A Series of Weakley-type Polyoxomolybdates: Synthesis

were performed with the software package of Rigaku RAPID AUTO. (Rigaku, 1998, Ver2.30). Structures were solved ... We have mixed the 21 sextets out of...
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

A Series of Weakley-type Polyoxomolybdates: Synthesis, Characterization, and Magnetic Properties by a Combined Experimental and Theoretical Approach Shan She,†,§ Chen Gao,‡,§ Kun Chen,† Aruuhan Bayaguud,† Yichao Huang,† Bing-Wu Wang,*,‡ Song Gao,*,‡ and Yongge Wei*,† †

Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China National Laboratory for Molecular Science, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China

‡

S Supporting Information *

ABSTRACT: Using DCC as the dehydrating agent, a series of Weakley-type polyoxomolybdates [Bu4N]3{Ln[Mo5O13(OMe)4(NO)]2} (Ln = Tb, Dy, Ho, Er) were synthesized in a one-pot reaction and structurally characterized by elemental, IR, UV−vis analysis, PXRD, and single-crystal Xray diffraction. Furthermore, the static and dynamic measurements were utilized to investigate their magnetic performances. Typically, slow relaxation of magnetization was observed for Dy analogues with an energy barrier for the reversal of the magnetization of 50 K, which is the highest barrier height observed on the polyoxomolybdates-based single-molecule magnets (SMMs). For a deep understanding of the appearance of the SMM behavior on Weakley-type polyoxomolybdates series, ab initio calculations on {Dy[Mo5O13(OMe)4(NO)]2}3− have been conducted.

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INTRODUCTION Polyoxometalates (POMs) are a large family of early transition metal (Mo, W, V, etc.) oxide cluster anions.1,2 They possess a wide range of properties and play an important role suitable in diverse fields such as catalysis,3−5electrochemistry,6,7 medicine,8 photochromic,9 and magnetism.10,11 In the past few years, these molecular objects have been considered as excellent inorganic coordination blocks for the construction of metal derivatives of POMs.12,13 Among them, lanthanide derivatives of POMs have been documented with interesting magnetic properties, such as single-molecule magnets (SMMs) behavior.14−16 Thanks to the pioneering work conducted by Coronado,14,17−19 Wang,16,20 Niu,35,36 Yang37 et al., several POMbased SMMs decorated by POM ligand have been reported, such as [Ln(W5O18)2]9−,14 [Ln(β2-SiW11O39)2]13−,17 and [Ln(α-PW11O39)2]9−.18 Then a large number of hybrid POM materials exhibiting SMMs’ properties have been prepared by dispersing high-spin anisotropic units into POMs’ anionic structure19,20 or employing POMs as a template to construct polynuclear structure with SMM behavior.16,21 A recent aspect of this research field is focused on the magneto-structural relationship on POM-based SMMs,22,23 but the research on the polyoxomolybdates-based SMMs is still in its infancy. Moreover, obtaining POM-based SMMs requires skills and experience, due to the precipitation of lanthanide cations with POM anions instead of forming the target molecules. © XXXX American Chemical Society

Therefore, it is necessary to design an easy-chemical route to obtain POM-based SMMs and investigate their magnetostructural relationship in depth. To this end, four novel Weakley-type polyoxomolybdates [Bu 4 N] 3 {Tb[Mo 5 O 13 (OMe) 4 (NO)] 2 } (1), [Bu 4 N] 3 {Dy[Mo5O13(OMe)4(NO)]2} (2), [Bu4N]3{Ho[Mo5O13(OMe)4(NO)]2} (3), and [Bu4N]3{Er[Mo5O13(OMe)4(NO)]2} (4) were designed and prepared using a one pot route. It is envisioned that such Weakley-type polyoxomolybdates could exhibit interesting magnetic performance, since the lanthanide ion is trapped by two functionalized lacunar Lindqvist-type fragments [Mo5O13(OMe)4(NO)]3−. Moreover, the structural similarity, between compounds 1−4 and reported POM-based SMMs [Ln(W5O18)2]9−, may provide a fundamental investigation on the ligand field difference (elemental difference) toward SMM behavior, to better understand the magneto-structural relationship.

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EXPERIMENTAL SECTION

General Methods and Materials. All chemicals were purchased and used as supplied without further purification. [Bu4N]4[α-Mo8O26] was prepared by the treatment of (NH4)6Mo7O24·4H2O with tetrabutylammonium bromide ([Bu4N]Br) in water. Other chemical Received: August 8, 2017

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DOI: 10.1021/acs.inorgchem.7b01971 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1. One-Pot Route To Fabricate [Bu4N]3{Ln[Mo5O13(OMe)4(NO)]2} series

(CH3OH, nm): λmax = 205; ESI-MS (CH3OH, m/z): 1046.6(calcd 1047.2) assigned to {[Bu4N]Er[Mo5O13(OMe)4(NO)]2}2−. X-ray Crystallography. Suitable crystals were mounted on glass fibers and transferred to the diffractometer immediately. All data collections were performed on a Rigaku RAXIS-SPIDER IP diffractometer at 50 kV and 20 mA, using graphite monochromatized Mo Kα radiation (λ = 0.71073 Å) at 94(2) K. Data collection, data reduction, cell refinement, and experimental absorption correction were performed with the software package of Rigaku RAPID AUTO (Rigaku, 1998, Ver2.30). Structures were solved by direct methods and refined against F2 by full matrix least-squares. All nonhydrogen atoms, except disordered atoms, were refined anisotropically. Hydrogen atoms were generated geometrically. All calculations were performed using the SHELXS-97 program package. Magnetic Measurements. Static (DC) susceptibility measurements were performed for polycrystalline sample of compounds 1−4 on a Quantum Design MPMS XL-5 SQUID magnetometer. Dynamic (AC) susceptibility measurements for same samples were performed on Quantum Design PPMS-9 with the ACMS option. Samples were fixed into a capsule by N-grease to avoid movement during measurement. Data were corrected for the diamagnetism of samples (using Pascal constants), N-grease, and the capsule. Theoretical Calculations. Complete active space self-consistent field (CASSCF) calculations on individual lanthanide fragments have been carried out with MOLCAS 8.0 program package. We did the calculation with the complete structures of compound 2 without counterions and the noncoordinated solvents. The basis sets for Dy and close O atoms are atomic natural orbitals from the MOLCAS ANO-RCC library: ANO-RCC-VTZP for Dy(III) ions; VDZ for close O. The basis of other atoms is from the ano-dk3 library. The calculations employed the second-order Douglas−Kroll−Hess Hamiltonian, where scalar relativistic contractions were taken into account in the basis set and the spin−orbit coupling was handled separately in the restricted active space state interaction (RASSI-SO) procedure. The active electrons in seven active spaces include all f electrons in the CASSCF calculation. We have mixed the 21 sextets out of 21, 128 quartets out of 224, and 130 doublets out of 490 of the spin-free state.

reagents used in the synthesis were analytical pure and used without further purification. IR spectra were measured by using a PerkinElmer FT-IR spectrophotometer in the range of 4000−400 cm−1 with the resolution of 4 cm−1. UV−vis spectra were measured in methanol using UV2100s spectrophotometer. Elemental analyses for N, C, and H were detected by Elementar Vario EL III, and Mo was detected by Flash EA 1112 full-automatic microanalyser. ESI-MS spectra were obtained by using a Finnigan LCQ Deca XP Plus ion trap mass spectrometer (San Jose, CA), and all experiments were carried out in the negative-ion mode. Synthesis of [Bu4N]3{Tb[Mo5O13(OMe)4(NO)]2} (compound 1). A mixture of [Bu4N]4[α-Mo8O26] (2.5 mmol, 5.38 g), NH2OH (2.4 mmol, 0.173 g), DCC (4.4 mmol, 0.908 g), and Tb(NO3)3·6H2O (2 mmol, 0.906 g) were added into 20 mL anhydrous methanol and refluxed for 3 h. During the reaction procedure, the color of solution turned to purple. By cooling it down to room temperature, white precipitate (N,N′-dicyclohexylurea) and yellow precipitate ([Bu4N]2[Mo6O19]) were removed by filtration. With the evaporation of methanol from the filtrate, the purple crystals appeared (1.60 g, yield 52%). Elemental analysis calcd (%) for C56H132TbMo10N5O36 (M = 2569.97): C, 26.17; N, 2.73; H, 5.18; Mo, 37.33. Found: C, 26.25; N, 2.73; H, 5.24; Mo, 37.28. IR (KBr pellet, major peaks, cm−1): 2961, 2931, 2874, 2815, 1630, 1481, 1380, 1034, 936, 837, 687; UV−vis (CH3OH, nm): λmax = 205; ESI-MS (CH3OH, m/z): 1042.1(calcd 1043.0) assigned to {[Bu4N]Tb[Mo5O13(OMe)4(NO)]2}2−. Synthesis of [Bu4N]3{Dy[Mo5O13(OMe)4(NO)]2} (compound 2). Compound 2 was prepared in the same way as compound 1 except that Dy(NO3)3·6H2O was used instead. With the evaporation of methanol from the filtrate, purple crystals appeared (2.12 g, yield 41%). Elemental analysis calcd (%) for C56H132DyMo10N5O36 (M = 2573.57): C, 26.13; N, 2.72; H, 5.17; Mo, 37.28. Found: C, 26.21; N, 2.69; H, 5.23; Mo, 37.12. IR (KBr pellet, major peaks, cm−1): 2961, 2931, 2874, 2815, 1630, 1481, 1380, 1034, 936, 837, 687; UV−vis (CH3OH, nm): λmax = 205; ESI-MS (CH3OH, m/z): 1044.6(calcd 1044.8) assigned to {[Bu4N]Dy[Mo5O13(OMe)4(NO)]2}2−. Synthesis of [Bu4N]3{Ho[Mo5O13(OMe)4(NO)]2} (compound 3). Compound 3 was prepared in the same way as compound 1 except that Ho(NO3)3·6H2O was used instead. With the evaporation of methanol from the filtrate, purple crystals appeared (2.50 g, yield 48%). Elemental analysis calcd (%) for C56H132HoMo10N5O36 (M = 2575.97): C, 26.11; N, 2.72; H, 5.16; Mo, 37.24. Found: C, 26.18; N, 2.72; H, 5.22; Mo, 36.12. IR (KBr pellet, major peaks, cm−1): 2961, 2931, 2874, 2815, 1630, 1481, 1380, 1034, 936, 837, 687; UV−vis (CH3OH, nm): λmax = 205; ESI-MS (CH3OH, m/z): 1045.6(calcd 1046.0) assigned to {[Bu4N]Ho[Mo5O13(OMe)4(NO)]2}2−. Synthesis of [Bu4N]3{Er[Mo5O13(OMe)4(NO)]2} (compound 4). Compound 4 was prepared in the same way as compound 1 except that Er(NO3)3·5H2O was used instead. With the evaporation of methanol from the filtrate, purple crystals appeared (1.15 g, yield 22%). Elemental analysis calcd (%) for C56H132ErMo10N5O36 (M = 2578.37): C, 26.08; N, 2.72; H, 5.16; Mo, 37.21. Found: C, 26.16; N, 2.68; H, 5.24; Mo, 37.06. IR (KBr pellet, major peaks, cm−1): 2961, 2931, 2874, 2815, 1630, 1481, 1380, 1034, 936, 837, 687; UV−vis

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RESULTS AND DISCUSSION Synthetic Methods. To synthesize compounds 1−4, the following procedure was designed (Scheme 1). According to literatures, [Bu4N]3{M[Mo5O13(OMe)4(NO)]2} (M = Ca2+, Sr2+, Ba2+, Ce3+, Eu3+ and Bi3+) could be obtained by replacing sodium from [Bu4N]2{[Na(MeOH)][Mo5O13(OMe)4(NO)]}· 3MeOH (short as NaMo5) with other metal cations, which is an effective but two-step approach.24,25 We wondered whether a one-pot reaction could be used to directly obtain compounds 1−4. Inspired by our previous works on imidoylization of POMs,26,27 we applied the DCC as the dehydrating agent to remove the water in the product. By mixing (Bu4N)4[αMo8O26], DCC, NH2OH, and Ln(NO3)3·6H2O in refluxing methanol for 3 h, the 2:1 co mp lexes o f {Ln[Mo5O13(OMe)4(NO)]2}3− were directly obtained. Based on B

DOI: 10.1021/acs.inorgchem.7b01971 Inorg. Chem. XXXX, XXX, XXX−XXX

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in agreement with the typical geometric features of Weakley structure.28 The MoN triple bond shows an extended bond length (1.76−1.78 Å) compared to previously reported organoimido functionalized polyoxomolybdate.29 With the trend in the lengthening of the MoN triple bond, there is a concomitant lengthening of the N−O bond for compounds 1−4 (1.20−1.21 Å) compared to [Mo6O18(NO)]2−(1.02−1.16 Å). This variation is consistent with the increase in ν(NO) from 1575 cm−1 ([Mo6O18(NO)]2−) to 1630 cm−1 ({Ln[Mo5O13(OMe)4(NO)]2}3−), which indicates that the net electron donating is less from the [Mo6O18(NO)]2− core than from the {Ln[Mo 5O 13(OMe)4(NO)]2 }3−. This is consistent with other lacunary Lindqvist-type polyoxometalates.25 We now focus on the coordination geometry of the lanthanide in compounds 1−4 (Table 1). On the one hand,

this method, a series of lanthanide metals (La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) containing Weakley-type polyoxomolybdates were successfully prepared and confirmed by various structural characterizations. Thus, this improved “one-pot” route is of considerable generality for the fabrication of Weakley-type polyoxomolybdates. Characterization. The as-prepared products were characterized and analyzed by IR and UV−vis spectroscopic studies. The IR spectra of LnMo10 series are very similar to each other and in agreement with the typical Lindqvist-type structures (Figure S1). The characteristic peaks at 936 and 837 cm−1 are assigned to the vibration of terminal MoOt units, and those at 687 cm−1 are assigned to the vibration of the Mo−Ob−Mo groups. In addition, the peaks at 1630 and 1030 cm−1 are diagnostic peaks of the −NO vibration and the C−O stretching vibrations of the −OCH3 groups, respectively. By comparing with the IR spectrum of NaMo5, the peaks of two hybrids in the range from 900 to 800 cm−1, which are assigned to MoOt vibration, are different from each other because of the different replacement of mono- or trivalent cations of two compounds. The formation of compounds 1−4 were further demonstrated by UV−vis spectra. As shown in Figure S2, the absorbance at 205 nm is attributed to O to Mo charge-transfer transition. And the shoulder band at 564 nm is assigned to the dxz,yz → dxy transition within the {Mo(NO)}3+ units. All of the above results demonstrate the formation of target Weakley-type polyoxomolybdates. Structure Description. Single-crystal X-ray diffraction studies further confirmed that the target compounds were successfully synthesized. The asymmetric unit contains one cluster anion of {Ln[Mo5O13(OMe)4(NO)]2}3−, three cations of [Bu4N] +, and two methanol or one ether solvent molecule, forming the molecular formula [Bu4N]3{Ln[Mo5O13(OMe)4(NO)]2}·2CH3OH (Ln = Dy, Ho, Er) or [Bu4N]3{Tb[Mo5O13(OMe)4(NO)]2}·C4H10O. As shown in Figure 1, the central Ln3+ cation interacts with two functionalized lacunary Lindqvist-type fragments {Mo5O13(OMe)4(NO)}3− acting as tetradentate inorganic ligands and providing an eight-coordination environment to form an anion cluster {Ln[Mo5O13(OMe)4(NO)]2}3−, which is

Table 1. Structural Parameters Concerning the Lanthanide Coordination Sphere compd

φ (deg)

Φ (deg)

din (Å)

dpp (Å)

1 2 3 4

38.3(3) 39.1(0) 39.5(5) 39.4(7)

1.99(4) 1.97(8) 1.96(3) 1.88(4)

2.80(9) 2.79(7) 2.78(3) 2.77(1)

2.67(2) 2.66(2) 2.63(7) 2.62(5)

depending on the skew angle (φ) between the two sets of donor oxygen atoms in monovacant POMs, compounds 1−4 are distorted square antiprismatic with φ values of 38.3° (compound 1), 39.1° (compound 2), 39.5° (compound 3) and 39.4° (compound 4), respectively. Moreover, the dihedral angle between two coordination planes (ϕ) was found to be around 2.0°. All of the above parameters confirm that compounds 1−4 correspond to approximate D4d local symmetry. On the other hand, the distance between two adjacent oxygen donors of the same subunit (din) ranges from 2.81 Å (compound 1) to 2.77 Å (compound 4) and the interplanar distance between two subunit (dpp) ranges from 2.67 Å (compound 1) to 2.62 Å (compound 4), which coordinates with the axial compressed exhibited by the [ErW10O36]9−.14 Therefore, compounds 1−4 are with compressed pseudo-D4d local symmetry. Magnetic Properties. The direct current (DC) magnetic susceptibilities of compounds 1−4 have been measured and are shown as χmT vs T plots (Figure 2). The χmT values at 300 K for compounds 1−4 are 11.72, 13.75, 13.80, and 11.36 cm3 K mol−1, respectively, which are close to the value expected for one free single Ln3+ cation (1: 11.82 cm3 K mol−1, 2: 14.17 cm3

Figure 1. (a) Crystal structure of compound 2 with thermal ellipsoids is drawn at the 50%. (b, c) Coordination environment of the central lanthanide cation: (b) top and (c) side projections.

Figure 2. Temperature dependence of χmT for compounds 1−4. Data are measured upon heating under 1k Oe. C

DOI: 10.1021/acs.inorgchem.7b01971 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. (a) In-phase (χm′) and out-of-phase (χm″) AC susceptibility vs temperature of compound 2 at 1k Oe applied field. (b) Fitted Orbach and Raman processes with the experimental data points.

K mol−1; 3: 14.07 cm3 K mol−1; 4: 11.48 cm3 K mol−1). An obvious decrease of χmT can be found for compounds 1−3 upon cooling, with χmT values of 2.09 cm3 K mol−1 (compound 1), 6.15 cm3 K mol−1 (compound 2), 6.69 cm3 K mol−1 (compound 3) at 2 K, respectively. However, for compounds 4, χmT is almost constant at low temperature, which is still 10.23 cm3 K mol−1 at 2K. Moreover, according to M vs H/T measurements (Figure S4), nonsuperposition and unsaturation in high field can be observed for all compounds, which indicates strong anisotropic susceptibility of central Ln3+ cation. In alternating current (AC) susceptibility measurements, the slow relaxation of magnetization is observed for compound 2 based on the appearance of out-of-phase signals below 6 K, suggesting a SMM behavior of compound 2. As shown in Figures 3a and S7, after applying 1k Oe DC field, temperaturedependent out-of-phase peaks can be found between 2.8 K (100 Hz) and 4.4K (10 kHz), which indicates the existence of thermal magnetic relaxation. If we only consider the Orbach process, the fitted Ueff is 49.6 K, with τ0 = 1.36 × 10−10 s. However, in Figure 3b, the curved line lg(τ) vs 1/T graph shows a different relaxation process existing. So multiprocess fitting should be carried out, but on the other hand, the limited number of the data points do not allow for many parameters. Considering the applied field and fast relaxation, it is assumed that the quantum tunneling is quenched, and the direct process is slow enough to be neglected. So the equation becomes

interaction, and dipole−dipole interaction. In compound 2, 6 H15/2 branched term can be split into eight Kramers doublets (Figure 4, calculated from ab initio below). The gap between

Figure 4. Energy level graph of eight double degenerates. The x axis is the theoretical magnetic moments of individual states, and the y axis is the relative energy. Arrows represent the possible relaxation process with the matrix element between linked states, indicating property of transition.

ground and first excited states is close to the energy barrier if the Orbach process is dominant. Compared to DyW10, the relaxation in compound 2 is much slower. In order to investigate the reason for the difference, ligand field fitting from DC data using CONDON is carried out.32 If we only take the skew angle into account, neglecting the dihedral angle, the ligand field would have B44 and B64 beside the axial term. The fitted gap between ground and exited states is 77.0 K, larger than the experimental result 50 K. Ueff would be smaller than the energy barrier of Orbach process because of the existence of the other relaxation process, like the Raman process. The ground state is mixed with |±15/2⟩, |±7/2⟩, |∓1/2⟩. Among them, |∓1/2⟩ is the main component. Because of the involvement of B44 and B64 terms, the states with ΔmJ = 4 are mixed. Moreover, it is possible that the easy axis is not parallel to the pseudo-S8 axis because of distortion. Theoretical Calculation. To explore the possibility, we performed ab initio calculations of the CASSCF type on the electronic structure of {Dy[Mo5O13(OMe)4(NO)]2}3− using MOLCAS 8.0.33 The calculated energy gap between ground and the first excited states is only 13 cm−1, which is much smaller than the fitted effective energy barrier and the same gap from DC fitting. The calculated ground state is mainly |±15/2⟩ with

1 1 = CT n + e(−Ueff / kT ) τ τ0

The fitted energy barrier is similar, Ueff = 50 K, with τ0 = 1.4 × 10−10 s and C = 2.2 with n = 5. The Raman process is rational according to literature.30,31 As shown in Figure S10, Cole−Cole fitting also provides evidence for a single Orbach process under DC field. A general Debye model is used to fit χm′ and χm″ data from 2.8K to 4.4K. The fitted α is 0.16−0.21, showing a single process in the temperature range. Such a magnetic behavior of compound 2 is mainly attributed to the following reasons. Considering the distance between lanthanide ions, the relaxation property is mainly contributed by single ions. Ligand field may strongly affect the relaxation. Although the Dy3+ ion is a Kramers ion, ground states can be mixed if the ligand field is not axial. The geometry of the eight coordinated atoms are twisted, deviated from D4d, which may generate a transverse term of anisotropy, causing the mixing of ground states and excited states. The fast relaxation can be attributed to quantum tunneling at zero field, but it is suppressed by applied field. The quantum tunneling may be caused by the transverse term of anisotropy, hyperfine D

DOI: 10.1021/acs.inorgchem.7b01971 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 5. (a) MOLCAS calculated easy axis (red vector), Magellan predicted easy axis (purple line), and main axis (blue line) of compound 2. Color code for atoms: Dy, green; Mo, blue; O, red; C, gray; N, purple; H, white. (b) Electro-potential energy map from Magellan. Colors represent the value of potential energy. Φ is the angle from the pseudo-main S8 axis. θ is the equational angle.

g = 18.4, which is lower than the theoretical Ising limit g value of 20. The ground state wave functions are dominantly with 89% |±15/2⟩, mixed with terms: 5.0% |±11/2⟩, 1.7% |±7/2⟩, 1.5% |±3/2⟩, and 1.3% |∓1/2⟩. Mixing also causes large offdiagonal terms in the crystal field matrix. The matrix elements between the ground state degenerate doublets are large (Figure 4), showing that relaxation processes other than Orbach process are likely to happen. Moreover, the direction of the ground-state easy axis is far from the pseudo-S8 main axis, with the angular difference 89.9° (Figure 5a and Table S4). This is almost perpendicular to the main axis. The easy axis of lowlying first excited states is also perpendicular to the main axis (86.6°) as well as perpendicular to those of the ground states (74.7°). According to the din and dpp (Figure 1c, d), the pseudoD4d coordination sphere is slightly compressed, so that the oblate |±15/2⟩ on the main axis direction is not favored according to energy. This means that compound 2 has an “easy plane”, although the calculated ground states are still an Ising type. To investigate the easy plane, the energy minimization by Magellan34 was conducted to confirm the situation when only the electrostatic repulsion was taken into consideration. As shown in Figure S11, the predicted easy axis is only 5.8° from the theoretical ground state easy axis. It is also perpendicular to the main axis (Figure 5a). The shape of the energy surface shows that the directions perpendicular to the main axis are favored (Figure 5b). Therefore, our work indicates that compound 2 has high magnetic anisotropy and slow relaxation from easy-plane anisotropy under applied field. The g-tensor from ab initio calculation suggests easy axis ground states. However, if the temperature increases, the first excited states would be populated and the susceptibility would turn into an easy plane. In Figure S12, the eigen values from of the susceptibility tensors at different temperatures are plotted and became a pseudo-easy plane at around 25 K.

analysis reveals that the Dy analogue is a SMM. Theoretical studies prove the existence of strong anisotropy and demonstrate the orientation of an easy plane. In addition, the relaxation processes other than Orbach process are likely to happen based on the analysis of the experimental results and ab initio calculations. All in all, this line of research represents an example of POM-based SMMs and provides guidance for investigating the magneto-structural relationship for the POMbased SMMs.

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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.7b01971. IR, UV−vis, supporting magnetic data and calculation data (PDF) Accession Codes

CCDC 1511993−1511996 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

Shan She: 0000-0003-1340-7558 Yongge Wei: 0000-0001-6105-0288

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Author Contributions

CONCLUSIONS In summary, a series of Weakley-type polyoxomolybdates [Bu4N]3{Ln[Mo5O13(OMe)4(NO)]2} (Ln = Tb, Dy, Ho, Er) were synthesized and structurally characterized. The magnetic

§

These authors contributed equally to this work.

Notes

The authors declare no competing financial interest. E

DOI: 10.1021/acs.inorgchem.7b01971 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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ACKNOWLEDGMENTS This work was sponsored by the National Natural Science Foundation of China (NSFC nos. 21225103, 21471087, and 21221062) and Tsinghua University Initiative Foundation Research Program (no. 20131089204). We thank our colleague, Mr. Zehuan Huang, for helpful discussions.

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DOI: 10.1021/acs.inorgchem.7b01971 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Dysprosium(III) Single-Molecule Magnet. Inorg. Chem. 2017, 56, 12687. (36) Ma, P.; Hu, F.; Huo, Y.; Zhang, D.; Zhang, C.; Niu, J.; Wang, J. Magnetoluminescent Bifunctional Dysprosium-Based Phosphotungstates with Synthesis and Correlations between Structures and Properties. Cryst. Growth Des. 2017, 17, 1947. (37) Xue, H.; Zhao, J. W.; Pan, R.; Yang, B. F.; Yang, G. Y.; Liu, H. S. Diverse Ligand-Functionalized Mixed-Valent Hexamanganese Sandwiched Silicotungstates with Single-Molecule Magnet Behavior. Chem. - Eur. J. 2016, 22, 12322.

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DOI: 10.1021/acs.inorgchem.7b01971 Inorg. Chem. XXXX, XXX, XXX−XXX