- Email: [email protected]
Inclusion compounds
514
Inclusion compounds Mark D Hollingsworth Since late 1994,
significant progress
has been made toward
the design, synthesis, and characterization compounds, properties
of new inclusion
including systems that exhibit guest exchange akin to zeolites, ferroelasticity
(domain reorientation
under applied stress) and selectivity for specific reactions. somewhat
by the difficult (and sometimes
nature of many crystal structures progress
has been fostered
diffraction
equipment
of structure molecular
by recent advances
methods
of the structures
of new
remains an elusive goal that awaits
computational
intermolecular
in X-ray
Just as with single-component
crystals, reliable prediction
more sophisticated
intractable)
of inclusion compounds,
and in the use of combined
determination.
inclusion compounds reliable
chemical
Although efforts in this field have been slowed
techniques
and more
supramolecular assemblies contain more than one kind of molecule, the opportunity for different stoichiometries and sequential patterns presents extra degrees of freedom for the crystal packing arrangement, and requires the inclusion chemist to remove other degrees of freedom from the system by judicious choice of complementary and directional intermolecular contacts. The multitude of energetically feasible packing arrangements and the severe limitations of intermolecular potential functions make it necessary to adopt an empirical approach to the design of new solid phase inclusion compounds. This brand of crystal engineering is often most successful when one recognizes or discovers an existing motif and exploits it in a logical manner.
potentials.
Design of new inclusion compounds Addresses Department of Chemistry, Indiana University, 7th Street, IN 47405, USA; e-mail: [email protected] Current Opinion 1514-521
in Solid State
0 Current Science
Ltd ISSN
& Materials
Science
Bloomington,
1996,
1359-0286
Abbreviations NLO UIC
nonlinear optical urea inclusion compound
Introduction As the field of solid state organic inclusion chemistry has become so diverse, it is impossible for a short review such as this to do justice to the many subfields within this discipline. Instead, I have chosen to focus on certain key aspects of inclusion chemistry, including the intentional design and construction of new systems (including ‘organic zeolites’), the state of the art of crystal structure determination, materials properties, and molecular recognition and reactivity. The field of solution phase inclusion chemistry and molecular recognition has grown tremendously in the past fifteen years, in part because it is ordinarily possible to design a solution phase receptor or complexing agent using simple molecular models or molecular mechanics techniques. The formation of crystalline 1:l molecular complexes follows naturally from the solution phase chemistry (and is often used in conjunction with X-ray crystallography as the principal means of characterization of these complexes). The design of new solid phase inclusion compounds, however, in which the extended structure of the host encapsulates the guest, is a much more formidable task that is often confounded by subtle factors such as packing efficiency, strain and longrange Coulombic interactions. Because these extended
As a result of these difficulties, most solid phase inclusion compounds that are not simple molecular complexes are discovered by accident. Nevertheless, several groups have made significant progress toward designing new inclusion compounds through the use of directed interactions. Work by MacNicol and co-workers [1,2] on ‘hexa-hosts’ has shown that it is possible to adapt common structural topologies used by known inclusion compounds to design new host materials. This same sort of approach has been followed most recently by Wuest [3-j, Moore [4’,5’], Toda [6], Weber [7], Aoyama [8,9*], Atwood [lo], Zimmerman [ 11.1, and their co-workers, among others.
Fioure
1
Formation of a prototypical
diamondoid
construction from a hypothetical with permission from 13.1.
network by supramolecular
molecule
or ‘tecton’
(1). Reproduced
Recent work has shown that it is possible to design inclusion compounds that can act as ‘organic zeolites’, that is, systems that retain the essential features of their solid structures during exchange of guest molecules. Following earlier work by Ermer et a/. [12,13*] on
Inclusion compounds
diamondoid hosts formed by adamantanetetracarboxylic acid (Fig. l), Wuest and co-workers have used the persistent Rzz(8) hydrogen bonding motif [ 14”,15] of 2-pyridones, such as 2, to form open framework structures that include and exchange various amounts of short chain carboxylic acids. In one example, suspension of crystals of ~~O.SCHJ(CH~)-$O~H~~CH&O~H in an acetic acid/ether mixture gave essentially complete internal replacement of valeric acid by acetic acid. The unit cell constants for this exchanged inclusion compound were virtually the same as those for the original clathrate containing valeric and acetic acid, and different from those for the acetic acid clathrate formed from acetic acid/ether. Consequently, these authors deduced that the exchanged clathrate was formed by replacement of guests within an intact microporous network, instead of recrystallization of the open framework.
Hollingsworth
515
CN
CN structure of 2
Sl(QO
),
“+-$=O==“h
‘H a
..
-.
0-
R + 4
Moore, Lee and co-workers [16**] have used strong nitrile-silver interactions to construct a 1:l complex of tris(Cethynylbenzonitrile)benzene (3) and silver triflate in which cavities of large diameter (15 A) are filled with benzene molecules. Essentially all of the benzene can be exchanged for benzene-d6 in a few days at
room temperature, apparently without diminution in the optical clarity or change in the powder X-ray diffraction pattern of the sample. These same workers have used these same nitrile-silver interactions to form even more robust coordination networks with zeolitic properties. Coordination of the tritopic ligand 4 with silver triflate in benzene gives a layered structure containing two moles
Figure 2 The supramolecular framework of the host in an orthogonal anthracene-bis(resorcinol) inclusion compound developed by Aoyama and co-workers. Reproduced with permission from [9-l.
HO
OH 5
516
Molecular
crystals
of benzene per mole of the silver criflate complex of 4. For this structure, in which sheets of [12]annulene-like structures are stacked in an ABCD... sequence, each unit cell contains sixteen benzene molecules, four of which are disordered. Upon heating to 1lO’C for 10 minutes, loss of one-fourth of the benzene molecules occurs without significant changes in unit cell parameters or optical properties of these crystals. Further heating gave rise to a collapse of the structure, concomitant with loss of the remaining benzene. Aoyama and co-workers [8,9’] have designed and constructed a series of inclusion compounds based on the packing requirements of an orthogonal anthracenebis(resorcino1) framework such as 5, shown in Figure 2. These hosts incorporate a wide variety of guests, such as alkyl benzoates, alkyl acetates and ketones, as well as nitrobenzene, 1,3-dimethoxybenzene and N,N-dimethylaniline. Competitive co-crystallization in the presence of similar guests showed remarkable selectivity of this host. For example, crystallization in the presence of a I:1 molar mixture of S-nonanone and 6-undecanone gave virtually exclusive formation of the 5nonanone clathrate. This class of inclusion compounds also undergoes significant guest exchange in solution. In contrast to the exchange of valeric for acetic acid in the diamondoid hosts, however, significant changes in the lattice accompanied exchange of methyl benzoate into a crystal containing ethyl benzoate. With low molecular weight guests, it is possible to heat these inclusion compounds under vacuum to generate the ‘apohost’, which takes up guest molecules rapidly in solution. This apohost is much less selective in its uptake of guests from the liquid phase than in the crystallization process. This is probably because the rate of infusion of guests into the apohost is dominated by lattice diffusion (which is favored for smaller guests), instead of site-specific or cooperative [17,18] recognition by the matrix. A key issue in the design of inclusion compounds containing large voids is the degree of interpenetration of the polygonal building blocks that make up the crystalline framework (Fig. 3). To make the largest void possible, it is necessary to minimize the degree of interpenetration of the networks, but these goals are, in a sense, mutually incompatible. Several approaches have been used to circumvent the problem of interpenetration, including first, crystallization in the presence of a guest that packs efficiently within the desired, noninterpenetrated structure; second, the use of branching substituents that prevent concatenation [12]; and third, removing specific topological features that allow interpenetration. Through a combination of the second and third approaches, Zimmerman and co-workers [ll’] have enclosed tetrahydrofuran (THF) molecules in the network shown schematically in Figure 4. Moore, Lee and co-workers [4’] have explored a related strategy for forming large pore (-9A diameter) inclusion compounds by using a rigid, hexagonal
/\ \ \ b cc
macrocycle subunits.
with exterior
phenols
as the linkers
between
Fiaure 3
1
2
3
4
A network of squares showing twofold interpenetration. Here, square 1 is concatenated with squares 2 and 3, square 2 is concatenated with squares 3 and 4, etc. Formation of microporous inclusion compounds with pores of large diameters requires that the degree of interpenetration be low.
An interesting strategy for preparing linear, solid state assemblies has been explored by Hosseini and coworkers [19*]. These workers have prepared bis(p-tttibutylcalix[4]arenes) possessing diverging cavities oriented 180’ from each other-they term these koilands. Cocrystallization of the koiland with a suitable connector (2,4_hexadiyne) gives a so-called linear ‘koilate,’ which is a linear array of koilands and connectors (Fig. 5). These linear arrays are held together by simple van der Waals interactions. Recent X-ray diffraction studies on functionalized tetraphenylmetalloporphyrin inclusion compounds [20*] and on inclusion compounds of the natural product gossypol [21] represent crystallographic tourdefones, and have been used to elucidate the factors affecting the supramolecular architectures of these two classes of inclusion compounds. In the gossypol system, a collection of 30 structures showed the existence of 20 distinct groups of isostructural clathrates, whereas in the porphyrins, comparison of 19 structures revealed relatively few distinct architectures, most likely because the porphyrin-porphyrin interactions dominate the crystal packing.
Combined
approaches
to structure solution
Both static and dynamic disorder of guest molecules cause great difficulties in the structure determination of many inclusion compounds. As new detection devices for X-ray diffractometers become more routinely available, previously intractable structures may become accessible. In many inclusion compounds, however, weak intermolecular coupling between distortions from guest molecules in
Inclusion compounds
Hollingsworth
517
Figure 4 Hydrogen bonding host network of one layer of an inclusion compound that shows no interpenetration. Crystals grown from THF include solvent molecules in the large voids.
Fiaure 5
0
Bu
0
Schematic showing supramolecular assembly of a koiland from a koilate and a connector.
symmetry that is higher than that predicted from the molecular symmetry. A combination of spectroscopic and diffraction techniques can be especially informative, as exemplified by the work of Ripmeester and co-workers [23*] on the 1:l inclusion complex of toluene with p-f&-butylcalix[4]arene. Earlier studies had shown that this crystal is tetragonal (space group P4/n) at room temperature, and that the toluene molecules (with their methyls pointing into the calix) show twofold disorder about the apparent fourfold axis of the symmetric calix host. The agreement factor (R-0.092) for the structure was poor, however, and the tefl-butyl groups exhibited complex positional disorder.
inclusion sites in the X-ray diffraction
Ripmeester’s [23*] solid state 2H NMR studies of the calixarene containing toluene-dg showed that at 337 K, the guest undergoes rapid 4-fold reorientation, and that at
adjacent
gives rise to diffuse scattering patterns (22’1, or space group
518
Molecular crystals
129 K, it is held rigidly. At 179 K, however, the 2H NMR lineshape is characteristic of rapid two-fold jumps about the long axis of the guest, indicating that each host-guest unit has at most two-fold symmetry. By constraining the refinement of the X-ray data collected at 150K so that each host-guest unit has two-fold symmetry and so that there are. two orientational states 90’ apart, these workers gained a dramatic improvement in the structure refinement. With the same constraints applied to a new set of diffraction data collected at 290K, an R value of 0.046 was obtained, and the problems regarding disorder of the tert-butyl groups were resolved. A combination of NMR and X-ray data further allowed Ripmeester et a/. to show that although the high and low temperature phases of this inclusion compound have the same apparent lattice symmetry and very similar unit cell constants, the high symmetry is due to dynamic disorder at 290K and static disorder at 115 K (Fig. 6). At intermediate temperatures (150 K) these workers identified a transient, ordered superstructure in which the unit cell is doubled in two dimensions because of correlated reorientational jumps of the guest molecules. As the temperature is lowered further, the guests lock into disordered configurations that show a variety of nearest neighbor orientations, and the superlattice reflections disappear. An analogous 1:l complex of p-ter+butylcalix[4]arene and nitrobenzene exhibited significant distortion away from tetragonal symmetry, even at room temperature [24].
Channel
Figure 6
(a)
EIEIEI q m1+1
(b)
inclusion compounds
For many channel inclusion compounds (such as those of urea and perhydrotriphenylene), the situation is even worse than with the calixarenes because these systems are quite often incommensurate structures in which there are no reasonably small integers (m and n) for which nC h = mcp (where Ch and Go are the host and guest repeat distances along the channel axis). A recent paper by van Smaalen and Harris [25’] has outlined the superspace group .descriptions of the symmetries of incommensurate urea inclusion compounds (UICs), but there are still no full crystal structures of these incommensurate systems, primarily because of the weak nature of the ‘guest’ diffraction patterns in these systems. The gross features of the ordering patterns for certain guest molecules have been characterized [Z-28], and the dynamic properties of these systems have been probed with several methods, including Brillouin scattering [29,30]. For thiourea inclusion compounds, there are relatively few ‘well behaved’ structures [31], but the situation is somewhat better than that for UICs because the hourglass-shaped inclusion channels of thiourea are more likely to form commensurate inclusion compounds with guests of appropriate shape. Problems of both static and dynamic disorder require methods such as EXAFS for accurate determination of local structural parameters [32].
Schematic
diagram showing the structural
behavior of the 1 :l
complex of toluene with ptert-butylcalix[4larene. At 290K guest shows P-fold dynamic disorder within the calixarene (to give time-averaged
(A) the cavities
4-fold symmetry). As the crystals are cooled
(B), correlated motions of guests gives rise to distortions in the host-guest units, and a transient superlattice that persists for a few hours at 150 K. Longer time or further cooling locks the guests into a statically disordered system (C) with average tetragonal symmetry and no well defined superlattice.
Hollingsworth and co-workers [33,34*,35*] have reported the structures of several commensurate UICs, and have used crystal habit studies, X-ray diffraction and atomic force microscopy on his-methylketone/UICs to demonstrate a template directed mechanism in the crystal growth of channel inclusion compounds. This mechanism provides a link between guest molecule ordering and crystal shape and should apply to many supramolecular
lndusion compounds Hollingsworth
519
Figure 7 (A) Schematic representation of a single domain of 2,10-undecanedionelurea before stress. Arrows represent carbonyl dipoles for guests in one layer as well as the direction of lattice distortion in this orthorhombic crystal. (B) Schematic depiction of partial domain reorientation after stress has been applied to the (110) face. Rotation of guest molecules about their long axes by -60’ relieves the stress by rotating the lattice distortion so that it is perpendicular to the applied stress. Reproduced by permission of (34.1.
assemblies, including certain zeolites and biological structures. This mechanism, as well as many other aspects of the inclusion chemistry of urea, thiourea and selenourea, are covered in a chapter in Comprehensive Supramo&cu/ar Chemistry and will appear shortly [36]. The eleven volume compendium of Compnhensive Supramolecular Chemirrry promises to be a landmark publication covering all aspects of supramolecular and inclusion chemistry [37”].
Materials
properties of inclusion
compounds
Although organic chemists are familiar with domain switching of polar materials (such as liquid crystals) in the presence of electric fields (ferroelectricity), the analogous domain switching process in the presence of uniaxial stress (ferroelasticity) is less well known. A recent paper by Brown and Hollingsworth [34’] shows how macroscopic domains in UICs of 2,10-undecanedione can be reoriented, in a single crystal to single crystal process, by application of anisotropic stress along a specific face of the crystal (Fig. 7). The domains in these crystals are organized by extensive host-guest hydrogen bonding, which can be disrupted by the introduction of various amounts of.2-undecanone impurity. At appropriate levels of impurity, the ferroelastic domain reorientation becomes spontaneously reversible, even under stresses that convert large amounts of the crystal to the new orientation. The 2-undecanone impurities effectively ‘catalyze’ an elastic response by providing nucleation sites for domain reorientation and by disrupting the cooperative networks that are broken and formed during the deformation. As there are so many ways to modify these inclusion systems in a controlled manner, this opens up a new area of research that probes the molecular basis of the elastic properties of crystalline materials. The coordination network of 3 and silver triflate (see above) may also exhibit interesting mechanical properties, including auxetic behavior (negative Poisson’s ratio) [ 16”]. Channel inclusion compounds have also been used as nonlinear optical (NLO) systems, as shown most recently by Hulliger et a/. [38*], who incorporated a number of NLO chromophores into the channels of perhydrotri-
phenylene. In most cases, the guests aligned themselves in polar arrays within the channels, and exhibited significant positional correlations between channels, as shown by X-ray diffraction studies. Many of these systems showed good NLO efficiencies.
Reactivity and selectivity compounds
of inclusion
Although it is beyond the scope of this review to cover the numerous studies of molecular recognition and complexation of guest molecules by solid phase inclusion compounds, a study by Atwood and co-workers [39**] deserves attention. These workers showed that if the toluene extract of soot from a carbon arc is crystallized in the presence of p-tee-butylcalix[8]arene, a selective complex between Cm and the calixarene is formed, and that recrystallizatian of this complex affords high purity C60 in excellent yield. In an analogous procedure, partial purification of C7u is achieved through a 2:l complex of C70 with p-te+butylcalix[6]arene. Toda [40*] has written a brief account that describes both reactivity and selectivity of inclusion compounds and molecular crystals. Although a significant portion of the inclusion chemistry builds upon early work with inclusion compounds of 1,1,6,6-tetraphenylhexa-2,4-diyne-1,6-dial, recent results show that excellent regioselectivities and stereoselectivities can be achieved in a variety of thermal and photochemical reactions of inclusion compounds. The mechanistic details of many of these reactions are poorly understood, but they provide .excellent opportunities for a number of mechanistic studies of solid state reactions.
Conclusions Although chemists are still laying the groundwork for the design and construction of new inclusion compounds, the state of the art of this field is rapidly becoming more and more sophisticated. Future work will obviously emphasize applications of these systems as sensors [41], catalysts, molecular sieves, switching devices, and NLO materials, and even dye lasers (42**]. Many of these applications will be limited, either by our ability to grow large high
520
Molecular
crystals
quality crystals of prescribed shape [43*], or by the extent to which we can integrate these inclusion compounds into industrial processes or devices. The solutions to such engineering challenges have their roots in the principles of supramolecular design [44”], and will require inclusion chemists to think broadly in terms of the chemical, physical and bulk materials properties of these systems.
Kolotuchin. SV, Fenlon EE, Wilson SR, Loweth CJ, Zimmerman SC: Self-assembly of 1,3,5+enzenetricarboxylic acids (trimesic acids) and several analogues in the solid state. Angew Chem Int Ed Engl 1995, 34:2654-2657’. This article includes a discussion of catameric hydrogen bonding motifs of carboxylic acids, and is a good example of one way to reduce the interpenetration of networks in porous organic solids.
Acknowledgements
13. .
I would like to thank Elizabeth A Crane and Michael E Brown for their help, as well as the National Science Foundation (CHE-9423726) and the donors of the Petroleum Research Fund, administered by the American Chemical Society (29932-AC4), for financial support during the writing of this review.
References
and recommended
reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
. ..
of special interest of outstanding interest
1.
MacNicol DD: Structure and design of inclusion compounds: The hexa-hosts and symmetry considerations. In Inclusion Compounds, vol 2. Edited by Atwood JL, Davies JED, MacNicol, DD. New York: Academic Press; 1964:123-l 66.
2.
Henderson K, MacNicol DD, Mallinson PR, Valiance I: 2,4,6-tris[4(1 -naphthyt)phenoxyl-1,3,5triazine: Formation of a unique piedfort-based host lattice with trigonal symmetry. Supramol Chem 1995, 5:301-304.
3. .
Wang X, Simard M, Wuest JD: Molecular tectonics. Threedimensional organic networks with zeolitic properties. I Am Chem Sot 1994, 116:12119-12120. This article describes new dlamondoid networks based on tetrahedral compounds bearing P-pyridones as the hydrogen bond donors and acceptors. Some of these inclusion compounds exhibit guest exchange without concomitant changes in the lattice parameters of the host.
11. .
12.
Ermer 0, Lindenberg L: 61. Double-diamond inclusion compounds of 26-dimethylideneadamantane-1,3,5,7tetracarboxylic acid. Helv Chim Acta 1991, 741625-677.
Ermer 0, Eling A: Molecular recognition among alcohols and amines: Super-tetrahedral crystal architectures of linear diphenol-diamine complexes and aminophenols. J Chem Sot Perkin Trans 2 1994:925-944. This is an excellent summary of Ermer’s work on diamondoid and related networks. 14. ..
Bernstein J, Davis RE, Shimoni L, Chang N-L: Patterns in hydrogen bonding: Functionality and graph set analysis in crystals. Angew Chem Int Ed Engl 1995,34:1555-l 573. An excellent overview of the relationships of graph sets to crystal engineering. This work describes important modifications in the rules for formulating graph sets, which were originally outlined by Etter (151. 15.
Etter MC: Encoding and decoding hydrogen-bond patterns of organic compounds. Account Chem Res 1990, 23:120-l 26.
16. ..
Gardner GB, Venkataraman D, Moore JS, Lee S: Spontaneous assembly of a hinged coordination network Nature 1995, 374:792-795. Although the materials properties of this system were not reported, this network has the correct topology to be an auxetic solid with a negative Poisson’s ratio. The solvent exchange properties of this host are notable. 1 7.
Caira MR, Home A. Nassimbeni LR, Okuda K, Toda F: Selective inclusion of Dhenvlenediamine isomers bv 1 .l -bis(4hydroxyphenylhzyclohexane. J Chem Sot be&in- fins 2 1995:1063-1067.
16.
Hayashi N, Mazaki Y, Kobayashi K: Channel-to-channel rearrangements of host lattices in clathrate crystals induced by guest exchange via gas-solid contacts. Advan Mater 1994, 6:654-656.
19. .
Venkataraman D, Lee S, Zhang J, Moore JS: An organic solid with wide channels based on hydrogen bonding between macrocycles. Nature 1994, 371:591-593. External phenolic ethers link hexagonal-shaped macrocycles into two-dimensional arrays. The three-dimensional packing generates channels that are filled with solvent molecules.
Hajek F, Graf E, Hosseini MW, Delaigue X, De Cian A, Fischer J: Molecular tectonics I: The first synthesis and X-ray analysis of a linear koilate obtained by self-assembly of linear koilands and hexadiyne. Tetrahedron Lett 1996, 37:1401-l 404. This paper describes the supramolecular assembly of an unusual one-dimensional molecular array in which a linear molecular connector (hexadiyne) is used to join two koilands (a hollow molecule possessing two divergent cavities).
5. .
20. .
4. .
Venkataraman D, Gardner GB, Lee S, Moore JS: Zeolite-like behavior of a coordination network. I Am Chem Sot 1995, 117:11600-11601. The robust inclusion compound described here loses one-fourth of the solvent molecules from its tunnels without significant changes in unit cell constants or loss of optical clarity. 6.
7.
9.
Toda F, Tanaka K, lmai T, Bourne SA: Design of new host compounds, cis-1.4-diphenylcyclohexane-1,4-dial, exo, exo-2,5-diphenytnorbornane-2,5-diol, exo-exo-2,6diphenylbicycloI3.3.1 lnonane-2,6-diol and their derivatives. Supramol Chem 1995, 5:269-295. CsBregh I, Gallardo 0, Weber E, Dbrpinghaus N: Supramolecular complexation of DMF and acetone involving singly bridged triarylmethanol and analogous hosts. X-ray crystal structures of four inclusion compounds. Supramol Chem 1995, 5:159-l 65. Aoyama Y, Endo K, Kobayashi K, Masuda H: Hydrogen-bonded network and enforced supramolecular cavities in molecular crystals: An orthogonal aromatic-triad strategy. Guest binding, molecular recognition, and molecular alignment properties of a bisresorcinol derivative of anthracene in the crystalline state. Supramol Chem 1995,4:229-241.
Goldberg I, Krupitsky H, Stein Z, Hsiou Y, Strouse CE: Supramolecular architectures of functionalized tetraphenylmetalloporphyrins in crystalline solids. Studies of the 4-methoxyphenyl, 4-hydroxyphenyl and 4-chlorophenyl derivatives. Supramol Chem 1995,4:203-221. An exhaustive survey of the crystallographic features of a number of porphyrin clathrates. 21.
lbragimov BT, Talipov SA, Zorky PM: Inclusion complexes of the natural product gossypol. Supramol Chem 1994, 3:147-l 65.
22. Welberry TR, Butler BD: Diffuse X-ray scattering from . disordered crystals. Chem Rev 1995, 95:2369-2403. An excellent review on the nature of diffuse scattering of X-rays, which is a common occurence in many inclusion compound studies. 23. .
Brouwer EB, Enright GD, Ratcliffe Cl, Ripmeester JA: Dynamic molecular recognition in solids: A synoptic approach to structure determination in p-tert-butylcalix[4larene-toluene. Supramol Chem 1996, 7:79-63. A nice demonstration of how solid state NMR and X-ray diffraction can be combined to solve problems of static and dynamic disorder, which appear to be widespread in calixI4Iarenes. 24.
9. .
Brouwer EB, Enright GD, Ripmeester JA: Guest-induced asymmetry in the structure of p-ter+butylcalix[4larenenitrobenzene. Supramol Chem 1996, 7:7-9.
Endo K, Sawaki T, Koyanagi M, Kobayashi K, Masuda H, Aoyama Y-: Guest-binding properties of organic crystals having an extensive hydrogen-bonded network: An orthogonal anthracene-bis(resorcinoD derivative as a functional organic analog of zeolites. J Am Chem Sot 1995, 117:6341-6352. Numerous exchange studies-are described for this versatile new inclusion system.
Van Smaalen S, Harris KDM: Superspace group descriptions of the symmetries of incommensurate urea inclusion compounds. Proc Roy Sot London Ser A 1996,452:677-700. This article describes the application of the superspace formalism to describe the symmetries of incommensurate urea inclusion compounds.
10.
26.
Zhang, H, Steed JW, Atwood JL: Inclusion chemistry of cyclotetreveratrylene. Supramol Chem 1995, 4:165-l 90.
25. .
Shannon IJ, Harris KDM. Guillaume F, Bocanegra EH, MacLean El: Phase transitions involving re-ordering of the guest molecules
inclusion
in a solid organic inclusion compound: Heptanoic urea. J Chem Sot Chem Commun 1995:2341-2342.
anhydride-
27.
Fukuo K: X-ray scattering and disordered structure of ntetracosane in urea adducts I. A model for the X-ray scattering pattern J Chem Phys 1994,101:7662-7692.
26.
Fukao K: X-ray scattaring and disordered structure of ntatracosane in urea adducts. II. Averaged disorder. spatial correlation, and phase transition. J Chem Phys 1994, 101:7693-7903.
29.
Schmicker D, Van Smselen S, Hsas C, Harris’ KDM: Elastic constants of the dioctanoyl peroxide/urea inclusion compound determinad by Brillouin scattering. Phys Rev B - Condens Matter 1994,49:11572-l 1579.
30.
Schmicker D, Van Smsslen S, De Boer JL, Hsas C, Harris KDM: Observation of the sliding mode in incommensurate intergrowth compounds. Brillouin scattering from the inclusion compound of urea and heptadecane. Phys Rev Lett 1995, 74:734-737.
31.
32.
33.
Gsmesu I, Raymond S, Brisse F: A thiourea-1 &cyclooctadiene clathrate at 173K Acts Crystellogr C - Cryst Str 1995, !51:536-541. Shannon IJ, Jones MJ, Hsnis KDM, Siddiqui MRH. Joynsr RW: Robin9 the conformational properties of guest molecules in solid inclusion compounds via EXAFS spectroscopy: Bromine K-edge EXAFS studies of the bromocyclohexane/thiourea and trans.1 -bromo-2_chlorocyclohexa&thiourea inclusion compounds. J Chem Sot Faraday Tmns 1995, 91 :1497-l 501. Hollingsworth MD, Ssntarsiero BD, Htis KDM: Zigzag channels in the structure of sebaconitrtle/uraa. Angew Chem Int Ed Engl 1994, 33:649-652.
34. .
Brown ME, Hollingswotth MD: Stress-induced domain reorientation in urea inclusion compounds. Nature 1995, 376:323-327. . This article shows how uniaxial stress can be used to reonent macrOsCOplC domains of a distorted urea inclusion compound. In addition to providing a detailed mechanism of the single crystal to single crystal domain reorientation, thii work shows how introduction of a tailor-made guest impurity csn trsnsfom, the response from a plastic one to an elastic one. 35. .
Hollingsworth MD, Brown ME, Santarsiero BD, Huffmsn JC, Goss CR: Template-directed synthesis of 1 :l Iayared complexes of ao-dinitrfles and uraa: Packing efficiency varsus specific functional group interacttons. Chem Mater 1994, 6:1227-l 244. This article compares packing effiiiency in crystals with and without intermolecular hydrogen bonds, and shows how homologous series can be advantageously used in studies of crystal packing of inclusion compounds and stoichiometric complexes.
36.
compounds
Hollingsworth
521
Hollingsworth MD, Harris KDM: Urea thiourea and selenourea. In Comprehensive Supramolecular Chemistry. Solid State Supramolecular Chemistry: Crystal Engineering, vol 6. Edited by MacNicol DD, Toda F, Bishop R. Oxford: Elsevier Science Ltd; 1996, in press.
Atwood JL, Davies JED, MacNicol DD, Vogtle F (Eds). Comprehensive Supramolecular Chemistry. Oxford: Elsevier Science Ltd; 1996, in press. This important publication is due to be published in the summer of 1996. In eleven volumes, it will be a major reference work for the field for decades. 37. ..
Hulliger J, K6nig 0, Hoss R: Polar inclusion compounds of parhydrotriphenylene (PHTP) and efficient nonlinear optical molecules. Advan Mater 1995, 7:719-721. A wide variety of NLO chromophores ere incorporated ss polar srrays into the channels of perhydrotriphenyfene. 36. .
Atwood JL, Koutsantonis GA, Rsston CL: Purification of Css and CT0 by salactfve complexation with calixarenes. Nature 1994, 369:229-231. Puriication of buckminsterlullerene (Cso) is achieved by selective recrystallization in the presence of p~ert_butylcalix[6]arene.
39. ..
40.
.
chemisbyz efficient reactions, remarkable yields, end stereoselectivity. Account Chem f?es
Toda F: Solid state organic
1996,28:460-406. A descriptive account of reactions, moleculsr recognition and stereoselectivity in organic crystals and inclusion compounds. 41.
Exstrom CL, Sowa JRJ, Daws CA, Janren D, Mann KR, Moore GA, Stewart FF: Inch&on of organic vapon by crystalline, sdvatochromlc CPt(atyl isonitrtle)SIPd(CN)S compounds “vapochromk’ environmental sensors. Chem Mater 1 Q95, 7:15-l 7.
Rifani M, Yin Y-Y, Elliott DS, Jay MJ, J~IIQ S-H, Kelley, MP, Bsstin, L, Kshr B: Solid state dya lasars from stereospacific host-guest interactions. J Am Chem Sot 1995, 117~7672-7573. The oriented inclusion of sulfonated pyrene and rhodsmine dyes into specific growth sectors of potassium sulfate provides a new medium for the generation.of bkte, green, snd red solid state dye lasers. Although not strictly sn organic system, this system represents sn exciting development in the use of organic inclusions ss practical optical devices. 42. ..
Hulliger J: Chemistry and crystal growth. Angew Chem lnt Ed Engl 1994, 33:143-l 62. b important paper describing methods of crystal growth that shoutd be of interest to inclusion chemists. 43.
44. ..
Desiraju GR: Supramolecular synthons in crystal engineer@ - a new organic synthesis. Angew Chem Int Ed Engl 1995,34:231 l-2327. An excellent review on crystal engineering and supramoleculsr chemistry.
Inclusion compounds Mark D Hollingsworth Since late 1994,
significant progress
has been made toward
the design, synthesis, and characterization compounds, properties
of new inclusion
including systems that exhibit guest exchange akin to zeolites, ferroelasticity
(domain reorientation
under applied stress) and selectivity for specific reactions. somewhat
by the difficult (and sometimes
nature of many crystal structures progress
has been fostered
diffraction
equipment
of structure molecular
by recent advances
methods
of the structures
of new
remains an elusive goal that awaits
computational
intermolecular
in X-ray
Just as with single-component
crystals, reliable prediction
more sophisticated
intractable)
of inclusion compounds,
and in the use of combined
determination.
inclusion compounds reliable
chemical
Although efforts in this field have been slowed
techniques
and more
supramolecular assemblies contain more than one kind of molecule, the opportunity for different stoichiometries and sequential patterns presents extra degrees of freedom for the crystal packing arrangement, and requires the inclusion chemist to remove other degrees of freedom from the system by judicious choice of complementary and directional intermolecular contacts. The multitude of energetically feasible packing arrangements and the severe limitations of intermolecular potential functions make it necessary to adopt an empirical approach to the design of new solid phase inclusion compounds. This brand of crystal engineering is often most successful when one recognizes or discovers an existing motif and exploits it in a logical manner.
potentials.
Design of new inclusion compounds Addresses Department of Chemistry, Indiana University, 7th Street, IN 47405, USA; e-mail: [email protected] Current Opinion 1514-521
in Solid State
0 Current Science
Ltd ISSN
& Materials
Science
Bloomington,
1996,
1359-0286
Abbreviations NLO UIC
nonlinear optical urea inclusion compound
Introduction As the field of solid state organic inclusion chemistry has become so diverse, it is impossible for a short review such as this to do justice to the many subfields within this discipline. Instead, I have chosen to focus on certain key aspects of inclusion chemistry, including the intentional design and construction of new systems (including ‘organic zeolites’), the state of the art of crystal structure determination, materials properties, and molecular recognition and reactivity. The field of solution phase inclusion chemistry and molecular recognition has grown tremendously in the past fifteen years, in part because it is ordinarily possible to design a solution phase receptor or complexing agent using simple molecular models or molecular mechanics techniques. The formation of crystalline 1:l molecular complexes follows naturally from the solution phase chemistry (and is often used in conjunction with X-ray crystallography as the principal means of characterization of these complexes). The design of new solid phase inclusion compounds, however, in which the extended structure of the host encapsulates the guest, is a much more formidable task that is often confounded by subtle factors such as packing efficiency, strain and longrange Coulombic interactions. Because these extended
As a result of these difficulties, most solid phase inclusion compounds that are not simple molecular complexes are discovered by accident. Nevertheless, several groups have made significant progress toward designing new inclusion compounds through the use of directed interactions. Work by MacNicol and co-workers [1,2] on ‘hexa-hosts’ has shown that it is possible to adapt common structural topologies used by known inclusion compounds to design new host materials. This same sort of approach has been followed most recently by Wuest [3-j, Moore [4’,5’], Toda [6], Weber [7], Aoyama [8,9*], Atwood [lo], Zimmerman [ 11.1, and their co-workers, among others.
Fioure
1
Formation of a prototypical
diamondoid
construction from a hypothetical with permission from 13.1.
network by supramolecular
molecule
or ‘tecton’
(1). Reproduced
Recent work has shown that it is possible to design inclusion compounds that can act as ‘organic zeolites’, that is, systems that retain the essential features of their solid structures during exchange of guest molecules. Following earlier work by Ermer et a/. [12,13*] on
Inclusion compounds
diamondoid hosts formed by adamantanetetracarboxylic acid (Fig. l), Wuest and co-workers have used the persistent Rzz(8) hydrogen bonding motif [ 14”,15] of 2-pyridones, such as 2, to form open framework structures that include and exchange various amounts of short chain carboxylic acids. In one example, suspension of crystals of ~~O.SCHJ(CH~)-$O~H~~CH&O~H in an acetic acid/ether mixture gave essentially complete internal replacement of valeric acid by acetic acid. The unit cell constants for this exchanged inclusion compound were virtually the same as those for the original clathrate containing valeric and acetic acid, and different from those for the acetic acid clathrate formed from acetic acid/ether. Consequently, these authors deduced that the exchanged clathrate was formed by replacement of guests within an intact microporous network, instead of recrystallization of the open framework.
Hollingsworth
515
CN
CN structure of 2
Sl(QO
),
“+-$=O==“h
‘H a
..
-.
0-
R + 4
Moore, Lee and co-workers [16**] have used strong nitrile-silver interactions to construct a 1:l complex of tris(Cethynylbenzonitrile)benzene (3) and silver triflate in which cavities of large diameter (15 A) are filled with benzene molecules. Essentially all of the benzene can be exchanged for benzene-d6 in a few days at
room temperature, apparently without diminution in the optical clarity or change in the powder X-ray diffraction pattern of the sample. These same workers have used these same nitrile-silver interactions to form even more robust coordination networks with zeolitic properties. Coordination of the tritopic ligand 4 with silver triflate in benzene gives a layered structure containing two moles
Figure 2 The supramolecular framework of the host in an orthogonal anthracene-bis(resorcinol) inclusion compound developed by Aoyama and co-workers. Reproduced with permission from [9-l.
HO
OH 5
516
Molecular
crystals
of benzene per mole of the silver criflate complex of 4. For this structure, in which sheets of [12]annulene-like structures are stacked in an ABCD... sequence, each unit cell contains sixteen benzene molecules, four of which are disordered. Upon heating to 1lO’C for 10 minutes, loss of one-fourth of the benzene molecules occurs without significant changes in unit cell parameters or optical properties of these crystals. Further heating gave rise to a collapse of the structure, concomitant with loss of the remaining benzene. Aoyama and co-workers [8,9’] have designed and constructed a series of inclusion compounds based on the packing requirements of an orthogonal anthracenebis(resorcino1) framework such as 5, shown in Figure 2. These hosts incorporate a wide variety of guests, such as alkyl benzoates, alkyl acetates and ketones, as well as nitrobenzene, 1,3-dimethoxybenzene and N,N-dimethylaniline. Competitive co-crystallization in the presence of similar guests showed remarkable selectivity of this host. For example, crystallization in the presence of a I:1 molar mixture of S-nonanone and 6-undecanone gave virtually exclusive formation of the 5nonanone clathrate. This class of inclusion compounds also undergoes significant guest exchange in solution. In contrast to the exchange of valeric for acetic acid in the diamondoid hosts, however, significant changes in the lattice accompanied exchange of methyl benzoate into a crystal containing ethyl benzoate. With low molecular weight guests, it is possible to heat these inclusion compounds under vacuum to generate the ‘apohost’, which takes up guest molecules rapidly in solution. This apohost is much less selective in its uptake of guests from the liquid phase than in the crystallization process. This is probably because the rate of infusion of guests into the apohost is dominated by lattice diffusion (which is favored for smaller guests), instead of site-specific or cooperative [17,18] recognition by the matrix. A key issue in the design of inclusion compounds containing large voids is the degree of interpenetration of the polygonal building blocks that make up the crystalline framework (Fig. 3). To make the largest void possible, it is necessary to minimize the degree of interpenetration of the networks, but these goals are, in a sense, mutually incompatible. Several approaches have been used to circumvent the problem of interpenetration, including first, crystallization in the presence of a guest that packs efficiently within the desired, noninterpenetrated structure; second, the use of branching substituents that prevent concatenation [12]; and third, removing specific topological features that allow interpenetration. Through a combination of the second and third approaches, Zimmerman and co-workers [ll’] have enclosed tetrahydrofuran (THF) molecules in the network shown schematically in Figure 4. Moore, Lee and co-workers [4’] have explored a related strategy for forming large pore (-9A diameter) inclusion compounds by using a rigid, hexagonal
/\ \ \ b cc
macrocycle subunits.
with exterior
phenols
as the linkers
between
Fiaure 3
1
2
3
4
A network of squares showing twofold interpenetration. Here, square 1 is concatenated with squares 2 and 3, square 2 is concatenated with squares 3 and 4, etc. Formation of microporous inclusion compounds with pores of large diameters requires that the degree of interpenetration be low.
An interesting strategy for preparing linear, solid state assemblies has been explored by Hosseini and coworkers [19*]. These workers have prepared bis(p-tttibutylcalix[4]arenes) possessing diverging cavities oriented 180’ from each other-they term these koilands. Cocrystallization of the koiland with a suitable connector (2,4_hexadiyne) gives a so-called linear ‘koilate,’ which is a linear array of koilands and connectors (Fig. 5). These linear arrays are held together by simple van der Waals interactions. Recent X-ray diffraction studies on functionalized tetraphenylmetalloporphyrin inclusion compounds [20*] and on inclusion compounds of the natural product gossypol [21] represent crystallographic tourdefones, and have been used to elucidate the factors affecting the supramolecular architectures of these two classes of inclusion compounds. In the gossypol system, a collection of 30 structures showed the existence of 20 distinct groups of isostructural clathrates, whereas in the porphyrins, comparison of 19 structures revealed relatively few distinct architectures, most likely because the porphyrin-porphyrin interactions dominate the crystal packing.
Combined
approaches
to structure solution
Both static and dynamic disorder of guest molecules cause great difficulties in the structure determination of many inclusion compounds. As new detection devices for X-ray diffractometers become more routinely available, previously intractable structures may become accessible. In many inclusion compounds, however, weak intermolecular coupling between distortions from guest molecules in
Inclusion compounds
Hollingsworth
517
Figure 4 Hydrogen bonding host network of one layer of an inclusion compound that shows no interpenetration. Crystals grown from THF include solvent molecules in the large voids.
Fiaure 5
0
Bu
0
Schematic showing supramolecular assembly of a koiland from a koilate and a connector.
symmetry that is higher than that predicted from the molecular symmetry. A combination of spectroscopic and diffraction techniques can be especially informative, as exemplified by the work of Ripmeester and co-workers [23*] on the 1:l inclusion complex of toluene with p-f&-butylcalix[4]arene. Earlier studies had shown that this crystal is tetragonal (space group P4/n) at room temperature, and that the toluene molecules (with their methyls pointing into the calix) show twofold disorder about the apparent fourfold axis of the symmetric calix host. The agreement factor (R-0.092) for the structure was poor, however, and the tefl-butyl groups exhibited complex positional disorder.
inclusion sites in the X-ray diffraction
Ripmeester’s [23*] solid state 2H NMR studies of the calixarene containing toluene-dg showed that at 337 K, the guest undergoes rapid 4-fold reorientation, and that at
adjacent
gives rise to diffuse scattering patterns (22’1, or space group
518
Molecular crystals
129 K, it is held rigidly. At 179 K, however, the 2H NMR lineshape is characteristic of rapid two-fold jumps about the long axis of the guest, indicating that each host-guest unit has at most two-fold symmetry. By constraining the refinement of the X-ray data collected at 150K so that each host-guest unit has two-fold symmetry and so that there are. two orientational states 90’ apart, these workers gained a dramatic improvement in the structure refinement. With the same constraints applied to a new set of diffraction data collected at 290K, an R value of 0.046 was obtained, and the problems regarding disorder of the tert-butyl groups were resolved. A combination of NMR and X-ray data further allowed Ripmeester et a/. to show that although the high and low temperature phases of this inclusion compound have the same apparent lattice symmetry and very similar unit cell constants, the high symmetry is due to dynamic disorder at 290K and static disorder at 115 K (Fig. 6). At intermediate temperatures (150 K) these workers identified a transient, ordered superstructure in which the unit cell is doubled in two dimensions because of correlated reorientational jumps of the guest molecules. As the temperature is lowered further, the guests lock into disordered configurations that show a variety of nearest neighbor orientations, and the superlattice reflections disappear. An analogous 1:l complex of p-ter+butylcalix[4]arene and nitrobenzene exhibited significant distortion away from tetragonal symmetry, even at room temperature [24].
Channel
Figure 6
(a)
EIEIEI q m1+1
(b)
inclusion compounds
For many channel inclusion compounds (such as those of urea and perhydrotriphenylene), the situation is even worse than with the calixarenes because these systems are quite often incommensurate structures in which there are no reasonably small integers (m and n) for which nC h = mcp (where Ch and Go are the host and guest repeat distances along the channel axis). A recent paper by van Smaalen and Harris [25’] has outlined the superspace group .descriptions of the symmetries of incommensurate urea inclusion compounds (UICs), but there are still no full crystal structures of these incommensurate systems, primarily because of the weak nature of the ‘guest’ diffraction patterns in these systems. The gross features of the ordering patterns for certain guest molecules have been characterized [Z-28], and the dynamic properties of these systems have been probed with several methods, including Brillouin scattering [29,30]. For thiourea inclusion compounds, there are relatively few ‘well behaved’ structures [31], but the situation is somewhat better than that for UICs because the hourglass-shaped inclusion channels of thiourea are more likely to form commensurate inclusion compounds with guests of appropriate shape. Problems of both static and dynamic disorder require methods such as EXAFS for accurate determination of local structural parameters [32].
Schematic
diagram showing the structural
behavior of the 1 :l
complex of toluene with ptert-butylcalix[4larene. At 290K guest shows P-fold dynamic disorder within the calixarene (to give time-averaged
(A) the cavities
4-fold symmetry). As the crystals are cooled
(B), correlated motions of guests gives rise to distortions in the host-guest units, and a transient superlattice that persists for a few hours at 150 K. Longer time or further cooling locks the guests into a statically disordered system (C) with average tetragonal symmetry and no well defined superlattice.
Hollingsworth and co-workers [33,34*,35*] have reported the structures of several commensurate UICs, and have used crystal habit studies, X-ray diffraction and atomic force microscopy on his-methylketone/UICs to demonstrate a template directed mechanism in the crystal growth of channel inclusion compounds. This mechanism provides a link between guest molecule ordering and crystal shape and should apply to many supramolecular
lndusion compounds Hollingsworth
519
Figure 7 (A) Schematic representation of a single domain of 2,10-undecanedionelurea before stress. Arrows represent carbonyl dipoles for guests in one layer as well as the direction of lattice distortion in this orthorhombic crystal. (B) Schematic depiction of partial domain reorientation after stress has been applied to the (110) face. Rotation of guest molecules about their long axes by -60’ relieves the stress by rotating the lattice distortion so that it is perpendicular to the applied stress. Reproduced by permission of (34.1.
assemblies, including certain zeolites and biological structures. This mechanism, as well as many other aspects of the inclusion chemistry of urea, thiourea and selenourea, are covered in a chapter in Comprehensive Supramo&cu/ar Chemistry and will appear shortly [36]. The eleven volume compendium of Compnhensive Supramolecular Chemirrry promises to be a landmark publication covering all aspects of supramolecular and inclusion chemistry [37”].
Materials
properties of inclusion
compounds
Although organic chemists are familiar with domain switching of polar materials (such as liquid crystals) in the presence of electric fields (ferroelectricity), the analogous domain switching process in the presence of uniaxial stress (ferroelasticity) is less well known. A recent paper by Brown and Hollingsworth [34’] shows how macroscopic domains in UICs of 2,10-undecanedione can be reoriented, in a single crystal to single crystal process, by application of anisotropic stress along a specific face of the crystal (Fig. 7). The domains in these crystals are organized by extensive host-guest hydrogen bonding, which can be disrupted by the introduction of various amounts of.2-undecanone impurity. At appropriate levels of impurity, the ferroelastic domain reorientation becomes spontaneously reversible, even under stresses that convert large amounts of the crystal to the new orientation. The 2-undecanone impurities effectively ‘catalyze’ an elastic response by providing nucleation sites for domain reorientation and by disrupting the cooperative networks that are broken and formed during the deformation. As there are so many ways to modify these inclusion systems in a controlled manner, this opens up a new area of research that probes the molecular basis of the elastic properties of crystalline materials. The coordination network of 3 and silver triflate (see above) may also exhibit interesting mechanical properties, including auxetic behavior (negative Poisson’s ratio) [ 16”]. Channel inclusion compounds have also been used as nonlinear optical (NLO) systems, as shown most recently by Hulliger et a/. [38*], who incorporated a number of NLO chromophores into the channels of perhydrotri-
phenylene. In most cases, the guests aligned themselves in polar arrays within the channels, and exhibited significant positional correlations between channels, as shown by X-ray diffraction studies. Many of these systems showed good NLO efficiencies.
Reactivity and selectivity compounds
of inclusion
Although it is beyond the scope of this review to cover the numerous studies of molecular recognition and complexation of guest molecules by solid phase inclusion compounds, a study by Atwood and co-workers [39**] deserves attention. These workers showed that if the toluene extract of soot from a carbon arc is crystallized in the presence of p-tee-butylcalix[8]arene, a selective complex between Cm and the calixarene is formed, and that recrystallizatian of this complex affords high purity C60 in excellent yield. In an analogous procedure, partial purification of C7u is achieved through a 2:l complex of C70 with p-te+butylcalix[6]arene. Toda [40*] has written a brief account that describes both reactivity and selectivity of inclusion compounds and molecular crystals. Although a significant portion of the inclusion chemistry builds upon early work with inclusion compounds of 1,1,6,6-tetraphenylhexa-2,4-diyne-1,6-dial, recent results show that excellent regioselectivities and stereoselectivities can be achieved in a variety of thermal and photochemical reactions of inclusion compounds. The mechanistic details of many of these reactions are poorly understood, but they provide .excellent opportunities for a number of mechanistic studies of solid state reactions.
Conclusions Although chemists are still laying the groundwork for the design and construction of new inclusion compounds, the state of the art of this field is rapidly becoming more and more sophisticated. Future work will obviously emphasize applications of these systems as sensors [41], catalysts, molecular sieves, switching devices, and NLO materials, and even dye lasers (42**]. Many of these applications will be limited, either by our ability to grow large high
520
Molecular
crystals
quality crystals of prescribed shape [43*], or by the extent to which we can integrate these inclusion compounds into industrial processes or devices. The solutions to such engineering challenges have their roots in the principles of supramolecular design [44”], and will require inclusion chemists to think broadly in terms of the chemical, physical and bulk materials properties of these systems.
Kolotuchin. SV, Fenlon EE, Wilson SR, Loweth CJ, Zimmerman SC: Self-assembly of 1,3,5+enzenetricarboxylic acids (trimesic acids) and several analogues in the solid state. Angew Chem Int Ed Engl 1995, 34:2654-2657’. This article includes a discussion of catameric hydrogen bonding motifs of carboxylic acids, and is a good example of one way to reduce the interpenetration of networks in porous organic solids.
Acknowledgements
13. .
I would like to thank Elizabeth A Crane and Michael E Brown for their help, as well as the National Science Foundation (CHE-9423726) and the donors of the Petroleum Research Fund, administered by the American Chemical Society (29932-AC4), for financial support during the writing of this review.
References
and recommended
reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
. ..
of special interest of outstanding interest
1.
MacNicol DD: Structure and design of inclusion compounds: The hexa-hosts and symmetry considerations. In Inclusion Compounds, vol 2. Edited by Atwood JL, Davies JED, MacNicol, DD. New York: Academic Press; 1964:123-l 66.
2.
Henderson K, MacNicol DD, Mallinson PR, Valiance I: 2,4,6-tris[4(1 -naphthyt)phenoxyl-1,3,5triazine: Formation of a unique piedfort-based host lattice with trigonal symmetry. Supramol Chem 1995, 5:301-304.
3. .
Wang X, Simard M, Wuest JD: Molecular tectonics. Threedimensional organic networks with zeolitic properties. I Am Chem Sot 1994, 116:12119-12120. This article describes new dlamondoid networks based on tetrahedral compounds bearing P-pyridones as the hydrogen bond donors and acceptors. Some of these inclusion compounds exhibit guest exchange without concomitant changes in the lattice parameters of the host.
11. .
12.
Ermer 0, Lindenberg L: 61. Double-diamond inclusion compounds of 26-dimethylideneadamantane-1,3,5,7tetracarboxylic acid. Helv Chim Acta 1991, 741625-677.
Ermer 0, Eling A: Molecular recognition among alcohols and amines: Super-tetrahedral crystal architectures of linear diphenol-diamine complexes and aminophenols. J Chem Sot Perkin Trans 2 1994:925-944. This is an excellent summary of Ermer’s work on diamondoid and related networks. 14. ..
Bernstein J, Davis RE, Shimoni L, Chang N-L: Patterns in hydrogen bonding: Functionality and graph set analysis in crystals. Angew Chem Int Ed Engl 1995,34:1555-l 573. An excellent overview of the relationships of graph sets to crystal engineering. This work describes important modifications in the rules for formulating graph sets, which were originally outlined by Etter (151. 15.
Etter MC: Encoding and decoding hydrogen-bond patterns of organic compounds. Account Chem Res 1990, 23:120-l 26.
16. ..
Gardner GB, Venkataraman D, Moore JS, Lee S: Spontaneous assembly of a hinged coordination network Nature 1995, 374:792-795. Although the materials properties of this system were not reported, this network has the correct topology to be an auxetic solid with a negative Poisson’s ratio. The solvent exchange properties of this host are notable. 1 7.
Caira MR, Home A. Nassimbeni LR, Okuda K, Toda F: Selective inclusion of Dhenvlenediamine isomers bv 1 .l -bis(4hydroxyphenylhzyclohexane. J Chem Sot be&in- fins 2 1995:1063-1067.
16.
Hayashi N, Mazaki Y, Kobayashi K: Channel-to-channel rearrangements of host lattices in clathrate crystals induced by guest exchange via gas-solid contacts. Advan Mater 1994, 6:654-656.
19. .
Venkataraman D, Lee S, Zhang J, Moore JS: An organic solid with wide channels based on hydrogen bonding between macrocycles. Nature 1994, 371:591-593. External phenolic ethers link hexagonal-shaped macrocycles into two-dimensional arrays. The three-dimensional packing generates channels that are filled with solvent molecules.
Hajek F, Graf E, Hosseini MW, Delaigue X, De Cian A, Fischer J: Molecular tectonics I: The first synthesis and X-ray analysis of a linear koilate obtained by self-assembly of linear koilands and hexadiyne. Tetrahedron Lett 1996, 37:1401-l 404. This paper describes the supramolecular assembly of an unusual one-dimensional molecular array in which a linear molecular connector (hexadiyne) is used to join two koilands (a hollow molecule possessing two divergent cavities).
5. .
20. .
4. .
Venkataraman D, Gardner GB, Lee S, Moore JS: Zeolite-like behavior of a coordination network. I Am Chem Sot 1995, 117:11600-11601. The robust inclusion compound described here loses one-fourth of the solvent molecules from its tunnels without significant changes in unit cell constants or loss of optical clarity. 6.
7.
9.
Toda F, Tanaka K, lmai T, Bourne SA: Design of new host compounds, cis-1.4-diphenylcyclohexane-1,4-dial, exo, exo-2,5-diphenytnorbornane-2,5-diol, exo-exo-2,6diphenylbicycloI3.3.1 lnonane-2,6-diol and their derivatives. Supramol Chem 1995, 5:269-295. CsBregh I, Gallardo 0, Weber E, Dbrpinghaus N: Supramolecular complexation of DMF and acetone involving singly bridged triarylmethanol and analogous hosts. X-ray crystal structures of four inclusion compounds. Supramol Chem 1995, 5:159-l 65. Aoyama Y, Endo K, Kobayashi K, Masuda H: Hydrogen-bonded network and enforced supramolecular cavities in molecular crystals: An orthogonal aromatic-triad strategy. Guest binding, molecular recognition, and molecular alignment properties of a bisresorcinol derivative of anthracene in the crystalline state. Supramol Chem 1995,4:229-241.
Goldberg I, Krupitsky H, Stein Z, Hsiou Y, Strouse CE: Supramolecular architectures of functionalized tetraphenylmetalloporphyrins in crystalline solids. Studies of the 4-methoxyphenyl, 4-hydroxyphenyl and 4-chlorophenyl derivatives. Supramol Chem 1995,4:203-221. An exhaustive survey of the crystallographic features of a number of porphyrin clathrates. 21.
lbragimov BT, Talipov SA, Zorky PM: Inclusion complexes of the natural product gossypol. Supramol Chem 1994, 3:147-l 65.
22. Welberry TR, Butler BD: Diffuse X-ray scattering from . disordered crystals. Chem Rev 1995, 95:2369-2403. An excellent review on the nature of diffuse scattering of X-rays, which is a common occurence in many inclusion compound studies. 23. .
Brouwer EB, Enright GD, Ratcliffe Cl, Ripmeester JA: Dynamic molecular recognition in solids: A synoptic approach to structure determination in p-tert-butylcalix[4larene-toluene. Supramol Chem 1996, 7:79-63. A nice demonstration of how solid state NMR and X-ray diffraction can be combined to solve problems of static and dynamic disorder, which appear to be widespread in calixI4Iarenes. 24.
9. .
Brouwer EB, Enright GD, Ripmeester JA: Guest-induced asymmetry in the structure of p-ter+butylcalix[4larenenitrobenzene. Supramol Chem 1996, 7:7-9.
Endo K, Sawaki T, Koyanagi M, Kobayashi K, Masuda H, Aoyama Y-: Guest-binding properties of organic crystals having an extensive hydrogen-bonded network: An orthogonal anthracene-bis(resorcinoD derivative as a functional organic analog of zeolites. J Am Chem Sot 1995, 117:6341-6352. Numerous exchange studies-are described for this versatile new inclusion system.
Van Smaalen S, Harris KDM: Superspace group descriptions of the symmetries of incommensurate urea inclusion compounds. Proc Roy Sot London Ser A 1996,452:677-700. This article describes the application of the superspace formalism to describe the symmetries of incommensurate urea inclusion compounds.
10.
26.
Zhang, H, Steed JW, Atwood JL: Inclusion chemistry of cyclotetreveratrylene. Supramol Chem 1995, 4:165-l 90.
25. .
Shannon IJ, Harris KDM. Guillaume F, Bocanegra EH, MacLean El: Phase transitions involving re-ordering of the guest molecules
inclusion
in a solid organic inclusion compound: Heptanoic urea. J Chem Sot Chem Commun 1995:2341-2342.
anhydride-
27.
Fukuo K: X-ray scattering and disordered structure of ntetracosane in urea adducts I. A model for the X-ray scattering pattern J Chem Phys 1994,101:7662-7692.
26.
Fukao K: X-ray scattaring and disordered structure of ntatracosane in urea adducts. II. Averaged disorder. spatial correlation, and phase transition. J Chem Phys 1994, 101:7693-7903.
29.
Schmicker D, Van Smselen S, Hsas C, Harris’ KDM: Elastic constants of the dioctanoyl peroxide/urea inclusion compound determinad by Brillouin scattering. Phys Rev B - Condens Matter 1994,49:11572-l 1579.
30.
Schmicker D, Van Smsslen S, De Boer JL, Hsas C, Harris KDM: Observation of the sliding mode in incommensurate intergrowth compounds. Brillouin scattering from the inclusion compound of urea and heptadecane. Phys Rev Lett 1995, 74:734-737.
31.
32.
33.
Gsmesu I, Raymond S, Brisse F: A thiourea-1 &cyclooctadiene clathrate at 173K Acts Crystellogr C - Cryst Str 1995, !51:536-541. Shannon IJ, Jones MJ, Hsnis KDM, Siddiqui MRH. Joynsr RW: Robin9 the conformational properties of guest molecules in solid inclusion compounds via EXAFS spectroscopy: Bromine K-edge EXAFS studies of the bromocyclohexane/thiourea and trans.1 -bromo-2_chlorocyclohexa&thiourea inclusion compounds. J Chem Sot Faraday Tmns 1995, 91 :1497-l 501. Hollingsworth MD, Ssntarsiero BD, Htis KDM: Zigzag channels in the structure of sebaconitrtle/uraa. Angew Chem Int Ed Engl 1994, 33:649-652.
34. .
Brown ME, Hollingswotth MD: Stress-induced domain reorientation in urea inclusion compounds. Nature 1995, 376:323-327. . This article shows how uniaxial stress can be used to reonent macrOsCOplC domains of a distorted urea inclusion compound. In addition to providing a detailed mechanism of the single crystal to single crystal domain reorientation, thii work shows how introduction of a tailor-made guest impurity csn trsnsfom, the response from a plastic one to an elastic one. 35. .
Hollingsworth MD, Brown ME, Santarsiero BD, Huffmsn JC, Goss CR: Template-directed synthesis of 1 :l Iayared complexes of ao-dinitrfles and uraa: Packing efficiency varsus specific functional group interacttons. Chem Mater 1994, 6:1227-l 244. This article compares packing effiiiency in crystals with and without intermolecular hydrogen bonds, and shows how homologous series can be advantageously used in studies of crystal packing of inclusion compounds and stoichiometric complexes.
36.
compounds
Hollingsworth
521
Hollingsworth MD, Harris KDM: Urea thiourea and selenourea. In Comprehensive Supramolecular Chemistry. Solid State Supramolecular Chemistry: Crystal Engineering, vol 6. Edited by MacNicol DD, Toda F, Bishop R. Oxford: Elsevier Science Ltd; 1996, in press.
Atwood JL, Davies JED, MacNicol DD, Vogtle F (Eds). Comprehensive Supramolecular Chemistry. Oxford: Elsevier Science Ltd; 1996, in press. This important publication is due to be published in the summer of 1996. In eleven volumes, it will be a major reference work for the field for decades. 37. ..
Hulliger J, K6nig 0, Hoss R: Polar inclusion compounds of parhydrotriphenylene (PHTP) and efficient nonlinear optical molecules. Advan Mater 1995, 7:719-721. A wide variety of NLO chromophores ere incorporated ss polar srrays into the channels of perhydrotriphenyfene. 36. .
Atwood JL, Koutsantonis GA, Rsston CL: Purification of Css and CT0 by salactfve complexation with calixarenes. Nature 1994, 369:229-231. Puriication of buckminsterlullerene (Cso) is achieved by selective recrystallization in the presence of p~ert_butylcalix[6]arene.
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chemisbyz efficient reactions, remarkable yields, end stereoselectivity. Account Chem f?es
Toda F: Solid state organic
1996,28:460-406. A descriptive account of reactions, moleculsr recognition and stereoselectivity in organic crystals and inclusion compounds. 41.
Exstrom CL, Sowa JRJ, Daws CA, Janren D, Mann KR, Moore GA, Stewart FF: Inch&on of organic vapon by crystalline, sdvatochromlc CPt(atyl isonitrtle)SIPd(CN)S compounds “vapochromk’ environmental sensors. Chem Mater 1 Q95, 7:15-l 7.
Rifani M, Yin Y-Y, Elliott DS, Jay MJ, J~IIQ S-H, Kelley, MP, Bsstin, L, Kshr B: Solid state dya lasars from stereospacific host-guest interactions. J Am Chem Sot 1995, 117~7672-7573. The oriented inclusion of sulfonated pyrene and rhodsmine dyes into specific growth sectors of potassium sulfate provides a new medium for the generation.of bkte, green, snd red solid state dye lasers. Although not strictly sn organic system, this system represents sn exciting development in the use of organic inclusions ss practical optical devices. 42. ..
Hulliger J: Chemistry and crystal growth. Angew Chem lnt Ed Engl 1994, 33:143-l 62. b important paper describing methods of crystal growth that shoutd be of interest to inclusion chemists. 43.
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Desiraju GR: Supramolecular synthons in crystal engineer@ - a new organic synthesis. Angew Chem Int Ed Engl 1995,34:231 l-2327. An excellent review on crystal engineering and supramoleculsr chemistry.