Anion-Dependent Assembly of Heterometallic 3d–4f Clusters Based

Jun 26, 2017 - A series of heterometallic 3d–4f clusters, formulated as Na17[Ln3(H2O)5NiII(H2O)3(Sb4O4)(SbW9O33)3(NiIIW6O24)(WO2)3(CH3COO)]·(H2O)65...
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Anion-Dependent Assembly of Heterometallic 3d−4f Clusters Based on a Lacunary Polyoxometalate Jing Cai,† Xiu-Ying Zheng,† Jing Xie, Zhi-Hao Yan, Xiang-Jian Kong,* Yan-Ping Ren,* La-Sheng Long,* and Lan-Sun Zheng Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China S Supporting Information *

ABSTRACT: A series of heterometallic 3d−4f clusters, formulated as Na 17 [Ln 3 (H 2 O) 5 Ni II (H 2 O) 3 (Sb 4 O 4 )(SbW 9 O 33 ) 3 (Ni II W 6 O 24 )(WO 2 ) 3 (CH 3 COO)]· (H2O)65 [abbreviated as Ln3Ni2, where Ln = La3+ (1), Pr3+ (2), and Nd3+ (3)], K5Na11[Ln3(H2O)3NiII3(H2O)6(SbW9O33)3(WO4)(CO3)]·(H2O)40 [abbreviated as Ln3Ni3, where Ln = La3+ (4), Pr3+ (5), and Nd3+ (6)], and K3Na27[Ln3NiII9(μ3OH)9(SbW9O33)2(PW9O34)3(CH3COO)3]·(H2O)80 [abbreviated as Ln3Ni9, where Ln = Dy3+ (7) and Er3+ (8)], were obtained through the reaction of the lacunary {SbW9O33} precursor with Ln(NO3)3·6H2O and NiCl2·6H2O in a NaAc/HAc buffer in the presence of different anions. Single-crystal X-ray structure analysis revealed that compounds 1−3 possessed tetrameric architectures featuring three Keggin-type {SbW9O33} and one Anderson-type {NiIIW6O24} building blocks encapsulating one {Sb4O4} cluster, three WO2 units, three Ln3+ metal ions, and two Ni2+ metal ions. Compounds 4−6 displayed cyclic trimeric aggregates of three {SbW9O33} units enveloping one CO32−-templated trinuclear [Ln3(CO3)]7+ and one WO42−-templated [NiII3(WO4)]+ unit. Compounds 7 and 8 exhibited unique pentameric architectures that featured three 3d−4f cubane clusters of {LnNi3(μ3-OH)3} capped by two {SbW9O33} and three {PW9O34} building blocks. Interestingly, the structural regulation of the heterometallic 3d−4f clusters in the polyoxometalate systems with trimers, tetramers, and pentamers was realized by introducing different anions.

1. INTRODUCTION Lacunary polyoxometalates (POMs) have attracted continuous attention in the past few decades because they can assemble with 3d or 4f metal ions to generate new types of cluster aggregations.1 Compared to plenary POMs, lacunary POMs have more well-defined vacant sites and higher negative charges.2 Therefore, lacunary POMs are useful multidentate inorganic ligands to form more stable metal−oxo cluster structures. Among them, POM-based 3d−4f heterometallic clusters are particularly interesting not only because of their beautiful configurations but also because of their interesting magnetic, catalytic, optical, and other properties3 derived from the inherent contributions of the 3d and 4f electrons and the cooperative effects between these metal ions. Although using lacunary POM fragments as structure-directing agents to induce the formation of 3d clusters has been widely studied, the design and synthesis of POM-based 3d−4f heterometallic clusters is still a challenge because of the different coordination capacities of 3d and 4f metal ions with lacunary POMs. A few synthetic strategies have been used to form POMbased 3d−4f heterometallic clusters, e.g., introducing auxiliary ligands to overcome competing reactions,4 using preformed heterometallic 3d−4f clusters as precursors5 or using 3dsubstituted POMs with labile M sites as precursors.6 However, only a few examples of lacunary-POM-based 3d−4f heterometallic clusters have been reported to date.5a,b,6,7 Inspired by © 2017 American Chemical Society

the successful anionic template strategy in the assembly of 3d− 4f clusters,8 we attempted to introduce anions as templates to control the formation of the 3d−4f cluster skeletons in lacunary POM systems. Following this idea, we selected the trilacunary Keggin-type POM {SbIIIW9O33} as a building block and introduced different anions as templates to construct POM-based 3d−4f clusters. Herein, a series of POM-based 3d−4f heterometallic clusters, Na17[Ln3(H2O)5NiII(H2O)3(Sb4O4)(SbW9O33)3(NiIIW6O24)(WO2)3(CH3COO)]·(H2O)65 [Ln3Ni2, where Ln = La3+ (1), Pr3+ (2), and Nd3+ (3)], featuring tetrameric architectures were synthesized through the reaction of the trilacunary {SbIIIW9O33} precursor, Ln(NO3)3·6H2O, and NiCl2·6H2O in a NaAc/HAc buffer solution. When K2CO3 was added to the above reaction system, we successfully obtained three new POM-based 3d−4f heterometallic clusters, K5Na11[Ln3(H2O)3Ni II 3 (H 2 O) 6 (SbW 9 O 33 ) 3 (WO 4 )(CO 3 )]·(H 2 O) 40 [Ln 3 Ni 3 , where Ln = La3+ (4), Pr3+ (5), and Nd3+ (6)], which display cyclic trimeric aggregates. More interestingly, when KH2PO4 was introduced, two unique compounds, K3Na27[Ln3NiII9(μ3OH)9(SbW9O33)2(PW9O34)3(CH3COO)3]·80H2O [Ln3Ni9, where Ln = Dy3+ (7) and Er3+ (8)], featuring novel pentameric architectures were prepared. Their structural difference Received: May 4, 2017 Published: June 26, 2017 8439

DOI: 10.1021/acs.inorgchem.7b01104 Inorg. Chem. 2017, 56, 8439−8445

Article

Inorganic Chemistry

Found: H, 1.12; Na, 2.80; K, 2.28; Ni, 1.90; Pr, 4.56; Sb, 4.44; W, 56.10. Synthesis of Compound 6. The synthesis of 6 was similar to that of 4, except that La(NO3)3·6H2O was replaced by Nd(NO3)3·6H2O (0.087 g, 0.198 mmol). Yellow block crystals were obtained after about 1 day. Yield: 12% [based on Nd(NO3)3·6H2O]. Selected IR data (KBr, cm−1): ν 3432 (s), 1627 (s), 1467 (m), 944 (s), 873 (vs), 783 (vs), 733 (m), 662 (m), 512 (w), 441 (m). Elem anal. Calcd: H, 1.08; Na, 2.76; K, 2.13; Ni, 1.92; Nd, 4.72; Sb, 3.98; W, 56.20. Found: H, 1.38; Na, 2.80; K, 2.02; Ni, 1.99; Nd, 4.36; Sb, 4.05; W, 56.90. Synthesis of Compound 7. Na9SbW9O33·19.5H2O (0.602 g, 0.213 mmol) was dissolved in a 2 M aqueous solution of a NaAc/HAc buffer (pH 5.5, 10 mL) and H2O (5 mL). Solid NiCl2·6H2O (0.095 g, 0.400 mmol) was added and stirred until a clear green solution was obtained. Dy(NO3)3·5H2O (0.087 g, 0.198 mmol) was added to the solution with vigorous stirring. Then, 300 μL of 0.3 M KH2PO4 was added to the above solution. The mixture was stirred for 2 h at 80 °C. The resulting solution was filtered and left to slowly evaporate at room temperature, and green platelike crystals were obtained after approximately 1 day. Yield: 15% [based on Dy(NO3)3·5H2O]. IR (KBr, cm−1): ν 3428 (s), 1634 (s), 1583 (s), 1412 (s), 1050 (vs), 939 (s), 889 (m), 819 (w), 778 (w), 718 (w), 516 (w), 448 (w). Elem anal. Calcd: H, 1.21; C, 0.49; Na, 4.19; K, 0.79; Ni, 3.56; Dy, 3.29; Sb, 1.64; W, 55.80. Found: H, 1.46; C, 0.51; Na, 4.18; K, 0.77; Ni, 3.33; Dy, 3.25; Sb, 1.62; W, 54.10. Synthesis of Compound 8. The synthesis of 8 was similar to that of 7, except that Dy(NO3)3·5H2O was replaced by Er(NO3)3·6H2O (0.092 g, 0.199 mmol). Green platelike crystals were obtained after approximately 1 day. Yield: 10% [based on Er(NO3)3·6H2O]. Selected IR data (KBr, cm−1): ν 3431 (s), 1627 (s), 1589 (s), 1412 (s), 1040 (vs), 938 (s), 884 (m), 809 (w), 775 (w), 720 (w), 519 (w), 482 (w). Elem anal. Calcd: H, 1.21; C, 0.49; Na, 4.18; K, 0.79; Ni, 3.56; Er, 3.38; Sb, 1.64; W, 55.80. Found: H, 1.38; C, 0.51; Na, 4.16; K, 0.77; Ni, 3.40; Er, 3.10; Sb, 1.60; W, 56.60. X-ray Crystallography. Data for compounds 1 and 8 were collected on an Agilent Technologies SuperNova Microfocus single diffractometer using Cu Kα radiation (λ = 1.54184 Å) at 100 K. Data collection of compounds 2−7 was performed on an Oxford Gemini S Ultra CCD area detector with monochromatic Mo Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods, and non-H atoms were refined anisotropically by a least-squares method on F2 using the SHELXTL-2013 program. H atoms of the organic ligands were generated geometrically (C−H, 0.96 Å). Crystal data as well as details of the data collection and refinement for the complexes are summarized in Tables S1−S3. Selected bond distances are shown in Tables S4−S11. CCDC contains the supplementary crystallographic data for this paper with deposition numbers 1545704−1545711 for 1− 8. The crystallographic data can be obtained free of charge from The Cambridge Crystallographic Data Center via http://www.ccdc.cam.ac. uk/data_request/cif.

indicates that the anionic templates play important roles in adjusting and controlling the formation of the clusters.

2. EXPERIMENTAL SECTION Materials and Physical Measurements. Na9SbW9O33·19.5H2O was prepared according to a reference and confirmed by its IR spectrum.9 Other chemicals were of reagent grade and were used without further purification. IR spectra were recorded on a Nicolet AVATAR FT-IR 330 spectrophotometer with pressed KBr pellets in the range of 4000−400 cm−1. Powder X-ray diffraction data were recorded on a X’pert PRO powder X-ray diffractometer (Cu Kα, λ = 1.54184 Å) at room temperature. C, H, and N microanalyses were carried out with a CE instruments EA 1110 elemental analyzer. Thermogravimetric analyses were performed on SDT-Q600 TG/DTA equipment in flowing air with a heating rate of 10 °C min−1. Magnetic susceptibility was measured by a Quantum Design MPMS superconducting quantum interference device. Syntheses of Compounds 1−8. Synthesis of Compound 1. Na9SbW9O33·19.5H2O (0.602 g, 0.213 mmol) was dissolved in a 2 M aqueous solution of a NaAc/HAc buffer (pH 5.5, 10 mL) and H2O (5 mL). Solid NiCl2·6H2O (0.095 g, 0.400 mmol) was added and stirred until a clear green solution was obtained. Then, La(NO3)3·6H2O (0.087 g, 0.201 mmol) was added to the solution with vigorous stirring. The mixture was stirred for 2 h at 80 °C. The resulting solution was filtered and left to slowly evaporate at room temperature, and green block crystals were obtained after approximately 1 week. Yield: 23% [based on La(NO3)3·6H2O]. Selected IR data (KBr, cm−1): ν 3431 (s), 1626 (s), 1384 (m), 1122 (w), 944 (s), 859 (vs), 803 (vs), 713 (vs), 619 (w), 503 (w), 441 (m). Elem anal. Calcd: H, 1.26; Na, 3.28; Ni, 0.99; La, 3.50; Sb, 7.16; W, 55.60. Found: H, 1.26; Na, 3.55; Ni, 1.06; La, 3.81; Sb, 6.80; W, 53.10. Synthesis of Compound 2. Compound 2 was synthesized in a way similar to that described for 1, except that La(NO3)3·6H2O was replaced by Pr(NO3)3·6H2O (0.087 g, 0.200 mmol). Green block crystals were obtained after approximately 1 week. Yield: 16% [based on Pr(NO3)3·6H2O]. Selected IR data (KBr, cm−1): ν 3444 (s), 1629 (s), 1408 (w), 945(s), 855 (vs), 805 (vs), 713 (vs), 624 (w), 512 (w), 442 (m). Elem anal. Calcd: H, 1.26; Na, 3.28; Ni, 0.99; Pr, 3.55; Sb, 7.16; W, 55.60. Found: H, 1.23; Na, 2.97; Ni, 0.966; Pr, 3.36; Sb, 5.77; W, 58.10. Synthesis of Compound 3. The synthesis of 3 was similar to that of 1, except that La(NO3)3·6H2O was replaced by Nd(NO3)3·6H2O (0.087 g, 0.198 mmol). Green block crystals were obtained after approximately 1 week. Yield: 18% [based on Nd(NO3)3·6H2O]. Selected IR data (KBr, cm−1): ν 3423 (s), 1625 (s), 1476 (w), 936 (w), 870 (s), 779 (vs), 728 (vs), 662 (w), 517 (w), 449 (m). Elem anal. Calcd: H, 1.26; Na, 3.28; Ni, 0.99; Nd, 3.63; Sb, 7.15; W, 55.60. Found: H, 1.34; Na, 2.98; Ni, 0.89; Nd, 3.32; Sb, 5.39; W, 60.80. Synthesis of Compound 4. Na9SbW9O33·19.5H2O (0.602 g, 0.213 mmol) was dissolved in a 2 M aqueous solution of a NaAc/HAc buffer (pH 5.5, 10 mL) and H2O (5 mL). Solid NiCl2·6H2O (0.095 g, 0.400 mmol) was added and stirred until a clear green solution was obtained. Then, La(NO3)3·6H2O (0.087 g, 0.201 mmol) was added with vigorous stirring, and 400 μL of 2 M K2CO3 was added to the above solution. The mixture was stirred for 2 h at 80 °C. The resulting solution was filtered and left to slowly evaporate at room temperature, and yellow block crystals were obtained after approximately 1 day. Yield: 35% [based on La(NO3)3·6H2O]. Selected IR data (KBr, cm−1): ν 3431 (s), 1627 (s), 1467 (m), 939 (s), 869 (vs), 778 (vs), 738 (vs), 668 (w), 527 (w), 447 (m). Elem anal. Calcd: H, 1.08; Na, 2.77; K, 2.14; Ni, 1.93; La, 4.56; Sb, 3.99; W, 56.30. Found: H, 1.09; Na, 2.84; K, 2.05; Ni, 2.03; La, 4.82; Sb, 4.03; W, 55.60. Synthesis of Compound 5. The synthesis of 5 was similar to that of 4, except that La(NO3)3·6H2O was replaced by Pr(NO3)3·6H2O (0.087 g, 0.200 mmol). Yellow block crystals were obtained after approximately 1 day. Yield: 15% [based on Pr(NO3)3·6H2O]. Selected IR data (KBr, cm−1): ν 3421 (s), 1642 (s), 1401 (m), 948 (s), 870 (vs), 800 (vs), 710 (m), 609 (m), 506 (w), 448 (m). Elem anal. Calcd: H, 1.08; Na, 2.76; K, 2.14; Ni, 1.92; Pr, 4.62; Sb, 3.99; W, 56.30.

3. RESULTS AND DISCUSSION Synthesis. The trilacunary Keggin-type POMs {XW9O33} (X = PV, AsIII, SiIV, and GeIV) are ideal candidates for constructing POM-based metal clusters10 because of their welldefined vacant sites, high negative charges, and high yields obtained in past years. However, most studies of POM-based 3d−4f clusters have focused on {AsW 9 O 3 3 } and {GeW9O34},6,7c,11 while only a few 3d−4f clusters based on {SbIIIW9O33} as a building block have been reported.7a,b,12 Therefore, exploration of the 3d−4f heterometallic clusters based on the lacunary inorganic ligand {SbW9O33} is an ongoing pursuit. To further explore novel aggregates, we utilized the trilacunary {SbW9O33} as an inorganic building unit to capture transition-metal and rare-earth (RE) ions for constructing 3d−4f clusters. As shown in Figure 1, compounds 1−3 were achieved after approximately 1 week by the reaction of [SbW9O33]9− with nitrate salts of the RE metals La, Pr, and 8440

DOI: 10.1021/acs.inorgchem.7b01104 Inorg. Chem. 2017, 56, 8439−8445

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Inorganic Chemistry

Figure 2. (a) Ball-and-stick structure of the metal core of {La3(H2O)5NiII(H2O)3(Sb4O4)(CH3COO)} in 1. Structures of (b) the trilacunary {B-α-SbW9O33} unit, (c) the {La3(H2O)5NiII(H2O)3(Sb4O4)(SbW9O33)3(CH3COO)} unit, (d) the trilacunary ε-Keggin {B-ε-NiIIW9O33} unit, and (e) the cluster metal core of [La3(H2O)5NiII(H2O)3(Sb4O4)(SbW9O33)3(NiW6O24)(WO2)3(CH3COO)]17−. Code: {WO6}, red octahedra; C, gray spheres; O, red spheres; Sb, blue spheres; Ni, green spheres; Ln, violet spheres.

Figure 1. Schematic view of the synthetic routes of compounds 1−8. Polyhedral representation of the polyoxoanion structures of {SbW9O33}. Code: {WO6}, red octahedra; C, gray spheres; O, red spheres; P, pink spheres; Sb, blue spheres; Ni, green spheres; Ln, violet spheres.

building block have rarely been reported. Three La3+ ions in 1 display similar distorted nine-coordinated geometries (Figure S4a), and two Ni2+ ions in 1 possess {NiIIO6} octahedral environments. The isostructural compounds 4−6 crystallize in the triclinic P1̅ space group and exhibit trimeric architectures. The polyoxoanion {La3 (H2 O) 3 Ni II3 (H2 O) 6 (SbW 9O 33 ) 3(WO4 )(CO3)}16− in 4 can be viewed as being constructed from three different subunits: one triangular {NiII3(WO4)(H2O)3} unit (unit I), one {Ln3(CO3)(H2O)6} unit (unit II), and three trilacunary α-Keggin {B-α-SbW9O33} units (unit III) (Figure 3). For unit I, {NiII3(WO4)(H2O)3}, three Ni2+ ions connect with each other through three O atoms from the templating WO42− anion (Figure 3a). In unit II, three Ln3+ ions are bridged by the templating CO32− and coordinated by six terminal water molecules, forming the triangular {Ln3(CO3)(H2O)6} unit (Figure 3b). As shown in Figure 3c, units I and II connect together through three shared O atoms from the

Nd and NiCl2 in a NaAc/HAc buffer (pH 5.5). When 400 μL of K2CO3 (2 M) was added to the above mixed solution, compounds 4−6 were produced. It is worth noting that unique compounds 7 and 8 containing two different types of trilacunary {PW9O34} and {SbW9O33} units were obtained when 300 μL of KH2PO4 (0.3 M) was introduced. The addition of PO43− as an anionic template with the {SbW9O33} precursor formed the new trilacunary Keggin-type {PW9O34} unit by an in situ reaction. Obviously, CO32− and PO43− as anionic templates have important significance in the assembly process. Besides, compared to La3+, Pr3+, and Nd3+ in compounds 1−6, only the smaller radii of RE ions (such as Dy3+ and Er3+) can form the corresponding structures of compounds 7 and 8, which may due to the effect of the lanthanide contraction effect. As a result of the lanthanide contraction effect, the coordination number decreases from 9 (for 1−6) to 8 (for 7 and 8). Therefore, both the anionic template and lanthanide contraction effect have important influences on the structures of the compounds. Single-crystal X-ray diffraction analysis confirmed that compounds 1−3 crystallize in the orthorhombic Pnma space group and display tetrameric structures. As shown in Figure 2a, two [La(H 2 O) 2 ] 3+ ions, one [La(H 2 O)Ni I I (H 2 O) 3 (CH3COO)]4+ ion, and one distorted [Sb4O4]4+ tetrahedron assemble into the metal core of {Ln3(H2O)5NiII(H2O)3(Sb4O4)(CH3COO)} in compound 1. The metal core is further linked by three trilacunary α-Keggin {SbW9O33} units, forming the {Ln3 (H 2 O) 5 Ni II (H 2 O) 3 (Sb 4 O 4)(SbW 9 O33 ) 3 (CH3COO)} cyclic unit (Figure 2c). The cyclic unit is capped with one trilacunary ε-Keggin {B-ε-NiIIW9O33} unit (Figure 2d), which can also be viewed as a classical Anderson−Evans {NiIIW6O24} fragment13 connected with three additional {WO2} groups through edge sharing (Figure S1), generating the tetrameric metal core structure of [Ln3(H2O)5NiII(H2O)3(Sb4O4)(SbW9O33)3(NiIIW6O24)(WO2)3(CH3COO)]17− (Figure 2e). The metal cluster displays the same tetrameric structure of Ce3Ni2 reported in 2016 by Artetxe et al.7a It is worth noting that POM-based metal clusters that construct the classical Anderson−Evans {NiIIW6O24} fragment acting as a

Figure 3. Structures of (a) the triangular unit {NiII3(WO4)(H2O)3} (unit I), (b) the triangular structural unit {La3(CO3)(H2O)6} (unit II), (c) the trigonal-prismatic unit {La3(H2O)3NiII3(H2O)6(WO4)(CO3)}, (d) the trilacunary α-Keggin {B-α-SbW9O33} units, and (e) the metal core of {La 3 (H 2 O) 3 Ni II 3 (H 2 O) 6 (SbW 9 O 33 ) 3 (WO 4 )(CO 3 )} 16− (La3Ni3). Code: {WO6}, red octahedra; C, gray spheres; O, red spheres; Sb, blue spheres; Ni, green spheres; Ln, violet spheres. 8441

DOI: 10.1021/acs.inorgchem.7b01104 Inorg. Chem. 2017, 56, 8439−8445

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Inorganic Chemistry

shown in Figure 5a, the observed χMT values of 2.14 and 3.15 cm3 mol−1 K for 1 and 4 at room temperature are slightly larger

tetrahedron {WO4} unit, generating a trigonal-prismatic topology of {La3(H2O)3NiII3(H2O)6(WO4)(CO3)}. The trigonal-prismatic {La3(H2O)3NiII3(H2O)6(WO4)(CO3)} unit is encapsulated and protected by three trilacunary α-Keggin {Bα-SbW9O33} units (unit III) (Figure 3d), producing the planar triangular configuration cluster of [La3(H2O)3NiII3(H2O)6(SbW9O33)3(WO4)(CO3)]16− (Figure 3e). Compared with the structure of 1, the different configuration of 4 is attributed to the introduction of additional CO32− anions, which suggests that CO32− plays an important role in the formation of the metal clusters in POM systems. In this system, the templating CO32− anion adjusts the tetrahedral configuration of Ln3Ni2 in 1 into the planar triangular configuration of Ln3Ni3 in 4. In compound 4, each La3+ ion exhibits a nine-coordinated mode by four O atoms from two Keggin units, two O atoms from the μ3-CO3 linker, one O atom from the tetrahedral {WO4} unit, and two O atoms from two terminal water ligands (Figure S4b). Three Ni2+ ions display a six-coordinated environment, with four O atoms derived from two Keggin units, one O atom from the tetrahedral {WO4} unit, and one O atom from a water molecule. The isostructural compounds 7 and 8 show unique pentameric architectures. The polyoxoanion of [Dy3NiII9(μ3OH)9(SbW9O33)2(PW9O34)3(CH3COO)3]30− in 7 consists of three trilacunary α-Keggin {B-α-PW9O33} units, two trilacunary α-Keggin {B-α-SbW9 O 33 } units, and three cubane-like {DyNiII3(μ3-OH)3(μ4-O)} units. The trilacunary α-Keggin {B-α-PW9O34} unit is formed by the in situ reaction of PO43− and the {SbW9O33} precursor. As shown in Figure 4,

Figure 5. Plots of the temperature dependence of χMT for compounds 1 and 4 (a) and 7 and 8 (b).

than the expected values of 2.0 and 3.0 cm3 mol−1 K (Ni2+, S = 1, g = 2), respectively. Upon cooling from 300 to 20 K, the χMT values rapidly increase to maximum values of 2.77 and 3.76 cm3 mol−1 K for 1 and 4, respectively, which may result from the significant orbital contributions of the distorted octahedral Ni2+ ions.14 The χMT values then sharply decrease to minimum values of 1.86 and 2.49 cm3 mol−1 K for 1 and 4 at 2 K, respectively, indicating the presence of weak zero-field splitting of the Ni2+ ions in the low-temperature range.8e,15 For compounds 7 and 8, the observed χMT values at room temperature are 51.38 and 43.96 cm3 mol−1 K, which are close to the calculated values of 51.50 and 43.43 cm3 mol−1 K (Dy3+, J = 15/2, g = 4/3; Er3+, J = 15/2, g = 6/5), respectively. Upon lowering of the temperature, the curve of 7 sharply decreases to a minimum value of 40.70 cm3 K mol−1 and then rapidly increases to a maximum value of 48.78 cm3 K mol−1 at 4 K, revealing the obvious antiferromagnetic interaction between the Dy3+ and Ni2+ ions.16 For compound 8, the experimental value slowly decreases in the range of 300−50 K and then sharply decreases to a minimum of 32.17 cm3 K mol−1 at 2 K, indicating the strong antiferromagnetic interaction between the metal ions. To estimate the intermolecular exchange constant, fitting of the curves of 1/χM versus T to a Curie−Weiss law in the range of 150−300 K (as shown in Figure S14c,d) for these compounds gives C = 1.93 cm3 K mol−1 and θ = 28.6 K for 1, C = 2.84 cm3 K mol−1 and θ = 29.4 K for 4, C = 47.66 cm3 K mol−1 and θ = −22.62 K for 7, and C = 59.91 cm3 K mol−1 and θ = −50.89 K for 8. Furthermore, the field dependences of magnetization for 1, 4, 7, and 8 were also measured at 2 K and 0−7 T (Figure S14a,b). The magnetization values of 4.60 NμB for 1 and 6.8 NμB for 4 are close to the saturation values of 4.30

Figure 4. Structures of (a) the {DyNiII3(μ3−OH)3(PW9O34)} unit and (b) the trilacunary α-Keggin [SbW9O33]9− units, (c) ball-and-stick structure of the acetate, and (d) structure of the metal core of [Ln3NiII9(μ3-OH)9(SbW9O33)2(PW9O34)3(CH3COO)3]30− (Ln3Ni9). Code: {WO6}, tea-green octahedra; C, gray spheres; O, red spheres; P, pink spheres; O, cyan spheres; Sb, orange spheres; Ni, green spheres; Ln, plum spheres.

one trilacunary {PW9O34} unit links with one cubane-like {DyNiII3(μ3-OH)3(μ4-O)} unit through one shared O atom from the cubane-like unit and six terminal O atoms from one Keggin unit, generating a unit of {DyNiII3(μ3-OH)3(PW9O34)} (Figure 4a). Three {DyNiII3(μ3-OH)3(PW9O34)} units are connected together by two trilacunary {B-α-SbW9O33} units (Figure 4b) and three bridged carboxyl groups from the acetate ligands, generating the novel and unique pentameric [Ln 3 Ni II 9 (μ 3 -OH)9 (SbW 9 O 33 ) 2 (PW 9 O 34 ) 3 (CH 3 COO) 3 ] 30− configuration (Figure 4d). It is worth noting that compound 7 is the first POM-based 3d−4f heterometallic cluster with a pentameric configuration to date. Furthermore, the acetate ligands also bridge two kinds of different lacunary Keggin-type units. All of the Ni2+ ions display six-coordinated modes, and three 4f Ln3+ metal centers exhibit the eight-coordinated modes in 7 (Figure S4c). Magnetic Properties. The temperature dependences of the magnetic susceptibilities of 1, 4, 7, and 8 were measured between 300 and 2 K with an applied field of 1000 Oe. As 8442

DOI: 10.1021/acs.inorgchem.7b01104 Inorg. Chem. 2017, 56, 8439−8445

Inorganic Chemistry

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ACKNOWLEDGMENTS This work was supported by the 973 Project (Grant 2014CB845601) from the Ministry of Science and Technology of China and by the National Natural Science Foundation of China (Grants 21422106, 21371144, 21431005, 21673184, and 21390391), the Fok Ying Tong Education Foundation (Grant 151013), and The Recruitment Program for Leading Talent Team of Anhui Province.

NμB for 1 and 6.9 NμB for 4, suggesting the lack of significant anisotropy and low-lying excited states. For compounds 7 and 8, the obverse values are 34.42 and 35.54 NμB, which are lower than the expected values of 48 and 45 NμB, respectively, proving the presence of strong anisotropy.

4. CONCLUSION In summary, a series of 3d−4f heterometallic clusters based on the trilacunary Keggin-type {SbW9O33} unit were obtained through the reaction of a {SbW9O33} precursor with Ln(NO3)3·6H2O and NiCl2·6H2O in the presence of different anions. The crystal structure analyses showed that compounds 1−3 possessed tetrameric architectures through three Keggintype {SbW9O33} and one {NiIIW9O33} building blocks encapsulating one {Sb4O4} cluster and three Ln3+ and two Ni2+ metal ions. Compounds 4−6 exhibited trimeric aggregates of three {SbW9O33} units enveloping one CO32−-templated and one WO42−-templated trigonal-prismatic {Ln3(H2O)3NiII3(H2O)6(WO4)(CO3)} units. Compounds 7 and 8 possessed pentameric architectures of two {SbW9O33} and three {PW9O34} building blocks embedded in three 3d−4f cubane clusters of {LnNiII3(μ3-OH)3}. Interestingly, the structural regulation of the heterometallic 3d−4f clusters in the POM systems with trimers, tetramers, and pentamers was realized by introducing different anions. These results suggest that the anions play important roles in regulating the structures of POM-based 3d−4f clusters. Continuous research of the aniondependent assembly of POM-based heterometallic clusters is currently in progress.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01104. Tables S1−S11 and additional figures of the structures (PDF) Accession Codes

CCDC 1545704−1545711 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Xiang-Jian Kong: 0000-0003-0676-6923 La-Sheng Long: 0000-0002-0398-4709 Author Contributions †

These authors (J.C. and X.-Y.Z.) contributed equally to this work. Notes

The authors declare no competing financial interest. 8443

DOI: 10.1021/acs.inorgchem.7b01104 Inorg. Chem. 2017, 56, 8439−8445

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DOI: 10.1021/acs.inorgchem.7b01104 Inorg. Chem. 2017, 56, 8439−8445