Structural Interconversion Controlled by Hydrogen-Bond Interactions: A Mononuclear Copper Triamine Complex and a Polynuclear Copper Triamine Sheet Way-Zen Lee,*,† Ya-Lin Kang,† Tzu-Li Wang,† Chan-Cheng Su,*,† and Ting-Shen Kuo‡
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 8 2614–2616
Department of Chemistry, National Taiwan Normal UniVersity, Taipei 11650, Taiwan, and Instrumentation Center, Department of Chemistry, National Taiwan Normal UniVersity, Taipei 11650, Taiwan ReceiVed March 20, 2008; ReVised Manuscript ReceiVed June 4, 2008
ABSTRACT: Because of the steric hindrance caused by the large bite angles of the employed dipropylenetriamine (dpt) ligand to the copper center, a five-coordinated copper triamine complex, [Cu(η3-dpt)(η2-dpt)](ClO4)2 (1), was prepared and structurally characterized. When water was added to a methanol solution of 1, the discrete mononuclear copper complex 1 was converted to a two-dimensional zigzag layer, and this conversion behavior was reversible as water was removed. Synthesis of coordination polymers has been a subject of great interest for decades due to their unique properties and fascinating structures.1 Recent developments include one-dimensional (1D) polymeric chains possessing conductivity by a small amount of dopant2 or chains with exclusively a right-handed helical structure,3 two-dimensional (2D) layers containing mixed-valence metal ions with ferroelectric properties,4 and three-dimensional (3D) networks having tunable magnetic properties.5 Many coordination polymers have been prepared by one-pot self-assembling synthesis, while there are some examples of multistep syntheses.6 For instance, 5-(4pyridyl)-4,6-dipyrrinate (4-pyrdpm) was employed to coordinate to a metal ion, such as Co(III), to produce a mononuclear [Co(4pyrdpm)3]; the subsequent addition of AgOTf to a benzene solution of the cobalt complex formed a heterometallic Co/Ag metal-organic framework (MOF).6a However, only a few examples have been reported in the literature in which a coordination polymer is converted from its discrete metallic monomer, and can be converted back to the monomer. Such behaviors can be controlled by solvent, pH value, or counterion.7–9 Recently, we have found that a copper dipropylenetriamine (dpt) complex, prepared by N. F. Curtis in 1968 without an X-ray structure,10 will convert to a 2D copper coordination polymer induced by the hydrogen-bond interaction between a water molecule and the dpt lignad. It is noteworthy that the interconversion between the mononuclear copper complex and the polynuclear copper sheet is reversible upon the addition and removal of water. Reaction of Cu(ClO4)2 · 6H2O with 2 equiv of dpt in acetonitrile or methanol produced a copper triamine complex, [Cu(η3-dpt)(η2dpt)](ClO4)2 (1). Recrystallization by the slow diffusion of diethyl ether into an acetonitrile solution of complex 1 afforded blue needlelike crystals. X-ray diffraction analysis of the blue crystal reveals that complex 1 possesses a five-coordinated ligand environment comprised of two dpt ligands asymmetrically coordinated to the copper center of complex 1.11 Interestingly, as seen in Figure 1, one dpt coordinates to the copper ion as a tridentate ligand, and the other dpt chelates to the copper center through an end amine (N4) and the central secondary amine (N5) tethering an end amine (N6) group out of the coordination sphere of the copper center. A νNH absorption of the uncoordinated amine at 3372 cm-1 was observed in the infrared spectrum of 1 agreed with the X-ray structure of 1. In addition, the uncoordinated amine (N6) has * Correspondence author. Address: 88 Sec. 4 Ting-Chow Road, Taipei 11650, Taiwan. Phone: 886-2-29318166. Fax: 886-2-29324249. E-mail:
[email protected]. † Department of Chemistry, National Taiwan Normal University ‡ Instrumentation Center, Department of Chemistry, National Taiwan Normal University
Figure 1. ORTEP drawing of 1 at the 50% probability level. Hydrogen atoms and perchlorate anions are omitted for clarity.
Figure 2. 2D presentation of the polynuclear 2 (hydrogen bonds caused from water molecules and dpt ligands cross-link the zigzag chains of polynuclear copper bis-triamine). Hydrogen atoms and perchlorate anions were omitted for clarity.
hydrogen bonds with an end amine (N1) of the tridentate dpt and the central secondary amine (N5) of the chelate dpt. Unlike the six-coordinated octahedral copper diethylenetriamine species,12 complex 1 possesses a distorted trigonal bipyramidal structure with a τ value of 0.68.13 The average Cu-N bond length for the bidentate dpt is slightly longer than that for the tridentate dpt by about 0.03 Å.14 Meanwhile, the bite angles in 1, where dpt bonds to Cu(II) forming six-member rings, are much larger than that of the sixcoordinated [Cu(dien)2]X2 (X ) NO3-, Cl-)15 causing complex 1 to adopt a distorted trigonal bipyramidal structure. It is noteworthy that the reaction of 2 equiv of dpt with Ni(II) ion afforded a six coordinated [Ni(dpt)2]2+ species.16 The six coordination of [Ni(dpt)2]2+ can be rationalized by the larger radius of a Ni(II) ion compared to that of a Cu(II) ion; that is, the Ni(II) ion has enough surface for the coordination of both dpt ligands.
10.1021/cg8002977 CCC: $40.75 2008 American Chemical Society Published on Web 07/01/2008
Communications
Crystal Growth & Design, Vol. 8, No. 8, 2008 2615
Figure 3. Ball-stick presentation of the zigzag chain of polynuclear 2, and ORTEP drawing surrounding a copper ion (50% probability level). Figure 5. Powder X-ray diffraction (PXRD) patterns of (a) polynuclear 2 (b) the obtained blue solid by removing water from polynuclear 2 (c) mononuclear 1 (radiation, λ ) 1.5418 Å).
Scheme 1
Figure 4. UV-vis spectra of (a) complex 1 in acetonitrile (black solid line) and the solid-state (red solid line), and polynuclear 2 in acetonitrile/ water mixed solvent (CH3CN:H2O ) 50:6, black dotted line) and the solid-state (red dotted line); (b) complex 1 in acetonitrile (black solid line) and polynuclear 2 (black dotted line) in acetonitrile/water mixed solvent (CH3CN: H2O ) 50:6, volume ratio). Gray lines are spectra of an acetonitrile solution of complex 1 with a gradual addition of water (CH3CN:H2O ) 50:1, 50:2, 50:3, 50:4, 50:5); (c) polynuclear 2 in acetonitrile/water mixed solvent (CH3CN:H2O ) 50:6, 50:4, 50:3, 50: 2; from bottom to top).
Addition of water in the methanol solution of 1 for recrystallization formed purple-blue crystals in a yield of 86.8%. X-ray diffraction analysis of the purple-blue crystal exhibited a 2D copper
coordination polymer, {[Cu(η3-dpt)(µ-η1,η1-dpt · H2O)](ClO4)2}n (2, Figure 2),17 which has been prepared and formulated as [Cu(dpt)2](ClO4)2 · H2O by Curtis.10 Unlike complex 1, the geometric structure for each copper center of polynuclear 2, as seen in Figure 3, is distorted square pyramidal with a τ value of 0.40.18,19 One dpt coordinates on the equatorial plane of the copper ion, and the chelating dpt in 1 becomes a linker, bridging adjacent [Cu(η3dpt)]2+ moieties to form zigzag chains (Figure 3); therefore, no νNH at 3372 cm-1 was observed in the infrared spectrum of 2. In addition, a water molecule is hydrogen-bonded to the central amine of the bridging dpt and the end amine of the tridentate dpt to form a 2D copper triamine sheet as displayed in Figure 2. A sharp absorption band exhibited at 3598 cm-1 in the infrared spectrum of 2 was assigned to be νOH of the hydrogen-bonded H2O. Hydrogen-bonding interactions between the water molecules and the dpt linkers is conceivably the key for the conversion of mononuclear 1 to polynuclear 2. When complex 1 was dissolved in dry methanol for recrystallization Via the slow diffusion of diethyl ether into the methanol solution of 1, blue crystals of mononuclear 1 were obtained, and no polynuclear 2 was found. This result suggests that water is necessary for the recrystallization of 2, although methanol molecules could also form hydrogen bonds with the dpt linkers. Three broad absorption bands at 625, 732, and 886 nm were observed in the solution and solid-state UV-vis spectra of complex 1, whereas the 2D zigzag sheet of 2 processed a broad absorption band at 610 nm in both solution and the solid-state spectra (Figure 4a). As water was gradually added to the acetonitrile solution of 1, the intensity of the absorption band of 2 increased, and that of complex 1 decreased (Figure 4b). An isosbestic point at 602 nm was found in the UV-vis spectra, indicating that mononuclear 1 was converting to the 2D zigzag sheet of 2 as the water containing ratio of the solution was increased. Interestingly, polynuclear 2 can
2616 Crystal Growth & Design, Vol. 8, No. 8, 2008
Communications eters, and hydrogen coordinates and isotropic displacement parameters, and X-ray crystallographic files for complexes 1 and 2 (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.
References
Figure 6. X-band EPR spectra of (a) mononuclear 1 (b) polynuclear 2 in frozen DMF at 77 K.
be converted back to mononuclear 1 by reducing the water containing ratio of the solution as seen in Figure 4c, or by removing water and solvent under a vacuum to form a blue solid which had the same infrared spectrum as complex 1. In addition, the powder X-ray diffraction (PXRD) of the obtained blue solid exhibited a pattern similar to that of complex 1 (Figure 5b,c), and was different from that of 2 (Figure 5a). According to UV-vis and PXRD data, mononuclear 1 is reversibly interconverted to 2D polynuclear 2 by adding or removing the water content of the complexes as depicted in Scheme 1. Since the geometries of the copper center in complexes 1 and 2 are different, the EPR spectra of 1 and 2 taken in frozen DMF at 77 K (Figure 6) displayed slightly different axial signals (g|| ) 2.244, A|| ) 176 G, g⊥ ) 2.035 for 1; g|| ) 2.243, A|| ) 174 G, g⊥ ) 2.039 for 2). In conclusion, we have successfully demonstrated the interconversion between a mononuclear copper triamine complex and a polynuclear copper triamine sheet. Interestingly, this interconversion was controlled by the hydrogen-bond interactions of water and the triamine ligands. Further studies of the properties of polynuclear 2 and syntheses of more complicated derivatives are currently underway.
Acknowledgment. The authors gratefully acknowledge the financial support from the National Science Council in Taiwan (NSC 93-2113-M-003-007 to W.-Z.L.) and National Taiwan Normal University (93091019). Mr. Wei-Min Ching is acknowledged for his kind help in taking EPR spectra. Our gratitude also goes to the Academic Paper Editing Clinic, NTNU. Supporting Information Available: Tables of crystal data, atomic coordinates, bond lengths and angles, anisotropic displacement param-
(1) (a) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001, 101, 1629–1658. (b) Oh, M.; Mirkin, C. A. Nature 2005, 438, 651–654. (2) Zhang, C.; Staunton, E.; Andreev, Y. G.; Bruce, P. G. J. Am. Chem. Soc. 2005, 127, 18305–18308. (3) Seitz, M.; Kaiser, A.; Stempfhuber, S.; Zabel, M.; Reiser, O. J. Am. Chem. Soc. 2004, 126, 11426–11427. (4) Okubo, T.; Kawajiri, R.; Mitani, T.; Shimoda, T. J. Am. Chem. Soc. 2005, 127, 17589–17599. (5) Wang, X.-Y.; Wang, L.; Wang, Z.-M.; Gao, S. J. Am. Chem. Soc. 2006, 128, 674–675. (6) (a) Halper, S. R.; Cohen, S. M. Inorg. Chem. 2005, 44, 486–488. (b) Noro, S.; Kitagawa, S; Yamashita, M.; Wada, T. Chem. Commun. 2002, 22, 2–223. (c) Lu, Y.-L.; Wu, J.-Y.; Chan, M.-C.; Huang, S.M.; Lin, C.-S.; Chiu, T.-W.; Liu, Y.-H.; Wen, Y.-S.; Ueng, C.-H.; Chin, T.-M.; Hung, C.-H.; Lu, K.-L. Inorg. Chem. 2006, 45, 2430– 2437. (d) Chen, W.; Liu, F.; Xu, D.; Matsumoto, K.; Kishi, S.; Kato, M. Inorg. Chem. 2006, 45, 5552–5560. (e) Youm, K.-T.; Huh, S.; Park, Y. J.; Park, S.; Choi, M.-G.; Jun, M.-J. Chem. Commun. 2004, 2384–2385. (7) Kawata, S.; Breeze, S. R.; Wang, S.; Greedan, J. E.; Raju, N. P. Chem. Commun. 1997, 717. (8) Liu, H.-J.; Hung, Y.-H.; Chou, C.-C.; Su, C.-C. Chem. Commun. 2007, 495–497. (9) Saha, S.; Koner, S.; Tuchagues, J.-P.; Boudalis, A. K.; Okamoto, K.I.; Banerjee, S.; Mal, D. Inorg. Chem. 2005, 44, 6379–6385. (10) Curtis, N. F.; Hay, R. W.; Curtis, Y. M. J. Chem. Soc., Sec. A 1968, 182. (11) The crystal yield of complex 1 is 91.2%. Anal. Calcd for C12H34Cl2CuN6O8: C, 27.46; H, 6.53; N, 16.01 Found: C, 27.38; H, 6.27; N, 16.26. IR (Nujol): 3372 m, 3334 m, 3274 m, 3244 m (νNH); 1087 s, 624 m (νClO-). (12) (a) Stephens, F. S. J. Chem. Soc., Sec. A 1969, 883–890. (b) Stephens, F. S. J. Chem. Soc., Sec. A 1969, 2233–2240. (13) Selected bond angles (°) of 1: N1-Cu1-N2 ) 89.31, N1-Cu1-N3 ) 134.13, N1-Cu1-N4 ) 117.36, N1-Cu1-N5 ) 87.78, N2-Cu1-N3 ) 88.03, N2-Cu1-N4 ) 96.37, N2-Cu1-N5 ) 174.99, N3-Cu1-N4 ) 108.45, N3-Cu1-N5 ) 91.06, N4-Cu1-N5 ) 88.60. (14) Selected bond lengths (Å) of 1: Cu1-N1 ) 2.075, Cu1-N2 ) 2.054, Cu1-N3 ) 2.104, Cu1-N4 ) 2.146, Cu1-N5 ) 2.073. (15) Bite angles (°) in 1: N1-Cu1-N2 ) 89.31, N2-Cu1-N3 ) 88.03, N4Cu1-N5 ) 88.60. Bite angles (°) in [Cu(dien)2]X2: N1-Cu1-N2 ) 78.8, N2-Cu1-N3 ) 82.0, N4-Cu1-N5 ) 81.9, N5-Cu1-N6 ) 81.8 (X ) NO3-); N1-Cu1-N2 ) 79.9, N2-Cu1-N3 ) 78.0, N4-Cu1-N5 ) 82.6, N5-Cu1-N6 ) 81.7 (X ) Cl-). (16) Biagini, S.; Cannas, M J. Chem. Soc., Sec. A, 1970, 239, 8–2408. (17) Anal. Calcd for C12H36Cl2CuN6O9: C, 26.55; H, 6.68; N, 15.48 Found: C, 26.62; H, 6.30; N, 15.45. IR (Nujol): 3598 m (νOH); 3320 m, 3271 m (νNH); 1091 s, 624 m (νClO4-). (18) Selected bond angles (°) of 2: N1-Cu1-N2 ) 89.79, N1-Cu1-N3 ) 146.90, N1-Cu1-N4 ) 87.20, N1-Cu1-N6 ) 104.82, N2-Cu1-N3 ) 90.32, N2-Cu1-N4 ) 171.09, N2-Cu1-N6 ) 95.70, N3-Cu1-N4 ) 87.65, N3-Cu1-N6 ) 108.11, N4-Cu1-N6 ) 93.18. (19) Selected bond lengths (Å) of 2: Cu1-N1 ) 2.035, Cu1-N2 ) 2.060, Cu1-N3 ) 2.054, Cu1-N4 ) 2.068, Cu1-N6 ) 2.198.
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