Mapping Out the Molecular Interplay in Monohalobenzene Inclusion Complexes of p-H-calix[5]arene Using Hirshfeld Surfaces Thomas E. Clark, Mohamed Makha, Alexandre N. Sobolev, and Colin L. Raston* Centre for Strategic Nano-Fabrication, School of Biomedical, Biomolecular and Chemical Sciences, The UniVersity of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 3 890–896
ReceiVed July 9, 2007; ReVised Manuscript ReceiVed August 27, 2007
ABSTRACT: Solid-state inclusion complexes of p-H-calix[5]arene with fluoro-, chloro-, bromo-, and iodobenzene have been structurally authenticated using X-ray diffraction data with a detailed analysis of the Hirshfeld surfaces facilitating an understanding of the type and nature of intermolecular interactions in the supermolecules and extended structures. All but the iodobenzene complexes areisostructuralformingcolumnararraysinvolvingthreecrystallographicallyrelated1:1host–guestsupermolecules(halobenzene∩calix[5]arene); three halobenzene molecules from different supermolecules are associated via C-H · · · X interactions for hydrogen atoms ortho to the halogen atoms, effectively creating a larger cavity from close proximity of three calix[5]arenes. The iodobenzene inclusion complex has sheets of calixarenes rather than columns in the extended packing, presumably due to the increased size of iodine circumventing the formation of the aforementioned interplay of three halobenzene molecules. Introduction Calixarenes are [1n]-metacyclophanes synthesized by the condensation of p-substituted phenols and formaldehyde in the presence of base or acid. These macrocyclic compounds can contain a well-defined cavity suitable for complexation of metal ions,1 or they can be used as scaffolds for further synthetic modification.2 Under specific reaction conditions, the evennumbered p-tert-butylcalix[n]arenes (n ) 4, 6, and 8) are accessible in good yield from p-tert-butylphenol using the protocols developed by Gutsche.3 The odd numbered p-tertbutylcalix[n]arenes (n ) 5, 7, and 9) are less studied mainly due to low yielding synthetic protocols.4 The larger calix[n]arenes (n g 6) are conformationally flexible and can adopt a variety of different conformations usually with flattened arrangements of the phenolic moieties. In contrast, the smaller calix[4,5]arenes usually adopt a cone- or bowl-shaped conformation due to the hydroxyl groups on the so-called “lower rim” forming a circular hydrogen-bonded network. The smaller cavity size for calix[4]arene means that it is able to bind only small guest molecules such as solvent molecules5 or associate with the rim of another calix[4]arene as in the case of trimeric calix[4]arene formed by sublimation.6 The larger cavity size for calix[5]arene is reflected in its ability to readily bind solvent molecules7 along with larger molecules such as ferrocene,8 carborane,9 and the globular-like fullerenes.10 Thus, calix[5]arene is an attractive host molecule for the complexation of a wide range of guest molecules. In this paper we report the crystal structures of four new inclusion complexes of p-H-calix[5]arene involving halosubstituted benzenes. These include the isostructural complexes with fluoro-, chloro-, and bromobenzene, in which the 1:1 host–guest supermolecules (halobenzene∩calix[5]arene) pack together into columnar arrays. The larger iodobenzene cannot adopt the same orientation in the cavity as the other halobenzenes, and the supermolecules pack into sheets in the extended structure. We also report a detailed analysis of the intermolecular interactions using Hirshfeld surfaces.11 Hirshfeld surfaces are very informative in mapping out the intermolecular interactions * Tel: +618 6488 3045. Fax: +618 6488 1005. E-mail: clraston@ chem.uwa.edu.au.
between molecules within the molecular crystal in a visual manner allowing for a rapid understanding of the nature of such interactions, even for complex supramolecular systems.10d,12 The related two-dimensional fingerprint plots give a quantitative analysis of the nature and type of interaction, which is of particular importance in structures that contain the same or structurally similar molecules.13 Results and Discussion There has only been a few reported small molecule inclusion complexes of p-H-calix[5]arene in the literature, which include complexes with dichloromethane,7 acetonitrile,8 acetone,14 and various methyl substituted benzenes.15 In all cases, the p-Hcalix[5]arene adopts the cone-shaped conformation, which is in contrast to the unsolvated R-polymorph of p-H-calix[5]arene, which is formed by sublimation.16 The R-polymorph adopts an inverted cone conformation, which seemingly controls the formation of helical stacks in the extended structure. A second unsolvated β-polymorph can also be isolated by sublimation or crystallization from isopropyl alcohol, which adopts the usual cone-conformation. Interestingly, only the β-polymorph is active for CO2 sorption.16 The p-H-calix[5]arene inclusion complexes 1–4 were prepared by slow evaporation from a solution of pure p-H-calix[5]arene in the respective solvent, with crystals suitable for single crystal diffraction studies forming over a period of 1-5 days (Scheme 1). From fluorobenzene, p-H-calix[5]arene crystallizes as a 1:1 inclusion complex 1, with one host–guest supermolecule, [fluorobenzene∩calix[5]arene], in the asymmetric unit, in the trigonal space group P3c1. Crystallization from either chloroor bromobenzene afforded the corresponding 1:1 inclusion complexes 2 and 3, respectively, which are isostructural with complex 1, crystallizing in the same space group. From iodobenzene, p-H-calix[5]arene crystallizes in the orthorhombic space group Pca21 also as a 1:1 inclusion complex 4, with one host–guest supermolecule, [iodobenzene∩calix[5]arene], in the asymmetric unit, albeit now with a different interplay of the components of the supermolecule. Structure of [X-Benzene∩calix[5]arene], X ) F, Cl, and Br, Complexes 1–3, Respectively. The calixarenes have a slightly distorted cone conformation as evident by analysis of
10.1021/cg070632y CCC: $40.75 2008 American Chemical Society Published on Web 02/14/2008
Inclusion Complexes of p-H-calix[5]arene
Figure 1. Projections for complex 1: (i) Asymmetric unit showing the aromatic C-H · · · π interactions in the supermolecule, [fluorobenzene∩ calix[5]arene]. (ii) The arrangement of three fluorobenzene molecules, showing the C-H · · · F hydrogen bonds. (iii) As for (ii) with space filling. For all figures, the following coloring scheme is adopted: purple for p-H-calix[5]arene carbons, green for solvent carbons, grey for hydrogens, gold for fluorine atoms, pink for chlorine atoms, yellow for bromine atoms, and light blue for iodine atoms.
Scheme 1. Schematic Representation for the Formation of Inclusion Complexes 1–4 from Their Respective Solvents
the angles between the least-squares planes of the “O” centers and phenyl rings varying from 124.6–140.1, 125.8–140.8 and 129.0–140.8° for complexes 1-3, respectively. Within each calixarene the five O-H groups form the expected disordered hydrogen-bonded array, with O · · · O distances in the range of 2.73–2.81, 2.73–2.83, and 2.72–2.84 Å for complexes 1–3, respectively. The fluorobenzene molecule is slightly offset from the center of the cavity with the fluorine atom residing in the cleft generated by two adjacent phenyl groups, presumably in relieving the steric congestion. This interplay involves several aromatic C-H · · · π interactions ranging from 2.67 (ortho), 3.14 (meta), and 3.52 (para) Å relative to the fluorine atom, Figure 1(i). The fluorobenzene molecule is tilted upward out of the cavity with the dihedral angle θ between the principal axis of the calixarene and the principal axis of the fluorobenzene being 34.0°. A measure of how deep the fluorobenzene molecule resides in the cavity is quantified by the distance between the center of the aromatic ring of fluorobenzene and the centroid of the five O-centers, which is 4.19 Å.
Crystal Growth & Design, Vol. 8, No. 3, 2008 891
Figure 2. Projections and packing diagram for complex 1 down the c axis: (i) Extended packing showing the hexagonal close packing arrangement (pink) and the star-shape motif (yellow). (ii) Extended packing showing the columnar arrangement with each column comprised of three closely associated calix[5]arenes.
The extended structure is comprised of columnar arrays of calixarenes containing a repeating unit of two segments with each segment of a column having three calixarenes around a 3-fold axis, Figure 1(ii and iii). The two segments in the repeating unit are offset by 60° relative to each other. The fluorobenzene molecules within each segment are associated via C-H · · · F hydrogen bonds at 2.77 Å and there are two aromatic C-H · · · F hydrogen bonds at distances of 2.86 and 3.33 Å between fluorobenzene and a neighboring p-Hcalix[5]arene. The two repeating segments are connected via a methylene C-H · · · π interaction between a calixarene and fluorobenzene at 3.28 Å and an aromatic C-H · · · π interaction between calixarenes at 3.35 Å. The peripheral of each column is lined with the lower rim of the calixarenes, and the fluorobenzene molecules are embedded within the columns. This is reminiscent of the columnar arrangement in the 1:1 complex of fullerene C60 and p-H-calix[5]arene.10a The principal axes of the calixarenes are not orthogonal to the principal axis of the columns but rather are skewed by 131.7°. The columns form an hexagonal closed packed arrangement with all the columns facing in the same direction, Figure 2(i and ii). This is in contrast to the hexagonal closed packed arrangement seen for the 1:1 inclusion complexes of p-Hcalix[5]arene with o-xylene or toluene where neighboring columns are directed in opposing directions.15 The asymmetric unit in this instance contains three host–guest supermolecules with two of these forming a back-to-back dimer, which imparts the different directions of neighboring columns. In the current case, there are no back-to-back dimers of calixarenes, and the columns are associated by two aromatic C-H · · · π interactions at distances of 2.74 and 3.26 Å. Each hexagon contains one full column and one-third of six columns giving three columns
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Figure 3. Projections and packing diagrams for complexes 2 and 3: (i) Asymmetric unit of complex 2 showing the aromatic C-H · · · π interactions in the supermolecule, [chlorobenzene∩calix[5]arene]. (ii) “Tricalix[5]arene” segment for complex 2, which forms the columnar arrays. (iii) Asymmetric unit of complex 3 showing the aromatic C-H · · · πinteractionsinthesupermolecule,[bromobenzene∩calix[5]arene]. (iv) “Tricalix[5]arene” segment for complex 3, which forms the columnar arrays.
in total, Figure 2(i). Within each hexagon, the circumferences around segments of the six neighboring columns that surround a complete central column create the outline of a star-shape motif, Figure 2(i). The structures of [chlorobenzene∩calix[5]arene] (2) and [bromobenzene∩calix[5]arene] (3) are isostructural with the fluorobenzene complex 1 and adopt the same columnar arrays in their extended packing. The interplay of the two components in the supermolecules involves aromatic C-H · · · π interactions at 2.81 (ortho), 3.03 (meta), and 3.21 (para) Å for chlorobenzene and 2.83 (ortho), 2.81 and 2.95 (meta), and 2.96 Å (para) for bromobenzene (positions are relative to the halogen atom), Figure 3(i and iii). It is noteworthy that the para aromatic C-H · · · π distances decrease as the size of the halogen atom increases (3.52 Å for F, 3.21 Å for Cl, and 2.96 Å for Br) indicating a slight shift in the positioning of the solvent guest molecule in the cavity. The dihedral angle, θ, for chloro- and bromobenzene are 37.3 and 36.1°, respectively, and chloro- and bromobenzene sit 4.09 and 4.02 Å deep in the cavity, respectively. The halobenzenes within each segment involve aromatic C-H · · · X interactions at distances of 2.91–2.93 and 2.92 Å for chloro- and bromobenzene, respectively, Figure 3(ii and iv). The C-H · · · X hydrogen bond distances between the halobenzene and a neighboring p-H-calix[5]arene are 2.93 and 3.30 Å for chlorobenzene and 3.05 and 3.45 Å for bromobenzene. Structure of [Iodobenzene∩calix[5]arene]: 4. Here the calixarenes also have a slightly distorted cone conformation as evident by analysis of the angles between the least-squares planes of the “O” centers and phenyl rings varying from 127.2–135.1°. In addition, within each calixarene the five O-H groups form the expected disordered hydrogen-bonded array, with O · · · O distances in the range of 2.75–2.83 Å. The iodobenzene molecule sits 4.17 Å deep within the cavity (ring center to the centroid of the five oxygen atoms of the
Figure 4. Projections and packing diagram for complex 4. (i) Asymmetric unit showing the aromatic C-H · · · π interactions in the supermolecule, [iodobenzene∩calix[5]arene]. (ii) Extended packing showing the alternating sheets as viewed down the b axis.
calixarene), with aromatic C-H · · · π interactions with the walls of the calixarenes at distances of 2.81–2.91 (meta) and 3.12 (para) Å relative to the iodine atom, Figure 4(i). There are no ortho aromatic C-H · · · π interactions in contrast to complexes 1-3, and the iodine atom does not reside in the cleft generated by two adjacent phenyl rings. Instead, the iodine atom points out of the cavity over one edge of a phenyl ring with the iodobenzene molecule having a dihedral angle of 30.2°. The larger size of the iodine atom means it cannot adopt the same orientation as the other halobenzenes and packs into sheets in the extended structure, Figure 4(ii). The calixarenes orientate themselves into alternating sheets in the extended packing with the principal axes of the calixarenes in different sheets offset by 72.6°. The supermolecules within a sheet are held together via aromatic C-H · · · π interactions at distances of 3.07–3.11 Å. The alternating sheets are associated via aromatic and methylene C-H · · · π interactions at distances of 2.97–3.51 and 3.34 Å, respectively. Hirshfeld Surface Analysis. We examined the intermolecular interactions present in complexes 1–4 using Hirshfeld surface
Inclusion Complexes of p-H-calix[5]arene
Crystal Growth & Design, Vol. 8, No. 3, 2008 893 Table 1. Summary of the various Contact Contributions to the Calixarene Hirshfeld Surface Area in Complexes 1-4a C-H · · · π acceptor C-H · · · π donor H· · ·H H· · ·F C· · ·C C· · ·X C· · ·O O· · ·H O· · ·X a
Figure 5. Hirshfeld surface analysis of the “tricalix[5]arene” segments in complexes 1-3. (i) dnorm surface. (ii) Two-dimensional fingerprint plots with the C-H · · · π interactions highlighted in color.
analysis, which is a useful tool to describe the surface characteristics of molecules.11 Hirshfeld surfaces offer a novel way of visualizing intermolecular interactions by color-coding short or long contacts, the color intensity indicating the relative strength of the interactions. Two-dimensional fingerprint plots complement these surfaces, quantitatively summarizing the nature and type of intermolecular contacts experienced by the molecules in the crystal. These plots, generated by triangulation of the Hirshfeld surface, depict the fraction of points on the surface as a function of the closet distances from the point to nuclei inside and outside the surface.13 The two-dimensional fingerprint plots can also be broken down to give the relative contribution to the Hirshfeld surface area from each type of interactions present, quoted as the “contact contribution”. The three surfaces used in this study are de, which is the distance from the surface to the nearest atom exterior to the surface, di, which is the distance from the surface to the nearest atom interior to the surface, and dnorm,17 which is a normalized contact distance taking into account the van der Waals (vdW) radius of the appropriate atom. The dnorm surface is important in the context of the current study where there is a considerable difference in size of the halogen atoms. dnorm is depicted in a red-white-blue color scheme whereby red highlights shorter than vdW contacts, white for contacts around the vdW separation, and blue is for longer than vdW contacts. Also as dnorm is symmetrical about de and di, both donor and accepter close contacts are depicted on the surface. Figure 5(i) displays the Hirshfeld surfaces mapped with dnorm for the p-H-calix[5]arene units that make up the three closely associated calix[5]arenes for inclusion complexes 1–3. The dnorm
complex 1
complex 2
complex 3
complex 4
19.3 11.1 55.0 2.3 3.3 0.5 0.7 7.8 0.0
19.2 10.8 54.8 2.6 3.3 0.6 0.8 7.9 0.0
19.2 10.9 54.8 2.5 3.2 0.6 0.8 7.9 0.0
20.0 9.1 55.6 3.3 3.0 0.9 0.1 7.8 0.3
Contacts may not sum to 100% due to rounding.
surfaces highlight the C-H · · · π close contacts between the included halobenzene and the inner walls of the calixarenes as increasing brighter red spots as the size of the halobenzene increases. This is clearly seen for the para position whereby there is no red spot for fluorobenzene, a light red spot for chlorobenzene, and a bright red spot for bromobenzene (C-H · · · π distances: 3.52 Å for F, 3.21 Å for Cl, and 2.96 Å for Br). The corresponding fingerprint plots for the calixarene Hirshfeld surfaces are shown in Figure 5(ii) with the characteristic “wings” in the upper left and lower right of the plot that represent the C-H · · · π close contacts, highlighted in color. The plots show pseudosymmetry on either side of the diagonal where de ) di with hydrogen-bond acceptors having di > de and hydrogen bond donors having de > di. The total C-H · · · π contact contribution for the calixarene Hirshfeld surface area is 30.4, 30.1, and 30.2% for complexes 1-3, respectively (Table 1). The remaining contact contributions to the calixarene Hirshfeld surface area in complexes 1-3 are summarized in Table 1. A noteworthy feature of the calixarene fingerprint plots of complexes 1-3 is the subtle change in the characteristic H · · · H fingerprint as the size of the included halobenzene increases. There is distinct splitting of the short H · · · H contacts at de ≈ di ≈ 1.02, 1.08, and 1.10 Å for complexes 1-3, respectively, which are associated with a short contact between three hydrogens from neighboring calixarenes. The short H · · · H contact distance increases as the size of the included halobenzene increases, which is accompanied by an increase in the a axis, from 19.324 Å to 19.500 and 19.552 Å, respectively, for complexes 1-3. The result is an expansion of the “tricalix[5]arene” segment, which can also be seen in the close contacts between the halogen atom of a halobenzene and a hydrogen atom (H35) on a neighboring calixarene increasing in distance from 2.86, 2.93, and 3.05 Å in complexes 1-3, respectively. The expansion of the “tricalix[5]arene” is manifested in the columns shrinking slightly as indicated by a decrease in the c axis, from 14.625, to 14.575 and 14.587 Å, respectively, for complexes 1-3. Figure 6(i) displays the Hirshfeld surfaces mapped with dnorm for two of the halobenzene molecules that make up the “tricalix[5]arene” segment in the isostructural complexes 1-3. There is a bright red spot on the upper Hirshfeld surface of the benzene ring system of all three halobenzenes, which is associated with a methylene C-H · · · π interaction with a neighboring calixarene. The Hirshfeld surface for fluorobenzene shows no short contacts on the fluorine or ortho-hydrogen, but these short contacts become more evident as the size of the halogen atom increases and bromobenzene shows two prominent spots indicating C-H · · · Br hydrogen-bonding interactions. The increase in size of the halogen results in more steric hindrance within the “tricalix[5]arene” segments, and these short contacts become more apparent. The final red spot to the right indicates a short C-H · · · π close contact between the components of the 1:1 supermolecule.
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Figure 7. Hirshfeld surface analysis of complex 4. (i) dnorm surface for p-H-calix[5]arene and the corresponding two-dimensional fingerprint plot. (ii) dnorm surface for iodobenzene and the corresponding twodimensional fingerprint plot. C-H · · · I close contacts are highlighted in color. Table 2. Summary of the Various Contact Contributions to the Halobenzene Hirshfeld Surface Area in Complexes 1–4a
Figure 6. Hirshfeld surface analysis of the halobenzene molecules in complexes 1–3. (i) dnorm surface. (ii) Two-dimensional fingerprint plots with the C-H · · · X interactions highlighted in color.
The corresponding fingerprint plots for the halobenzene Hirshfeld surfaces in complexes 1–3 are shown in Figure 6(ii) with the C-H · · · X close contacts highlighted in color. The C-H · · · X close contacts show the characteristic “wing” type feature as seen for the C-H · · · π interactions earlier. For the chloro- and bromobenzene fingerprint plots, the C-H · · · X close contacts overlap substantially with the C-H · · · π close contacts, whereas in fluorobenzene the spikes appear more toward the H · · · H close contacts region. This difference in separation of the spikes across the diagonal is a result of the relative sizes of the halogen atoms, F ) 1.47 (H ) 1.20), Cl ) 1.75, and Br ) 1.85 Å,18 with the larger halogen atoms creating more separation. The minimum values of di for chloro- and bromobenzene are 1.70 and 1.76 Å, which compare favorably with the analogous values for isostructural 1,3,5-trichlorobenzene and 1,3,5-tribromobenzene, di values of 1.80 and 1.89 Å, respectively.19 The C-H · · · X contact contributions for the halobenzene Hirshfeld surface areas are 14.5, 20.3, and 21.6% for the acceptor and 5.7, 5.3, and 5.3% for the donor contacts in complexes 1-3, respectively (Table 2). It is noteworthy that as the size of the halogen atom increases the percentage of halobenzene C-H · · · X acceptor close contacts increases due to an increase in the steric strain within the “tricalix[5]arene” segment. To compensate for the increase in C-H · · · X acceptor close contacts the percentage of H · · · H close contacts decreases, and this effect is more clearly seen in fluorobenzene due to the much smaller size of the fluorine atom compared to the chlorine or bromine atom. The remaining contact contributions to the halobenzene Hirshfeld surface area in complexes 1-3 are summarized in Table 2.
C-H · · · X acceptor C-H · · · X donor C-H · · · π H· · ·H C· · ·C C· · ·X X· · ·X O· · ·X a
complex 1
complex 2
complex 3
complex 4
14.5 5.7 40.5 30.4 7.0 1.9 0.0 0.0
20.3 5.3 39.9 25.8 6.6 2.1 0.0 0.0
21.6 5.3 40.2 23.3 6.3 2.5 0.8 0.0
23.2 0.0 38.5 23.8 9.2 3.5 0.0 1.7
Contacts may not sum to 100% due to rounding.
Figure 7 displays the Hirshfeld surfaces mapped with dnorm for p-H-calix[5]arene and iodobenzene in complex 4. The dnorm Hirshfeld surface for p-H-calix[5]arene highlights the two meta and one para C-H · · · π interactions as bright red spots on the inner walls of the calixarene cavity, which is in contrast to complexes 1-3, which all have one ortho C-H · · · π interaction, among others. The dnorm surface for iodobenzene shows three bright red spots (there are no red spots on the other side of the molecule hidden from view) with the far right spot being a C-H · · · π close contact and the far left spot being a methylene C-H · · · I close contact. The corresponding fingerprint plots for the p-H-calix[5]arene and iodobenzene Hirshfeld surfaces are shown in Figure 7 for complex 4 with the C-H · · · I close contacts highlighted in color. The fingerprint plot for p-H-calix[5]arene shows short H · · · H close contacts at de ) di ) 1.10 Å and C-H · · · I donor contacts contributing 3.3% to the calixarene Hirshfeld surface area. The fingerprint plot for iodobenzene shows a spike at di ) 1.24 Å and de ) 1.31 Å, which is associated with a close H · · · H contact between a methylene C-H and an aromatic C-H, and C-H · · · I acceptor contacts contribute 23.2% to the halobenzene Hirshfeld surface area. The lack of both donor and acceptor contributions reflects the lack of C-H · · · I attractive interactions between components in the supermolecule and extended packing and seemingly the iodobenzene molecule is too large to form the “tricalix[5]arene” segment.
Inclusion Complexes of p-H-calix[5]arene
Crystalline chlorinated, brominated, and iodinated hydrocarbons are often isostructural, while many fluorinated compounds have identical structures as their hydrocarbon analogues.20 This is due to a combination of the van der Waals radii (H ) 1.20, F ) 1.47, Cl ) 1.75, Br ) 1.85, and I ) 1.98 Å) and the electronegativity (H ) 2.1, F ) 4.0, Cl ) 3.0, Br ) 2.8, and I ) 2.5 Å) of the various atoms, among other things. The series of complexes reported in this paper do not follow this sequence. This stems from the larger iodine atom being too sterically demanding to form the “tricalix[5]arene” array. This correlates well with the corresponding toluene 1:1 inclusion complex,15 which forms similar “tricalix[5]arene” segments, but it is not isostructural with complexes 1–3, noting that iodine atoms are larger and bromine atoms are smaller than CH3 groups. The benzene 1:1 inclusion complex21 is isostructural with the toluene 1:1 inclusion complex indicating that the electronegativity difference between H and F is important in determining which of the two “tricalix[5]arene” arrays are formed, that found in the toluene complex or in complex 1. Conclusion We have structurally authenticated four new inclusion complexes of p-H-calix[5]arene and undertaken a detailed analysis of their Hirshfeld surfaces to gain a greater understanding of the intermolecular interactions involved in the crystal packing for assembled arrays containing large molecules. The complexes with fluoro-, chloro-, and bromobenzene are all isostructural forming columnar arrays in the extended structure which are associated with the formation of “tricalix[5]arene” arrays involving C-H · · · X hydrogen bonds. The fingerprint plots for the calixarene Hirshfeld surfaces indicate an expansion of the tricalix[5]arene segments as the size of the included halobenzene increases, which is accompanied by an increase in the a axis. The complex with iodobenzene forms sheets of calixarenes in the extended structure which arises from the more bulky iodine atoms blocking the formation of the interlocked “tricalix[5]arene” array. Overall, the interplay of host–guest supermolecules within the four complexes is readily mapped out using Hirshfeld surfaces and the associated fingerprint plots, and the technique is clearly destined to become a general analytical tool in analyzing supramolecular complexes. Experimental Section All solvents were purchased from commercial suppliers and used without further purification. p-H-Calix[5]arene22 was prepared from p-But-calix[5]arene4a as described previously in the literature. Complexes 1–4 were prepared by slow evaporation of a pure solution of p-H-calix[5]arene (15 mg/mL) in the respective solvent, with crystals suitable for single-crystal diffraction studies forming over 1-5 days. Crystal uniformity of each sample was checked by determining unit cell dimensions on crystals from the same preparation and from different preparations. Hirshfeld surfaces and fingerprint plots were produced with CrystalExplorer23 with bond lengths to hydrogen atoms set to standard values.24 The orientational disorder of the lower rim hydroxyl groups on p-H-calix[5]arene was not resolved before analysis of the structures as the disorder had little overall effect on the results. X-ray Crystallography. The X-ray diffracted intensities were measured from single crystals at about 100 K on an Oxford Diffraction Xcalibur CCD diffractometer using monochromatized Mo-KR (λ ) 0.71073 Å.) Data were corrected for Lorentz and polarization effects and absorption correction applied using multiple symmetry equivalent reflections. The structures were solved by direct method and refined on F2 using the SHELX-97 crystallographic package25 and the X-Seed interface.26 A full matrix least-squares refinement procedure was used, minimizing w(Fo2 - Fc2), with w ) [σ2(Fo2) + (AP)2 + BP]-1, where P ) (Fo2 + 2Fc2)/3. Agreement factors (R ) Σ|Fo| - |Fc|/Σ|Fo|, wR2 )
Crystal Growth & Design, Vol. 8, No. 3, 2008 895 {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]}1/2 and GOF ) {Σ[w(Fo2 - Fc2)2]/(n p)}1/2 are cited, where n is the number of reflections and p is the total number of parameters refined). Non-hydrogen atoms were refined anisotropically using a unique set of all reflections. The positions of hydrogen atoms calculated from geometrical consideration and their atomic parameters were constrained to the bonded atoms during the refinement. CCDC deposition numbers are 652323–652326. Crystal/refinement details for complex 1: C41H35FO5, M ) 626.69, F(000) ) 1980 e, trigonal, P3c1, Z ) 6, T ) 100(2) K, a ) 19.3236(4), c ) 14.6250(2) Å, V ) 4729.36(12) Å3, Dc ) 1.320 g/cm3, sin θ/λmax ) 0.5946, N(unique) ) 2757 (merged from 77183, Rint ) 0.0813, Rsig ) 0.0394), No (I > 2σ(I)) ) 2524, R ) 0.0922, wR2 ) 0.2276 (A,B ) 0.15, 10.0), GOF ) 1.002, |∆Fmax| ) 0.4(1) e Å-3. Crystal/refinement details for complex 2: C41H35ClO5, M ) 643.14, F(000) ) 2028 e, trigonal, P3c1, Z ) 6, T ) 100(2) K, a ) 19.500(1), c ) 14.5746(4) Å, V ) 4799.5(3) Å3, Dc ) 1.335 g/cm3, sin θ/λmax ) 0.5946, N(unique) ) 2823 (merged from 37912, Rint ) 0.0780, Rsig ) 0.0610), No (I > 2σ(I)) ) 1882, R ) 0.0455, wR2 ) 0.1007 (A,B ) 0.07, 0.00), GOF ) 1.004, |∆Fmax| ) 0.52(5) e Å-3. Crystal/refinement details for complex 3: C41H35BrO5, M ) 687.60, F(000) ) 2136 e, trigonal, P3c1, Z ) 6, T ) 100(2) K, a ) 19.552(1), c ) 14.5870(3) V ) 4829.2(3) Å3, Dc ) 1.419 g/cm3, sin θ/λmax ) 0.5946, N(unique) ) 2836 (merged from 26673, Rint ) 0.0652, Rsig ) 0.0538), No (I > 2σ(I)) ) 2134, R ) 0.0557, wR2 ) 0.1374 (A,B ) 0.09, 5.00), GOF ) 1.003, |∆Fmax| ) 1.16(7) e Å-3. Crystal/refinement details for complex 4: C41H35IO5, M ) 734.59, F(000) ) 1496 e, orthorhombic, Pca21 (No. 29), Z ) 4, T ) 100(2) K, a ) 18.0409(4), b ) 11.9567(3), c ) 15.2864(4) Å, V ) 3297.42(14) Å3, Dc ) 1.480 g/cm3, sin θ/λmax ) 0.6497, N(unique) ) 3817 (merged from 37837, Rint ) 0.0742, Rsig ) 0.0864), No (I > 2σ(I)) ) 2331, R ) 0.0325, wR2 ) 0.0544 (A,B ) 0.02, 0.00), GOF ) 1.001, |∆Fmax| ) 1.07(6) e Å-3.
Acknowledgment. We thank the ARC for financial support of this work and the University of Western Australia for a SIRF award to T.C. Supporting Information Available: Crystallographic information file (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.
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