Hierarchical Assembly of a {Co24} Cluster from Two Vertex-Fused

May 3, 2018 - Han-Fu Liu,. †. Di Yao,. † and Fu-Ping Huang*,†. †. State Key Laboratory for the Chemistry and Molecular Engineering of Medicina...
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Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Hierarchical Assembly of a {Co24} Cluster from Two Vertex-Fused {Co13} Clusters and Their Single-Molecule Magnetism Peng-Fei Yao,†,‡ Yun-Kai Chen,† Chao-Feng Lai,† Hai-Ye Li,† He-Dong Bian,*,†,§ Han-Fu Liu,† Di Yao,† and Fu-Ping Huang*,†

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†

State Key Laboratory for the Chemistry and Molecular Engineering of Medicinal Resources, School of Chemistry and Pharmacy, Guangxi Normal University, Guilin, 541004, People’s Republic of China ‡ Key Laboratory of Regional Ecological Environment Analysis and Pollution Control of West Guangxi, College of Chemistry and Environmental Engineering, Baise University, Baise, Guangxi 533000, People’s Republic of China § School of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Key Laboratory of Chemistry and Engineering of Forest Products, Nanning 530008, People’s Republic of China S Supporting Information *

ABSTRACT: We present the synthesis, structural characterization, and magnetic properties of two high-nuclearity cobalt clusters formulated as [Co13(μ3-OH)3(μ3-Cl)(dpbt)5(ptd)Cl10 ][Co(H 2O)2 Cl2 ]·(CH 3) 2 CHOH (1) and [Co24 (μ3 OH)6(μ3-Cl)2(dpbt)10(ptd)2Cl16]·2CH3CH2OH (2), respectively (H2dpbt = 5,5′-bis(pyridin-2-yl)-3,3′-bis(1,2,4-triazole) and H2ptd = 3-(pyridin-2-yl)-1,2,4-triazine-5,6-diol). Compound 1 is composed of an inner [Co4(μ3-OH)3(μ3-Cl)] cubane and an outer [Co9(dpbt)5(ptd)Cl10] defective adamantane. Compound 2 reveals a giant {Co24} cluster possessing a dual-[Co12] skeleton from 1. The hierarchical assembly from 1 to 2 has been established and tracked through high-resolution electrospray ionization (HRESI-MS) analyses from the solvothermal reaction mother solution. Magnetic studies of 1 and 2 revealed the highly correlated spins, a glasslike magnetic phase transition at ca. 8 K, and slow relaxation behavior of SMM nature in the lower-temperature region (below 4 K).

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INTRODUCTION Much attention is being devoted to the synthesis, characterization, and magnetism of high-nuclearity clusters with large spin ground states since the discovery of “single-molecule magnets” (SMMs) due to their potential applications in information storage, quantum computing, magnetic refrigeration, and spintronics.1,2 Different from the well-documented MnIII SMMs with large magnetic anisotropy (Dmol < 0), CoII ions always have exceptionally large single ion anisotropy (Dion > 0) and weak Jahn−Teller distortion. For CoII SMMs, it is necessary to design an appropriate metal skeleton which displays large spin multiplicity and Ising magneto-anisotropy (Dmol < 0), leading to a high thermal barrier (U) for magnetization reversal.3 Previous investigations of CoII-based SMMs4,5 imply that a μ3-O bridged Co4O4 cubane skeleton favors ferromagnetic coupling between neighbors, in which orthogonal hard-axis alignment of four positive Dion values may result in a negative Dmol value for the clusters.6 High-nuclearity CoII clusters with a range of coordination geometries are favorable for generating intriguing magnetic characteristics of SMMs for their high-spin ground © XXXX American Chemical Society

states and significant anisotropy. Although remarkable success has been achieved in the field of high-nuclearity CoII clusters, there are only limited examples of {Con} superclusters with n ≥ 20.7 For the conventional formation of a high-nuclearity cluster, a “one-pot” procedure is usually involved from simple cobalt(II) salts. Recently, a technique called “hierarchical assembly”, starting from substable low-nuclearity units that can respond to environmental change, was introduced for the construction of various sophisticated aggregations.8 Along this direction, our group had reported the hierarchical assembly of an infinite 2-D cluster-organic framework facilitated by discrete {Co14} clusters in which the mutual interdigitation of adjacent {Co14} clusters is stimulated by pH control, displaying slow magnetic relaxation behavior.9 Inspired by the success of pH-stimuli hierarchical assembly, we took up the challenge to hierarchically construct discrete higher-nuclearity metal arrays on optimization of the Received: May 3, 2018

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DOI: 10.1021/acs.inorgchem.8b01211 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Crystal and Structure Refinement Data for 1 and 2 (Squeezed) empirical formula formula wt cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (Mg m−3) F(000) no. of collected/unique rflns Rint final R indices (I > 2σ(I)) R indices (all data)

1

2

C78H48Cl13Co14N44O7 2999.47 monoclinic P21/n 18.3838(6) 33.310(2) 22.7862(12) 90 97.810(4) 90 13824.1(12) 4 1.432 5880 55219/24716 0.091 R1 = 0.1119, wR1 = 0.2848 R2 = 0.2135, wR2 = 0.3390

C158H98Cl18Co24N88O10 5441.66 monoclinic P21/c 18.6258(5) 44.1431(9) 19.1469(6) 90 114.701(3) 90 14302.1(6) 2 1.247 5312 45524/27598 0.046 R1 = 0.0697, wR1 = 0.1800 R2 = 0.1156, wR2 = 0.2007

in isopropyl alcohol (15 mL) were stirred in a Teflon-lined autoclave and placed under autogenous pressure at 120 °C for 3 days. Blue needlelike X-ray-quality crystals were obtained and picked out, washed with isopropyl alcohol, and dried in air (yield ca. 31% based on Co(II)). Anal. Calcd for C81H56Cl13Co14N44O8: C, 31.80; H, 1.84; N, 20.14. Found: C, 31.54; H, 1.58; N, 20.38. IR (KBr): 3428(s), 1613(s), 1546(m), 1529(m), 1476(s), 1452(s), 1424(s), 1385(w), 1308(w), 1259(m), 1196(m), 1154(s), 1105(w), 1038(w), 1013(m), 838(w), 800(m), 751(m), 722(s), 638(m), 575(w), 491(w), 418(w) cm−1. Synthesis of 2. Method 1. H2dpbt (0.145 g, 0.5 mmol), H2ptd (0.019 g, 0.1 mmol), CoCl2·6H2O (0.143 g, 0.6 mmol), and triethylamine (0.25 mL) in methanol (1 mL) and ethanol (15 mL) were stirred in a Teflon-lined autoclave and placed under autogenous pressure at 160 °C for 3 days. Dark green block X-ray-quality crystals (Figure S1) were obtained; they were picked out, washed with ethanol, and dried in air (yield ca. 37% based on Co(II)). Anal. Calcd for C166H110Cl18Co24N88O12: C, 35.72; H, 1.99; N, 22.08. Found: C, 35.35; H, 2.26; N, 22.33. IR (KBr): 3422(s), 2368(w), 2341(w), 1624(m), 1599(s), 1567(m), 1506(w), 1457(m), 1427(m), 1383(s), 1303(w), 1278(m), 1262(m), 1248(s), 1174(w), 1158(s), 1117(m), 1051(m), 1029(s), 999(w), 881(s), 798(w), 752(w), 730(w), 716(w), 631(w), 554(w) cm−1. Method 2. As-synthesized 1 (ca. 20 mg of single crystals) and triethylamine (0.25 mL) in methanol (1 mL) and ethanol (15 mL) were stirred in a Teflon-lined autoclave and placed under autogenous pressure at temperatures of 130, 140, 150, and 160 °C for 3 days, respectively. The resulting dark green block crystals of 2 mixed with the residual blue needle crystals of 1 were obtained in yields of about 7%, 11%, 19%, and 27% (based on 1), respectively. In method 2, we also attempt to hydrothermally synthesize 2 from 1 in isopropyl alcohol, butanol, DMF, DMSO, CH3CN, etc. at higher temperature. No crystalline sample of 2 could be obtained, indicating that the higher temperature is conducive to the formation of compound 2 and the solvent environment also plays an important role in the crystallization of 2. X-ray Crystallography. Diffraction data were collected on an Oxford Supernova diffractometer (Mo, λ = 0.71073 Å) by using the θ−ω scan technique at 150 K, and the absorption corrections were applied by SADABS. The structures were solved by direct methods using ShelXS and refined using a full-matrix least-squares technique within ShelXL2015 and OLEX.2.11 C-bound H atoms were placed geometrically and refined as riding atoms. Solvent molecules in 1 and 2 are significantly disordered and could not be modeled properly due to the lack of well-defined atomic positions; thus, the SQUEEZE procedure implemented in PLATON was used to calculate the solvent disorder volume and remove its contribution to the overall intensity

environmental factors (e.g. pH, anions, solvent, and temperature). In the present study, a discrete Co13 cluster formulated as [Co 13 (μ 3 -OH) 3 (μ 3 -Cl)(dpbt) 5 (ptd)Cl 10 ][Co(H 2 O) 2 Cl 2 ]· (CH3)2CHOH (1) (here H2dpbt = 5,5′-bis(pyridin-2-yl)-3,3′bis(1,2,4-triazole) and H2ptd = 3-(pyridin-2-yl)-1,2,4-triazine5,6-diol) was obtained. 1 is composed of an inner [Co4(μ3OH)3(μ3-Cl)] cubane and an outer [Co9(dpbt)5(ptd)Cl10] defective adamantane. The nested [Co4⊂Co9] skeleton of 1 has a reduced symmetry compared to the mentioned {Co14} clusters with [Co4⊂Co10] skeleton, when dpbt is replaced with ptd.9 Interestingly, on hydrothermal reaction starting from the crystalline precursor of 1 in methanol/ethanol at higher temperature, we can obtain a novel {Co24} supercluster, [Co 24 (μ 3 -OH) 6 (μ3 -Cl)2 (dpbt)10 (ptd) 2 Cl 16 ]·2CH 3 CH 2 OH (2), in which two of the Co(II) vertices from the neighboring {Co13} cluster of 1 are fused to form a giant cluster with a double-[Co12] skeleton. In addition, the assembly process from 1 to 2 was briefly tracked from the reaction solutions by mass spectrometry. Magnetic studies of 1 and 2 revealed highly correlated spins, a glasslike magnetic phase transition at ca. 8 K, and slow relaxation behavior of SMM nature below 4 K. The TB (blocking temperature) of 2 is slightly higher than that of 1.

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EXPERIMENTAL SECTION

Materials and Physical Measurements. All reagents were used as received without further purification. IR spectra were taken on a PerkinElmer Spectrum One FT-IR spectrometer in the range 4000− 400 cm−1 by transmission through KBr pellets. Elemental analyses for C, H, and N were carried out on a PerkinElmer Model 2400 II elemental analyzer. X-ray powder diffraction (XRPD) intensities were measured at 293 K on a Rigaku D/max-IIIA diffractometer (Cu Kα, λ = 1.54056 Å). The crystalline powder samples were prepared by crushing the single crystals and scanned from 3 to 65° at a rate of 5°/min. Calculated patterns of 1 and 2 were generated with PowderCell. All magnetic measurements (solid state) were carried out on a Quantum Design MPMS-XL SQUID magnetometer in a temperature range of 2.0−300 K and a dc field of 1000 Oe. Diamagnetic corrections were made using Pascal’s constants.10 TG-DTA tests were performed on a PerkinElmer thermal analyzer from room temperature to 1000 °C under an N2 atmosphere at a heating rate of 5 °C min−1. Synthesis of 1. H2dpbt (0.145 g, 0.5 mmol), H2ptd (0.019 g, 0.1 mmol), CoCl2·6H2O (0.238 g, 1 mmol), and triethylamine (0.25 mL) B

DOI: 10.1021/acs.inorgchem.8b01211 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry data. SQUEEZE results of 1 and 2 are described in the Supportting Information. Experimental details of the X-ray analyses are provided in Table 1. Selected bond distances and angles are given in Tables S1 and S2. Crystallographic data for the structural analyses have been deposited at the Cambridge Crystallographic Data Centre, with reference numbers 1420281 for 1 and 1420282 for 2. Mass Spectrometry Measurements. HRESI-MS measurements were conducted at a capillary temperature of 275 °C. Aliquots of the solution were injected into the device at 0.3 mL/h. The mass spectrometer used for the measurements was a ThermoExactive instrument, and the data were collected in positive and negative ion mode. The spectrometer was previously calibrated with the standard tune mix to give a precision of ca. 2 ppm in the region of m/z 400−2000. The capillary voltage was 50 V, the tube lens voltage was 150 V, and the skimmer voltage was 25 V. The in-source energy was set to a range of 0 eV with a gas flow rate at 10% of the maximum.

The Co24 cluster in 2 can be viewed as a vertex-fused double[Co4⊂Co9] skeleton, in which two cubic [Co4(μ3-OH)3(μ3Cl)] cores are encapsulated into a [Co16(dpbt)10(ptd)2Cl14] defected vertex-fused double-adamantane periphery (Figure 2).

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RESULTS AND DISCUSSION Crystal Structure. The asymmetric unit of 1 contains a [Co13(μ3-OH)3(μ3-Cl)(dpbt)5(ptd)Cl10] cluster and a [Co(H2O)2Cl2] molecule as well as a highly disordered isopropyl alcohol molecule. As shown in Figure 1, the Co13 cluster with

Figure 2. Crystal structure and cluster topology of the [Co24(μ3OH)6(μ3-Cl)2(dpbt)10(ptd)2Cl16] cluster in 2.

Eight encapsulated Co atoms in a distorted N3O2Cl or N2O4 octahedral environment are held together tightly by Cl− or OH− ions, forming two [Co4(μ3-OH)3(μ3-Cl)] cubic cores. The remaining 16 exterior Co atoms consist of 2 types of Co centers according to their coordination modes: (1) 8 Co atoms in a distorted N6 or N4O2 octahedral environment are coordinated by 2 ptd and 10 dpbt ligands, binding the 2 [Co4(μ3-OH)3(μ3Cl)] cores; (2) 6 Co atoms in a distorted N2Cl2 tetrahedral environment are coordinated by 6 dpbt and 12 Cl− anions; (3) 2 ambient Co atoms in a distorted N4Cl2 octahedral environment are coordinated by four dpbt2− and four Cl− anions. A detailed comparison of the above two closely related clusters revealed that 2 consists of two edge-sharing clusters of 1, which are mutually interdigitated through two Co(II) atoms in a distorted N4Cl2 octahedral geometry. Hierarchical Assembly from 1 to 2. Supramolecular coordination clusters originating in their potential active sites (coordinately unsaturated metal ions, ligands, anions, etc.) can be organized to hierarchical soft materials and transform within two or multiple states after inducing outer stimuli, including light, templates, heating, pH, solvent, and crystallization.12 Electrospray ionization mass spectrometry (ESI-MS) is a powerful tool to determine the assembly intermediates in solutions by matching experimental mass spectra with calculated isotope distributions. The real-time monitoring of the dynamic molecular species in solution by ESI-MS could provide rich information (such as structural integrity, fragment composition, the degree of protonation, and even revelation of the assembly mechanism) about bonding and the way reactions progress, which are the deeper aim in assembly chemistry.13−15 By immersion of reasonably sized blue needle crystals (ca. 20 mg) of 1 in methanol/ethanol in a Teflon-lined autoclave at a higher temperature range of 130−160 °C for 3 days, the

Figure 1. Crystal structure and cluster topology of the [Co13(μ3OH)3(μ3-Cl)(dpbt)5(ptd)Cl10] cluster in 1.

nested [Co4⊂Co9] structure consists of 3 types of Co centers according to their coordination mode: 4 inner Co atoms in distorted N3O2Cl (for Co1−Co3) and N2O4 (for Co4) octahedral environments lie at the vertices of the distorted cubic [Co4(μ3-OH)3(μ3-Cl)] core, held together tightly by 1 μ3Cl− and 3 μ3-OH− ions, with the Co−O/Cl distances ranging from 2.018 to 2.590 Å, the Co−O/Cl−Co angles ranging from 80.66 to 110.0°, and the Co···Co distances lying in the range 2.994−3.324 Å. Another 4 outer Co atoms in distorted N6 (for Co5−Co7) and N4O2 (for Co8) octahedral environments are coordinated by 1 ptd and 5 dpbt ligands, to form a distortedtetrahedral Co4L5L′ cage with Co···Co distances in the range of 9.294−9.623 Å separated by the long dpbt and 7.182 Å separated by the short ptd. The remaining 5 Co atoms (for Co9−Co13) in the distorted N2Cl2 tetrahedron are coordinated by 5 dpbt2− ligands and 10 Cl− anions. The cubic Co4 core is bridged to 9 exterior Co atoms, through 5 dpbt and 1 ptd mixed ligands, resulting in a discrete Co13 cluster with a nested [Co4⊂Co9] skeleton, in which a cubic [Co4(μ3-OH)3(μ3-Cl)] core is encapsulated by a [Co9(dpbt)5(ptd)Cl10] defected adamantane shell. C

DOI: 10.1021/acs.inorgchem.8b01211 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 3. (a) Conversion from 1 to 2, showing the different coordination environments of the two peripheral cobalt atoms. (b) Peaks of the timedependent HRESI-MS spectra of the dimerization reaction from Co13 to Co24 clusters: (red) observed isotope patterns; (black) simulated isotope patterns. Inset: expanded spectra of F1−F3. (c) ESI-MS spectral intensity−time profiles of F1−F3.

Figure 4. Temperature dependence of magnetic susceptibility of 1 (a) and 2 (c). Inset: FC magnetization of 1 and 2 in different fields. Zero-field ac magnetic susceptibilities from 2 to 20 K for 1 (b) and 2 (d).

below 130 °C. This result indicates that the higher temperature may be conducive to the formation of compound 2. Indeed, the CoCl2 and Cl− ions tend to diffuse into the mother liquid. When

resulting dark green block crystals of 2 were eventually harvested and characterized. However, no crystalline-state change can be observed upon immersing crystals of 1 in methanol/ethanol D

DOI: 10.1021/acs.inorgchem.8b01211 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 5. Temperature dependence of χM′ and χM″ for 1 and 2, measured at a fixed 100 Hz but different applied static fields (top) and at fixed Hdc = 1000 Oe but different frequencies (bottom).

while the signals of Co18 fragments increased (Figure 3c). This further supports the hierarchical assembly reaction from Co13 to Co24 clusters. Magnetic Properties. Magnetic susceptibility measurements for 1 and 2 were carried out over the temperature range of 2−300 K under an applied field of 1000 Oe (Figure 4). The χMT values decrease gradually from the room-temperature values of 43.32 and 75.33 cm3 K mol−1 to a minimum of 18.06 and 21.84 cm3 K mol−1 at 12 K. These values then increase to reach a maximum of 21.22 and 24.34 cm3 K mol−1 at 8 K and then drop sharply to a minimum of 7.81 and 12.94 cm3 K mol−1 at 2 K, respectively. The final up−down behavior may be attributed to a canted antiferromagnetism induced by the magnetic anisotropy of 1 and 2.16,17 The reciprocal molar susceptibilities at 25−300 K follow the Curie−Weiss law of 1/χM = (T − Θ)/C with Curie constants C = 32.64 and 87.57 cm3 K mol−1 and Weiss constants Θ = −32.17 and −22.76 K for 1 and 2, respectively. The negative Θ values suggest dominant antiferromagnetic interactions between the metal centers and/or the strong spin−orbit coupling effect of octahedral Co(II) with a 4T1g ground term. FC (field-cooled) magnetizations were measured under different applied fields at low temperatures (2−20 K). The magnetic behaviors of 1 and 2 are both markedly field dependent, in which the increases of the χMT values at low temperature become less pronounced at higher fields. Magnetizations measured for both compounds in zero-fieldcooled (ZFC) and field-cooled (FC) modes in fields of 200, 500, 1000, and 2000 Oe show bifurcation around 8 K for the smallest field that moves to lower temperatures with increasing field (Figure S10 and S11). This strong dependence on field suggests highly correlated spins within the cluster that are enhanced by anisotropy.10,18 However, we cannot rule out the possibility of long-range magnetic ordering that may be caused by the weak intercluster interactions.19

1 was treated at a higher temperature, two of the peripheral Co atoms in a distorted N2Cl2 tetrahedral geometry can possibly bind to the exposed dpbt ligands to form a stable octahedral geometry, thereby aggregating the adjacent clusters of 1 to the giant cluster of 2 (Figure 3a and Table S3). Considering the poor solubility of crystals of 1 and 2, the electrospray mass spectrometric experiment of the reaction solutions as a function of time (1, 10, 24, 34, and 48 h) of the solvothermal treatment at a temperature of 160 °C was used to search for information on the reaction process (Figure 3b and Table S3). The spectrum after 1 h shows two main sets of peaks at m/z 1094.47 and 1180.45. Through assigning the fragment ions observed and by analyzing the structural features of the clusters, we were able to propose that the peaks could be assigned to the respective species [Co8(dpbt)5(ptd)(OH)3Cl +2H] 2+ (F1, m/z 1094.47) and [Co 9 (dpbt) 5 (ptd)(OH)2(CH3O)3Cl2+3H]2+ (F3, m/z 1180.45). The F1 fragment has a Co8 composition, which was derived from de(CoCl2)5 of 1. The F3 fragment has a Co9 composition, which could also be derived from de-(CoCl2)4 of 1 after one Cl− ion and one OH− ion were replaced by two CH3O− ions and one CH3OH molecule. After 10 h, the main F1 and F3 peaks are still present and the intensity of F3 has changed marginally. In addition, six new species appeared at m/z 1109.43, 1113.92, 1117.44, 1122.17, 1125.92, and 1129.92, which were assigned to the respective species [Co18(dpbt)10(ptd)2(OH)x(CH3O)yCl8−x−y−z-zH]4+ (F2: (a) x = 7, y = 0, z = 1, m/z 1093.46; (b) x = 6, y = 0, z = 1, m/z 1113.92; (c) x = 5, y = 1, z = 1, m/z 1117.44; (d) x = 4, y = 1, z = 1, m/z 1122.17; (e) x = 3, y = 2, z = 1, m/z 1125.92; (f) x = 4, y = 2, z = 0, m/z 1129.92). These fragments all contain Co18 clusters which were derived from de(CoCl2)6 of 2 (F2f), as well as a series of substitution reactions between the coordination OH−, CH3O− and Cl− anions (F2a− e). Over time, the signals of fragments Co8 and Co9) faded away, E

DOI: 10.1021/acs.inorgchem.8b01211 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry The zero-field alternating-current (ac) magnetic susceptibility measurements of 1 and 2 were performed under Hac = 2.5 Oe and a frequency of 10−999 Hz. Surprisingly, two separated frequency-dependent signals, suggesting a two-step slow relaxation process, were observed respectively in the hightemperature region (4−12 K) and low-temperature region (2−4 K). For the high-temperature region, both components of the ac susceptibilities of 1 and 2 show a peak at ca. 8 K that is weakly dependent on frequency. However, the temperature dependence and magnitude of the magnetization differ. The frequency shifts in 1 and 2 give ϕ ≈ 0.071 and 0.028 (ϕ = ΔTp/[TpΔ(log f)], where Tp is the peak temperature and f is the frequency), respectively, consistent with a glasslike magnetic behavior.20,21 This observation confirms the blocking of the moments in both compounds.22 For the low-temperature region, the in-phase and out-of-phase signals in 1 and 2 both display noticeable frequency dependence. The more obvious frequency shift in 2 gives ϕ = 0.31, consistent with a typical slow relaxation process characteristic of SMM behavior.20,21 In order to better characterize the two-step slow relaxation behaviors in 1 and 2, the ac susceptibilities have been measured first under different applied static fields at a fixed frequency of 100 Hz, as shown in Figure 5. The χ′ and χ″ peak signals at 4−12 K are both gradually suppressed with an increase in the applied static field, consistent with the existence of spin-glass-like behavior.23,24 No obvious field dependence is observed below 4 K, confirming that the second slow relaxation is of different origin. When a fixed Hdc of 1000 Oe is applied, the peaks of the ac susceptibilities for 1 and 2 below 4 K become frequency dependent. The shifting of the χ″ peak to higher temperature for the moderate static field “suppressing tunneling” effect is consistent with SMM slow relaxation behavior.25−27 For 2, the relaxation time τ0 was obtained from the least-squares fitting to the Arrhenius law of the frequency dependence of the ac magnetic susceptibility from 10 to 1000 Hz under Hdc = 0 Oe. This fit gave the parameters τ0 = 8.38 × 10−7 s and ΔE/kB = 18.3 K, where ΔE is the energy barrier and kB is the Boltzmann constant (Figure S12). The Cole−Cole plots of 2 were further fitted using the generalized single-relaxation process Debye model (Figures S13−S15).28 The parameter α is in the range of 0.22−0.32 and is found to increase with a decrease in temperature (Table S4), which further indicates the SMM behavior in 2.

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CONCLUSION

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ASSOCIATED CONTENT

Structural and measurement details (PDF) Accession Codes

CCDC 1420281−1420282 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 for H.-D.B.: [email protected]. *E-mail for F.-P.H.: [email protected]. ORCID

Fu-Ping Huang: 0000-0003-4227-9815 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially sponsored by the National Natural Science Foundation of China (Nos. 21461003 and 21361003), the Guangxi Natural Science Foundation (2016GXNSFFA380010, 2016GXNSFAA380206), and Guangxi Colleges and Universities Key Subject of Material Physics and Chemistry (Nos. KS17ZD02 and KS16ZD04).

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REFERENCES

(1) (a) Kurmoo, M. Magnetic metal−organic frameworks. Chem. Soc. Rev. 2009, 38, 1353−1379. (b) Craig, G. A.; Murrie, M. 3d single-ion magnets. Chem. Soc. Rev. 2015, 44, 2135−2147. (c) Zheng, Y. Z.; Zhou, G. J.; Zheng, Z. P.; Winpenny, R. E. P. Molecule-based magnetic coolers. Chem. Soc. Rev. 2014, 43, 1462−1475. (2) (a) Bi, Y. F.; Du, S. C.; Liao, W. P. Thiacalixarene-based nanoscale polyhedral coordination cages. Coord. Chem. Rev. 2014, 276, 61−72. (b) Novitchi, G.; Shova, S.; Lan, Y. H.; Wernsdorfer, W.; Train, C. Verdazyl Radical, a Building Block for a Six-Spin-Center 2p−3d−4f Single-Molecule Magnet. Inorg. Inorg. Chem. 2016, 55, 12122−12125. (c) Chorazy, S.; Kumar, K.; Nakabayashi, K.; Sieklucka, B.; Ohkoshi, S. Fine Tuning of Multicolored Photoluminescence in Crystalline Magnetic Materials Constructed of Trimetallic EuxTb1−x[Co(CN)6] Cyanido-Bridged Chains. Inorg. Chem. 2017, 56, 5239−5252. (3) (a) Oshio, H.; Nakano, M. High-Spin Molecules with Magnetic Anisotropy toward Single-Molecule Magnets. Chem. - Eur. J. 2005, 11, 5178−5185. (b) Goodenough, J. B. Magnetism and the Chemical Bond; Interscience: New York, 1963. (c) Murrie, M. Cobalt(II) singlemolecule magnets. Chem. Soc. Rev. 2010, 39, 1986−1995. (4) (a) Ma, Y.-S.; Song, Y.; Tang, X.-Y.; Yuan, R.-X. Synthesis and structural and magnetic characterization of a hexadecanuclear cobalt phosphonate compound. Dalton Trans. 2010, 39, 6262−6265. (b) Lisnard, L.; Tuna, F.; Candini, A.; Affronte, M.; Winpenny, R. E. P.; McInnes, E. J. L. Supertetrahedral and Bi-supertetrahedral Cages: Synthesis, Structures, and Magnetic Properties of Deca- and Enneadecametallic Cobalt(II) Clusters. Angew. Chem., Int. Ed. 2008, 47, 9695−9699. (c) Boudalis, A. K.; Raptopoulou, C. P.; Abarca, B.; Ballesteros, R.; Chadlaoui, M.; Tuchagues, J.-P.; Terzis, A. CoII Chemistry of 2,6-Bis(2-pyridylcarbonyl)pyridine: An Icosanuclear Co Cluster Exhibiting Superparamagnetic Relaxation. Angew. Chem., Int. Ed. 2006, 45, 432−435. (d) Shiga, T.; Matsumoto, T.; Noguchi, M.; Onuki, T.; Hoshino, N.; Newton, G. N.; Nakano, M.; Oshio, H. Cobalt Antiferromagnetic Ring and Grid Single-Molecule Magnet. Chem. Asian J. 2009, 4, 1660−1663. (e) Zhang, Y.-Z.; Gao, S.; Sato, O. In situ tetrazole templated chair-like decanuclear azido-cobalt(II) SMM containing both tetra- and octa-hedral Co(II) ions. Dalton Trans. 2015, 44, 480−483.

In this work, an interesting hierarchical assembly from a novel Co13 cluster with a nested [Co4⊂Co9] skeleton to a giant Co24 cluster has been established, accompanied by fusing two CoN2Cl2 tetrahedra into one CoN4Cl2 octahedron. Magnetic studies of 1 and 2 revealed the coexistence of highly correlated spins and spin-glass behavior. Below 4 K, the higher-nuclearity cluster showed interesting SMM at a higher blocking temperature in comparison to the low-nuclearity cluster. The type of hierarchical assembly may provide a general implications in the control of assembly of giant nanoclusters with interesting structural and magnetic features.

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01211. F

DOI: 10.1021/acs.inorgchem.8b01211 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

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DOI: 10.1021/acs.inorgchem.8b01211 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.8b01211 Inorg. Chem. XXXX, XXX, XXX−XXX