Structural Versatility in Praseodymium Complexes of p-Sulfonatocalix[4]

Department of Chemistry, UniVersity of Leeds, Woodhouse Lane, Leeds LS2 9JT ... and Chemical Sciences, UniVersity of Western Australia, Crawley, Perth...
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Structural Versatility in Praseodymium Complexes of p-Sulfonatocalix[4]arene Scott J. Dalgarno,†,‡ Jerry L. Atwood,‡ and Colin L. Raston*,§

CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 9 1762-1770

Department of Chemistry, UniVersity of Leeds, Woodhouse Lane, Leeds LS2 9JT, U.K., Department of Chemistry, UniVersity of MissourisColumbia, Columbia, Missouri 65211, and School of Biomedical and Chemical Sciences, UniVersity of Western Australia, Crawley, Perth, WA 6909, Australia ReceiVed January 15, 2007; ReVised Manuscript ReceiVed June 4, 2007

ABSTRACT: Addition of excess praseodymium(III) nitrate or perchlorate to aqueous solutions of sodium p-sulfonatocalix[4]arene (Na5SO3[4]) results in the formation of a 3-D coordination polymer and a 4:3 Pr/SO3[4] complex, respectively. Concentration of the solution containing crystals of the latter resulted in the dissolution and regrowth of crystals that were subsequently found to be a bilayer arrangement of SO3[4] containing perchlorate anions, therefore suggesting that concentration effects may be an important route to new supramolecular architectures based on the versatile host. Introduction Calixarenes are polyphenolic compounds that have provided the supramolecular chemist with a virtually limitless library of compounds to employ in the formation of host-guest complexes.1 This is in part because these molecules typically possess cavities for inclusion of various species and can be easily (or selectively) functionalized at either the “upper” or “lower” rim to suit a particular need. Of the various types of water-soluble calixarenes known, we have focused efforts on using p-sulfonatocalix[n]arenes (where n ) 4-8, general notation SO3[n]) for the formation of new supramolecular architectures with lanthanide metals. The majority of complicated supramolecular architectures incorporating SO3[4] typically involve the calixarene adopting a bowl conformation, often with inclusion of a suitably sized guest molecule in the form of molecular capsules, Ferris wheels, amino acid complexes, or variations thereof.2-12 In the former arrangements, the molecule often packs into “up-down” antiparallel bilayer arrangements while incorporating the guests/ metals in the resulting architecture. However, the most interesting supramolecular architectures based on SO3[4] are formed when the molecule packs in an alternative manner, often with curvature being induced in the resultant structure.13-15 Under these rather rare circumstances, the host can form nanometerscaled spheroids or tubules, the former of which are dodecameric and are based on the Platonic (icosahedron) or Archimedean (cuboctahedron) solids depending on the guest molecule employed for the calixarene cavity. Recent times have witnessed a significant expansion into similar structural chemistry for the larger analogues.12,15 For SO3[5], the molecule typically (although not exclusively16) adopts a bowl conformation similar to the tetramer in the presence of various guest molecules and metal counterions.17 Guest-induced conformational distortion can afford a bismolecular capsule arrangement,18 and similar bis-capsules can be formed for SO3[6] and SO3[8] with 18-crown-6 and tetraphenylphosphonium guest species respectively, as parts of lanthanide metal complexes.15,19 * Corresponding author. E-mail: [email protected]. † University of Leeds. ‡ University of MissourisColumbia. § University of Western Australia.

Considering the substantial number of complicated multicomponent supramolecular solid-state complexes reported for SO3[4] and the larger analogues, relatively few simple metal complexes of the SO3[4] (other than alkali metals and some formed in the absence of guest) have been reported.20-23 Herein we report the formation of three metal complexes either with incorporation or exclusion of the metal salt anion. The metal salts examined were praseodymium nitrate, oxalate, and perchlorate, although only the former and the latter were successful in complex formation. Complexes were formed by the addition of excess metal salt to an aqueous solution of pentasodium p-sulfonatocalix[4]arene, resulting in a 3-D coordination polymer {from Pr(NO3)3}, a discrete 4:3 Pr(III)/SO3[4] supermolecule {from Pr(ClO4)3}, and a discrete complex containing perchlorate anions (that forms by very slow concentration of the 4:3 Pr(III)/SO3[4] supermolecule in the original crystallization solution of the second complex). Summary of Transition and Lanthanide Metal Complexes of p-Sulfonatocalix[4]arene Formed in the Absence of Guest Molecules (Other than Solvent Molecules). In the few “guest absent” metal complexes reported to date, Atwood et al. showed that addition of copper(II) chloride to a solution of sodium p-sulfonatocalix[4]arene results in the formation of an interesting bilayer motif that shows copper ions linking calixarenes in hydrophobic layers.20 Additional copper ions span the hydrophilic layer separating adjacent hydrophobic layers, generating an unusual coordination polymer. Brechbiel, Rogers, and coworkers reported that addition of lead nitrate to a solution of p-sulfonatocalix[4]arene resulted in the formation of a complex that also showed lead ions to span the hydrophilic layer and link hydrophobic layers in a similar bilayer motif.23 Notably, the structure had four different lead coordination environments with varied degrees of hydration. In closer relation to the present contribution, Atwood et al. reported the formation of a hepta-aqua yttrium/sodium/SO3[4] complex that adopted the typical bilayer arrangement in the extended structure,2 as well as a 3-D coordination network incorporating lanthanum nitrate, SO3[4], and DMSO molecules.21 The latter study showed there to be two different lanthanum centers participating in coordination network formation. Both of these metal centers have one coordinated nitrate anion, while one also has a coordinated DMSO molecule that was positioned within a calixarene cavity. Detellier et al.

10.1021/cg070043s CCC: $37.00 © 2007 American Chemical Society Published on Web 08/10/2007

Praseodymium Complexes of p-Sulfonatocalix[4]arene

Crystal Growth & Design, Vol. 7, No. 9, 2007 1763

Results and Discussion

Figure 1. Stick diagrams of (A) the 2-D coordination polymer formed by addition of the early Ln(III) triflates to sodium p-sulfonatocalix[4]arene25 and (B) the encapsulation of the golubular diprotonated cryptand between adjacent layers of a 2-D coordination polymer,26 similar to that shown in panel A. Figures are not to scale.

reported the formation of a remarkable discrete 8:6 La(III)/ SO3[4] complex from the addition of lanthanum(III) chloride to a solution of SO3H[4].24 They also showed that the structural formation was independent of reactant concentration by determining the unit cell dimensions of crystals grown from several reaction mixtures. More recently, Raston et al. reported the formation of a 2-D coordination polymer Via the addition of early lanthanide(III) trifluoromethanesulfonates (Ce and Pr) to a solution containing sodium p-sulfonatocalix[4]arene (Figure 1A).25 This coordination polymer (for Ce and Nd) can be used to encapsulate diprotonated cryptand in the splayed cavities of the hosts, a feature that results from the metal-sulfonate coordination within the polymer layers (Figure 1B).26

3-D Coordination Polymer [(M(H2O)4(NO3))(M(H2O)5)psulfonatocalix [4]arene]‚7H2O (M3+ ) Pr, Nd, Sm), 1. Single crystals of the complex [(Pr(H2O)4(NO3))(Pr(H2O)5)(p-sulfonatocalix[4]arene - H+)]‚7H2O, 1, grew slowly upon addition of excess praseodymium nitrate to a solution of pentasodium p-sulfonatocalix[4]arene (Scheme 1). The crystal structure was solved in the triclinic space group P1h. The asymmetric unit in 1 consists of a tetra-aquo praseodymium nitrate/SO3[4]/penta-aquo praseodymium complex in addition to seven waters of crystallization disordered over nine positions. There are two types of praseodymium center in 1, and the first, Pr(1), has four aquo ligands and one coordinated nitrate anion while being tethered to the S(1) sulfonate group of the calixarene through the O(1) atom. The second, Pr(2), has five aquo ligands and is tethered to the S(2) sulfonate group of the calixarene through the O(2) atom. The two metal centers have different coordination environments; Pr(1) is nonacoordinate with tricapped trigonal prismatic geometry, whereas Pr(2) is octacoordinate and has square antiprismatic geometry (Figures 2 and 3). Upon symmetry expansion, the asymmetric unit forms a 3-D coordination polymer that is based around an extended bilayer arrangement. Inspection of this bilayer arrangement shows the calixarenes to pack through two crystallographically unique π-stacking interactions with aromatic centroid‚‚‚centroid distances of 3.616 and 3.778 Å (Figure 2). The calixarene is pinched in a C2 symmetric fashion, and the cavity is occupied by a water molecule (SO3[4] opposing pairs have dihedral angles of 104.94° and 132.96°). The quality of data allowed the refinement of the majority of hydrogen atoms on both coordinated and free water molecules. The hydrogen atoms of the water molecule (O(29)) held within the cavity were located from the Fourier difference map, assigned, and refined and show that there is an OH‚‚‚π interaction to one of the calixarene aromatic rings (O(29)‚‚‚aromatic centroid and OH‚‚‚aromatic centroid distances of 3.623 and 2.808 Å, respectively, Figure S1, Supporting Information). This phenomenon was first documented by Atwood et al. and the OH‚‚‚π distance observed here is consistent with those reported.27 The overall 3-D coordination polymer is complex and is most easily understood in parts. First, the coordination sphere of Pr(1) shows that the metal center joins coplanar calixarenes within a hydrophobic layer of the bilayer arrangement through coordination to the O(1) and O(9) oxygen atoms of the S(1) and S(3) sulfonate groups, respectively (Figure 2). The metal center also has a coordinated nitrate anion that is directed downward into the hydrophobic layer. In addition to these features, Pr(1) also coordinates to the oxygen atom (O16) of a deprotonated base hydroxyl group of the calixarene located directly beneath the metal center and within the same hydrophobic layer of the bilayer arrangement. This metal/“calixarene base” coordination is the link in forming the 3-D coordination polymer through the hydrophobic layer and examples of lanthanide/“p-sulfonatocalix[n]arene base” coordination are limited.21,28 Similar scrutiny of the coordination sphere of Pr(2) shows the metal center to span the hydrophilic layer, and this occurs through coordination to oxygen atoms of three different calixarene sulfonate groups (indicated by the middle Pr(2) labeled atom in Figure 3). The first coordination is to the O(5) atom of the S(2) calixarene sulfonate group, and the metal coordinates to the symmetry equivalent O(11) and O(15) atoms of the S(3) and S(4) calixarene sulfonate groups, respectively. In order to understand the coordination polymer topology, each metal center can be treated as a three-connecting center

1764 Crystal Growth & Design, Vol. 7, No. 9, 2007

Dalgarno et al. Scheme 1

as each connects to three symmetry-equivalent calixarene molecules. Similarly, each calixarene can thus be treated as a six-connecting center. Once connected, the Pr(1) metal centers and SO3[4] centroids form a near linear rectangular chain (indicated as A in Figure 4). When the Pr(2) metal centers are connected to the SO3[4] centroids, the result is the formation of a stepped ladder arrangement (indicated as B in Figure 4). As mentioned above, the SO3[4] molecules act as six-connecting centers and the two different chains, A and B, meet at the SO3[4]-common nodes. The overall network structure is found to be a 3-D arrangement of the chains running perpendicular to one another as illustrated in Figure 5 (chains A and B are represented entirely in orange and green respectively). Isostructural complexes with Nd3+ and Sm3+ in place of Pr3+ were synthesized and characterized by single-crystal unit cell determination, the unit cell parameters of which are listed in the experimental section. When praseodymium oxalate was

Figure 2. Selectively labeled section of the 3-D coordination polymer from the crystal structure of complex 1 emphasizing the Pr(1) linkages with calixarene “upper rim” sulfonate groups and “base” phenoxy groups.

Figure 3. Selectively labeled section of the 3-D coordination polymer from the crystal structure of complex 1 emphasizing the Pr(2) linkages spanning the hydrophilic layer between calixarene “upper rim” sulfonate groups.

employed as the metal salt, the reactants formed a thick oil on solution concentration and single crystals could not be obtained. When praseodymium perchlorate was employed, an excess of the metal salt was added to a solution containing Na5SO3[4] resulting in the formation of single crystals of a discrete 4:3 Pr(III)/SO3[4] complex. Structure of the Discrete 4:3 Pr(III)/SO3[4] Complex [(Pr(H2O)8)2(Pr(H2O)6)(Pr(H2O)7)(p-sulfonatocalix[4]arene)3][(Pr(H 2 O) 8 ) 2 (Pr(H 2 O) 7 ) 2 (p-sulfonatocalix[4]arene) 3 ]‚ 25.5H2O, 2. Crystals of the complex [(Pr(H2O)8)2(Pr(H2O)6)(Pr(H2O)7)(p-sulfonatocalix[4]arene)3] [(Pr(H2O)8)2(Pr(H2O)7)2(p-sulfonatocalix[4]arene)3]‚25.5H2O, 2, grew slowly upon addition of excess praseodymium(III) perchlorate to a solution of pentasodium p-sulfonatocalix[4]arene (Scheme 2). Complex 2 crystallizes in a triclinic cell, and the structural solution was performed in the space group P1h. The asymmetric unit consists of two large, near-linear, and discrete 4:3 Pr(III)/SO3[4] complexes, A and B, and a total of 25.5 water molecules of crystallization that are disordered over 46 positions (eq 2 and labeled according to Figure 6). All the metal centers in both discrete units are nonacoordinate and the praseodymium centers that are ordered have tricapped trigonal prismatic geometry. Despite there being significant disorder associated with some of the metal centers in addition to some of their respective aquo ligands, the praseodymium coordination spheres are of near tricapped trigonal prismatic geometry. In addition to the disorder associated with some of the metal centers, several calixarene sulfonate groups and one SO3[4] molecule are also significantly disordered. Despite this extensive disorder in the overall structure, the data was modeled satisfactorily as indicated by a final value of R1 ) 0.105. It should be mentioned at this point that the crystals were extremely sensitive to solvent loss and were weakly diffracting. Because

Figure 4. The two coordination network chains A and B formed between SO3[4] molecules and praseodymium centers in the crystal structure of complex 1 when the metal centers and SO3[4] molecules are treated as three and six-connecting centers, respectively. The calixarene centroids are shown as red balls, while the praseodymium centers are represented in green. The near-linear rectangular chain, A, forms between SO3[4] and Pr(1), while the stepped ladder chain, B, forms between SO3[4] and Pr(2).

Praseodymium Complexes of p-Sulfonatocalix[4]arene

Figure 5. The network topology diagram from the crystal structure of complex 1. The stepped ladder chains (shown as B in Figure 4) are represented entirely in green. The near-linear chains (shown as A in Figure 4) are represented entirely in orange and are shown to join the stepped ladders at the six-connecting calixarene nodes.

this was the case, a number of non-hydrogen atoms in part B were refined isotropically. Notably, similar treatment was also applied to the 8:6 discrete La(III)/SO3[4] complex reported by Detellier et al. (described in the introductory section), the crystals of which presumably diffracted in a manner similar to those of complex 2.24 Each of the discrete 4:3 Pr(III)/SO3[4] fragments in complex 2 are similar in structure to half of the superstructure reported by Detellier et al., which was formed by the addition of lanthanum(III) chloride to a solution of the sulfonic acid form of SO3[4].24 Although complex 2 formed with Na5SO3[4] rather than the sulfonic acid, it is unclear at this stage whether the presence of perchlorate anions plays a role in determining the overall supramolecular structure. Such a role is partly suggested by the fact that addition of praseodymium triflate to a solution containing Na5SO3[4] results in the formation of the 2-D coordination polymer shown in Figure 1A. Given the size and varied praseodymium/sulfonate coordination associated with A and B, each will be discussed as separate entities before discussing the overall extended structure. The two “end” SO3[4] molecules (S(1)-S(5) and S(10)S(13)) in the near-linear arrangement, fragment A, each have a sulfonate bound octa-aqua praseodymium metal center (Pr(1) and Pr(2) as shown in Figure 6 and Figure S2). The central SO3[4] molecule (S(6)-S(9)) is joined to the S(1)-S(5) calixarene by a hepta-aqua praseodymium metal center (Pr(5)). The central SO3[4] is also joined to the S(10)-S(13) calixarene by a hexa-aqua praseodymium metal center (Pr(6)). The difference in the number of aquo ligands associated with each of the central praseodymium metal centers is because Pr(6) forms a chelate ring with two oxygen atoms (O(34) and O(35))

Crystal Growth & Design, Vol. 7, No. 9, 2007 1765

of the S(7) sulfonate group of the S(6)-S(9) calixarene. There are few reported examples of such lanthanide chelation with p-sulfonatocalix[n]arenes, although chelation of an aryl sulfonate to lanthanum has also been reported.25,29,30 The bond distances and angles associated with the chelate in complex 2 are of a greater magnitude to the similar documented examples. This difference is likely to be because the metal center is only bound to O(34) when in one of two disordered positions.25,29,30 In addition to this, if a centroid is generated between the two disordered positions, the resultant angles conform far more closely to those documented for ordered systems. In contrast to part A, several sulfonate groups, aquo ligands and a quarter of one SO3[4] molecule in B show significant disorder (Figures 6 and S3). All the praseodymium metal centers in part B are nonacoordinate and are of tri-capped trigonal prismatic geometry. The SO3[4] molecules in B are also arranged in a similar manner to those in A, the only apparent difference between the two parts being a disparate number of aquo ligands associated with the central praseodymium coordination spheres. Both of the central praseodymium atoms in B have seven aquo ligands, whereas one central metal center in A has six aquo ligands, while the other has seven (as reflected in eq 2). All six SO3[4] molecules in the asymmetric unit are pinched in the C2 symmetric fashion (Figure 6), and the dihedral angles range from 99.46° to 109.80° and 134.41° to 145.54° between the pinching and splaying pairs of phenyl rings, respectively. There are numerous disordered water molecules residing within the molecular clefts, and these are positioned within typical hydrogen-bonding distances with sulfonate groups or praseodymium aquo ligands. Only one of these water molecules is positioned with the possibility of OH‚‚‚π interactions with the aromatic groups of the S(6)-S(9) SO3[4] molecule (three possible interactions with O‚‚‚aromatic centroid distances ranging from 3.154 to 3.656 Å), although the limited data quality precluded structural confirmation of this. The extended structure reveals the calixarenes to pack in a bilayer arrangement. Interestingly, there appear to be no direct hydrophobic π-stacking or ArH‚‚‚π interactions between parts A and B. Instead of this, each of the parts assembles in a unicomposite columnar manner as illustrated by the alternating color scheme in Figure 7. Within these columns, A packs through four crystallographically unique π-stacking interactions (aromatic centroid‚‚‚centroid distances ranging from 3.340 to 3.679 Å), while B packs through a total of six crystallographically unique π-stacking interactions (aromatic centroid‚‚‚centroid distances ranging from 3.522 to 3.767 Å). In addition to this intracolumnar π-stacking, there are numerous hydrogen bonds between praseodymium aquo ligands and calixarene sulfonate groups within these columns. Finally, parts A and B are linked at either end through a total of six crystallographically unique hydrogen-bonding interactions that lie in the range of 2.6872.893 Å. Upon sitting over a period of 3 months, a crystallization mixture containing crystals of complex 2 very slowly evaporated, resulting in concomitantly slow concentration. During this time, the color of the mixture darkened, and upon inspection, all of the crystals of complex 2 (large thin colorless plates) had redissolved and regrown as large green/yellow prisms. This result has not yet been reproduced but shows that concentration may strongly affect the self-assembly process, an avenue that we are currently exploring. The X-ray structure analysis of the resulting crystals revealed a bilayer arrangement of an unusual praseodymium/SO3[4]/sodium/perchlorate complex.

1766 Crystal Growth & Design, Vol. 7, No. 9, 2007

Dalgarno et al. Scheme 2

Figure 6. Stick representation of part of the asymmetric unit from the crystal structure of complex 2. The two sections of the structure have been labeled A and B to aid discussion. Waters of crystallization and hydrogen atoms have been omitted for clarity.

Figure 7. Extended structure of complex 2 showing the alternate columnar packing of parts A (red) and B (blue).

Structure of the Complex [(Pr(H2O)8)(p-sulfonatocalix[4]arene)][(Pr(H2O)8)2 (Na(H2O)2)(ClO4)2(p-sulfonatocalix[4]arene)]‚9.5H2O, 3. Crystals of the complex [(Pr(H2O)8)(psulfonatocalix[4]arene)][(Pr(H 2 O) 8 ) 2 (Na(H 2 O) 2 )(ClO 4 ) 2 (p-

sulfonatocalix[4]arene)]‚9.5H2O, 3, grew over 3 months with very slow evaporation of a reaction mixture containing crystals of complex 2 (Scheme 3). Over this period, the crystals (thin colorless plates) of complex 2 appeared to have redissolved and

Praseodymium Complexes of p-Sulfonatocalix[4]arene

Crystal Growth & Design, Vol. 7, No. 9, 2007 1767 Scheme 3

regrown as large green/yellow prisms. Complex 3 crystallizes in a triclinic cell, and the structural solution was performed in the space group P1h. The asymmetric unit, as shown in Figure 8, comprises one praseodymium/SO3[4] complex, one bimetallic praseodymium/ sodium/SO3[4]/perchlorate complex, one free perchlorate anion, and a total of 9.5 water molecules that are disordered over a total of 11 positions. To aid clarity, each of the parts A and B (as depicted by the dashed line in Figure 8) will be discussed separately before going on to examine the extended structure. Part A is a 1:1 Pr(III)/SO3[4] moiety, and Pr(1) is bound to the calixarene through the O(2) atom of the S(1) sulfonate group (Figure 8). The praseodymium metal center is nonacoordinate with eight aquo ligands and has tricapped trigonal prismatic geometry. Part B is markedly different from A in several respects (Figure 8). The first and most striking difference is the presence of three sulfonate-bound metal centers. One of these is an octa-aqua praseodymium metal center (Pr(2)) that is bound to the O(33) atom of the S(6) sulfonate group of the SO3[4] molecule. In

Figure 8. Stick representation of the asymmetric unit of the crystal structure of complex 3. A dashed line has been inserted to clarify the components of the complex that are included in the discussion of parts A and B.

addition to this, a sodium atom and a praseodymium atom (disordered over two positions) are both bound through oxygen atoms to the S(5) sulfonate group. The praseodymium atom that is disordered over two positions is bound through a disordered oxygen atom of the sulfonate group (O(30) and O(29) for Pr(3) and Pr(4), respectively). Despite the disorder associated with Pr(3) and Pr(4), both metal centers are nonacoordinate and have typical near tricapped trigonal prismatic geometry. The sodium atom is of distorted octahedral geometry and forms a chelate ring with the O(30) and O(31) oxygen atoms of the SO3[4] S(5) sulfonate group. The sodium atom has two aquo ligands, is coordinated to one of the aquo ligands of the Pr(3) metal center (O(58)), and is also bound to a perchlorate anion through the O(63) atom (Figure 8). Bond distances and selected angles relating to the metal coordination spheres and the sodium/SO3[4] sulfonate chelate ring are listed in Table S2 (listed relative to Figure S4). Notably, the angles relating to the sodium/sulfonate chelate ring are of comparable magnitude to those observed in the tetrasodium salt of p-sulfonatocalix[4]arene reported by Atwood et al.31,32 Another unusual feature associated with complex 3 is that the perchlorate anions are nestled (free) or directed (bound) into voids in the hydrophobic layer (Figure 9). A survey of all of the crystal structures containing SO3[4] on the Cambridge Crystallographic Data Centre shows only one other structure that has an anion included in a bilayer arrangement.5 The report by Raston et al. showed perchlorate anions to be bound by sodium ions that also coordinated to sulfonate groups of the calixarenes. The perchlorate anions were directed into a hydrophobic layer of an extended bilayer arrangement, a situation similar to that found in B. In the reported structure, the calixarenes were part of “Russian dolls” with sodium bisaqua/18-crown-6 guests and polynuclear rhodium counterions.5 Clearly, perchlorate anions are of a suitable size for inclusion in hydrophobic layers of SO3[4] bilayer arrangements, and the formation of complex 3 has demonstrated that this can occur in the absence of metal/perchlorate coordination (Figure 9). In particular, the formation of complex 3 has demonstrated the true ability of bilayer arrangements containing SO3[4] to adapt to many different chemical environments while maintaining their common form. The extended structure of complex 3 shows the

1768 Crystal Growth & Design, Vol. 7, No. 9, 2007

Dalgarno et al.

Figure 9. The extended bilayer structure in the crystal structure of complex 3 showing the inclusion of the perchlorate anions (shown in space filling) within the hydrophobic layers. Table 1. X-ray Crystallographic Data for Complexes 1-3 complex number formula Mr crystal system space group T, K a, Å b, Å c, Å R, deg β, deg γ, deg U, Å3 Z F(000) Fcalc, g cm-3 µ, cm-1 Θmin,max, deg data collected unique data Rint obsd data (I > 2σ(I)) params restraints R1 (obsd data) ωR2 (all data) S max/min residuals [e Å3]

1 C28H51N1O35Pr2S4 1371.76 triclinic P1h 150(2) 10.4483(1) 15.0282(2) 16.7750(2) 65.385(1) 83.952(1) 73.595(1) 2296.92(5) 2 1376 1.983 2.389 3.09, 27.5 40564 10502 0.0542 9778 762 28 0.0313 0.0838 1.04 1.116, -1.939

calixarenes to pack in a bilayer arrangement. This occurs through a total of four crystallographically unique π-stacking interactions with aromatic centroid‚‚‚centroid distances ranging from 3.831 to 4.159 Å, and there appear to be no other significant hydrophobic interactions between the SO3[4] molecules. Conclusion Relatively few metal complexes of p-sulfonatocalix[4]arene that are formed in the absence of guest molecules (other than solvent) have been reported to date (excepting alkali metal salts). The structures reported herein are the result of a short study of lanthanide metal salts in combination with Na5SO3[4], in addition to previous studies with the sulfonic acid of SO3[4]. We have shown that simple lanthanide complexes of p-sulfonatocalix[4]arene, formed in the absence of large guest species, can form remarkably complex supramolecular architectures based on coordination polymers or discrete supermolecules. We have also shown that concentration effects can dramatically change

2 C168H299O180.50Pr8S24 7103.79 triclinic P1h 150(2) 15.0234(1) 15.5928(1) 58.5798(6) 93.8115(4) 91.1433(6) 89.9803(4) 13689.63(19) 2 7214 1.723 1.694 1.9, 27.5 187167 57777 0.1453 30778 2841 27 0.105 0.3284 1.037 4.36, -2.239

3 C56H109Cl2NaO74.50Pr3S8 2747.53 triclinic P1h 150(2) 17.4508(1) 18.1033(1) 19.1983(2) 96.5645(3) 109.229(4) 115.5645(4) 4926.68(6) 2 2782 1.852 1.809 2.86, 27.5 98651 22520 0.126 20038 1453 0 0.0544 0.1595 1.026 1.915, -2.14

supramolecular architecture. Although this result is a byproduct of the formation of complex 2 and although it is yet to be repeated given the length of time for solution concentration, it indicates that this variable should be included in a number of previously reported and future experiments involving dynamic combinatorial chemistry with the p-sulfonatocalix[n]arenes. Future studies will incorporate this aspect within a larger screen of lanthanide(III) salts and the sulfonic acids and sodium salts of the larger p-sulfonatocalix[n]arenes. Experimental Procedures Sodium p-sulfonatocalix[4]arene was synthesized by literature methods and purity was checked via 1H NMR spectroscopy.1 All lanthanide metal salts were purchased from Aldrich and used as supplied without further purification. X-ray data for complexes 1-3 were collected at 150(2) K on an Enraf-Nonius KappaCCD diffractometer with Mo KR radiation. Data were corrected for Lorentz and polarization effects and absorption corrections were applied using multiscan techniques. The structures of complexes 1 and 3 were solved by direct

Praseodymium Complexes of p-Sulfonatocalix[4]arene methods using SHELXS-97 and refined with full-matrix least-squares on F2 using SHELXL-97. The structure of complex 2 was solved by direct methods using SHELXS-97 and refined with BLOC-matrix leastsquares on F2 using SHELXL-97. Hydrogen atoms were placed at geometrically calculated positions in all complexes. Hydrogen atoms for water molecules of crystallization and praseodymium aquo ligands were located in the Fourier difference map of complex 1, assigned, and refined accordingly. Microanalyses were not obtained for complexes 2 and 3 because the crystals were sensitive to solvent loss. CCDC reference numbers 633487-633489 contain the crystallographic data for structures 1-3, respectively. Crystallographic information files can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data Centre, 12 Union Rd, Cambridge, CB2 IEZ, UK; fax (internat.) +44-1223/336-033; e-mail [email protected]. Synthesis of the 3-D Coordination Polymer [(M(H2O)4(NO3))(M(H2O)5)p-sulfonatocalix [4]arene]‚7H2O (M3+ ) Pr, Nd, Sm), 1. Praseodymium(III) nitrate hexahydrate (40 mg, 90 µmol) and pentasodium p-sulfonatocalix[4]arene (20 mg, 19 µmol) were dissolved in distilled water (2 cm3). On standing over 2 days, large green crystals that were suitable for X-ray diffraction studies formed. Yield 22 mg, 87%. Microanalysis calculated for C28H51N1O35S4Pr2: C, 24.52; H, 3.75; N, 1.02; S, 9.35. Found: C, 24.55; H, 3.65; N, 0.90; S, 9.40. Isostructural Complexes of 1. For Nd3+, the sample preparation procedure was identical except that neodymium(III) nitrate was used in place of the praseodymium analogue. The unit cell measurements were a ) 10.5293(17) Å, b ) 15.1203(12) Å, c ) 16.8779(18) Å, R ) 65.9260(75)°, β ) 84.1774(61)°, γ ) 72150(80)°, T ) 150(2) K. For Sm3+, the sample preparation procedure was identical except that samarium(III) nitrate was used in place of the praseodymium analogue. The unit cell measurements were a ) 10.5068(15) Å, b ) 15.1559(24) Å, c ) 16.8234(21) Å, R ) 65.3561(107)°, β ) 83.6572(84)°, γ ) 73.0631(108)°, T ) 150(2) K. On this basis, all three unit cell determinations suggest isostructural complexes to that for praseodymium. X-ray Crystallography of 1. Some bond lengths were restrained to be chemically meaningful. X-ray crystallographic date for the complex is collected in Table 1. Synthesis of the Discrete 4:3 Pr(III)/SO3[4] Complex [(Pr(H2O)8)2(Pr(H2O)6)(Pr(H2O)7)(p-sulfonatocalix[4]arene)3][(Pr(H2O)8)2(Pr(H2O)7)2(p-sulfonatocalix[4]arene)3]‚25.5H2O, 2. Praseodymium(III) perchlorate (41 mg, 90 µmol) and pentasodium p-sulfonatocalix[4]arene (20 mg, 19 µmol) were dissolved in distilled water (2 cm3). On standing over 2 days, large green crystals that were suitable for X-ray diffraction studies formed. Yield 10 mg, 58%. X-ray crystallography of 2. One Pr(6) aquo ligand was disordered over three positions with partial occupancies of 0.25, 0.5, and 0.25. A sulfonate group of the S(1)-S(5) calixarene was disordered over two positions with equal occupancies. In the third position, the atom was refined isotropically. Two oxygen atoms of the S(1) sulfonate group are disordered over two positions at equal occupancy. Two oxygen atoms of the S(12) sulfonate group are disordered over two positions at partial occupancies of 0.7 and 0.3. The oxygen atoms of the S(16) sulfonate group are disordered over two positions at equal occupancy. A sulfonate group of the S(14)-S(18) calixarene was disordered over two positions with equal occupancies. Two praseodymium metal centers and respective aquo ligands are disordered over two positions with partial occupancies of 0.6 and 0.4. Two oxygen atoms of the S(23) sulfonate group are disordered over two positions at equal occupancy. One-quarter of the S(19)-S(23) calix[4]arene sulfonate was disordered over two positions with equal occupancies. A sulfonate group of the S(24)-S(29) calixarene was disordered over three positions with partial occupancies of 0.4, 0.2, and 0.4. The oxygen atoms of the S(29) sulfonate group are disordered over two positions at equal occupancy. One oxygen atom of the S(24) sulfonate group is disordered over two positions at equal occupancy. Some water molecules of crystallization and several calixarene sulfonate oxygen atoms were refined isotropically. X-ray crystallographic date for the complex is collected in Table 1. Synthesis of the Complex [(Pr(H2O)8)(p-sulfonatocalix[4]arene)][(Pr(H2O)8)2 (Na(H2O)2)(ClO4)2(p-sulfonatocalix[4]arene)]‚9.5H2O, 3. A sample vial containing a reaction solution and crystals of complex 3 was left to stand and very slowly evaporate over 3 months. The crystals of complex 2 appeared to have redissolved and crystallized complex 3 as large yellow/green crystals. Yield 12 mg, 46%.

Crystal Growth & Design, Vol. 7, No. 9, 2007 1769 X-ray Crystallography. Three oxygen atoms of the Cl(1) perchlorate anion are disordered over two positions with partial occupancies of 0.8 and 0.2. The Pr(3) and Pr(4) metal centers, in addition to related aquo ligands, are disordered over two positions with partial occupancies of 0.7 and 0.3. One Pr(4) aquo ligand (O(57)) was refined isotropically. One S(5) oxygen atom is disordered over two positions (O(29) and O(30)) with partial occupancies of 0.7 and 0.3. The O(29) partial occupancy sulfonate oxygen atom was refined isotropically. The oxygen atoms of the S(3) sulfonate group are disordered over two positions at partial occupancies of 0.8 and 0.2. Residual electron density is associated with the disordered sulfonate group oxygen atoms that coordinate to the Pr(3) and Pr(4) metal centers.X-ray crystallographic date for the complex is collected in Table 1.

Acknowledgment. We would like to thank the EPSRC for financial assistance with this work as part of an ongoing international collaboration. We would also like to thank Dr. M. J. Hardie for helpful discussions. Supporting Information Available: Figures and tables of bond lengths in relation to complexes 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org.

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