Solid-State Complexes of Calix[4]arene Dihydroxyphosphonic Acid

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Solid-State Complexes of Calix[4]arene Dihydroxyphosphonic Acid with Bipyridyl Ligands Adina N.

Lazar,‡,#

Nathalie

Dupont,†,#

Alda

Navaza,†

and Anthony W.

Coleman*,‡

Institut de Biologie et Chimie des Prote´ ines, CNRS UMR 5086, 7 passage du Vercors, F-69367 Lyon Cedex 07, France, and LPBC-CSSB, CNRS UMR 7033, UFR SMBH, UniVersite´ Paris 13, 74 rue Marcel Cachin, 93017 Bobigny, France

CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 3 669-674

ReceiVed July 28, 2005

ABSTRACT: The robustness of calix[4]arene dihydroxyphosphonic acid and its ubiquitous dimeric motif offers perspectives for predefined solid-state complexation with small molecules. In the current article, we describe the complex of calix[4]arene dihydroxyphosphonic acid with three different forms of bipyridyl ligand: 2,2′-bipyridine, 4,4′-bipyridine, and 1,2-bipyridylethane. A number of resemblances and differences in the interactions between the components in the complexes are pointed out. All the complexes are based on layers of calixarene dimers alternated with layers of bipyridyl molecules. While the complex with 2,2′bipyridine is encaged by a dense network of hydrogen bonds, the complexes with 4,4′-bipyridine and 1,2-bipyridylethane generate an extended 1-D ladder network. All of the complexes present π-π interactions between the bipyridyl moieties and the calix[4]arene dihydroxyphosphonic acid. Introduction

Experimental Section

Calix[4]arene dihydroxyphosphonic acid, 1, is a water-soluble calix[n]arene derivative that shows a remarkable structural diversity in its solid-state complexes with diamines. All are based on the motif of an interdigitating aromatic-aromatic stacked dimer of calix[4]arene dihydroxyphosphonic acid.1 For the aliphatic diamines, caging of the dimeric building block of 1 has been observed in the case of the complex with hexanediamine,2 while the complex of 1 with propanediamine generates an aqua-channel structure based on a hexagonal arrangement of the calixarene dimers.3 In the case of the heterocyclic diamine phenanthroline,4 the dimers of 1 cage π-π stacked dimers of phenanthroline via edge-to-face and face-to-face aromaticaromatic interactions coupled with hydrogen-bonded water networks. The interplay of weak interactions,5,6 including hydrogen bonding, aromatic-aromatic stacking and hydrogen-aromatic interactions, is responsible for the structuring of the various assemblies. However, to use this interplay to allow predefined structures to be generated, studies in which the various interaction parameters are systematically modified are necessary. To this end, we describe in this paper the study of the solid-state structures of calix[4]arene dihydroxyphosphonic acid with 2,2′bipyridine (A), 4,4′-bipyridine (B), and 1,2-bipyridylethane (C). The structural differences in the three heterocyclic diamine ligands allowed us to probe the effects of the geometry and position of the nitrogen atoms and the spacing of the aromatic rings on the assembly of the complexes in the solid state. A secondary consideration was to investigate whether extended solid-state networks could be formed by complexation with the dimer building blocks of 1. 4,4′-Bipyridine is one of the most widely used ligands in crystal engineering, both in the construction of networks based on metal coordination complexes7 and with di- and tricarboxylic acids,8 while 1,2bipyridylethane has been used to a lesser extent in the same ways.9

Synthesis and Crystal Growth. Calix[4]arene dihydroxyphosphonic acid (1) was prepared by a literature method, physical data being in full accord with published data.10 All three complexes have been prepared by the same general protocol: A solution of 0.01 M of 1 in alcohol (methanol or ethanol) has been added slowly to an aqueous solution of A, B, or C at the same molar concentration to obtain an interface between the two solutions. Crystals were obtained by liquid diffusion at room temperature after several days. X-ray Crystallographic Study. The crystal structures were solved by direct methods and Fourier techniques (SIR2002 and SHELXS 97 through the winGX gui11) and were refined by full matrix least squares on F2 (I > 2σ(I)) using the program SHELXL 97.12 Methylene, methyl, and aromatic hydrogen atoms were placed from Fourier difference maps synthesis. Data were corrected for Lorentz and polarization effects but not for absorption. Crystal and refinement data are summarized in Table 1.

* Corresponding author. Tel (+33) 4 72 72 26 40. Fax: (+33) 4 72 72 26 90; (+33) 4 72 72 26 01. E-mail: [email protected]. † Universite ´ Paris 13. ‡ Institut de Biologie et Chimie des Prote ´ ines. # Contributed equally to the publication.

Results and Discussion The chemical structures of calix[4]arene dihydroxyphosphonic acid (1), 2,2′-bipyridine (A), 4,4′-bipyridine (B), and 1,2bipyridylethane (C) are given in Figure 1. As expected, the complexes 1-A, 1-B, and 1-C are based on the interdigitating aromatic-aromatic stacked dimeric motif of 1, Figure 2. The angles of interpenetration are 155.4° in the complex 1-A, 161.8° in the complex 1-B, and 152.4° in the complex 1-C showing only small variations around the value of 158.8° present in the base structure of 1.1 The cone conformation in the three complexes shows relatively small variations in the cone angles and is stabilized by intramolecular hydrogen bonding between the phenolic hydroxyl groups acting as H-bond donors and the oxygen atoms connected to the phosphonic acid groups as H-bond acceptors, Table 2. For the three complexes, the overall structure is based on alternating layers of dimers of 1 intercalating a single layer of the heterocyclic diamine molecules in the case of the complex 1-A and bilayers of the heterocyclic diamine molecules in the cases of the complexes 1-B and 1-C, Figure 2. In all three structures, the layers of heterocyclic diamines are hydrated. Solvent molecules, methanol in the structures of 1-A and 1-C and ethanol in the structure of 1-B, are located in the

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670 Crystal Growth & Design, Vol. 6, No. 3, 2006

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Figure 1. Chemical formulas for compounds 1 (calix[4]arene dihydroxyphosphonic acid), A (2,2′-bipyridine), B (4,4′-bipyridine), and C (1,2bipyridylethane).

Figure 2. Comparison among projections of the structure of the complexes of 1 with A (left, perpendicular to b-axis), B (center, perpendicular to a-axis), and C (right, perpendicular to b-axis). Table 1. X-ray Crystallographic and Experimental Data for Compounds 1-A, 1-B, and 1-C 1-A

1-B

1-C

formula mass (g‚mol-1) space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) Z V (Å3) Fcalc (g‚cm-3)

Crystal Data C28H24O10P2‚C10H8N2 3H2O‚2CH3OH 778.7 P21/c 15.170(3) 13.343(3) 18.523(4) 90 105.42(3) 90 4 3614.2(13) 1.431

C28H24O10P2‚C10H8N2 3H2O‚C2H5OH 840.7 P1h 10.469(2) 12.253(3) 16.179(3) 97.38(3) 96.86(3) 105.42(3) 2 1958.3(7) 1.426

C28H24O10P2C12H14N2 3H2O‚2CH3OH 886.8 P1h 11.970(2) 12.096(2) 16.905(3) 103.46(3) 95.46(3) 114.09(3) 2 2122.6(7) 1.387

diffractometer detector radiation λ (Å) T (K) θ range (deg) crystal color crystal size (mm3) θ (mm-1) no. of reflns measured Rint no. of independent reflns no. of reflns with F0 > 4σ(F0) no. of params (restraints) R(F2) R(F2) [I > 2σ(I)] goodness of fit on F2

Data Collection κCCD Mo KR 200 2.8-25.7 colorless 0.35 × 0.35 × 0.35 0.194 11503 0.065 6774 4091 512 (9) 0.135 0.080 1.057

κCCD Mo KR 200 1.8-25.3 colorless 0.20 × 0.08 × 0.08 0.184 11372 0.110 6658 3551 559 (0) 0.155 0.069 1.022

κCCD Mo KR 200 1.9-25.4 colorless 0.36 × 0.10 × 0.10 0.175 12442 0.077 7287 4491 584 (0) 0.115 0.064 1.047

chemical formula

hydrophobic zone of the dimeric layer of 1, their exact roles being discussed in detail later. With regard to the protonation of the aromatic diamines, the known pKa values are 4.33 for A and 4.82 for B13 and estimated as 5.26 for C.14 For the complexes 1-B and 1-C, residual electron density maps have shown protonation of both of the nitrogen atoms of the bipyridyl ligands; however, for complex 1-A,

the situation is less clear and the nitrogen atoms are probably not protonated. This is in agreement with the pKa values. The structure of the complex 1-A shows a simple intercalated monolayer of 2,2′-bipyridine parallel to the dimeric layer of 1. The molecules of A are present in a parallel arrangement with no edge to edge interactions between adjacent molecules, the shortest distance being 6.37 Å. The nitrogen atoms of A are

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Crystal Growth & Design, Vol. 6, No. 3, 2006 671

Table 2. Cone Conformation of Calix[4]arene Dihydroxyphosphonic Acid complex cone angle (deg) phenolic rings phosphonated rings hydrogen bond distances between phenolic groups in 1 (Å)

1-A

1-B

1-C

105.2 23.9 2.972

107.9 25.6 2.827

103.5 29.0 2.829

2.978

2.817

2.820

situated in a trans configuration and, as the shortest distance between the nitrogen atoms of two neighboring bipyridine moieties is 8.83 Å and in view of their orientation, no extended networks are present in the structure. A compact network of hydrogen bonds formed between the water molecules and the hydroxyl groups of the phosphonic acid generates a hydrophilic cage for each bipyridine molecule (Figure 3). The oxygen atoms of one of the solvent molecules (S2) ensure connectivity along the b-axis by hydrogen bonds with the calixarene phosphonates, characterized by distances of 2.564(6) Å and 2.440(6) Å. The oxygen atoms of the other solvent molecule (S1) connect two different layers of 1 along the a-axis via hydrogen bonds with three water molecules, (POH-O1S 2.537(6) Å; O1S-O3W 2.729(7) Å; O3W-O2W 2.690(9) Å; O2W-O1W 2.622(9) Å; O1W-POH 2.788(9) Å). A major feature of the structure is the face-to-face aromaticaromatic interactions between molecules of 1 and A, Figure 4. Each aromatic ring of A interacts via parallel face-to-face stacking with an aromatic ring of the macrocycle of 1, but of different layers, at 3.7 Å with no offset of the rings. The molecules of A are thus held in a planar conformation. While the structure of the complex 1-A is essentially determined by aromatic-aromatic interactions, the situation in complex 1-B involves a wider and more complicated set of weak intermolecular interactions. Here the position of the

Figure 4. Details of the face-to-face aromatic-aromatic interactions (distance of 3.7 Å) in complex 1-A.

Figure 5. Detail of the competitive effects of hydrogen bonds (in blue) and parallel face-to-face aromatic-aromatic interactions (in green) in the complex 1-B.

Figure 3. Hydrophilic cage entrapping one bipyridine molecule. A network of hydrogen bonds between three water molecules and two solvent molecules (W1-W2 2.622(9) Å; W2-W3 2.690(9) Å; W3S1 2.729(7) Å) is presented in green, a network between water or solvent molecules and the phosphonic acid group of 1 (W2‚‚‚PO 2.744(7) Å; W3‚‚‚PO 2.795(9) Å; W1‚‚‚PO 2.788(9) Å; S2‚‚‚PO 2.564(6) Å; S2‚‚‚POH 2.440(6) Å) is presented in blue, a network between W1 and a phenolic group (2.920(7) Å) is presented in magenta, and four possible POH‚‚‚PO of 2.453(6) Å are colored in black.

Figure 6. Projection of the structure of the complex 1-B along the a-axis highlighting the 1-D ladder structure.

nitrogen atoms on the bipyridyl skeleton is propitious for hydrogen bond bridging between two molecules of 1 to yield extended solid-state networks. So, there is a competitive interplay between hydrogen bonding, aromatic-aromatic interactions, and steric effects generated either by the constrained geometry of B or by the presence of ethanol molecules in the hydrophobic zones of the bilayers of 1.

672 Crystal Growth & Design, Vol. 6, No. 3, 2006

Figure 7. Representation of the solvent channel present in the complex 1-B.

In the structure of the complex 1-B, the bipyridine is protonated and nonplanar with a dihedral angle of 43.3°, as compared to a planar conformation in the solid-state complex with the perchlorate15 and nonplanar structures with a 15.2° dihedral angle in the complex with para-sulfonatocalix[4]arene,16 and bridges two adjacent molecules of 1. The bridge is nonsymmetric (Figure 5) with one nitrogen atom involved in direct hydrogen bonding to a phosphonate group (distance 2.629(5) Å) and the other one, hydrogen bonded to a bridging water molecule, O2W (2.557(5) Å), which is further involved in hydrogen bonds with another phosphonate group (2.617(6) Å). This is rather unexpected because the length of B (calculated with respect to the opposite hydrogens of the aromatic rings, 8.97 Å) corresponds to the intermolecular separations present in the complex with diaminohexane (distance of 8.8 Å between the phenolic oxygen atoms)2 and is even slightly greater than

Dupont et al.

the distance between the dimers in the solid-state system with phenanthroline (distance between the phenolic oxygen atoms of 8.42 Å).4 Thus B might reasonably be expected to directly bridge molecules of 1. The aromatic-aromatic interactions are quite complex, the pyridinium ring Q, involved in hydrogen bonding to the water molecule (see Figure 5), is symmetrically stacked by face-to-face aromatic-aromatic interactions of 3.90 Å. It is also involved in nonsymmetric face-to-face stacking with one aromatic ring of 1 (dihedral angle with an aromatic ring of 1 of 8°), as is the ring of the second molecule of B to an aromatic ring of a second molecule of 1, thus generating a sandwiched bilayer, as was previously seen in the complex of 1 with phenanthroline.4 The other pyridinium ring (R) interacts only via nonsymmetric (dihedral angle of 11.8°) face-to-face stacking (distance of 4.18 Å) with rings of one molecule of 1 adjacent to those described above. The network formed by the bridging molecules of B may best be described as a 1-D ladder structure17 with the rungs formed by the dimers of 1, Figure 6. A hydrophobic channel visible on the a direction is formed between the neighboring dimers of 1. The hydrophobic cage view along the a-axis is formed by two dimers of 1 together with two pyridine molecules. Its dimensions are 12.87 Å × 8.95 Å (see Figure 7), and it includes molecules of solvent offset from the central line; the oxygen atoms of these solvent molecules are involved in hydrogen bonds with both a water molecule and a hydroxyl group of the phosphonic acid function of 1. Thus, the distances between molecules of 1 are strongly increased, explaining why there is a water molecule assisting in the pyridinium bridging of the phosphonate groups of 1. However, the question remains, is the particular structure observed here due to the presence of the ethanol molecules or does the water

Figure 8. Detail of the competitive effects of hydrogen bonds (in blue) and face-to-face parallel displaced weak interactions (in green) in 1-C.

Complexes of Calix[4]arene Dihydrophosphonic Acid

Crystal Growth & Design, Vol. 6, No. 3, 2006 673

distances between the nitrogen atoms and geometry of the ligand as compared to B.18 This flexibility should permit the complex to settle into a more relaxed form. This is indeed the case as the structures of 1-B and 1-C show strong similarities in the general nature of the packing, both having the 1-D ladder network with solvent molecules situated in the channels/cavities between the ladder rungs. However while the generalities are the same, the details are not and demonstrate the relaxation of the structure. In Figure 8, the interactions within the continuous twisted tape formed by C and the interactions of the molecules forming the tape with various molecules of 1 are shown. In the structure, both aromatic rings present in C are involved in face-to-face stacking interactions with aromatic rings of other molecules of C. The stacking distances are alternately short, 3.89 Å, and long, 4.22 Å, and are within the known range of aromatic-aromatic interactions;19 both forms are symmetric with the aromatic rings parallel and show no offset of the rings. Much weaker face-toface interactions occur between the aromatic rings on the surface of the tapes and the aromatic rings of 1 (mean distances of 4.75 Å). Here, the stackings are nonsymmetric and show offset of the aromatic rings (dihedral angles between Q ring of C and the ring of 1 is 15.6°). The hydrogen bonding type interactions between 1 and C show the same alternation as observed in the structures of 1-B. At one extremity of the molecule of C, one of the pyridinium groups (R) is also involved in hydrogen bonding to a water molecule (distance between N of ring R and O3W is 2.610(4) Å). However, here the water molecule forms hydrogen bonds with two opposing phosphonate groups (O3W-OP1 2.755(5) Å and O3W-OP2 2.652(5) Å) spanning the bilayer of C. Figure 9. (a) Projection of the structure of the complex 1-C along b-axis showing the 1-D ladder structure and (b) representation of the solvent channel in the complex 1-C.

molecule have a determinant role thus creating the cavity in which the ethanol molecules are situated? The presence of an ethylene bridge in C between the two opposing pyridinium groups leads to a flexibility in both

In this structure, the 1-D ladder is along the b-axis; a channel containing solvent, here methanol, is again present (Figure 9). This channel is generated by two dimeric units of 1 and two molecules of C. The size of the cavity is 12.89 Å × 5.05 Å, and the area is smaller than in the case of complex 1-B (65.1 Å2 as compared to the value of 89.5 Å2 observed corresponding to the complex 1-B).

Table 3. Hydrogen Bonding Distances between the Protonated Nitrogen Atoms (which are donors, N-H+) and the Acceptor Atoms (A) and the Corresponding Angles and Hydrogen Bond Distances between Polar Groups of Calixarene Molecules compound N-H+‚‚‚A

1-A N not protonated

distances (Å); angles (deg) P-O‚‚‚H-A distances (Å); angles (deg)

P6B-O‚‚‚H-O2S 2.564; 178.8 P6B-O‚‚‚H-O1W 2.787; 159.8 P6B-O‚‚‚H-O2W 2.743; 158.9 P6D-O‚‚‚H-O3W 2.808; 180

P-O-H‚‚‚A distances (Å); angles (deg)

P6B-O-H‚‚‚O1S 2.537; 160.5 P6D-O-H‚‚‚O2S 2.441; 156.2 P6B-O‚‚‚H-O-P6D 2.453; 180

others distances (Å); angles (deg)

1-B

1-C

N4R-H4R‚‚‚O4BP 2.629; 173.1 N4Q-H4Q‚‚‚O2W 2.557; 171.0 P1B-O‚‚‚H-O1W 2.663; 173.4 P1B-O‚‚‚H-O2W 2.735; 165.3 P1B-O‚‚‚H-O3W 2.749; 161.7 P1D-O‚‚‚H-O1S 2.707; 176.5 P1D-O‚‚‚H-O2W 2.617; 164.9 P1D-O‚‚‚H-O3W 2.737; 153.6

N4R-H4R‚‚‚O3W 2.609; 161.5 N4Q-H4Q‚‚‚O3DP 2.634; 172.5 P1B-O‚‚‚H-O3W 2.755; 166.7 P1B-O‚‚‚H-O2W 2.984; 161.2 P1B-O‚‚‚H-O2S 2.727; 164.9 P1B-O‚‚‚H-O3W 2.652; 171.5 P1B-O‚‚‚H-O1W 2.819; 149.6 P1D-O‚‚‚H-O2W 2.759; 177.2 P1D-O‚‚‚H-O1S 2.641; 167.3 P1B-O-H‚‚‚O1S 2.611; 150.1 P1D-O-H‚‚‚O1W 2.638; 172.3

P1B-O-H‚‚‚O1W 2.521; 172.0 P1D-O-H‚‚‚O3W 2.612; 171.7

674 Crystal Growth & Design, Vol. 6, No. 3, 2006

Conclusion In general, several points have been demonstrated with regard to the interplay of molecular interactions in the complexes formed by 1 with diamines. First, as expected, the change from 2,2′-bipyridine to 4,4′-bipyridine and 1,2-bipyridylethane is notable, as the ligands led to a switch from a discrete cage structure to formation of an extended network, in this case a 1-D ladder. Second, increasing the flexibility of the bipyridine unit on going from 4,4′-bipyridine to 1,2-bipyridylethane allowed an increase in the face-to-face aromatic stacking interactions in the bilayer formed by the different bipyridine molecules. Finally it is interesting to note that in the structures of the complexes of calix[4]arene dihydroxyphosphonic acid both with 4,4′-bipyridine and with 1,2-bipyridylethane, there are alternating direct pyridinium-phosphonate and pyridiniumwater-phosphonate hydrogen bonding systems, which suggests that the presence of the water molecules is a key element in the structural nature of the complexes. Supporting Information Available: Crystallographic information files for complexes 1-A, 1-B, and 1-C. This material is available free of charge via the Internet at http://pubs.acs.org. Tables of crystal data, structural solutions and refinement, atomic coordinates, bond lengths and angles, and anisotropic thermal parameters for 1-A, 1-B and 1-C are deposited with the Cambridge Crystallographic Data Center as CCDC nos. XX1, XX2, and XX3, respectively. This material is available free of charge from [email protected].

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