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Synthesis and characterization of macrocyclic nickel(II) complexes with α-methylbenzyl groups as chiral pendants
Inorganic Chemistry Communications 11 (2008) 745–748
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Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis and characterization of macrocyclic nickel(II) complexes with a-methylbenzyl groups as chiral pendants Jeong Hyeong Han a, Min Ju Cha a, Bong Gon Kim b, Seog K. Kim c, Kil Sik Min a,* a
Department of Chemistry Education, Kyungpook National University, Daegu 702-701, Republic of Korea Department of Chemistry Education and Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, Republic of Korea c Department of Chemistry, Yeungnam University, Kyongsan 712-749, Republic of Korea b
a r t i c l e
i n f o
Article history: Received 31 January 2008 Accepted 21 March 2008 Available online 29 March 2008 Keywords: Chirality Circular dichroism Nickel(II) complex Macrocyclic ligand Crystal structure
a b s t r a c t Novel nickel(II) hexaaza macrocyclic complexes, [Ni(LR,R)](ClO4)2 (1) and [Ni(LS,S)](ClO4)2 (2), containing chiral pendant groups have been synthesized by an efficient one-pot template condensation and characterized (LR,R/S,S = 1,8-di((R/S)-a-methylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane). The crystal structures of 1 and 2 were determined by single-crystal X-ray analysis. Each complex has a square-planar coordination environment for the nickel(II) ion, and is either an R or an S enantiomorph depending on the pendant groups. The circular dichroism spectrum of 1 showed a negative, positive and negative peak at 345, 440, and 492 nm, respectively, and that of 2 exhibited an enantiomeric pattern. Ó 2008 Elsevier B.V. All rights reserved.
Chiral compounds have attracted much attention in chemistry, material science and the chemical industry because of their potential and/or practical applications for molecular recognition, catalysis, magnetic materials and separation [1]. Recently transition metal complexes with chiral ligands have been studied in asymmetric catalysis and self-assembly for luminescent materials [2]. Furthermore, macrocyclic metal complexes with various pendant groups have been extensively prepared and investigated in coordination chemistry [3], but those with chiral ligands have received only limited study [4]. To date, many nickel(II) macrocyclic complexes have been exploited in self-assembly for the construction of coordination polymers showing interesting properties as gas sorption and magnetic ordering [5]. However, macrocyclic nickel(II) complexes bearing chiral pendant arms have not been reported, even though such complexes can be good candidates as chiral building blocks. Due to this lack of research we sought chiral nickel(II) macrocyclic complexes. Thus, to prepare chiral macrocyclic nickel(II) complexes as building blocks for chiral open frameworks, (R)(+)-a-methylbenzylamine and (S)-( )-a-methylbenzylamine were utilized as pendant groups in the template synthesis. Herein, we report the synthesis and crystal structure of novel chiral nickel(II) macrocyclic complexes, [Ni(LR,R)](ClO4)2 (1) and [Ni(LS,S)](ClO4)2 (2), as well as their circular dichroism spectra (LR,R = 1,8-di((R)-amethylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane and LS,S = 1, 8-di((S)-a-methylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane) * Corresponding author. Tel.: +82 53 9505906; fax: +82 53 9505899. E-mail address: [email protected] (K.S. Min). 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.03.027
(Chart 1). In addition, noncovalent interactions such as hydrogen bonding and p–p interactions are displayed to induce intra-/intermolecular interactions in 1 and 2, which lead to supramolecular compounds. Compounds 1 and 2 were synthesized in methanol by the onepot template condensation reaction of ethylenediamine, formaldehyde, and (R)-(+)-a-methylbenzylamine/(S)-( )-a-methylbenzylamine in the presence of nickel(II) ion, respectively [6]. The complexes were isolated from the reaction mixture by adding the acid HClO4. Both compounds are soluble in DMF, Me2SO, and MeCN, but insoluble in H2O. The complexes were clearly characterized by elemental analysis, infrared, UV/vis, and X-ray diffraction. The infrared spectrum of 1 (KBr pellet) shows mNH of the secondary amines at 3200 cm 1 and mClO of the perchlorate anions at 1085 and 624 cm 1. Similarly, the infrared spectrum of 2 (KBr pellet) shows mNH of the secondary amines at 3200 cm 1 and mClO of the perchlorate anions at 1090 and 623 cm 1. In the complexes, the bands at 3062 and 2972 cm 1 for 1 and 3063 and 2971 cm 1 for 2 are consistent with the C–H stretching frequencies of the macrocyclic ligand with chiral pendants. UV/vis spectra indicate that d–d transitions of 1 and 2 occur at 452 nm, respectively. Yellow plate-shaped crystals of 1 and 2 suitable for X-ray diffraction were obtained by solvent diffusion of diethyl ether into MeCN solutions of 1 and 2, respectively. Both complexes crystallize in the orthorhombic P212121 space group, and the atom labeling ORTEP drawings of 1 and 2 are shown in Fig. 1 [7]. The core structure of 1 is composed of one [Ni(LR,R)]2+ cation and two perchlorate anions. The nickel(II) ion displays a square-planar
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J.H. Han et al. / Inorganic Chemistry Communications 11 (2008) 745–748
H N
CH3 *
H
N
H N
II
*
N
Ni N H
N H
N4 O6 = 3.007(4) Å, \N4–H4–O6 = 152°; N5 O1 = 3.131(4) Å, \N5–H5–O1 = 156°. Additionally there exist the inter-molecularly herringbone p–p interactions between the pendant benzene rings, which gives rise to a one-dimensional chain. The distance between the centroids is 4.570(5) Å, and the dihedral angle between the pendant benzene groups is 42.38(13)° [10]. As expected, the overall structure of 2 is essentially same as that of 1 except for the chirality of the pendant arms [11]. Thus, complex 2 is shown to be the enantiomer of 1 as depicted in Fig. 1b. Fig. 2 shows the packing diagrams of both complexes 1 and 2, viewed along the a axis. The circular dichroism (CD) spectra measured in MeCN solutions further confirm the enantiomeric nature of the optically active complexes 1 and 2 as shown in Fig. 3. Complex 1 (R isomer) shows a negative Cotton effect around 345 and 492 nm and a positive signal centered around 440 nm. In complex 1, the shoulder absorption band with a maximum at 330 nm is assigned to the metal-to-ligand charge transfer (MLCT) of NiII to LR,R transition. The CD spectrum of 1 shows a negative Cotton effect (CE) in the MLCT region. In the absorption band at 452 nm, which assigned to NiII d–d transition, the CD spectrum displays a strong bisignate CD pattern (+ and ) in the region of the NiII d–d transition in which the pattern can be attributed to the regional rule correlating the optical activity of the d–d transitions with substituent positions [12]. Contrary to 1, complex 2 (S isomer) exhibits Cotton effects of the opposite sign at the same wavelengths. The weak negative/positive CD spectra in the d–d transition region are observed, indicating that the optical activities are resulted from the vicinal effects of the asymmetric carbons of (R)-(+)-amethylbenzylamine and (S)-( )-a-methylbenzylamine in pendant groups, respectively. In conclusion, new hexaaza macrocyclic nickel(II) complexes bearing chiral pendant groups have been synthesized by an efficient one-pot template condensation and characterized. Each
CH3
H (ClO4)2
[NiII(LR,R)](ClO4)2 (1) II S,S [Ni (L )](ClO4)2 (2) * = (R,R) and (S,S) Chart 1. Chemical structure of 1 and 2.
coordination geometry by binding the four secondary nitrogen atoms of macrocyclic ligand with the average Ni–N bond distance of 1.929(2) Å. The pendant methylbenzyl groups of the macrocycle are not involved in either intra- or inter-molecular coordination of nickel(II) ion. The complex do not have an inversion center at the nickel atom, due to the chiral pendants of the macrocyclic ligand. The azamacrocyclic ligand adopts thermodynamically the most stable R,R,S,S configuration [8] and thus the chiral pendants are situated above and below the square-coordination plane. The sixmembered chelate rings adopt a chair conformation and the fivemembered chelate rings assume a gauche conformation. The average C–N bond distance and the C–N–C angles relating the tertiary nitrogen atoms N3 and N6 are 1.460(2) Å and 108.7(3)–117.4(3)°, respectively, which is indicative of significant contribution of sp2 hybridization for the nitrogen atoms. In complex 1, the secondary amines of the macrocycle form N–H O hydrogen bonds with the oxygen atoms of perchlorate anions:[9] N1 O2 = 2.982(5) Å, \N1–H1–O2 = 152°; N2 O5 = 3.172(5) Å, \N2–H2–O5 = 158°;
C2
a C1
C16 C15
C3 N2
N1
C10 C12
N3
Ni1
C14
C13
C21
C19 C22
C18 N6 C8
C9
N4
N5 C7
b
C20 C4
C11
C5
C24
C17
C23
C6
C9 C21 C3
N1 C16
C20
C10 C11
N6
N2
Ni1
C23 C4
C8 C15
C14
C12
C22
C2
C1
C19 N3
N5
C18
C24
N4
C7 C13 C6
C5 C17
Fig. 1. ORTEP (40% probable thermal ellipsoid) views of the dications [Ni(LR,R)]2+ (a) and [Ni(LS,S)]2+ (b) in crystals of 1 and 2, respectively. Hydrogen atoms and perchlorate anions are omitted for clarity. Relevant distances (Å) and angles (°): For 1, Ni1–N1 1.925(3), Ni1–N2 1.931(3), Ni1–N4 1.929(3), Ni1–N5 1.929(3), N3–C4 1.444(5), N3–C5 1.444(5), N3–C18 1.472(5), N6–C1 1.453(5), N6–C8 1.457(5), N6–C10 1.491(5), C9–C10 1.513(5), C17–C18 1.535(5), N1–Ni1–N2 87.28(13), N1–Ni1–N4 179.24(13), N1–Ni1– N5 91.78(13), N2–Ni1-N4 93.46(13), N2–Ni1–N5 178.75(14), N4–Ni1–N5 87.49(13). For 2, Ni1–N1 1.923(4), Ni1–N2 1.931(4), Ni1–N4 1.925(4), Ni1–N5 1.927(3), N3–C4 1.439(6), N3–C5 1.438(6), N3–C18 1.474(6), N6–C1 1.446(6), N6–C8 1.445(6), N6–C10 1.495(6), C9–C10 1.508(7), C17–C18 1.552(7), N1–Ni1–N2 87.28(16), N1–Ni1–N4 178.88(17), N1–Ni1–N5 91.75(16), N2–Ni1–N4 93.60(16), N2–Ni1–N5 178.97(17), N4–Ni1–N5 87.37(16).
J.H. Han et al. / Inorganic Chemistry Communications 11 (2008) 745–748
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Fig. 2. The packing diagrams of 1 (a) and 2 (b), viewed along the a axis.
complex has a square-planar environment around the nickel(II) ion and the intramolecular N–H O hydrogen bonds as well as the herringbone p–p stacking interactions. The observation of the Cotton effect and the X-ray crystal structure clearly provided evidence for the chirality of 1 and 2. Further studies on the self-assembly of the complexes and organic building blocks for the construction of chiral open frameworks and chiral separation are ongoing.
10
2
CD / mdeg
5
0
Acknowledgement This research was supported by Kyungpook National University Research Fund, 2007.
-5
Appendix A. Supplementary data
1 -10 350
400
450
500
550
Wavelength / nm Fig. 3. CD spectra of 1 (solid line) and 2 (dotted line).
600
CCDC-658376 (for 1) and CCDC-658377 (for 2) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2008.03.027.
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J.H. Han et al. / Inorganic Chemistry Communications 11 (2008) 745–748
References [1] (a) J.-M. Lehn, Supramolecular chemistry, Concepts and Perspectives, VCH, Weinheim, 1995; (b) G. Chelucci, R.P. Thummel, Chem. Rev. 102 (2002) 3129; (c) E.-Q. Gao, Y.-F. Yue, S.-Q. Bai, Z. He, C.-H. Yan, J. Am. Chem. Soc. 126 (2004) 1419; (d) J.S. Seo, D. Whang, H. Lee, S. Jun, J. Ok, Y. Jin, K. Kim, Nature 404 (2000) 982; (e) I. Katsuki, N. Matsumoto, M. Kojima, Inorg. Chem. 39 (2000) 3350; ¯ kawa, Angew. Chem. Int. Ed. 42 (2003) (f) K. Inoue, K. Kikuchi, M. Ohba, H. O 4810; (g) Z.-G. Gu, Y. Song, J.-L. Zuo, X.-Z. You, Inorg. Chem. 46 (2007) 9522; (h) Y. Numata, K. Inoue, N. Baranov, M. Kurmoo, K. Kikuchi, J. Am. Chem. Soc. 129 (2007) 9902. [2] (a) R.G. Konsler, J. Karl, E.N. Jacobsen, J. Am. Chem. Soc. 120 (1998) 10780; (b) J.P. Leonard, P. Jensen, T. McCabe, J.E. O’Brien, R.D. Peacock, P.E. Kruger, T. Gunnlaugsson, J. Am. Chem. Soc. 129 (2007) 10986. [3] (a) K.S. Min, M.P. Suh, Chem. Eur. J. 7 (2001) 303; (b) K.S. Min, M.P. Suh, Eur. J. Inorg. Chem. (2001) 449; (c) T.-B. Lu, H. Xiang, R.L. Luck, Z.-W. Mao, X.-M. Chen, L.-N. Ji, Inorg. Chim. Acta 355 (2003) 229. [4] (a) G. Du, A. Ellern, L.K. Woo, Inorg. Chem. 42 (2003) 873; (b) J. Gao, J.H. Reibenspies, R.A. Zingaro, F.R. Woolley, A.E. Martell, A. Clearfield, Inorg. Chem. 44 (2005) 232. [5] (a) E.Y. Lee, M.P. Suh, Angew. Chem. Int. Ed. 43 (2004) 2798; (b) B. Nowicka, M. Rams, K. Stadnicka, B. Sieklucka, Inorg. Chem. 46 (2007) 8123. [6] Compound 1: Ethylenediamine (3.4 mL, 0.05 mol), paraformaldehyde (3.0 g, 0.10 mol), and (R)-(+)-a-methylbenzylamine (6.12 g, 0.05 mol) were slowly added to a stirred solution of NiCl26 H2O (5.95 g, 0.025 mol) in MeOH (40 mL). The mixture was heated to reflux for 1 day. The solution was filtered while hot and the filtrate was concentrated to about 1/4 of the original volume. HClO4 (60%, 10 mL) was added to the yellow–brown solution. Bright yellow precipitate was formed, which was filtered off, washed with H2O, MeOH, and ether, and dried in air. Yield: ca. 30%. C24H38Cl2N6NiO8 (668.21): calcd. C 43.14, H 5.73, N 12.58; found C 43.20, H 5.74, N 13.01. IR (KBr pellet): mNH 3200, mCH 3062, 2972, mClO 1085, 624 cm 1. UV/vis (MeCN): kmax, nm (e, M 1 cm 1) = 330(35, sh), 452(50). Compound 2 was prepared as yellow solid in a manner similar to the synthesis of 1 except that (S)-( )-amethylbenzylamine (6.12 g, 0.05 mol) instead of (R)-(+)-amethylbenzylamine. Yield: ca. 30%. C24H38Cl2N6NiO8 (668.21): calcd. C 43.14, H 5.73, N 12.58; found C 42.81, H 5.72, N 13.04. IR (KBr pellet): mNH 3200, mCH 3063, 2971, mClO 1090 (s), 623 cm 1. UV/vis (MeCN): kmax, nm (e, M 1 cm 1) = 330(28, sh), 452(49). Safety note: Although we have experienced no
[7]
[8] [9] [10]
[11]
[12]
problem with the compounds reported in this work, perchlorate salts of metal complexes with organic ligands are often explosive and should be handled with great caution. X-ray data for 1 and 2 were collected at 173(2) K on a Bruker P4 diffractometer equipped with the SMART CCD system and using Mo Ka radiation (k = 0.71073 Å, graphite monochromator). The raw data were processed to give structure factors using the SAINT program and corrected for Lorentz and polarization effects. No absorption corrections were made. The crystal structures were solved by direct methods, and refined by full-matrix leastsquares refinement using the SHELXL97 computer program. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were positioned geometrically and refined using a riding model. Crystallographic data for C24H38Cl2N6NiO8 (1):M = 668.21 g/mol, yellow block, 0.10 0.10 0.40 mm, T = 173(2) K, orthorhombic, space group P212121 (No. 19), a = 8.2605(5) Å, b = 16.2712(10) Å, c = 21.8854(14) Å, a = b = c = 90°, V = 2941.6(3) Å3, Z = 4, Dc = 1.509 g/cm3, l = 0.898 mm 1, F(000) = 1400, GOF = 0.961. Flack parameter v = 0.007(18). Of the 18872 reflections, 6847 were unique (Rint = 0.0918), 4498 observed [I > 2r(I)], which refined to R1 = 0.0463, wR2 = 0.0918, and for all data R1 = 0.0971, wR2 = 0.1088. For C24H38Cl2N6NiO8 (2):M = 668.21 g/mol, yellow plate, 0.10 0.20 0.60 mm, T = 173(2) K, orthorhombic, space group P212121 (No. 19), a = 8.2607(3) Å, b = 16.2591(6) Å, c = 21.8651(9) Å, a = b = c = 90°, V = 2941.6(3) Å3, Z = 4, Dc = 1.511 g/cm3, l = 0.899 mm 1, F(000) = 1400, GOF = 1.230. Flack parameter v = 0.05(2). Of the 18528 reflections, 6842 were unique (Rint = 0.0486), 6134 observed[I > 2r(I)], which refined to R1 = 0.0689, wR2 = 0.1275, and for all data R1 = 0.0789, wR2 = 0.1310. R.D. Hancock, Acc. Chem. Res. 23 (1990) 253. G.R. Desiraju, Acc. Chem. Res. 29 (1996) 441. (a) G.R. Desiraju, Crystal Engineering: The Design of Organic Solids, Elsevier, New York, 1989 (Chapter 4); (b) A.S. Shetty, J. Zhang, J.S. Moore, J. Am. Chem. Soc. 118 (1996) 1019. For 2, av. Ni–N bond distance is 1.927(2) Å, and the C–N bond distance and the C–N–C angle involving the N3 and N6 are average 1.456(2) Å and 108.4(4)– 117.7(4)°, respectively. The NH groups of the macrocycle are involved in the hydrogen bonding interaction with oxygen atoms of perchlorate anions: N1 O2 = 3.130(6) Å, \N1–H1–O2 = 157°; N2 O7 = 3.012(6) Å, \N2–H2– O7 = 152°; N4 O8 = 3.178(6) Å, \N4–H4–O8 = 158°; N5 O3 = 2.970(6) Å, \N5–H5–O3 = 151°. Between the pendant benzene groups, the intercentroid distance is 4.575(6) Å, and the dihedral angle is 42.59(17)°. ¯ kawa, N. Matsumoto, S. Kida, Inorg. Chim. Acta 162 (a) H. Sakiyama, H. O (1989) 65; (b) S. Arakawa, T. Nozawa, M. Hatano, Bull. Chem. Soc. Jpn. 47 (1974) 2643; (c) M. Suzuki, Y. Nishida, Inorg. Chem. Acta 25 (1977) 185; (d) Y. Nishida, S. Kida, Bull. Chem. Soc. Jpn. 43 (1970) 3814.
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Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Synthesis and characterization of macrocyclic nickel(II) complexes with a-methylbenzyl groups as chiral pendants Jeong Hyeong Han a, Min Ju Cha a, Bong Gon Kim b, Seog K. Kim c, Kil Sik Min a,* a
Department of Chemistry Education, Kyungpook National University, Daegu 702-701, Republic of Korea Department of Chemistry Education and Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, Republic of Korea c Department of Chemistry, Yeungnam University, Kyongsan 712-749, Republic of Korea b
a r t i c l e
i n f o
Article history: Received 31 January 2008 Accepted 21 March 2008 Available online 29 March 2008 Keywords: Chirality Circular dichroism Nickel(II) complex Macrocyclic ligand Crystal structure
a b s t r a c t Novel nickel(II) hexaaza macrocyclic complexes, [Ni(LR,R)](ClO4)2 (1) and [Ni(LS,S)](ClO4)2 (2), containing chiral pendant groups have been synthesized by an efficient one-pot template condensation and characterized (LR,R/S,S = 1,8-di((R/S)-a-methylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane). The crystal structures of 1 and 2 were determined by single-crystal X-ray analysis. Each complex has a square-planar coordination environment for the nickel(II) ion, and is either an R or an S enantiomorph depending on the pendant groups. The circular dichroism spectrum of 1 showed a negative, positive and negative peak at 345, 440, and 492 nm, respectively, and that of 2 exhibited an enantiomeric pattern. Ó 2008 Elsevier B.V. All rights reserved.
Chiral compounds have attracted much attention in chemistry, material science and the chemical industry because of their potential and/or practical applications for molecular recognition, catalysis, magnetic materials and separation [1]. Recently transition metal complexes with chiral ligands have been studied in asymmetric catalysis and self-assembly for luminescent materials [2]. Furthermore, macrocyclic metal complexes with various pendant groups have been extensively prepared and investigated in coordination chemistry [3], but those with chiral ligands have received only limited study [4]. To date, many nickel(II) macrocyclic complexes have been exploited in self-assembly for the construction of coordination polymers showing interesting properties as gas sorption and magnetic ordering [5]. However, macrocyclic nickel(II) complexes bearing chiral pendant arms have not been reported, even though such complexes can be good candidates as chiral building blocks. Due to this lack of research we sought chiral nickel(II) macrocyclic complexes. Thus, to prepare chiral macrocyclic nickel(II) complexes as building blocks for chiral open frameworks, (R)(+)-a-methylbenzylamine and (S)-( )-a-methylbenzylamine were utilized as pendant groups in the template synthesis. Herein, we report the synthesis and crystal structure of novel chiral nickel(II) macrocyclic complexes, [Ni(LR,R)](ClO4)2 (1) and [Ni(LS,S)](ClO4)2 (2), as well as their circular dichroism spectra (LR,R = 1,8-di((R)-amethylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane and LS,S = 1, 8-di((S)-a-methylbenzyl)-1,3,6,8,10,13-hexaazacyclotetradecane) * Corresponding author. Tel.: +82 53 9505906; fax: +82 53 9505899. E-mail address: [email protected] (K.S. Min). 1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2008.03.027
(Chart 1). In addition, noncovalent interactions such as hydrogen bonding and p–p interactions are displayed to induce intra-/intermolecular interactions in 1 and 2, which lead to supramolecular compounds. Compounds 1 and 2 were synthesized in methanol by the onepot template condensation reaction of ethylenediamine, formaldehyde, and (R)-(+)-a-methylbenzylamine/(S)-( )-a-methylbenzylamine in the presence of nickel(II) ion, respectively [6]. The complexes were isolated from the reaction mixture by adding the acid HClO4. Both compounds are soluble in DMF, Me2SO, and MeCN, but insoluble in H2O. The complexes were clearly characterized by elemental analysis, infrared, UV/vis, and X-ray diffraction. The infrared spectrum of 1 (KBr pellet) shows mNH of the secondary amines at 3200 cm 1 and mClO of the perchlorate anions at 1085 and 624 cm 1. Similarly, the infrared spectrum of 2 (KBr pellet) shows mNH of the secondary amines at 3200 cm 1 and mClO of the perchlorate anions at 1090 and 623 cm 1. In the complexes, the bands at 3062 and 2972 cm 1 for 1 and 3063 and 2971 cm 1 for 2 are consistent with the C–H stretching frequencies of the macrocyclic ligand with chiral pendants. UV/vis spectra indicate that d–d transitions of 1 and 2 occur at 452 nm, respectively. Yellow plate-shaped crystals of 1 and 2 suitable for X-ray diffraction were obtained by solvent diffusion of diethyl ether into MeCN solutions of 1 and 2, respectively. Both complexes crystallize in the orthorhombic P212121 space group, and the atom labeling ORTEP drawings of 1 and 2 are shown in Fig. 1 [7]. The core structure of 1 is composed of one [Ni(LR,R)]2+ cation and two perchlorate anions. The nickel(II) ion displays a square-planar
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J.H. Han et al. / Inorganic Chemistry Communications 11 (2008) 745–748
H N
CH3 *
H
N
H N
II
*
N
Ni N H
N H
N4 O6 = 3.007(4) Å, \N4–H4–O6 = 152°; N5 O1 = 3.131(4) Å, \N5–H5–O1 = 156°. Additionally there exist the inter-molecularly herringbone p–p interactions between the pendant benzene rings, which gives rise to a one-dimensional chain. The distance between the centroids is 4.570(5) Å, and the dihedral angle between the pendant benzene groups is 42.38(13)° [10]. As expected, the overall structure of 2 is essentially same as that of 1 except for the chirality of the pendant arms [11]. Thus, complex 2 is shown to be the enantiomer of 1 as depicted in Fig. 1b. Fig. 2 shows the packing diagrams of both complexes 1 and 2, viewed along the a axis. The circular dichroism (CD) spectra measured in MeCN solutions further confirm the enantiomeric nature of the optically active complexes 1 and 2 as shown in Fig. 3. Complex 1 (R isomer) shows a negative Cotton effect around 345 and 492 nm and a positive signal centered around 440 nm. In complex 1, the shoulder absorption band with a maximum at 330 nm is assigned to the metal-to-ligand charge transfer (MLCT) of NiII to LR,R transition. The CD spectrum of 1 shows a negative Cotton effect (CE) in the MLCT region. In the absorption band at 452 nm, which assigned to NiII d–d transition, the CD spectrum displays a strong bisignate CD pattern (+ and ) in the region of the NiII d–d transition in which the pattern can be attributed to the regional rule correlating the optical activity of the d–d transitions with substituent positions [12]. Contrary to 1, complex 2 (S isomer) exhibits Cotton effects of the opposite sign at the same wavelengths. The weak negative/positive CD spectra in the d–d transition region are observed, indicating that the optical activities are resulted from the vicinal effects of the asymmetric carbons of (R)-(+)-amethylbenzylamine and (S)-( )-a-methylbenzylamine in pendant groups, respectively. In conclusion, new hexaaza macrocyclic nickel(II) complexes bearing chiral pendant groups have been synthesized by an efficient one-pot template condensation and characterized. Each
CH3
H (ClO4)2
[NiII(LR,R)](ClO4)2 (1) II S,S [Ni (L )](ClO4)2 (2) * = (R,R) and (S,S) Chart 1. Chemical structure of 1 and 2.
coordination geometry by binding the four secondary nitrogen atoms of macrocyclic ligand with the average Ni–N bond distance of 1.929(2) Å. The pendant methylbenzyl groups of the macrocycle are not involved in either intra- or inter-molecular coordination of nickel(II) ion. The complex do not have an inversion center at the nickel atom, due to the chiral pendants of the macrocyclic ligand. The azamacrocyclic ligand adopts thermodynamically the most stable R,R,S,S configuration [8] and thus the chiral pendants are situated above and below the square-coordination plane. The sixmembered chelate rings adopt a chair conformation and the fivemembered chelate rings assume a gauche conformation. The average C–N bond distance and the C–N–C angles relating the tertiary nitrogen atoms N3 and N6 are 1.460(2) Å and 108.7(3)–117.4(3)°, respectively, which is indicative of significant contribution of sp2 hybridization for the nitrogen atoms. In complex 1, the secondary amines of the macrocycle form N–H O hydrogen bonds with the oxygen atoms of perchlorate anions:[9] N1 O2 = 2.982(5) Å, \N1–H1–O2 = 152°; N2 O5 = 3.172(5) Å, \N2–H2–O5 = 158°;
C2
a C1
C16 C15
C3 N2
N1
C10 C12
N3
Ni1
C14
C13
C21
C19 C22
C18 N6 C8
C9
N4
N5 C7
b
C20 C4
C11
C5
C24
C17
C23
C6
C9 C21 C3
N1 C16
C20
C10 C11
N6
N2
Ni1
C23 C4
C8 C15
C14
C12
C22
C2
C1
C19 N3
N5
C18
C24
N4
C7 C13 C6
C5 C17
Fig. 1. ORTEP (40% probable thermal ellipsoid) views of the dications [Ni(LR,R)]2+ (a) and [Ni(LS,S)]2+ (b) in crystals of 1 and 2, respectively. Hydrogen atoms and perchlorate anions are omitted for clarity. Relevant distances (Å) and angles (°): For 1, Ni1–N1 1.925(3), Ni1–N2 1.931(3), Ni1–N4 1.929(3), Ni1–N5 1.929(3), N3–C4 1.444(5), N3–C5 1.444(5), N3–C18 1.472(5), N6–C1 1.453(5), N6–C8 1.457(5), N6–C10 1.491(5), C9–C10 1.513(5), C17–C18 1.535(5), N1–Ni1–N2 87.28(13), N1–Ni1–N4 179.24(13), N1–Ni1– N5 91.78(13), N2–Ni1-N4 93.46(13), N2–Ni1–N5 178.75(14), N4–Ni1–N5 87.49(13). For 2, Ni1–N1 1.923(4), Ni1–N2 1.931(4), Ni1–N4 1.925(4), Ni1–N5 1.927(3), N3–C4 1.439(6), N3–C5 1.438(6), N3–C18 1.474(6), N6–C1 1.446(6), N6–C8 1.445(6), N6–C10 1.495(6), C9–C10 1.508(7), C17–C18 1.552(7), N1–Ni1–N2 87.28(16), N1–Ni1–N4 178.88(17), N1–Ni1–N5 91.75(16), N2–Ni1–N4 93.60(16), N2–Ni1–N5 178.97(17), N4–Ni1–N5 87.37(16).
J.H. Han et al. / Inorganic Chemistry Communications 11 (2008) 745–748
747
Fig. 2. The packing diagrams of 1 (a) and 2 (b), viewed along the a axis.
complex has a square-planar environment around the nickel(II) ion and the intramolecular N–H O hydrogen bonds as well as the herringbone p–p stacking interactions. The observation of the Cotton effect and the X-ray crystal structure clearly provided evidence for the chirality of 1 and 2. Further studies on the self-assembly of the complexes and organic building blocks for the construction of chiral open frameworks and chiral separation are ongoing.
10
2
CD / mdeg
5
0
Acknowledgement This research was supported by Kyungpook National University Research Fund, 2007.
-5
Appendix A. Supplementary data
1 -10 350
400
450
500
550
Wavelength / nm Fig. 3. CD spectra of 1 (solid line) and 2 (dotted line).
600
CCDC-658376 (for 1) and CCDC-658377 (for 2) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2008.03.027.
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J.H. Han et al. / Inorganic Chemistry Communications 11 (2008) 745–748
References [1] (a) J.-M. Lehn, Supramolecular chemistry, Concepts and Perspectives, VCH, Weinheim, 1995; (b) G. Chelucci, R.P. Thummel, Chem. Rev. 102 (2002) 3129; (c) E.-Q. Gao, Y.-F. Yue, S.-Q. Bai, Z. He, C.-H. Yan, J. Am. Chem. Soc. 126 (2004) 1419; (d) J.S. Seo, D. Whang, H. Lee, S. Jun, J. Ok, Y. Jin, K. Kim, Nature 404 (2000) 982; (e) I. Katsuki, N. Matsumoto, M. Kojima, Inorg. Chem. 39 (2000) 3350; ¯ kawa, Angew. Chem. Int. Ed. 42 (2003) (f) K. Inoue, K. Kikuchi, M. Ohba, H. O 4810; (g) Z.-G. Gu, Y. Song, J.-L. Zuo, X.-Z. You, Inorg. Chem. 46 (2007) 9522; (h) Y. Numata, K. Inoue, N. Baranov, M. Kurmoo, K. Kikuchi, J. Am. Chem. Soc. 129 (2007) 9902. [2] (a) R.G. Konsler, J. Karl, E.N. Jacobsen, J. Am. Chem. Soc. 120 (1998) 10780; (b) J.P. Leonard, P. Jensen, T. McCabe, J.E. O’Brien, R.D. Peacock, P.E. Kruger, T. Gunnlaugsson, J. Am. Chem. Soc. 129 (2007) 10986. [3] (a) K.S. Min, M.P. Suh, Chem. Eur. J. 7 (2001) 303; (b) K.S. Min, M.P. Suh, Eur. J. Inorg. Chem. (2001) 449; (c) T.-B. Lu, H. Xiang, R.L. Luck, Z.-W. Mao, X.-M. Chen, L.-N. Ji, Inorg. Chim. Acta 355 (2003) 229. [4] (a) G. Du, A. Ellern, L.K. Woo, Inorg. Chem. 42 (2003) 873; (b) J. Gao, J.H. Reibenspies, R.A. Zingaro, F.R. Woolley, A.E. Martell, A. Clearfield, Inorg. Chem. 44 (2005) 232. [5] (a) E.Y. Lee, M.P. Suh, Angew. Chem. Int. Ed. 43 (2004) 2798; (b) B. Nowicka, M. Rams, K. Stadnicka, B. Sieklucka, Inorg. Chem. 46 (2007) 8123. [6] Compound 1: Ethylenediamine (3.4 mL, 0.05 mol), paraformaldehyde (3.0 g, 0.10 mol), and (R)-(+)-a-methylbenzylamine (6.12 g, 0.05 mol) were slowly added to a stirred solution of NiCl26 H2O (5.95 g, 0.025 mol) in MeOH (40 mL). The mixture was heated to reflux for 1 day. The solution was filtered while hot and the filtrate was concentrated to about 1/4 of the original volume. HClO4 (60%, 10 mL) was added to the yellow–brown solution. Bright yellow precipitate was formed, which was filtered off, washed with H2O, MeOH, and ether, and dried in air. Yield: ca. 30%. C24H38Cl2N6NiO8 (668.21): calcd. C 43.14, H 5.73, N 12.58; found C 43.20, H 5.74, N 13.01. IR (KBr pellet): mNH 3200, mCH 3062, 2972, mClO 1085, 624 cm 1. UV/vis (MeCN): kmax, nm (e, M 1 cm 1) = 330(35, sh), 452(50). Compound 2 was prepared as yellow solid in a manner similar to the synthesis of 1 except that (S)-( )-amethylbenzylamine (6.12 g, 0.05 mol) instead of (R)-(+)-amethylbenzylamine. Yield: ca. 30%. C24H38Cl2N6NiO8 (668.21): calcd. C 43.14, H 5.73, N 12.58; found C 42.81, H 5.72, N 13.04. IR (KBr pellet): mNH 3200, mCH 3063, 2971, mClO 1090 (s), 623 cm 1. UV/vis (MeCN): kmax, nm (e, M 1 cm 1) = 330(28, sh), 452(49). Safety note: Although we have experienced no
[7]
[8] [9] [10]
[11]
[12]
problem with the compounds reported in this work, perchlorate salts of metal complexes with organic ligands are often explosive and should be handled with great caution. X-ray data for 1 and 2 were collected at 173(2) K on a Bruker P4 diffractometer equipped with the SMART CCD system and using Mo Ka radiation (k = 0.71073 Å, graphite monochromator). The raw data were processed to give structure factors using the SAINT program and corrected for Lorentz and polarization effects. No absorption corrections were made. The crystal structures were solved by direct methods, and refined by full-matrix leastsquares refinement using the SHELXL97 computer program. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were positioned geometrically and refined using a riding model. Crystallographic data for C24H38Cl2N6NiO8 (1):M = 668.21 g/mol, yellow block, 0.10 0.10 0.40 mm, T = 173(2) K, orthorhombic, space group P212121 (No. 19), a = 8.2605(5) Å, b = 16.2712(10) Å, c = 21.8854(14) Å, a = b = c = 90°, V = 2941.6(3) Å3, Z = 4, Dc = 1.509 g/cm3, l = 0.898 mm 1, F(000) = 1400, GOF = 0.961. Flack parameter v = 0.007(18). Of the 18872 reflections, 6847 were unique (Rint = 0.0918), 4498 observed [I > 2r(I)], which refined to R1 = 0.0463, wR2 = 0.0918, and for all data R1 = 0.0971, wR2 = 0.1088. For C24H38Cl2N6NiO8 (2):M = 668.21 g/mol, yellow plate, 0.10 0.20 0.60 mm, T = 173(2) K, orthorhombic, space group P212121 (No. 19), a = 8.2607(3) Å, b = 16.2591(6) Å, c = 21.8651(9) Å, a = b = c = 90°, V = 2941.6(3) Å3, Z = 4, Dc = 1.511 g/cm3, l = 0.899 mm 1, F(000) = 1400, GOF = 1.230. Flack parameter v = 0.05(2). Of the 18528 reflections, 6842 were unique (Rint = 0.0486), 6134 observed[I > 2r(I)], which refined to R1 = 0.0689, wR2 = 0.1275, and for all data R1 = 0.0789, wR2 = 0.1310. R.D. Hancock, Acc. Chem. Res. 23 (1990) 253. G.R. Desiraju, Acc. Chem. Res. 29 (1996) 441. (a) G.R. Desiraju, Crystal Engineering: The Design of Organic Solids, Elsevier, New York, 1989 (Chapter 4); (b) A.S. Shetty, J. Zhang, J.S. Moore, J. Am. Chem. Soc. 118 (1996) 1019. For 2, av. Ni–N bond distance is 1.927(2) Å, and the C–N bond distance and the C–N–C angle involving the N3 and N6 are average 1.456(2) Å and 108.4(4)– 117.7(4)°, respectively. The NH groups of the macrocycle are involved in the hydrogen bonding interaction with oxygen atoms of perchlorate anions: N1 O2 = 3.130(6) Å, \N1–H1–O2 = 157°; N2 O7 = 3.012(6) Å, \N2–H2– O7 = 152°; N4 O8 = 3.178(6) Å, \N4–H4–O8 = 158°; N5 O3 = 2.970(6) Å, \N5–H5–O3 = 151°. Between the pendant benzene groups, the intercentroid distance is 4.575(6) Å, and the dihedral angle is 42.59(17)°. ¯ kawa, N. Matsumoto, S. Kida, Inorg. Chim. Acta 162 (a) H. Sakiyama, H. O (1989) 65; (b) S. Arakawa, T. Nozawa, M. Hatano, Bull. Chem. Soc. Jpn. 47 (1974) 2643; (c) M. Suzuki, Y. Nishida, Inorg. Chem. Acta 25 (1977) 185; (d) Y. Nishida, S. Kida, Bull. Chem. Soc. Jpn. 43 (1970) 3814.