Communication pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Incorporation of Silicon−Oxygen Tetrahedron into Novel HighNuclearity Nanosized 3d−4f Heterometallic Clusters Qing-fang Lin,†,‡,# Jing Li,§,# Xi-ming Luo,† Chen-hui Cui,† You Song,*,§ and Yan Xu*,†,§ †
College of Chemical Engineering, State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing 210009, P. R. China § Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, P. R. China ‡ Department of Chemistry, Bengbu Medical College, Bengbu 233030, P. R. China S Supporting Information *
zeotype materials, although rare, usually have good chemical/ thermal stability and special space structures, which were beneficial in their biomedical and catalytic applications.31 We therefore anticipate that silica-incorporated high-nuclearity clusters should have some novel architectures and interesting properties. However, to our knowledge, no 3d−4f heterometallic complexes templated by silicate have been reported. Herein, by using SiO44− as the anionic template, we successfully synthesized two silica-containing high-nuclearity 3d−4f clusters, [Na2(Gd78Ni64(IDA)58(OAc)2(SiO4)6(Cl)4(μ2OH)4(μ4-O)4(μ3-O)38(μ3-OH)126(H2O)82]·(Cl)4(H2O)37(1) and [Na2(Eu78Ni62(IDA)60(OAc) 2(SiO4)6(Cl)6(μ4-O) 8(μ3O)24(μ3-OH)136(H2O)72]·(Cl)4(H2O)40 (2). Structural analysis indicates that novel {Si6Ln8} 14-membered rings are successfully introduced into the nanosized Ln−Ni clusters [Ln78Ni64(62)Si6] in both 1 and 2. More interestingly, compound 1 shows a maximum −ΔSm of 40.63 J kg−1 K−1 in the silica-containing clusters. It is worth noting that some amount of imidazole was essential for the crystal’s formation because it had not participated in the final crystal structure. In our opinion, the protonated imidazole in the acidic environment might work as a buffer during the reaction. Details of the synthesis conditions can be seen in the experimental section. Both compounds 1 and 2 crystallize in the monoclinic space group P21/n. Only the molecular structure of 1 is described in detail. The distinction between compounds 1 and 2 is that compound 2 lacks two NiIII ions, which results in a trivially different coordination sphere (Figures S1 and S2). As shown in Figure 1, the crystal structure of compound 1 can be separated into two pairs of symmetrical motifs: {Ni20Gd24} (fragment A) and {Ni12.5Gd15Si3} (fragment B). The bowlshaped fragment A (Figure 2a) consists of four gradually increasing loops from bottom to top, that is, 4 octacoordinated GdIII ions, 8 GdIII ions with two coordination models, 12 nonacoordinated GdIII ions, and 20 hexacoordinated NiII ions (Figure S3). The loops connect with each other by bridging O atoms to define a topology space of the bowl. All of the GdIII ions are linked by μ3-OH and μ4-O groups to form a concave configuration (Figure 2c), while 20 NiII ions at the top connect to
ABSTRACT: By the anionic template strategy, we have, for the first time, succeeded in introducing SiO44− into 3d−4f huge clusters, obtaining two novel nanosized clusters with interesting nanosized cores of [Ln78Ni64(62)Si6] (1, Ln = Gd; 2, Ln = Eu). To the best of our knowledge, they are the largest heterometallic clusters incorporated with Si−O tetrahedra. In addition, compound 1 shows a maximum magnetic entropy (−ΔSm) of 40.63 J kg−1 K−1 at 3.0 K at 7 T.
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igh-nuclearity heterometallic complexes based on 3d−4f ions have been attracting considerable attention because of their fascinating structures as well as intriguing magnetic,1−5 luminescent,6−8 and some other potential applications.9−11 In recent years, great efforts have been made in increasing the nuclearity in 3d−4f clusters because such clusters usually contain some special metal motifs and numerous metal ions. A unique metal motif could generate intermediating magnetic exchanges among 3d and 4f ions and results in promising magnetic applications.12,13 Moreover, a cluster with plenty of metal ions usually has a large metal/ligand mass ratio, which is anticipated to achieve a large magnetocaloric effect (MCE).14−20 Recently, such a huge cluster with 160 nuclearity has been successfully synthesized.11 However, there are still challenges for this research topic because of the competitive reactions between 3d and 4f metals chelating to the organic ligand.3,21 Until now, there were no more than 10 clusters with nucleartiy greater than 100.11,18,20,22,23 On the basis of numerous previous literatures, to synthesize the above-mentioned clusters, the anionic template strategy has attracted great attention of researchers. Recent work by Lewiński clearly demonstrated the template behavior of CO32− in the syntheses of such clusters.24 Cl−, Br−, I−, NO3−, and ClO4− also played great roles in the formation of clusters.14,15,25−30 They usually locate within the cavities of the cluster cores to act as small inorganic ligands and templates to induce the formation of cluster skeletons and simultaneously stabilize the highly positive charges of the clusters. Thus, these anions determine the nuclearity and connectivity of the cluster structures. Bearing the above in mind, we wondered whether SiO44− could be incorporated into these high-nuclearity clusters. Si− metal composite materials, famously known as zeolites or © XXXX American Chemical Society
Received: February 7, 2018
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DOI: 10.1021/acs.inorgchem.8b00327 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry
octacoordinated GdIII ions and four Si−O tetrahedra (including two half-occupied Si atoms), where two GdIII ions are finished by two μ3-OH, a Cl atom, an O atom from the water, and the other four O atoms from silicates. These GdIII ions and Si atoms alternatively connect with each other by O atoms to form a curved chain (Figure 3c). The left wing consists of one {Ni7Gd6} unit (including two half-occupied NiII ions; Figure 3b). The {Ni7Gd6} unit shows a sandwich configuration: the peripheral four NiII ions are hexacoordinated, finished by four O atoms, one μ3-OH, and one N atom from IDA; the middle part is four GdIII ions, which show a linear arrangement; the inner three NiII ions and two GdIII ions are coordinated not only by O or N atoms from IDA but also by O atoms from silicates, so as to join the right wing with the center body. The right wing {Ni6Gd7} also takes a sandwich structure, but different from that of the left wing, its inside plane is composed of two GdIII and two NiII ions (Figure 3d). The middle curved chain of the main body links with the two wings, thus outlining the butterfly-like framework (fragment B). Then, the whole butterfly acts as a linkage to tightly bridge two fragments A and is further connected by IDA ligands, forming the huge cluster. To our surprise, the cluster shows an interesting zeolite-like 14-membered ring formed by six Si−O polyhedra and eight Gd− O polyhedra (Figures 4 and S4). As is known, it is the first
Figure 1. Ball-and-stick representation of the nanocluster of compound 1: (A) {Gd24Ni20}; (B) {Gd15Ni12Si3}. Color code: purple, Gd; blue, Ni; green, Si.
Figure 2. Ball-and-stick views of fragment A of compound 1: (a) bowllike view of fragment A ({Gd24Ni20}); (b) ball-and-stick view of {Gd24}; (c) ball-and-stick view of {Ni20}. Color code: purple, Gd; blue, Ni.
the adjacent GdIII ions by μ3-OH and the carboxylate O atoms from iminodiacetic acid (IDA; Figure 2b); this coordinate mode can be found in other Ln−Ni clusters.18,22,23 As shown in Figure 3a, fragment B shows a fascinating butterfly-like configuration and can be divided into three sections. The “butterfly” center body is composed of two
Figure 4. 14-membered ring channel formed by six Si−O polyhedra and eight Gd−O polyhedra in the core of compound 1.
example of the incorporation of SiO44− into the structure to stabilize a high-nuclearity 3d−4f cluster. Also, the 14-membered ring {Ln8Si6} is not found in other Ln−Ni compounds. Variable-temperature (1.8−300 K) direct-current (dc) magnetic susceptibility of 1 was performed from 1.8 to 300 K in a 1.0 kOe dc field with a polycrystalline sample (Figure S5). The room temperature χMT value of 685.6 cm3 K mol−1 for 1 is consistent with the anticipated value calculated from 78 isolated GdIII and 64 isolated NiII ions (678.2 cm3 K mol−1, S = 7/2, and g = 2 for GdIII and S = 1 and g = 2 for NiII ion). The χMT value gradually decreases and reaches 513.4 cm3 K mol−1 at 1.8 K, manifesting that antiferromagnetic interaction exists among the metal ions. Fitting the curve of χM−1 versus T with the Curie−Weiss law [χM = C/(T − θ)] in the range of 1.8−300 K obtains parameters C = 714.28 cm3 mol−1 K and θ = −2.93 K, showing a stronger antiferromagnetic interaction than that reported for highnuclearity clusters. The isothermal field-dependent magnetization of compound 1 was measured in the low-temperature range (2.0−10.5 K; Figure S6). At 2.2 K, magnetization increases slowly with increasing dc field and reaches 606 NB at 7 T, which is
Figure 3. Ball-and-stick views of section B of compound 1: (a) butterflylike view of section B {Gd15Ni12Si3}; (b) ball-and-stick view of {Gd6Ni7}; (c) ball-and-stick and polyhedron view of {Gd2Si3}; (d) ball-and-stick view of {Ni6Gd7}. Color code: purple, Gd; blue, Ni; green, Si; dark blue, Cl; red, O. B
DOI: 10.1021/acs.inorgchem.8b00327 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry Author Contributions
smaller than the calculated value of 674 NB for 1. This can be attributed to the intramolecular antiferromagnetic interaction. To further evaluate the MCE, the magnetic entropy change ΔSm was calculated based on the Maxwell equation (ΔSm(T)ΔH = ∫ [∂M(T,H)/∂T]H dH) from the experimental magnetization data. As exhibited in Figure 5, the maximum of −ΔSm is 40.63 J
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Q.-F.L. and J.L. contributed equally to this work.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the NSFC (Grant 21571103, 91622115, 21571097), and the Major Natural Science Projects of the Jiangsu Higher Education Institution (Grant 16KJA150005).
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Figure 5. Values of −ΔSm calculated from the magnetization data according to the Maxwell equation for 1 at various fields (1−7 T) and temperatures (2.2−10.2 K).
kg−1 K−1 at 3.0 K and 7 T, which is among the top seven values of the measured magnetic entropies (Table S1). The −ΔSm values for 1 are smaller than the theoretical value of −ΔSm (65.2 J kg−1 K−1) calculated using the equation −ΔSm = nNiR ln(2SNi + 1) + nLnR ln(2SLn + 1). The difference can be due to the weak antiferromagnetic magnetic interactions between the metal-ion centers. In summary, two novel silica-containing 3d−4f high-nuclearity clusters have been successfully synthesized for the first time. The metal atoms are up to 142. In addition, compound 1 shows a large MCE at ultralow temperatures. Crystal structure analysis shows that SiO44− was successfully induced into the transition− lanthanide (3d−4f) heterometallic system.
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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.8b00327. Synthesis and characterization details, including Figures S1−S10 and Tables S1−S5 (PDF) Accession Codes
CCDC 1815592−1815593 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
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[email protected]. ORCID
You Song: 0000-0002-0289-7830 Yan Xu: 0000-0001-6059-075X C
DOI: 10.1021/acs.inorgchem.8b00327 Inorg. Chem. XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.inorgchem.8b00327 Inorg. Chem. XXXX, XXX, XXX−XXX
