A two-dimensional coordination polymer with a brick wall structure and hydrophobic channels: synthesis and structure of a macrocyclic nickel(II) complex with 1,3,5-benzenetricarboxylate

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Abstract

The reaction of 1,3,5-benzenetricarboxylate, BTC³⁻, with a macrocyclic complex [NiL](ClO₄)₂ (L⊕=⊕ 3,10-bis((2-phenethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) containing hydrophobic pendant groups results in a two-dimensional coordination polymer with a brick wall structure and hydrophobic channels.

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Supramolecular assembly and molecular architecture have been areas of rapid growth in recent years.¹ Many supramolecular species with one-, two- and three-dimensional networks of various sizes and shapes have been synthesized, and some show useful properties, such as in the areas of molecular recognition, electronic, optical, magnetic and catalytic fields.² 1,3,5-Benzenetricarboxylate anion (BTC³⁻) is often used as a building block due to its three equally spaced carboxylate groups and a rigid disk-like conformation. Thus, reactions of BTC³⁻ with metal ions or metal complexes usually result in two-dimensional coordination polymers with large cavities and channels which can incorporate and recognize small guest molecules or ions.³ However, two-dimensional coordination polymers with hydrophobic channels have so far not been constructed.

We report here the synthesis and structure of a 2-D coordination polymer [NiL]₃[BTC]₂·6H₂O formed by BTC³⁻ with a macrocyclic nickel(II) complex containing a hydrophobic pendant group, in which all the macrocyclic pendant groups point to the center of the cavity to form hydrophobic channels via edge-to-face aromatic interactions.

The coordination polymer was synthesized by the reaction of the macrocyclic nickel(II) complex

[NiL](ClO₄)₂ with BTC³⁻.⁴ The results of an X-ray diffraction analysis (Table 1) indicate that the complex shows a 2-D brick wall structure. In the complex, each Ni(II) ion lies on an inversion center and is six-coordinated with four nitrogen atoms from the macrocyclic ligand in the equatorial plane, and two carboxylate oxygen atoms from two different BTC³⁻ anions in the axial position, forming a slightly distorted octahedral geometry (Fig. 1).

Fig. 1 Molecular structure of the complex [NiL]₃[BTC]₂·6H₂O. Click image or 1.htm to access a 3D representation.

Table 1 Crystallographic data for [NiL]₃[BTC]₂·6H₂O^a,b,c,d

Parameter
a All data were collected at T⊕=⊕293(2) K using a Bruker SMART 1000 CCD with MoKα radiation (λ⊕=⊕0.71073 Å). b The atoms of the C1–C6 ring are disordered and were treated with restraints, and refined isotropically. c Intensities were reduced using the SAINT ^6aprogram; the structure was solved by direct methods and refined by a full-matrix, least squares technique based on F^2 using SHELXL97.^6b d Click b106490h.txt for full crystallographic data (CCDC 167896).
Empirical formula	C90H132N18O18Ni3
Crystal dimensions/mm	0.26⊕×⊕0.07⊕×⊕0.05
M	1930.41
Crystal system	Triclinic
Space group	P1̄
a/Å	14.217(3)
b/Å	14.439(3)
c/Å	14.914(3)
α/°	100.087(4)
β/°	96.311(4)
γ/°	109.958(3)
U/Å^3	2785.2(10)
Z	1
D c/Mg m^−3	1.333
μ(MoKα)/mm^−1	0.587
F(000)	1188
GoF	0.991
Number of reflections (unique)	16 259 (11 936)
R int	0.0216
Number of observed reflections [I⊕>⊕2σ(I)]	7274
Number of refined parameters	541
R 1	0.0709
wR 2	0.2316

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The Ni–N bond distances [ca. 2.046(4)–2.067(4) Å] are slightly shorter than the Ni–O bond distances [ca. 2.134(3)–2.173(3) Å]. Each BTC³⁻ anion binds to three metal ions in a C₁ symmetry, resulting in a 2-D brick wall-like network along the bc plane (Fig. 2).

Fig. 2 Brick wall structure of the 2-D coordination polymer (macrocyclic and water molecules are omitted for clarity).

In the 2-D network structure, six phenyl rings from six macrocyclic nickel(II) complexes form a hydrophobic cavity (Fig. 3) via edge-to-face aromatic interactions (distances from the plane of C₆ rings to the nearest C of neighboring phenyl rings are in the range ca. 3.80–4.32 Å). One of the water molecules forms a hydrogen bond with a free carbonyl oxygen atom of BTC³⁻ (Ow3⋯O6⊕=⊕2.711 Å), while the rest of the water molecules are incorporated in the crystal lattice. (The hydrogen atoms of the water molecules are not located.)

Fig. 3 The hydrophobic cavity formed by six phenyl groups via edge-to-face aromatic interactions.

The 2-D sheets stack along the a-axis via π⋯π interactions between two neighboring C25–C30 phenyl rings, forming a 3-D network with parallel hydrophobic channels along the a-axis (Fig. 4). The shortest intersheet separation is 9.427 Å. The size of the cavity is 6.0⊕×⊕9.8 Å, and no hydrophilic DMF or water guest molecules are located within these hydrophobic channels. The hydrophobic channels may selectively incorporate aromatic molecules such as benzene and toluene, and this guest inclusion property is being investigated.

Fig. 4 Space-filling view of the 2-D sheets packing along the a-axis and showing the hydrophobic channels. (Color scheme: C grey, H white, N blue, Ni green, O red.)

Acknowledgements

This work was supported by the NSFC (29801005), the NSF of CCHE-0079158, and the Ministry of Education of China.

Notes and references

1. (a) S. R. Batten and R. Robson, Angew. Chem., Int. Ed., 1998, 37, 1460; (b) S. Leininger, B. Olenyuk and P. J. Stang, Chem. Rev., 2000, 100, 853; (c) M. Fujita, K. Umemoto, M. Yoshizawa, N. Fujita, T. Kusukawa and K. Biradha, Chem. Commun., 2001, 509; (d) S. R. Batten, CrystEngComm, 2001, 20.
2. (a) K. Umemoto, K. Yamaguchi and M. Fujita, J. Am. Chem. Soc., 2000, 122, 7150; (b) K. Kasai, M. Aoyagi and M. Fujita, J. Am. Chem. Soc., 2000, 122, 2140; (c) K. Biradha, Y. Hongo and M. Fujita, Angew. Chem., Int. Ed., 2000, 39, 3843; (d) B. L. Chen, M. Eddaoudi, T. M. Reineke, J. W. Kampf, M. O'Keeffe and O. M. Yaghi, J. Am. Chem. Soc., 2000, 122, 11 559; (e) H. L. Li, M. Eddaoudi, J. Plevert, M. O'Keeffe and O. M. Yaghi, J. Am. Chem. Soc., 2000, 122, 12 409; (f) X. Y. Huang and J. Li, J. Am. Chem. Soc., 2000, 122, 8789; (g) M. Ohba, N. Usuki, N. Fukita and H. Ōkawa, Angew. Chem., Int. Ed., 1999, 38, 1795; (h) M. L. Tong, X. M. Chen, B. H. Ye and L. N. Ji, Angew. Chem., Int. Ed., 1999, 38, 2237.
3. (a) O. M. Yaghi, G. M. Li and H. L. Li, Nature, 1995, 378, 703; (b) G. Smith, A. N. Reddy, K. A. Byriel and C. H. L. Kennard, J. Chem. Soc., Dalton Trans., 1995, 3565; (c) O. M. Yaghi, H. L. Li and T. L. Groy, J. Am. Chem. Soc., 1996, 118, 9096; (d) C. J. Kepert and M. J. Rosseinsky, Chem. Commun., 1998, 31; (e) H. J. Choi and M. P. Suh, J. Am. Chem. Soc., 1998, 120, 10 622; (f) H. J. Choi, T. S. Lee and M. P. Suh, Angew. Chem., Int. Ed., 1999, 38, 1405; (g) M. J. Plater, M. R. St. J. Foreman, E. Coronado, C. J. Gómez-García and A. M. Z. Slawin, J. Chem. Soc., Dalton Trans., 1999, 4209; (h) T. J. Prior and M. J. Rosseinsky, CrystEngComm, 2000, 24.
4. A water solution (4 mL) of Na₃BTC (0.055 g, 0.2 mmol) was layered with a dimethylformamide solution (8 mL) of [NiL](ClO₄)₂ (0.20 g, 0.3 mmol)⁵ at room temperature. After about two weeks, pink crystals suitable for X-ray analysis formed from the solution .
5. T. B. Lu, H. Xiang, X. Y. Li, Z. W. Mao and L. N. Ji, Inorg. Chem. Commun., 2000, 3, 597.
6. (a) SAINT, Program for Reduction of Data Collected on a Bruker CCD Area Detector Diffractometer, Bruker AXS Inc., Madison, WI, 1999; (b) G. M. Sheldrick, SHELXL97, Program for Crystal Structure Determination, University of Göttingen, Germany, 1997.

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