe:26 the tetraiodide is formed by I− approaching the linear I3− from one end, and I− is released from the other. On the basis of DFT results, Mealli et al. recently associated the longer peripherial I−I bonds in the tetraatomic residue with orbital overlap even at longer distances and proposed charge stabilization of the I42− anion with respect to the gas phase.23 The disposition of two countercations at either periphery of the tetraiodide in 4 matches these requirements very well. This arrangement of the I42− about a crystallographic inversion center is depicted in Figure 5.

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RESULTS AND DISCUSSION Compound 1 occurs in two packing polymorphs. In both crystal forms, the neutral N-(6-methyl-2-pyridyl)mesitylenesulfonamide molecules exhibit zwitterionic character: the presumably less basic N atom in the picoline ring is protonated, whereas the sulfonamide N formally retains a negative charge. A detailed comparison between these polymorphs is provided in our recent report.21 Reaction of 1 with hydriodic acid gives the simple iodide of the protonated sulfonamide, a salt stabilized by classic N−H···I hydrogen bonds (Figure 1). As a consequence of the protonation at N2, the interatomic distances C1−N2 and N2−S1 in this cation are significantly longer than in neutral 1.

Figure 1. The asymmetric unit of the monoiodide 2. 1059



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Figure 3. The packing modes in (a) 2 and (b) 3 are closely related; the structures are viewed along [100].

Figure 4. Cation packing in 2 and 3; the overall arrangement is similar but different types of weak interactions dominate: in 2, contacts A (C−H···π) = 2.85 Å and B (π···π) = 3.4177(8) Å; in 3, contacts A (C−H···π) = 2.95 Å and B (S−O···π) = 3.052(3) Å.

7 allows for the examination of the key influences during crystallization and the templating effect exerted by the cation. A common feature in the crystal structures of the pentaiodides 5, 6α, 6β, and the heptaiodide 7 is their composition, with one polyiodide per monocationic sulfonamide pair. For the pairwise arrangement of sulfonamide moieties with a total monopositive charge per pair, we have encountered three cases: (a) In 6β, a (neutral) molecule of 1 and a cation protonated at N2 join by hydrogen bonds. All atoms are ordered, and the bond between sulfur and the protonated nitrogen S1−N2 [1.654(9) Å] is longer than the corresponding distance S2−N4 in the neutral molecule [1.608(9) Å]. (b) In 6α and 7, two sulfonamide residues are arranged about a crystallographic center of inversion; they share a negative charge, and the extra proton is situated on (6α) or very close (7) to the inversion center. The interpretation concerning the location of the central H upon or close to the −1 site relies on Fourier difference maps, which indicate a single broad feature in the former and a split residual in the latter case. Our intensity data are of good quality and reasonable resolution, but nevertheless we are well aware of the limitations of any statement concerning the precise localization of hydrogen atoms by X-ray diffraction. Obviously, the S−N distances in both residues are symmetry-equivalent. (c) In 5, two independent sulfonamide residues are arranged about a noncrystallographic (local) center of inversion. The proton is disordered, and consequently the S−N distances associated with the independent molecules do not differ significantly [S1−N2 = 1.620(4), S2−N4 = 1.630(4) Å]. The cases (a−c) are summarized in Figure 7; the closest polyiodides have been included. The protonation patterns for the monocationic sulfonamide pairs cover all possible variants almost in a textbook fashion; graphical information about their

Figure 5. I42− unit stabilized by two cations in the crystal structure of 4 (i = 2−x, −1 − y, −z).

Similar to the situation in 2 and 3, the ions of opposite charge interact via classical N−H···I hydrogen bonds. The dotted lines in Figure 5 emphasize the strong interaction between the peripheral I− and I2, with I1−I2 = 3.3794(4) Å; the covalent bond I2−I2i in the central diiodine part amounts to 2.7587(3) Å and is hardly elongated with respect to the situation in elementary diiodine.27 The cocrystallized benzene plays a crucial role in stabilizing the overall structure, linking two sulfonamide cations via π···π stacking with their picolyl rings and T stacking H···π interactions with their mesitylene moieties (Figure 6, top right). The sulfonamide−benzene− sulfonamide aggregates such formed are interconnected via π···π contacts to 1D chains along [001]. Nonclassical C−H···O hydrogen bonds (blue dashed lines in Figure 6) extend these chains into the ac plane. The resulting positively charged 2D layers are linked together by interjacent tetraiodide anions (green residues in Figure 6). The formation of polyiodides according to Scheme 1 depends on stoichiometry and solvent. A systematic comparison of the structurally related higher polyiodides 5, 6α, 6β, and 1060



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Figure 6. Stepwise analysis of the formation of the 3D network in 4 via secondary interactions.

Figure 7. The monocationic sulfonamide pairs and neighboring polyiodides in 6α, 6β, 5, and 7. Interatomic distances: in 5, I1−I2 3.1784(6), I2−I3 2.7656(6), I1−I4 2.9801(6), I4−I5 2.8452(6); in 6α, I1−I2 2.9924(8), I2−I3 2.8323(8); in 6β, I1−I2 3.0030(11), I2−I3 2.8302(11), I1−I4 3.0044(12), I4−I5 2.8239(12); in 7, I1−I2 2.9060(5), I2−I3 3.2244(6), I3−I4 2.7454(6).

atom is located on a crystallographic inversion center and the iodide counterion on a 2-fold axis. The alternative polymorph 6β crystallizes from ethanol in the noncentrosymmetric space group Pc. In this phase, the asymmetric unit contains a neutral and a protonated MPMS residue as well as a pentaiodide anion. Presence and absence of crystallographic inversion centers in

difference Fourier maps is provided in Figure S2 of the Supporting Information. 6α and 6β are polymorphs and may be obtained as phasepure solids, depending on the solvent of crystallization. 6α precipitates from methanol and crystallizes in space group C2/ c, with a sulfonamide group in the general position; the extra H 1061



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Figure 8. Similarity between the two polymorphs 6α and 6β. Top: space filling model, showing an iodide layer in-between sulfonamide cations; bottom: packing in the [010] direction.

the crystal structures of 6α and 6β may be perceived by inspecting the distribution of normalized structure factors:28 ⟨E2-1⟩ amounts to 0.998 (expectation value 0.968) for 6α and to 0.748 (expectation value 0.736) for 6β. Figure 8 shows the pronounced similarity between both polymorphs 6α and 6β with respect to packing. 5 is a benzene solvate and crystallizes in the space group P21/ c, with all ionic residues in general position and the solvent molecule on a crystallographic center of inversion. The pentaiodide 5 and the heptaiodide 7 are related in terms of lattice parameters a (for 5) ≈ c (for 7), b (for 5) ≈ b (for 7), c (for 5) ≈ 2a (for 7), cf. Table S1 of the Supporting Information) and packing. The projections of both structures in Figure 9 (top) show that the benzene molecule in 5 is situated within a chain of polyanions; in 7, two iodine atoms are located in this position. The close relationship between both structures is also reflected in space filling models (Figure 9 bottom). We now wish to focus on the polyiodide substructures in 5, 6α, 6β, and 7. If we accept the Coppens limit5 and take only I− I distances up to 3.3 Å as intraresidue contacts into account, the former three solids can be addressed as pentaiodides, whereas 7 represents a heptaiodide. Considerably longer I···I contacts above 3.7 Å will be discussed below. Even the short interactions as defined above vary over a longer range, covering 2.7454(6)− 3.2244(6) Å, thus indicating the inherent softness of the bonding situation in the polyanions. We recall that higher polyiodides can be understood as formed by molecular iodine, iodide, and triiodide as building blocks. The pentaiodides share the same V-shape, with the angle at the central iodine ranging

from 83.43(3)° in 6β to 92.53(1)° in 5, and also show a common trend with respect to interatomic distances: all terminal I−I bonds in the pentaiodides are shorter than their central neighbors. The polyanions in 5 and in the polymorphic forms 6α and 6β differ, however, with respect to symmetry: the arms of the pentaiodide in the former are significantly asymmetric; the bonding situation tends toward an adduct between I3− (I1−I4−I5) and I2 (I2−I3) (Figure 7). In contrast, the anions in both polymorphs of 6 are symmetric: in the α form by virtue of crystallographic symmetry and in the β modification within an agreement of 0.01 Å. The heptaiodide in 7 may be understood as an adduct of two terminal diiodine molecules to a central I3−. Our assumption is also supported by the Raman spectra (Figure S3 of the Supporting Information). Three intense bands at 107, 141, 157 and a shoulder at 90−100 cm−1 are observed in both 5 and 6β and attributed to four stretching vibrations. They correspond to two outer stretches (141 and 157 cm−1) and two inner stretches (90−100, 107 cm−1), respectively.24a,b It is also possible to determine the formation of the pentaiodide from these intensites. In detail, Raman bands at 107 and 157 cm−1 represent the ν1 of I3− and the weakly coordinated I2, respectively. In addition, weak and broad shoulders at 70−80 cm−1 can be assigned as ν2 of I3−. Accordingly, the I5− anions can be understood as adducts of I2 to I3−.6,24a The comparison of their Raman spectra allows us to distinguish the two pentaiodides: the relatively weak intensity of the peak at 141 cm−1 in compound 5 might be accounted for by the more symmetric I3− component in 5 than in 6β. On the basis of the same principle, the heptaiodide in 7 is regarded as the combination of two I2 with one I3−: the very strong peaks at 1062



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Figure 9. Top: packing in 5 and 7; the highlighted region contains a benzene molecule in 5 and four iodine atoms of the polyiodide chain in 7. Bottom: space filling models of 5 and 7.

Figure 10. Halogen bonds in (a) 5 and (b) 7 shown as broken lines. The interatomic distances are in 5, I3···I3i = 3.8541(6) Å, ∠I2−I3−I3i = 83.18(2)°, ∠I3−I3i−I3ii = 167.35(2) (i = −x, 1/2 + y, 1/2 − z, ii = x, 1 + y, z); in 7, I4···I4i = 3.7067(7) Å, ∠I3−I4−I4i = 83.470(10)°, ∠I3−I4−I4ii = 168.340(10)° (i = 2 − x, 1/2 + y, 1/2 − z, ii = 2 − x, −1/2 + y, 1/2 − z).

108 and 114 cm−1 prove the existence of the I3− component,

bands to the coordination interactions between the terminal I2 residues and the central I3−. Additional I···I interactions in the range of 3.7−3.9 Å occur in 5 and 7, whereas no interhalogen contacts within the van der Waals radii are observed in 6α and 6β. In 5, I···I halogen bonds of 3.8541(6) Å link pentaiodides to a strand perpendicular to

and the νI−I shows up at 177 cm−1, close to that in isolated I2 moieties, thus revealing the very weak coordination of I2 to I3−. Although the central triiodide is centrosymmetric, two Raman bands appear in the range of 150−160 cm−1. We assign these 1063



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Figure 11. Anion (left) and cation (right) layers in the polyiodides; in the case of 5, the benzene molecules have been included in the anion layer. Red and blue labels represent layers of cationic pairs in different orientation.

the extension of each anion, in the direction of the b axis. Figure 10a underlines that the angles I2−I3···I3i of 83° and I2i−I3i···I3 (i = x, 0.5 − y, 0.5 + z) of 167° match the requirements for so-called “type I interactions”29 very well. In 7, slightly shorter halogen bonds of 3.7066(6) Å and also in suitable angular geometry are responsible for the aggregation of the heptaiodides in the bc plane (Figure 10b). The segregation of the crystalline solids 5, 6α, 6β, and 7 in regions dominated by cationic pairs on the one and polyiodides on the other hand has already been indicated in Figures 8 and 9. For easier inspection, the corresponding substructures are shown separately in Figure 11. The right part of this figure reveals a pronounced similarity of the cationic layers between all these structures: the monocationic pairs of neighboring sulfonamides occur in two orientations labeled as A and B. In

6α, 6β, and 7, the dimers aggregate in an alternating ABAB sequence, whereas double layers following an AABBAABB mode occur in 5. Irrespective of these stacking differences, the negatively charged sulfonyl groups30 are oriented toward a neighboring sulfonamide (cf. Figure 7), whereas the protonated picolyl residues point toward the polyiodide layers. As a consequence, the electrostatic attraction between layers of opposite charge is strong even in the absence of specific short contacts. Classical hydrogen bonds between two sulfonamides, formally a neutral and a monoprotonated one, result in the formation of monocations; additionally, lone-pair π and C− H···π interactions help to assemble the cationic regions as illustrated in Figure 12. 1064



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ASSOCIATED CONTENT

S Supporting Information *

Tables of crystal data, data collection parameters, and convergence results; tables of iodine−iodine interactions in compounds 3−7 as well as secondary intermolecular interactions in all the compounds; X-ray powder diffraction patterns, difference Fourier maps documenting the assignment of the protonation sites in the cations of 5−7, Raman spectra of polyiodides 3, 5, 6β, and 7, and CheckCIF reports for 2−7 are included. This material is available free of charge via the Internet at http://pubs.acs.org. CCDC 966358 (2), 966359 (3), 966360(4), 966361(5), 920533(6α), 920534(6β), and 966362 (7) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif.

Figure 12. Lone-pair···π (highlighted in purple) and C−H···π (highlighted in green) interactions between translation-related neighboring cations in 6α; the situation in 6β and 7 is very similar.

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Charge matching plays an important role: in the sulfonamides, the positive charge cannot be assigned to a specific site but rather is distributed over all peripheral hydrogen atoms,30 whereas the negative charge resides on the easily polarizable polyiodides. As for size matching, the polyiodides owe a certain flexibility to the wide range of halogen bonds from 3.4 to 3.7 Å. Figure 13 shows that the cationic aggregates act similar to a staircase and stimulate interaction with the anions: the pentaiodides lie on top of each individual step (Figure 13, left), whereas the heptaiodides bridge two consecutive steps (Figure 13, right).

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +46 241 8092 288. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Irmgard Kalf for help with the Raman spectra. Financial support for F.P. from the China Scholarship Council is gratefully acknowledged.

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REFERENCES

(1) The I−I distance in elementary iodine has been determined as 2.715(6) Å by X-ray (Van Bolhuis, F.; Koster, P. B. Migchelsen, T. Acta Crystallogr. 1967, 23, 90−91) and as 2.714(2)−2.721(1) Å by neutron diffraction (Ibberson, R. M.; Moze, O. Petrillo, C. Mol. Phys. 1992, 76, 395) in the solid and as 2.667(2) Å in the gas phase (Karle, I. L. J. Chem. Phys. 1955, 23, 1739). The average I−I distance from 327 observations in nondisordered, error-free crystal structures in the Cambridge Structural Database (CSD) (Allen, F. Acta Crystallogr., Sect. B 2002, 58, 380−388) containing co-crystallized diiodine molecules amounts to 2.761 Å. (2) The I−I distance in isolated I3− units is either 2.91 Å in symmetric I3− (Kloo, L.; Rosdahl, J.; Svensson, P. H. Eur. J. Inorg. Chem. 2002, 1203−1209) or up to 3.21 (Blake, A. J.; Gould, R. O.; Li, W.-S.; Lippolis, V.; Parsons, S.; Schroder, M. Cryst. Eng. 1999, 2, 153− 170) in asymmetric species. The average I−I distance from 974 observations based on non-disordered, error-free crystal structures from the CSD in both geometries amounts to 2.921 Å.

CONCLUSIONS

We have shown that protonation of N-(6-methyl-2-pyridyl)mesitylene-sulfonamide results in suitable cations for stabilizing of I−, I3−, I42‑, I5−, and I7−. Mono- and tri-iodide anions are hydrogen-bonded to a single cation, whereas the dianionic I42−, a significantly less popular species, is subtended between two protonated sulfonamides. The asymmetry in the triiodide and the stabilization of the tetraiodide may be understood as redistribution of electron density under the influence of the counter cations, as suggested by Mealli et al.23 The more iodine-rich V-shaped I5− and I7− are stabilized by templating effects with respect to size, charge, and shape matching. The use of alternative large cations for the stabilization of higher polyiodides is the subject of ongoing research.

Figure 13. Templating effect of sulfonamide cations and the relative orientation of penta (left) or hepta-iodide (right) anions. 1065



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(3) Bondi (Bondi, A. J. Phys. Chem. 1964, 68, 441−451) has suggested a van der Waals radius of 1.98 Å, Batsanov (Batsanov, S. S. Izvest. Akad. Nauk, Ser. Khim. 1995, 24, Russ. Chem. Bull. 1995, 44, 18) has suggested 2.1 Å and Rowland (Rowland, R. S.; Taylor, R. J. Phys. Chem. 1996, 100, 7384−7391) has suggested 2.03 Å for I. (4) Alcock, N. W. Adv. Inorg. Chem. Radiochem. 1972, 15, 1. (5) Coppens, P. In Extended Linear Chain Compounds; Miller, J. S., Ed.; Plenum Press: New York, 1982; 1, 333−356. (6) Kloo, L.; Rosdahl, J.; Svensson, P. H. Eur. J. Inorg. Chem. 2002, 1203−1209. (7) Svensson, P. H.; Kloo, L. Chem. Rev. 2003, 103, 1649−1684. (8) (a) Tebbe, K.-F.; El Essawi, M. Z. Anorg. Allg. Chem. 1998, 624, 1046−1050. (b) Tebbe, K.-F.; Kavoosian, A. Z. Naturforsch., B 1993, 48, 438−442. (c) Tebbe, K.-F.; El Essawi, M.; Abd El Khalik, S. Z. Naturforsch., B 1995, 50, 1429−1439. (d) El Essawi, M.; Tebbe, K.-F. Z. Naturforsch., B 1998, 53, 263−265. (e) Tebbe, K. F.; Kavoosian, A. Acta Crystallogr., Sect. C 1995, 51, 562−565. (9) (a) Blake, A. J.; Gould, R. O.; Parsons, S.; Radek, C.; Schröder, M. Acta Crystallogr., Sect. C 1996, 52, 24−27. (b) Blake, A. J.; Gould, R. O.; Li, W.-S.; Lippolis, V.; Parsons, S.; Radek, C.; Schröder, M. Angew. Chem. 1998, 110, 305−308. (10) J. Blake, A.; Li, W.-S.; Lippolis, V.; Schröder, M.; A. Devillanova, F.; O. Gould, R.; Parsons, S.; Radek, C. Chem. Soc. Rev. 1998, 27, 195− 206. (11) Horn, C.; Scudder, M.; Dance, I. CrystEngComm 2001, 3, 9−14. (12) Millan, A.; Bailey, P. M.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1982, 73−77. (13) Abate, A.; Brischetto, M.; Cavallo, G.; Lahtinen, M.; Metrangolo, P.; Pilati, T.; Radice, S.; Resnati, G.; Rissanen, K.; Terraneo, G. Chem. Commun. 2010, 46, 2724−2726. (14) Garcia, M. D.; Marti-Rujas, J.; Metrangolo, P.; Peinador, C.; Pilati, T.; Resnati, G.; Terraneo, G.; Ursini, M. CrystEngComm 2011, 13, 4411−4416. (15) Lin, J.; Martí-Rujas, J.; Metrangolo, P.; Pilati, T.; Radice, S.; Resnati, G.; Terraneo, G. Cryst. Growth Des. 2012, 12, 5757−5762. (16) Bruker SAINT; Bruker AXS Inc.: Madison, WI, 2009. (17) Bruker SADABS; Bruker AXS Inc.: Madison, WI, 2008. (18) Sheldrick, G. Acta Crystallogr., Sect. A 2008, 64, 112−122. (19) Beloso, I.; Castro, J.; García-Vázquez, J. A.; Pérez-Lourido, P.; Romero, J.; Sousa, A. Z. Anorg. Allg. Chem. 2003, 629, 275−284. (20) (a) Kimura, M.; Hara, T.; Tsukahara, K. Bull. Chem. Soc. Jpn. 1995, 68, 2853−2857. (b) Masaru, K.; Tomoko, H.; Tsukahara, K. Chem. Soc. Jpn. 1995, 68, 2853−2857. (c) Kimura, M.; Sato, M.; Murase, T.; Tsukahara, K. Bull. Chem. Soc. Jpn. 1993, 66, 2900−2906. (21) Pan, F.; Englert, U. Acta Crystallogr. 2013, Sect. C69, 1217− 1220. (22) Pimentel, G. C. J. Chem. Phys. 1951, 19, 446−468. (23) Manca, G.; Ienco, A.; Mealli, C. Cryst. Growth Des. 2012, 12, 1762−1771. (24) (a) Deplano, P.; Ferraro, J. R.; Mercuri, M. L.; Trogu, E. F. Coord. Chem. Rev. 1999, 188, 71−95. (b) Nour, E. M.; Chen, L. H.; Laane, J. J. Phys. Chem. 1986, 90, 2841−2846. (c) Blake, A. J.; Devillanova, F. A.; Gould, R. O.; Li, W. -S.; Lippolis, V.; Parsons, S.; Radek, C.; Schroder, M. Chem. Soc. Rev. 1998, 27, 195−206. (25) Müller, M.; Albrecht, M.; Gossen, V.; Peters, T.; Hoffmann, A.; Raabe, G.; Valkonen, A.; Rissanen, K. Chem.Eur. J. 2010, 16, 12446−12453. (26) Kawano, R.; Watanabe, M. Chem. Commun. 2005, 2107−2109. (27) Ibberson, R. M.; Moze, O.; Petrillo, C. Mol. Phys. 1992, 76, 395−403. (28) Dunitz, J. D. X-Ray Analysis and the Structure of Organic Molecules, 2nd ed.; Verlag Helvetica Chimica Acta: Basel, Switzerland, 1995. (29) (a) Desiraju, G. R.; Parthasarathy, R. J. Am. Chem. Soc. 1989, 111, 8725−8726. (b) Sakurai, T.; Sundaralingam, M.; Jeffrey, G. A. Acta Crystallogr. 1963, 16, 354−363. (30) Pan, F.; Wang, R.; Englert, U. CrystEngComm 2013, 15, 1164− 1172.

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6-Methyl-2-pyridyl - American Chemical Society

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