A Metal Coordination Polymer with Hexagonal Diamondoid (or Lonsdaleite) Network Topology Bellam Sreenivasulu and Jagadese J. Vittal* Department of Chemistry, National University of Singapore, Singapore 117543 Received April 4, 2003;
CRYSTAL GROWTH & DESIGN 2003 VOL. 3, NO. 5 635-637
Revised Manuscript Received June 23, 2003
W This paper contains enhanced objects available on the Internet at http://pubs.acs.org/crystal. ABSTRACT: The Cu(II) complex [Cu2(scp11)2(H2O)2] (1) when recrystallized in DMF/MeCN solvent mixture gave dark green cubic single crystals of [Cu2(scp11)2]‚H2O (2) (cubic space group, Ia-3d, No. 230). The three-dimensional network structure has hexagonal diamondoid (or Lonsdaleite) architecture (if the net is defined by considering four fused dinuclear units as a single node) with starlike channels along the body diagonal of the unit cell and partially occupied guest water molecules, leaving about 27% empty space in the crystal lattice. Compound 1 on crystallization from DMF/acetone solvent mixture afforded single crystals of 2 and [Cu2(scp11)2(H2O)2]‚2Me2CO (3), which has one-dimensional hydrogen-bonded polymeric structure in the solid-state (triclinic space group P1h , No. 2). When the precipitating solvent is evaporated from the solution, 2 and 3 slowly converted to microsize tubular crystals of 1. Multidimensional network structure can be described in terms of well-known inorganic structures based on the topology or connectivity present using the concept of net.1 For tetrahedral nodes, two types of topologies are possible, namely, cubic and hexagonal diamondoid architectures. A variety of interpenetrating and noninterpenetrating organic, organometallic, and inorganic cubic diamondoid structures have been successfully prepared by connecting the tetrahedral nodes.2-5 It is, therefore, obvious that the cubic diamondoid topology is predominant for tetrahedral nodes, despite the fact that both structural motifs are expected to be energetically very similar. The well-known hexagonal diamondoid structures include ice (Ih form), wurtzite, and tridymite.1 The supramolecular hydrogenbonded solid-state structures of 4-aminophenol and 4′aminobiphenyl-4-ol are the organic examples having hexagonal diamondoid or wurtzite structures reported by Ermer.6 On the other hand, metal coordination network structures having hexagonal diamondoid topology are rare.7 Herein we describe the hexagonal diamondoid structure present in [Cu2(scp11)2]. Reaction of disodium salt of the H2scp11 (H2scp11 ) N-(2-hydroxybenzyl)-1-aminocyclopentyl-1-carboxylic acid), shown in Figure 1a with Cu(OAc)2 in an equimolar ratio gave a green crystalline powder, [Cu2(scp11)2(H2O)2], 1.8 Recrystallization of 1 from DMF/MeCN solvent mixture furnished dark green cubic crystals of [Cu2(scp11)2]‚H2O (2) suitable for X-ray crystallographic analysis.9 Compound 2 crystallized in the cubic space group, Ia-3d (No. 230). The basic building of 2 consists of a dinuclear unit (Figure 1b) in which the two phenoxo O atoms of the reduced Schiff base ligands bridge the two Cu(II) centers, the N and O donors form the base of a highly distorted square plane. The two apexes of the two distorted square pyramids are occupied by the oxygen atoms from the neighboring scp11 to form syn geometry. The dimeric unit is highly puckered as illustrated in Figure 1c with a crystallographic 2-fold symmetry at the center of Cu2O2 ring. Four such dinuclear units fused to form a 16-membered square as shown in Figure 2a. The Cu‚‚‚Cu distances between the sides and corners are 5.43 and 7.48 Å, respectively. The Cu(II) and the carbonyl oxygen atoms at the periphery of this ring are further connected to form a three-dimensional network. The network connectivity of * To whom correspondence should be addressed. Fax: (65)-6779 1691. Tel: (65) 6874-2975. E-mail:
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triconnected nodes of the square in Figure 2a can be described as (4.122) net by Wells’ definition.10 On the other hand, if the center of this square is taken as a node, then the network connectivity can be described as having a hexagonal diamond topology structure11 as shown in Figure 2b. It is well-known that the conformational changes at the backbone of the flexible ligands often generate different but closely related network architectures.12,13 The conformationally flexible reduced Schiff base ligand is ideal for this purpose. It may be noted that the network topology present in [M2(sala)2] (M ) Zn and Cu, sala ) N-(2-hydroxybenzyl)L-alanine) is that of cubic diamondoid architecture.14,15 The structure of 2 clearly demonstrates that the substituents at the backbone of the ligand can influence the network topology from cubic to hexagonal diamondoid architecture. The packing of 2 along the body diagonal axis created a starlike cavity shown in Figure 3 due to the presence of -3 crystallographic symmetry. A similar cavity in a molecular hexagon was reported recently by Zaworotko.16 The shortest non-hydrogen interatomic distance across the channel is 8.5 Å. The potential solvent area was calculated17 to be ∼10396 Å3, which accounts for 27.6% of the cell volume. This is also reflected in the calculated density, 1.292 g cm-3. Recrystallization of 1 from DMF/acetone afforded mainly rodlike bluish green crystals of [Cu2(scp11)2(H2O)2]‚ 2Me2CO (3) along with 2 in equal amounts. Interestingly, 3 crystallized in the triclinic space group, P1 h (No. 2) with Z ) 1. The structure18 of 3 consists of [Cu2(scp11)2] units similar to 2 as shown in Figure 4a, which indicates that the two water molecules are indeed bonded to Cu(II) but in anti fashion. In the crystal lattice 3 forms an interesting one-dimensional hydrogen bonded polymer as shown in Figure 4b. In the crystal structure of 3 the close Cu(I)‚‚‚O(3) interactions (2.808(2) Å) are sustained by strong O-H‚‚‚O and weak N-H‚‚‚O hydrogen bonds congenial for the formation of new Cu-O bonds and supramolecular transformation to take place in the solid state. The TG trace of 3 reveals that the weight loss occurs in two irresolvable steps in the temperature range 76-151 °C. The total weight loss observed (20.9%) agrees with the calculated value (20.4%) for the loss of two acetone and two water molecules. The anhydrous 3 absorbs moisture instantly in air, which is confirmed by running TG of the anhydrous sample after cooling to room temperature. It shows the weight loss of 5.2% (calculated, 5.7% for the loss
10.1021/cg034052m CCC: $25.00 © 2003 American Chemical Society Published on Web 07/31/2003
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Figure 1. (a) A schematic diagram of the ligand, (b) the coordination geometry at Cu(II) centers in 2, and (c) side view showing the bow-like conformation of the backbone in 2. W 3D rotatable image in .xyz format is available.
Figure 3. A part of network architecture is shown with starlike channel in [111] direction. The oxygen atoms of the disordered lattice water molecules and the hydrogens are omitted for clarity. W 3D rotatable image in .xyz format is available.
Figure 2. (a) A portion of the 3D structure showing the 16membered ring and (b) the hexagonal diamondoid architecture in 2. Only selected atoms are included for clarity. W 3D rotatable images of the W 16-membered ring and the W hexagonal diamondoid in .xyz format are available.
of two water molecules) in the temperature range, 60-110 °C, and this behavior is similar to that of 1. Hence, it is concluded that the crystal structure of 1 must be different from 3, and moreover, 3 can be converted to 1 by a heating and cooling cycle. It is obvious that the driving force for the removal of aqua ligands below 120 °C in 1 is due to the formation of new bonds between Cu(II) and carboxylate oxygen atom. It appears that repulsive interactions exist in the solid-state after the formation of new Cu-O bonds, which is likely to contribute to the observed behavior.19 However, the solvent medium provided opportunity to reorient these dimeric building blocks to form 1. Further, the diffusion (precipitating) liquid plays a major role in controlling the ratio of 2 and 3. In a crystallization experiment involving diffusion of Et2O into DMF solution of 1 furnished roughly equal amounts of cubic 2 and rodlike 3 within a week. If the contents are exposed to air, Et2O slowly evaporated and both 2 and 3 changed to microtubular crystals of 1 in due course of time, indicating the influence of solvents on crystal structures. In summary, this report constitutes a 3D network structure that displays the rare hexagonal diamondoid (or
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Crystal Growth & Design, Vol. 3, No. 5, 2003 637 Acknowledgment. Financial support from NUS (R143000-153-112) is gratefully acknowledged. We sincerely thank one of the referees for suggesting an alternative description for the simplified network topology. Supporting Information Available: Elemental analysis, IR spectral data, and TG analysis of compound 2 and 3, XRPD of 1, and X-ray crystallographic information files (CIF) for 2 and 3 are available. This material is available free of charge via the Internet at http://pubs.acs.org.
References
Figure 4. (a) Molecular structure of 3. (b) A segment of the 1D hydrogen-bonded polymer. W 3D rotatable images of W 3 and the W hydrogen-bonded polymer are in .xyz format are available.
Lonsdaleite) network topology with interesting star-shaped channels. Studies to utilize these channels for host-guest chemistry are in progress. Simple one-pot crystallization produced crystals that belong to two extreme ends of the space group table (No. 2 and No. 230).20 Experimental Section. N-(2-hydroxybenzyl)-1-amino1-cyclopentane carboxylic acid, H2Scp11: To a clear solution of 1-amino-1-cyclopentane carboxylic acid (0.608 g, 4.71 mmol) and NaOH (0.188 g, 4.71 mmol) in 20 mL of MeOH was added salicylaldehyde (0.5 mL, 4.71 mmol), and the resulting yellow solution was stirred for 45 min at room temperature. The intermediate Schiff base was reduced in situ with slight excess of NaBH4 (0.266 g, 7.03 mmol). The yellow color was slowly discharged after stirring for 20 min. Then the solution was acidified with acetic acid to maintain a pH of 5-6. The resulting colorless solid was filtered after 1 h, washed with MeOH and Et2O, and dried under vacuum. Yield: 0.98 g (87%). EI-MS 235.3, [C13H17NO3]+. Anal. calcd for C13H17NO3: C, 66.36; H, 7.28; N, 5.95. Found: C, 66.03; H, 7.24; N, 5.93. 1H NMR (CD3OD): δ1.75-2.14 (m, 8H) δ 3.72 (s, 2H) δ 6.5-7.02 (m, 4H). IR (KBr, cm-1): υ(OH) 3460; υ(NH) 2960; υas(CO2-) 1573; υs(CO2-) 1388; υ(phenolic CO) 1276. [Cu2(scp11)2(H2O)2], 1: To the clear solution obtained after stirring the mixture of H2Scp11 (0.050 g, 0.21 mmol) and NaOH (0.017 g, 0.42 mmol) in 20 mL MeOH, was added copper acetate monohydrate (0.042 g, 0.21 mmol) in 5 mL methanol and stirred for 3 h. The resulting green product was filtered, washed with MeOH and Et2O, and then dried under vacuum. Yield: 0.06 g (89%). Anal. calcd. for C26H30N2O6Cu2‚2H2O: C, 49.60; H, 5.44; N, 4.45. Found: C, 49.75; H, 5.45; N, 4.49. IR (KBr, cm-1): υ(OH) 3398; υ(NH) 2934; υas(CO2-) 1617, υs(CO2-) 1376, υ(phenolic C-O) 1266.
(1) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon Press: Oxford, 1984; pp 116-129. (2) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460-1494. (3) Batten, S. R. CrystEngComm 2001, 18, 1-7. (4) Zawarotko, M. J. J. Chem. Soc. Rev. 1994, 23, 283-288. (5) Wuest, J. D. In Mesomolecules: From Molecules to Materials; Mendenhall, G. D., Greenberg, A., Liebman, J. F., Eds.; Chapman & Hall: New York, 1995; pp 107-131. (6) Ermer, O.; Eling, A. J. Chem. Soc. Perkin Trans. 1994, 925944. (7) Kitazawa, T.; Kikuyama, T.; Takeda, M.; Iwamoto, T. J. Chem. Soc., Dalton Trans. 1995, 3715-3720. (8) The formulation of 1 is supported by analytical data (see Experimental Section) and TG data (Supporting Information). 1 forms light green microtubular crystals; however, they are not suitable for single-crystal intensity data collection. In the absence of a crystal structure, it is not proved that the two water molecules are bound to the metal atom. (9) X-ray structure determination of 2: C26H30Cu2N2O6‚H2O: cubic, Ia-3d (no. 230), a ) 33.5375(3) Å, V ) 37721.8 (6) A3, Z ) 48, Fcalcd ) 1.292 g cm-3. In the final least-squares refinement cycles on |F|2, the model converged at R1 ) 0.0417, wR2 ) 0.147, and GOF ) 1.046 for 2364 reflections with Fo > 2σ(Fo) and 177 parameters. The hydrogen bond parameters are N(1)-H(1) 0.81(4) Å, H(1)‚‚‚O(2a) 2.09(4) Å, N(1)‚‚‚O(2a) 2.844(4) Å and N(1)-H(1)‚‚‚O(2) 155(3)° (where a refers to symmetry operator, y - 1/4, -x + 1/4, z + 7/4). (10) Wells, A. F. Further Studies of Three-dimensional Nets; ACA Monograph: Washington, DC, 1979; Vol. 8, p 10. (11) This is of course an oversimplified picture of the network structure. However, depending on the point of connectivity or redefining the node, this network can also be visualized based on S* (6.6.62.62.62.62) net derived from S lattice complexes. For details see O’Keeffe, M.; Hyde, B. G. Crystal Structures I. Patterns and Symmetry; Mineralogical Society of America: Washington, DC, 1996; p 320. (12) Zawarotko, M. J. Chem. Commun. 2001, 1-9. (13) Moulton, B.; Zawarotko, M. J. Chem. Rev. 2001, 101, 16291658. (14) Ranford, J. D.; Vittal, J. J.; Wu, D. Angew. Chem., Int. Ed. 1998, 37, 1114-1116. (15) Ranford, J. D.; Vittal, J. J.; Wu, D.; Yang, X. Angew. Chem., Int. Ed. 1999, 38, 3498-3501. (16) Abourahma, H.; Moulton, B.; Kravtsoy, V.; Zawarotko, M. J. J. Am. Chem. Soc. 2002, 124, 9990-9991. (17) Spek, A. L. Acta Crystallogr. 1990, A46, C34. (18) X-ray structure determination of 3: C26H34Cu2N2O8‚ 2Me2O: triclinic, P1 h , a ) 7.5399(6) Å, b ) 10.3300(8) Å, c ) 11.3540(9) Å, R ) 81.523(2) °, β ) 73.016(2) °, γ ) 78.365(2) °, V ) 824.7 (1) Å3, Z ) 1, Fcalcd ) 1.502 g cm-3. In the final least-squares refinement cycles on |F|2, the model converged at R1 ) 0.0434, wR2 ) 0.0866, and GOF ) 1.022 for 3613 reflections with Fo > 2σ(Fo) and 222 parameters. Relevant hydrogen bond parameters are O(4)-H(4a) 0.70(3) Å, O(4)H(4b) 0.69(3) Å, H(4a)‚‚‚O(5) 2.11(4) Å, H(4b)‚‚‚O(3a) 2.13(3) Å, O(4)‚‚‚O(5) 2.812(4) Å, O(4)‚‚‚O(3a) 2.818(3) Å, O(4)H(4a)‚‚‚O(5) 170(3)°, O(4)-H(4b)‚‚‚O(3a) 174(3)°, N(1)-H(1) 0.89(3) Å, H(1)‚‚‚O(2a) 2.56(3) Å, N(1)‚‚‚O(2a) 3.237(3) Å and N(1)-H(1)‚‚‚O(2a) 133(2)° (where O(3a) and O(2a) are related by symmetry operations x - 1, y, z, and 2 - x, 1 - y, 1 - z, respectively). (19) Vittal, J. J.; Yang, X. Cryst. Growth Des. 2002, 2, 259-262. (20) Steed, J. W. CrystEngComm 2003, 5, 169-179.
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