Solvent-induced two heterometallic coordination polymers based on a flexible ferrocenyl ligand

Inorganic Chemistry Communications 13 (2010) 19–21

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Solvent-induced two heterometallic coordination polymers based on a flexible ferrocenyl ligand Chun-Yan Cao, Kai-Ju Wei *, Jia Ni, Yangzhong Liu * Department of Chemistry, University of Science and Technology of China, Hefei 230026, PR China

a r t i c l e

i n f o

Article history: Received 26 August 2009 Accepted 10 October 2009 Available online 11 November 2009 Keywords: Ferrocene Coordination polymer Cd complex Electrochemical properties

a b s t r a c t The bidentate ferrocenyl sandwich molecule N,N0 -bis-3-pyridylmethyl-1,10 -ferrocenedicarboxamide (3BPMFA) has been employed as an organometallic coordination ligand in reaction with CdBr2 to construct heterobimetallic architectures. By assembling the flexible arm-like molecule with CdBr2, two novel bimetallic 1D chain structures are constructed in different solvent systems: the solvated [Cd(l-3-BPMFA)2Br2]nnMeOH (1) from methanol and the unsolvated [Cd(3-BPMFA)(l-Br)2]n (2) from DMF–Et2O. Different roles of bromine ions have been observed in these two complexes. In 1, bromine ions only act as terminal coordinated ligand, while they play bridging roles in 2. Electrochemistry properties of the ligand and complexes were discussed preliminarily. Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved.

Recently, intense effort has been devoted to the design and controlled crystallization of coordination polymers based on transition–metal ions and multifunctional bridging ligands owing to their potential applications as optoelectronic, magnetic, porous materials, and catalyst [1]. However, it is still a challenge to obtain the desired complexes because the structures of assembled products are greatly affected by a variety of conditions, such as temperature [2], pH value [3], molar ratio of reactants [4] and solvent systems [5]. Many investigations are required to establish proper synthetic strategies leading to the desired species. On this aspect, ferrocenyl-ligands are widely investigated since Fe atoms supplied in ferrocene molecule can form mixed-metal complexes by coordination with additional metal center, which might display novel chemical and physical properties [6]. Some metal linkers such as pyridyl and carboxylic linked directly or through molecular spacers to ferrocene group result in a series of ferrocenyl-based ligands [7], which tend to give discrete structures, such as macrocycle, cage and cluster [8]. To the best of our knowledge, hetero-bimetallic coordination polymers based on ferrocene are rare [9]. Recently, we have designed and synthesized a flexible ditopical ligand N,N0 -bis-3-pyridyl-1,10 -ferrocenedicarboxamide (3BPFA) and obtained a series of cage-type assemblies [8a]. However, the assembled cavity could not provide enough space for guest molecules owing to the short ‘‘arm” of 3-BPFA. In this work, N,N0 -bis-3-pyridylmethyl-1,10 -ferrocenedicarboxamide (3-BPMFA) with a longer ‘‘arm” linker was selected in order to obtain more space to accommodate guest molecule. Without formation of cavity cage, the reaction of 3-BPMFA reacts with * Corresponding authors. E-mail addresses: [email protected] (K.-J. Wei), [email protected] (Y. Liu).

CdBr2 formed two novel coordination polymers containing different macrocyclic units [Cd(l-3-BPMFA)2Br2]n nMeOH (1) and [Cd(3-BPMFA)(l-Br)2]n (2) from different solvents. The formation of two coordination polymers does not depend on the ligand-tometal ratio, which confirms the solvent induced structure discrepancy in the two complexes. The complexes have been characterized by IR, elemental analyses and single crystal X-ray diffraction (see Supplementary data). The complexes 1 and 2 are insoluble in CH2Cl2, CHCl3, THF, CH3CN, but moderately soluble in MeOH, and soluble in DMF. 3-BPMFA were prepared according to the modified literature procedure for 3-BPFA [8a] and was crystallized from methanol– ether solution. X-ray analysis demonstrated that 3-BPMFA was a flexible long-arm molecule (Fig. S1), which constructs into infinite chains containing macrocyclic units through double N–H  N (N(1)  N(2) = 2.97 Å and N(1)–H(1A)  N(2) = 151.76°) hydrogen bonding interactions (Fig. 1). Fe  Fe distance is 6.42 Å in macrocycle. Obviously, N–H  N hydrogen bonding is essential factor to construct this structure. In comparison with 3-BPFA, the addition of methylene groups increases the flexibility of 3-BPMFA. As a result, this ligand coordinated to transitional-metal centers, the flexible groups such as amide, methyl and pyridine can rotate and/or bend for the requirement of coordination. Orange block of 1 was crystallized by reaction of 3-BPMFA with CdBr2 in methanol solution. The crystal structure of complex 1 exhibits infinite chains. The CdII center is six coordinated in a slighted elongated octahedron environment by two bromine anions and four pyridyl nitrogen atoms from four 3-BPMFA ligands. The distances of Cd–N are 2.40 Å for Cd(1)–N(2) and 2.42 Å for Cd(1)–N(4), respectively. The distance of Cd–Br is 2.73 Å, which is of the typical Cd–Br bond lengths [10]. This complex is extended

1387-7003/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2009.10.006

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by repeating of macrocycle units, which is consisted of two Cd metal centers and two 3-BPMFA molecules (Fig. 2). The metal–metal distances are 19.20 Å for Cd  Cd and 6.89 Å for Fe  Fe, respectively, which makes the macrocyclic unit large enough for guest molecules. However, the co-crystallization with several solvent molecules, including benzene, toluene, phenol, nitrobenzene, bromobenzene and chlorobenzene, was failed by the guest template method and titration method [11], which indicates that these host-macrocycles cannot sense these guest-molecules tested in this work. Analogously, no obvious interaction was observed with addition of amino acids (Val, Phe, Arg and Asp, which have different polarity and charge) to the solution of methanol based on NMR measurements. These 1-D chains arrange along the ab plane to form 2D networks which are connected by methanol molecules via intermolecular hydrogen bonding interactions (O(3)  O(2) = 2.65 Å, O(3)– H(3)  O(2) = 161.69°; N(1)–H(1)  O(3) = 2.89 Å, N(1)  O(3) = 135.48°). Thus, methanol molecules are located between two adjacent chains (Fig. S2). Complex 2 was obtained from DMF–Et2O solution. CdII ion also has six coordinated sphere, and the complex forms 1-D infinite chain structure (Fig. 3). Different from 1, each Cd center in 2 is coordinated by four Br ions and two N atoms from same 3-BPMFA. Obviously, Br anions play bridging role to link adjacent CdII metal to extend infinite 1-D chain. The distances of Cd–Br range from 2.72 Å to 2.89 Å, which are slightly longer than 1 in average. It is a well-known that the length of bridge bond is longer than nonbridge, which has been observed in many complexes previously [12]. Interestingly, the flexible ‘‘arms” of 3-BPMFA arrange in different mode located in two sides of Cd–Br chain, twofold left-hand helix on one side and right-hand helix on the other side (Fig. S3). Furthermore, two ‘‘arms” also hold together via intramolecular hydrogen bonding interactions (N(3)–H(3A)  O(2) = 138.72°, N(3)  O(2) = 2.86 Å). The parallel pyridyl rings from adjacent chains form p  p stacking with an interplane distance of 3.52 Å, which extends the 1D chains into 2D networks along the ab plane. Thermogravimetric analysis of the free ligand 3-BPMFA and complexes 1–2 was performed by heating the complexes from 20 to 600 °C under flowing N2. The TGA curve for complex 1 showed the first major weight loss occurred between 120 and 180 °C, which lose lattice methanol molecules by 2.14% (Calc. 2.57%),

Fig. 1. 1D chain structure in 3-BPMFA, showing N  H intermolecular hydrogen bond. Most hydrogen atoms are omitted for clarity.

Fig. 3. The 1D chain structure of complex 2, showing intramolecular hydrogen bond of O  H. Most hydrogen atoms are omitted for clarity.

which implies that methanol molecules could not easily escape from the crystal lattice of 1 due to intermolecular hydrogen bonding interactions. As shown in Fig. S4, further thermogravimetric data show a high stability up to about 320 °C for complexes 1 and 2, similar to free ligand 3-BPMFA. Those values are quite high as compared to those of supramolecules based on flexible ligands [13], which are compositionally and structurally closely related. After this point the compounds starts to decompose. The UV–Vis spectra of ligand 3-BPMFA and corresponding complexes 1–2 are determined in H2O solutions. The strong absorption ranging from 200 to 270 nm (Fig. S5) originates from ligand itself. In DMF, almost no difference has been found between the ligand’ and complex’ emission spectra, which has broad fluorescent emission band, with kmax of 432 nm upon excitation at 350 nm. This implies that the polymeric complex could disaggregate into oligomers or starting materials in DMF (Fig. S6). The electrochemistry behavior of 3-BPMFA ligand and 1–2 has been investigated by differential pulse voltammetry (DPV) in DMF (Fig. 4). Iron redox peak of 3BPMFA (Ep = 0.784 V) corresponds to a single ferrocene/ferrocenium redox ðFc =Fþ c Þ couple similar to ferrocene. This redox peak which results from the electron-withdraw of substituents were shifted toward more positive values in comparison with unsubstituted ferrocene (Ep = 0.456 V). This can be traced back to the substituted groups of ferrocene can decrease the density of Cp ring and make the ferrocene unit more difficulty to oxidize [14]. Complex 1 shows two peaks with Ep at 0.792 V and 1.180 V, respectively. The first one of 0.792 V is slightly shifted toward positive values compared to 3-BPMFA which is caused by coordination

Fig. 2. The 1D double chain of complex 1 containing macrocyclic units, hydrogen atoms are omitted for clarity.

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4.0x10-6 2.0x10-6

Current (A)

0.0 -2.0x10-6 -4.0x10-6 -6.0x10-6 -8.0x10-6 -1.0x10-5

Ferrocene 3-BPMFA Complex 1 Complex 2

-1.2x10-5 -1.4x10-5 -1.6x10-5

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Potential (V) Fig. 4. Differential pulse voltammetry (DPV) spectra in DMF (1  103 M) for 3-BPMFA and complexes 1 and 2.

interaction [15], another peak of 1.180 V corresponds to the two single-electron oxidations of the ferrocene moieties [16]. Similar result was observed in complex 2 with Ep at 0.788 and 1.144 V. In conclusion, two novel 1D coordination polymers constructed from a long flexible two-arm ligand 3-BPMFA have been synthesized and characterized. Bromine ions play different roles in these two complexes. The structural diversity of 1 and 2 can attributed to the solvent effects generated by solvent molecules. Obviously, ‘‘arm” of 3-BPMFA are manipulated by solvent molecules to adapt to the requirement of coordination interaction and obtain these two unexpected coordination polymers.

[2] [3] [4] [5] [6] [7] [8]

Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 50903081), the China Postdoctoral Science Foundation (No. 20070420724) and the Natural Science Foundation of Jiangsu Province (No. BK2008579).

[9]

[10] [11]

Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.inoche.2009.10.006. References [1] (a) L. Chen, J. Kim, T. Ishizuka, Y. Honsho, A. Saeki, S. Seki, H. Ihee, D. Jiang, J. Am. Chem. Soc. 131 (2009) 7287; (b) D. Fiedler, D.H. Leung, R.G. Bergman, K.N. Raymond, Acc. Chem. Res. 38 (2005) 351;

[12]

[13] [14] [15] [16]

(c) J.L.C. Rowsell, O.M. Yaghi, Micropor. Mesopor. Mater. 73 (2004) 3; (d) S. Hasegawa, S. Horike, R. Matsuda, S. Furukawa, K. Mochizuki, Y. Kinoshita, S. Kitagawa, J. Am. Chem. Soc. 129 (2007) 2607. J.Y. Lee, S.Y. Lee, W. Sim, K.M. Park, J. Kim, S.S. Lee, J. Am. Chem. Soc. 130 (2008) 6902. M.L. Tong, B.H. Ye, X.M. Chen, S.W. Ng, Inorg. Chem. 37 (1998) 2645. M.L. Tong, S. Hu, J. Wang, S. Kitagawa, S.W. Ng, Cryst. Growth Des. 5 (2005) 837. B.C. Tzeng, H.T. Yeh, T.Y. Chang, G.H. Lee, Cryst. Growth Des. 9 (2009) 2552. X.C. Wang, Y.P. Tian, Y.H. Kan, C.Y. Zuo, J.Y. Wu, B.K. Jin, H.P. Zhou, J.X. Yang, S.Y. Zhang, X.T. Tao, M.H. Jiang, Dalton Trans. (2009) 4096. D. Braga, M. Polito, D. D0 Addario, E. Tagliavini, Organometallics 22 (2003) 4553. (a) K.J. Wei, J. Ni, Y.S. Xie, Y.Z. Liu, Q.L. Liu, Dalton Trans. (2007) 3390; (b) E.P. Zhang, H.W. Hou, X.R. Meng, Y. Liu, Y. Liu, Y.T. Fan, Cryst. Growth Des. 9 (2009) 903; (c) K. Ghosh, Y. Zhao, H.B. Yang, B.H. Northrop, H.S. White, P.J. Stang, J. Org. Chem. 73 (2008) 8553. (a) Y.B. Dong, M.D. Smith, H.C. Loye, Inorg. Chem. 39 (2000) 1943; (b) N. Schultheiss, C.L. Barnes, E. Bosch, Cryst. Growth Des. 3 (2003) 573; (c) P.Y. Cheng, C.Y. Chen, H.M. Lee, Inorg. Chim. Acta 362 (2009) 1840. C.A. Hester, H.L. Coller, Polyhedron 15 (1996) 4255. The solvent titration method: upon a solution of 3-BPMFA (0.0454 g, 0.1 mmol) in methanol were successively dropped added to a solution of CdBr2 (0.0272 g, 0.1 mmol). The vial was covered with aluminium foil and the solvents were allowed to diffuse slowly. The orange deposit was obtained several days later. No crystals were formed. (a) I.V. Borisova, C. Eaborn, M.S. Hill, V.N. Khrustalev, M.G. Kuznetzova, J.D. Smith, Y.A. Ustynyuk, V.V. Lunin, N.N. Zemlyansky, Organometallics 21 (2002) 4005; (b) P.J. Stang, O. Bogdan, Acc. Chem. Res. 30 (1997) 502. (a) H. Yin, S.X. Liu, Polyhedron 26 (2007) 3103; (b) M.O. Awaleh, A. Badia, F. Brisse, Inorg. Chem. 44 (2005) 7833. T. Moriuchi, I. Ikeda, T. Hirao, Inorg. Chim. Acta 248 (1996) 129. X.J. Shi, H.W. Hou, L.W. Mi, Y.L. Sang, Y.T. Fan, R.Y. Liu, Inorg. Chim. Acta 362 (2009) 3364. Y.N. Liu, G. Orlowski, G. Schatte, H.B. Kraatz, Inorg. Chim. Acta 358 (2005) 1151.