Controlling the Polymorph of LnIII(NO3) - American Chemical Society

Department of Chemistry, UniVersity of Michigan, Ann Arbor, Michigan ... of Chemistry, Shippensburg UniVersity, Shippensburg, PennsylVania 17257-2200...
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CRYSTAL GROWTH & DESIGN

Controlling the Polymorph of LnIII(NO3)3-x(OH)x[15-MCCuII(N)S-pheHA-5] Complexes through Solvent Type and LnIII Ion Choice

2007 VOL. 7, NO. 6 1098-1105

Curtis M. Zaleski,§ Annabel D. Cutland-Van Noord,† Jeff W. Kampf,† and Vincent L. Pecoraro*,† Department of Chemistry, UniVersity of Michigan, Ann Arbor, Michigan 48108-1005 and Department of Chemistry, Shippensburg UniVersity, Shippensburg, PennsylVania 17257-2200 ReceiVed October 23, 2006; ReVised Manuscript ReceiVed February 25, 2007

ABSTRACT: Two general polymorphs of LnIII(NO3)3-x(OH)x[15-MCCuII(N)S-pheHA-5] (where LnIII ) LaIII, SmIII, GdIII, TbIII, DyIII, HoIII, ErIII, LuIII, or YIII and x ) 0, 0.5, or 1) have been previously reported; however, no general hypothesis had been proposed for a method to control the resulting polymorph. We now demonstrate that both solvent and LnIII ion choice play a pivotal role in the resulting three-dimensional structure. By using only water as the solvent, a dimer structure can be achieved; however, if a 5:1 methanol/water solvent is used, a helical chain is produced. Of interest, even in the 5:1 methanol/water solvent, LaIII 15-MC-5 complexes will only produce dimer structures in the solid state, and the helical chain has never been produced. We suggest that this restriction is due to the difference in size and preferred coordination number for LaIII, which does not allow for the proper positioning of nitrate anions to form the helical structure. Introduction The controlled preparation of chiral coordination polymers has been the subject of numerous accounts due to the potential applications of such materials.1 Solids composed of chiral structures promise uses ranging from new optical materials to chiral catalysts to new materials for separations.2 In addition, chiral magnetic materials have the potential to generate solids capable of magnetochiral properties.3 While chiral structures are clearly a desirable objective, the rational and reproducible synthetic approach to achieve such materials is still in its infancy.2a,4 One approach to prepare chiral solids is to take inherently chiral modular synthons and organize them into chiral assemblies as new polymorphs.5,6 Polymorph control is an increasingly studied issue in chemical research, as different polymorphs of the same compound can have different physical and chemical properties.7 This particularly is true in the medical field of drug development as different polymorphs of a drug may have dissimilar results on a patient8 and with magnetic materials in which long range ordering phenomena can dramatically influence the properties of the materials.9 Metallacrowns (MC), the first recognized metallamacrocycles, are a class of molecules known for a variety of functions.10 They have potential applications as MRI contrasting agents11,12 and have been used as building blocks for one-, two-, and threedimensional (1D, 2D, and 3D) solids.5a-d,6,13 They have been synthesized in a variety of sizes including but not limited to 9-MC-3,14 12-MC-4,5a-d,15 15-MC-5,16 18-MC-6,13 24-MC-8,17 40-MC-10,18 and 60-MC-20.19 The research within our laboratory has focused on the 12-MC-45a-d,15 and 15-MC-516 complexes in particular, with the chiral metallacrowns LnIII(NO3)3-x(OH)x[15-MCCuII(N)S-pheHA-5] complexes (where LnIII ) LaIII, SmIII, GdIII, TbIII, DyIII, HoIII, ErIII, LuIII, or YIII, S-pheHA ) S-phenylalanine hydroxamic acid, and x ) 0, 0.5, or 1) being exceptionally interesting.6,11,16e,f,20 These complexes have shown * Author to whom correspondence should be addressed. Phone: 734763-1519. Fax: 734-936-7628. E-mail: [email protected]. Web: wwwpersonal.umich.edu/∼vlpec/index.html. † University of Michigan. § Shippensburg University.

the ability to bind anions selectively16e,f,20 and possess relaxivity values higher than GdIII-DOTA and GdIII-DTPA.11 Maybe most interestingly, several metallacrowns have shown captivating magnetic properties including single-molecule magnet behavior.21 Among these novel magnetic materials are the DyIII(NO3)3-x(OH)x[15-MCCuII(N)S-pheHA-5] complexes.21d We previously reported the ability of the LnIII(NO3)3-x(OH)x[15-MCCuII(N)S-pheHA-5] complexes shown schematically as Figure 1 to crystallize in two distinct polymorphs: dimer20 (Figures 2 and 3) and helical motifs (Figure 4).6 Cutland-Van Noord and co-workers showed in these studies that the choice of solvent is crucial to which polymorph is obtained;6,20 however, we were unable to provide a rationale explaining the resulting structures nor to predict the range of lanthanide ions capable of supporting both polymorph types. Herein we report that we can not only control the formation of the desired polymorph through choice of solvent and the identity of the LnIII ion, but we also understand from the atomic level why the LaIII(NO3)3-x(OH)x[15-MCCuII(N)S-pheHA-5] helical complex should not be formed. Experimental Procedures Synthetic Methods. The lanthanide nitrate hydrated salts [La(NO3)3· 6H2O, Gd(NO3)3·6H2O, Tb(NO3)3·5H2O, Dy(NO3)3·5H2O, Ho(NO3)3· 5H2O, Er(NO3)3·5H2O], the yttrium nitrate hexahydrate [Y(NO3)3·6H2O], and the copper acetate monohydrate [Cu(O2CCH3)2·H2O] were obtained from Aldrich Chemical and used as received. ACS certified grade methanol was obtained from Fisher Scientific and used as received. Deionized water was used for all syntheses. S-Phenylalanine hydroxamic acid (S-pheHA) was synthesized as previously described.22 The metallacrown syntheses were previously reported.6,20 Yields for all reactions are between 50-60%. Note on naming scheme used in this manuscript: The different Ln[15-MCCuII(N)ligand-5] complexes will be denoted by the LnIII, by the [15-MCCuII(N)S-pheHA-5] core as 1, and by the polymorph Dimer or Helix. Synthesis of Dimer Metallacrowns with S-Phenylalanine Hydroxamic Acid.20 LaIII(NO3)3[15-MCCuII(N)S-pheHA-5]·2H2O, LaIII-1Dimer. One millimole of Cu(O2CCH3)2·H2O, 1 mmol of S-pheHA, and 0.25 mmol of La(NO3)3·6H2O were dissolved in 25 mL of water. The solution initially had a green color, but after ∼15 min of stirring the solution turned a deep blue color. The solution was stirred overnight (∼12 h). The solution was then filtered. Some green material was

10.1021/cg060743h CCC: $37.00 © 2007 American Chemical Society Published on Web 05/12/2007

Polymorph Control of 15-MC-5 Complexes

Figure 1. Synthesis of LnIII(NO3)2(OH)[15-MCCuII(N)S-pheHA-5]. Use of water leads to the dimer polymorph, while a 5:1 methanol/water mixture leads to the helical polymorph. isolated and discarded. The deep blue filtrate was set aside for crystal growth. After slow evaporation of the solvent at room-temperature, rectangular platelike crystals were obtained and washed with cold H2O. Elemental analysis for LaCu5C45H54N13O21 [FW ) 1569.62 g/mol] found % (calculated): C ) 31.80 (32.09), H ) 3.17 (3.47), N ) 3.94 (3.94). Unit cell dimensions: a ) 15.267(1) Å, b ) 15.267(1) Å, c ) 48.270(5) Å, R ) 90°, β ) 90°, γ ) 90°, V ) 9743.15(1.45) Å.3 Space group: P3221 (No. 154). Crystal habit: rectangular plates. GdIII(NO3)2(OH)[15-MCCuII(N)S-pheHA-5]·6H2O, GdIII-1-Dimer. Synthesis was similar to LaIII-1-Dimer except that 0.25 mmol of Gd(NO3)3·6H2O was used in the synthesis. Elemental analysis for GdCu5C45H63N12O23 [FW ) 1615.03 g/mol] found % (calculated): C ) 33.42 (33.46), H ) 3.92 (3.93), N ) 10.66 (10.41). Unit cell dimensions: a ) 27.592(3) Å, b ) 14.796(4) Å, c ) 33.290(6) Å, R ) 90°, β ) 93.54(1)°, γ ) 90°, V ) 13564.89(3.21) Å.3 Space group: C2 (No. 5). Crystal habit: rectangular plates. TbIII(NO3)3[15-MCCuII(N)S-pheHA-5]·3H2O, TbIII-1-Dimer. Synthesis was similar to LaIII-1-Dimer except that 0.25 mmol of Tb(NO3)3·5H2O was used in the synthesis. Elemental analysis for TbCu5C45H56N13O22 [FW ) 1607.65 g/mol] found % (calculated): C ) 33.66 (33.62), H ) 3.57 (3.51), N ) 11.38 (11.33). Unit cell dimensions: a ) 25.255(5) Å, b ) 39.319(9) Å, c ) 27.291(4) Å, R ) 90°, β ) 93.68(8)°, γ ) 90°, V ) 27100 Å.3 Space group: P21 (No. 4). Crystal habit: rectangular plates. DyIII(NO3)2(OH)[15-MCCuII(N)S-pheHA-5]·5H2O, DyIII-1-Dimer. Synthesis was similar to LaIII-1-Dimer except that 0.25 mmol of Dy(NO3)3·5H2O was used in the synthesis. Elemental analysis for DyCu5C45H61N12O22 [FW ) 1602.26 g/mol] found % (calculated): C ) 33.80 (33.73), H ) 3.81 (3.84), N ) 10.48 (10.49). Unit cell dimensions: a ) 24.631(6) Å, b ) 35.157(6) Å, c ) 14.721(3) Å, R ) 90°, β ) 90°, γ ) 90°, V ) 12748 Å.3 Space group: P21212 (No. 18). Crystal habit: rectangular plates. HoIII(NO3)2(OH)[15-MCCuII(N)S-pheHA-5]·5.5H2O, HoIII-1-Dimer. Synthesis was similar to La-1-Dimer except that 0.25 mmol of Ho(NO3)3·5H2O was used in the synthesis. Elemental analysis for HoCu5C45H62N12O22.5 [FW ) 1613.70 g/mol] found % (calculated): C ) 33.46 (33.49), H ) 3.84 (3.87), N ) 10.32 (10.41). Unit cell dimensions: a ) 24.383 Å, b ) 35.231 Å, c ) 14.745 Å, R ) 90°, β ) 90°, γ ) 90°, V ) 12770 Å.3 Space group: P21212 (No. 18). Crystal habit: rectangular plates. YIII(NO3)3[15-MCCuII(N)S-pheHA-5]·4H2O, YIII-1-Dimer. Synthesis was similar to LaIII-1-Dimer except that 0.25 mmol of Y(NO3)3·5H2O was used in the synthesis. Elemental analysis for YCu5C45H58N13O23 [FW ) 1555.65 g/mol] found % (calculated): C ) 34.84 (34.74), H ) 3.80 (3.76), N ) 11.48 (11.70). Unit cell dimensions: a ) 27.53(1) Å, b ) 14.790(6) Å, c ) 33.144(9) Å, R ) 90°, β ) 93.51(2)°, γ ) 90°, V ) 13490(7) Å.3 Space group: C2 (No. 5). Crystal habit: rectangular plates. Synthesis of Helical Metallacrowns with S-Phenylalaine Hydroxamic Acid.6 GdIII(NO3)2(OH)[15-MCCuII(N)R-pheHA-5]·6H2O, GdIII-1Helix. One millimole of Cu(O2CCH3)2·H2O, 1 mmol of S-pheHA, and 0.25 mmol of Gd(NO3)3·6H2O were dissolved in 25 mL of water and 5 mL of methanol. The solution initially had a green color, but after ∼5 min of stirring the solution turned a deep blue color. The solution was stirred overnight (∼12 h). The solution was then filtered. No green material was isolated. The deep blue filtrate was set aside for crystal growth. After slow evaporation of the solvent at room-temperature

Crystal Growth & Design, Vol. 7, No. 6, 2007 1099 octahedron-shaped crystals (multifaceted) were obtained and washed with cold H2O. Elemental analysis for GdCu5C45H63N12O23 [FW ) 1615.03 g/mol] found % (calculated): C ) 33.23 (33.46), H ) 3.93 (3.93), N ) 10.64 (10.41). Unit cell dimensions: a ) 19.286(4) Å, b ) 19.286(4) Å, c ) 18.860(5) Å, R ) 90°, β ) 90°, γ ) 90°, V ) 7105(3) Å.3 Space group: P43 (No. 78). Crystal habit: octahedron. TbIII(NO3)2.5(OH)0.5[15-MCCuII(N)S-pheHA-5]·4.5H2O, TbIII-1-Helix. Synthesis was similar to GdIII-1-Helix except that 0.25 mmol of Tb(NO3)3·5H2O was used in the synthesis. Elemental analysis for TbCu5C45H59.5N12.5O22.5 [FW ) 1612.18 g/mol] found % (calculated): C ) 33.50 (33.52), H ) 3.73 (3.72), N ) 10.89 (10.86). Unit cell dimensions: a ) 19.231 Å, b ) 19.231 Å, c ) 18.386 Å, R ) 90°, β ) 90°, γ ) 90°, V ) 6799.68(2.37) Å.3 Space group: P41 (No. 76). Crystal habit: octahedron. DyIII(NO3)3[15-MCCuII(N)S-pheHA-5]·3H2O, DyIII-1-Helix. Synthesis was similar to GdIII-1-Helix except that 0.25 mmol of Dy(NO3)3·5H2O was used in the synthesis. Elemental analysis for DyCu5C45H56N13O22 [FW ) 1611.23 g/mol] found % (calculated): C ) 33.54 (33.54), H ) 3.59 (3.50), N ) 11.18 (11.30). Unit cell dimensions: a ) 19.203(6) Å, b ) 19.203(6) Å, c ) 18.330(1) Å, R ) 90°, β ) 90°, γ ) 90°, V ) 6760 Å.3 Space group: P41 (No. 76). Crystal habit: octahedron. HoIII(NO3)3[15-MCCuII(N)S-pheHA-5]·4H2O HoIII-1-Helix. Synthesis was similar to GdIII-1-Helix except that 0.25 mmol of Ho(NO3)3·5H2O was used in the synthesis. Elemental analysis for HoCu5C45H58N13O23 [FW ) 1631.68 g/mol] found % (calculated): C ) 33.20 (33.10), H ) 3.58 (3.58), N ) 10.99 (11.16). Unit cell dimensions: a ) 19.200(2) Å, b ) 19.200(2) Å, c ) 18.338(1) Å, R ) 90°, β ) 90°, γ ) 90°, V ) 6760.2(9) Å3. Space group: P41 (No. 76). Crystal habit: octahedron. ErIII(NO3)3[15-MCCuII(N)S-pheHA-5]·3.5H2O, ErIII-1-Helix. Synthesis was similar to GdIII-1-Helix except that 0.25 mmol of Er(NO3)3·5H2O was used in the synthesis. Elemental analysis for ErCu5C45H57N13O22.5 [FW ) 1625.00 g/mol] found % (calculated): C ) 33.17 (33.26), H ) 3.53 (3.54), N ) 11.03 (11.20). Crystal habit: octahedron. YIII(NO3)2.5(OH)0.5[15-MCCuII(N)S-pheHA-5]·10H2O, YIII-1-Helix. Synthesis was similar to GdIII-1-Helix except that 0.25 mmol of Y(NO3)3·5H2O was used in the synthesis. Elemental analysis for YCu5C45H70.5N12.5O28 [FW ) 1641.24 g/mol] found % (calculated): C ) 32.79 (32.93), H ) 4.33 (4.40), N ) 10.66 (10.51). Crystal habit: octahedron. Physical Methods. X-ray Crystallography. The crystals were mounted on a standard Bruker SMART CCD-based X-ray diffractometer equipped with a LT-2 low-temperature device and normal focus Mo-target X-ray tube (λ ) 0.71073 Å) operated at 2000 W power (50 kV, 40 mA). GdIII(NO3)2(OH)[15-MCCuII(N)S-pheHA-5]·6H2O, GdIII-1-Helix. A crystal of dimensions 0.76 × 0.60 × 0.60 mm was mounted on a standard Bruker SMART CCD-based X-ray diffractometer. The X-ray intensities were measured at 118(2) K; the detector was placed at a distance 4.980 cm from the crystal. A total of 2718 frames were collected with a scan width of 0.3° in ω and phi with an exposure time of 20 s/frame. The frames were integrated with the Bruker SAINT software package with a narrow frame algorithm. The integration of the data yielded a total of 84 316 reflections to a maximum 2θ value of 56.62° of which 16 827 were independent and 15911 were greater than 2σ(I). The final cell constants (Table 1) were based on the xyz centroids of 7855 reflections above 10σ(I). Analysis of the data showed negligible decay during data collection; the data were processed with SADABS and corrected for absorption. The structure was solved and refined with the Bruker SHELXTL (version 5.10) software package, using the space group P43 with Z ) 4 for the formula [C45H50N10O10Cu5Gd](NO3) 2(CH3O)(H2O)10. All non-hydrogen atoms were refined anisotropically with the hydrogen placed in idealized positions. Full matrix least-squares refinement based on F2 converged at R1 ) 0.0368 and wR2 ) 0.0964 [based on I > 2σ(I)], R1 ) 0.0413 and wR2 ) 0.0990 for all data. Experimental parameters and crystallographic data are provided in Table 1. Important bond distances are provided in Table 2.

Results Synthesis and Structural Description. The LnIII[15MCCuII(N)S-pheHA-5]3+ complexes can be synthesized using the stoichiometric ratio of 5:5:1 of S-pheHA/Cu(OAc)2/Ln(NO3)3 in relatively high yield, 50-60% (Figure 1). The choice of solvent is paramount to the resulting solid-state arrangement

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Figure 2. X-ray crystal structure of LaIII(NO3)3[15-MCCuII(N)S-pheHA-5].20 (a) When viewed along the pseudo-fivefold axis, the arrangement of the phenyl rings is observed with two phenyl rings lying under the face of the MC and three of the phenyl rings lying to the periphery of the MC face. In addition, the bridging nitrate (CPK display) could prevent the binding of additional ligands to the metallacrown. (b) A side view displays the phenyl rings directed to one face of the metallacrown. Color scheme: aqua sphere, LaIII; gold spheres, CuII; gray lines, carbon; red tubes, oxygen; blue tubes, nitrogen. Copper-water bonds, hydrogen atoms, and lattice solvent have been removed for clarity. [This figure is modified from the supporting material of Zaleski, C. M.; Depperman, E. C.; Kampf, J. W.; Kirk, K. M.; Pecoraro, V. L. Inorg. Chem. 2006, 45, 10022.]

No matter which unit cell is measured, each crystal has the same habit: a rectangular platelike shape. The helix polymorph has until now been detected with only one set of unit cell dimensions: a = 19.2 Å, b = 19.2 Å, c = 18.5 Å, R ) 90°, β ) 90°, γ ) 90°, V = 6900 Å3, space group P41 (No. 76) when S-pheHA was used and P43 (No. 78) when R-pheHA was used. The crystal habit is markedly different from that of the dimer structures. The crystals are shaped like an octahedron. By using the crystal habit to distinguish between dimer and helical polymorphs, the compounds can be quickly and inexpensively identified with a light microscope. Discussion

Figure 3. A water solvent system provides a solid-state structure where two metallacrowns of LaIII-1-Dimer come together to form a dimer.20 See Figure 2 for color scheme. Copper-water bonds, hydrogen atoms, and the lattice nitrate and solvent have been removed for clarity. [This figure is modified from the supporting material of Zaleski, C. M.; Depperman, E. C.; Kampf, J. W.; Kirk, K. M.; Pecoraro, V. L. Inorg. Chem. 2006, 45, 10022.]

of the complexes. The choice of water results in a dimer formation in the solid state. The use of a 5:1 methanol/water solvent results in the helical polymorph. The two polymorphs have distinct unit cell parameters and crystal habits, which allow for structural differentiation without collecting full X-ray crystallographic data sets. The dimer LaIII[15-MCCuII(N)S-pheHA5] structure has unit cell parameters of a = 15.3 Å, b = 15.3 Å, c = 48.3 Å, R ) 90°, β ) 90°, γ ) 90°, V = 9700 Å3, space group P3221 (No. 154) while GdIII[15-MCCuII(N)S-pheHA5] and YIII[15-MCCuII(N)S-pheHA-5] dimer structures have unit cell parameters of a = 27.6 Å, b = 14.8 Å, c = 33.2 Å, R ) 90°, β = 93.5°, γ ) 90°, V = 13500 Å3, space group C2 (No. 5). A third set of unit cell parameters was observed for the DyIII[15MCCuII(N)S-pheHA-5] and HoIII[15-MCCuII(N)S-pheHA-5] dimer structures (a = 24.5 Å, b = 35.2 Å, c = 14.7 Å, R ) 90°, β ) 90°, γ ) 90°, V = 12700 Å3, space group P21212 (No. 18)). In addition, a fourth set of unit cell parameters was observed for the TbIII[15-MCCuII(N)S-pheHA-5] dimer structure (a = 25.2 Å, b = 39.3 Å, c = 27.3 Å, R ) 90°, β ) 93.7°, γ ) 90°, V = 27100 Å3, space group P21 (No. 4)). To date, there has not been found a way to control which dimer polymorph is crystallized. Identical experimental parameters will yield all four polymorphs, although the first two polymorphs mentioned are most common.

Because complete structural descriptions of the “dimer” and “helical” polymorphs have been communicated previously,6,20 only a general structural description will be given here. In the individual LnIII(NO3)3-x(OH)x[15-MCCuII(N)S-pheHA-5] complexes, an overall planar metallacrown results from the use of the R-amino hydroxamic acid. Within the complex, the metals are placed 108° relative to each other, and the ligand supports a planar metallacrown structure with pseudo-fivefold symmetry. In addition, by using S-phenylalanine hydroxamic acid (an R-amino hydroxamic acid), chiral metallacrowns can by synthesized. This is accomplished by each ligand placing the R group on the same face of the metallacrown, thus providing face differentiation. This R group orientation is enforced by the metallacrown repeat unit: metal-nitrogen-oxygen. If the ligand “flips” to place the R group on the opposite face, the metallacrown connectivity is not repeated and a macrocyclic complex is not synthesized. Therefore, by choosing enantiopure chiral ligands, enantiopure chiral face-differentiated metallacrowns can be synthesized as evident from previously published equal and opposite circular dichroism spectra for NdIII[15-MCCuII(N)S-alaHA5]3+ and NdIII[15-MCCuII(N)R-alaHA-5]3+, where alaHA is alanine hydroxamic acid.23 The initial studies by Cutland-Van Noord and co-workers revealed that the choice of solvent was crucial for defining the type of obtained polymorph.6,20 By using exclusively water as the solvent, a Ln[15-MCCuII(N)pheHA-5] dimer was observed in the solid state.20 For the individual metallacrown, two of the phenyl rings are orientated directly under the MC surface, while the other three are splayed to the outside (Figure 2). In addition, individual metallacrowns interact with each other in the solid state to form a dimer (Figure 3). The phenyl rings of each metallacrown are orientated toward each other to form a hydrophobic pocket capable of selectively binding a variety of

Polymorph Control of 15-MC-5 Complexes

Crystal Growth & Design, Vol. 7, No. 6, 2007 1101

Figure 4. X-ray crystal structure of GdIII-1-Helix. The helical structure is the result of a 5:1 methanol/water solvent system. (a) Three of the phenyl rings lie under the face of the MC, and two of the phenyl rings lie to the periphery of the MC face. The view is down the pseudo-fivefold axis. (b) As in LaIII-1-Dimer, the phenyl rings of GdIII-1-Helix are directed to one face of the metallacrown. However, the central GdIII has only one bound water molecule. (c) The helical nature of the solid is due to a CuII-Ocarbonyl bond between adjacent metallacrowns. (d) Phenyl rings (CPK display) coat the outside of the helix, while water molecules line the inside of the helix. The view is down the z-axis of the helix. (e) The helical nature of the solid is easily discerned from the arrangement of the MC oxygen atoms, CuII ions, and the GdIII ions. (f) The helices are tightly packed; however, the phenyl rings serve as a hydrophobic region between the water lined channels of the solid. See Figure 2 for color scheme. Copper-water bonds, hydrogen atoms, and lattice solvent have been removed for clarity. [This figure is modified from the supporting material of Zaleski, C. M.; Depperman, E. C.; Kampf, J. W.; Kirk, K. M.; Pecoraro, V. L. Inorg. Chem. 2006, 45, 10022.]

guests.16e-f,20 However, to understand the nature of the observed polymorphism, only MC complexes that bind nitrate anions within the pocket have been fully examined. A helical structure is observed in the solid state if a 5:1 mixture of methanol/water is used as the solvent (Figure 4).6 In this structure, a carbonyl oxygen of one metallacrown binds axially to a CuII ion of an adjacent metallacrown (Figure 4c). The metallacrowns are placed at 90° angles with respect to each other, with the interior of the helix formed by the side free of phenyl rings. Because of the pseudo-fivefold symmetry of the metallacrown a molecular square cannot be obtained. Instead, the carbonyl oxygen to CuII ion bond is perpetuated down an S4 screw axis to give a helical chain. The screw axis is parallel to the faces of the metallacrowns. Thus, when viewed along the screw axis, the metallacrowns appear to form a square with the phenyl rings coating the outer surface of the helix (Figure 4d). In addition, neighboring helices are isolated from one another by the phenyl rings (Figure 4e). Furthermore, the

enantiomer of the ligand determines the pitch of the helix. Thus, by using enantiopure ligands, homochiral solids can be synthesized. The Plus (P) helix (space group P41) is synthesized from the S enantiomer of phenylalanine hydroxamic acid, while the Minus (M) helix (space group P43) is synthesized from the R enantiomer. To assess the generality of the preparation of these polymorphs, we attempted to prepare both solid types covering the range of LnIII ions. From these studies, we have observed that neither dimer nor helical polymorphs can be isolated if the LnIII cation is equal or smaller in size than YbIII. With either YbIII or LuIII, the color of the solution (either water or methanol/ water mixtures) converts from green (reported as a 12-MC-4 containing S-pheHA23) to the blue-violet color indicative of the Ln(15-MC-5); however, in less than 30 min, the color reverts to green. The ErIII[15-MCCuII(N)S-pheHA-5] complex can be synthesized in water as is evident by the characteristic deep blue-violet solution color; however, the complex is extremely

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Table 1. Crystallographic Data for GdIII-1-Helix chemical formula formula weight (g/mol) space group a b c R β γ temperature λ Fcalc µ volume Z R1a.b wR2a,c

GdCu5C45H63N12O23 1615.03 P43 (No. 78) 19.2377(14) Å 19.2377(14) Å 18.325(3) Å 90° 90° 90° 118(2) K 0.71073 Å 1.666 mg/m3 2.588 mm-1 6781.9(12) Å3 4 0.0368 [I > 2σ(I)]; 0.0413 (all data) 0.0964 [I > 2σ(I)]; 0.0990 (all data)

a 18317 unique data with I > 2σ(I). b R ) ∑(|F | - |F |)/∑|Fo|. c wR 1 o c 2 ) [∑[w(Fo2 - Fc2)2]/∑[w(F°)2]]1/2; w ) 1/[σ2(Fo2) + (mp)2 + np]; p ) [max(Fo2,0) + 2Fc2]/3 (m and n are constants); σ ) [Σ[w(Fo2 - Fc2)2]/(n - p)]1/2.

Table 2. Selected Bond Distances (Å) for GdIII-1-Helix Gd(1)-O(103) Gd(1)-O(10) Gd(1)-O(2) Gd(1)-O(4) Gd(1)-O(6) Gd(1)-O(8) Gd(1)-O(101) Gd(1)-O(100) Gd(1)-N(100) Cu(1)-N(2) Cu(1)-O(10) Cu(1)-O(9) Cu(1)-N(1) Cu(2)-N(4) Cu(2)-O(2) Cu(2)-O(1) Cu(2)-N(3)

2.360(4) 2.388(4) 2.389(3) 2.399(3) 2.412(3) 2.433(3) 2.456(4) 2.514(4) 2.913(4) 1.910(4) 1.919(4) 1.950(4) 2.022(5) 1.907(4) 1.942(3) 1.946(4) 2.018(4)

Cu(3)-N(6) Cu(3)-O(4) Cu(3)-O(3) Cu(3)-N(5) Cu(4)-N(8) Cu(4)-O(6) Cu(4)-O(5) Cu(4)-N(7) Cu(5)-N(10) Cu(5)-O(8) Cu(5)-O(7) Cu(5)-N(9)

1.894(4) 1.916(4) 1.926(4) 2.018(4) 1.900(4) 1.909(3) 1.929(3) 1.991(4) 1.899(4) 1.912(4) 1.921(4) 1.999(5)

soluble in water. When the water is allowed to evaporate at a relatively fast pace, a film is produced. When the evaporation rate is slowed down, the blue solution converts to a green solid byproduct when highly concentrated at low volumes. This result is probably due to the long time needed to concentrate the solution. While MS-ESI+ measurements show the violet solution contains the desired ErIII15-MC-5, MS-ESI+ measurements show the green solid to be an oligomer of CuII ions and the ligand S-pheHA. The ErIII ion (ionic radius ) 1.00 Å; CN ) 8)24 may thus be at the limit of preparing stable LnIII 15MC-5 complexes over long periods. All other tested LnIII ions successfully lead to crystals of the dimer polymorph. Given these observations, it seemed reasonable that one might also be able to prepare the helical polymorphs across the lanthanide series until ErIII. However, repeated attempts were made to grow crystals of a LaIII[15-MCCuII(N)S-pheHA-5] helix with no success. LaIII[15-MCCuII(N)S-pheHA-5] was synthesized many times in pure methanol and methanol/water mixtures, but the dimer polymorph always resulted. Similar results were obtained with praseodymium and neodymium. The reason behind this conundrum may lie in the preferred coordination number (C.N.) of nine for these larger LnIII ions (e.g., LaIII ionic radius 1.16 Å; C. N. ) 8)24 and the preference of the other LnIII ions for coordination numbers of 8 and 7 due to their smaller ionic radii (C.N. ) 8, ionic radii: GdIII ) 1.05 Å; TbIII ) 1.04 Å; DyIII ) 1.03 Å; HoIII ) 1.02 Å; ErIII ) 1.05 Å; YIII ) 1.02 Å).24 In the helical structure, a nitrate anion binds as a bidentate ligand inside the hydrophobic pocket to the LnIII, and one water molecule binds axially to the LnIII (C.N. ) 8)

Figure 5. In LaIII-1-Dimer the nitrate anion bridges between the central LaIII ion and a ring CuII ion. In addtion, the nitrate anion bridges to a ring CuII ion on an opposite MC face. The LaIII ion of the second MC binds to two water ions and a hydroxide anion instead of a nitrate anion for charge balance. The lattice solvent has been removed for clarity since it is not involved in hydrogen bonding between the MC faces.

Figure 6. Side view of the hydrogen bond network existing between one complex of GdIII-1-Helix and the lattice water molecules and the nitrate anions. Green lines signify the hydrogen bonds. See Figure 2 for color scheme.

on the opposite face (Figure 4b). In the LaIII dimer, one water molecule binds inside the hydrophobic cavity, while two water molecules and one nitrate anion bind to the LaIII (C.N. ) 9) on the opposite face along a pseudo-threefold axis (Figure 2). The coordination of nitrate is particularly important. In the helical structures, this anion is found on the hydrophobic face, but in the dimer structures with the nine-coordinate LnIII ions the nitrate anion appears on the hydrophilic face. Moreover, the nitrate is one of three ligands to the LaIII in the dimer motif, whereas it is the sole ligand on the hydrophobic face to an eight-coordinate LnIII ion of the helical structure. In addition, the nitrate of the dimer structure binds bidentate to the hydrophilic side of the metallacrown spanning the LaIII ion and a ring CuII ion (Figure 3). In the lower coordination structures, the nitrate is bound as a bidentate ion solely to LnIII ions. Most importantly, the bridging bidentate nitrate also spans two metallacrowns forming a bridge to a CuII ion of an adjacent metallamacrocyle in the LaIII structure (Figure 5). This bridging motif is impossible in eight-coordinate structures both because the nitrate is on the hydrophobic side of the ring (the additional bulk of the phenyl rings block the approach of another metallacrown) and because being bound symmetrically as a bidentate ion solely to the LnIII it is not in a position to span across copper ions of adjacent metallacrowns. Furthermore, the CuII-O(nitrate)-CuII bridge of the larger LnIII (LaIII-NdIII) metallacrowns aligns the faces

Polymorph Control of 15-MC-5 Complexes

Figure 7. View down the pseudo-fivefold axis of GdIII-1-Helix highlighting some of the hydrogen bonds that exist between the complex and the lattice water molecules and the nitrate anions. For clarity, some of the hydrogen bonds have been omitted. Green lines signify the hydrogen bonds. See Figure 2 for color scheme.

Crystal Growth & Design, Vol. 7, No. 6, 2007 1103

Figure 9. Two MCs of different helices (GdIII-1-Helix) also interact via a hydrogen bond network. Lattice water molecules serve as bridges between bound and unbound nitrate anions and the MC faces. Green lines signify the hydrogen bonds. See Figure 2 for color scheme.

Figure 10. Side view of the hydrogen bond network existing between one complex of LaIII-1-Dimer and the lattice water molecules and the nitrate anions. For clarity, some of the hydrogen bonds have been omitted. Green lines signify the hydrogen bonds. See Figure 2 for color scheme. Figure 8. View down the z-axis of GdIII-1-Helix highlighting the hydrogen bond network within an individual helix. Green lines signify the hydrogen bonds. In addition, the CuII-Ocarbonyl (sphere representations) interactions, which stitch together the helix, are also displayed with a green line. See Figure 2 for color scheme.

of the two metallacrowns at the improper orientation to form the helical structure. The angle produced between the adjacent metallacrowns is 76°, vastly smaller than the 90° required for the helical polymorph. One might then ask why one observes such different nitrate orientations between the lanthanides. The LaIII ion with its larger radius (LaIII ) 1.36 Å, C. N. ) 9)24 is situated above the mean plane created by the hydroxamic oxygen atoms toward the face free of phenyl rings by 0.68 Å.20 In contrast, the GdIII ion in GdIII-1-Helix is situated below the mean plane created by hydroxamic oxygen atoms by 0.20 Å. Critically, the nitrate ion binds to the metallacrown face toward which the lanthanide has been displaced. Within the 1D helical structure, an extensive hydrogen bond network exists between the solvent molecules and the nitrate anions (Figures 6-9). This hydrogen bond network may serve to fasten the structure together. In contrast, the presence of the

nine-coordinate LaIII, with its asymmetric nitrate bridge between CuII ions of different metallacrowns disrupts this intricate hydrogen bond network and alters the orientation of two adjacent metallacrowns from the right angles necessary to propagate a helix (Figures 10-12). Within an individual helical MC molecule, many hydrogen bonds exist (Figures 6 and 7). For instance, an unbound nitrate anion is hydrogen bonded to an amine nitrogen of the MC, and several water molecules are hydrogen bonded to the periphery of the complex. Within the 1D helix the hydrogen bond network becomes even more important to the overall helical structure (Figure 8). A water molecule bonded to a ring CuII ion is hydrogen bonded to a lattice water molecule; this water molecule is then hydrogen bonded to a water molecule bonded to the central GdIII ion. This sequence is repeated parallel to the S4 screw axis. In addition to this intrahelical hydrogen bonding, numerous interhelical hydrogen bonds exist (Figure 9). Two MCs that face each other from different helices interact through lattice water molecules that simultaneously hydrogen bond to the face of the MC and to an unbound nitrate anion. The unbound nitrate anion then hydrogen bonds to a second lattice water molecule which also hydrogen bonds to the bound nitrate anion. Hydrogen bonds also exist in the dimer polymorph, but the hydrogen bond

1104 Crystal Growth & Design, Vol. 7, No. 6, 2007

Zaleski et al.

significantly different hydrogen-bonding pattern results when the more hydrophobic methanol solvent is added. In this case, the phenyl groups, while still associating, no longer are driven into a bilayer structure. Because there are no major perturbations of the nitrate binding mode within the series of eight-coordinate LnIII structures, the relative solvation dictates the final product. Conclusion

Figure 11. View down the pseudo-fivefold axis of LaIII-1-Dimer highlighting some of the hydrogen bonds that exist between the complex and the lattice water molecules and the nitrate anions. For clarity, some of the hydrogen bonds have been omitted. Green lines signify the hydrogen bonds. See Figure 2 for color scheme.

Polymorph control has become an increasingly interesting and important area of chemical research, and this manuscript demonstrates that simple choices of ions and solvents can lead to vastly different 3D structures. Using a water-only solvent, the dimer polymorph may be achieved with all of the LnIII ions larger than ErIII; however, if a methanol-water mixture is used, a helical polymorph can be produced for most of the LnIII ions investigated. A LaIII helix has not been produced in methanol or a methanol-water mixture despite repeated attempts. The reason is directly related to the size and coordination number (C.N.) preference. LaIII ions prefer a C.N. of 9, while for the other LnIII ions investigated (GdIII, TbIII, DyIII, HoIII, ErIII, and YIII) a C.N. of 8 or 7 is preferred. The larger LaIII ion is displaced toward the hydrophilic side of the metallacrown causing a nitrate anion to bind on this side of the metallamacrocycle. In contrast, the smaller lanthanides are displaced toward the hydrophobic side of the metallacrown and bind a nitrate anion in a different manner. This leads to a change in intermetallacrown association due to direct nitrate bridging, steric repulsion, and altered hydrogen bond networks. Thus, only the dimer polymorph can be produced with nine-coordinate lanthanides under these experimental conditions. Acknowledgment. V.L.P. thanks the National Science Foundation for financial support (CHE-0111428). Supporting Information Available: X-ray crystallographic information files of GdIII-1-Helix in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.

References

Figure 12. The two MCs of LaIII-1-Dimer also interact via a hydrogen bond network. Lattice water molecules serve as bridges between the LaIII bound water molecule and the MC face. These hydrogen bonds only occur within the hydrophobic pocket of the MCs. Green lines signify the hydrogen bonds. See Figure 2 for color scheme.

network is not nearly as extensive. Hydrogen bonds between the MC and the lattice water molecules exist, but they are fewer in number when compared to the helical counterpart (Figures 10 and 11). In addition, hydrogen bonds only exist between MC molecules that form the hydrophobic pocket (Figure 12). No hydrogen bonds exist between the hydrophilic faces of the MC molecules (Figure 5). At this point, we can explain the difference between the realization of dimer and helix structures for ions that are eightvs nine-coordinate; however, one must still address why lanthanides that prefer to be eight coordinate can form either polymorph. Our best explanation for this observation is the difference in solvation of the phenyl rings in water versus water/ methanol mixtures. In water alone, the side chain phenyl groups associate to make bilayers in the dimer structure. In contrast, a

(1) (a) Lin, W. J. Solid State Chem. 2005, 178, 2486. (b) Cho, S.-H.; Ma, B.; Nguyen, S. T.; Hupp, J. T.; Albrecht-Schmitt, T. E. Chem. Commun. 2006, 2563. (c) Wu, C.-D.; Hu, A.; Zhang, L.; Lin, W. J. Am. Chem. Soc. 2005, 127, 8940. (d) Burchell, T. J.; Puddephatt, R. J. Inorg. Chem. 2006, 45, 650. (e) Li, F.; Li, T.; Li, X.; Li, X.; Wang, Y.; Cao, R. Cryst. Growth Des. 2006, 6, 1458. (2) (a) Lin, W.; Evans, O. R. Acc. Chem. Res. 2002, 35, 511. (b) Janiak, C. Dalton Trans. 2003, 2781. (c) Becker, J. J.; Gagne, M. R. Acc. Chem. Res. 2004, 37, 798. (d) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334. (e) Ye, Q.; Wang, X.-S.; Zhao, H.; Xiong, R.-G. Chem. Soc. ReV. 2005, 34, 208. (3) (a) Caneschi, A.; Gatteschi, D.; Rey, P.; Sessoli, R. Inorg. Chem. 1991, 30, 3936. (b) Coronado, E.; Gomez-Garcia, C. J.; Nuez, A.; Romero, F. M.; Rusanov, E.; Stoecki-Evans, H. Inorg. Chem. 2002, 41, 4615. (c) Inoue, K.; Kikuchi, K.; Ohba, M.; Okawa, H. Angew. Chem., Int. Ed. 2003, 42, 4810. (d) Gruselle, M.; Train, C.; Boubekeur, K.; Gredin, P.; Ovanesyan, N. Coor. Chem. ReV. 2006, 250, 2491. (4) (a) Bradshaw, D.; Claridge, J. B.; Cussen, E. J.; Prior, T. J.; Rosseinsky, M. J. Acc. Chem. Res. 2005, 38, 273. (b) Janiak, C. Chem. Soc. ReV. 2005, 34, 208. (5) (a) Bodwin, J. J.; Pecoraro, V. L. Inorg. Chem. 2000, 39, 3434. (b) Halfen, J. A.; Bodwin, J. J.; Pecoraro, V. L. Inorg. Chem. 1998, 37, 5416. (c) Pecoraro, V. L.; Bodwin, J. J.; Cutland, A. D. J. Solid State Chem. 2000, 152, 68. (d) Bodwin, J. J.; Cutland, A. D.; Malkani, R. G.; Pecoraro, V. L. Coor. Chem. ReV. 2001, 216-217, 489. (e) Ranford, J. D.; Vittal, J. J.; Wu, D.; Yang, X. Angew. Chem. Int. Ed. 1999, 38, 3498. (f) Brammer, L. Chem. Soc. ReV. 2004, 33, 476. (6) Cutland-Van Noord, A. D.; Kampf, J. W.; Pecoraro, V. L. Angew. Chem., Int. Ed. 2002, 41, 4668.

Polymorph Control of 15-MC-5 Complexes (7) (a) Rogers, R. D. Cryst. Growth Des. 2003, 3, 867. (b) Blagden, N.; Davey, R. J. Cryst. Growth Des. 2003, 3, 873. (c) Chopra, D.; Mohan, T. P.; Rao, S.; Row, T. N. G. CrystEngComm 2005, 62, 374. (8) Yu, L. X.; Furness, M. S.; Raw, A.; Woodland Outlaw, K. P.; Nashed, N. E.; Ramos, E.; Miller, S. P. F.; Adams, R. C.; Fang, F.; Patel, R. M.; Holcombe, F. O.; Chiu, Y.; Hussain, A. S. Pharm. Res. 2003, 20, 531. (9) (a) Leznoff, D. B.; Rancurel, C.; Sutter, J.-P.; Rettig, S. J.; Pink, M.; Paulsen, C.; Kahn, O. J. Chem. Soc., Dalton Trans. 1999, 3593. (b) Kurmoo, M.; Estournes, C.; Oka, Y.; Kumagai, H.; Inoue, K. Inorg. Chem. 2005, 44, 217. (10) Pecoraro, V. L.; Stemmler, A. J.; Gibney, B. R.; Bodwin, J. J.; Wang, H.; Kampf, J. W.; Barwinski, A. In Prog. Inorg. Chem.; Karlin, K. D., Ed.; John Wiley and Sons, Inc.: New York, 1997; Vol. 45, pp 83. (11) Stemmler, A. J.; Kampf, J. W.; Kirk, M. L.; Atasi, B. H.; Pecoraro, V. L. Inorg. Chem. 1999, 38, 2807. (12) (a) Parac-Vogt, T. N.; Pacco, A.; Nockemann, P.; Laurent, S.; Muller, R. N.; Wickleder, M.; Meyer, G.; Vander Elst, L.; Binnemans, K. Chem. Eur. J. 2006, 12, 204. (b) Parac-Vogt, T. N.; Pacco, A.; Nockemann, P.; Yuan, Y.-F.; Gorller-Walrand, C.; Binnemans, K. Eur. J. Inorg. Chem. 2006, 1466. (13) (a) Moon, M.; Kim, I.; Lah, M. S. Inorg. Chem. 2000, 39, 2710. (b) Moon, D.; Song, J.; Kim, B. J.; Suh, B. J.; Lah, M. S. Inorg. Chem. 2004, 43, 8230. (c) Kwak, B.; Rhee, H.; Park, S.; Lah, M. S. Inorg. Chem. 1998, 37, 3599. (14) Pecoraro, V. L. Inorg. Chim. Acta 1989, 155, 171. (15) Lah, M. S.; Pecoraro, V. L. J. Am. Chem. Soc. 1989, 111, 7258. (16) (a) Kessissoglou, D. P.; Kampf, J. W.; Pecoraro, V. L. Polyhedron 1994, 13, 1379. (b) Stemmler, A. J.; Kampf, J. W.; Pecoraro, V. L. Angew. Chem., Int. Ed. Engl. 1996, 35, 2841. (c) Stemmler, A. J.;

Crystal Growth & Design, Vol. 7, No. 6, 2007 1105

(17) (18) (19) (20) (21)

(22) (23) (24)

Barwinski, A.; Baldwin, M. J.; Young, V.; Pecoraro, V. L. J. Am. Chem. Soc. 1996, 118, 11962. (d) Cutland, A. D.; Malkani, R. G.; Kampf, J. W.; Pecoraro, V. L. Angew. Chem., Int. Ed. 2000, 39, 2689. (e) Lim, C. S.; Van Noord, A. C.; Kampf, J. W.; Pecoraro, V. L. Eur. J Inorg. Chem. 2007, 1347. (f) Mezei, G.; Kampf, J. W.; Pan, S.; Poeppelmeier, K.; Watkins, B.; Pecoraro, V. L. Chem. Commun. 2007, 1148. Saarinen, H.; Orama, M. Acta Chem. Scand. 1998, 52, 1209. Brasey, T.; Scopelliti, R.; Severin, K. Inorg. Chem. 2005, 44, 160. Moon, D.; Lee, K.; John, R. P.; Kim, G. H.; Suh, B. J.; Lah, M. S. Inorg. Chem. 2006, 45, 7991. Cutland, A. D.; Halfen, J. A.; Kampf, J. W.; Pecoraro, V. L. J. Am. Chem. Soc. 2001, 123, 6211. (a) Dendrinou-Samara, C.; Alexiou, M.; Zaleski, C. M.; Kampf, J. W.; Kirk, M. L.; Kessissoglou, D. P.; Pecoraro, V. L. Angew. Chem., Int. Ed. 2003, 42, 3763. (b) Zaleski, C. M.; Depperman, E. C.; Kampf, J. W.; Kirk, M. L.; Pecoraro, V. L. Angew. Chem., Int. Ed. 2004, 43, 3912. (c) Zaleski, C. M.; Depperman, E. C.; Dendrinou-Samara, C.; Alexiou, M.; Kampf, J. W.; Kessissoglou, D. P.; Kirk, M. L.; Pecoraro, V. L. J. Am. Chem. Soc. 2005, 127, 12862. (d) Zaleski, C. M.; Depperman, E. C.; Kampf, J. W.; Kirk, K. M.; Pecoraro, V. L. Inorg. Chem. 2006, 45, 10022. Cutland-Van Noord, A. D. Dissertation, University of Michigan, Ann Arbor, MI, 2003. Seda, S. H.; Janczak, J.; Lisowski, J. Inorg. Chim. Acta 2006, 359, 1055. Shannon, R. D. Acta Crystallogr. 1976, A32, 751.

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