Two-dimensional hydrogen-bonded assemblies: the influence of sterics and competitive hydrogen bonding on the structures of guanidinium arenesulfonate networks Victoria A. Russell and Michael D.Ward* Department of Chemical Engineering and Materials Science, University ofMinnesota, Amundson Hall, 421 Washington Ave. SE,Minneapolis, MN 55455, USA Guanidinium and organosulfonate ions self-assemble into crystalline lattices described by robust two-dimensional hydrogenbonded networks with the general formula [C(NH2)3]+RSO3-.These networks, which typically have quasihexagonal symmetry due to favourable hydrogen bonding between six guanidinium proton donors and six sulfonate electron lone pair acceptors, assemble in the third dimension by stacking in a manner which maximizes van derWaals interactions between R groups.The steric requirements of the R groups dictate whether this assembly results in interdigitated bilayer stacking in which all the R groups are orientated to one side of a given sheet or interdigitated single layer stacking in which R groups are orientated to both sides of a given hydrogen-bonded sheet. The two-dimensional network tolerates very dierent steric requirements of the R groups due to the ability to form either of these stacking motifs and to the inherent flexibility of the hydrogen-bonded network about onedimensional hydrogen-bonding ‘hinges’.This flexibility allows the sheets to pucker in order to accommodate steric strain between R groups within the layers. We describe here the influence of substituents on the R groups whose steric and hydrogen bonding capacity influence the puckering of the two-dimensional guanidinium sulfonate network.In particular, we examine the X-ray crystal structures of the guanidinium salts of ferrocenesulfonate and methyl- and nitro-substituted benzenesulfonates. The retention of the hydrogen-bonding motif in spite of steric and hydrogen bonding interference by the R group substituents illustrates the robustness of the guanidinium sulfonate network. However, additional competing hydrogen bonding and sterics influence the crystal packing, and in the case of multiple substituents on the R groups, these factors may disrupt the guanidinium sulfonate network.Overall, this work demonstrates that the use of robust two-dimensional supramolecular modules can reduce the crystal engineering problem to the last remaining dimension, which can simplify the design of functional molecular materials.materials, or are susceptible to dramatic changes in crystal Introduction packing upon such changes. A reasonable strategy for sur- Crucial to the design and synthesis of molecular materials is a mounting these obstacles is to use robust supramolecular thorough understanding, and ultimately control, of the ‘modules’11,12 or ‘synthons’,13 where robust is defined as the assembly of constituent molecules into the supramolecular ability of the module to maintain its dimensionality and general motif that defines the solid state structure.It is instructive to structural features upon changes in ancillary functional groups consider the constituent molecules of a material as the funda- or other molecular species in the lattice.Robust n-dimensional mental building blocks of the solid state. The formation of modules can reduce the crystal engineering problem to 3-n ordered solid-state networks with a desired arrangement and dimensions, thereby simplifying materials design.dimensionality relies on an appropriate ‘topological director’, Recently, we reported molecular layered materials based on that is, a module having a well-defined functional group that a two-dimensional hydrogen-bonded (HB) network composed can recognize complementary functional groups on other like of guanidinium cations (G) and the sulfonate groups of alkane- molecules (homomeric assembly) or dierent molecules (heter- and arene-substituted monosulfonate anions (S).14–17 The omeric assembly).A crucial property of a director is its ability topological equivalence of the guanidinium ions and sulfon- to participate in intermolecular interactions which are strong ate groups and strong (guanidinium)NMH,O(sulfonate) and highly directional relative to competing ones.Formation hydrogen bonds favoured the formation of quasihexagonal of extended networks also requires ‘polyvalent’ modules, that two-dimensional GS networks in over 30 dierent crystalline is, molecules having more than one bonding functionality. phases containing various sulfonate functionalities (Fig. 1). All These capabilities are provided by molecules containing hydro- the hydrogen bonding capacity is fulfilled within this network, gen bonding functionalities.which is important in forming robust networks. The networks Several examples of ordered, extended hydrogen bonding assembled in the third dimension via van derWaals interactions networks have been reported that illustrate the important between sulfonate R groups extending from the GS sheets, influence of this interaction on directing the organization of either as densely packed bilayers or continuous stacks of molecules in the crystallization of solid-state materials.These interdigitated single layers. The pervasiveness of the GS sheets reports have demonstrated that the local supramolecular was attributed to their ability to form ‘accordion’ or ‘pleated’ organization about each module can be predicted with reason- sheets by puckering about (guanidinium)NMH,O(sulfonate) able confidence based on molecular topology.Flat molecules HB ‘hinges’ joining adjacent one-dimensional hydrogen- having one-dimensional hydrogen-bonding topologies form bonded ribbons. This puckering, which can be defined by inter- ‘ribbon’ or ‘tape’ networks,1–5 while tetrahedral-like hydrogen- ribbon dihedral angles of hIR<180°, enables the sheets to adapt bonding topologies have aorded diamondoid networks.6–10 to the steric demands of dierent R groups.In a few cases However, control of packing in three dimensions can be elusive these steric demands were also accommodated by the formation owing to the contribution of numerous intermolecular inter- of a shifted ribbon HB motif.Although considered to be less actions in the crystal, many of which are nondirectional, optimal than the quasihexagonal motif because of the loss of resulting in a multiplicity of structural possibilities. Further- one strong hydrogen bond, two-dimensional sheet formation more, most of the aforementioned systems either do not in the shifted motif was enforced by the one remaining strong provide for the systematic introduction of ancillary molecu- inter-ribbon hydrogen bond.Such motifs oer unique opportunities for new layered materials based on the GS network lar functionality that is required for the synthesis of functional J. Mater. Chem., 1997, 7(7), 1123–1133 1123least as a first approximation, from the gross steric requirements of the R group extending from the GS sheets (Fig. 2). If the R group is described by either spheres or cylinders it can be shown that interdigitation in a bilayer motif is possible only if the diameter of the R group, as viewed normal to the hydrogen-bonded sheet, is less than dS-S /Ó3, where dS-S is the centre-to-centre distance between nearest sulfonate residues (typically ca. 7.5 A° ). If the diameter exceeds this value of ca. 4.4 A° ,interdigitation is not possible in the bilayer motif. Rather, the networks resort to the continuously stacked single layer motif in which the interdigitation is possible because the R groups of adjacent ribbons are orientated to opposite sides of the GS sheet. Previously, we illustrated several examples that conformed to this model (although in most cases the sulfonate residueis not rigorously cylindrical).For example,guanidinium naphthalene-2-sulfonate, (G)(1), assembles into the bilayer stacking motif (with hIR=146°), whereas the sterically more demanding naphthalene-1-sulfonate homologue (G)(2) assembles into the single layer stacking motif (with hIR=77°).14 The eect of steric demand is also evident in the structure of the guanidinium salt of ferrocenesulfonate (3), which exhibits the continuously stacked single layer stacking motif (Fig. 3). Although the steric ‘footprint’ of 3 (43 A° 2) is larger than that of 2 (31 A° 2), the puckering of the GS sheet is less severe. This reflects the need for the network to pucker more in (G)(2) in order to recover the dense packing lost by forming the single layer motif.The dense packing in (G)(2) is achieved through Fig. 1 (Top) Schematic representation of the sheet-like HB networks p–p stacking interactions between neighbouring naphthyl resi- formed from guanidinium cations and alkane- and arene-substituted dues (distance between neighbouring ring planes ca. 4.1 A° ). In monosulfonates and disulfonates. The most commonly observed net- contrast, the cross-sectional area of the ferrocene residue is work is quasihexagonal, in which every sulfonate oxygen atom is comparable to the molecular area of a guanidinium sulfonate hydrogen bonded to two guanidinium protons (typical dO H=2.0 A° ) so that all HB capacity is fulfilled.These sheets can be considered as assembling from one-dimensional HB ribbons (shaded) via hydrogen bonds.In some compounds these hydrogen bonds behave as hinges, resulting in a pleated GS network that can adapt to the steric requirements of the R groups. The inter-ribbon puckering angle is described by hIR. (Bottom) Schematic representations of layered materials synthesized from guanidinium cations and alkane- and arenesubstituted monosulfonates, as viewed along the long axis of the HB ribbons contained in the nominally planar GS networks.The white and shaded rectangles represent the narrow edge of the ribbons. Bilayer motifs (left) are observed for R groups which are small enough to allow interdigitation of R groups in the non-polar region separating the GS sheets. If the alkane or arene groups are too large, the R groups of adjacent ribbons are orientated to opposite sides of each sheet, which provides room for interdigitation and the continuous single layer stacking of the GS sheets (right).The sheets can adapt further to the steric requirements of the R groups in either layering motif by puckering about (guanidinium)N-H,O(sulfonate) HB ‘hinges’ between adjacent ribbons (hIR). with optical, magnetic, or conducting properties that will depend upon the choice of molecules in the region spanning the layers.However, a precise understanding of the influence of R group substituents, specifically the proximity of these substituents to and their ability to interact with the HB network, is required for rational design of such materials. This prompted us to examine systematically the influence of substituents on arenesulfonates whose steric and hydrogen bonding capacity influence the puckering of the two-dimensional GS network. The layered motif is retained in spite of steric interference and competing hydrogen bonding interactions in a majority of cases, illustrating the robustness of this network.Most importantly, our results demonstrate that the use of robust two-dimensional supramolecular Fig. 2 Schematic representation illustrating the steric influence of the R group on the layering motif in guanidinium sulfonate salts. modules can reduce the crystal engineering problem to the last Interdigitation of R groups all arranged on the same side of the remaining dimension. hydrogen-bonded sheet is possible if the R group projected diameter <dS-S /Ó3 (ca. 4.4 A° ) where dS-S is the distance between nearest sulfonate Results and Discussion groups. This results in the bilayer structure (top). If the diameter >dSS/ Ó3, interdigitation is not possible (centre) and the single layer motif Substituent sterics and hydrogen bonding (bottom), in which R groups on adjacent ribbons are orientated to The occurrence of either the interdigitated bilayer or the opposite sides, is formed as this allows interdigitation and ecient packing between the hydrogen-bonded sheets.continuously stacked single layer motif can be predicted, at 1124 J. Mater. Chem., 1997, 7(7), 1123–1133and the nitro group in p-nitrobenzenesulfonate (6), whose structures exhibited the single layer motif with substantial corrugation of the GS sheet (hIR=51° and 72°, respectively).In contrast, the guanidinium salt of p-toluenesulfonate (7), which has a size similar to that of 5 and 6 but no hydrogen bonding capability, exhibited the bilayer motif with modest puckering (hIR=151°). This demonstrated that the layering motif adopted by these materials was influenced by both steric and hydrogen bonding eects.Although the bilayer motif should have been accessible to 5 and 6 based on steric eects alone, a highly puckered single layer motif was formed owing to modest hydrogen bonding competition by the hydroxy and nitro groups for the sulfonate oxygens and guanidinium protons, respectively. In order to elucidate the relative contributions of steric and hydrogen-bonding competition eects from substituents forced to be in close proximity to the GS sheet, we have examined the guanidinium salts of various ortho- and meta-substituted methyl- and nitro-benzenesulfonates (8–16).An ortho substituent may sterically block the sulfonate oxygen acceptor sites by hindering the approach of the potential guanidinium donor (Scheme 1). The oxygen atoms of the nitro groups, as hydrogen- bonding acceptors, may compete for the guanidinium protons in the GS sheet.Nitro groups generally are not strong hydrogen-bond acceptors, particularly when compared to the sulfonate oxygen atoms, suggesting that the perturbation of the GS network may not be so severe that its formation is prohibited. Our previous observation that the p-nitrobenzenesulfonate compound (G)(6) possesses the quasihexagonal Fig. 3 (Top) Crystal structure of guanidinium ferrocenesulfonate GS network, in contrast to (G)(4) which contains the stronger (G)(3), as viewed along the hydrogen-bonded ribbon direction, which hydrogen-bonding carboxylic acid group, supports this conten- extends out of the plane of the page.This view illustrates the tion. Investigation of the ortho- and meta-substituted phases segregation of the non-polar ferrocene-containing regions and the allows comparison between residues with identical volumes polar hydrogen-bonding regions into a puckered interdigitated single but with substituents in dierent positions.The conformational layer motif. The filled circles denote the hydrogen-bonded quasihexagonal GS sheet. (Bottom) Space-filling representation of the packing freedom of the ortho substituents also can provide steric relief of two adjacent ferrocene residues contained within the (100) galleries and minimize the perturbation of the GS sheet.of (G)(3). The C–H dipole of one of the residues projects into the centre of the cyclopentadiene ring of the neighbouring ferrocene, Synthesis of guanidinium arenesulfonates suggesting Cd-–Hd+,p-electron interactions. Guanidinium salts of variously substituted methyl- and nitrobenzenesulfonates were prepared by slow evaporation crys- unit (ca. 45A° 2), therefore requiring less puckering than (G)(2) tallization techniques. Several of these compounds appeared to recover lost packing density. The CMH dipole of each to form unstable solvated crystalline phases, as evidenced by ferrocene projects into the centre of the cyclopentadiene ring the physical transformation of transparent crystals to opaque of a neighbouring ferrocene, suggesting a role for solids soon after their removal from the mother liquor.Low Cd-MHd+,p-electron interactions in the ordering of these temperature broad endotherms observed by dierential scan- residues (see Fig. 3). The ferrocene containing phase introduces ning calorimetry (DSC) of samples characterized immediately redox centres into ‘galleries’ between the robust two-dimen- after their removal from solution also suggested the loss of sional layers, suggesting interesting possibilities for charge solvent from the crystals, and IR spectroscopy confirmed the trapping and electron transport.The structure of this salt presence of solvent molecules in the solids. IR spectroscopy resembles recently reported materials which are based on two- also revealed that several of these phases did not contain the dimensional zirconium phosphonate (ZrP) networks with desired quasihexagonal HB sheet motif. Consequently, we redox centres within the galleries defined by ZrP layers.19–21 pursued characterization of phases which were stable under While the aforementioned model has been useful in the ambient conditions and/or that contained the two-dimensional design and synthesis of over 30 crystalline GS salts containing HB motif.Although unstable phases were sometimes isolated, the two-dimensional hydrogen-bonded network,12 it does not stable, high quality crystals suitable for single crystal X-ray address the more subtle eects of positional substitution.diraction were obtained readily for most of the substituted Proximity of functional groups to the GS sheet may perturb arenesulfonates depicted above. Experimental details of the X- significantly the planarity of these networks, and in severe ray structural determinations are given in Table 1.All of the cases, may actually prohibit formation of the two-dimensional phases described here for which crystal structures have been network. If these functional groups are hydrogen-bond donors determined exhibit typical molecular geometries, including the or acceptors, competition with complementary sites of the GS guanidinium ions and MSO3 groups.Therefore, detailed sheet may perturb the hydrogen bonding and geometry of the descriptions of the molecular structures are not presented here. GS network. Previously, we discovered that the guanidinium salt of p-carboxybenzenesulfonate (4) did not form layered Methyl-substituted sulfonates networks because of hydrogen-bonding competition of the carboxylic acid group for guanidinium proton donor and Crystal structures were determined for guanidinium salts of toluene-3-sulfonate (G)(9), and mesitylenesulfonate (G)(11), sulfonate oxygen acceptor sites.15 However, the two-dimensional layer structure was preserved for guanidinium salts of which crystallize in orthorhombic space group Pnma (Fig. 4). The salt (G)(9) crystallizes with quasihexagonal GS sheets benzenesulfonates with weaker hydrogen-bonding substituents such as the phenolic group in p-hydroxybenzenesulfonate (5) which are extremely puckered (hIR=88°) and assemble into the J.Mater. Chem., 1997, 7(7), 1123–1133 1125Scheme 1 interdigitated single layer stacking motif. The structural details (dstk=8.71 and 10.51 A° for (G)(9) and (G)(11), respectively). The arene–arene interactions in the organic region are best of the layering motifs are summarized for these compounds, and for the other layered materials described below, in Table 2.described as oset p-stacking interactions in both salts, whereas in the (G)(7) and other guanidinium arenesulfonate salts, The packing of (G)(9) into a puckered single layer rather than a bilayer motif is somewhat surprising, as the para-tolyl herringbone motifs are present.The crystal structures of the 2-methylbenzenesulfonate (tolu- compound (G)(7) crystallizes into a bilayer structure with a herringbone arrangement of adjacent arene rings within the ene-2-sulfonate) (G)(8) and its 2,4-dimethylbenzenesulfonate homologue (G)(10) could not be determined because of poor bilayer galleries. The meta-methyl substituent does not block the approach of the guanidinium protons to the sulfonate crystal quality.In the case of (G)(8), the fine needles obtained were not large enough and attempts to crystallize an unsolvated acceptor sites, so a similar bilayer motif may be expected. However, the interactions between neighbouring inversion- form always led to opaque solids with poor crystallinity.Crystallographic data for (G)(10) could not be refined satisfac- related arene rings in the region between the GS sheets in (G)(9) appear to dier from the herringbone orientations torily. However, the IR spectral features for (G)(8) and (G)(10), particularly in the nN-H region, are essentially identical to those observed in (G)(7) and other guanidinium arenesulfonates, with each methyl group in (G)(9) lying over the p-system of a of (G)(9), (G)(11) and (G)(7) (Fig. 5). Correlation of IR spectral data and X-ray crystal structures for over 30 GS salts neighbouring arene ring (see Fig. 4). Highly puckered quasihexagonal GS sheets (hIR=86°) and in our laboratory has demonstrated that a particular absorption band profile in the nN-H region from 3500–3100 cm-1 (as the interdigitated single layer stacking motif also are observed in (G)(11).The presence of the quasihexagonal topology, in in Fig. 5) is highly diagnostic of the quasihexagonal HB sheet motif. Consequently, we surmise from examination of the IR which all six sulfonate oxygen lone electron pairs participate in hydrogen bonding to the guanidinium protons with typical absorption band structures observed for the unsolvated forms of (G)(8) and (G)(10) that these compounds also form layered hydrogen bond distances, indicates that the ortho methyl substituents in (G)(11) do not prohibit the formation of this structures containing the quasihexagonal HB sheet.network. However, the mesitylenesulfonate ion does not exceed the steric limit of ca. 4.4 A° which is considered the threshold Nitro-substituted sulfonates of stability for the interdigitated bilayer structure.Steric interference by the ortho-methyl substituents hinders coplanar Each guanidinium salt of the variously substituted nitrobenzenesulfonates, guanidinium 2-nitrobenzenesulfonate approach of the hydrogen-bonded ribbons to form a twodimensional sheet if the mesitylene groups are orientated to (G)(12), 3-nitrobenzenesulfonate (G)(13), 2,4-dinitrobenzenesulfonate (G)(14), 2,4-dinitrobenzenesulfonate mono- the same side of the HB sheet (see Scheme 1).Thus, the ribbons are forced to approach each other nearly orthogonally, with hydrate (G)(14) H2O, and picrylsulfonate (G)(15) crystallizes in space group P1� with one ion pair per asymmetric unit.The the mesitylene groups of neighbouring ribbons orientated to opposite sides of the hydrogen-bonding plane, resulting in nitro NMO bond geometries compare well with those determined from a search of the Cambridge Crystallographic substantial puckering. The nearly identical packing of (G)(11) and (G)(9) is reflected in the similarities of the b and c Database, which revealed a mean dN-O of 1.217±0.011 for 1116 aromatic nitro compounds.18 The twisting of the ortho nitro crystallographic lattice constants in these phases.The repeat distances parallel and perpendicular to the hydrogen bonding groups out of the arene ring plane in compounds (G)(12), (G)(14), (G)(14) H2O and (G)(15) is 50–60°. In contrast, the ribbon in the GS network, denoted as ddrib and d)rib, respectively, are nearly identical in (G)(9) and (G)(11).The stacking para nitro group is nearly coplanar in (G)(6), (G)(14), (G)(14) H2O and (G)(15). A value of 16° is observed for the repeat distance, dstk, is larger for (G)(11) than for (G)(9) due to the steric demand of the para-methyl substituent in (G)(11) meta nitro group in (G)(13). The severe twisting of the ortho 1126 J.Mater. Chem., 1997, 7(7), 1123–1133Table 1 Crystallographic data for guanidinium sulfonates compound (G)(3) (G)(9) (G)(11) (G)(12) (G)(13) (G)(14) (G)(14) H2O (G)(15) formula C11H15N3O3SFe C8H13N3O3S C10H17N3O3S C7H10N4O5S C7H10N4O5S C7H9N5O7S C7H11N5O8S C7H8N6O9S MW 325.16 231.27 259.33 262.25 262.24 307.24 324.24 352.23 crystal size/mm3 0.67×0.57×0.05 0.57×0.47×0.27 0.50×0.30×0.08 0.50×0.38×0.25 0.60×0.30×0.25 0.55×0.50×0.42 0.55×0.50×0.42 0.55×0.50×0.42 crystal system orthorhombic orthorhombic orthorhombic triclinic triclinic triclinic triclinic triclinic space group Pna21 Pnma Pnma P1� P1� P1� P1� P1� a/A° 17.160(6) 17.410(8) 21.021(2) 7.2416(8) 7.196(8) 7.761(3) 7.715(2) 7.782(6) b/A° 7.693(4) 7.595(6) 7.5584(6) 7.596) 7.842(4) 8.314(4) 8.187(2) c/A° 10.740(4) 8.613(4) 8.3710(6) 12.1475(14) 11.694(5) 11.591(3) 10.987(5) 10.813(2) a (°) 90 90 90 88.257(2) 76.45(5) 97.87(3) 82.73(4) 100.83(2) b (°) 90 90 90 78.135(2) 78.32(8) 95.33(3) 72.25(3) 92.32(4) c (°) 90 90 90 62.150(1) 62.94(9) 118.32(4) 77.88(2) 99.20(6) V/A° 3 1418(2) 1139(2) 1330.0(2) 576.12(11) 552(2) 605(1) 655(1) 666(1) Z 4 4 4 2 2 2 2 2 Dcalc/g cm-3 1.523 1.349 1.295 1.512 1.577 1.686 1.645 1.756 F (000) 672 488 552 272 272 316 334 360 m (Mo-Ka) (cm-1) 12.09 2.64 2.45 2.98 2.97 2.97 2.84 2.93 T /°C 24 24 25 24 24 24 24 24 diractometer type Enraf-Nonius Enraf-Nonius Siemens Siemens Enraf-Nonius Enraf-Nonius Enraf-Nonius Enraf-Nonius scan mode v v — — v-2h v-2h v v-2h scan speed (deg/min in v) 1.8–16.5 16.5 — — 8.2 8.2 8.2–16.5 16.5 2hmax (°) 52.0 47.9 48.2 48.2 56.0 55.9 55.9 63.9 range of hkl -21,±9,±13 ±8,-9,±19 -24 to 22,-4 ±8,±8,-5 +9,±9,±14 ±10,±10,±15 ±10,±11,±14 ±10,±11,±15 to 8,±9 to+13 no.refl. collected 4087 3727 5066 2470 5310 2989 3256 6019 no. unique refl. 2595 1077 1134 1742 2655 2919 3138 4613 Rint 0.054 0.048 0.045 0.0313 0.040 0.022 0.024 0.023 corrections applieda abs, 2 ext abs, 2 ext abs abs abs, 2 ext abs abs, 2 ext 2 ext Rb 0.045 0.060 0.050 0.0405 0.042 0.052 0.070 0.047 Rwb 0.046 0.075 0.111 0.1052 0.055 0.056 0.067 0.058 D(r) e/A°-3 0.39 0.94 0.154 0.281 0.42 0.47 0.46 0.48 no.indep refl obs I>2s(I) 1571 735 1134 1742 2287 2218 2018 3544 No/Nv 9.13 8.65 11.57 8.98 12.78 12.25 10.35 15.21 GOF 1.12 2.26 1.098 1.073 2.01 1.74 2.05 1.55 aAll structures were corrected for Lorentz and polarization eects. abs=empirical absorption using DIFABS (N.Walker and D. Stuart, Acta Crystallogr. Sect. A, 1983, 39, 158.); 2 ext=secondary extinction. bR(F)=S||Fo|-|Fc ||/S|Fo |. cR(wF)=[(Sw(|Fo|-|Fc |)2 /SwFo2)]1/2; w=4Fo2/s2(Fo2). J. Mater. Chem., 1997, 7(7), 1123–1133 1127Fig. 5 Comparison of the solid-state IR spectra (Nujol mulls) of guanidinium toluenesulfonates (G)(8) (ortho-substituted), (G)(9) (metasubstituted), and (G)(7) (para-substituted).The structure of the nN-H absorption bands, which is diagnostic of the quasihexagonal GS network, is essentially identical in these spectra. This argues that (G)(8), for which a single crystal structure could not be obtained, possesses a quasihexagonal hydrogen-bonding motif.nitro groups out of the ring planes most likely arises from the need to relieve steric crowding with the ortho sulfonate groups and to alleviate repulsive interaction with the negatively chargedsulfonate groups. A database study of ortho-substituted nitro groups found an average twist angle of 27±1° for nitro groups with one substituent in the ortho position (n=392, n= number of observations).24 When the substituent is a sulfonate group (a substantially smaller sample, n=7), both steric hindrance and a negative charge are important factors, resulting in a much larger mean twist angle of 65±3°, very close to that observed in our guanidinium nitrobenzenesulfonate compounds. The database study also revealed that for nitro groups Fig. 4 Crystal structures of guanidinium toluene-3-sulfonate (G)(9), with two sterically undemanding hydrogen atoms in the guanidinium mesitylenesulfonate (G)(11), and guanidinium toluene-4- positions ortho to the nitro group (as in the 4-, 2,4-, and sulfonate (G)(7) as viewed along the hydrogen-bonded ribbon direc- 2,4,6-dinitrobenzenesulfonate compounds), a nearly coplanar tion, which extends out of the plane of the page.These views illustrate arrangement with the benzene rings is favoured (average twist the segregation of the non-polar arene-containing regions and the angle of 7.3±0.3°, n=270). Steric eects clearly play a role in polar hydrogen-bonding regions into bilayers for (G)(7), and severely puckered interdigitated single layers for (G)(9) and (G)(11). The filled determining the geometry of the ortho nitro substituents.circles denote the hydrogen-bonded quasihexagonal GS sheet. The guanidinium salts of mono-substituted nitrobenzenesulfonates crystallize with structures similar to those of other Table 2 Summary of key structural parameters and layering motifs for layered guanidinium sulfonates compound (G)(3) (G)(9) (G)(11) (G)(12) (G)(13) repeat distance d ribbon, ddrib/A° b=7.69 b=7.60 b=7.56 b=7.59 b=7.63 repeat distance ~) ribbon, d)rib/A° c=10.74 c=8.61 c=8.37 a=7.24 a=7.20 HB plane (100) (100) (100) (001) (001) layering motif single layer single layer single layer bilayer bilayer interribbon dihedral angle, hIR/° 153 88 86 180 180 stacking repeat distance, dstk/A° 8.58 8.71 10.51 11.89 11.45 1128 J.Mater.Chem., 1997, 7(7), 1123–1133guanidinium organosulfonates, with the nitro groups influenc- 3.34 A° between neighbouring ring planes in (G)(12) and (G)(13), respectively. These structures dier from those of ing the crystal packings in subtle ways (Fig. 6). Guanidinium 2- and 3-nitrobenzenesulfonates (G)(12) and (G)(13) possess other guanidinium arenesulfonates, in which the arene rings in the bilayer galleries adopt the herringbone (edge-to-face) planar quasihexagonal hydrogen-bonded sheets (hIR=180°) arranged in a bilayer stacking motif (the latter contrasts with arrangement. The inversion symmetry within the layers results in a favourable configuration in which nitrobenzene dipoles the single layer motif observed for (G)(9), the meta methyl substituted analogue).The planarity of these networks is are opposed. As in many organic crystals, the nitro groups in (G)(12) and (G)(13) do not participate in strong hydrogen unusual when compared to other guanidinium arenesulfonates with bilayer structures, which exhibit hIR values of 150–165°. bonds. While the major driving force controlling the crystal packing in both (G)(12) and (G)(13) is the hydrogen bonding Inspection of the structures of (G)(12) and (G)(13) reveals p–p stacking between arene rings in the bilayer galleries, in within the GS sheets, inspection of the structures suggests that secondary CMH,O interactions25–29 may play a role in which the rings are laterally oset in a manner commonly observed for p–p stacks.These interactions appear to be influencing the orientations of the molecules in the van der Waals interlayer regions.Additionally, one short contact of a significant, as indicated by the very short distances of 3.46 and nitro oxygen to a guanidinium ion is present in (G)(12), with a bifurcated nitrogen oxygen acceptor forming a four-membered ring with one guanidinium NH2 group. The ddrib and d)rib values are nearly identical in (G)(12) and (G)(13).However, the dstk values dier due to the dierent steric demands along the layer stacking direction imposed by the dierent position of the nitro groups (Table 2). We note that the bilayer structures of (G)(12) and (G)(13) dier markedly from the single layer motif found in guanidinium 4- nitrobenzenesulfonate (G)(6). This dierence can be attributed to (guanidinium)NMH,O(nitro) hydrogen-bonding interactions in (G)(6), in which a nitro group extending from a GS sheet hydrogen bonds to two guanidinium protons on an opposing GS sheet.These examples illustrate that weak electrostatic interactions, steric eects, and hydrogen-bonding all contribute to the solid state packing in these salts. Guanidinium 2,4-dinitrobenzenesulfonate (G)(14), its monohydrate (G)(14) H2O, and picrylsulfonate (G)(15) salts do not exhibit quasihexagonal layered GS sheets (Fig. 7 and 8). Rather, these compounds form complex hydrogen bonding networks that organize the hydrophobic arene-containing regions into galleries separated by two-dimensional polar regions containing the hydrogen bonding guanidinium ions, sulfonate groups and nitro groups.The major dierence between the structures of (G)(14) and (G)(15) arises from the orientation of guanidinium ions with respect to the arene ring planes. Hydrogen-bonding between guanidinium protons and sulfonate and nitro acceptors is extensive in these compounds. The orientations of the guanidinium ions allow them to participate in multiple hydrogen bonds with both sulfonate and nitro acceptor sites of neighbouring anion sheets.The strongest hydrogen bonding occurs for (guanidinium) NMH,O(sulfonate) hydrogen bonds as expected, but many (guanidinium)NMH,O(nitro) CMH,O intermolecular contacts are also observed. Although weak attractive nitro,nitro intermolecular N,O contacts have been suggested to direct crystal packing in complexes of N,N-dipicrylamine,30 this type of interaction is not present in the guanidinium nitrobenzenesulfonate salts described here.The nitro group substituents in (G)(14), (G)(14) H2O and (G)(15) so severely perturb the GS HB network that even the GS hydrogen-bonded ribbon motif, which is pervasive and has been observed in all previously determined structures of guanidinium alkane- and arene-sulfonates, is absent. However, six-membered GS ring motifs are present that dier from the eight-membered ring dimers in the GS sheets, but are similar to those found in guanidinium carboxylates and phosphates.31,32 These structures reveal that the presence of numerous weak hydrogen bonding interactions can steer the crystal packing away from the quasihexagonal Fig. 6 Crystal structures of guanidinium 2-nitrobenzenesulfonate (G)(12), guanidinium 3-nitrobenzenesulfonate (G)(13), and guanidin- GS motif.A more detailed description of these complex ium 4-nitrobenzenesulfonate (G)(6) as viewed along the hydrogen- hydrogen-bonding motifs has been reported previously.33 bonded ribbon direction, which extends out of the plane of the paper. These views illustrate the segregation of the non-polar arene-containing regions and the polar hydrogen-bonding regions into bilayers for Comparison of methyl and nitro substitution (G)(12) and (G)(13), and severely puckered interdigitated single layers A comparison of the layering structures of the guanidinium for (G)(6).The filled circles denote the hydrogen-bonded quasihexagonal GS sheet. methyl- and nitro-benzenesulfonates reveals that bilayer motifs J.Mater. Chem., 1997, 7(7), 1123–1133 1129are observed for guanidinium tosylate (G)(7) and 2- and 3- nitrobenzenesulfonates (G)(12) and (G)(13), while puckered single layer motifs are observed for guanidinium toluene-3- (G)(9), mesitylene- (G)(11), and 4-nitrobenzene-sulfonates (G)(6). The van der Waals volume of the nitro group is significantly larger than its methyl counterpart, with volumes of 23.5 and 15.3 A° 3 , respectively.34 However, the shape of the planar nitro group may provide some relief from steric crowding around the sulfonate group as it can twist out of the arene ring plane, whereas the geometry of the methyl group is more isotropic.However, twisting of the nitro group may not have a large eect, as the steric bulk of the nitro group is still larger than the methyl group.The substitution of methyl for nitro in the case of the meta-substituted salts (G)(9) and (G)(13) results in an unexpected change in the layering motif, with the former crystallizing in an extremely puckered single layer structure and the latter crystallizing in the bilayer motif.This is counterintuitive as the smaller volume of 9 should make the bilayer structure more favourable for this compound. These structures reveal that steric eects are quite subtle, particularly when comparing substituents with diering substitutional position or hydrogen bonding ability. The presence of two or more nitro groups on an arenesulfonate so severely perturbs hydrogen bonding that the GS sheet network, so pervasive in these materials, is completely absent in compounds derived from these anions.Conclusion This work demonstrates that crystal packing can be controlled through use of the guanidinium-sulfonate module as a topological director of crystal packing. Guanidinium salts of benzenesulfonates containing a single methyl or nitro substituent or multiple methyl substituents crystallize with the predicted quasihexagonal GS network, with layers assembling into either bilayer or single layer motifs.The robustness and prevalence of the GS network suggests that this module can be used in the design and synthesis of new crystalline materials. Its twodimensional nature reduces crystal engineering to the last remaining dimension.However, unanticipated dierences in layering motif, i.e. bilayer versus single layer packing, for analogous methyl versus nitro substituted benzenesulfonate salts shows that subtle steric and hydrogen-bonding eects can have a dramatic eect in determining crystal packing in the third dimension. In the cases of multiple substitution of nitro groups, the quasihexagonal HB sheets and layering structures are completely disrupted in order to form multiple weak hydrogen bonds to nitro groups.These studies illustrate that even if robust modules are employed, the presence of ancillary intermolecular interactions can limit the predictability of the entire 3D structure. However, we anticipate that restricting ancillary residues to galleries within the robust 2D HB networks, thereby limiting the degrees of freedom available for crystal packing, will facilitate computational predictions of these structures.Fig. 7 Crystal structures of guanidinium 2,4-dinitrobenzenesulfonate (G)(14), guanidinium 2,4-dinitrobenzenesulfonate monohydrate (middle) (G)(14) H2O, and guanidinium 2,4,6-trinitrobenzenesulfonate Experimental (G)(15) as viewed normal to their (100) planes.These views Materials illustrate the segregation, on (001) planes, of the non-polar arenecontaining regions and the polar hydrogen-bonding regions (indicated Guanidine chloride and guanidine carbonate were purchased by the open squares) containing the guanidinium ions, nitro and from Aldrich Chemical Co. All other starting materials were MSO3 groups. The severe tilting of guanidinium ions and the presence purchased from the companies indicated and used as received. of nitro groups in the polar region prohibit the formation of the quasihexagonal GS sheet.The (100) planes of (G)(14 ) and (G)(15) Spectroscopic-grade solvents and/or deionized water were used consist of arenesulfonate layers in which the arene rings lie in the for all crystallizations.plane. The arenesulfonate layers in (G)(14) H2O actually lie in the (102) plane. These layers are evident in the views depicted in Fig. 8. Characterization Melting points were determined by dierential scanning calorimetry (DSC) with a Mettler FP80/FP84 system (100 mV, 1°C min-1). Solid-state IR spectra were recorded on a Nicolet 1130 J. Mater. Chem., 1997, 7(7), 1123–1133Fig. 8 Crystal structures of guanidinium 2,4-dinitrobenzenesulfonate (G)(14), guanidinium 2,4-dinitrobenzenesulfonate monohydrate (G)(14) H2O, and guanidinium 2,4,6-trinitrobenzenesulfonate (G)(15) as viewed normal to their (010) planes. These views illustrate the segregation, on (001) planes, of the non-polar arene-containing regions and the polar hydrogen-bonding regions (indicated by the open squares) containing the guanidinium ions, nitro and MSO3 groups.The (100) planes of (G)(14) and (G)(15) consist of arenesulfonate layers in which the arene rings lie in the plane. The arenesulfonate layers in (G)(14) H2O actually lie in the (102) plane. Because of its severe tilt, the guanidinium cation bridges these layers by hydrogen bonding in all three compounds, resulting in a three-dimensional hydrogen-bonding network. 510M spectrometer (4 cm-1 resolution) as Nujol mulls. 1H {s, 6 H, [C(NH2 )3 ]}, 2.52 (s, 3 H, Ar-CH3), 2.08 (s, 3 H, CH3CN). The presence of acetonitrile is confirmed by IR (nCN NMR spectra were recorded on an IBM NR200AF spectrometer (200MHz) in (CD3)2SO unless stated otherwise at 2252 cm-1) and by observation of its methyl protons in the 1H NMR spectrum at 2.08 ppm, as well as a broad desolvation (Cambridge Isotope Laboratories) relative to internal standard SiMe4; J in Hz.Experimental details of the X-ray structural endotherm in the DSC. The crystals desolvate soon after their removal from solution, resulting in an opaque solid having an determinations are given in Table 1, and atomic coordinates are available as supplementary material or at our World Wide IR spectrum identical to (G)(8).Web site (http://www.cems.umn.edu/research/ward). Structures (G)(3), (G)(9), (G)(13), (G)(14), (G)(14) H2O and (G)(15) Guanidinium toluene-2-sulfonate, [C(NH2)3]+ were determined using an Enraf-Nonius CAD4 diractometer 2-CH3(C6H4)SO3-, (G)(8) with graphite monochromated Mo-Ka radiation at l This phase was isolated from a 151 methanol–acetonitrile 0.71069 A° .Structures (G)(11) and (G)(12) were determined solution containing equimolar quantities of guanidine hydro- using a Siemens SMART system diractometer with graphite chloride and toluene-2-sulfonic acid (Aldrich). This compound monochromated Mo-Ka radiation at l 0.71069 A° . All data formed as an opaque solid on the sides of the crystallization were collected at room temp.(24°C). vessel or after desolvation of solvated crystals (G)(8) MeCN. Atomic coordinates, thermal parameters, and bond lengths Attempts to isolate single crystals of (G)(8) from solution were and angles have been deposited at the Cambridge dicult, but clear thin needles of unsolvated (G)(8) were Crystallographic Data Centre (CCDC).See Information for isolated together with opaque solid (presumably, desolvated Authors, J. Mater. Chem., 1997, Issue 1. Any request to the (G)(8) H2O or (G)(8) EtOH) from 20% aqueous ethanol. CCDC for this material should quote the full literature citation However, these needles were not large enough for single crystal and the reference number 1145/37. X-ray diraction. DSC mp 220–222°C; n/cm-1 3365 (s), 3332 (s), 3259 (m), 3186 (s), 1683 (s), 1588 (m), 1463 (s), 1378 (s), Guanidinium toluene-2-sulfonate acetonitrile solvate, 1302 (w), 1281 (w), 1208 (m), 1169 (s), 1146 (s), 1094 (m), 1052 [C(NH2)3]+ 2-CH3(C6H4)SO3- CH3CN, (G) (8) MeCN (vw), 1036 (vw), 1017 (s), 808 (w), 751 (m), 708 (s); d 7.73 (~d, This phase was recrystallized as colourless plates from a 151 1 H, ortho to SO3-), 7.21–7.12 (m, 3 H, meta/para to SO3-), methanol–acetonitrile solution containingequimolar quantities 6.95 {s, 6 H, [C(NH2)3]}, 2.52 (s, 3 H, Ar-CH3).of guanidine hydrochloride and toluene-2-sulfonic acid (Aldrich). The following characterization was performed Guanidinium toluene-3-sulfonate, [C(NH2)3]+ immediately after removal of the crystals from solution. DSC 3-CH3(C6H4)SO3-, (G)(9) 30–52°C (broad endotherm, loss MeCN), mp 222–224 °C; n/cm-1 3363 (s), 3330 (s), 3255 (m), 3190 (s), 2252 (m, sharp), This phase was crystallized from methanol or 10% aqueous acetonitrile solutions containing equimolar quantities of guani- 1677 (s), 1582 (m), 1463 (s), 1378 (m), 1283 (w), 1208 (s), 1187 (s), 1171 (s), 1144 (s), 1094 (s), 1050 (m), 1038 (m), 1017 (s), 918 dine hydrochloride and toluene-3-sulfonic acid monohydrate (Lancaster) or from aqueous solutions containing 152 molar (vw), 808 (w), 768 (m), 741 (m), 708 (s), 614 (s); d 7.73 (~d, 1 H, ortho to SO3-), 7.21–7.12 (m, 3 H, meta/para to SO3-), 6.95 quantities of guanidine carbonate and toluene-3-sulfonic acid J.Mater. Chem., 1997, 7(7), 1123–1133 1131monohydrate as colourless needles: DSC with concurrent Guanidinium 2-nitrobenzenesulfonate hydrate, [C(NH2)3]+ 2-NO2(C6H4)SO3- H2O, (G) (12) xH2O visual observation 152–156 (slightly broad endotherm, crystals fracture, turn somewhat cloudy), mp 215–216 °C; visual obser- This phase was crystallized from 10% aqueous acetonitrile vation of single crystals on a Fisher–Johns hot stage: solution containing equimolar quantities of guanidine hydro- 155–160 °C: very slight clouding, but crystal remained some- chloride and 2-nitrobenzenesulfonic acid (Pfaltz and Bauer) or what clear, possibly melting and resolidifying; 218–219 °C: from aqueous or 10% aqueous methanol solutions containing melting; n/cm-1 3371 (s), 3328 (s), 3257 (m-s), 3190 (s), 1677 152 molar quantities of guanidine carbonate and 2-nitroben- (s), 1586 (m), 1463 (s), 1378 (s), 1304 (w), 1225 (m, sh), 1194 (s, zenesulfonic acid as colourless needles:DSC endotherms: 72–76 sh), 1169 (s), 1115 (s), 1090 (m), 1038 (s), 996 (m), 783 (m), 741 (br), 90–95 (br), mp 134–136°C; n/cm-1 3656 (m), 3558 (m), (w), 708 (m), 681 (s), 627 (s); d 7.43 (~d, 2 H, Ar-H ortho to 3440 (sh, s), 3367 (s), 3274 (s), 3205 (s), 3095 (m), 1675 (s), 1613 SO3-), 7.22–7.15 (m, 2 H, J 7.9, Ar-H meta and para to SO3-), (w), 1596 (w), 1582 (m), 1540 (s, nN-O asym), 1530 (s, nN-O asym), 6.96 {s, 6 H, [C(NH2)3]+}, 2.32 (s, 3 H, Ar-CH3).The X-ray 1465 (s), 1374 (s, nN-O sym), 1364 (s, nN-O sym), 1300 (w), 1214 crystal structure of this compound was solved. (s), 1164 (m), 1142 (s), 1079 (s), 1040 (m), 1025 (s), 855 (m), 780 (m), 743 (s), 733 (s), 702 (m), 664 (s), 646 (s), 614 (s), 581 (s); d 7.85 (~d, 1 H, 6-Ar-H), 7.60–7.55 (m, 3 H, 3,4,5-Ar-H), 6.93 Guanidinium 2,4-dimethylbenzenesulfonate [C(NH2 )3 ]+ 2,4- {s, 6 H, [C(NH2)3]+}, 3.41 (s, H2O, ~5 H, hydrate and (CH3)2(C6H3)SO3-, (G)(10) exchange with water in Me2SO).The stoichiometric amount of hydrated water in the crystal was not determined.However, This phase was crystallized from 351 methanol–toluene solu- this salt may be a dihydrate, as indicated by the two broad tion containing equimolar quantities of guanidine hydro- endotherms in the DSC. The integration of the water peak in chloride and sodium 2,4-dimethylbenzenesulfonate (Kodak) as the NMR to a value corresponding to nearly four hydrogens colourless needles; DSC mp 281 °C; n/cm-1 3373 (s), 3330 (s), also suggests that the complex may be a dihydrate.The sharp 3263 (m), 3188 (s), 1677 (s), 1588 (m), 1463 (s), 1378 (s), 1189 IR nO-H at high wavenumber positions indicate that the water (m), 1158 (s), 1092 (m), 1017 (s), 822 (w), 816 (w), 745 (w), 726 is not strongly associated by hydrogen bonding in the lattice.(w), 685 (m); d 7.60 (d, 1 H, J=7.6), 6.95 with 6.92 side peak The existence of split IR nN–O bands at 1540/1530 cm-1 and {s, 8 H, [C(NH2 )3 ]+, Ar-H ortho to SO3-}, 2.48 (s, 3 H, Ar- 1374/1364 cm-1 suggests two dierent solid-state environments CH3), 2.25 (s, 3 H, Ar-CH3). An attempt was made to solve for the nitro group and possibly two ion pairs in the asymmet- the X-ray crystal structure, but refinement was not successful.ric unit. The structure determination was not pursued further. Guanidinium 3-nitrobenzenesulfonate, [C(NH2)3]+ 3-NO2(C6H4)SO3-, (G)(13) Guanidinium mesitylenesulfonate (guanidinium 2,4,6- This phase was crystallized from 25% aqueous acetonitrile or trimethylbenzenesulfonate), [C(NH2)3]+ 2,4,6- 35351 methanol–ethyl acetate–water solutions containing equi- (CH3)3(C6H2)SO3-, (G)(11) molar quantities of guanidine hydrochloride and sodium 3- This phase was crystallized from methanol or 30% aqueous nitrobenzenesulfonate (Kodak) as light-yellow elongated acetonitrile solutions containing equimolar quantities of guani- diamonds/parallelograms: DSC endotherm 178–180, dine hydrochloride and mesitylenesulfonic acid dihydrate mp 184–187 °C; visual observation of a single crystal on a (Aldrich) or from aqueous or methanol solutions containing Fisher–Johns hot stage showed no obvious change at 180 °C 152 molar quantities of guanidine carbonate and mesitylene- and melting at 185–190 °C; n/cm-1 3400 (s), 3371 (s), 3249 (m), sulfonic acid dihydrate as aggregates of colourless rectangular, 3207 (s), 3105 (w), 1673 (s), 1580 (m), 1573 (m), 1532 (s, nN-O flat plates: DSC mp 270–300 (decomp.)°C; n/cm-1 3375 (s), asym), 1465 (s, Nujol), 1378 (s, Nujol), 1356 (s, nN-O sym), 1277 3323 (s), 3259 (m-s), 3186 (s), 1675 (s), 1605 (w), 1586 (m), 1569 (w), 1208 (s), 1150 (m), 1096 (m), 1079 (m), 1038 (m-s), 1001 (w), 1461 (s), 1378 (s), 1252 (w), 1191 (m), 1183 (m), 1158 (s), (w), 934 (w), 907 (w), 882 (w), 812 (m), 762 (m), 737 (m), 671 1092 (s), 1013 (s), 841 (m), 743 (m), 689 (s); d 6.97 {s, 6 H, (s); d 8.34 (m, 1 H, 2-Ar-H), 8.22 (d, 1 H, J 9.1, 6-Ar-H), 8.03 [C(NH2)3]+}, 6.77 (s, 2 H, arene ring H), 2.50 (s, ~6 H, 2,6- (d, 1 H, J 7.7, 4-Ar-H), 7.67 (t, 1 H, J 7.9, 5-Ar-H), 6.93 {s, 6 CH3, overlaps with (CH3)2SO solvent peak), 2.18 (s, 3 H, 4- H, [C(NH2)3]+}.The X-ray crystal structureof this compound CH3); d (D2O) 7.05 (s, 2 H, arene ring H), 4.91 {s, [C(NH2 )3 ]+, was solved. overlaps with H2O solvent impurity peak}, 2.57 (s, 6 H, 2,6- Guanidinium 2,4-dinitrobenzenesulfonate, [C(NH2)3]+ CH3), 2.29 (s, 3 H, 4-CH3). The X-ray crystal structure of this 2,4-(NO2)2(C6H3)SO3-, (G)(14) compound was solved. This phase was crystallized from 151 methanol–ethyl acetate solution containing equimolar quantities of guanidine hydro- Guanidinium 2-nitrobenzenesulfonate, [C(NH2)3]+ chloride and 2,4-dinitrobenzenesulfonic acid (Eastman) as 2-NO2(C6H4)SO3-, (G)(12) hard, light tan needles or from 10% aqueous acetonitrile solution as opaque cream-coloured powder.The opaque This phase was crystallized from methanol solution containing material is probably a dehydrated form of (G)(14) H2O, as equimolar quantities of guanidine hydrochloride and 2-nitro- dehydration of (G)(14) H2O yields an identical solid based on benzenesulfonic acid (Pfaltz and Bauer) as colourless thick IR spectroscopy.DSC mp 176°C; n/cm-1 3477, 3433, 3365, hexagonal plates and wide needles or from methanol–toluene 3272, 3199, 3095, 1675, 1663, 1605, 1551 (s, nN-O asym), 1542, solution as colourless needles: DSC endotherm 117–118, 1465, 1378, 1368, 1356 (s, nN-O sym), 1227, 1136, 1119, 1069, mp 129–135°C; n/cm-1 3406 (s), 3381 (s), 3284 (m), 3255 (m), 1028, 906, 849, 834, 750, 739, 724, 662, 635; d 8.58 (d, 1 H, 3213 (s), 1679 (s), 1598 (w), 1578 (m), 1538 (s, nN-O asym), 1463 J 2.3), 8.42 (dd, 1 H, J1 8.6, J2 2.3), 8.11 (d, 1 H, J 8.6), 6.92 (s, Nujol), 1378 (s, Nujol, overlapping with nN-O sym), 1302 (s, 6 H).The X-ray crystal structure of this compound was (w), 1270 (w), 1208 (s), 1171 (m), 1146 (m), 1079 (m), 1042 (w), solved. 1025 (s), 857 (w-m), 776 (m), 743 (m), 733 (m), 662 (s), 614 (s); d 7.85 (~d, 1 H, 6-Ar-H), 7.63–7.55 (m, 3 H, 3,4,5-Ar-H), 6.94 Guanidinium 2,4-dinitrobenzenesulfonate monohydrate, {s, 6 H, [C(NH2)3]+}; d (D2O) d 8.02–8.00 (m, 1 H, 6-Ar-H), [C(NH2)3]+ 2,4-(NO2)2(C6H3)SO3- H2O, (G) (14) H2O 7.77–7.71 (m, 3 H, 3,4,5-Ar-H), 4.80 {s, ~10 H, [C(NH2 )3 ]+, also contains HDO peak}.The X-ray crystal structure of this This phase was crystallized from aqueous or 10% aqueous acetonitrile solutions containing equimolar quantities of compound was solved. 1132 J. Mater. Chem., 1997, 7(7), 1123–1133guanidine hydrochloride and 2,4-dinitrobenzenesulfonic acid (~d, 1 H, 3-Ar-H), 8.09 (dd, 1 H, 5-Ar-H), 7.47 (d, 1 H, J 8.4, 6-Ar-H), 6.94 {s, 6 H, [C(NH2)3]+}, 2.66 (s, 3 H, Ar-CH3). (Eastman) as light tan parallelograms/plates: DSC endotherm 60–69 (br, determined to be loss of H2O by comparison of IR The authors gratefully acknowledge the National Science spectra), mp 173–175 °C.Note that the dehydration endotherm Foundation and the Oce of Naval Research for financial position may vary depending upon sample, but occurs at support, and Professor J. Doyle Britton and Dr Victor Young 50–90° and within a 10–15° range; n/cm-1 3587, 3494, 3452, for crystallographic services. 3404, 3365, 3265, 3203, 3107, 3099, 1675, 1636, 1605, 1574, 1547 (s, nN-O asym), 1536, 1465, 1378, 1364 (s, nN-O sym), 1312, 1239, 1227, 1154, 1138, 1119, 1067, 1032, 974, 920, 905, 859, References 837, 754, 745, 718, 641, 594; d 8.57 (d, 1 H, J 2.2), 8.42 (dd, 1 1 J.-M.Lehn, M. Mascal, A. DeCian and J. J. Fisher, J. Chem. Soc., H, J1 8.6, J2 2.3), 8.10 (d, 1 H, J 8.6), 6.92 (s, 6 H), 3.37 [s, ~3 Perkin T rans. 2, 1992, 461.H: 2 H from hydrated water of the crystal, ~1 H from H2O 2 E. Fan, L. Yang, S. J. Geib, T. C. Stoner, M. D. Hopkins and A. D. impurity in (CD3)2SO]. Crystals of (G)(12) H2O are stable Hamilton, J. Chem. Soc., Chem. Commun., 1995, 1251. for days to weeks after removal from solution, but eventually 3 J. C. MacDonald and G. M. Whitesides, Chem.Rev., 1994, 94, 2383. dehydrate, as suggested by a loss of crystal transparency and 4 J. A. Zerkowski, J. C. MacDonald, C. T. Seto, D. A. Wierda and confirmed by IR spectroscopy. The low temperature of dehy- G. M. Whitesides, J. Am. Chem. Soc., 1994, 116, 4305. dration characterized by DSC suggests that the water molecules 5 J.-M. Lehn, M. Mascal, A. DeCian and J. J. Fisher, J.Chem. Soc., are loosely bound in the lattice, as also suggested by the high Chem. Commun., 1990, 479. wavenumber nO-H IR band at 3587 cm-1. The X-ray crystal 6 X. Wang, M. Simard and J. D. Wuest, J. Am. Chem. Soc., 1994, structure of this compound was solved. No hydrogens were 116, 12119. 7 M. Simard, D. Su and J. D. Wuest, J. Am. Chem. Soc., 1991, 113, refined in the structure determination except one water proton, 4696.H10, which was identified on the dierence map and refined. 8 O. Ermer and L. A. Lindenberg, Helv. Chim. Acta, 1991, 74, 825. The other water proton could not be located on the dierence 9 O. Ermer, J. Am. Chem. Soc., 1988, 111, 3747. map and was left out. 10 M. J. Zaworotko, Chem. Soc. Rev., 1994, 283. 11 V. A. Russell, C. C. Evans, W.Li and M. D.Ward, Science, in press. 12 V. A. Russell and M. D. Ward, Chem.Mater., 1996, 8, 1654. Guanidinium picrylsulfonate (guanidinium 13 G. R. Desiraju, Angew. Chem., Int. Ed. Engl., 1995, 34, 2311. 2,4,6-trinitrobenzenesulfonate), [C(NH2)3]+ 14 V. A. Russell, M. C. Etter and M. D. Ward, J. Am. Chem. Soc., 2,4,6-(NO2)3(C6H2)SO3-, (G)(15) 1994, 116, 1941. 15 V. A. Russell, M.C. Etter and M. D. Ward, Chem. Mater., 1994, This phase was crystallized from a methanol–toluene solution 6, 1206. containing equimolar quantities of guanidine hydrochloride 16 V. A. Russell and M. D. Ward, Acta Crystallogr. Sect. B, 1996, and picrylsulfonic acid trihydrate (Kodak) as very high quality 52, 209. light-yellow, thick plates with well-developed faces: DSC 17 V. A. Russell and M.D. Ward, Proceedings of the NATO Advanced ResearchWorkshop on Modular Chemistry, September exotherms 230–233, 239–241 °C (decomp.); visual observation 9–12, Estes Park, Colorado, in press. of single crystals on a Fisher–Johns hot stage confirmed the 18 M. C. Etter, J. Phys. Chem., 1991, 95, 4601. decomposition: crystals begin to turn brown at 225 °C and 19 M. E. Thompson, Chem.Mater., 1994, 6, 1168.eventually turn black with bubbling occurring from 20 K. P. Reis, V. K. Joshi and M. E. Thompson, J. Catal., 1996, 236–240 °C; n/cm-1 3492 (m), 3456 (m-s), 3377 (m), 3290 (m), 161, 62. 21 G. Cao and T. E. Mallouk, J. Solid State Chem., 1991, 94, 59. 3213 (w), 3095 (w), 3083 (m), 1661 (s, sl br), 1609 (m), 1559 (s, 22 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen nN-O asym), 1546 (s,` nN-O asym), 1465 (s), 1378 (s, possibly nN-O and R. Taylor, J. Chem. Soc., Perkin T rans. 2, 1987, S1. sym), 1356 (s, nN-O sym), 1252 (s), 1233 (s), 1131 (m), 1073 (m), 23 G. R. Desiraju, Crystal Engineering: T he Design of Organic Solids, 1030 (m), 974 (w), 926 (w), 907 (w), 753 (m), 735 (m), 724 (m), Elsevier, New York, 1989, p. 92. 631 (m); d 8.85 (s, 2 H, Ar-H), 6.90 {s, 6H, [C(NH2)3]+}. The 24 D. J. A. De Ridder and H. Schenk, Acta Crystallogr. Sect. B, 1995, X-ray crystal structure of this compound was solved. 51, 221. 25 G. R. Desiraju, Acc. Chem. Res., 1996, 29, 441. 26 G. R. Desiraju, Acc. Chem. Res., 1991, 24, 290. Guanidinium 4-nitrotoluene-2-sulfonate, [C(NH2)3]+ 27 J. A. R. P. Sarma and G. R. Desiraju, Acc. Chem. Res., 1986, 4-(NO2)-2-(CH3 )-(C6H3)SO3-, (G)(16) 19, 222. 28 J. A. R. P. Sarma and G. R. Desiraju, J. Chem. Soc., Perkin T rans. This phase was crystallized from methanol or 10% aqueous 2, 1987, 1195. acetonitrile solutions containing equimolar quantities of guani- 29 Z. Berkovitch-Yellin and L. Leiserowitz, Acta Crystallogr. Sect. B, dine hydrochloride and 4-nitrotoluene-2-sulfonic acid dihy- 1984, 40, 159. 30 K. Wozniak, H. He, J. Klinowski, W. Jones and E. Grech, J. Phys. drate (Pfaltz and Bauer) or from aqueous or methanol solutions Chem., 1994, 98, 13755. containing 152 molar quantities of guanidine carbonate and 31 D. M. Salunke and M. Vijayan, Int. J. Peptide Protein Res., 1981, 4-nitrotoluene-2-sulfonic acid dihydrate as very fine colourless 18, 348. to light tan aggregates of needles. An opaque solid was also 32 Y. Yokomori and D. J. Hodgson, Int. J. Peptide Protein Res., 1988, isolated on the sides of the crystallization vessels, suggesting 31, 289. 33 V. A. Russell, PhD Thesis, University of Minnesota, 1995. that the solid may be a desolvated solvate form. The IR 34 A. Gavezzotti, in Structure correlation ed. H.-B. Burgi and J. D. spectrum of the opaque solid matched that of the colourless Dunitz, VCH, New York, 1994, vol. 2, ch. 12. The van der Waals needles. DSC mp 249 °C; n/cm-1 3469 (m), 3369 (s), 3340 (s, volumes have also been reported as 13.67 and 16.8 (for nitro sh), 3267 (m), 3193 (s), 1673 (m), 1585 (m), 1519 (s, nN-O asym), attached to carbon atom) cm3 mol-1 for methyl and nitro groups, 1465 (m), 1380 (m), 1355 (s, nN-O sym), 1308 (w), 1268 (w), 1229 respectively: A. Bondi, J. Phys. Chem., 1964, 68, 441. (s), 1198 (m), 1150 (m), 1079 (s), 1028 (s), 922 (w), 915 (w), 895 (w), 833 (w), 801 (w), 741 (m), 720 (m), 704 (m), 617 (s); d 8.51 Paper 7/00023E; Received 2nd January, 1997 J. Mater. Chem., 1997, 7(7), 1123–1133 1133