Inorganic Chemistry Communications 16 (2012) 95–99

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Inorganic Chemistry Communications

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Two novel 3D microporous heterometallic 3d–4f coordination frameworks withunique (7, 8)-connected topology: Synthesis, crystal structure andmagnetic properties

Xia Zhao a, Xiao-Ping Ye a,b, Li-Mei Chang a, Zhi-Qiang Wei a, Wen-Jing Liu a, Shan-Tang Yue a,⁎,Ying-Liang Liu c, Hai-Hong Mo a, Yue-Peng Cai a

a School of Chemistry and Environment, South China Normal University, Guangzhou 510006, PR Chinab Department of Chemical Engineering, Huizhou University, Huizhou 516007, PR Chinac Department of Chemistry, Jinan University, Guangzhou 510632, PR China

⁎ Corresponding author. Tel./fax: +86 20 39310187.E-mail address: yuesht@scnu.edu.cn (S.-T. Yue).

1387-7003/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.inoche.2011.12.004

a b s t r a c t

a r t i c l e i n f o

Article history:Received 7 November 2011Accepted 1 December 2011Available online 10 December 2011

Keywords:Hydrothermal synthesisHeterometallicMicroporousMagnetism

Two new 3D 3d–4f heterometallic microporous metal-organic frameworks, named, [Ln2Ni(Himdc)2(aip)2(H2O)4]·6H2O [Ln=Nd (1), La (2); H3imdc=imidazole-4,5-dicarboxy acid; aip=5-aminoisophthalic acid],have been successfully synthesized through the reaction of Ln2O3, NiSO4·6H2O, H3imdc, aip and H2O. Com-pounds 1 and 2 are isomorphic, displaying rare interesting 3D heterometallic networks with (7, 8)-connectedtopology based on the linkages of 2D layers and 1D zigzag chains. In addition, the magnetic properties of thetwo compounds have been investigated.

© 2011 Elsevier B.V. All rights reserved.

The current interests in microporous metal-organic frameworks(MMOFs) is increasing because of their potential applications in mag-netism, photoluminescence, gas storage, ion exchange, separation,and fascinating structural topologies [1–6]. Up to now, most reportshave been focused on monometallic 3D MMOFs [7], while theheterometallic MMOFs received less attention [8]. From a syntheticview, the assembly of extended structure with 3D lanthanide-transition heterometallic coordination frameworks is a challengingwork, because there are many complicated factors: (1) the choice of or-ganic ligands; (2) the control of second ligands; (3) the competitive re-action between lanthanide and transition metal ions. Fortunately,lanthanide and transition metal ions have different affinities for N- andO- donors, providing a basis that can be used in construction of unusualmulti-dimensional heterometallic coordination frameworks with usefulphysical–chemical properties and various structural topologies. The li-gands used should possess ligating functional groups that are able to ef-fectively coordinate to both lanthanide and transition metal ionssimultaneously. The ligands containing mixed-donor atoms, such as pyr-idinecarboxylate [9], pyrazinecarboxylate [10], imidazolecarboxylate[11], can be used to construct heterometallic coordination polymerseffectively.

Recently, our interest is focused on the ligand imidazole-4, 5-dicarboxylate acid (H3imdc), which is an excellent proton donor

rights reserved.

that provides various coordination modes [13b]. H3imdc can becompletely or partially deprotonated at different pH values [12].Within the ligand, the two adjacent carboxylate groups of H3imdccould coordinate with both Ln(III) ions and transition metals, andthe two nitrogen atoms of the imidazole ring could connect simulta-neously 3d metal ions in suitable reaction conditions. As reported,some 3d–4f heterometallic transition–lanthanide metal-organicframeworks have been synthesized using H3imdc as a multi-functional ligand [11c,13]. However, most of the transition metal cen-ter is always Zn(II) [13b,e] or Ag(I) [13d], Ni(II) center is rarelyreported. With this in mind, we chose 5-aminoisophthalic acid (aip)as a secondary ligand, and the hydrothermal reaction of NiSO4·6H2O,Ln2O3, H3imdc,with aip gave rise to twonewNi(II)–Ln(III) heterometallicMMOFs, [Ln2Ni(Himdc)2(aip)2(H2O)4]·6H2O [Ln=Nd (1) , La (2)] [14].

Both of the two compounds were characterized by element analy-sis, IR spectroscopy, and single-crystal X-ray diffraction. Their mag-netic properties were studied with dc magnetic susceptibilitymeasurements. In the IR spectra of compounds 1 and 2, the featuresat 1551–1611 cm−1 and 1383–1431 cm−1 can be associated withthe asymmetric and symmetric stretching vibrations of carboxylategroups. Broad band in 3130–3424 cm−1 can be ascribed to the vibra-tions of water molecules.

Single crystal X-ray diffraction studies [15] revealed that com-pounds 1 and 2 are isomorphic, thus the structure of compound 1 isselected to describe in detail here. Compound 1 crystallizes in triclinicsystem, space group Pī. As shown in Fig. 1, there are one Ni(II) ion,one Nd(III) ion, one Himdc anion, one aip anion, two coordinated

Fig. 1. Coordination environments of the Ni and Nd atoms in 1. All H atoms and noncoordi-nated water molecules are omitted for clarity. Symmetry code: (a: 1+x, –1+x, z; b: 1−x,1−y, –z; c: 1+x, y, z; d: 1−x, 1−y, 1−z).

96 X. Zhao et al. / Inorganic Chemistry Communications 16 (2012) 95–99

and three free water molecules in the asymmetric unit. The Nd(III)center is coordinated by ten oxygen donors: four from two H3imdc li-gands, four from two aip ligands and two oxygen atoms from two co-ordinated water molecules. To our knowledge, the coordinationnumber of Nd(III) is usually eight or nine, however, the coordinationnumber in this case is ten [16]. The Nd–O bond distances range from2.072 (3) to 2.667(4) Å. The bond angles of O–Nd–O are in range of49.23(11) to 160.22(12)°. The Ni(II) is six-coordinated with twoHimdc–N atoms, two aip–N atoms and two Himdc–O atoms. TheNi–N bond distances are in the range of 2.034(4) to 2.178(4) Å, Ni–O bond distance is 2.072(3) Å.

In this structure, the Himdc ligand exhibits only one coordinationmode (Scheme 1): the nitrogen atom and one of the 4-carboxylateoxygen atom chelates to the Ni(II) center, the rest of the oxygenatom from 4-carboxylate and one oxygen atom from the 5-carboxylate coordinates to Nd(III) center via a chelating mode, and

Scheme 1. Coordination modes of Himdc and aip ligands.

the two oxygen atoms in 5-carboxylate also exhibit a chelatingmode coordinating with another Nd(III) center. It should be notedthat, two Himdc ligands link two different Nd(III) centers to formNd2 structure. To the aip ligand, its two carboxylate groups coordi-nate to two different Nd(III) centers through chelating coordinationmode respectively, and the nitrogen atom only coordinates with Ni(II) center. As the bridging coordination of aip ligands, the adjacentNd2 structures are connected to form 1D polymer zigzag chain archi-tectures (Fig. 2). Furthermore, the Himdc and aip ligands connect 1Dzigzag chains and Ni(II) centers to form 2D heterometallic layer struc-tures (Fig. 3a). Due to the coordination mode of the aip ligands, the2D heterometallic layers are further linked by bridging aip ligandsto form 3D heterometallic networks that generate microporous struc-tures (Fig. 3b). Calculating using PLATON [17] based on crystal struc-ture show that the total solvent-accessible volume comprises of 14%of the crystal volume. Topological studies performed using the soft-ware package TOPOS 4.0 [18b] reveal that this topology is a new(7,8)-connected net (Fig. 4) with Schläfli symbol (34;410;510;64)(34;48;58;6)2 [18].

To examine the thermal stabilities of the two compounds, thermo-gravimetric analyses were carried out at a heating rate of10 °C min−1 under an air atmosphere as shown in Fig. S1. The twocompounds show similar thermal behaviors and undergo two stepsof weight loss. In the temperature range of 30–90 °C, the three freewater molecules and one coordinated water molecule were lost stepby step, a weight loss approximate 11% was noticed (calcd 10.6%).The continuous loss from 280 to 330 °C is caused by the other threecoordinated water molecules (calcd/found: 4.3%/4.5%). Above390 °C, the ligands decompose, resulting in the collapse of theframework.

The solid-state dc magnetic susceptibility measurements for com-pounds 1 and 2 were performed in the range of 2–300 K under thefield of 5 KOe. The magnetic behavior of 1 is shown in Fig. 5 as plotsof χMT vs T and 1/χM vs T, where χM is the molecular magnetic sus-ceptibility. The room temperature χMT is 4.51 cm3·K·mol−1, higherthan the spin-only value 3.38 cm3·K·mol−1, expected for one NiII

and two NdIII cations. [19]. As the temperature was lowed from300 K to 2 K, the χMT value steadily decreased to 1.83 cm3·K·mol−1,which reveals an antiferromagnetic behavior in 1. The temperaturedependent 1/χM value obey the Curie–Weiss law with Curie constantC=4.53 cm3·K·mol−1 and Weiss constant θ=−11.72 K. The nega-tive Weiss constant also gives the evidence of antiferromagnetic in-teractions existing in compound 1.

The magnetic behavior of 2 is shown in Fig. 6, as plots of χMT vs Tand 1/χM vs T, where χM is the molecular magnetic susceptibility.The room-temperature χMT value is 1.22 cm3·K·mol−1(μeff=3.12μB),which is slightly higher than the calculated value of μeff=2.83μB(S=1, g=2) [20]. The magnetic properties of the compound weremainly ascribed to the paramagnetic Ni(II) cations and their magneticcouplings. As the temperature lowered from 300 K to 2 K, the χMTvalue decreased steadily from 1.22 cm3·K·mol−1 to0.88 cm3·K·mol−1, which reveals an antiferromagnetic behavior incompound 2. The temperature dependent 1/χM value obey the Curie–Weiss law with Curie constant C=1.22 cm3·K·mol−1 and Weiss con-stant θ=−1.82 K. The negativeWeiss constant also gives the evidenceof antiferromagnetic interactions existing in compound 2.

Fig. 2. View of a 1D zigzag chain architecture in compound 1.

Fig. 3. (a) The 2D layer structure of compound 1. (b) View of 3D framework for 1.

97X. Zhao et al. / Inorganic Chemistry Communications 16 (2012) 95–99

Up to date, the understandings of the magnetic interactions con-taining rare-earth ions in molecular magnets are still a challenge.There exist antiferromagnetic and/or ferromagnetic couplings withinthe 3d–4f heterometallic compounds as depicted in literatures [21].However, in compound 2, the magnetic properties were mainly as-cribed to the paramagnetic Ni(II) cations and their magnetic cou-plings. Further experiments are needed for better understanding thenature of the 3d–4f magnetic interactions.

In summary, we have successfully synthesized two novel 3D 3d–4fheterometallic microporous compounds under hydrothermal condi-tions. The compounds show an interesting 3D heterometallic networkwith (7, 8)-connected topology, containing 2D layer based on thelinkage of Ni(II) ions and the 1D zigzag chains. The key point of thesynthetic procedures has been well established. The hydrothermalsynthesizing method has been proved to be effective to obtain thesecompounds. Moreover, both compounds exhibit antiferromagneticbehaviors.

Acknowledgements

We are thankful for the financial support from NSFC (Grants20971047 and U0734005), Guangdong Provincial Science and Tech-nology Bureau (Grant 2008B010600009) and Key Research Programof Guangdong Provincial Universities Science and Technology Innova-tion (Grant cxzd1020).

Appendix A. Supplementary material

CCDC 836711, 836712 contain the supplementary crystallographicdata for 1–2. These data can be obtained free of charge from The Cam-bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/

Fig. 4. The (7, 8) net where the Ni(II) and Nd(III) centers are treated as nodes and theHimdc and aip ligands are treated as linkers.

data_request/cif, or from the Cambridge Crystallographic Data Cen-tre, 12 Union Road, CambridgeCB2 1EZ, UK[Fax:+44(1223)336-033; E-mail: deposit@ccdc.cam.ac.uk]. Supplementary data associated

Fig. 5. χMT vs T and 1/χM vs T of compound 1.

Fig. 6. χMT vs T and 1/χM vs T of compound 2.

98 X. Zhao et al. / Inorganic Chemistry Communications 16 (2012) 95–99

with this article can be found, in the online version, at doi:10.1016/j.inoche.2011.12.004.

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[14] Synthesis of compound 1 and 2: A mixture of NiSO4 (0.3 mmol), Ln2O3

(0.3 mmol), 5- aminoisophthalic acid (0.5 mmol), imidazole-4, 5-dicarboxylicacid (0.3 mmol) and water (10 ml) was loaded into a 25 mL Telflon-linedautoclave, and heated at 160 °C for 4 days. After it was cooled to room temperatureat a rate of 4 °C /h, purple block crystals were collected and dried in air. 1: Anal.Calcd for C26H34N6Nd2O26Ni: C, 26.12; H, 2.87; N, 7.09%. Found: C, 26.16; H, 2.85;N, 7.84%. IR(KBr, cm-1): 3366 m, 3131 s, 1612vs, 1554vs, 1385vs, 1151 s, 954 m,804 m, 727 m, 660w, 545 m. 2: Anal. Calcd for C26H34N6La2O26Ni: C, 26.35; H,2.82; N, 7.13%. Found: C, 26.39; H, 2.87; N, 7.09%. IR(KBr, cm-1): 3427 m, 3128w,1619 s, 1556vs, 1378vs, 1151 s, 961 m, 815 m, 733w, 536 m.

[15] Crystal data for compound 1: Triclinic, Pī, a=7.2904(16) Å, b=9.2414(15) Å,c=14.014(2) Å, α=83.886(2) ° β=85.398(2)° γ=72.647(3) ° V=894.9(2) Å3,Z=1, Dc =2.215, F(000)=588.0, GOF=1.024, R1(I>2σ(I))=0.0332(3178), and

wR2 (all data)=0.0838(3628). 2: Triclinic, Pī, a=7.2918(16) Å, b=9.340(2) Å,c=14.129(3) Å, α=83.816(3) ° β=85.461(3)° γ=72.646(3) ° V=912.0(3) Å3,Z=1, Dc=2.154, F(000)=582.0, GOF=1.017, R1(I>2σ(I))=0.0415(2874), andwR2 (all data)=0.0961(3380).

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