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One three-dimensional Gd(III) coordination polymer with 1,2-phenylenediacetate exhibiting ferromagnetic interaction and large magnetocaloric effect
Inorganic Chemistry Communications 87 (2018) 20–23
Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Short communication
One three-dimensional Gd(III) coordination polymer with 1,2-phenylenediacetate exhibiting ferromagnetic interaction and large magnetocaloric effect Zhong-Yi Li a, Jing-Yu Li b, Lian-Lian Pei a, Xiang-Fei Zhang a, Guang-Xiu Cao a,⁎, Chi Zhang a, Su-Zhi Li a, Bin Zhai a,⁎ a
Engineering Research Center of Photoelectric Functional Material, Henan Key Laboratory of Biomolecular Recognition and Sensing, College of Chemistry and Chemical Engineering, Shangqiu Normal University, Shangqiu 476000, PR China b School of business administration, Zhengzhou University of Aeronautics, Zhengzhou 450046, PR China
a r t i c l e
i n f o
Article history: Received 30 September 2017 Received in revised form 13 November 2017 Accepted 22 November 2017 Available online 27 November 2017 Keywords: Gadolinium(III) 3D polymer Ferromagnetic behaviour Magnetocaloric effect
a b s t r a c t One three-dimensional Gd(III) coordination polymer with 1,2-phenylenediacetate (PDA2 −), [Gd2(PDA)3(H2O)2]·3H2O (1), has been successfully synthesized and characterized. Single crystal X-ray diffraction analysis shows that 1 consists of 1D wave Gd-based chain unit and PDA2− linker. Magnetic studies suggest the presence of ferromagnetic Gd⋯Gd coupling in the 1D chain unit of 1. Meanwhile, 1 has a significant cryogenic magnetocaloric effect with the maximum −ΔSm of 33.44 at 2 K and 7 T. © 2017 Published by Elsevier B.V.
In the last two decades, lanthanide-based coordination polymers (Ln-CPs) have attracted an increasing interest because of not only their various fascinating topologies, but also their potential applications in cryogenic magnetic refrigeration and high-density information storage [1–3]. For the different local magnetic anisotropy and the largespin multiplicity of the spin ground-state, Ln3+ ions have been used to construct either single-molecule magnets (SMMs) and single-chain magnets (SCMs), especially for highly anisotropic Tb- and Dy-based systems [4,5], or as low-temperature molecular magnetic coolers for isotropic Gd-containing analogues [6–8]. Specifically, magnetic refrigerants, which were appraised by magnetocaloric effect (MCE), is of great interest to chemists in recent years due to the energy-efficient and environmentally friendly advantages as well as the potential to replace the rare and expensive He-3 in ultralow-temperature refrigeration [9–11]. The MCE stands for the change of isothermal magnetic entropy (− ΔSm) and adiabatic temperature (ΔTad) in change of applied magnetic field [12,13]. To obtain a large –ΔSm, it is usually requisite that a molecular contains the features of a large spin ground state S, negligible magnetic anisotropy, low-lying excited spin states, weak coupling and a high magnetic density (or a large metal/ligand mass ratio) [14–16]. Thus, Gd-containing CPs with light and multidentate organic ligands are promising candidates because the isotropic Gd(III) ion has a large spin ⁎ Corresponding authors. E-mail addresses: [email protected] (G.-X. Cao), [email protected] (B. Zhai).
https://doi.org/10.1016/j.inoche.2017.11.014 1387-7003/© 2017 Published by Elsevier B.V.
value (S = 7/2) and usually shows weak superexchange interactions, and the light ligands could promote a large metal/ligand mass ratio [13,15]. So far, a lot of Gd-based molecular clusters and coordination polymers with significant MCE have been reported under this principle [12–18]. Compared with the discrete and one-dimensional (1D) analogues, the Gd-based two- (2D) and three-dimensional (3D) CPs may be better for obtaining a promising MCE, when considering the enhanced magnetic density due to the sharing of bridging ligands between magnetic centers and that the nonmagnetic guest or solvent molecules are more difficult to trap in such structures [19–21]. However, the highdimensional, especially for 3D Gd-based CPs with remarkable MCEs are still limited, and further systematic study is still necessary and important to find their potential for cryogenic application. To build such material, 1,2-phenylenediacetic acid (H2PDA), which could display various bridging modes to metal ions [22], was selected as functional ligand to react hydrothermally with Gd(III) ion. As a result, one 3D Gd-based coordination polymer, [Gd2(PDA)3(H2O)2]·3H2O (1), was obtained, and its crystal structure and magnetic properties were discussed. Single crystal X-ray diffraction analysis reveals that compound 1 crystallizes in the monoclinic C2/c space group and has a 3D framework structure. As shown in Fig. 1a, the asymmetric unit of 1 contains one Gd(III) ion, one and a half PDA2− ligands, one coordinated water molecule as well as one and a half lattice water molecules. The Gd(III) ion is nine-coordinated and has a distorted monocapped square antiprismatic
Z.-Y. Li et al. / Inorganic Chemistry Communications 87 (2018) 20–23
Fig. 1. (a) Coordination environment of the asymmetric Gd3+ ion in 1. Symmetry codes: A, x, 1-y, −0.5 + z; B, 0.5 − x, −0.5 + y, 1.5 − z; C, 0.5 − x, 1.5 − y, 1 − z; (b) The 1D chain-shaped [Gd(COO)3] building unit formed by the neighboring Gd(III) ions and carboxyl group of the PDA2− ligand in 1; (c) View of the 3D framework structure of 1 along c axis.
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110.13(15)°. For mode II, the PDA2− ligand uses two tridentate bridging carboxylate groups to link four Gd(III) ions with the Gd-O-Gd angle of 111.37(15)°. Around every Gd(III) ion, there are six PDA2 − ligands. The neighboring Gd(III) ions are connected together by one bidentate bridging carboxyl and two tridentate bridging carboxyls from three PDA2 − ligands (mode I and mode II) to result in a 1D wave [Gd(COO)3] chain unit (Fig. 1b). The Gd·Gd distance is 4.03(1) Å and the Gd–O–Gd–O dihedral angle is 12.78(1)° (Fig. S1). The neighboring chains are linked together by the other carboxyls of the PDA2− ligands to form a 3D framework structure (Fig. 1c and S2). As shown in Fig. S3, when the lanthanide connectivity alone is considered in the structure, a 3D quasi-honeycomb arrangement is observed. For each hexagonal “honeycomb” unit, two paralleled sides are fastened by the PDA2− ligands of mode II with the shortest interchain Gd·Gd distance of 9.40(1) Å. While the others are fixed by the PDA2− ligands of mode I. The shortest interchain Gd···Gd distance is 7.84(1) Å. The thermal stability of 1 was studied by thermogravimetric (TG) analysis in a nitrogen atmosphere from 25 to 900 °C. As shown in Fig. S4, the TG curve of 1 displays three mass steps. In the first step, the weight loss of 1 in the range of 25–140 °C is 9.48%, which can be attributed to the loss of two coordinated and three free water molecules for each formula unit (calculated 9.18%). Then, the weight of 1 keeps constant between 140 and 334 °C, suggesting that it is thermal stable even up to 334 °C. After 334 °C, a striking weight loss was observed, indicating the complete decomposition of the framework. The experimental and computer simulated powder X-ray diffraction (PXRD) patterns of 1 are shown in Fig. S5. The PXRD pattern of the bulk sample is in good agreement with its simulated pattern from the single crystal structure, demonstrating the phase purity. The magnetic susceptibility of 1 has been researched in the temperature range of 2–300 K under an applied direct current (dc) magnetic field of 1000 Oe (Fig. 2). At 300 K, the χMT value of 1 is 15.24 cm3 mol−1 K, which is close to the expected value of 15.76 cm3 mol−1 K calculated for two spin-only Gd(III) (S = 7/2, g = 2) ions. With lowering the temperature, the χMT values of 1 remain almost constant before 30 K, and then increase quickly to 20.12 cm3 mol−1 K at 2 K. The data fit the Curie– Weiss law well in the temperature range of 2–300 K with Curie constant C = 15.38 cm3 K mol−1 and Weiss constant θ = 0.46 K (Fig. S6). The positive θ value and the increase of χMT values suggest the presence of ferromagnetic interactions between adjacent Gd(III) ions in the 1D chain unit of 1.
geometry, completed by eight oxygen atoms (O1, O1A, O1A, O3B, O4C, O5, O5A and O6A) from six PDA2− ligands and one oxygen atom (O7) from terminal water molecule. The bond lengths of Gd–O and the angles of O–Gd–O are in the range of 2.309(4)–2.512(5) Å and 52.24(15)– 151.48(15)°, respectively, which are consistent with those in the reported Gd-containing compounds [5,11]. In the structure, the PDA2− ligands adopt two coordination modes, μ4-η2: η1: η1: η1 and μ4-η2: η1: η2: η1 (Scheme 1). For mode I, the PDA2− ligand has one tridentate bridging and one bidentate bridging carboxylate group to bridge four Gd(III) ions. The angle of Gd-O-Gd is
Scheme 1. Coordinate modes of PDA2− ligands in 1.
Fig. 2. Temperature dependence of the χMT (−■-) and χM (−●-) values for 1 at 1000 Oe dc magnetic field. The red solid lines represent the best fit to the data. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Z.-Y. Li et al. / Inorganic Chemistry Communications 87 (2018) 20–23
Fig. 3. (a) Field dependence of the magnetization plots of 1 at the indicated temperatures. (b) − ΔSm calculated from the magnetization data of 1 at various fields and temperatures.
According to the crystal structure of 1 mentioned above, the Gd⋯Gd distance within the uniform chain unit is 4.03(1) Å, shorter than those between adjacent chains linked through the PDA2 − bridge (longer than 7.8 Å). Therefore, the main exchange interactions can be assumed to be 1D chain model, and the following expressions deduced by Fisher could be used to quantitatively analyze the interaction between adjacent Gd3+ ions with S = 7/2 [3,23,24]. χchain ¼
Ng2 β2 1 þ u SðS þ 1Þ 3kT 1‐u
ð1Þ
where, u = cth(JS(S + 1)/kT) − kT/JS(S + 1) χM ¼
χ 0 chain 1‐ zJ χchain =Ng 2 β2
ð2Þ
In the equation, N is Avogadro's number, β is the Bohr magnetron, k is the Boltzmann constant, J is the exchange coupling parameter between adjacent intrachain spins, and the interchain interaction (zJ′) is treated by the molecular field approximation. The best fit results in g = 2.00(1), J = 0.012(1) cm−1, zJ′ = 0.031(1) cm−1 and R = 7.82 × 10−4, where R is calculated from Σ[(χMT)obsd − (χMT)calcd]2/ Σ[(χMT)obsd]2. The positive and small J value is in good agreement with the reported values for other carboxyl-bridged Gd-containing complexes [3,24,25], verifying the presence of weak Gd–Gd ferromagnetic coupling interaction in the 1D chain in 1. When the magnetostructural relationship was considered, the ferromagnetic behavior may be closely related with the bigger Gd−O−Gd angle (N 110°) and suitable Gd−Gd bond length (4.06 Å) as well as the Gd–O–Gd–O dihedral angle of 12.78(1)° in the 1D chain unit, which is in keeping with the results reported in some literatures [3,25,26]. Magnetization measurements for 1 were carried out in a field of 0–7 T between 2 and 7 K (Fig. 3a). The M versus H data reveal a steady increase in magnetization to come up to a maximum value of 13.95 Nβ for 1 at 2 K and 7 T, which is close to the expected value of 14 Nβ for two uncoupled Gd(III) (S = 7/2, g = 2) ions. To evaluate the MCE, the magnetic entropy change of 1 can be obtained from the magnetization change as a function of applied field and temperature (Fig. 4b) by using the Maxwell equation ΔSm(T) = [∂M(T,H)/∂T]HdH [4,17]. The resulting maximum − ΔSm is 33.44 J K−1 kg−1 for ΔH = 7 T at 2.0 K, which is considerable large value, and comparable with those for the reported interesting Gd-based frameworks [15,25]. Theoretically, the full entropy change per mole of complex corresponding to two Gd3 + ions is 35.24 J K−1 kg−1, as calculated from the equation 2Rln(2S + 1) with S = 7/2. The difference of −ΔSm between the theoretical and experimental values may be due to the MW/NGd ratio of 491 (where MW is the molecular mass of 981.07 g mol−1 and NGd is the number of Gd3+ ion in per mole of 1) and the weak magnetic interaction in 1 [16,17].
In summary, one 3D Gd-based coordination polymer (1) with 1D wave chain unit has been successfully synthesized hydrothermally based on PDA2 − ligand. Magnetic studies reveal that 1 displays intrachain Gd ⋯ Gd ferromagnetic coupling and significant cryogenic MCE with the maximum −ΔSm value of 33.44 at 2 K and 7 T. These results confirm that multidentate organic ligand may be promising candidate for constructing high-dimensional Gd-based magnetic refrigerant. Acknowledgements The work on this paper were supported by the National Natural Science Foundation of China (NSFC) (grant numbers 21401126, 21371114, 21571123, 21601119, 21471095), Scientific and Technological Projects of Science and Technology Department of Henan province (172102210437). Appendix A. Supplementary material Experimental section, Crystallographic data, additional structure, magnetic data and TGA curve, PXRD patterns. CCDC 1576909 (1) contains the supplementary crystallographic data for this paper. Supplementary data to this article can be found online at https://doi.org/10. 1016/j.inoche.2017.11.014. References [1] (a) Y. Liu, Z. Chen, J. Ren, X.Q. Zhao, P. Cheng, B. Zhao, Inorg. Chem. 51 (2012) 7433–7435; (b) M. Zhu, X.L. Mei, Y. Ma, L.C. Li, D.Z. Liao, J.P. Sutter, Chem. Commun. 50 (2014) 1906–1908; (c) Z.Y. Li, J.S. Yang, R.B. Liu, J.J. Zhang, S.Q. Liu, J. Ni, C.Y. Duan, Dalton Trans. 41 (2012) 13264–13266; (d) P. Hu, H.F. Guo, Y. Li, F.P. Xiao, Inorg. Chem. Commun. 59 (2015) 91–94. [2] Z.Y. Li, B. Zhai, S.Z. Li, G.X. Cao, F.Q. Zhang, X.F. Zhang, F.L. Zhang, C. Zhang, Cryst. Growth Des. 16 (2016) 4574–4581. [3] A.K. Mondal, H.S. Jena, A. Malviya, S. Konar, Inorg. Chem. 55 (2016) 5237–5244. [4] Y.L. Hou, G. Xiong, P.F. Shi, R.R. Cheng, J.Z. Cui, B. Zhao, Chem. Commun. 49 (2013) 6066–6068. [5] Y.C. Chen, L. Qin, Z.S. Meng, D.F. Yang, C. Wu, Z.D. Fu, Y.Z. Zheng, J.L. Liu, R. Tarasenko, M. Orendáč, J. Prokleška, V. Sechovskýe, M.L. Tong, J. Mater. Chem. A 2 (2014) 9851–9858. [6] X. Li, C.Y. Wang, X.J. Zheng, Y.Q. Zou, J. Coord. Chem. 61 (2008) 1127–1136. [7] Z.Y. Li, Y. Chen, X.Y. Dong, B. Zhai, X.F. Zhang, C. Zhang, F.L. Zhang, S.Z. Li, G.X. Cao, Cryst. Growth Des. 17 (2017) 3877–3884. [8] S.W. Zhang, W. Shi, L.L. Li, E.Y. Duan, P. Cheng, Inorg. Chem. 53 (2014) 10340–10346. [9] M.E. Fisher, Am. J. Phys. 32 (1964) 343–346. [10] Y.L. Hou, R.R. Cheng, G. Xiong, J.Z. Cui, B. Zhao, Dalton Trans. 43 (2014) 1814–1820. [11] F.S. Guo, J.D. Leng, J.L. Liu, Z.S. Meng, M.L. Tong, Inorg. Chem. 51 (2012) 405–413. [12] T. Rajeshkumar, S.K. Singh, G. Rajaraman, Polyhedron 52 (2013) 1299–1305. [13] Y.Z. Zheng, G.J. Zhou, Z.P. Zheng, R.E.P. Winpenny, Chem. Soc. Rev. 43 (2014) 1462–1475. [14] S.W. Zhang, E.Y. Duan, P. Cheng, J. Mater. Chem. A 3 (2015) 7157–7162. [15] (a) Y.F. Han, X.Y. Li, L.Q. Li, C.L. Ma, Z. Shen, Y. Song, X.Z. You, Inorg. Chem. 44 (2010) 10781–10787;
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Contents lists available at ScienceDirect
Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche
Short communication
One three-dimensional Gd(III) coordination polymer with 1,2-phenylenediacetate exhibiting ferromagnetic interaction and large magnetocaloric effect Zhong-Yi Li a, Jing-Yu Li b, Lian-Lian Pei a, Xiang-Fei Zhang a, Guang-Xiu Cao a,⁎, Chi Zhang a, Su-Zhi Li a, Bin Zhai a,⁎ a
Engineering Research Center of Photoelectric Functional Material, Henan Key Laboratory of Biomolecular Recognition and Sensing, College of Chemistry and Chemical Engineering, Shangqiu Normal University, Shangqiu 476000, PR China b School of business administration, Zhengzhou University of Aeronautics, Zhengzhou 450046, PR China
a r t i c l e
i n f o
Article history: Received 30 September 2017 Received in revised form 13 November 2017 Accepted 22 November 2017 Available online 27 November 2017 Keywords: Gadolinium(III) 3D polymer Ferromagnetic behaviour Magnetocaloric effect
a b s t r a c t One three-dimensional Gd(III) coordination polymer with 1,2-phenylenediacetate (PDA2 −), [Gd2(PDA)3(H2O)2]·3H2O (1), has been successfully synthesized and characterized. Single crystal X-ray diffraction analysis shows that 1 consists of 1D wave Gd-based chain unit and PDA2− linker. Magnetic studies suggest the presence of ferromagnetic Gd⋯Gd coupling in the 1D chain unit of 1. Meanwhile, 1 has a significant cryogenic magnetocaloric effect with the maximum −ΔSm of 33.44 at 2 K and 7 T. © 2017 Published by Elsevier B.V.
In the last two decades, lanthanide-based coordination polymers (Ln-CPs) have attracted an increasing interest because of not only their various fascinating topologies, but also their potential applications in cryogenic magnetic refrigeration and high-density information storage [1–3]. For the different local magnetic anisotropy and the largespin multiplicity of the spin ground-state, Ln3+ ions have been used to construct either single-molecule magnets (SMMs) and single-chain magnets (SCMs), especially for highly anisotropic Tb- and Dy-based systems [4,5], or as low-temperature molecular magnetic coolers for isotropic Gd-containing analogues [6–8]. Specifically, magnetic refrigerants, which were appraised by magnetocaloric effect (MCE), is of great interest to chemists in recent years due to the energy-efficient and environmentally friendly advantages as well as the potential to replace the rare and expensive He-3 in ultralow-temperature refrigeration [9–11]. The MCE stands for the change of isothermal magnetic entropy (− ΔSm) and adiabatic temperature (ΔTad) in change of applied magnetic field [12,13]. To obtain a large –ΔSm, it is usually requisite that a molecular contains the features of a large spin ground state S, negligible magnetic anisotropy, low-lying excited spin states, weak coupling and a high magnetic density (or a large metal/ligand mass ratio) [14–16]. Thus, Gd-containing CPs with light and multidentate organic ligands are promising candidates because the isotropic Gd(III) ion has a large spin ⁎ Corresponding authors. E-mail addresses: [email protected] (G.-X. Cao), [email protected] (B. Zhai).
https://doi.org/10.1016/j.inoche.2017.11.014 1387-7003/© 2017 Published by Elsevier B.V.
value (S = 7/2) and usually shows weak superexchange interactions, and the light ligands could promote a large metal/ligand mass ratio [13,15]. So far, a lot of Gd-based molecular clusters and coordination polymers with significant MCE have been reported under this principle [12–18]. Compared with the discrete and one-dimensional (1D) analogues, the Gd-based two- (2D) and three-dimensional (3D) CPs may be better for obtaining a promising MCE, when considering the enhanced magnetic density due to the sharing of bridging ligands between magnetic centers and that the nonmagnetic guest or solvent molecules are more difficult to trap in such structures [19–21]. However, the highdimensional, especially for 3D Gd-based CPs with remarkable MCEs are still limited, and further systematic study is still necessary and important to find their potential for cryogenic application. To build such material, 1,2-phenylenediacetic acid (H2PDA), which could display various bridging modes to metal ions [22], was selected as functional ligand to react hydrothermally with Gd(III) ion. As a result, one 3D Gd-based coordination polymer, [Gd2(PDA)3(H2O)2]·3H2O (1), was obtained, and its crystal structure and magnetic properties were discussed. Single crystal X-ray diffraction analysis reveals that compound 1 crystallizes in the monoclinic C2/c space group and has a 3D framework structure. As shown in Fig. 1a, the asymmetric unit of 1 contains one Gd(III) ion, one and a half PDA2− ligands, one coordinated water molecule as well as one and a half lattice water molecules. The Gd(III) ion is nine-coordinated and has a distorted monocapped square antiprismatic
Z.-Y. Li et al. / Inorganic Chemistry Communications 87 (2018) 20–23
Fig. 1. (a) Coordination environment of the asymmetric Gd3+ ion in 1. Symmetry codes: A, x, 1-y, −0.5 + z; B, 0.5 − x, −0.5 + y, 1.5 − z; C, 0.5 − x, 1.5 − y, 1 − z; (b) The 1D chain-shaped [Gd(COO)3] building unit formed by the neighboring Gd(III) ions and carboxyl group of the PDA2− ligand in 1; (c) View of the 3D framework structure of 1 along c axis.
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110.13(15)°. For mode II, the PDA2− ligand uses two tridentate bridging carboxylate groups to link four Gd(III) ions with the Gd-O-Gd angle of 111.37(15)°. Around every Gd(III) ion, there are six PDA2 − ligands. The neighboring Gd(III) ions are connected together by one bidentate bridging carboxyl and two tridentate bridging carboxyls from three PDA2 − ligands (mode I and mode II) to result in a 1D wave [Gd(COO)3] chain unit (Fig. 1b). The Gd·Gd distance is 4.03(1) Å and the Gd–O–Gd–O dihedral angle is 12.78(1)° (Fig. S1). The neighboring chains are linked together by the other carboxyls of the PDA2− ligands to form a 3D framework structure (Fig. 1c and S2). As shown in Fig. S3, when the lanthanide connectivity alone is considered in the structure, a 3D quasi-honeycomb arrangement is observed. For each hexagonal “honeycomb” unit, two paralleled sides are fastened by the PDA2− ligands of mode II with the shortest interchain Gd·Gd distance of 9.40(1) Å. While the others are fixed by the PDA2− ligands of mode I. The shortest interchain Gd···Gd distance is 7.84(1) Å. The thermal stability of 1 was studied by thermogravimetric (TG) analysis in a nitrogen atmosphere from 25 to 900 °C. As shown in Fig. S4, the TG curve of 1 displays three mass steps. In the first step, the weight loss of 1 in the range of 25–140 °C is 9.48%, which can be attributed to the loss of two coordinated and three free water molecules for each formula unit (calculated 9.18%). Then, the weight of 1 keeps constant between 140 and 334 °C, suggesting that it is thermal stable even up to 334 °C. After 334 °C, a striking weight loss was observed, indicating the complete decomposition of the framework. The experimental and computer simulated powder X-ray diffraction (PXRD) patterns of 1 are shown in Fig. S5. The PXRD pattern of the bulk sample is in good agreement with its simulated pattern from the single crystal structure, demonstrating the phase purity. The magnetic susceptibility of 1 has been researched in the temperature range of 2–300 K under an applied direct current (dc) magnetic field of 1000 Oe (Fig. 2). At 300 K, the χMT value of 1 is 15.24 cm3 mol−1 K, which is close to the expected value of 15.76 cm3 mol−1 K calculated for two spin-only Gd(III) (S = 7/2, g = 2) ions. With lowering the temperature, the χMT values of 1 remain almost constant before 30 K, and then increase quickly to 20.12 cm3 mol−1 K at 2 K. The data fit the Curie– Weiss law well in the temperature range of 2–300 K with Curie constant C = 15.38 cm3 K mol−1 and Weiss constant θ = 0.46 K (Fig. S6). The positive θ value and the increase of χMT values suggest the presence of ferromagnetic interactions between adjacent Gd(III) ions in the 1D chain unit of 1.
geometry, completed by eight oxygen atoms (O1, O1A, O1A, O3B, O4C, O5, O5A and O6A) from six PDA2− ligands and one oxygen atom (O7) from terminal water molecule. The bond lengths of Gd–O and the angles of O–Gd–O are in the range of 2.309(4)–2.512(5) Å and 52.24(15)– 151.48(15)°, respectively, which are consistent with those in the reported Gd-containing compounds [5,11]. In the structure, the PDA2− ligands adopt two coordination modes, μ4-η2: η1: η1: η1 and μ4-η2: η1: η2: η1 (Scheme 1). For mode I, the PDA2− ligand has one tridentate bridging and one bidentate bridging carboxylate group to bridge four Gd(III) ions. The angle of Gd-O-Gd is
Scheme 1. Coordinate modes of PDA2− ligands in 1.
Fig. 2. Temperature dependence of the χMT (−■-) and χM (−●-) values for 1 at 1000 Oe dc magnetic field. The red solid lines represent the best fit to the data. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 3. (a) Field dependence of the magnetization plots of 1 at the indicated temperatures. (b) − ΔSm calculated from the magnetization data of 1 at various fields and temperatures.
According to the crystal structure of 1 mentioned above, the Gd⋯Gd distance within the uniform chain unit is 4.03(1) Å, shorter than those between adjacent chains linked through the PDA2 − bridge (longer than 7.8 Å). Therefore, the main exchange interactions can be assumed to be 1D chain model, and the following expressions deduced by Fisher could be used to quantitatively analyze the interaction between adjacent Gd3+ ions with S = 7/2 [3,23,24]. χchain ¼
Ng2 β2 1 þ u SðS þ 1Þ 3kT 1‐u
ð1Þ
where, u = cth(JS(S + 1)/kT) − kT/JS(S + 1) χM ¼
χ 0 chain 1‐ zJ χchain =Ng 2 β2
ð2Þ
In the equation, N is Avogadro's number, β is the Bohr magnetron, k is the Boltzmann constant, J is the exchange coupling parameter between adjacent intrachain spins, and the interchain interaction (zJ′) is treated by the molecular field approximation. The best fit results in g = 2.00(1), J = 0.012(1) cm−1, zJ′ = 0.031(1) cm−1 and R = 7.82 × 10−4, where R is calculated from Σ[(χMT)obsd − (χMT)calcd]2/ Σ[(χMT)obsd]2. The positive and small J value is in good agreement with the reported values for other carboxyl-bridged Gd-containing complexes [3,24,25], verifying the presence of weak Gd–Gd ferromagnetic coupling interaction in the 1D chain in 1. When the magnetostructural relationship was considered, the ferromagnetic behavior may be closely related with the bigger Gd−O−Gd angle (N 110°) and suitable Gd−Gd bond length (4.06 Å) as well as the Gd–O–Gd–O dihedral angle of 12.78(1)° in the 1D chain unit, which is in keeping with the results reported in some literatures [3,25,26]. Magnetization measurements for 1 were carried out in a field of 0–7 T between 2 and 7 K (Fig. 3a). The M versus H data reveal a steady increase in magnetization to come up to a maximum value of 13.95 Nβ for 1 at 2 K and 7 T, which is close to the expected value of 14 Nβ for two uncoupled Gd(III) (S = 7/2, g = 2) ions. To evaluate the MCE, the magnetic entropy change of 1 can be obtained from the magnetization change as a function of applied field and temperature (Fig. 4b) by using the Maxwell equation ΔSm(T) = [∂M(T,H)/∂T]HdH [4,17]. The resulting maximum − ΔSm is 33.44 J K−1 kg−1 for ΔH = 7 T at 2.0 K, which is considerable large value, and comparable with those for the reported interesting Gd-based frameworks [15,25]. Theoretically, the full entropy change per mole of complex corresponding to two Gd3 + ions is 35.24 J K−1 kg−1, as calculated from the equation 2Rln(2S + 1) with S = 7/2. The difference of −ΔSm between the theoretical and experimental values may be due to the MW/NGd ratio of 491 (where MW is the molecular mass of 981.07 g mol−1 and NGd is the number of Gd3+ ion in per mole of 1) and the weak magnetic interaction in 1 [16,17].
In summary, one 3D Gd-based coordination polymer (1) with 1D wave chain unit has been successfully synthesized hydrothermally based on PDA2 − ligand. Magnetic studies reveal that 1 displays intrachain Gd ⋯ Gd ferromagnetic coupling and significant cryogenic MCE with the maximum −ΔSm value of 33.44 at 2 K and 7 T. These results confirm that multidentate organic ligand may be promising candidate for constructing high-dimensional Gd-based magnetic refrigerant. Acknowledgements The work on this paper were supported by the National Natural Science Foundation of China (NSFC) (grant numbers 21401126, 21371114, 21571123, 21601119, 21471095), Scientific and Technological Projects of Science and Technology Department of Henan province (172102210437). Appendix A. Supplementary material Experimental section, Crystallographic data, additional structure, magnetic data and TGA curve, PXRD patterns. CCDC 1576909 (1) contains the supplementary crystallographic data for this paper. Supplementary data to this article can be found online at https://doi.org/10. 1016/j.inoche.2017.11.014. References [1] (a) Y. Liu, Z. Chen, J. Ren, X.Q. Zhao, P. Cheng, B. Zhao, Inorg. Chem. 51 (2012) 7433–7435; (b) M. Zhu, X.L. Mei, Y. Ma, L.C. Li, D.Z. Liao, J.P. Sutter, Chem. Commun. 50 (2014) 1906–1908; (c) Z.Y. Li, J.S. Yang, R.B. Liu, J.J. Zhang, S.Q. Liu, J. Ni, C.Y. Duan, Dalton Trans. 41 (2012) 13264–13266; (d) P. Hu, H.F. Guo, Y. Li, F.P. Xiao, Inorg. Chem. Commun. 59 (2015) 91–94. [2] Z.Y. Li, B. Zhai, S.Z. Li, G.X. Cao, F.Q. Zhang, X.F. Zhang, F.L. Zhang, C. Zhang, Cryst. Growth Des. 16 (2016) 4574–4581. [3] A.K. Mondal, H.S. Jena, A. Malviya, S. Konar, Inorg. Chem. 55 (2016) 5237–5244. [4] Y.L. Hou, G. Xiong, P.F. Shi, R.R. Cheng, J.Z. Cui, B. Zhao, Chem. Commun. 49 (2013) 6066–6068. [5] Y.C. Chen, L. Qin, Z.S. Meng, D.F. Yang, C. Wu, Z.D. Fu, Y.Z. Zheng, J.L. Liu, R. Tarasenko, M. Orendáč, J. Prokleška, V. Sechovskýe, M.L. Tong, J. Mater. Chem. A 2 (2014) 9851–9858. [6] X. Li, C.Y. Wang, X.J. Zheng, Y.Q. Zou, J. Coord. Chem. 61 (2008) 1127–1136. [7] Z.Y. Li, Y. Chen, X.Y. Dong, B. Zhai, X.F. Zhang, C. Zhang, F.L. Zhang, S.Z. Li, G.X. Cao, Cryst. Growth Des. 17 (2017) 3877–3884. [8] S.W. Zhang, W. Shi, L.L. Li, E.Y. Duan, P. Cheng, Inorg. Chem. 53 (2014) 10340–10346. [9] M.E. Fisher, Am. J. Phys. 32 (1964) 343–346. [10] Y.L. Hou, R.R. Cheng, G. Xiong, J.Z. Cui, B. Zhao, Dalton Trans. 43 (2014) 1814–1820. [11] F.S. Guo, J.D. Leng, J.L. Liu, Z.S. Meng, M.L. Tong, Inorg. Chem. 51 (2012) 405–413. [12] T. Rajeshkumar, S.K. Singh, G. Rajaraman, Polyhedron 52 (2013) 1299–1305. [13] Y.Z. Zheng, G.J. Zhou, Z.P. Zheng, R.E.P. Winpenny, Chem. Soc. Rev. 43 (2014) 1462–1475. [14] S.W. Zhang, E.Y. Duan, P. Cheng, J. Mater. Chem. A 3 (2015) 7157–7162. [15] (a) Y.F. Han, X.Y. Li, L.Q. Li, C.L. Ma, Z. Shen, Y. Song, X.Z. You, Inorg. Chem. 44 (2010) 10781–10787;
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