A series of 2D metal–quinolone complexes: Syntheses, structures, and physical properties

doi:10.1016/j.jssc.2012.10.015

Journal of Solid State Chemistry

Volume 198, February 2013, Pages 279-288

https://doi.org/10.1016/j.jssc.2012.10.015 Get rights and content

Abstract

Six novel 2D metal–quinolone complexes, namely [Cd(cfH)(bpdc)] radical dot H₂O (1), [M(norfH)(bpdc)]H₂O (M=Cd (2) and Mn (3)), [Mn₂(cfH)(odpa)(H₂O)₃]0.5H₂O (4), [Co₂(norfH)(bpta)(μ₂-H₂O)(H₂O)₂]H₂O (5) and [Co₃(saraH)₂(Hbpta)₂(H₂O)₄]9H₂O (6) (cfH=ciprofloxacin, norfH=norfloxacin, saraH=sarafloxacin, bpdc=4,4′-biphenyldicarboxylate, odpa=4,4′-oxydiphthalate, bpta=3,3′,4,4′-biphenyltetracarboxylate) have been synthesized and characterized. Compounds 1–3 consist of 2D arm-shaped layers based on the 1D {M(COO)}_nⁿ⁺ chains. Compounds 4 and 5 display 2D structures based on tetranuclear manganese or cobalt clusters with (3,6)-connected kgd topology. Compound 6 exhibits a 2D bilayer structure, which represents the first example of metal–quinolone complexes with 2D bilayer structure. By inspection of the structures of 1–6, it is believed that the long aromatic polycarboxylate ligands are important for the formation of 2D metal–quinolone complexes. The magnetic properties of compounds 3–6 was studied, indicating the existence of antiferromagnetic interactions. Furthermore, the luminescent properties of compounds 1–2 are discussed.

Graphical abstract

Six novel 2D metal–quinolone complexes have been prepared by self-assemblies of the quinolones and metal salts in the presence of long aromatic polycarboxylates

Highlights

►Compounds 1–3 consist of novel 2D arm-shaped layers based on the 1D {M(COO)}_nⁿ⁺ chains. ► Compounds 4 and 5 are two novel 2D layers based on tetranuclear Mn or Co clusters with kgd topology. ► Compound 6 is the first example of metal–quinolone complexes with 2D bilayer structure. ► Compounds 1–6 represent six unusual examples of 2D metal–quinolone complexes.

Introduction

Metal–organic frameworks (MOFs) are a burgeoning field in the last two decades, not only stems from their tremendous potential applications in areas such as catalysis, molecular adsorption, magnetism, nonlinear optics, and molecular sensing, but also from their novel topologies and intriguing structural diversities [1], [2], [3]. Aided by the rapid growth of network-based crystal engineering, a large number of attractive networks with various structural motifs have been designed and extensively discussed in comprehensive reviews by Yaghi, Kitagawa, Rao, Chen, and their co-workers [4]. On the other hand, many organic drugs, which possess modified pharmacological and toxicological properties administered in the form of metallic complexes [5], have the potential to act as ligands and the resulting metal–drug complexes are particularly important both in coordination chemistry and biochemistry [6], [7], [8], [9], [10], however, the study of metal–drug complexes is still in its early stages, thus representing a great challenge in current synthetic chemistry and coordination chemistry.

Quinolones represent a large group of synthetic antibacterial agents widely used in clinical practice and are characterized by a broad-spectrum antibacterial activity. Ciprofloxacin (cfH), norfloxacin (norfH) and sarafloxacin (saraH) (Schemes 1 and S1) are typical members of this group and are used for the treatment of certain diseases [7], [8], [9], [11], [12]. The mechanisms of action of the quinolone antibacterial drugs are either their inhibition of the supercoiling of DNA catalyzed by the enzyme DNA gyrase or their interaction with the DNA molecule via a metal complex intermediate [6], [7], [8], [9]. Recently new theoretical–experimental studies on the activity of quinolones and their metal complexes have supported the hypothesis that the mechanism of action of quinolones could be mediated by a metal ion [7], [9], [10]. It is obvious that the metal ions may play a very important role in the mechanism of action of the quinolone antibacterial agents. However, the structurally characterized metal–quinolone complexes, especially for high-dimensional extended complexes [6], [8], to our knowledge, are still rare, as evidenced in a review by Iztok Turel [7]. Only a few two-dimensional (2D) metal–quinolone complexes have been reported up to now [6], [8]. The possible reason is that the steric demands of the bulky quinolone ligands will increase the steric hindrance at the metal center, which may restrain spatial extension of the skeleton and thus prevent the formation of a 2D structure. Therefore, the construction of 2D metal–quinolone complexes is still a great challenge for synthetic chemists, and much work is still necessary to enrich and develop this branch.

Ongoing research in our laboratory has been directed toward the design and construction of high-dimensional extended metal–quinolone complexes [8] with the aim of enriching the structural chemistry of metal–quinolone complexes and preparing new metal–drug complexes with particular functions. As an extension of our previous work [8], for our synthetic strategy we chose the long aromatic polycarboxylates as bridging ligands in an attempt to link metal–quinolone fragments into 2D metal–quinolone complexes. In our experiment, the long aromatic polycarboxylates and quinolones are simultaneously introduced based on the following considerations: (i) on the one hand, multidentate carboxylates are known to be essential in chelating metal ions and locking their position into metal clusters [4a], and it should be feasible to link discrete clusters by polycarboxylate bridges to give an extended network containing highly connected nodes. On the other hand, the use of carboxylate-bridged metal clusters as second building units (SBUs) to build 2D structures is relatively mature [13], [14]. Therefore, the topologies of resulting structures can be predicted and designed [15]. (ii) Coordination polymers constructed from the mixed quinolones and aromatic polycarboxylate ligands are still very rare, which may be attributed, at least in part, to the fact that two carboxyl-containing ligands would yield more negative charges and make the charge balance difficult [8], [8]. Because poor solubility of the ligands, and the mixing of metal salt and quinolone solution usually results in a precipitation, making it difficult to grow single crystals of complexes, we employed hydrothermal technique to put the designed strategy in practice and successfully synthesized a series of novel 2D metal–quinolone complexes, namely [Cd(cfH)(bpdc)] radical dot H₂O (1), [M(norfH)(bpdc)]H₂O (M=Cd (2) and Mn (3)), [Mn₂(cfH)(odpa)(H₂O)₃]0.5H₂O (4), [Co₂(norfH)(bpta)(μ₂-H₂O)(H₂O)₂]H₂O (5) and [Co₃(saraH)₂(Hbpta)₂(H₂O)₄]9H₂O (6) (bpdc=4,4′-biphenyldicarboxylate, odpa=4,4′-oxydiphthalate, bpta=3,3′,4,4′-biphenyltetracarboxylate). The syntheses, crystal structures and physical properties of these compounds will be represented and discussed in this paper. This work may provide new structural information that will aid in understanding the mechanisms of action of the quinolone antibacterial agents.

Section snippets

Materials and methods

All chemicals were commercially purchased and used without further purification. The elemental analyses (C, H and N) were carried out with a Perkin-Elmer 2400 CHN Elemental Analyzer. Cd, Mn and Co were determined by a tps-7000 Plasma-Spec(I) inductively coupled plasma atomic emission spectrometer (ICP-AES). IR spectra were recorded in the range 400–4000 cm⁻¹ on a Bio-Rad FTS-185 FT/IR Spectrophotometer using KBr pellets. TG analyses were performed on a NETZSCH STA 449C instrument in flowing N₂

Crystal structures of 1–3

Compounds 2 (Fig. S1) and 3 (Fig. S2) are isostructural, and the structures of 1 and 2 are close to being isostructural, so only the structure of 1 will be discussed in detail. In the crystal structure of 1, the asymmetric unit contains one Cd atom, one cfH ligand, one bpdc ligand, and one lattice H₂O molecule (Fig. 1). Each Cd atom is coordinated by two oxygen atoms (Cd–O 2.2221(17)–2.2339(15) Å) from one cfH ligand and four oxygen atoms (Cd–O 2.2569(19)–2.5367(19) Å) from three bpdc ligands,

Conclusions

In summary, we have successfully prepared a series of novel 2D metal–drug complexes by self-assembly of quinolone antibacterial agents with metal salts in the presence of long aromatic polycarboxylate ligands under hydrothermal conditions. The successful isolation of these species not only enriches the realm of 2D metal–quinolone complexes, but also provides new structural information that may help to understand the mechanisms of action of the quinolone antibacterial drugs. This work further

Acknowledgments

This work was financially supported by the NSFC (20801044), the China Postdoctoral Science Foundation (20080430205, 200902282), the Science and Technology Foundation of Southwest University (SWUB2007035), the Fundamental Research Funds for the Central Universities (XDJK2009B014, XDJK2012B011), and the Program for Chongqing Excellent Talents in University.

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A series of 2D metal–quinolone complexes: Syntheses, structures, and physical properties

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Materials and methods

Crystal structures of 1–3

Conclusions

Acknowledgments

Angew. Chem. Int. Ed.

J. Am. Chem. Soc.

Angew. Chem. Int. Ed.

Coord. Chem. Rev.

Angew. Chem. Int. Ed.

Coord. Chem. Rev.

Polyhedron

Chem. Pharm. Bull.

Chem. Rev.

Dalton Trans.

Aust. J. Chem.

Chem. Soc. Rev.

Angew. Chem. Int. Ed.

Angew. Chem. Int. Ed.

Coord. Chem. Rev.

Chem. Rev.

Acc. Chem. Res.

J. Am. Chem. Soc.

Coord. Chem. Rev.

Nature

Angew. Chem. Int. Ed.

Angew. Chem. Int. Ed.

Coord. Chem. Rev.

J. Inorg. Biochem.

J. Inorg. Biochem.

Inorg. Chim. Acta