Elsevier

Inorganica Chimica Acta

Volume 387, 30 May 2012, Pages 308-313
Inorganica Chimica Acta

Syntheses, crystal structures and physical properties of two unusual 4d–4f heterometallic coordination polymers

https://doi.org/10.1016/j.ica.2012.02.010Get rights and content

Abstract

Two novel heterometallic coordination polymers, [AgSm(pydc)2]·2H2O (1) and [AgTb(pydc)2]2·H2O (2) (H2pydc = pyridine-3,4-dicarboxylic acid), have been synthesized under hydrothermal conditions, and characterized by elemental analysis, IR, thermogravimetric analysis and single-crystal X-ray diffraction. Complexes 1 and 2 are isomorphous and exhibit 3D open framework heterometallic coordination polymer containing 1D channels occupied by lattice water molecules. To our knowledge, both compounds represent the rare examples of 3D open-framework 4d–4f heterometallic coordination polymers with open framework structure. Moreover, their luminescent and magnetic properties have also been investigated.

Graphical abstract

Two novel heterometallic coordination polymers, [AgSm(pydc)2]·2H2O and [AgTb(pydc)2]2·H2O (H2pydc = pyridine-3,4-dicarboxylic acid), have been synthesized under hydrothermal conditions. They possess 3D open framework heterometallic coordination polymer containing 1D channels occupied by lattice water molecules. Moreover, their luminescent and magnetic properties have also been investigated.

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Highlights

► Two heterometallic coordination polymers were prepared under hydrothermal conditions. ► They possess 3D open framework containing 1D channels. ► Antiferromagnetic interactions dominate between the Ln(III) centers.

Introduction

In the last two decades, metal–organic frameworks (MOFs) with well-regulated network structures have provoked significant interest as functional materials displaying potential applications in such fields as magnetism, molecular separation, catalysis, luminescence, and molecule storage [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Consequently, a variety of MOFs have been reported. However, much work on MOFs has been focusing on the design of lanthanide homometallic system, some interesting efforts have been contributed in the field of the molecular magnetism of lanthanide ions [13], [14], [15]. However, the chemistry towards heterometallic MOFs has attracted much less attention. Recently, some lanthanide–transition heterometallic complexes have been successfully obtained from spontaneous assembly of mixed metal ions and ligands containing hybrid donor atoms, such as cyanide [16], carbonyl [17], pyridine-carboxylate ligand [18], amino acids [19], [20] and so on. The assembly of three-dimensional (3D) heterometallic complexes, however, is still a formidable task due to the variable and versatile coordination numbers of the lanthanide ions, their low stereochemical preference and also because of competitive reactions between lanthanide and transition metals coordinated to the same organic ligands. As is well-known, the lanthanides have a strong tendency to coordinate to O-donor atoms to form lanthanide-carboxylate coordination polymers [21], and compared to the Ln(III) ions, the transition metal easily bonds to the N-donor atoms [22]. Thus, if a ligand containing both N-donor and O-donor atoms and the transition metal could be introduced to link the lanthanide-carboxylate subunits successfully, the novel heterometallic coordination polymers may be obtained through the recognition of the metal ions and their coordinating atoms [23].

On the other hand, great interest in Ln–Ag heterometallic complexes is recently focused on the nicotinic acid or isonicotinic acid [24], [25], [26], [27], [28]. Compared with these two N-heterocyclic acids, pyridine-3,4-dicarboxylic acid (H2pydc) can show richer coordination modes due to its two carboxylate groups, accordingly, it is an excellent candidate for the construction of metal organic frameworks. Although the synthesis of the monometallic coordination polymers based on H2pydc ligand has become widespread over the recent years [29], [30], [31], [32], [33], [34], [35], investigations on heterometallic coordination polymers containing H2pydc has not been extensively explored until now [24]. In this paper, we chose pyridine-3,4-dicarboxylic acid as a bifunctional bridging ligand possesses of oxygen and nitrogen donors, which can be chose to as a potential linker between the lanthanide centers and the Ag centers. Herein, we report on the syntheses, crystal structures, luminescence and magnetic properties of two novel 4d–4f heterometallic coordination polymers, [AgSm(pydc)2]·2H2O (1) and [AgTb(pydc)2]2·H2O (2).

Section snippets

Materials and methods

All commercially available chemicals and solvents are of reagent grade and were used as received without further purification. Elemental analyses (C, H and N) were performed on a Vario EL III elemental analyzer. Infrared spectra were performed on a Nicolet AVATAR-360 spectrophotometer with KBr pellets in the 400–4000 cm−1 region. The luminescent spectra for the powdered solid samples were measured at room temperature on an Aminco Bowman Series 2 spectrophotometer with a xenon arc lamp as the

Crystal structure of complexes 1 and 2

Since 1 and 2 are isostructural, the structure of 1 is described representatively. The single-crystal X-ray analysis reveals complex 1 crystallizes in the triclinic space group P1¯ and exhibits a novel 3D heterometallic coordination framework. As shown in Fig. 1, there are one Sm(III) ion, one Ag(I) ion, two crystallographically unique pydc ligands and two lattice water molecules in the asymmetric unit. Each Sm(III) ion is coordinated by nine oxygen atoms from six pydc ligands in a distorted

Conclusion

In conclusion, we have successfully synthesized two new 4d–4f coordination polymers based on pyridine-3,4-dicarboxylic acid. It represents an unusual structural example of heterometallic coordination polymer by spontaneous assembly of N-/O-donor ligands. The strong photoluminescent properties of complexes 1 and 2 may make it excellent candidates for potential photoactive materials. Magnetic study on complexes 1 and 2 shows that antiferromagnetic interactions dominate between the Ln(III)

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Nos. 20971004, 21171097), the Key Project of Chinese Ministry of Education (No. 210102) and the Natural Science Foundation of Anhui Province (No. 11040606M45).

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