Architectural diversity and elastic networks in hydrogen-bonded host frameworks: From molecular jaws to cylinders

Published on Web 11/07/2007

Architectural Diversity and Elastic Networks in

Hydrogen-Bonded Host Frameworks: From Molecular Jaws to

Cylinders

Matthew J. Horner,^§K. Travis Holman,^‡and Michael D. Ward*^,†

Contribution from the Department of Chemistry and the Molecular Design Institute, New York

UniVersity, 100 Washington Square East, New York, New York 10003-6688, and the Department

of Chemistry, Georgetown UniVersity, Washington, D.C. 20057

Received June 7, 2007; E-mail: mdw3@nyu.edu

Abstract: Guest-free guanidinium organomonosulfonates (GMS) and their inclusion compounds display a

variety of lamellar crystalline architectures distinguished by different “up-down” projections of the

organomonosulfonate residues on either side of a two-dimensional (2D) hydrogen-bonding network of

complementary guanidinium ions (G) and sulfonate moieties (S), the so-called GS sheet. Using a

combinatorial library of 24 GMS hosts and 26 guest molecules, a total of 304 inclusion compounds out of

a possible 624 possible host-guest combinations were realized, revealing a remarkable capacity of the

GMS hosts to form inclusion compounds despite the facile formation of the corresponding guest-free

compounds and the absence of “predestined” inclusion cavities like those in related guanidinium

organodisulfonate host frameworks. The GS sheets in the inclusion compounds behave as “molecular

jaws” in which organomonosulfonate groups projecting from opposing sheets clamp down on the guest

molecules, forming ordered interdigitated arrays of the host organic groups and guests. Both the guest-

free and inclusion compounds display a variety of architectures that reveal the structural integrity of two-

dimensional GS sheet and the unique ability of these hosts to conform to the steric demands of the organic

guests. Certain GMS host-guest combinations prompt formation of tubular inclusion compounds in which

the GS sheet curls into cylinders with retention of the 2D GS network. The cylinders assemble into hexagonal

arrays through interdigitation of the organosulfonate residues that project from their outer surfaces,

crystallizing in high-symmetry trigonal or hexagonal space groups. This unique example of network curvature

and structural isomerism between lamellar and cylindrical structures, with retention of supramolecular

connectivity, is reminiscent of the phase behavior observed in surfactant microstructures and block

copolymers. The large number of host-guest combinations explored here permits grouping of the inclusion

compound architectures according to the shape of the guests and the relative volumes of the organo-

monosulfonate groups, enabling more reliable structure prediction for this class of compounds than for

molecular crystals in general.

solid-state structure.^3,4This has prompted the development of

empirical guidelines for steering molecular assembly into

Introduction

The delicate and noncovalent nature of intermolecular forces

responsible for packing in molecular crystals often frustrates

solid-state design, which in turn limits the synthesis of functional

materials. Computational methods for complete crystal structure

prediction, including space group, lattice parameters, and atomic

positions, continue to improve, but the lattice energy of different

calculated forms of the same compound can differ by as little

as a few kJ mol^-1, making an unambiguous assignment of the

lowest energy structure difficult.^1,2Indeed, the complexity of

crystal packing forces has been compared to that of protein

folding, and even the most innocent structural modification to

a molecular constituent can lead to a completely unanticipated

prescribed crystal architectures based on well-defined structure-

directing interactions, such as hydrogen bonding or metal

coordination, which can override the cumulative effect of the

multitude of weaker forces, such as van der Waals interactions.

In this manner, lattice architectures often can be anticipated from

the symmetry of the molecular building blocks and the propaga-

tion of bonding between the structure-directing groups. Although

empirical guidelines rarely lead to complete and precise structure

prediction, architectures based on supramolecular networks that

are robust toward the introduction of ancillary groups can permit

systematic and rational manipulation of solid-state structure.^5-13

(3) Dunitz, J. D. Chem. Commun. 2003, 545.

^§Ph.D. thesis, University of Minnesota.

^‡Georgetown University.

(4) Dunitz, J. D.; Scheraga, H. A. Proc. Natl. Acad. Sci. U.S.A. 2004, 102,

14309.

^†New York University.

(5) (a) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N.; Chae, H. K.; Eddaoudi, M.;

Kim, J. Nature 2003, 423, 705. (b) Rowsell, J.; Millward, A.; Park, K.;

Yaghi, O. M. J. Am. Chem. Soc. 2004, 126, 5666.

(1) Gavezzottti, A. Acc. Chem. Res. 1994, 27, 309.

(2) Dunitz, J. D.; Gavezzotti, A. Angew. Chem. Int. Ed. 2005, 44, 1766.

9

14640

J. AM. CHEM. SOC. 2007, 129, 14640-14660

Hydrogen-Bonded Host Frameworks

A R T I C L E S

Figure 1. (A) The 2-D sheet formed by hydrogen bonds between the

complementary guanidinium (G) ions and organosulfonates (S). (B) A

typical GS sheet as viewed along the ribbon direction, illustrating the

conformational flexibility of the hydrogen-bonded GS network that leads

to accordion-like puckering in lamellar architectures.

Figure 2. Schematic representations of (A) guest-free GMS bilayer

architecture, (B) guest-free GMS simple continuously layered (s-CL)

architecture, (C) GDS inclusion compound with the discrete bilayer

architecture, and (D) GDS inclusion compound with the simple brick

architecture. The organic groups in the GMS s-CL and GDS simple brick

frameworks have identical “up-down” projection topologies on each GS

sheet (see Figure 5).

Our laboratory has reported a series of crystalline materials

based on guanidinium cations (G ) (C(NH₂)₃⁺) and the

sulfonate moieties of organomonosulfonates (S ) R-SO₃^-) or

organodisulfonate anions (S ) ^-O₃S-R-SO₃^-). The threefold

symmetry and hydrogen-bonding complementarity of the G ions

and S moieties prompt the formation of a two-dimensional (2D)

quasi-hexagonal hydrogen-bonding network (Figure 1), which

has proven to be remarkably robust toward the introduction of

various organic pendant groups attached to the sulfonate

moieties. The resilience of the GS network simplifies crystal

design and synthesis by constraining the crystal packing in two

dimensions so that the remaining third dimension can be

engineered reliably through the introduction of interchangeable

organic groups. The guanidinium organomonosulfonates (GMS)

assemble through interdigitation of the sulfonate organic groups

that project from the surfaces of the GS sheets,^14-18commonly

forming either a bilayer or simple continuously layered (s-CL)

architecture,¹⁹depending on the cross-sectional area of the

organic group (Figure 2A,B). Guanidinium organodisulfonates

(GDS) assemble via organodisulfonate “pillars” that connect

opposing GS sheets, thus enforcing inclusion cavities in the

gallery regions between adjacent GS sheets (Figure 2C,D).²⁰

GDS compounds have been found to exhibit numerous frame-

work architecturessdiscrete bilayer, simple brick, double brick,

zigzag brick, V-bricksas a consequence of templating by the

guests during assembly of the crystal lattice.^21-23

The GS sheet has been observed for a wide range of organic

substituents in GMS compounds and numerous pillar-guest

combinations in GDS compounds. Its extraordinary persistence

can be attributed to (i) the ionic character of the N-H‚‚‚O-S

hydrogen bonding, (ii) an inherent structural compliance of the

GS sheet (through puckering), (iii) the availability of an

alternative “shifted ribbon” motif in which GS ribbons are joined

by only a single N-H‚‚‚O-S hydrogen bond between the

cations and anions, and (iv) access to multiple architectural

isomers, the last three features permitting efficient packing of

a variety of organic components.²⁴In the case of GDS inclusion

compounds, the reliability of the GS sheet as a supramolecular

building block has permitted systematic modification of the host

frameworks, enabling control of crystal symmetry, lattice

metrics, and the design of functional materials.^25-28

(6) MacDonald, J. C.; Dorrestein, P. C.; Pilley, M. M.; Foote, M. M.; Lundburg,

J. L.; Henning, R. W.; Schultz, A. J.; Manson, J. L. J. Am. Chem. Soc.

2000, 122, 11692.

(7) Paraschiv, C.; Ferlay, S.; Hosseini, M. W.; Bulach V.; Planeix, J.-M. Chem.

Commun. 2004, 2270.

(8) Ferlay S.; Hosseini, M. W. Chem. Commun. 2004, 788.

(9) Palacin, S.; Chin, D. N.; Simanek, E. E.; MacDonald, J. C.; Whitesides,

G. M.; McBride, M. T.; Palmore, G. T. R. J. Am. Chem. Soc. 1997, 119,

11807.

(10) Aakeroy, Christer B.; Beatty, Alicia M.; Leinen, Destin S. CrystEngComm

2000, 145.

(11) Zaworotko, M. J. Chem. Commun. 2001, 1.

(12) Hoffart, D. J.; Dalrymple, S. A.; Shimizu, G. K. H. Inorg. Chem. 2005,

44, 8868.

A preliminary study in our laboratory revealed the unexpected

formation of GMS inclusion compounds, even though inclusion

(13) Wang, X.-Y.; Justice, R.; Sevov, S. C. Inorg. Chem. 2007, 46, 4626.

(14) Russell, V. A.; Etter, M. C.; Ward, M. D. J. Am. Chem. Soc. 1994, 116,

1941-1952.

(15) Russell, V. A.; Etter, M. C.; Ward, M. D. Chem. Mater. 1994, 6, 1206-

1217.

(20) Russell, V. A.; Evans, C. C.; Li, W.; Ward, M. D. Science, 1997, 276,

575-579.

(21) Swift, J. A.; Pivovar, A. M.; Reynolds, A. M. J. Am. Chem. Soc. 1998, 24,

5887.

(22) Swift, J. A.; Reynolds A. M.; Ward, M. D. Chem. Mater. 1998, 10, 4159.

(23) Holman, K. T.; Martin, S. M.; Parker, D. P.; Ward, M. D. J. Am. Chem.

Soc. 2001, 123, 4421.

(24) Architectural isomerism is a term used to describe framework isomers

having identical composition and supramolecular connectivity (e.g., the

H-bonded GS sheet) but different connectivity patterns in the third

dimension owing to the different up-down configurations.

(16) Burke, N. J.; Burrows, A. D.; Mahon, M. F.; Teat, S. J. CrystEngComm

2004, 6, 429.

(17) Burrows, A. D.; Harrington, R. W.; Mahon, M. F.; Teat, S. J. Eur. J. Inorg.

Chem. 2003, 1433.

(18) Katho´, A.; Be´nyei, A. C.; Joo´, F.; Sa´gi, M. AdV. Synth. Catal. 2002, 344,

278.

(19) The s-CL architecture previously was denoted only as CL because no other

architecture had yet been discovered. The discovery of the new architectures

described herein, however, demand a more definitive nomenclature.

9

J. AM. CHEM. SOC. VOL. 129, NO. 47, 2007 14641

A R T I C L E S

Horner et al.

ated tubular inclusion compounds (TICs) in which guest-filled

cylinders, constructed from the quasihexagonal GS motif,

organized into hexagonal arrays through interdigitation of the

organic groups projecting from the outer surface of each cylinder

(Figure 3B). This behavior contrasts with GDS inclusion

compounds, which can form only lamellar structures. Further-

more, the TICs crystallized in hexagonal space groups, which

are rare among molecular crystals. This lamellae-cylinder

isomerism, which results from curvature of the elastic GS sheet

with retention of its supramolecular connectivity, is unusual for

molecular crystals, resembling more the structural isomerism

often associated with “soft matter” surfactant assemblies and

block copolymers.^31-35

Figure 3. Schematic representations of the GMS s-CLIC and TIC

architectures. Guest molecules (g) are included in the framework cavities.

The TICs contain guest molecules within and between the cylinders.

The persistence of the GS network for different organosul-

fonates offers a rare opportunity for comprehensive and sys-

tematic examination of the relationship between framework

architectures and the molecular components. We describe herein

GMS inclusion compounds, prepared from libraries of 24

benzenesulfonates and 26 guest molecules. Although all of the

GMS compounds readily form guest-free phases, 304 inclusion

compounds out of a possible 624 were realized, revealing a

remarkable capacity of GMS compounds for guest inclusion.

In addition to the s-CLIC and TIC forms, these libraries pro-

duced several new architectures, some with topologies identical

to those observed in the GDS compounds. The host architectures

can be grouped into sectors on a “structural phase diagram” on

the basis of simple molecular parameters, enabling more reliable

cavities in these compounds are not predestined, as they are in

the GDS frameworks. Certain GMS-guest combinations gener-

ated a lamellar architecture, denoted as a simple continuously

layered inclusion compound (s-CLIC),²⁹in which the organo-

monosulfonates adopted a projection topology identical to that

of the guest-free s-CL compounds but with guests confined

between the organic groups of the organomonosulfonates (Figure

3A).³⁰The GS sheets in these inclusion compounds can be

viewed as “molecular jaws” in which organomonosulfonate

groups projecting from opposing sheets close around the guest

molecules. Surprisingly, some host-guest combinations gener-

Scheme 1

9

14642 J. AM. CHEM. SOC. VOL. 129, NO. 47, 2007

Hydrogen-Bonded Host Frameworks

A R T I C L E S

structure prediction for this class of compounds than for

molecular crystals in general.

Results and Discussion

Molecular Libraries. Crystalline guest-free GMS compounds

and GMS inclusion compounds were prepared from a library

of 24 organomonosulfonates, which were chosen to span a range

of sizes and shapes (Scheme 1). Crude GMS salts were first

prepared by combining acetone solutions of guanidinium

tetrafluoroborate and a select organomonosulfonic acid, which

produced a crystalline precipitate of the corresponding white

or off-white guest-free GMS compound. Single crystals of the

guest-free GMS compounds for all 24 organomonosulfonates

in Scheme 1 were obtained either by slow cooling or slow

evaporation (at room temperature) of saturated methanol solu-

tions. Except for guest-free G4SBBS, which formed extremely

thin plates that diffracted poorly, these procedures produced

crystals suitable for single-crystal X-ray diffraction. GMS

inclusion compounds with the general formula GMS•n(guest)

were prepared either by slow cooling or evaporation of methanol

solutions of a particular GMS compound and a guest selected

from Scheme 1. Inclusion compounds of guests that were liquids

at room temperature (guests 1-24) could be grown at the

interface between the liquid guest and a methanol solution of a

GMS salt. Guest 27, 1,4-di-tert-butylbenzene, is included in

Scheme 1 even though its inclusion was examined only with

respect to G4TBBS•(27), which was discovered during attempts

to prepare guest-free G4TBBS (27 was a minor impurity in

4TBBS owing to its presence in the tert-butylbenzene starting

material). The combination of the 24 organomonosulfonates and

26 arene guests in Scheme 1 (i.e., excluding guest 27)

corresponds to 624 unique host-guest combinations.

Figure 4. (A) Guest-free GMS bilayer G4BBS (PT-I) and (B) s-CL G4IBS

(PT-II) as viewed down the GS ribbon axes (top) and perpendicular to the

GS sheets (bottom). The G ions and S oxygen atoms in the GS sheets have

been removed in the bottom panels to reveal the packing of the organic

groups. M denotes the major ribbon direction.

determined here (Supporting Information, Table S1) reinforce

the role of the size and shape of the organomonosulfonate group

in crystal architecture. For convenience, the description of the

structures of these guest-free compounds, as well as nine

previously reported ones, have been grouped into four categories

according to the number, position, and size of substituents

attached to the arene ring of the organomonosulfonate: (A) H,

F, CH₃, Cl, Br, I substituents on the para position; (B) bulky

substituents (ethyl, isopropyl, sec-butyl, tert-butyl, methoxy,

nitro) on the para position; (C) CH₃, F, and Cl on the ortho and

meta positions; (D) multiple methyl substituents. This grouping

also is used later for the corresponding inclusion compounds

(crystallographic details reported in Table S1 pertain to new

guest-free GMS compounds only).

Guest-Free GMS Compounds. Guest-free GMS compounds

previously reported by our laboratory (44 total) crystallized

predominantly in layered structuressthe bilayer and s-CL

architecturessenforced by the GS sheet (39 of 44).^14,15Orga-

nomonosulfonate substituents with larger cross-sectional areas

favored formation of the s-CL architecture, which creates more

area on the GS sheet, compared with the bilayer, enabling

interdigitation of larger organic groups. The 15 new structures

(25) Holman, K. T.; Pivovar, A. M.; Swift, J. A.; Ward, M. D. Acc. Chem. Res.

2001, 34, 107.

(26) Although the GS sheet has proven remarkably robust, it can be disrupted

by strong hydrogen-bonding substituents on the organomonosulfonate or

organodisulfonate components that compete for the (guanidinium)N-H and

sulfonate(S-O) binding sites, see: Russell, V. A.; Etter, M. C.; Ward, M.

D. Chem. Mater. 1994, 6, 1206. Consequently, components of this type

generally are avoided. Although rare, the quasihexagonal GS motif also

can be disrupted by large numbers of dispersive contacts between the

organic components, as observed in G^.SO₃-(C₆H₄)(CH₂)₁₃CH₃), for which

alkyl-alkyl packing requirements compete with the hydrogen bonds of

the quasihexagonal sheet, see: Martin, S. M.; Yonezawa, J.; Horner, M.

J.; Macosko, C. W.; Ward, M. D. Chem. Mater. 2004, 16, 3045.

(27) Pivovar, A. M.; Holman, K. T.; Ward, M. D. Chem. Mater. 2001, 13, 3018.

(28) Holman, K. T.; Pivovar, A. M.; Ward, M. D. Science 2001, 294, 1907.

(29) The s-CLIC architecture previously was denoted as simply CLIC in ref 41

because no other lamellar architecture for GMS inclusion compounds had

yet been discovered. The discovery of the new architectures described herein

demands a more definitive nomenclature.

Group A: Para-Substituted Benzenesulfonates. Guest-free

GBS, G4CBS, G4MBS, and G4BBS crystallized in the bilayer

architecture with the quasihexagonal GS sheet, as depicted here

for G4BBS (Figure 4; a summary of key structural features for

the guest-free GMS compounds is included in Table 1). Using

a classification scheme described for organodisulfonate pillars

in GDS compounds,²³the quasihexagonal GS sheet can be

described as consisting of one “major” (M) and two “minor”

(m) ribbons, and the “up-down” projections of the organomono-

sulfonate groups from the two sides of the GS sheet can be

represented on a “projection topology” diagram as filled or open

circles (Figure 5; up ) filled circles, down ) open circles).

Because the GS sheet is infinite in two dimensions, the number

of possible “up-down” arrangements of organosulfonate groups

is indefinite. The bilayer architecture has a projection topology

(PT) in which the organic groups on each sheet project from

the same side; thus, all the sulfonate nodes are decorated with

filled circles (PT-I).

(30) Horner, M. J.; Holman, K. T.; Ward, M. D. Angew. Chem., Int. Ed. 2001,

40, 4045.

(31) Whitten, T. A.; Pincus, P. A., Structured Fluids: Polymers, Colloids,

Surfactants; Oxford University Press: Oxford, England, 2004.

(32) Seddon, J. M.; Hogan, J. L.; Warrender, N. A.; Pebay-Peyroula, E. Prog.

Colloid Polym. Sci. 1990, 81, 189.

(33) (a) Luzzati, V. In Biological Membranes; Chapman, D., Ed.; Academic

Press: London, 1968; Vol. 1, pp 71-123. (b) Biochim. Biophys. Acta 1990,

1031, 1.

(34) Matsen, M. W.; Bates, F. S. J. Chem. Phys. 1997, 106, 2436.

(35) Bates F. S.; Frederickson, G. H. Phys. Today 1999, 52 (2), 32.

9

J. AM. CHEM. SOC. VOL. 129, NO. 47, 2007 14643

A R T I C L E S

Horner et al.

Table 1. Selected Structural Features for GMS Guest-free Compounds Exhibiting the Bilayer (BL), Opposed Cylinder (LC), Simple

Continuously Layered (s-CL), Double Bilayer (DL), and Double Continuously Layered (d-CL) Architectures

b

c

d

c

space

group

L_sulf

V_sulf

V_host

d

ring offset^e

(Å)

arene

packing^f

arene

−

arene

V_cell

compound^a

(Å)

(Å³)

architecture

(Å)

dihedral angle^g

(Å³)

θ_IR

PF

Group A

GBS

P2₁/c

Pnma

6.74

7.26

8.06

8.33

8.67

118

124

136

140

141

168

174

186

190

191

BL

LC

BL

s-CL

11.64

0.14

HB

54.4°

263

268

292

295

299

288

169.7°

0.67

0.65

0.64

0.66

G4FBS

G4CBS

G4MBS

G4BBS

G4IBS

NA^h

0.2, 0.4

1.0, 1.7

1.2, 1.7

1.6, 2.1

1.1

58.0°, 35.0°

56.2°, 70.4°

50.3°, 71.0°

55.0°, 73.2°

0° ^l

176.2°

173.7°

174.2°

175.1°

69.2°

12.72

12.80

13.00

11.26

Group B

G4EBS

G4IPBS

G4TBBS

G4AS

G4NBS

Ama2

Pbca

P2₁/c

Ama2

P2₁/c

8.93

8.82

8.75

8.08

147

166

182

145

146

197

216

232

195

196

s-CL(p)^l

DBL

10.92

23.79

11.06

13.75

10.35

10.51

1.4

2.7

1.7

1.7, 2.6

1.0

FTF

HB

FTF

HB

0°

293

365

335

310

284

267

72.7°

180°

172.9°

75.0°

NA^k

0.67

0.59

0.69

0.63

0.69

0.73

81.0°, 81.6°

zz-CL(A)

NA^j

BL

70.7°, 72.2°

0°

72.5°

s-CL(p)^l

disrupted

1.4

Group C

G2FBS

G3FBS

G2CBS

G3CBS

G2MBS

G3MBS

C2/c

P1h

6.68

6.67

6.70

6.65

6.63

125

126

133

132

134

132

175

176

183

182

184

182

BL

s-CL

10.60

10.97

11.48

11.57

8.16

0.8

0.4

0.7

1.0

1.1

1.3

FTF

0°

269

256

270

274

284

285

180°

103.0°

92.2°

0.65

0.69

0.68

0.67

0.65

0.64

P1h

Pnma

8.71

Group D

G2,4DMBS

G2,5DMBS

G3,4DMBS

G2,3,4TMBS

G2,4,5TMBS

G2,4,6TMBS

Pmc2₁

Pnma

7.76

6.62

7.76

7.77

152

151

166

167

172

202

201

216

217

222

d-CL

s-CL

12.06

8.31

9.35

10.02

9.26

10.46

1.5

1.0

1.8

2.6

2.0

1.9

FTF

0°

313

297

295

323

326

333

70.2°, 141.4°

0.64

0.68

0.70

0.67

0.66

104.0°

72.7°

91.8°

101.0°

83.6°

b

^aCompounds in italics have been reported previously. L_sulfrepresents the length of the organomonosulfonates as measured from the center of the sulfur

c

atom to the most distant atom, accounting for its van der Waals radius of the distant atom. V_sulfrepresents the molecular volume of the organomonosulfonates

as calculated with Connolly surfaces in the Cerius²environment. V_hostrepresents the sum of V_sulfand the volume of the guanidinium ion. V_cellcorrespond

to one GS formula unit. ^dd is calculated as one-half of the unit cell constant in the direction normal to the GS sheet, which represents the lamella thickness

in the bilayer architecture and the interplaner GS sheet distance in the remaining architectures. ^eLateral offset of arene rings projecting from opposing GS

sheets (see Figure 5). Entries with two values signify two crystallographically unique pairs of arene rings projecting from opposing sheets. In the case of

G4FBS, the first entry corresponds to the offset of the arene rings inside the cylinder and the second to the offset of arene rings between the cylinders. ^fFTF

) face-to-face, HB ) herringbone. ^gAngle measured between mean planes of adjacent arene groups on adjacent organomonosulfonates. ^hThe value of d

for G4FBS is not applicable because the GS sheet is not lamellar. ⁱThe arene rings were modeled as face-to-face in the structure solution; however, there

was sufficient electron density, out of the plane of the arene ring, to indicate slight herringbone character. ^jThe arene-arene dihedral angle for G4TBBS

k

is not applicable because the bulky isopropyl group prevents close packing of adjacent rings. q_IRis not applicable because the GS sheet is discontinuous.

^ls-CL(p) denotes simple continuously layered in a polar space group.

The bilayer topology creates narrow channels on the surface

of each sheet that can be filled by organic groups from the

opposing sheet, provided the organic groups are sufficiently

small to allow interdigitation. In the case of GBS, G4CBS,

G4MBS, and G4BBS, the aromatic groups on opposing sheets

form interdigitated arrays with a herringbone motif (denoted in

Table 1 as HB), which is observed in crystals of small arenes.³⁶

The in-plane lattice constants for these compounds are nearly

identical, GBS ) 7.50, 12.06 Å; G4CBS ) 7.44, 12.33 Å;

G4MBS ) 7.42, 12.44 Å, and G4BBS ) 7.42, 12.39 Å,

reflecting the structure-enforcing metrics of the GS sheet and

the similar footprint areas of the arene rings. The organomono-

sulfonate arene rings in each of these compounds are tilted

somewhat with respect to the direction perpendicular to the

sheet, which forces the sulfonate groups to rotate slightly out

of the mean plane of the GS sheet. Consequently, the metrics

of a strictly planar GS sheet appear to be slightly incompatible

with optimum packing of the organic groups but not to the extent

that the GS sheet loses its quasihexagonal connectivity.

length (L_sulf, as measured from the sulfur atom to the para

substituent, including its van der Waals radius; Table 1). Because

of steric interactions between the para substituents and the

opposing GS sheet, an increase in L_sulfis necessarily ac-

companied by an increasing offset (Figure 6) of the interdigitated

arene rings in the order GBS ) 0.14 Å < G4CBS ) 1.0, 1.7

Å < G4MBS ) 1.2, 1.7 Å < G4BBS ) 1.6, 2.1 Å (pairs of

values reflect crystallographically unique pairs of arene rings).

An increase in the arene offset, which reduces the intermo-

lecular overlap between the arene rings on opposing GS sheets,

would be expected to reduce the stability of the interdigitated

bilayer. This offset apparently reaches a stability limit for 4IBS,

as G4IBS adopts the s-CL architecture (PT-II) rather than a

more expanded bilayer. The GS sheets in G4IBS are highly

puckered, which permits 4IB rings on opposing sheets in G4IBS

to achieve a ring offset of 1.1 Å.³⁷This value is comparable to

those observed for the G4MBS and G4CBS bilayer structures,

suggesting recovery of the cohesive intermolecular forces

required for crystallization. The accordion-like puckering is

The lamellar thickness, d , for the bilayer compounds in group

(37) Although the structure solution portrays adjacent iodobenzene rings as

coplanar, the large isothermal parameters of the arene carbons suggest that

the arene groups are slightly disordered on two positions indicating a degree

of herringbone character between organic groups from opposing GS sheets.

A increases monotonically with increasing organomonosulfonate

(36) Gavezotti, A.; Desiraju, G. R. J. Chem. Soc., Chem. Comm. 1989, 621.

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14644 J. AM. CHEM. SOC. VOL. 129, NO. 47, 2007

Hydrogen-Bonded Host Frameworks

A R T I C L E S

vs 2.90 Å), but still within acceptable limits for hydrogen

bonding. The internal volume of the cylinders is occupied by

one-third of the fluorobenzene groups. The remaining 4FB

groups projected outward from the cylinders, which assemble

into layers by interdigitation. Consequently, the projection

topology of G4FBS is CPT-I in Figure 5 (C denotes cylinder,

in order to distinguish the topology from the lamellar forms).

The structural characterization of numerous GS compounds has

revealed that the spacing between sulfonate groups along the

GS ribbon is effectively immutable, with an average value of

d_S‚‚‚S) 7.5 ( 0.2 Å, ideal for interdigitation of groups from

opposing ribbons. Indeed, the respective distances between the

centroids of the intracylinder and intercylinder fluorobenzene

rings in G4FBS is 3.72 Å, effectively equivalent to d_S‚‚‚S/2 (ca.

3.75 Å). Consequently, d_S‚‚‚Simposes an upper limit on the

number of fluorobenzene rings that can project into the cylinder

(the open circles in the topology diagram in Figure 5). Moreover,

because the GS cylinder contains an even number of ribbons,

the fluorobenzene groups on the two opposing ribbons naturally

are shifted by d_S‚‚‚S/2, producing the registry required for

interdigitation. The asymmetric projection topology of the

cylindersstwo 4FB rings inward and four outwardsresults in

a rhomboid morphology instead of the perfectly cylindrical

morphology observed for the TIC architecture (see below).

Group B: Benzenesulfonates with Bulky Para Substitu-

ents. Guest-free GMS compounds with benzenesulfonates

having bulky para substituents adopted architectures unlike those

observed for the compounds in group A. Previous work in our

laboratory^38,39revealed a polar s-CL architecture (PT-II) for

G4EBS and R-G4NBS, both crystallizing in space group

Ama2,⁴⁰resembling the orthorhombic polar frameworks ob-

served for GDS inclusion compounds with “banana-shaped”

pillars.⁴¹The GS sheets in G4EBS and R-G4NBS adopt the

quasihexagonal motif and are highly puckered (θ_IR) 72.7° and

75.0°, respectively; Figure 8). The organic groups from adjacent

layers are stacked face-to-face (denoted FTF in Table 1) with

centroid-to-centroid distances of 3.72 Å, as prescribed by the

intraribbon d_S‚‚‚S/2 value. As a consequence of the puckering,

the long axes of the 4EB and 4NB groups are oriented along

the polar c-axis, forming angles of 46.8° and 47.3° with respect

to the c axes. The ethyl groups in G4EBS are directed toward

the V-shaped nook of the puckered GS sheet and one oxygen

atom on each of the nitro groups in G4NBS forms a weak

hydrogen-bonding contact with the guanidinium cations (Figure

8).

Figure 5. Projection topologies (PT) for GS sheets observed in the guest-

free and guest-inclusion architectures. The projected topologies are denoted

by Roman numerals, and architectures containing these topologies are listed

below each example. Filled and open circles depict organic groups projecting

from the sulfonate nodes above and below the sheet, respectively. The G

ions sit on the undecorated nodes of the hexagonal tiling. PT-I illustrates

the major ribbon (M) and minor ribbons, m(1) and m(2). The parallelograms

depict the translational repeat unit of each sheet. The loops sketched on

the cylindrical projection topologies (CPT-I and CPT-II) denote hydrogen-

bonded fusion of the edges of the GS ribbons at the top and bottom of

each diagram, which results in formation of cylinders enclosed by a

continuous guanidinium-sulfonate network. Key for acronyms: s-CL )

simple continuous layered; s-CLIC ) simple continuous layered inclusion

compound; d-CL ) double continuous layered; d-CLIC ) double continuous

layered inclusion compound; zz-CL ) zigzag continuous layered; zz-CLIC

) zigzag continuous layered inclusion compound (two versions); TIC )

tubular inclusion compound.

substantial (θ_IR) 69°), reflecting the small volume of the

iodobenzene group compared with the amount of free volume

available in a hypothetical unpuckered s-CL architecture, which

can be discerned from a comparison of the bilayer s-CL

projection topology diagrams. Puckering reduces the free volume

and allows denser packing of the organic groups. In the case of

G4IBS, the 4IB groups are canted along the direction perpen-

dicular to the major ribbons (that is, perpendicular to the pleats

of the accordion), producing edge-to-edge contacts between

adjacent 4IB groups that create channels on the GS sheet. These

channels become occupied by the 4IB groups from the opposing

sheet.

Guest-free G4FBS adopts a unique and unexpected archi-

tecture consisting of layers of discrete rhomboid cylinders

(Figure 7). Each cylinder consists of six GS ribbons fused edge-

to-edge, closing to form a continuous surface with the quasi-

hexagonal motif, that is, the same hydrogen-bond connectivity

observed in the GMS bilayer and s-CL architectures. The d_N...O

hydrogen-bond distances connecting the corners at the acute

ends of the rhomboid are slightly longer than the typical values

for the quasihexagonal GS sheet (d_N...O) 3.044 and 3.112 Å

Guest-free G4IPBS adopted a new architecture, a “double

bilayer”, which contained structural features of both the discrete

(38) Martin, S. M.; Yonezawa, J.; Horner, M. J.; Macosko, C. W.; Ward, M.

D. Chem. Mater. 2004, 16, 3045.

(39) Russell, V. A.; Etter, M. C.; Ward, M. D. Chem. Mater. 1994, 6, 1206.

(40) During the course of these studies, a second polymorph of G4NBS was

discovered, hereafter denoted as â-G4NBS that crystallized in the cen-

trosymmetric P2₁/c space group. The guanidinium ions and sulfonate

moieties in â-G4NBS adopt an uncharacteristic motif in which the strongest

hydrogen bonds between guanidinium ions and the sulfonate moieties

(d_{N-H‚‚‚O}< 2.1 Å) wind about the a axis like a helix, effectively forming

bridges between opposing rows of 4NBS molecules. Inspection of the crystal

structure also reveals short contacts between the nitro oxygen atoms and

the guanidinium nitrogen atoms (3.04 Å), which interfere with the formation

of the quasihexagaonal hydrogen-bonding motif and compensate for the

subsequent loss of some of the N-H‚‚‚O(sulfonate) hydrogen bonds. The

arene rings on adjacent assemblies interdigitate through edge-to-face

interactions, resulting in formation of a layered architecture. The arene offset

value for â-G4NBS is slightly larger (1.5 Å) than that of R-G4NBS (1.0

Å), but within the range observed for the guest-free GMS compounds.

(41) Holman, K. T.; Pivovar, A. M.; Ward, M. D. Science 2001, 294, 1907.

9

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A R T I C L E S

Horner et al.

Figure 6. Increasing the size of para substituents, rendered as van der Waals spheres for (A) GBS and (B) G4BBS, increases the separation between

opposing GS sheets for guanidinium para-substituted benzenesulfonates. The crystal structure of the s-CL architecture in G4IBS, as viewed normal to the

(C) ab and (D) ac planes. Dense packing of the p-iodobenzene groups is achieved through puckering of the GS sheets, which maintain their quasihexagonal

connectivity. Two of the iodine substituents are rendered as van der Waals spheres. The puckering allows the p-iodobenzene groups to recover a 1.1 Å ring

offset, which is typical of the bilayer compounds.

Figure 8. Guest-free R-G4NBS, which adopts a polar s-CL architecture

(PT-II). The center panel depicts a view perpendicular to the GS sheets,

where the G ions and S oxygen atoms in the GS sheets have been removed

to reveal the packing of the organic groups. The right panel is a schematic

representation of the compound. M denotes the major ribbon direction.

Figure 7. Guest-free G4FBS, which adopts an opposed-cylinder archi-

tecture (projection toplogy cylinder I). The left panel depicts the view along

the GS ribbons. The center panel depicts the view perpendicular to the GS

sheets, where the G ions and S oxygen atoms in the GS sheets have been

topology PT-IV, generating an architecture identical to that

observed in zz-CL(IV) compounds. Because only one-half of

the organic groups project from each side of the center sheet,

the zigzag channels can accommodate two outer-sheet 4IPB

groups for each IPB group on the center sheet. The PT-IV

topology is an “egg-carton-like” puckering of the GS sheet

instead of the accordion-like puckering observed in the s-CL

architecture (PT-II); the latter is allowed only if the organic

substituents project from the same side along a major ribbon.

Guest-free G4TBBS adopted yet another new architecture

in which hydrogen-bonded quasihexagonal GS “rafts” stacked

continuously along the b-axis through interdigitation of the bulky

4TBB groups projection from opposing sheets, which adopted

removed to reveal the packing of the organic groups. The right panel is a

schematic representation of the G4FBS compound. M denotes the major

ribbon direction.

bilayer and s-CL architectures (Figure 9). Although this is the

only example to date of a mixed topology in a single GMS

compound, the same topology was reported recently for

[C(NH₂)₂(NHMe)][1-naphthalenesulfonate].⁴²The two outer

sheets in G4IPBS exhibit the PT-I bilayer topology, with all

of the 4IPB groups projecting toward the interior. The 4IPB

groups on the center GS sheet form zigzag channels with

(42) Burke, N. J.; Burrows, A. D.; Mahon, M. F.; Warren, J. E. CrystEngComm

2006, 8, 931.

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A R T I C L E S

G2FBS, which crystallized in the monoclinic C2/c space group,

exhibits an ABAB stacking of discrete bilayers; that is, the A

and B bilayers are crystallographically distinct. The 2FBS rings

from opposing sheets formed interdigitated face-to-face arrays

within each bilayer, but the arene rings in bilayer A were rotated

by 90° with respect to the arene rings in bilayer B. This unusual

ordering between apparently disconnected bilayers signals subtle

structure-directing contacts between GS sheets of adjacent

bilayers. Despite molecular volumes that are nearly identical

with their chloro-substituted homologues, methyl-substituted

G2MBS and G3MBS crystallized in the s-CL architecture (PT-

II). The GS sheets were highly puckered (θ_IR) 103° and 92.2°,

respectively), which reflects the small volume of the organic

groups relative to the amount of space available in the s-CL

lattice. The arene rings from opposing sheets form face-to-face

stacks, again reflecting the frustration of edge-to-face ordering

by the ortho and meta substituents.

Group D: Multiply Methyl-Substituted Benzenesulfonates.

Guest-free G2,5DMBS, G3,4DMBS, G2,3,4TMBS, G2,4,

5TMBS, and G2,4,6TMBS adopted highly puckered s-CL

architectures (PT-II) with quasi-hexagonal GS sheets, with θ_IR

ranging from 72.7° for G3,4DMBS to 104° for G2,5DMBS

(Figure 11). The lamellae were assembled by face-to-face stack-

ing of interdigitated arene rings with interplanar spacing of 3.72

Å. In contrast, the G2,4DMBS adopted a new architecture,

double CL (d-CL), with the PT-III topology (Figure 5), identical

to that observed in the GDS continuous “double brick”

framework.²³The puckering of the GS sheet in G2,4DMBS is

more complex than for s-CL forms as it exhibits two distinct

puckering angles. This characteristic adds yet another degree

of flexibility to the GS sheet so that packing can be optimized

for these sterically encumbered organosulfonates. Indeed, the

packing fraction for G2,4DMBS (PF ) 65%) is comparable

with all other s-CL structures in this and groups A-C (PF )

67%-68%). The wide ranges of puckering angles and ring offset

values for this group (G2,4DMBS ) 1.5 Å, G2,5DMBS ) 1.0

Å, G3,4DMBS ) 1.8 Å, G2,3,4TMBS ) 2.6 Å, G2,4,5TMBS

) 2.0 Å, and G2,4,6TMBS ) 1.9 Å) reflect the different steric

demands of the organomonosulfonate groups.

Figure 9. Guest-free GMS compounds: (A) G4IPBS, which exhibits the

double bilayer (DBL) architecture in which the top and bottom sheets adopt

PT-I and the inner sheets adopt topology IV. (B) G4TBBS, which adopts

a ladderlike architecture in which rafts having the zigzag PT-IV stack

continuously but are truncated by serpentine ribbons that span the gallery

separating the rafts. The center panels depict views perpendicular to the

GS sheets, where the G ions and S oxygen atoms in the GS sheets have

been removed to reveal the packing of the organic groups. In the case of

the G4IPBS, the perpendicular view depicted corresponds to the sheet in

the center of the double bilayer. M denotes the major ribbon direction. The

bottom panels are schematic representations.

Structural Trends. The discovery of several new lamellar

architectures for guest-free GMS compounds, realized by

varying the sizes and shapes of the organic groups, reveals the

inherent ability of these compounds to optimize packing while

retaining the hydrogen-bond connectivity of the quasihexagonal

GS sheet and the overall lamellar organization. The persistence

the GS sheet, which is uncharacteristic of the organic solid state,

can be attributed to several factors: (i) the large number of

hydrogen bonds, which are further enforced by the ionic charge

of the constituents; (ii) the ability of the 2D sheet to access

different projection topologies, which provides a mechanism

for accommodating the steric demands of the organic groups;

(iii) the compliant character of the GS network, which allows

accordion-like puckering in the s-CL and d-CL architectures

so that dense packing of the organic constituents can be achieved

with retention of the quasi-hexagonal connectivity. This low-

energy deformation of the GS network occurs with preservation

of the linearity of the N-H‚‚‚O(sulfonate) hydrogen bonds. If

the GS network was rigid, dense packing would not be

achievable and it is likely that either crystallization would not

occur or that non-lamellar structures with disrupted GS sheets

PT-IV (Figure 9B). The edges of the rafts are truncated

serpentine GS ribbons that coincide with the a-axis and span

the thickness of the gallery region, generating a ladderlike archi-

tecture. Water molecules bridge the edges of the raft and

the serpentine ribbon through linear (ribbon)S-O‚‚‚H(water)

O‚‚‚H-N(raft) hydrogen bonds (Figure 9). The projection of

the 4TBB groups on each serpentine ribbon alternates, up, down,

up, down, ..., permitting interdigitation of the 4TBB groups

projecting from the GS rafts.

Group C: Ortho- and Meta-Substituted Benzenesulfonates.

The halogen-substituted GMS compounds G2FBS, G3FBS,

G2CBS, and G3CBS adopted bilayer architectures (PT-I;

Figure 10). G3FBS, G2CBS, and G3CBS are isostructural, all

crystallizing in the same space group (P1h) with similar in-plane

lattice parameters. The groups projecting from opposing sheets

form interdigitated arrays with the arene rings stacked face-to-

face, reflecting frustration of the edge-to-face (C-H‚‚‚π)

approach due to the ortho and meta substituents. Surprisingly,

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A R T I C L E S

Horner et al.

Figure 10. Guest-free GMS compounds with ortho and meta substituents: (A,B) G2CBS and G2FBS, which both adopt the a bilayer architecture (PT-I).

G2FBS, however, displays an ...ABAB... stacking in which adjacent bilayers are crystallographically distinct. (C,D) G2MBS and G3MBS, which both

adopt the s-CL architecture (PT-II). The bottom panels depict views perpendicular to the GS sheets, where the G ions and S oxygen atoms in the GS sheets

have been removed to reveal the packing of the organic groups. M denotes the major ribbon direction.

Figure 11. Guest-free GMS compounds with multiple methyl substitutions: (A) Double continuously layered (d-CL) G2,4DMBS, which adopts projection

topology PT-III; (B, C) G2,5DMBS and G2,3,4TBBS, which both adopt the s-CL architecture with the PT-II topology. The top panels depict side views

along the major ribbon axes. The bottom panels depict views perpendicular to the GS sheets, where the G ions and S oxygen atoms in the GS sheets have

been removed to reveal the packing of the organic groups. The interribbon puckering angles (θ_IR) are given in the upper panels. M denotes the major ribbon

direction.

would form. Notably, polymorphism does not appear to be

common for guanidinium organosulfonate compounds. With the

exception of G4NBS, no polymorphs were detected by X-ray

powder diffraction for the guest-free compounds derived from

the library in Scheme 1.

One consequence of the robustness of the GS frameworks is

the emergence of predictable relationships between certain

structural parameters, which can be gleaned only when the

number of isostructural compounds available is statistically

meaningful. We previously demonstrated that the puckering of

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Hydrogen-Bonded Host Frameworks

A R T I C L E S

Figure 12. Metric relationships between select structural parameters for guest-free GMS compounds with the s-CL architecture: (A) P exhibits a linear

dependence on sin (θ_IR/2), as expected from simple solid geometry. The dashed line represents the ideal dependence based on eq 1. The solid line represents

a least-squares fit for the s-CL GMS compounds (the open square, which corresponds to G3,4DMBS, is not included in the fit). The slope is 12.0 Å, which

is slightly less than the value expected from eq 1, and the regression coefficient is R ) 0.99. The values of P are approximately 0.5 Å less than the expected

value in the region of interest here, but this can be attributed to an effective ribbon width that is smaller than the assumed value of 6.5 Å. (B) The dependence

of P on V_sulf/L_sulf, which provides an approximation of the “footprint” of the organomonosulfonates on the GS sheet surface. (C) The dependence of d

,obs

the lattice spacing perpendicular to the GS sheet, on the length of the organomonosulfonates. (D) Comparison of d

2b, assuming φ ) 90 - θ_IR/2, which is valid when each organosulfonate is perpendicular to its ribbon.

with the values calculated with eq

,obs

the GS sheets in the orthorhombic simple brick architecture of

guanidinium organodisulfonates was well-behaved, to the extent

that b₁, the lattice constant perpendicular to the major ribbons,

decreased monotonically with decreasing puckering angle, θ_IR,

according to the simple algebraic relationship described by eq

1a, in which w is the effective width of a GS ribbon (6.5 Å).

Furthermore, the lattice constant perpendicular to the sheets,

c₁, conformed to eq 2a, in which l is the length of the

organodisulfonate pillar and φ its angle of tilt with from a normal

to the GS sheet.

Similar trends emerge from the 10 guest-free GMS com-

pounds that crystallize in the s-CL architecture, for which the

variables P (the generic lattice constant perpendicular to the

major ribbons), d (the distance between the centers of adjacent

lamellae), and L_sulf(the sulfur-to-end length of the organosul-

fonate) correspond to b₁, c₁, and l in the simple brick

architecture, respectively (eqs 1b, 2b). The linear dependence

of P on sin(θ_IR/2) (Figure 12A) reveals that the puckering-

induced contraction of the lattice along P is well behaved and

occurs without any substantial contributions from other structural

distortions.⁴³The effect of steric factors is demonstrated further

L_sulf(Figure 12B), a quantity that is dimensionally equivalent

to the “footprint” of the organosulfonate group on the opposing

GS sheet (V_hostis the combined volume of a particular

organomonosulfonate ion and a guanidinium ion; the guani-

dinium ion has a volume of 50 Å³). Figure 12C reveals that d

increases with L_sulfas expected. Figure 12D displays the

comparison between the observed d values and those calculated

using eq 2b, wherein φ is not actually measured but is assigned

the value φ ) 90 - θ_IR/2, which is valid when each organo-

monosulfonate is perpendicular to its GS ribbon, as is generally

the case. Although some scatter exists, the anticipated trend is

apparent. One noteworthy feature is the somewhat larger-than-

expected observed values of d , which probably can be attributed

to inefficient packing of the organic substituents in the pockets

of the puckered sheets.

b₁) 2w sin(θ_IR/2) Å ) 13.0 sin(θ_IR/2) Å

P ) 2w sin(θ_IR/2) Å ) 13.0 sin(θ_IR/2) Å

c₁) 13.0 cos(θ_IR/2) + 2l cos φ Å

(1a)

(1b)

(2a)

(2b)

d ) 6.5 cos(θ_IR/2) + L_sulfcos φ Å

by the monotonic increase of θ_IRwith increasing values of V_host

/

GMS Inclusion Compounds. The facile formation of guest-

free GMS compounds for every example in the host library of

Scheme 1 would seem to make formation of inclusion com-

pounds unlikely, as GMS compounds are not “predestined” to

include guests. Nonetheless, an earlier study in our laboratory

(43) The data reveal a slightly reduced slope (12.0 Å instead of 13.0 Å) and a

small reduction of the actual P values (ca. 0.5 Å) compared with that

expected from eq 1b. This minor discrepancy reflects a slight displacement

of the sulfur atoms from the ribbon edges. Convenience and accuracy, q_IR

,

is measured using discrete sulfur atoms on adjacent ribbons. Equation 1a

and 1b rigorously hold only when θ_IRis defined by the intersection of the

mean planes of two adjacent ribbons.

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A R T I C L E S

Horner et al.

Table 2. Selected Structural Features of Guest Molecules and GMS Inclusion Compound Architectures for Organomonosulfonates in Group

A. (entries shaded in gray represent combinations for which only guest-free GMS compounds crystallized in the presence of the respective

guests)

^aV_sulfrepresents the molecular volume of the organomonosulfonates as calculated with Connolly surfaces in the Cerius²environment. V_hostrepresents the

b

sum of V_sulfand the volume of the guanidinium ion. V_guestrepresents the molecular volume of the guest as calculated with Connolly surfaces in the Cerius²

c

environment. L_guestrepresents the length of the guest molecule as measured between the two most distal atoms, accounting for the van der Waals radius.

^dThe guest eccentricity, e_guest, was calculated by dividing the maximum length by the molecular width, including van der Waals radii. The host/guest

stoichiometries are 1:0.67 (CIC), 1:0.5 and 1:1 (sCLIC), and 1:0.5 (d-CLIC). s-CLIC(||) and s-CLIC( ) denote subclasses of the s-CLIC architecture in

which the inclusion channels are parallel and perpendicular to the major ribbons, respectively.

produced a small number of GMS-based inclusion compounds

with the s-CLIC and TIC frameworks (Figure 3).³⁰The limited

number of examples, however, precluded evaluation of the

factors responsible for the formation of these architectures,

prompting a search for new inclusion compounds based on the

libraries in Scheme 1. Of the 624 possible host-guest combina-

tions, 304 inclusion compounds were obtained in crystalline

form. In cases for which inclusion was not observed, the

expected guest-free compounds crystallized (i.e., identical to

those described in the previous section), with no detectable

amounts of other polymorphs by powder X-ray diffraction. Fully

refined structures were determined for 42 of these compounds:

18 from our preliminary study and 24 new ones reported here

(Table S2). The unit cells were determined for 15 additional

compounds. X-ray powder diffraction analysis of compounds

for which structures were fully refined or unit cells were

obtained did not detect any polymorphs. Using these structure

determinations as a basis, the architectures of most of the

remaining compounds could be assigned through a combination

of thermogravimetric analysis and ¹H NMR (determination

of host/guest stoichiometry) and optical microscopy (identifica-

tion of crystal habit, which was characteristic of the archi-

tecture). No polymorphs appear to be present for these

compounds, although the possibility of small amounts cannot

be entirely excluded. The inclusion compounds are described

below according to the classification used for the guest-free

compounds.

Group A: Para-Substituted Benzenesulfonates. GBS,

G4FBS, G4CBS, G4MBS, G4BBS, and G4IBS formed 131

inclusion compounds out of 156 possible host/guest combina-

tions in Scheme 1 (Table 2). Single-crystal XRD afforded

satisfactory structural characterization for 41 of the 131 inclusion

compounds. An additional 10 compounds were characterized

by unit cell determinations. The GMS compounds with the larger

halogen substituents, G4CBS, G4BBS, and G4IBS, formed

inclusion compounds with nearly all 26 guests; only the G4IBS-

isopropylbenzene combination failed to produce an inclusion

compound. The halogenated host with the smallest L_sulfvalue,

G4FBS, did not form inclusion compounds with some of the

larger guest molecules, specifically n-propylbenzene (12), N,N-

dimethyl-3-nitroaniline (25), and 4-(dimethylamino)benzonitrile

(26). GBS and G4MBS did not include benzene, toluene,

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A R T I C L E S

Figure 13. Photograph of single crystals of G4BBS‚(m-xylene), G4BBS‚

0.5(tert-butylbenzene), G4BBS‚0.67(o-xylene) and G4TBBS‚0.67(benzene),

which adopted the s-CLIC, d-CLIC, TIC, and zz-CLIC(V) architectures,

respectively. Crystals of the zz-CLIC(IV) and zz-CLIC(V) have identical

morphologies. Although crystals of d-CLICs and TICs grow as needles,

the cross sections for the d-CLICs were rectangular, while the TICs were

hexagonal. The long axes of the s-CLIC, d-CLIC, and TIC crystals were

always parallel to the major GS ribbon axis. Following single-crystal

structure determinations for a sufficient number of compounds with each

architecture, most of the GMS inclusion compounds could be identified by

crystal morphology, with corroboration by TGA (s-CLIC, monoclinic habit

and either 1:1 or 1:0.5 host/guest stoichiometry; d-CLIC, needle habit with

rectangular cross section and 1:0.5 host/guest stoichiometry; TIC, needle

habit and 1:0.67 host/guest stoichiometry; zz-CLIC(IV), hexagonal-like

plates and 1:0.67 host/guest stoichiometry: zz-CLIC(V), hexagonal-like

plates and 1:0.5 host/guest stoichiometry).

ethylbenzene, n-propylbenzene, and n-butylbenzene molecules.

Indeed, the GBS host, which has the smallest L_sulfvalue in this

series, was highly discriminating, forming lamellar inclusion

compounds only with guests having volumes within the range

110 Å³< V_guest< 135 Å³.

The reduced occurrence of inclusion compounds for hosts

with small L_sulfvalues is not entirely unexpected. The GS sheets

of the GMS host framework can be viewed as “molecular jaws,”

in which organosulfonate groups projecting from opposing

sheets close around the guest molecules. Guests that are large

relative to L_sulfwould tend to obstruct the approach of opposing

sheets, thereby inhibiting intermolecular overlap between the

organic components (host and guest) and reducing the cohesive

energy required for crystallization. Under these conditions,

formation of the guest-free compounds would become preferred.

Interestingly, the aforementioned guest-free G4BBS, which

exhibits the largest arene offset value of the guest-free bilayer

compounds in group A, forms inclusion compounds with the

largest range of guests. The large arene offset of G4BBS

suggests this is the least stable of the guest-free bilayer

compounds in this group, which would favor inclusion com-

pound formation.

The majority of the inclusion compounds in group A adopted

the s-CLIC architecture (84 of 131) for a surprisingly broad

range of guest sizes and shapes. This architecture is constructed

from the projection topology PT-II, identical to the guest-free

s-CL architecture. Single-crystal structures and unit-cell deter-

minations were used to verify the s-CLIC architecture for 31

of these compounds, which always grew as well-defined

monoclinic plates. These were distinguished easily from the

crystal habits exhibited by the other framework architectures

(Figure 13), enabling confident assignment of the remaining

53 compounds on the basis of crystal morphology alone. The

host/guest stoichiometries, which were either 1:0.5 or 1:1 for

the s-CLICs, were consistent with these assignments.

Figure 14. GMS inclusion compounds: (A) G4BBS‚(toluene) and (B)

G4BBS‚(m-xylene) which adopted the s-CLIC architectures (PT-II) with

inclusion channels aligned parallel and perpendicular to the major ribbon,

respectively. Top and center panels depict side views parallel and transverse

to the major ribbons, respectively. The bottom panels depict views

perpendicular to the GS sheets, where the G ions and S oxygen atoms in

the GS sheets have been removed to reveal the packing of the organic

groups. In the upper and center panels, the host framework is depicted as

wire-frame and the included guests as space-filled. In the lower panels the

hosts and guests all are depicted as space-filled, but the guests are rendered

with darker shading.

The s-CLIC framework assembled by interdigitation of

organosulfonate groups from opposing GS sheets and guest

molecules in the galleries. The PT-II topology creates channels

on each sheet that are occupied by the organosulfonate groups

from the opposing sheet, but yet are sufficiently large for

inclusion of guest molecules as well (Figure 14). Of the s-CLICs

characterized by single-crystal XRD, the channels are oriented

either parallel or perpendicular to the major ribbon, the former

occurring more often. In the parallel mode, interdigitated

organomonosulfonate groups from opposing GS sheets exhibit

edge-to-face contacts and form the walls of channels occupied

by guests, which in turn adopt edge-to-face arrangements among

themselves and with the organomonosulfonate groups. In the

perpendicular mode, the channel walls consisted of interdigitated

organomonosulfonate groups from opposing GS sheets arranged

face-to-face, and guests organize face-to-face along the channel,

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A R T I C L E S

Horner et al.

but the guests adopted edge-to-face arrangements with the

organomonosulfonate groups.

A “double continuously layered inclusion compound” (d-

CLIC) was observed in 18 of the 131 inclusion compounds in

Group A. This architecture is constructed from projection

topology PT-III, identical to the guest-free d-CL architecture.

Single-crystal structures and unit cell determinations were used

to verify the d-CLIC architecture for nine of these compounds,

and the remaining nine compounds were assigned as d-CLICs

by inspection of the crystal morphology, which was quite distinct

(well-defined needles with rectangular cross sections; Figure

13). This architecture, which was limited to the bulkier guest

molecules, displays a projection topology identical with the

guest-free d-CL. Assuming a flat GS sheet, this configuration

creates channels on each sheet surface that are twice as wide

as the channels in the s-CLIC form, enabling interdigitation of

organosulfonate groups from adjacent sheets with sufficient

space remaining for the inclusion of even larger aromatic guests

(Figure 15). Puckering of the sheets creates U-shaped pockets

that are occupied by the bulky substituents (n-propyl, n-butyl,

i-propyl, tert-butyl, sec-butyl) of the guests. Like the guest-

free d-CL compounds, the d-CLIC puckering is defined by two

puckering angles.

The topology of the d-CLIC architecture is the same as the

GDS “double brick” architecture, which has been observed for

only three GDS compounds.²¹The greater number of GMS

d-CLIC compounds suggests that the absence of covalent

connections between the GS sheets relaxes the constraints for

puckering and structural registry between the sheets, thereby

facilitating formation of the U-shaped cavities that accommodate

bulky guest molecules. Because the host volumes of the s-CLIC

and d-CLIC architectures are identical for a given organomono-

sulfonate, their total inclusion cavity volumes are identical as

well. Consequently, the host/guest stoichiometry of the d-CLICs,

which was favored by large guests, was always 1.0:0.5 rather

than the 1:1 value observed for most of the s-CLICs.

Figure 15. GMS inclusion compounds (A) G4CBS‚0.5(butylbenzene) and

(B) G4BBS‚0.5(butylbenzene), which both adopt the d-CLIC architecture

with projection topology PT-III. The top and center panels depict side views

parallel and transverse to the major ribbons, respectively. The bottom panels

depict views perpendicular to the GS sheets, where the G ions and S oxygen

atoms in the GS sheets have been removed to reveal the packing of the

organic groups. In the top and center panels, the host framework is depicted

as ball-and-stick and the included guests as space-filled. In the lower panels

the hosts and guests all are depicted as space-filled, but the guests are

rendered with darker shading. The inter-ribbon puckering angles (θ_IR) are

given in the top panels.

Whereas GDS inclusion compounds are naturally restricted

to lamellar architectures because of the covalent connections

between adjacent sheets, the GMS hosts are not subject to this

constraint. Certain host-guest combinations afforded morpho-

logically distinct needles, with hexagonal cross-sections and

often 2 cm long, during crystallization at the interface of a

methanol solution containing the host components and neat guest

(Figure 16). The habit of these crystals reflects the formation

of TICs, in which the GS sheet curls into a cylinder consisting

of six GS ribbons organized in the same quasihexagonal motif

as the lamellar architecture (Figure 17). The organic groups

attached to the sulfonate nodes project outward from the surface

of each cylinder, generating the topology CPT-II (Figure 5).

Interdigitation of these groups produces hexagonal arrays of

cylinders, crystallizing in trigonal or hexagonal space groups

(P3h or P6₃/m). The cylinders can be viewed as puckered with

θ_IR) 120°, but with constant curvature instead of the accordion-

like puckering of the lamellar architectures (negative curvature

in the parlance of surfactant microstructures). The internal

“pore” diameter, measured from the centers of atoms on opposite

side of the cylinder, is slightly less than 12 Å, corresponding

to an actual diameter of approximately 8.5-9 Å. Group A

organomonosulfonates form TICs quite readily (41 of the 131

inclusion compounds).

Each cylinder of the TICs contains uniformly spaced guest

molecules stacked face-to-face along the length of the cylinder

with an interplanar spacing of 3.72 Å. This value is equivalent

to one-half the intraribbon sulfonate-sulfonate distance (d_S‚‚‚

^S/2) and signifies commensurate ordering of the guest molecules

along the cylinder axis. The guests, however, exhibit 3-fold

rotational disorder about the cylinder axis. Analysis of the

residual electron density revealed that one-half of the guests

are contained within the cylinders, as expected from the

commensurate stacking (two guest molecules traverse the width

of a band of six GS units along the cylinder axis). The remaining

guest molecules are located in the interstices between the

cylinders, resulting in the overall stoichiometry GMS‚2/3(guest).

The formation of the TIC architecture is somewhat surprising

given that nonpolar guests are included inside cylinders with

polar walls, suggesting commensurism and guest-guest interac-

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A R T I C L E S

Figure 16. Snapshots of the crystallization of the TIC G4CBS‚²/₃(o-xylene) at the interface of a methanol solution, which contains the host components,

and neat o-xylene. Rapid crystal growth was observed after a long induction time (the needle axis coincides with the long axes of the tubes).

Figure 17. The tubular inclusion compound G4BBS‚²/₃(o-xylene): (A) model illustrating the quasihexagonal hydrogen bond connectivity of the GS network,

which comprises six GS ribbons and forms the surface of the cylinder; (B) space filled rendering of a single cylinder, illustrating the outward projection of

the 4BBS groups and the roughly 8 Å tube diameter; (C) view perpendicular to the cylinder axis, illustrating the commensurism between the o-xylene guests

(3.72 Å interplanar spacing) and the GS cylinder (d_S‚‚‚S) 7.44 Å). The hydrogen atoms of the guests and all but the R-C atoms of the 4BBS molecules are

omitted for clarity. The guanidinium ions are rendered as wireframe for better viewing of the guest molecules.

tions play an important role in the stability of these compounds.

The inclusion of nonpolar guests in polar channels is not without

precedent, however, as evidenced by the numerous examples

of urea inclusion compounds formed with alkane guests.⁴⁴

The most notable feature of the TICs is the tendency to

incorporate disk-shaped guests, that is, guests with a low

eccentricity (ꢀ)⁴⁵and volumes within the range 110 Å³< V_guest

< 143 Å³(see below). The only exceptions were N,N-

dimethylaniline and ethylbenzene, which have eccentricities of

ꢀ ) 1.44 and 1.47, respectively. Interestingly, 11 of the 41 host-

guest combinations that produced the TIC architecture afforded

the s-CLIC architecture, albeit with different stoichiometries.

This suggests that the TICs and CLICs have similar lattice

energies.

Group B: Para-Substituted Benzenesulfonates with Bulky

Substituents. G4EBS, G4AS, G4NBS, G4IPBS, G4SBBS, and

G4TBBS formed 115 inclusion compounds out of 156 possible

host/guest combinations based on the libraries in Scheme 1

(Table 3). Single-crystal structures were obtained for 14 of the

115 inclusion compounds, with an additional 7 characterized

by unit cell determination. Single-crystal XRD and crystal

morphology revealed that the G4EBS, G4AS, and G4NBS hosts

adopted the s-CLIC architecture (PT-II) nearly exclusively. The

lone exception was G4EBS·2/3(ethylbenzene), which adopted

the TIC form (CPT-II).

Interestingly, the hosts with the bulkiest organosulfonates

from this groupsG4IPBS, G4SBBS, G4TBBSsincluded guests

readily, producing 76 inclusion compounds out of a possible

78 combinations. Most of these inclusion compounds, however,

did not form crystals suitable for single-crystal XRD or unit-

cell determination (crystals were either too thin or diffracted

poorly). Nonetheless, single-crystal XRD of a few compounds

in this group, combined with morphology analysis and TGA,

(44) Hollingsworth, M. D.; Harris, K. D. M. In ComprehensiVe Supramolecular

Chemistry; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Vo¨gtle, F.,

Suslick, K. S., Eds.; Elsevier: Oxford, 1996; Vol. 6, pp 177-237.

(45) The eccentricity is a measure of the shape of a given guest molecule and

is defined by the ratio of the maximum length to minimum width. Guest

with an eccentricity of 1.0 are round disks such as benzene, while an

eccentricity of 1.44 are ellipses such as ethylbenzene.

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Table 3. Selected Structural Features of Guest Molecules and GMS Inclusion Compound Architectures for Organomonosulfonates in

Groups B-D. (entries shaded in gray represent combinations that did not form inclusion compounds, such that only guest-free GMS

compounds crystallized)

^aV_sulfrepresents the molecular volume of the organomonosulfonates as calculated with Connolly surfaces in the Cerius²environment. V_hostrepresents the

b

sum of V_sulfand the volume of the guanidinium ion. V_guestrepresents the molecular volume of the guest as calculated with Connolly surfaces in the Cerius²

c

environment. L_guestrepresents the length of the guest molecule as measured between the two most distal atoms, accounting for the van der Waals radius.

^dThe guest eccentricity, e_guest, was calculated by dividing the maximum length by the molecular width, including van der Waals radii. Lam refers to crystalline

inclusion compounds that have lamellar architecture (s-CLIC, d-CLIC, zz-CLIC), but for which an unambiguous assignment was not possible. The host/

guest stoichiometries are 1:0.67 (TIC), 1:0.5 and 1:1 (s-CLIC), 1:0.5 (d-CLIC), 1:0.67 (zz-CLIC(IV)), and 1:0.5 (zz-CLIC(V)). s-CL(p) denotes simple

continuously layered in a polar space group.

permitted assignment of the framework architectures, which

included s-CLIC (PT-II) and two new “zigzag” forms. G4IPBS‚

0.67(3,4-dimethylanisole) and G4IPBS‚0.67(p-xylene), for which

single-crystal structures were determined, adopted the zz-CLIC-

(IV) architecture with the PT-IV topology. In contrast, the

crystal structure of G4TBBS‚0.25(1,4-di-tert-butylbenzene)

revealed a PT-V topology with different projection sequences

along the minor ribbons. The PT-V topology in this kind of

inclusion compound, denoted zz-CLIC(V), contains inclusion

cavities that can accommodate the shape of the 1,4-di-tert-

butylbenzene guest molecules. The 3,4-dimethylanisole and

p-xylene guest molecules in the zz-CLIC(IV) architecture are

oriented perpendicular to the GS sheet (Figure 18). The length

of the 1,4-di-tert-butylbenzene guest, however, precludes a

perpendicular orientation, requiring larger and differently shaped

cavities that allow the 1,4-di-tert-butylbenzene guest to lay with

its long axis parallel to the GS sheet. The large footprint of the

1,4-di-tert-butylbenzene guest is reflected in its 1:0.5 host/guest

stoichiometry. Only one host-guest combination from this

group, G4IPBS‚0.5(sec-butylbenzene), could be confirmed as

the d-CLIC architecture by single-crystal XRD. The projection

sequence along the major ribbons and the puckering of the GS

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A R T I C L E S

Figure 18. GMS inclusion compounds: (A) G4IPBS‚(3,4-dimethylani-

sole), which adopts the zz-CLIC(IV) architecture with the PT-IV projection

topology. (B) G4TBBS‚(1,4-di-tert-butylbenzene), which adopts the zz-

CLIC(V) architecture with the PT-V topology. The top panels represent

side views parallel to the major ribbons. The bottom panels depict views

perpendicular to the GS sheets, where the G ions and S oxygen atoms in

the upper GS sheet have been removed to reveal the packing of the organic

groups. In the upper panels, the host framework is depicted as ball-and-

stick and the included guests as space-filled. In the lower panels the hosts

and guests all are depicted as space-filled, but the guests are rendered with

darker shading.

Figure 19. GMS inclusion compounds (A) G3MBS‚(p-xylene) and (B)

G2MBS‚0.5(1,2,3,4-tetramethylbenzene), which both adopt the s-CLIC

architecture with the PT-II projection topology. The bottom panels depict

views perpendicular to the GS sheets, where the G ions and S oxygen atoms

in the upper GS sheet have been removed to reveal the packing of the

organic groups. In the upper panels, the host frameworks are depicted as

ball-and-stick and the included guests as space-filled. In the lower panels

the hosts and guests all are depicted as space-filled, but the guests are

rendered with darker shading. θ_IRrepresents the interribbon puckering angle.

The guest disorder in panel B has been removed for clarity.

sheet combine to create U-shaped pockets occupied by the bulky

sec-butyl substituents of the guests.

inclusion compounds with only three guests (p-xylene, 1,2,4-

trimethylbenzene, tert-butylbenzene), each crystallizing in the

s-CLIC architecture. G2MBS and G3MBS, however, form 36

inclusion compounds out of a possible 52 combinations. The

single-crystal structures of G2MBS‚(1,2,3,4-tetramethylbenzene)

and G3MBS‚(p-xylene) revealed the s-CLIC architecture (Figure

19). Unlike the s-CLIC inclusion compounds in group A (para

substituted organosulfonates), the presence of ortho and meta

substituents obstruct edge-to-face packing of the interdigitated

organosulfonate groups from opposing sheets. Instead, the host

arene rings stack face-to-face to form the walls of channels

oriented parallel with the major ribbon of the s-CLIC topology.

The guest molecules organized as inclined stacks in these

channels, exhibiting edge-to-face packing with the arene rings

of the host.

Unlike all other host-guest combinations, the correlation of

crystal morphology with crystal architecture for G4IPBS,

G4SBBS, G4TBBS inclusion compounds, as determined by

single-crystal XRD, was found to be unreliable. For these three

hosts, the s-CLICs, zz-CLICs, and d-CLICs that could be

characterized by X-ray diffraction crystallized as very thin plates

or clusters of microcrystals. Many crystals were small and poorly

shaped, to the extent that a credible characterization of crystal

morphology was not feasible. This precluded assignment of the

framework architecture for many of the host-guest combina-

tions in this subgroup. These unassigned compounds, which

account for 67 of the 78 possible host/guest combinations from

these three hosts, are designated only as “Lam” (i.e., lamellar)

in Table 3.

Group C: Ortho- and Meta-Substituted Benzenesulfonates.

G2MBS, GMFBS, G2CBS, G3CBS, G2FBS, and G3FBS

formed 39 inclusion compounds out of 156 possible host/guest

combinations based on the libraries in Scheme 1 (Table 3).

Although single-crystal XRD was performed on only two of

the 39 inclusion compounds, G2MBS·(1,2,3,4-tetramethylben-

zene) and G3MBS·(p-xylene), it was apparent from the well-

defined crystal habits that these and the remaining compounds

adopted the s-CLIC architecture (PT-II). The formation of

inclusion compounds with GMS hosts having meta and ortho

substituents on the arenesulfonate rings was sensitive to the

nature of the substituents. The halogenated compounds G2FBS,

G3FBS, G2CBS did not form inclusion compounds, preferring

instead to form their guest-free bilayer phases. G3CBS formed

Group D: Multiply Methyl Substituted Benzenesulfonates.

Of the six GMS compounds in this groupsG2,4DMBS,

G2,5DMBS, G3,4DMBS, G2,3,4TMBS, G2,4,5TMBS, and

G2,4,6TMBSsonly G2,4DMBS and G3,4DMBS formed in-

clusion compounds, and only with a rather small number of

guest molecules from Scheme 1 (19 inclusion compounds of a

possible 156; see Table 3). The reduced ability of this group to

include guests most likely reflects the large volume of the

organosulfonate groups, which could inhibit inclusion by the

host frameworks. Except for p-xylene and 3,4-dimethylanisole,

the guests included by G2,4DMBS and G3,4DMBS were found

to template TIC architectures for the para-substituted benzene-

sulfonates in group A. This indicates that the presence of a

second methyl group on the arenesulfonate is sufficient to

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A R T I C L E S

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Figure 20. Metric relationships between select structural parameters for GMS inclusion compounds with the s-CLIC architecture. (A) Unlike the guest-free

compounds, no discernible trend is observed for the dependence of d on L_sulf. (B) Dependence of d on the combined volume of the organosulfonate and

the guest molecules, tantamount to a swelling of the lamella. The line represents a least-squares fit to all the data. (C) θ_IR(0) and P (9) exhibit no obvious

correlation with the combined volume of the organosulfonate and the guest molecules. (D) Likewise, θ_IR(0) and P (9) are not correlated with the combined

“footprint areas” calculated from V_sulf/L_sulf+ nV_guest/L_guest. (E) P exhibits a linear dependence on sin(θ_IR/2) for most of the GMS s-CLICs, as expected from

eq 1b. The solid line represents a least-squares fit of these variables for the compounds corresponding to the filled squares only. The slope and intercept of

this fit are 13.3 and 0.3 Å, nearly identical to the values expected from eq 1b.⁴⁶(F) A plot of V_host+ nV_guestand V_cellproduces a slope of m ) 0.66, which

represents the average packing fraction for the s-CLICs.

frustrate the formation of the TIC architecture, reflecting rather

stringent requirements for interdigitation-driven assembly of the

cylinders.

molecules also exert an influence on the lamellar spacing,

masking the contribution of L_sulf. On the other hand, the values

of d do exhibit a reasonable correlation with the combined

volume of the host and guests (Figure 20B), signifying an

effective “swelling” of the galleries as the combined volume

of the organic moieties, V_sulf+ nV_guest, is increased. No apparent

Structural Trends. The frequency of inclusion compound

formation decreases in the order group A (131/156) > group B

(115/156) > group C (39/156) > group D (19/156), a trend

that reflects more facile guest inclusion for para-substituted

benzenesulfonates and a reduced tendency for inclusion with

increasing V_sulfand awkwardly shaped organomonosulfonates.

The introduction of ortho and meta substituents clearly frustrates

guest inclusion, as gleaned from the entries on the right side of

Table 3 (guest-free only combinations are shaded gray). The

role of shape was apparent from the large number of inclusion

compounds formed by the para-substituted G4IPBS, G4AS, and

G4TBBS; even though these hosts have large V_sulfvalues, they

readily form lamellar inclusion compounds.

The large number of inclusion compounds that crystallize with

the s-CLIC architecture permits examination of certain metric

relationships in a manner similar to that for the guest-free s-CL

compounds. Unlike the guest-free compounds, however, many

of these metric relationships are not well behaved. For example,

the dependence of d on L_sulf, does not display any discernible

trend (Figure 20A). This is understandable as the guest

correlations between θ_IRor P and either V_sulf+ nV_guestor V_sulf

/

L_sulf+ V_guest/L_guest(the area of the “footprint”) can be gleaned

(Figure 20C, 20D). The most plausible explanation for the poor

correlations between these variables is the absence of any

constraints on orientations of the guest molecules, which are

not appended to the GS sheet. This extra degree of freedom

permits a variety of packing motifs among the organomono-

sulfonates and the guests, to the extent that the puckering angles

cannot be expected to depend on volume alone. Similarly, the

footprint areas deduced from V_guest/L_guestpresumes that the long

axes of the guest molecules are perpendicular to the GS sheet,

which is not observed in all s-CLIC compounds.

Except for a few outliers, the dependence of P on sin(θ_IR/

2), is linear and conforms to eq 1b (Figure 20E). Like the guest-

free s-CL compounds, this indicates that the puckering-induced

contraction of the lattice along P in response to the packing

of the organic components occurs without any substantial

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A R T I C L E S

Figure 21. Structural phase diagram for GMS inclusion compounds using V_sulf/V_guestand ꢀ_guestas independent variables. This plot contains 206 data points

representing unique host-guest combinations. Some of the data points are obscured by overlap. Because the G4IPBS, G4sBBS, and G4TBBS inclusion

compounds could not be assigned to specific lamellar architectures, these are not included in the figure.

contributions from other structural distortions. Unlike the guest-

free compounds, the values of P are nearly identical to those

expected for ideal puckering with a value of 6.5 Å assigned to

the ribbon width. The linearity in Figure 20E does not contradict

the conclusions reached from the data in panels C and D, as P

and sin(θ_IR/2) are linked through the geometric changes in the

lattice as it responds to the packing orientations and volume of

the various organic components. Comparison of Figures 20E

and 12A reveals that the θ_IRvalues are larger overall in the

inclusion compounds (i.e., less puckering) compared with the

guest-free compounds, with some inclusion compounds having

conditions favorable for packing arrangements between the GS

sheets that are superior to those in the guest-free phases, and

(ii) the absence of a covalent connection between the GS sheets,

which removes the constraint of registry between adjacent

sheets, thereby allowing opposing GS sheets to “float” parallel

and perpendicular to the layers so that packing with guest

molecules can be optimized. Perhaps, therefore, it is not

surprising that the proclivity of the GMS compounds for

inclusion rivals that of the GDS hosts. The TIC architecture,

which is not possible for the GDS frameworks, provides an

additional avenue to the formation of GMS inclusion com-

pounds.

θ_IRvalues approaching 180°. This behavior simply reflects the

expansion of the framework to accommodate the extra volume

introduced by the guests. Figure 20F illustrates uniform packing

fractions for a large number of s-CLIC compounds, reflecting

a tendency toward constant packing densities made possible by

puckering of the compliant GS framework and packing freedom

introduced by unrestrained guests.

The extraordinary number of GMS inclusion compounds

derived from a common hydrogen-bonded network creates a

unique, possibly unparalleled, opportunity for systematic ex-

amination of the relationship between the structures of the

molecular components and crystal structure. Using the 206 GMS

inclusion compounds for which framework architectures could

be assigned, a structural “phase diagram” can be constructed

to sort the various architectural isomers according to well-

defined, simple molecular parameters, specifically the sulfonate

volume/guest volume ratio, V_sulf/V_guest, and the guest eccentricity,

ꢀ_guest, both measured readily from molecular models (Figure 21).

The guest eccentricity, defined as the length of the guest divided

by its width after accounting for van der Waals radii, ranges

from ꢀ_guest) 1.0 (benzene) to ꢀ_guest)1.75 (4-ethylnitrobenzene).

The TIC and d-CLIC architectures reside primarily in separate

sectors. The TIC architecture was preferred for guests that are

smaller and disk-shaped, as these fit more comfortably in the

highly symmetric cylinders and are more suitable templates for

the cylindrical geometry. The host-guest combinations produc-

ing the TIC architecture occupy a phase region bounded by 0.8

< V_sulf/V_guest< 1.3 and values between 1.0 < ꢀ_guest< 1.2. Only

N,N-dimethylaniline (20, ꢀ_guest) 1.44), which forms TICs with

G4CBS and G4BBS, and ethylbenzene (11, ꢀ_guest) 1.47), which

forms TICs with G4FBS, G4CBS, G4BBS, and G4IBS, lie

outside the TIC sector.⁴⁷

Architectural Sorting and Soft Matter Correspondence.

Guest-free compounds were observed for every organomono-

sulfonate in Scheme 1. Formation of a GMS inclusion compound

always competes with formation of its corresponding guest-

free phase and, unlike the pillared GDS frameworks, inclusion

cavity formation is not predestined. The formation of 304 out

of 624 possible host-guest combinations therefore seems quite

remarkable. The propensity to form inclusion compounds

certainly can be attributed to the unique ability of the GS sheets

to pucker, effectively enabling a host framework to “shrink-

wrap” about guest molecules so that reasonable packing densities

of the organic host groups and the guests can be achieved.

Furthermore, the GMS hosts can adopt a variety of lamellar

architectures with differently sized and shaped inclusion cavities

that can accommodate a wide range of guests, and rotation about

the C-S bond in the organosulfonate groups permits further

optimization of the host-host and host-guest packing. These

modes of structural adaptability, however, also are available to

the guest-free phases. The principal differences between the

guest-free and inclusion compounds are (i) the presence of

unconstrained guest molecules that are not anchored to the GS

sheet, which can increase the degree of freedom for intermo-

lecular packing among the organic constituents, thereby creating

(46) The open squares are regarded as outliers (G4FBS‚(20); G4BBS‚(4);

G4IBS‚(4); G4IBS‚(20)). If the open squares are included in the least

squares fit, the slope and intercept do not change appreciably (13.2 and

0.4 Å, respectively) but the regression coefficient is reduced from R )

0.94 to R ) 0.69.

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Except for G4EBS‚2/3(ethylbenzene), the TIC architecture

was not observed for organosulfonates in groups B-D. Bulky

substituents on the organomonosulfonate ring (large V_sulf) appear

to frustrate the interdigitation required for intercylinder packing;

this defines the upper boundary of the TIC sector. The s-CLIC

architecture, however, appears across much of the phase

diagram. This can be attributed to the facile puckering of the

s-CLIC framework, which makes this framework sufficiently

pliable to accommodate a broad range of guest molecules. The

s-CLICs are absent, however, for ꢀ_guest> 1.45, at which the

d-CLICs are overwhelmingly favored. The host-guest combi-

nations producing the d-CLIC architecture are located at the

lower right of the diagram, in a sector bounded by 1.4 < ꢀ_guest

< 1.6 and 0.8 < V_sulf/V_guest< 1.2. The five guests that promote

this architecturesn-propylbenzene (12), n-butylbenzene (13),

isopropylbenzene (14), sec-butylbenzene (15), and tert-butyl-

benzene (16)sapparently are unable to fit within the relatively

narrow inclusion channels of the s-CLIC framework or the

relatively small cylinders of the TICs. These examples illustrate

that the d-CLIC framework, with its wider U-shaped channels,

is better able to accommodate larger guest molecules with an

elliptical shape. Overall, Figure 21 reveals that the large number

of host-guest combinations explored here permits grouping of

the inclusion compound architectures according to the shape

of the guests and the relative volumes of the organomono-

sulfonate groups, enabling more reliable structure prediction

for this class of compounds than for molecular crystals in

general.

The isomerism displayed by the various CLICs and TICs is

somewhat reminiscent of “soft matter,”³¹specifically lamellar

and hexagonal cylinder phases observed in aqueous surfactant

assemblies and block copolymers.^32,34,35Distinct polar (i.e., the

GS sheet) and nonpolar (the organosulfonate groups and guest

molecules) regions define the GMS guest-free and inclusion

compounds, similar to the segregation observed in soft matter

microstructures. This correspondence is even more apparent for

guanidinium phenylalkanesulfonates, biphenylalkanesulfonate,

and alkanesulfonates, which are crystalline with lamellar

architectures at room temperature and form smectic liquid crystal

phases upon heating and lamellar organogels in certain organic

solvents.^48-51Like soft matter microstructures, the GMS inclu-

sion compounds are equipped with a well-defined, elastic

interface, the GS sheet, that is common to both the lamellar

and hexagonal architectures. In the case of the TICs, the GS

sheet curls into a closed cylinder, generating a structure that

resembles the H_|inverse hexagonal phases for surfactant

microstructures. Whereas the “lamellar” CLICs can be viewed

as having zero mean curvature and zero Gaussian curvature,

the TICs can be viewed as having negative mean curvature and

zero Gaussian curvature.⁵²As noted by Seddon,³²an inextensible

yet flexible surface (e.g., a sheet of paper) can be deformed

easily into a shape of arbitrary mean curvature, but only if the

Gaussian curvature remains zero. The GS sheet represents a

supramolecular hydrogen-bonded version of this kind of surface,

deforming into a cylinder while the curvature along the cylinder

axis remains zero. The curvature spreads the organic groups on

the outer surface of the cylinder to allow interdigitation of

neighboring cylinders. Finally, the structural phase diagram in

Figure 21 is not unlike soft matter microstructure phase

diagrams, which also are based on relatively simple param-

eters.⁵³The length-scale defining curvature and periodicity in

soft matter is larger, however, typically ranging from tens to

hundreds of nanometers.

Although high-symmetry space groups that demand curvature

(i.e., cubic, hexagonal) are common in soft matter, most small

molecules crystallize in low-symmetry space groups (i.e.,

triclinic, monoclinic). The space group constraints on molecular

crystals can be gleaned from a search of the Cambridge

Structural Database (v5.28, November 2006 release), which

indicated that of 390081 entries, only 4437 (1.1%) were trigonal/

hexagonal and 1895 (0.5%) were cubic. These statistics reflect

the incompatibility between the low point-group symmetry

characteristic of molecules and the special positions in high-

symmetry space groups. This constraint is circumvented in soft

matter because the interface that defines the separation between

the dissimilar components is very elastic and the radii of

curvature are large, to the extent that the supramolecular

aggregates can conform about the high-symmetry special

positions with minimal energetic penalty at the local level. The

symmetry constraints are relaxed further in soft matter because

disordered molecular aggregates sit on special positions. Of the

304 inclusion compounds generated from the libraries in Scheme

1, 42 (14%) crystallized as TICs with trigonal or hexagonal

space-group symmetry. This high frequency of occurrence can

be attributed to soft matter-like elastic character of the GS sheet,

an aggregate of molecules that deforms into cylinders situated

about key special positions⁵⁴in the trigonal or hexagonal

systems. Furthermore, although the GS sheet is crystallographi-

cally ordered, the organosulfonate groups, intracylinder guests,

and intercylinder guests are disordered, which relaxes the

symmetry constraints imposed by 3h, 6h, m, and i special positions.

We note that hexagonal crystal symmetry has been observed

in (H₃O)[V₃O₄)(H₂O)(PhPO₃)₃]‚2.33H₂O, which crystallizes in

the hexagonal P3h space group as cylinders assembled into

hexagonal arrays through interdigitation of phenyl rings that

project from their outer surfaces, not unlike the TIC architecture.

This compound, however, appears to be an isolated example in

a class of compounds that typically exhibit lamellar structures.⁵⁵

The well-documented urea inclusion compounds (UICs) crystal-

(52) The mean and Gaussian curvatures are defined as H ) 1/2(c₁+ c₂) and K

) c₁c₂, respectively, where c₁and c₂are the principal curvatures at a point

on the surface (c₁) c₂) 0 for CLICs; c₁) negative, c₂) 0 for TICs).

(53) Surfactant-water microstructures are governed by the volume (V) of the

hydrophobic chain of the surfactant, the area (a) of the hydrophilic head

group, and the length (l) of the hydrocarbon chain. Block copolymer

microstructures are governed by the immiscibility of the dissimilar segments,

described by the Flory-Huggins parameter ø, the molecular weight N, and

the relative volume fractions of the dissimilar segments, which are presumed

to behave as random coils.

(47) The idealized length of N,N-dimethylaniline and ethylbenzene (9.21 and

9.50 Å, respectively), is somewhat longer than the internal diameter of the

cylinder based on the van der Waals diameter. The single crystal structures

of these compounds, although poorly refined, support the presence of face-

to-face stacks of guest molecules within the cylinder, but the poor

refinement for these structures has prohibited an accurate determination of

the orientation of the aromatic rings or the disposition of the substituents.

(48) Mathevet, F.; Masson, P.; Nicoud, J.-F.; Skoulios, A. Chem. Eur. J. 2002,

8, 2248.

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1

2

1

2

1

or hexagonal space groups P3h, No. 147: 3-fold axis at /₃, /₃, /₄; /₃, /₃,

³/₄; ²/₃, ¹/₃, ¹/₄; ¹/₃, ²/₃, ³/₄and ¹/₃, ²/₃, jz; P6₃/m, No. 176: 6h at ¹/₃, ²/₃, ¹/₄; ²/₃,

¹/₃, ³/₄; ²/₃, ¹/₃, ¹/₄; ¹/₃, ²/₃, ³/₄.

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9

14658 J. AM. CHEM. SOC. VOL. 129, NO. 47, 2007

Hydrogen-Bonded Host Frameworks

A R T I C L E S

lize in hexagonal or near-hexagonal symmetry through the

formation of hydrogen-bonded cylinders,⁵⁶but these do not

display the lamellae-cylinder isomerism exhibited by the GMS

compounds. Perhydrotriphenylene and tris(o-phenylenedioxy)-

spirocyclotriphosphazene form cylindrical host lattices with

hexagonal space group symmetry through van der Waals

interactions,,^57-60as do guest-free phases of various alkoxy-

substituted triphenylenes.⁶¹In these examples, however, the high

space-group symmetry results from propagation of the threefold

point-group symmetry of the molecular constituents, whereas

the trigonal/hexagonal order in the TICs stems from curvature

of the 2D GS network into cylinders of hexagonal symmetry.

The structural resemblance of GMS inclusion compounds to

soft matter lamellar and hexagonal phases prompts the question

of whether concepts of amphiphile segregation, volume fraction

of dissimilar components, curvature, and interfacial tension can

be used, in general, to describe the solid-state structure of

molecular crystals. A structural correspondence between crystal

structures and soft matter microstructures has been invoked for

Ag⁺-based coordination networks, generated from various

polynitrile ligands, which formed cylindrical, perforated layer,

lamellar, gyroid network topologies.^62,63Periodic minimal

surfaces, on which the curvature vanishes on every point on

the surface,⁶⁴have been invoked for inorganic networks

comprising atoms of different sizes, which pack more efficiently

on a curved surface than on a plane.⁶⁵The structure of some

inorganic compounds has been described in terms of periodic

equipotential or zero-potential surfaces.⁶⁶Periodic minimal

surfaces also were invoked for a metal-organic framework that

crystallized in a cubic space group.⁶⁷Constant curvature and

minimal surface concepts invoked in these cases can provide a

convenient way to visualize space partitioning and structural

order,⁶⁸but inorganic and metal-organic networks typically do

not possess deformable elastic interfaces that are the signature

of soft matter microstructures, and the network topologies reflect

the propagation of the local symmetries. Perhaps more interest-

ing in this regard are molecular crystals that assemble through

“soft” and less directional intermolecular forces, such as van

der Waals and hydrogen bonding.⁶⁹Constant curvature surfaces

and polar/nonpolar volume ratios have been used to describe

the structures of various aromatic polyethers, polyalcohols,

aromatic and cyclohexylammonium carboxylates, and ether-

thioethers.⁶³Hydrogen-bond networks and a large unit cell

appear to play a role in the formation of one of only two single-

component compounds with the cubic Ia3hd space group (No.

230).⁷⁰A hydrate of a calix[4]resorcinarene has been reported

to crystallize (with nitrobenzene solvent molecules) in the cubic

I432 space group,⁷¹each unit cell containing an octahedral cubic

spheroid assembled through 60 O‚‚‚H‚‚‚O hydrogen bonds that

produce a structure with “saddle surfaces” of zero mean

curvature and zero Gaussian curvature. Compounds like these

seem to support the notion that high space-group symmetries

are more likely for molecular aggregates assembled by soft

intermolecular interactions, such as hydrogen bonds. Interest-

ingly, lattices constructed from the centers of the atomic

positions of small molecules in low-symmetry space groups

closely resemble hexagonal or cubic close-packed lattices,

suggesting that the packing in many molecular crystals ap-

proaches high space-group symmetry.⁷²This is underscored by

a recent analysis of the CSD and the Protein Data Bank (PDB)

that determined that a plurality of proteins crystallizing in

hexagonal space groups exhibit a c/a ratio of (8/3)^1/2, charac-

teristic of sphere-packing.⁷³

Conclusion

The observation of 304 inclusion compounds out of a possible

624 host-guest demonstrates the remarkable versatility of the

GMS compounds as host materials. Unlike the related guani-

dinium organodisulfonate compounds, inclusion by GMS com-

pounds is not “predestined” as cavities between adjacent sheets

are not enforced by covalent connections provided by the

disulfonate pillars. Instead, the formation of inclusion com-

pounds in GMS hosts relies on collective, noncovalent dispersive

interactions among the arene rings of the hosts and guests,

including host-host, guest-guest, and host-guest interactions.

The GS sheets of the lamellar GMS host frameworks can be

viewed as “molecular jaws,” in which the organosulfonate

groups projecting from opposing sheets close around the guest

molecules. The ubiquity of the lamellar GMS inclusion com-

pounds and their crystal structures suggests that introduction

of guest molecules, which are not anchored to the GS sheet,

reduces packing constraints and facilitates the achievement of

more optimum packing modes, thereby providing an enthalpic

benefit compared with the guest-free phases. The persistence

of the GS network allows a comprehensive examination of the

effect of interchanging hosts and guests in a systematic manner.

The distinction between the GMS and GDS inclusion com-

pounds is most apparent from the formation of the hexagonal

TIC architecture, in which the use of a organomonosulfonate

allows constant curvature into cylinders, which is not possible

for GDS frameworks. To our knowledge, the observation of

lamellar and cylindrical architectures that are related through

curvature by a common elastic 2D network (i.e., the GS sheet)

is unique among molecular crystals. Furthermore, the classifica-

tion of crystal architectures according to simple molecular

variables, though common for soft matter, is rare for molecular

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9

J. AM. CHEM. SOC. VOL. 129, NO. 47, 2007 14659

A R T I C L E S

Horner et al.

Sulfonation of Arenes: Guanidinium 4-Isopropylbenzene-

sulfonate (G4IPBS). Chlorosulfonic acid (10.66 g 1.1 equiv) was added

dropwise to a chloroform solution (100 mL) of isopropylbenzene (10.00

g, 83.20 mmol) over a period of 10 min, and the mixture was stirred

at room temperature for 2 h. The solvent was removed under reduced

pressure to obtain 4-isopropylbenzenesulfonic acid as a brown oil, which

was dissolved in acetone (50 mL). An acetone solution (25 mL) of

guanidinium tetraflouroborate (18.3 g, 1.5 equiv) then was added,

producing guanidinium 4-isopropylbenzenesulfonate as a white crystal-

crystals, suggesting further studies aimed at uniting the behavior

of molecular crystals and soft matter is warranted.

Experimental Section

Materials and Methods. Reagents were used as received from the

following commercial sources: ethylbenzene, anisole, and m-xylene

(Acros Organics); 4-nitrobenzenesulfonic acid (Kodak); chloroform,

methylene chloride, and toluene (Fisher); 1,2,3-trimethylbenzene and

1,2,3,4-tetramethylbenzene (TCI America); benzenesulfonic acid, chlo-

rosulfonic acid, substituted benzenesulfonyl chlorides, starting materials

used to prepare the organosulfonates other than those listed above, and

guests other than those listed above (Aldrich). Methanol, the principal

crystallization solvent, was used as received from Pharmco (ACS grade).

Crude GMS salts were prepared by combining acetone solutions of

guanidinium tetrafluoroborate and a select organomonosulfonic acid,

which produced a crystalline precipitate of the corresponding white or

off-white guest-free GMS compound. Single crystals of the guest-free

GMS compounds for all 24 organomonosulfonates in Scheme 1 were

obtained either by slow cooling or slow evaporation (at room temper-

ature) of saturated methanol solutions. Except for G4SBBS, which

formed extremely thin sheets that diffracted poorly, these procedures

produced crystals suitable for single-crystal XRD analysis. GMS

inclusion compounds with the general formula GMS·n(guest) were

prepared either by slow cooling or evaporation of methanol solutions

of a particular GMS compound and a guest selected from the right

side of Scheme 1. This typically was achieved by dropwise addition

of approximately 0.75 mL of guest to approximately 4 mL of methanol

solution saturated with the GMS salt. This mixture was heated to

dissolve any precipitate that formed, and then cooled to room

temperature, typically producing crystals within 1 day. In cases where

crystals did not appear, the solution was allowed to evaporate slowly

at room temperature, which usually produced crystals of the inclusion

compound within days. Alternatively, inclusion compounds of guests

that were liquids at room temperature (guests 1-24) could be grown

by slow diffusion of a methanol solution of a GMS salt across a layer

of neat methanol covering the neat liquid guest. This method usually

produced high-quality single crystals at the interface of the methanol

solution and liquid guest. The stoichiometries of GMS guest inclusion

compounds were determined by ¹H NMR in DMSO-d₆(Varian INOVA

300 MHz spectrometer) and thermogravimetric analysis (Perkin-Elmer

TGA 7). Crystal morphologies were characterized with an Olympus

stereoscope (SZH10).

Synthetic Procedures. The organomonosulfonates in Scheme 1 were

either available commercially, synthesized by sulfonation of com-

mercially available arenes, or synthesized by hydrolysis of arene

sulfonyl chlorides, depending upon the availability of starting materials.

The syntheses of three representative guanidinium organomonosul-

fonates, each made by one of these approaches, are described here.

The detailed syntheses of the remaining guanidinium salts formed with

the organomonosulfonates in Scheme 1 are provided in the Supporting

Information.

Commercially Available Sulfonic Acids: Guanidinium Benze-

nesulfonate (GBS). Benzenesulfonic acid (7.03 g, 44.44 mmol, Aldrich

90%) was dissolved in acetone (25 mL) and added to an acetone

solution (50 mL) of guanidinium tetrafluoroboric acid (9.79 g, 1.5

equiv). After being cooled in the freezer the precipitate was filtered

and washed with cold acetone to obtain guanidinium benzenesulfonate

as a white crystalline solid (4.07 g, 42.2%). The filtrate was placed in

the freezer overnight, and additional crystalline solid was harvested

(1.12 g)(5.19 g, 53.8% overall); mp 214-218 °C. ¹H NMR (300 MHz,

[D₆]DMSO): δ 7.59-7.63 (m, 2H), 7.31-7.33 (m, 3H), 6.93 (s, 6H).

1

line solid (6.78 g 31.5%); mp 276-280. H NMR (300 MHz, [D₆]-

DMSO): δ 7.49-7.53 (m, 2H), 7.17-7.20 (m, 2H), 6.95 (s, 6H), 2.83-

2.91 (m, 1H), 1.15-1.20 (m, 6H).

Hydrolysis of Sulfonyl Chlorides: Guanidinium 2-Methylben-

zenesulfonate (G2MBS). o-Toluenesulfonyl chloride (5.08 g, 26.65

mmol) was dissolved in a mixture of dioxane (50 mL) and water (50

mL) and heated under reflux for 6 h. The solvent was removed under

reduced pressure to produce 2-methylbenzenesulfonic acid as a brown

oil. The oil was dissolved in 25 mL of acetone and mixed with

guanidinium tetrafluoroboric acid (5.87 g, 1.5 equiv) dissolved in 25

mL of acetone. This mixture was chilled in a freezer, which afforded

a precipitate that was filtered and washed with cold acetone to produce

guanidinium 2-methylbenzenesulfonate as a white crystalline solid (4.39

g, 70.9%); mp 221-224 °C. ¹H NMR (300 MHz, [D₆]DMSO): δ 7.72

(d, 1H), 7.13-7.21 (m, 3H), 6.97 (s, 6H), 2.09 (s, 9H).

Crystallography. Single-crystal X-ray diffraction characterization

was performed in the Department of Chemistry at the University of

Minnesota. Experimental parameters and crystallographic information

pertaining to the single-crystal X-ray analyses are given in Tables S1

and S2 (see Supporting Information). Full structure solutions were

obtained by collecting a hemisphere of data on either Siemens or Bruker

SMART CCD platform diffractometers with graphite monochromated

Mo KR radiation (l ) 0.71073 A) at 173(2) K. The structures were

solved by direct methods and refined with full-matrix least-squares/

difference Fourier analysis using the SHELXTL package (Structure

Analysis Program 5.1; Bruker AXS, Inc.: Madison, WI, 1997). All

non-hydrogen atoms were refined with anisotropic displacement

parameters and all hydrogen atoms were calculated and placed in

idealized positions and refined with a riding model. Data were corrected

for the effects of absorption using the Siemens area detector absorption

program (SADABS). Unit-cell determinations were made by refinement

on three sets of 20 matrix frames. Powder X-ray diffraction analysis

was performed on either a Bruker-AXS (Siemens) D5005 or a Siemens

D500 diffractometer.

Acknowledgment. This work was supported by the National

Science Foundation (Grant DMR-0305278/0720655). The au-

thors thank Victor G. Young, Jr. and William Brennessel of

the X-ray Crystallographic Laboratory in the Department of

Chemistry at the University of Minnesota for assistance with

single-crystal X-ray structural analysis.

Supporting Information Available: X-ray experimental de-

tails in the form of crystallographic information file (CIF);

crystallographic information for 39 new guest-free guanidinium

organomonosulfonates and guanidinium organomonosulfonate

inclusion compounds (Tables S1 and S2). This material is

available free of charge via the Internet at http://pubs.acs.org.

JA0741574

9

14660 J. AM. CHEM. SOC. VOL. 129, NO. 47, 2007

Article Doi

Architectural diversity and elastic networks in hydrogen-bonded host frameworks: From molecular jaws to cylinders

DOI: 10.1021/ja0741574

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Article abstract of DOI:10.1021/ja0741574

Full text of DOI:10.1021/ja0741574

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