Microporous Nanotubular Self-Assembly of a Molecular Chair

CRYSTAL GROWTH & DESIGN

Microporous Nanotubular Self-Assembly of a Molecular Chair

2009 VOL. 9, NO. 7 2979–2983

N. N. Adarsh, D. Krishna Kumar,# and Parthasarathi Dastidar* Department of Organic Chemistry, Indian Association for the CultiVation of Science (IACS), 2A & 2B Raja S C Mullick Road, JadaVpur Kolkata - 700032, West Bengal, India ReceiVed December 19, 2008; ReVised Manuscript ReceiVed May 25, 2009

ABSTRACT: A M6L6 type molecular chair, [(Zn6(µ-L4)6Cl12) · X] 4 (X ) disordered lattice included solvents), has been isolated by reacting N,N′-bis-(4-pyridyl)amido-2-oxo-imidizolidine (L4) with ZnCl2, and characterized by single crystal X-ray diffraction. The structure of 4 revealed a microporous nanotubular self-assembly having a pore size as large as zeolites. The robustness and microporosity of 4 was evident from thermogravimetric and X-ray powder diffraction experiments. Isolation of 4 was a consequence of the exploratory studies on the effect of the hydrogen bonding backbone, ligating topologies of the ligands on the supramolecular structures of the resulting compounds derived from various pyridyl based ditopic ligands, namely, N,N′-bis-(3-pyridyl)ethylene-bis-urea (L1), N,N′-bis-(4-pyridyl)ethylene-bisurea (L2), and their corresponding 2-oxoimidazolidine derivatives, namely, N,N′-bis-(3-pyridyl)amido-2-oxo-imidizolidine (L3) and N,N′bis-(4-pyridyl)amido-2-oxo-imidizolidine (L4). Single crystal structures of [(Zn(µ-L1)Cl2) · 2MeOH]n (1), [(Zn(µ-L2)Cl2) · X]n (2) (X ) disordered lattice included solvents), and [((L3)(Cl)2Zn(µ-L3)Zn(L3)(Cl)2] (3) are also discussed in this context. Metal-organic frameworks (MOFs) are an important class of supramolecular compounds because of their various potential applications.1 Among the various structures in MOFs, metallamacrocycles2 are important to study because of their fundamental importance in getting access to nanoscale objects with definite shapes and geometries that are otherwise inaccessible. Metallamacrocycles with well-defined shapes such as molecular triangles,3 squares,4 pentagons,5 hexagons,6 and circular helicates7 have all been achieved. Strategies used by Stang,2a Fujita, Newkome and many others8 to synthesize intriguing metallamacrocycles rely on the use of relatively rigid ditopic N-donor ligands with predefined ligating topology and metal-complex species with coordinatively unsaturated transition-metal centers; metallamacrocycles synthesized by using linear ditopic ligands and naked transition-metal ions have also been reported.9 Most of the discrete metallamacrocycles2 are comprised of ditopic ligands (having innocent, i.e., nonfunctional backbone) and transition-metal centers having either square planar or octahedral geometry. On the other hand, examples of metallamacrocycle comprised of tetrahedral metal center (inspired by the hydrocarbon based polygon structures wherein nodal point is a tetrahedral C atom) and N-donor ditopic ligand (having noninnocent, i.e., functional backbone) are scarce.10 In this communication, we report the supramolecular self-assembly of a hexanuclear Zn(II) compound, namely, [(Zn6(µ-L4)6Cl12) · X] 4 (X ) disordered lattice included solvents) that resembles a molecular chair. Compound 4 was obtained as a consequence of our exploratory studies on the effect of a hydrogen bonding backbone and ligating topologies of the ligands on the supramolecular structures of the resulting MOFs.11 The hydrogen bonding backbone of the ligand is important to study because it offers further supramolecular binding sites that can help self-assemble to form hierarchical superstructures,11b,12 recognize anions,13 and trap guests molecules in the crystal lattice.14 Thus, for the reasons stated above, we decided to react two bispyridyl-bis-urea based ditopic ligands, namely, N,N′-bis-(3-pyridyl)ethylene-bis-urea (L1), N,N′-bis-(4-pyridyl)ethylene-bis-urea (L2) and their corresponding 2-oxoimidizolidine derivatives, namely, N,N′-bis-(3-pyridyl)amido-2-oxo-imidizolidine (L3) and N,N′-bis(4-pyridyl)amido-2-oxo-imidizolidine (L4) separately with ZnCl2 (Scheme 1, for synthesis see Supporting Information). While the urea/2-oxoimidazolidine functionalities provided the hydrogen bonding backbone, the tetrahedral Zn(II) metal center was kept fixed * To whom correspondence should be addressed. E-mail: parthod123@ rediffmail.com; [email protected]. # Present address: Department of Chemistry, University at Albany State University of New York, 1400 Washington Avenue, Albany, NY 12222.

Scheme 1

in order to study the effect of the hydrogen bonding backbone, positional isomerism and consequently ligating topologies of the ligands on the resulting structures. Since formation of metallamacrocycle is always a thermodynamic possibility in such a supramolecular event, we selected Zn(II) in order to incorporate tetrahedral metal center in the plausible metallamacrocycle. [(Zn(µ-L1)Cl2) · 2MeOH]n (1) belonged to the centrosymmetric monoclinic space group C2/c.15 The asymmetric unit was comprised of one Zn(II) (located on a 2-fold axis), half a molecule of L1 (located around a center of symmetry and coordinated to the metal center via pyridyl N atom), one chloride (coordinated to the metal center), and a lattice included MeOH. The backbone of the ligand adopted an energetically more favorable staggered conformation around the central C-C bond keeping the urea >CdO groups anti to each other in order to nullify the >CdO dipole. The terminal pyridyl moieties which were coordinated to the adjacent metal center were oriented in anti-anti fashion (relative to the adjacent urea >CdO) resulting in a linear ligating topology. Interestingly, the free ligand structure reported by us13f and also by others16 displayed a similar conformation. The structure of 1 can be best described as a 1D coordination polymer. The typical hydrogen bonded network of urea17 (wherein the bifurcated hydrogen bonding interactions of the carbonyl O atom with the two N-H moieties of the adjacent urea molecule lead to the formation of 1D hydrogen bonded tape) was absent in the structure. Instead, the lattice included MeOH took part in hydrogen bonding interactions with the urea >CdO and N-H [O · · · O ) 2.759(6) Å; ∠O-H · · · O ) 174.1° and N · · · O ) 2.807(6)-3.110(6) Å; ∠N-H · · · O ) 144.4-167.0] of the adjacent polymeric chains resulting in the formation of a two-dimensional sheet structure (Figure 1). Thermogravimetric (TG) data showed a weight loss of 9.0% in the temperature range of 23-145 °C, which matched reasonably well with the X-ray data (calcd. weight loss for two MeOH ) 12.8%). A 4% difference in the weight loss may be due to the fast escape of MeOH molecules from the crystal lattice

10.1021/cg8013859 CCC: $40.75  2009 American Chemical Society Published on Web 06/02/2009

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Figure 1. Illustration of single crystal structure of 1; (a) conformation of the ligand L1 in 1 displaying linear ligating topology; (b) 2D sheet structure as a result of MeOH bridging of the 1D coordination polymeric chains.

before loading the sample for TG experiments (Figure S3, Supporting Information). [(Zn(µ-L2)Cl2) · X]n 2 (X ) disordered lattice included solvents) crystallized in the monoclinic space group P21/m.15 The asymmetric unit was comprised of one Zn(II), half a molecule of L2 (located across a mirror plane and coordinated to the metal center via pyridyl N atoms), two chloride ions (coordinated to the metal center), and some disordered lattice included solvents entrapped in the crystal lattice. The central C-C bond of L2 was found to be disordered over two positions and the ligand adopted an energy expensive eclipsed conformation. Thus, the angularly disposed pyridyl moieties of L2 were coordinated to the adjacent metal centers resulting in the formation of a 1D zigzag polymeric chain propagating along the b-axis. Two such chains were packed in parallel fashion via C-H · · · O [C · · · O ) 3.256(7)-3.275(7) Å] interactions involving pyridyl C-H and urea carbonyl moieties resulting in a 1D hydrogen bonded tape. Such tapes were further self-assembled via C-H · · · π [C · · · C ) 3.380(12) Å; the parameters involving hydrogen could not be obtained due to the disorder of the ethylene moiety] interactions involving the central ethylene and pyridyl moieties of the adjacent tapes resulting in a 2D corrugated sheet (Figure 2). The disordered lattice included solvents that were located in between the 2D sheets. The contribution of the disordered lattice included solvents were subtracted from the overall diffraction data following a well-established method SQUEEZE18 which showed a total solvent accessible area volume of 372.1 Å3. The relatively noise free data, thus obtained, were then used for further crystallographic refinement. SQUEEZE calculations indicated the presence of a 47e per monomer unit which may be attributed to half a molecule of ethylene glycol (EG), half a molecule of MeOH, and two H2O molecules. Thermogravimetric (TG) data showed a weight loss of 17.4% in the temperature range of 24-125 °C, which corroborated well with the SQUEEZE results (calc. weight loss for 1/2 EG + 1/2 MeOH + 2 H2O ) 16%) (Figure S4, Supporting Information). It may be noted that the urea moieties of L2 did not display any hydrogen bonding, although its interactions with the disordered lattice included solvent molecules could not be ruled out. Thus, the positional isomeric ligands L1 and L2, although they displayed very different ligating topologies (linear in L1 and angular in L2), resulted in quite a similar 1D polymeric structure in the corresponding MOFs 1 and 2. To reduce the flexibility of the ligand backbone and consequently limit the conformations and ligating topologies of the ligands, we synthesized two new ligands L3 and L4 which are positional isomers; the 2-oxoimidazolidine moiety in these ligands ensured the rigidity and planarity of the backbone of the ligands.

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Figure 2. Illustration of single crystal structure of 2; (a) energy expensive eclipsed conformation of the ligand L2 in 2 displaying angular ligating topology; note the disordered backbone of the ligand; (b) 2D corrugated sheet resulting from self-assembly of 1D tapes via C-H · · · π interactions.

[((L3)(Cl)2Zn(µ-L3)Zn(L3)(Cl)2] (3) crystallized in the orthorhombic centrosymmetric space group Pbcn.15 The asymmetric unit was comprised of one Zn(II) metal center, one molecule of L3, half a molecule of L3 (located on a 2-fold axis passing through the central CdO bond, both coordinated to the metal center), and two chloride ions also coordinated to the metal center. Structure of 3 can be best described as a dinuclear Zn(II) complex. The ligand molecule which was located on a 2-fold axis adopted a syn-syn conformation and acted as the bridge between the adjacent metal centers. Interestingly, the terminally coordinated ligand molecules displayed anti-anti conformation. The backbone of both the ligand molecules in the crystal structure of 3 was found to be rigid and planar as expected because of the intramolecular hydrogen bonding involving the >CdO and N-H of the adjacent 2-oxoimidazolidine moieties [N · · · O ) 2.6952(15)-2.7393(19) Å; ∠N-H · · · O ) 129.96(10)-136.60(11)°]. While both the pyridyl moieties of the bridging ligand were in plane with the 2-oxoimidazolidine backbone, one of the metal coordinated pyridyl rings of the terminally coordinated ligands displayed nonplanarity with the 2-oxoimidazolidine backbone (the dihedral angle involving 2-oxoimidazolidine and pyridyl ring is 44.6°). Such deviation from planarity could be because of the steric requirement for the intermolecular hydrogen bonding involving 2-oxoimidazolidine moieties positioned next to the deviated pyridyl rings (vide infra). The bimetallic complex was arranged in a parallel fashion stabilized by various weak nonbonded interactions such as C-H · · · O [C · · · O ) 3.333(2) Å; ∠C-H · · · O ) 136.47(11)°], C-H · · · Cl [3.6220(17) Å)], and C-H · · · π [3.566(3) Å], interactions resulting in a 1D wavy tape. Such tapes are further self-assembled in a 2D corrugated sheet via N-H · · · O hydrogen bonding interactions [N · · · O ) 3.036(2) Å; ∠N-H · · · O ) 128.2°] involving the 2-oxoimidazolidine moieties of the terminally coordinated ligands. CdO · · · π interactions [CdO · · · pyridylcentroid ) 3.790(3) Å] involving carbonyl and pyridyl moieties of interacting complexes were also present in the supramolecular architecture. It may be noted that the backbone of the bridging ligand abstained from any typical intermolecular hydrogen bonding interactions and displayed only weak intermolecular C-H · · · O interactions (Figure 3). Pure L4 was found to be almost insoluble in any organic common solvents, and therefore, crude L4 (soluble in MeOH) was used for the synthesis of [(Zn6(µ-L4)6Cl12) · X] 4 (X ) disordered lattice included solvents) (see Supporting Information). The asymmetric unit of the crystal of 4 (space group, rhombohedral R3j)15 contained one Zn(II), one ligand L4, two chloride and disordered lattice included solvents. 4 is a giant hexanuclear metallamacrocycle

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Figure 3. Illustration of single crystal structure of 3; (a) 1D wavy tape via weak interactions; (b) 2D corrugated sheet architecture.

resembling a hexagon in its chair conformation. The macrocycle was made up of six Zn(II) centers coordinated by six L4 molecules. The ligand molecule L4 in 4 adopted a reasonably planar conformation wherein all the carbonyl groups of the hydrogen bonding backbone were oriented anti to each other. The free ligand also showed a similar conformation (Figure S1, Supporting Information). The Zn(II) metal center took up the nodal position of the hexagonal metallamacrocycle. The molecular chair had an effective pore size of ∼15 × 14 Å (measured by the shortest interatomic distances with corresponding van der Waals radii taken into account) remained uninterpenetrated and packed exactly on top of each other along the c-axis stabilized by π-π stacking and Cl-π interactions involving the π cloud of the pyridyl ring and conjugated π backbone [3.228(8)Å], and metal bound Cl and π cloud of 2-oxoimidazolidine moieties [3.257(5)Å] of the interacting macrocyclic rings, respectively. Such self-assembly of the macrocyclic rings leads to the formation of a nanotubular assembly which was further packed in hexagonal close packing fashion stabilized byC-H · · · O[C · · · O)3.168-3.219Å;∠C-H · · · O)122.4-123.4°], C-H · · · Cl [C · · · Cl ) 3.692(6)Å; ∠C-H · · · Cl ) 149.4(3)°] and π-π stacking [3.130(6) Å] interactions involving the ligand backbone (Figure 4). SQUEEZE18 calculations (which showed a total solvent accessible area volume of 4903.9 Å3) indicated the presence of 621e in the asymmetric unit, which may be attributed to 17 MeOH (306e) and 31 H2O (310e) molecules per macrocycle. Thus, in the TG data, a weight loss of 15.0% at the temperature range of 21-77 °C may be attributed to 17 MeOH molecules (calcd. weight loss for 17 MeOH ) 14%). A further weight loss of 29% at the temperature range of 77-325 °C may be attributed to 31 H2O and 2 ligand molecules (calcd. weight loss for 31 H2O + 2 L4 ) 31%). The rest of the four ligands were released within the temperature range of 325-700 °C with a weight loss of 36% (calcd. weight loss for 4 L4 ) 34%) (Figure S5, Supporting Information). The fact that the XRPD patterns of the as-synthesized bulk solid of 4 and a dried sample after heating at 265 °C matched quite well with that of the simulated XRPD pattern obtained from the single crystal data indicated the stability of the microporous self-assembly of 4 (Figure 5a). It is interesting to note that readsorption of the solvent of crystallization in the crystal lattice of 4 was possible by soaking a dried sample of 4 (dried at 265 °C) in MeOH/water for

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Figure 4. Illustration of single crystal structure of 4; (a) molecular structure of the hexanuclear Zn(II) complex displaying chair conformation; (b) nanotubular packing of the metallamacrocycle displaying various weak interactions (in red dotted line) shown in the inset; (c) hexagonal close packing of the nanotubular structures viewed down the c-axis displaying various weak interactions (in cyan dotted line) shown in the inset.

Figure 5. (a) XRPD patterns and (b) TG plot of 4 under various conditions.

4 days. The dried sample did not show any weight loss until 265 °C in TG data indicating the absence of the lattice included solvents. The resemblance of the TG plots of the soaked sample with that of the as-synthesized sample of 4 clearly indicated the readsorption of the solvent of crystallization (Figure 5b). Although the starting reaction stoichiometry in synthesizing compounds 1-4 was a 1:1 metal/ligand ratio, compound 3 turned out to be a complex of 2:3 metal/ligand ratio, whereas the rest of the compounds showed a 1:1 metal/ligand stoichiometry. Thus, it was considered worthwhile to study the synthesis of the compounds as a function of reaction stoichiometry. Stoichiometry experiments

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were conducted by taking various metal/ligand ratios (2:3, 1:2, and 1:3) under the conditions in which compounds 1-4 were originally isolated. The reaction products were characterized by elemental analysis, X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FT-IR). The elemental analysis (Table S1, Supporting Information) results revealed that in the cases of compounds 1, 2, and 4, the isolated products were of a 1:1 metal/ ligand ratio; in the case of 3, the metal/ligand ratio was found to be 2:3. While the XRPD patterns of the crystalline products isolated from various stoichiometric experiments performed at the synthetic conditions of 3 and 4 match well with that of the simulated XRPD patterns obtained from the corresponding single crystal data, the same is not observed in the cases of 1 and 2; the mismatch of the various XRPD patterns in these cases could be due to the absence of lattice included solvents as well as the presence of other crystalline phases (Figures S6-S9, see Supporting Information for a detailed explanation). In summary, we have explored pyridyl based, hydrogen bond functionalized ditopic ligands L1-L4 to search for a metallamacrocycle having a tetrahedral metal center. Interestingly, both L1 and L2, which are positional isomers, showed 1D coordination polymeric chains in their crystal structures. On the other hand, the positional isomeric ligands L3 and L4 whose backbone is planar due to the 2-oxoimidazolidine moiety displayed binuclear Zn(II) metal complex 3 and hexanuclear Zn(II) metallamacrocycle 4. Synthesis of 1-4 as a function of reaction stoichiometry revealed that various reaction stoichiometries did not affect the metal/ligand ratio of the isolated products. The bis-urea backbone of L1 displayed hydrogen bonding interactions with the lattice included solvent (MeOH) in 1. On the other hand, the 2-oxoimidazolidine moieties in the bimetallic complex 3 showed limited N-H · · · O hydrogen bonding interactions, whereas such interactions were completely absent in 4; this could be because of the intramolecular N-H · · · O hydrogen bonding of the 2-oxoimidazolidine backbone of the ligands in 3 and 4. Desolvation at 265 °C and readsorption of the lattice included solvents (MeOH/H2O) in 4 as evidence by XRPD and TG data clearly indicated the robustness and microporosity of the metallamacrocycle which displayed, in its crystal structure, open pores as large as zeolites.

Acknowledgment. We thank Department of Science & Technology (DST), New Delhi, India, for financial support. N.N.A. thanks IACS for research fellowships. Single crystal X-ray diffraction was performed at the DST-funded National Single Crystal Diffractometer Facility at the Department of Inorganic Chemistry, IACS. All the referees are thanked for their fruitful comments and suggestions.

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Supporting Information Available: Synthetic details of the ligands L2-L4 and compounds 1-4, details of single crystal data collection, solution and refinement, crystal structure of L4 (Figures S1 and S2), thermogravimetric plots (Figures S3-S5), XRPD data collection details, XRPD plots (Figure S6-S9), FT-IR plots (Figure S10), elemental analysis (Table S1) under various stoichimetric conditions, and crystallographic data in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

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Des. 2007, 7, 2096. (i) Adarsh, N. N.; Krishna Kumar, D.; Dastidar, P. Inorg. Chem. Commun. 2008, 11, 636. (j) Banerjee, S.; Adarsh, N. N.; Dastidar, P. CrystEngComm 2009, 11, 746. (a) Uemura, K.; Kitagawa, S.; Kondo, M.; Fukui, K.; Kitaura, R.; Chang, H.-C.; Mizutani, T. Chem.sEur. J. 2002, 8, 3586. (b) Sarkar, M.; Biradha, K. Chem. Commun. 2005, 2229. (c) Takaoka, K.; Kawano, M.; Tominaga, M.; Fujita, M. Angew. Chem., Int. Ed. 2005, 44, 2151. (a) Blondeau, P.; van der Lee, A.; Barboiu, M. Inorg. Chem. 2005, 44, 5649. (b) Byrne, P.; Lloyd, G. O.; Clarke, N.; Steed, J. W. Angew. Chem., Int. Ed. 2008, 47, 5761. (c) Bondy, C. R.; Gale, P. A.; Loeb, S. J. J. Am. Chem. Soc. 2004, 126, 5030. (d) Amendola, V.; Boiocchi, M.; Colasson, B.; Fabbrizzi, L. Inorg. Chem. 2006, 45, 6138. (e) Custelcean, R.; Remy, P.; Bonnesen, P. V.; Jiang, D. E.; Moyer, B. A. Angew. Chem.-Int. Edit. 2008, 47, 1866. (f) Adarsh, N. N.; Krishna Kumar, D.; Dastidar, P. CrystEngComm 2008, 10, 1565. (g) Adarsh, N. N.; Krishna Kumar, D.; Dastidar, P. CrystEngComm 2009, 11, 796. (a) Krishna Kumar, D.; Das, A.; Dastidar, P. Inorg. Chem. 2007, 46, 7351. X-ray crystallography: All structures were solved by direct method and refined in a routine manner (see Supporting Information for details). CCDC 702748-702752 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44) 1223-336-033; or [email protected]). Crystal data 1: empirical formulae ) C16H24N6O4ZnCl2, FW ) 500.68, monoclinic, space group C2/c (No. 15), a ) 17.904(3), b ) 6.5317(12), c ) 19.129(4) Å, β ) 109.182(4)0. V ) 2112.9(7) Å3, T ) 100 K, Z ) 4. Fcalcd ) 1.574 g cm-3. F (000) ) 1032 λ (Mo-KR) ) 0.71073 Å, µ MoKR /mm-1 ) 1.451, 2θmax ) 52.00°, 5418 reflections measured, 1653 observed (I > 2σ(I)) 134 parameters; Rint ) 0.0558, R1 ) 0.0723; wR2 ) 0.1389 (I > 2σ (I)), R1 ) 0.0944; wR2 ) 0.1499 (all data) with GOF ) 1.166. 2: empirical formulae )

Crystal Growth & Design, Vol. 9, No. 7, 2009 2983 C14H10N6O2ZnCl2, FW ) 430.55, monoclinic, space group P2(1)/m (No. 11) a ) 7.7022(14), b ) 15.578(3), c ) 10.475(2) Å, β ) 111.553(2)0. V ) 1168.9(4)Å3, T ) 298 K, Z ) 2. Fcalcd ) 1.223 g cm-3. F (000) ) 432, λ (Mo-KR) ) 0.71073 Å, µ MoKR /mm-1 ) 1.295, 2θmax ) 41.38°, 7583 reflections measured, 1111 observed (I > 2σ(I)) 118 parameters; Rint ) 0.0457, R1 ) 0.0419; wR2 ) 0.1312 (I > 2σ(I)), R1 ) 0.0482; wR2 ) 0.1365 (all data) with GOF ) 1.009. 3: empirical formulae ) C45H42N18O9Zn2Cl4, FW ) 1251.51, orthorhombic, space group Pbcn (No. 60) a ) 31.710(3), b ) 7.8001(9), c ) 20.153(2) Å, V ) 4984.7(9) Å3, T ) 100 K, Z ) 4. Fcalcd ) 1.668 g cm-3. F(000) ) 2552, λ (Mo-KR) ) 0.71073 Å, µ MoKR/mm-1 ) 1.254, 2θmax ) 55.9°, 50673 reflections measured, 5058 observed (I > 2σ(I)) 353 parameters; Rint ) 0.0307, R1 ) 0.0293; wR2 ) 0.0723 (I > 2σ(I)), R1 ) 0.0362; wR2 ) 0.0755 (all data) with GOF ) 1.030. 4: empirical formulae ) C90H84N36O18Zn6Cl12, FW ) 2775.55, trigonal, space group R3j (No. 148) a ) 37.1385(14), b ) 37.1385(14), c ) 10.1490(8) Å. V ) 12122.8(12) Å3, T ) 100 K, Z ) 3. Fcalcd ) 1.141 g cm-3. F(000) ) 4212, λ (Mo-KR) ) 0.71073 Å, µ MoKR /mm-1 ) 1.130, 2θmax ) 54.00°, 22424 reflections measured, 3887 observed (I > 2σ(I)) 244 parameters; Rint ) 0.0962, R1 ) 0.0699; wR2 ) 0.1450 (I > 2σ(I)), R1 ) 0.1175; wR2 ) 0.1608 (all data) with GOF ) 1.057. (16) Byrne, P.; Turner, D. R.; Lloyd, G. O.; Clarke, N.; Steed, J. W. Cryst. Growth Des. 2008, 8, 3335. (17) Hollingsworth, M. D.; Harris, K. D. M. In ComprehensiVe Supramolecular ChemistryMacNicol, D. D.; Toda, F.; Bishop, R. , Eds.; Pergamon: Oxford, 1996, Vol. 6, p 177. (18) Van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46 (19), 194. (a) Santos-Contreras, R. J.; Martı´nez-Martı´nez, F. J.; Garcı´aBa´ez, E. V.; Padilla-Martı´nez, I. I.; Peraza, A. L.; Ho¨pfl, H. Acta Crystallogr. 2007, C63, o239. (b) Gautrot, J. E.; Hodge, P.; Cupertino, D.; Helliwell, M. New J. Chem. 2006, 30, 1801.

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