Centrosymmetric and Noncentrosymmetric R44(12 ... - ACS Publications

Centrosymmetric and Noncentrosymmetric R44(12) Rings As Primary Motifs in Salts of Sulfonate Anions and Chiral Primary Ammonium Cations: Their Occurrence in Hydrates, Nonhydrates, and the Zo¨llner Illusion

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 5 2265–2279

Andreas Lemmerer,*,† Susan A. Bourne,*,† and Manuel A. Fernandes‡ Centre for Supramolecular Chemistry Research, Department of Chemistry, UniVersity of Cape Town, Rondebosch 7701, South Africa, and Molecular Sciences Institute, School of Chemistry, UniVersity of the Witwatersrand, Johannesburg 2050, South Africa ReceiVed September 21, 2008; ReVised Manuscript ReceiVed February 18, 2009

ABSTRACT: The acid-base reaction of naphthalene-1,5-disulfonic acid and naphthalene-2-sulfonic acid with homochiral (R)-1phenylethylamine or (S)-1-phenylethylamine or heterochiral (RS)-1-phenethylamine give rise to 9 new organic salts: ((R)-1phenylethylammonium)2•(naphthalene-1,5-disulfonate)•(H2O)2 (2), ((S)-1-phenylethylammonium)2•(naphthalene-1,5-disulfonate)•(H2O)2 (3), ((RS)-1-phenylethylammonium)2•(naphthalene-1,5-disulfonate)•(H2O)2 (4), ((R)-1-phenylethylammonium)2•(naphthalene-1,5disulfonate) (5), ((S)-1-phenylethylammonium)2•(naphthalene-1,5-disulfonate) (6) ((RS)-1-phenylethylammonium)2•(naphthalene1,5-disulfonate) (7), ((R)-1-phenylethylammonium)•(naphthalene-2-sulfonate) (8), ((S)-1-phenylethylammonium)•(naphthalene-2sulfonate) (9) and ((RS)-1-phenylethylammonium)•(naphthalene-2-sulfonate) (10). All nine ammonium sulfonate salts have different 1-D hydrogen bonded columns, some containing water molecules (2-4), which are made up of different sequences of hydrogen bonded rings. The most common hydrogen bonded ring formed by the ammonium and sulfonate ions has graph set notation R44(12). Structures 2-7 have the columns linked to form 2-D hydrogen bonded sheets and 8-10 have simple 1-D chains. The results of this work as well as an analysis of the Cambridge Structural Database indicate that the R44(12) is a dominant motif in crystals composed of ammonium sulfonate salts in the same way that R22(8) is the dominant motif in carboxylic acids. Introduction The search for robust and predictable hydrogen bonding interactions between two different chemical moieties in the solid state is one of the aims of the current crystal engineering drive.1 When the hydrogen bonding interactions are strengthened using charged species D(+)-H · · · A(-), the stronger interaction is expected to be more robust.2 The strength of the charge assisted hydrogen bonding can be useful in combining two or more different chemical moieties with vastly different liquid and solidstate properties provided they contain complementary acidic and basic functional groups that are able through proton transfer to form cations and anions in the solid state. Such functional groups can be basic amines, amides, etc. and acids such as carboxylic, sulfonic and phosphoric.3 However, the strength of the interaction can be detrimental in attempts to efficiently pack the charged species in the salt structures. An unfavorable consequence of this is crystal structures with Z′ > 1, which contain more than one crystallographic independent species of one particular moiety.4 A useful and more accurate descriptor of this Z′ > 1 phenomenon is the number of crystallographically nonequivalent molecules, Z′′.5 For salt structures this translates into having more than a single cation-anion pair with Z′′ g 2 (the simplest Z′′ value for a cation-anion pair is 2). Z′′ is also more accurate in describing hydrated structures as it reports the total number of refined entities and not simply that of the residue in the asymmetric unit.5 Previously, it has been established that the hydrogen bonding motif between salts of primary ammonium cations and car* To whom correspondence should be addressed. E-mail: andreas.lemmerer@ gmail.com, [email protected]. Fax: +27-21-689-7499. Tel: +27-21-6502563. † University of Cape Town. ‡ University of the Witwatersrand.

Figure 1. Asymmetric unit of 1 showing the atomic numbering scheme and 50% displacement ellipsoids. Only the symmetry independent hydrogen bonds are shown. Atoms labeled with (i) are at symmetry position (1 - x, 1 - y, 1 - z).

boxylate anions, (R-NH3+) • (R′-COO-) produces reproducible interactions in one of two forms: 1-D hydrogen bonded columns made up of linked R34(10) hydrogen bonded rings or alternating R24(8) and R44(12) rings.6,7 If the anion has two carboxylate groups, general formula (R-NH3+)2 • (-OOC-R′-COO-), the 1-D hydrogen bonded columns are conjoined by the two carboxylate groups to form 2-D hydrogen bonded sheets. Factors influencing which type of column is observed in the solid state are not fully understood but appear to depend on the chirality of the ammonium group (homochiral structures have R34(10) rings and heterochiral structures alternating R24(8)/R44(12) rings) and on the steric size of either of the two molecules.8 We plan on extending on this class of salts by matching up the number of donor and acceptor atoms on the anions and cations respectively. To this end, it was decided to start investigating salts of

10.1021/cg8010585 CCC: $40.75  2009 American Chemical Society Published on Web 04/20/2009

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Table 1. Crystallographic Data for Compounds 1-4

Formula Mr Temperature (K) Crystal size (mm3) Crystal system Space group (No.) a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z F (calcd) (Mgm-3) µ(Mo KR) (mm-1) Theta range for data collection (deg) Reflections collected No. unique data [R(int)] No. data with I > 2σ(I) final R (I > 2σ(I)) final wR2 (all data) Flack parameter

Formula Mr Temperature (K) Crystal size (mm3) Crystal system Space group (No.) a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z F (calcd) (Mgm-3) µ(Mo KR) (mm-1) Theta range (deg) Reflections collected No. unique data [R(int)] No. data with I > 2σ(I) final R (I > 2σ(I)) final wR2 (all data) Flack parameter

1

2

3

4

5

(C10H6S2O6)• (H3O)2•(H2O)2 360.35 173 0.32 × 0.30 × 0.03 Monoclinic P21/c (14) 11.413(2) 9.0487(18) 7.1954(14) 90 100.38(3) 90 730.9(3) 2 1.637 0.414 1.81 to 25.49

((R)-C8H9NH3)2• (C10H6S2O6)•(H2O)2 566.67 173 0.53 × 0.44 × 0.15 Monoclinic P21 (4) 12.8947(6) 6.9936(3) 15.6410(4) 90 98.775(3) 90 1394.00(10) 2 1.350 0.242 3.20 to 28.00

((S)-C8H9NH3)2• (C10H6S2O6)•(H2O)2 566.67 173 0.29 × 0.14 × 0.08 Monoclinic P21 (4) 12.9026(10) 7.0112(4) 15.6618(13) 90 98.626(3) 90 1400.78(18) 2 1.344 0.240 2.87 to 28.00

((RS)-C8H9NH3)2• (C10H6S2O6)•(H2O)2 566.67 173 0.34 × 0.33 × 0.15 Triclinic P1j (2) 6.9709(5) 9.3885(7) 11.5361(7) 68.520(4) 79.357(3) 87.696(3) 690.16(8) 1 1.363 0.244 2.42 to 28.00

((R)-C8H9NH3)2• (C10H6S2O6) 530.64 173 0.25 × 0.23 × 0.06 Monoclinic P2 (3) 10.6886(3) 11.2210(3) 21.3919(7) 90 93.741(2) 90 2560.21(13) 4 1.377 0.252 1.81 to 28.00

7333 1338 [0.0605] 1251 0.0333 0.0905 -

30493 6675 [0.0618] 6009 0.0354 0.0925 0.02(5)

30585 6720 [0.0794] 4498 0.0469 0.1124 -0.02(7)

15439 3320 [0.0626] 2864 0.0357 0.0967 -

58706 12320 [0.0820] 8317 0.0430 0.0985 -0.06(5)

6

7

8

9

10

((S)-C8H9NH3)2• (C10H6S2O6) 530.64 173 0.56 × 0.31 × 0.06 Monoclinic P2 (3) 10.6875(3) 11.2208(2) 21.4087(7) 90 93.765(1) 90 2561.84(12) 4 1.376 0.252 1.81 to 28.00 57371 12360 [0.0819]

((RS)-C8H9NH3)2• (C10H6S2O6) 530.64 173 0.50 × 0.45 × 0.04 Orthorhombic Pbcn (60) 20.9153(9) 11.1980(5) 10.7591(5) 90 90 90 2519.9(2) 4 1.399 0.257 2.80 to 28.00 26258 3043 [0.0802]

((R)-C8H9NH3)• (C10H7SO3) 329.40 173 0.25 × 0.23 × 0.06 Triclinic P1 (1) 5.9861(5) 7.5878(5) 18.2064(16) 89.154(4) 81.962(4) 89.104 818.67(11) 2 1.336 0.212 2.93 to 25.50 21981 5915 [0.0972]

((S)-C8H9NH3)• (C10H7SO3) 329.40 173 0.56 × 0.31 × 0.06 Triclinic P1 (1) 5.9629(3) 7.5551(4) 18.1340(9) 89.131(2) 81.986(2) 89.098(2) 808.79(7) 2 1.353 0.215 2.27 to 25.50 12721 6006 [0.0675]

((RS)-C8H9NH3)• (C10H7SO3) 329.40 173 0.50 × 0.25 × 0.056 Triclinic P1j (2) 6.0783(6) 7.5053(5) 18.2131(18) 86.341(6) 83.473(4) 86.509(6) 822.60(13) 2 1.330 0.211 4.22 to 25.50 8747 3014 [0.0779]

8931 0.0435 0.1028 0.06(5)

2244 0.0366 0.0961 -

4563 0.0537 0.1171 0.01(11)

4808 0.0434 0.1094 -0.01(8)

2294 0.0607 0.1581 -

ammonium cations and sulfonate anions. Most sulfonates themselves exist with a hydronium cation as a counterion, which has the same number of donor hydrogens as the ammonium cation and has a similar geometry, trigonal pyramidal versus tetrahedral. The three acceptor oxygen atoms on the sulfonate anion themselves have a closely related tretrahedral geometry to the three donor H atoms on the ammonium cation. A search of the Cambridge Structural Database (version 5.29, November 2007 release),9 reveals a number of ammonium sulfonate salt structures. For those salts containing only the ammonium and sulfonate functional group, a variety of hydrogen bonded rings are found. An analysis of the crystal structures, the results of which will be discussed below, reveals that the R44(12) ring, made up of 2 sulfonate and 2 ammonium groups in a ringshaped motif, is frequently encountered. To establish more clearly what hydrogen bonding motifs are formed in ammonium sulfonates salts containing no other possible acidic or basic functional groups, we have chosen the 1,5-naphthalenedisulfonic acid and 2-naphthalenesulfonic acid molecules as the anion and the homochiral or heterochiral solutions of 1-phenylethylamine as the cation (Chart 1). This

allows us to monitor the effect, if any, the chiral nature of the crystal solution has on the observed hydrogen bonding motif and the dimensionality of the anion. In the course of investigating these compounds, the phenomenon of high Z′ values occurred due to the strong nature of the NH3+ · · · SO3- charge assisted hydrogen bonds overriding the ability to pack efficiently. Experimental Procedures Compounds. All reagents were purchased from commercial sources and used without further purification. (H3O)2•(C10H6S2O6)•(H2O)2 (1). 1,5-Dinaphthalenesulfonic acid tetrahydrate (0.100 g, 0.279 mmol) was dissolved in AP-grade methanol (5 mL) and left to evaporate at room temperature. ((R)-C8H9NH3)2•(C10H6S2O6)•(H2O)2 (2). 1,5-Naphthalenedisulfonic acid tetrahydrate (0.300 g, 0.837 mmol) and 0.22 g of (R)-1phenylethylamine (1.80 mmol) was added into a sample vial. Heat given off from the acid-base reaction confirmed that the salt had formed. The solid was further dissolved in AP-grade methanol (5 mL) and left to evaporate at room temperature. The colorless crystals turn opaque after a day due to loss of the water molecules. ((S)-C8H9NH3)2•(C10H6S2O6)•(H2O)2 (3). 1,5-Naphthalenedisulfonic acid tetrahydrate (0.300 g, 0.837mmol) and 0.22 g of (S)-1-phenyl-

Centrosymmetric and Noncentrosymmetric R44(12) Rings

Crystal Growth & Design, Vol. 9, No. 5, 2009 2267

Chart 1. Cationic and Anionic Species Investigated in This Report

ethylamine (1.80 mmol) was added into a sample vial. Heat given off from the acid-base reaction confirmed that the salt had formed. The solid was further dissolved in AP-grade methanol (5 mL) and left to

Figure 2. Hydrogen bonding interactions between the three different chemical moieties in 1.

Figure 3. (a) Complex 3-D network of hydrogen bonds in 1. The hydrocarbon fragments of the naphthalene-1,5-disulfonate anion are omitted for clarity. (b) Packing diagram of 1 down the b-axis, showing the alternating ionic hydrocarbon layers and the parallel but offset stacking of the naphthalene rings. evaporate at room temperature. The colorless crystals turn opaque after a day due to loss of the water molecules. ((RS)-C8H9NH3)2•(C10H6S2O6)•(H2O)2 (4). 1,5-Naphthalenedisulfonic acid tetrahydrate (0.300 g, 0.837mmol) and 0.22 g of (RS)-1phenylethylamine (1.80 mmol) was added into a sample vial. Heat given off from the acid-base reaction confirmed that the salt had formed. The solid was further dissolved in AP-grade methanol (5 mL) and left to evaporate at room temperature. The colorless crystals turn opaque after a day due to loss of the water molecules. ((R)-C8H9NH3)2•(C10H6S2O6) (5). Opaque crystals of 2 were ground up using a pestle and mortar and the white powder placed in a sample vial on a hot plate. The vial was left on the hot plate for a few days and the white powder turned off-white. The powder was dissolved with AP-grade methanol (5 mL). Molecular sieves were added to the vial and the vial placed in a desiccator to slowly evaporate to form colorless crystals again. These did not turn opaque, confirming the absence of any water molecules. ((S)-C8H9NH3)2•(C10H6S2O6) (6). The same procedure as in 5 was followed, however, this time with crystals of 3. ((RS)-C8H9NH3)2•(C10H6S2O6) (7). The same procedure as in 5 was followed, however, this time with crystals of 4. ((R)-C8H9NH3)•(C10H6SO3) (8). 2-Naphthalenesulfonic acid hydrate (0.150 g, 0.663 mmol) and 0.08 g of (R)-1-phenylethylamine (0.655 mmol) was added into a sample vial. Heat given off from the acid-base reaction confirmed that the salt had formed. The solid was further dissolved in AP-grade methanol (5 mL) and left to evaporate at room temperature. ((S)-C8H9NH3)•(C10H6SO3) (9). 2-Naphthalenesulfonic acid hydrate (0.150 g, 0.663 mmol) and 0.08 g of (S)-1-phenylethylamine (0.655 mmol) was added into a sample vial. Heat given off from the acid-base

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Figure 4. Asymmetric units of 2 and 3 showing the atomic numbering scheme and 50% displacement ellipsoids. Only the symmetry independent hydrogen bonds are shown. For clarity all C-H hydrogen atoms have been omitted.

Figure 5. All the hydrogen bonding interactions between between the cations, anions and water molecules of 2 (a) and their detailed geometric parameters (b). Packing diagram of 2 viewed down the b-axis, showing the N-H · · · O and O-H · · · O hydrogen bonds (dashed red lines) and C-H · · · π hydrogen bonds (dashed blue lines) (c). Detailed view of the two different hydrogen bonded columns formed, one containing water molecules and the other not (d). Most C-H hydrogen atoms have been omitted in (a) and (c) and all the hydrocarbon fragments in (d). reaction confirmed that the salt had formed. The solid was further dissolved in AP-grade methanol (5 mL) and left to evaporate at room temperature.

((RS)-C8H9NH3)•(C10H6SO3)•(10). 2-Naphthalenesulfonic acid hydrate (0.150 g, 0.663 mmol) and 0.08 g of (RS)-1-phenylethylamine (0.655 mmol) was added into a sample vial. Heat given off from the



Figure 6. Asymmetric unit of homochiral 4 with the completed anionic fragment showing the atomic numbering scheme and 50% displacement ellipsoids. Only the symmetry independent hydrogen bonds are shown. Atoms labeled with (ii) are at the symmetry position (1 - x, 1 - y, 2 - z).

Figure 8. (a) View of the single unique hydrogen bonded column, containing the cations, anions and water molecules of 4. (b) Packing diagram of 4 viewed down the a-axis, showing the 2-D hydrogen bonded sheet formed by the columns shown in (a). Color schemes of hydrogen bonds are as in Figure 5. Most C-H hydrogen atoms have been omitted in (b) and the naphthalene fragment in (a). Powder X-Ray Diffraction. X-ray powder diffraction data were collected on a HUBER Guinier 670 Imaging Plate diffractometer with ˚ . The sample was ground and placed on Mylar Cu KR radiation, 1.542 A film and placed on a vertical stage. A diffractogram was acquired under ambient conditions at a power setting of 40 kV and 20 mA in transmission mode while the sample oscillates perpendicular to the beam. Comparisons between the measured and calculated diffractograms, provided in the Supporting Information, confirm the bulk identity of compounds 2-10. X-Ray Crystallography. Diffraction data for all compounds except 9 were collected on a Nonius KappaCCD diffractometer with graphitemonochromated Mo KR radiation (λ ) 0.71073 Å) at 173 K using an Oxford Cryostream 600. Data reduction and cell refinement where done using DENZO10 and space groups of these compounds were determined from systematic absences by XPREP11 and further justified by the refinement results. Diffraction data for 9 was collected on a Bruker APEX-212 diffractometer with graphite-monochromated Mo KR radia˚ ) at 173 K using an Oxford Cryostream 700. Data tion (λ ) 0.71073 A reduction and cell refinement were carried out using SAINT-PLUS.13 Face indexed absorption corrections were performed on all crystals

Figure 7. Detailed information of the hydrogen bonding interactions between the three different chemical moieties in 4. acid-base reaction confirmed that the salt had formed. The solid was further dissolved in AP-grade methanol (5 mL) and left to evaporate at room temperature.

Table 2. C-H · · · π Hydrogen Bonding Details of 2-4 D-H · · · A

D-H (Å)

H · · · A (Å)

D · · · A (Å)

C6-H6 · · · Cg C15A-H15A · · · Cg

0.95 0.95

2.78 2.95

3.622(2) 3.878(2)

(D-H · · · A) (deg)

symmetry transformations

2 148 167

1 - x, 1/2 + y, 1 - z 1 - x, 1/2 + y, 1 - z

147 166

1 - x, -1/2 + y, 1 - z 1 - x, -1/2 + y, 1 - z

147 134

-x, -y, 2-z -1+x, -1+y, z

3 C6-H6 · · · Cg C15A-H15A · · · Cg

0.95 0.95

2.78 2.96

3.618(3) 3.887(3)

C13-H13 · · · Cg C14-H14 · · · Cg

0.95 0.95

2.78 2.84

3.708(2) 3.558(2)

4

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Figure 9. Asymmetric units of homochiral 5 and 6 with completed anionic fragment of heterochiral 7 showing the atomic numbering scheme and 50% displacement ellipsoids. Only the symmetry independent hydrogen bonds are shown. For clarity most C-H hydrogen atoms have been omitted. Atoms labeled with (iii) are at the symmetry position (1 - x, -y, 1 - z).

Figure 10. Asymmetric units of the enantiomorphic pair 5 and 6. The two figures are shown as nonsuperimposable mirror images of another. The four cations in each compound are crystallographically distinct due to their differences in their respective C10-C11-C16-H16 torsion angles, shown in green. using XPREP.11 In all cases, the structures were solved in the WinGX14 Suite by direct methods using SHELXS-9715 and refined using fullmatrix least-squares/difference Fourier techniques using SHELXL-97.15 After that, all hydrogen atoms were placed at idealized positions and refined as riding atoms with isotropic parameters relative to those of the heavy atoms to which they are attached. Diagrams and publication material were generated using ORTEP-3,16 PLATON17 and DIAMOND.18 Experimental details of the X-ray analyses are provided in Table 1.

Results Crystal Structure of (H3O)2•(C10H6S2O6)•(H2O)2 (1). The structure of the naphthalene-1,5-disulfonic compound in its simplest form does not exist in the CSD, however hydronium

structures are relatively common in compounds containing sulfonates, featuring 39 times in the CSD.19 One of the simplest related structures with a hydronium cation has a solvent dimethylformamide (DMF) molecule.20 We present here the structure of one of the starting materials in the form in which it was purchased, as a tetrahydrate. More correctly, it crystallizes out as a dihydronium salt with two water molecules of hydration. The asymmetric unit consists of half a naphthalene-1,5disulfonic anion and sits on a center of inversion in space group P21/c (Figure 1). All three oxygen atoms on the sulfonate group (O1, O2, and O3) participate as hydrogen bond acceptors. The geometry of the sulfonate group is approximately tetrahedral. The S1-O1 distance (1.4706(13) Å) is the longest of the three,



Figure 11. All the hydrogen bonding interactions between between the cations and anions of 5 (a) and their detailed geometric parameters (b). (c) Packing diagram of 5 viewed down the a-axis, showing the 2-D hydrogen bonded sheets parallel to the ab-plane. (d) Detailed view of the two different hydrogen bonded columns formed and the sequence of their hydrogen bonded rings. All C-H hydrogen atoms have been omitted in (a) and (c) and all the hydrocarbon fragments in (d).

presumably as a consequence of it acting as a 2-fold acceptor with a hydrogen, one each from the water molecule O1W and the hydronium cation O2W. Conversely, the S1-O2 and S1-O3 distances, respectively 1.4468(14) Å and 1.4537(14) Å, are shorter as they both act as a single acceptor atom to O1W and O2W respectively. The three charge-assisted hydrogen bonds between the hydronium cation and sulfonate anion are characterized by one short and two long interactions (see Figure 2); a similar trend is observed in the above-mentioned structure which has DMF included as a solvent. The shortest hydrogen bond is between a hydrogen on the hydronium cation and the oxygen atom of the water molecule with a D · · · A distance of 2.425(2) Å. The crystal packing has alternating layers of the neutral organic naphthalene unit and charged hydrated layers, in the direction of the crystallographic a-axis (Figure 3). The naphthalene unit stacks in a parallel fashion along the c-axis but with adjacent molecules offset by half the distance of the b-axis leading to a lack of π · · · π interactions.

Crystal Structures of ((R)-C8H9NH3)2•(C10H6S2O6)• (H2O)2 (2) and ((S)-C8H9NH3)2•(C10H6S2O6)•(H2O)2(3). The first attempted crystallizations of (2) were successful, with the cation and anion packing together and having two waters of hydration. In effect, the (R)-1-phenylethylammonium cation has replaced the hydronium cation, forming stronger hydrogen bonds. The geometry of the two cations is similar, being tetrahedral in the chiral ammonium cation in 2 and 3 and tetragonal pyramidal in the hydronium cation in 1. The geometry of the sulfonate group is approximately tetrahedral. The asymmetric unit has one complete naphthalene-1,5-disulfonate anion, two (R)-1-phenylethylammonium cations, labeled cationN1 (containing atom N1) and cationN2 (containing atom N2), and associated with them two neutral waters of hydration, labeled O1W and O2W (Figure 4). The sulfonate anion is labeled into two anions for convenience, labeled anionS1 (containing atoms S1, O1, O2, O3) and anionS2 (S2, O4, O5, and O6). There are six hydrogen bond acceptor oxygen sites and six hydrogen bond

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Figure 12. (a) Detailed information of the hydrogen bonding interactions between the two different chemical moieties in heterochiral 7. (b) Packing diagram of 7 viewed down the c-axis, showing the same general 2-D hydrogen bonded sheet as seen in homochiral 5 and 6 but with a different relative arrangement of the cations. All C-H hydrogen atoms have been omitted in (a).

donor N-H sites on the parent ions and the usual two donor/ one acceptor site on the water molecules. Every site is used, summing up to a total of 10 unique hydrogen bond interactions (Figure 5a and b). The chiral carbon atom is labeled C16A in cationN1 and C16B in cationN2. Anomalous dispersion confirms the absolute stereochemistry of the cation to be R with a Flack parameter of 0.02(5). There is an asymmetry in the hydrogen bonded interactions between the two cations and the two anionic sites on the naphthalene group. CationN1 associates itself

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exclusively with the sulfonate group on the 1-position on the naphthalene ring (anionS1) and cationN2 with the 5-position on the naphthalene ring (anionS2). The water molecules only hydrogen bond with anionS1, so that the three N-H atoms hydrogen bond to the oxygen atom O2 on the sulfonate group and to O1W and O2W. The hydrogens on the water molecules themselves interact with all three oxygen atoms on the sulfonate group. The hydrogen bonded network thus formed has a cube shape hydrogen bonded column with the four sides made up of three hydrogen bonded rings: R44(9) and R54(9) are approximately planar to the ab-plane forming two sides of the cube and a larger R56(13) ring forming the floor and roof of the box parallel to the bc-plane (see Figure 5d). The hydrogen bonded interactions between cationN2 and anionS2 is much simpler as they are exclusively between the sulfonate anion and ammonium cation, with all three oxygen atoms used. The hydrogen bonded motif consists of R44(12) rings around the 2-fold screw axis to form (R)-21-columns. These two different hydrogen bonded columns, linked by the dianion then form 2-D hydrogen bonded sheets parallel to [-101] (Figure 5c). Adjacent hydrogen bonded sheets interdigitate through the aromatic rings of the cations. Adjacent sheets are linked by two different C-H · · · π interactions as shown in Figure 5c and listed in Table 2. The crystal structure of 3, displays the same structural features as 2, and both 2 and 3 form an enantiomorphic pair. The detailed hydrogen bonding geometries for 3 are given as Supporting Information and reflect the similarities between the two crystal structures in terms of the relative positions between the cations, anions and waters of hydration. Crystal Structure of ((RS)-C8H9NH3)2•(C10H6S2O6)• (H2O)2 (4). The effect of the heterochirality of the moieties in the crystal structures is seen in structure 4. Here, only one type of hydrogen bonded network is formed on either side of the naphthalene-1,5-disulfonate anion and these are related by an inversion center. The ASU has half a naphthalene molecule, labeled anionS1, a (S)-1-phenylethylammonium cation, labeled cationN1, and one water molecule of hydration (Figure 6). The chirality of the cation is chosen arbitrarily to be the (S) enantiomer with the mirror image cation being related by the inversion center. The hydrogen bond pattern observed in 4 is different to any of those in the homochiral structures 2 and 3 (Figure 7 and 8a). A smaller R44(10) ring is formed by two hydrogens on the water molecule and two hydrogen on the ammonium group (either from a (R)-cationN1 or (S)-cationN1) and by one oxygen on the sulfonate and two oxygens on another sulfonate. Only one cation is used. Two larger R66(14) rings are formed by two hydrogens each on a (R)- and (S)-cationN1, one H each from a water molecule and two oxygen atoms each on two sulfonates. These three rings alternate along the a-axis and are joined along the c-axis by the naphthalene moiety to form 2-D sheets of hydrogen bonds parallel to the ac-plane. The aromatic rings of the cations extend out normal to the sheets and interdigitate with adjacent sheets along the b-axis and are linked by two C-H · · · π interactions from the aromatic ring to the two π systems of the naphthalene (see Table 2 and Figure 8b). Crystal Structures of ((R)-C8H9NH3)2•(O3SC10H6SO3) (5) and ((S)-C8H9NH3)2•(O3SC10H6SO3) (6). The nonhydrated versions of 2 and 3 show a phenomenal change in packing and hydrogen bonding compared to the hydrate structures. There are two complete naphthalene-1,5-disulfonate molecules in the asymmetric unit and four (R)-1-phenylethylammonium cations in (5) and four (S)-1-phenylethylammonium cations in (6) (Figure 9). The two structures again form an enantiomorphic



Figure 13. Comparative packing views of homochiral 5 (a) and heterochiral 7 (b). The tilting effect of the 2-D hydrogen bonded sheets is striking in 7 and is created by the different geometric arrangement of the cations in between the 2-D hydrogen bonded sheets in 7 when compared to 5. This Zo¨llner Line Illusion can be shown schematically using the parallel lines drawn and the small intersecting lines at right angles (c) and at an angle of 60° (d).

pair as did 2 and 3. Figure 10 shows the two asymmetric units as mirror images of each other and shows clearly that the cations are nonsuperimposable mirror-images (the anions are achiral and superimposable). Both structures crystallize in the relatively unusual space group P2; its rarity is probably due to it not possessing any of the favored symmetry elements for the packing of organic molecules, such as the screw-axis, mirror plane and glide plane.21 Dianion1 contains atoms S1 and S2 and dianion2 contains atoms S3 and S4. There are two types of cations in the ASU: One type has its methine H on the chiral carbon atom C16 approximately perpendicular with the plane of the aromatic ring. The torsion angles for these two particular cations, which are labeled cationN1 (A) and cationN2 (B), are respectively 105.3(3)° (C11A-C10A-C16A-H16A) and 71.0(3)° (C11B-C10B-C16B-H16B). The second type has its methine H in line with the aromatic ring and are labeled cationN3 (C) and cationN4 (D). The torsion angles for the second type are -179.0(3)° (C11C-C10C-C16C-H16C) and 177.7(3)° (C11D-C10D-C16D-H16D). In other words, the pairs N1/N2 and N3/N4 have respectively different geometries of their cations but most importantly, the torsion angles within each pair are sufficiently different to make them crystallographically distinct. The underlying cause for the two groups of cations and anions can be observed by their different hydrogen bonding patterns. CationN1 (A) and cationN3 (C) together with dianion1 form chains of alternating rings of R24(8) and R44(12), and cationN2 (B) and cationN4 (D) together with dianion2 form chains made up of only R44(12) rings (Figure 11d). By virtue of the two dianions having two sulfonates attached at the 1and 5- position of the naphthalene backbone, both dianion1 and dianion2 form 2-D sheets of hydrogen bonds, with one sheet made up of dianion1/cationN1(A)/cationN3(C) at z ) 0.5 and a second sheet made up of dianion2/cationN2 (B)/cationN4 (D) at z ) 0 and 1 (Figure 11c). The homochiral hydrogen bonded sheets interdigitate through the cations along the c-axis direction,

with the (R)-cations (5) and (S)-cations (6) being aligned almost directly along [001] (Figure 13a). Crystal Structure of ((RS)-C8H9NH3)2•(C10H6S2O6) (7). The heterochiral version of structures 5 and 6 shows a subtle difference in the observed hydrogen bonding pattern. The asymmetric unit is much simpler (as in 4), consisting of half a naphthalene-1,5-disulfonate anion (dianionS1), a (S)-1-phenylethylammonium cation ((S)-cationN1), and no waters of hydration (Figure 9 and 12a). The chirality of the cation is chosen arbitrarily to be the (S) enantiomer with the mirror image cation being related by the inversion center. The hydrogen bond pattern observed in 7 is identical to that observed by the dianion2/ CationN2 (B)/cationN4 (D) grouping in 5 and 6, made up of only R44(12) rings. The formed 2-D heterochiral hydrogen bonded sheets are similar to those in 5 and 6, except that the (R)-cationsN1 and (S)-cationsN1 are aligned now along the [110] direction (Figure 12b and 13b). This has a remarkable optical effect on the packing diagram when viewed down the b-axis. The individual heterochiral sheets appear to diverge and converge from each other instead of being perfectly parallel. This is a classic line illusion known as the Zo¨llner illusion.22 The Zo¨llner illusion is an optical illusion that turns parallel lines into either diverging or converging lines if the parallel lines are intersected by a series of short lines tilted at an acute angle. The relation to the packing diagrams of 5 and 7 is thus: The layers consisting of the hydrogen bonds between the sulfonates and ammonia groups are the parallel lines; the aromatic rings of the (R)-1-phenethylammonium cations on either side of the hydrogen bond layer are the short lines. In 5, these short lines (aromatic rings) are almost perpendicular to the parallel lines (hydrogen bond layer) and the Zo¨llner effect subsequently does not occur (Figure 13a). However, in 7, the hydrogen bonded sheets have both (R)-1phenethylammonium and (S)-1-phenethylammonium cations and

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Figure 14. Asymmetric units of homochiral 8 and 9 and heterochiral 10 showing the atomic numbering scheme and 50% displacement ellipsoids. Only the symmetry independent hydrogen bonds are shown. For clarity most C-H hydrogen atoms have been omitted.

these tilt away from the normal to the sheets, thus creating the angled short lines necessary for the Zo¨llner illusion (Figure 13b). Crystal Structures of ((R)-C8H9NH3)•(C10H6SO3) (8) and ((S)-C8H9NH3)•(C10H6SO3) (9). The crystal structure of 8 has two molecules each of (naphthalene-2-sulfonate) and (R)1-phenylethylammonium in the asymmetric unit and crystallizes in the space group P1 (Figure 14, Table 3). The two cations, (R)-cationN1 and (R)-cationN2, are conformationally different with regards to the torsion angle, respectively -123.9(5)° and 161.6(5)°, between the aromatic ring and chiral functional group as observed in 5 and 6. The torsion angle between the naphthalene and SO3 groups are also different in the two anions, anionS1 (C3-C2-S1-O2: 27.9°) and anionS2 (C6-C5S2-O6: -22.5°). All three donor H atoms on the two cations form charge-assisted hydrogen bonds to all three acceptor O atoms on the two anions (the four ions form a unique R44(12) hydrogen bonded ring as shown in Figure 14). This hydrogen bonded motif is repeated along the a-axis via unit cell translations only to form one-dimensional columns and are classified as homochiral (R)-1-columns (Figure 15). The columns pack parallel to each other along the b-axis direction and interact via a weak C-H · · · π interaction between the H4 atom on the naphthalene ring of anionS1 and the ring centroid of cationN1 only (Figure 16a). There are no C-H · · · π interactions within

Lemmerer et al.

3.0 Å to adjacent columns between anionS1 and cationN2. Adjacent columns are separated by the naphthalene rings along the c-axis direction to form alternating ionic-hydrocarbon layers (Figure 16a). The structure of enantiomorphic 9 is closely related and will not be discussed in further detail. Crystal Structure of ((RS)-C8H9NH3)•(C10H6SO3) (10). The crystal structure of 10 has one molecule each of (naphthalene2-sulfonate) (anionS1) and (S)-1-phenylethylammonium (cationN1) in the asymmetric unit and crystallizes in the space group P1j (Figure 14). The chirality of the cation is chosen arbitrarily to be the (S) enantiomer with the mirror image cation being related by the inversion center. The C11-C1-C16-H16 torsion angle is -161.8(2)° (same absolute value as (R)-cationN2 in 8). The torsion angle between the naphthalene and SO3 groups is 31.1° (C3-C2-S1-O2). All three donor H atoms form charge-assisted hydrogen bonds to all three acceptor O atoms on the anion to form a R44(12) hydrogen bonded ring. This hydrogen bonded motif is repeated along the a-axis via inversion centers to form one-dimensional columns and are classified as heterochiral i-columns. The columns pack parallel to each other along the b-axis direction and interact via a weak C-H · · · π interaction between the H14 atom on the aromatic ring of cationN1 and one of the ring centroids on the naphthalene ring of anionS1 (Figure 16b). Adjacent columns are separated by the naphthalene rings along the c-axis direction to form alternating ionic-hydrocarbon layers as seen in 8 and 9. Occurrence of R44(12) Ring Motifs in Ammonium Sulfonate Structures in the CSD. The CSD contains a number of crystal structures with NH3 and SO3 groups. Most of them also contain a number of other functional groups. Of the 84 accurately determined structures of general formula C1-40H1-80N1-2O3-8 found in the CSD that have a NH3 and SO3 group, only 35 have no other functional groups on the main constituent molecules (solvent molecules such as dioxane, methanol and water were included as well as those also containing neutral NH2 groups).23 It was decided to look at only the 35 structures and observe those that have at least one R44(12) ring. Twenty-one structures were found that have the R44(12) ring, either exclusively (6/21) or in combination with other motifs (15/21) and are listed in detail in Table 4. The hydrogen bonding patterns of those 21 vary from 0-D clusters to infinite 1-D chains, 2-D sheets, and 3-D frameworks. Of the 14 structures that did not contain any R44(12) rings and have only NH3 and SO3 groups (listed in Table 5), there are four structures that consist exclusively of only one type of hydrogen bonded ring that is larger than the twelve-membered R44(12) ring. Examples are HOTAUR10, TAYWEV, MIHGUG, and ZZZRQI01, that consist exclusively of R66(18) rings. A further three structures, AFAZEM, ANISAC03, and TAURIN05, which are structurally simple ammonium sulfonates, do not have the R44(12) ring. This could be due to steric constraints, as the two functional groups are on the same molecule and so might be unable to form a 12 membered ring. Interestingly, of the remaining seven structures out of the 14 that do not have the ring (8-14), all of those seven are hydrates (the 21 structures that have the ring are all unhydrated). This would suggest that the presence of water has a disruptive influence on the formation of the R44(12) ring. Discussion Structural Comparison of 2-4. We know that sulfonates often crystallize out with hydronium cations. Hence, when compounds 2-4 were prepared, the chiral ammonium cations were not able to displace the hydronium counterion entirely.



Figure 15. Homochiral hydrogen bonded columns of enantiomorphic 8 (a) and 9 (b). The two figures are shown as nonsuperimposable mirror images of another. The two cations in each compound are crystallographically distinct due to their differences in their respective C10-C11-C16H16 torsion angles, shown in green. Most C-H hydrogen atoms have been omitted for clarity. Table 3. Hydrogen Bonding Details and Short Contacts for Compounds 8-10 D-H · · · A

D-H (Å)

H · · · A (Å)

D · · · A (Å)

(D-H · · · A) (deg)

symmetry transformations

8 N1-H1A · · · O3 N1-H1B · · · O5 N1-H1C · · · O1 N2-H2A · · · O4 N2-H2B · · · O2 N2-H2C · · · O6 C4-H4 · · · Cg

0.91 0.91 0.91 0.91 0.91 0.91 0.95

1.96 1.92 1.87 1.94 1.89 1.87 2.92

2.827(6) 2.830(6) 2.769(6) 2.836(6) 2.796(6) 2.771(6) 3.578(6)

N1-H1A · · · O3 N1-H1B · · · O5 N1-H1C · · · O1 N2-H2A · · · O4 N2-H2B · · · O2 N2-H2C · · · O6 C4-H4 · · · Cg

0.91 0.91 0.91 0.91 0.91 0.91 0.95

1.94 1.91 1.85 1.92 1.88 1.86 2.88

2.814(6) 2.816(6) 2.752(6) 2.824(6) 2.790(6) 2.767(6) 3.546(4)

N1-H1A · · · O1 N1-H1B · · · O3 N1-H1C · · · O2 C14-H14 · · · Cg

0.91 0.91 0.91 0.95

1.93 1.85 1.91 2.95

2.816(6) 2.762(6) 2.820(6) 3.523(3)

159 177 170 170 172 171 128

x - 1, y, z x + 1, y, z x + 1, y + 1, z

161 177 171 171 174 177 128

x + 1, y, z x - 1, y, z x - 1, y - 1, z

165 174 179 120

x + 1, y, z -x + 1, -y + 1, -z + 1 x + 1, y - 1, z

9

10

However, compounds 2 and 3 show attempts at separating out the hydronium and ammonium cations. As described above, the single naphthalene-1,5-disulfonate anion in the asymmetric unit in 2 and 3 is engaged in the formation of two different hydrogen bonding columns, one with both hydronium and ammonium cations and one with only ammonium cations. This occurs when only one type of enantiomer is present in the crystal solution. However, the presence of both enantiomers in the solution mixture generates a similar 2-D hydrogen bonded sheets as in 2 and 3 but now there is only one type of hydrogen bonding column, involving all charged species in a symmetrical fashion that was not possible in the structures of 2 and 3. Table 6 summarizes some relevant structural features of the hydrated salts.

Comparison of Unit Cells and Symmetry in 5-10. By removing the waters of hydration in compounds 2-4, we were able to prepare the unhydrated ammonium salts 5-7. Compounds 8-10, although prepared from the hydrated anion naphthalene-2-sulfonic acid, did not include water molecules in the crystal structure. The structures 5-10 described above turned out to be not as simple as expected. Initially we were only interested in relating the differences, if any, between the hydrogen bond patterns of ammonium carboxylate and ammonium sulfonate salts. Unexpectedly but not surprisingly in hindsight and as will be explained below, the structures themselves display interesting features related to their hydrogen bonding patterns. Due to the strong nature of the hydrogen bond between ammonium and sulfonate ions and the limited degree

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Figure 16. Comparative packing diagrams of homochiral 8 (a) and heterochiral 10 (b), both viewed down the 1-D hydrogen bonded columns (a-axis). Note the different C-H · · · π hydrogen bonds found in 8 and 10, where the donor H atom is on a naphthalene ring in 8 and on a phenyl ring in 10. Note that only cationN1 participates in C-H · · · π hydrogen bonds in 8. Table 4. Twenty-one Ammonium Sulfonate Structures That Have at Least One R44(12) Ring CSD ref code

charged species

other rings present

other functional groups present

0-D cluster 0-D cluster 3-D network

1-D 1-D 3-D 1-D 2-D

1) DICGOM 2) DICGUS 3) FAXYUZ

triphenymethylammonium and benzensulfonate trphenylmethylammonium and methanesulfonate 6-amino-2-aminotoluene-4-sulfonate

No Yes Yes

4) HORHOL 5) KEYRUC 6) KEYSAJ 7) KEYSEN 8) KEYSIR 9) LAQDIR 10) MIHGOA 11) NEKYAE 12) NEKYEI 13) OTANAC 14) PAMCOW 15) PAMDAJ 16) PEPREI

methylammonium sufanilate bis(isopropylammonium) biphenyl-4,4′-disulfonate benzene clathrate bis(isopropylammonium) biphenyl-4,4′-disulfonate 1,4-dioxane clathrate bis(n-propylammonium) biphenyl-4,4′-disulfonate benzene clathrate bis(n-propylammonium) biphenyl-4,4′-disulfonate 1,4-dioxane clathrate 2-ammoniocyclohexane-1-amine p-tolylsulfonate bis(Neopentylammonium) anthracene-2,6-disulfonate dioxane clathrate bis(benzylammonium) anthracene-2,6-disulfonate bis(Butylammonium) anthracene-2,6-disulfonate aniline-o-sulfonic acid bis(methylammonium) anthracene-2,6-disulfonate bis(pentylammonium) anthracene-2,6-disulfonate bis(rac-S- isobutylammonium) anthracene-2,6-disulfonate 1,4-dioxane solvate 1,4-phenylenediammonium bis(toluene-4-sulfonate) 4-aminotoluene-3-sulfonic acid 2,4-diaminobenzenesulfonic acid (DL)-2,3-diaminobutane bis(toluenesulfonate) meso-2,3-diammonio-butane bis(toluenesulfonate)

Yes No No Yes Yes Yes Yes Yes Yes Yes Yes No Yes

No No NH2 (involved in R44(12) ring) NH2 No No No No NH2 No No No No No No No

Yes No Yes No No

No No NH2 No No

17) 18) 19) 20) 21)

QERWOA RATBIX ULEQIL YAVPOA YAVPUG

of conformational freedom of the ions, the probability of structures having high Z′ values is increased.24 This phenomenon has been observed in the oxo-anion structure of 1,2-phenylenediammonium, which crystallizes out with six sulfate and four hydrogen sulfate counterions. Included are eight waters of hydration. The packing of the cation is at the mercy of the hydrogen bonding between the sulfate and hydrogen sulfate anions and the water molecules such that the cations are forced to pack face-to face instead of the preferred face to edge.25 In this work, structures 5 (and 6) and 8 (and 9) appear to be influenced by the same phenomenon, where the driving force for the assembly of the four structures is the charge assisted

hydrogen bond pattern

Ribbon 2-D sheets 2-D sheets 2-D sheets 2-D sheets 2-D sheets 2-D sheets 2-D sheets 3-D network 1-D chains 2-D sheets 2-D sheets 2-D sheets thick ribbon chains chain sheets

hydrogen bonding between the NH3+ and SO3- groups which overrides the ideal packing of their parent benzene and naphthalene rings. However, it is to be noted that it is only the optically active ammonium cations that are unable to pack efficiently, that is, the homochiral cations are not able to pack well in 5 and 6 and contain four (R)- and (S)-1-phenylethylammonium cations in the asymmetric unit. All four cations have different torsion angles and hence show a similar degree of pseudosymmetry between the cations similar to that observed in the 1,2-phenylenediammonium structure.25 A lesser degree of pseudosymmetry is shown by the anion, where the moduli of the generic torsion angles C-C-S-O are in the 10.2(2)-



Table 5. Fourteen Ammonium Sulfonate Structures That Do Not Contain a R44(12) Ring CSD ref code

CSD ref code

charged species

1) AFAZEM 2) ANISAC03 3) HOTAUR10

4-aminobenzenesulfonic acid 3-aminobenzenesulfonic acid 3-Aminopropane sulfonic acid

8) HEKSIZ 9) HEKSOF 10) IDOQEY

4) MIHGUG

bis((R)-2-butylammonium) anthracene-2,6-disulfonate 2-Aminoethane sulfonic acid (S)-2-aminopropane sulfonic acid 5-Amino-2-naphthalenesulfonate

11) KIXJUX

5) TAURIN05 6) TAYWEV 7) ZZZRQI01

charged species and hydrate 2-Aminotoluene-4-sulfonic acid monohydrate 4-Amino-2-toluene-2-sulfonic acid monohydrate bis(2,6-di-isopropylphenylammonium) ethane-1,2-disulfonate dehydrate bis(4,4′-methylenedianilinium) naphthalene1,5-disulfonate dehydrate 4-Aminotoluene-3-sulfonic acid monohydrate Sulfanilic acid monohydrate 5-Aminonaphthalene-1-sulfonic acid monohydrate

12) RATBOD 13) SANACM01 14) ZZZLGC01

Table 6. Geometric summary for hydrates 2-4

Hydrogen bonded rings in each symmetry independent column KPIa Z′′ torsion angles of cation C11-C10-C16-H16 (deg) geometry of SO3 relative to ring (C2-C1-S1-O3) (C6-C5-S2-O6) a

2

3

4

-R44(12)-R44(9)-R54(9)-R56(13)68.1 5 N1: 179.7(2) N2: -177.3(2) 8.0(2) -4.9(2)

-R44(12)-R44(9)-R54(9)-R56(13)67.7 5 N1: -179.1(3) N2: 177.3(3) -6.9(3) 5.2(2)

-R44(10)-R66(16)-R66(16)68.8 3 N1: 164.4(1) -1.8(1)

Kitaigorodskii Packing Index calculated using PLATON.16 Table 7. Geometric Summary for Non-Hydrates 5-10 5

-R44(12)-R44(12)-R24(8)KPIa 68.7 Z″ 6 torsion angles of cation N1: 105.3(3) N2: 71.0(3) C11-C10-C16-H16 (deg) N3: -179.0(3) N4: 177.7(3) average d(D · · · A) (Å) 2.84(6) range 1 (Z′′ g 2) in 5-10. The N-H · · · O-S hydrogen bonding interactions in structures 5-10 have an average N · · · O distance in the 2.79(3)-2.84(6) Å range (Table 7). This is slightly longer than the average calculated for N-H · · · O-C hydrogen bonds in ammonium carboxylate salts reported by Braga et al. (3a). Nonetheless, the distances are characteristic when compared to the average 2.857(95) Å calculated from the 30 known ammonium sulfonate structures in the CSD mentioned above.28 Structures 8-10 have the same 1-D hydrogen bonded columns of alternating R44(12) rings which is the expected motif when considering the dominant ring motif in previously reported structures. However, the rings have different symmetries, center of inversion (10) versus identity (8 and 9) and this gives further clues as to why Z″ is greater in the homochiral versus heterochiral structures. Compound 10 has one only unique cation and interestingly, the conformation of that cation

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(C11-C1-C16-H16: -161.8(2)°) is the same as the torsion angle of cationN2 in 8 and 9 (see Table 5). This suggests that the preferred arrangement of any two cations in the construction of the R44(12) ring has this conformation and ideally has a center of inversion as symmetry. This center of inversion is not possible when the two cations are homochiral as in 8 and the trade off is to twist cationN1 into a different conformation (-123.9(5)°) to that of cationN2 (161.6(5)°) to generate a better fit. The same goes for 9 (See Table 3). The difference in Z” is three times greater in 5 and 6 than in 7. This is not solely a consequence of the symmetry of the rings but also, as discussed above, of having two different kinds of hydrogen bonded columns in 5 and 6 that then generate two crystallographically independent 2-D hydrogen bonded sheets. The reason for this is not clear as the two sheets have the exact same chiral building blocks. This distinction completely vanishes when the cations are heterochiral. In 7, there is only one crystallographically independent hydrogen bonded sheet built up entirely of centrosymmetric R44(12) rings. Conclusion This investigation of ammonium sulfonates between a chiral ammonium cation and two different aromatic sulfonate anions revealed both hydrated (2-4) and unhydrated (5-7) 2-D hydrogen bonded sheets (2-7) and unhydrated hydrogen bonded columns (8-10). The R44(12) ring appears in almost all of the structures (except 4) and is consistently observed in all the unhydrated compounds. In the hydrate versions of these salts, different hydrogen bonded rings are observed in addition to the R44(12) ring. There is an indication that the extra symmetry elements possible with a heterochiral solution compared to a homochiral solution mixture have an effect on the symmetry of the final hydrogen bonding motif as observed previously in ammonium carboxylate salts. If the center of inversion is absent, the cations have to find alternative ways to efficiently close pack in the structures, thereby leading to high Z′′ structures by taking several molecular conformations.29 By combining the results of the six unhydrated ammonium sulfonates together with the 35 ammonium sulfonate structures extracted from the Cambridge Structural Database, one can conclude that the dominant hydrogen bonded ring motif formed by ammonium and sulfonate groups consists of the twelve membered R44(12) ring, provided the crystal structures do not contain any water molecules. In the process of investigating the characteristic hydrogen bonding motifs in primary ammonium sulfonates, an unexpected visual effect was observed that again illustrates the link between science and art that occurs in molecular graphics.30

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(4)

(5) (6) (7)

(8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)

(22) (23)

(24)

Supporting Information Available: Crystallographic information. This material is available free of charge via the Internet at http:// pubs.acs.org.

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