Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Humidity Sensitive Structural Dynamics and Solvatomagnetic Effects in a 3D Co(II)-Based Coordination Polymer Long-Fei Wang,† Jiang-Zhen Qiu,† Si-Guo Wu,† Yan-Cong Chen,† Cui-Jin Li,‡ Quan-Wen Li,† Jun-Liang Liu,*,† and Ming-Liang Tong*,† †
Key Lab of Bioinorganic and Synthetic Chemistry of Ministry of Education, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, P. R. China ‡ College of Chemistry and Chemical Engineering, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, P. R. China S Supporting Information *
ABSTRACT: A chiral Co(II)-based coordination polymer, [Co3(pimda)2(H2O)5] (1, H3pimda = 2-propyl-1H-imidazole4,5-dicarboxylic acid) with 3D hyperkagomé topology is reported. Upon heating/cooling, the water molecules which are coordinated to a pair of crystallographically symmetric Co(II) ions are removed/recovered discretely in two steps, giving [Co3(pimda)2(H2O)4] (2) and [Co3(pimda)2(H2O)3] (3), which is evidenced by the reversible single-crystal-tosingle-crystal (SCSC) structural transformations. As the coordination geometry of the two Co(II) ions changes from octahedron to trigonal bipyramid, obvious color change from pink for 1 to dark violet for 2 and 3 is observed. Further magnetic measurements demonstrate the presence of a solvatomagnetic effect from paramagnets for 1 and 2 to weak ferromagnet for 3. Moreover, as revealed by the variable-temperature crystallographic measurements, the first and second dehydration temperatures could be controlled from 298 K (25 °C) and 383 K (110 °C) sealed in a capillary (high humidity) to 255 K (−18 °C) and 307 K (34 °C) in dry N2 (low humidity), indicating the strong humidity sensitivity of the structural dynamics.
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spin-canting antiferromagnetic ordering.16 The symmetrybreaking coordination environment around Co(II) ions induced by thermally activated rotation of oxalate (ox2−) counteranions leads to the change of anisotropic magnetic susceptibility for [Co(en)3](ox).18 Moreover, humidity-induced switching of the magnetic ordering was reported in a (CoxMn1−x)[Cr(CN)6]2/3·zH2O network with 1/3 vacant [Cr(CN)6]3−, owing to the reversal of sublattice magnetization of Co(II) in different humidity.20 Herein, we present a reversible two-step single-crystal-tosingle-crystal (SCSC) structural transformation of a chiral Co(II)-based framework, [Co3(pimda)2(H2O)5] (1), triggered by the two-step release of coordinated water molecules. A series of interesting changes in crystallographic symmetry, color, and magnetism have been clarified. Particularly, through variabletemperature single-crystal unit-cell measurements under different humidity environments, a strong humidity effect on the structural dynamics is observed, as confirmed by the obvious shifting of two-step dehydration temperatures for 1 from 298 K (25 °C) and 383 K (110 °C) in a capillary (high humidity) of 45% to 255 K (−18 °C) and 307 K (34 °C) in dry N2 (low humidity).
INTRODUCTION Due to the intrinsic hybrid organic−inorganic nature of the frameworks, which can provide a wide range of novel physical properties such as magnetism,1,2 conductivity,3 and luminescence,4 coordination polymers (CPs) have attracted great attention in chemistry and materials science over the past few decades. Additionally, taking advantage of the structural flexibility of organic ligands, various coordination spheres of metal ions, or the strength of supramolecular host−guest interactions, some CPs could undergo solid-state structural transformation accompanied by breaking, making, or rearrangement of bonds under external stimulus such as heat, light, pressure, and guest exchange.5−7 Moreover, for a deeper understanding of the structures unequivocally before and after solid-state structural transformation, single-crystal to singlecrystal (SCSC) transformations of CPs are of particular importance and interest.8−11 In this context, designing switchable magnetic materials assisted by synergism of magnetic properties and structural sensitivities of CPs has become one of the hottest topics and such dynamic magnetic materials have shown potential applications as magnetic sensors, magnetic molecular recognizing, or magnetic switchs.12−23 For instance, Cheng et al. reported a structural transformation from 0D dimeric molecules, [Co2(8-qoac)2(N3)2(H2O)2], to a 2D coordination polymer, [Co2(8-qoac)2(N3)2]n, accompanied by the drastic change of magnetism from short-range coupling to long-range © XXXX American Chemical Society
Received: January 30, 2018
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DOI: 10.1021/acs.inorgchem.8b00235 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 1. Coordination environment of Co(II) ions for 1 (a), 2 (b), and 3 (c) in the ORTEP views (60% thermal ellipsoids); a side view of the 3D structure which is constructed by the corner shared {Co3(pimda)} units (d) and the corresponding simplified distorted hyperkagomé topology (e) along the c axis for 1. The propyl groups of pimda3− ligands are omitted for clarity. Symmetry code: (A) − 1/2 + y, 1/2 − x, 1/4 + z; (B) 1 − y, 1 − x, −1/2 − z.
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The structures of all complexes were solved by direct methods, and all non-hydrogen atoms were refined anisotropically by least-squares methods on F2 using the SHELXTL 2014 and Olex2 program suite.24,25 The hydrogen atoms attached to carbon and oxygen atoms were placed in idealized positions and refined using a riding model to the atom to which they were attached. CCDC reference numbers are 1525445 (1), 1525446 (1_Int), 1525448 (2), 1525449 (3), and 1525447 (1_Re) for the crystal under the direct blowing of dry N2 flow; 1525450 (1_seal), 1525451 (2_seal), and 1525452 (3_seal) for the crystal sealed in a capillary. These data can be obtained free of charge via www.ccdc.cam.ac.uk/structures/ (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44)1223-336-033).
EXPERIMENTAL SECTION
Materials and General Procedures. All chemicals were commercially available and used as received without further purification. The C, H, and N microanalyses were carried out with an Elementar Vario-EL CHNS elemental analyzer. The thermogravimetric (TG) analyses were performed on a PerkinElmer TGA7 thermogravimetric analyzer in a N2 flow with a heating rate of 5 K/min from ambient temperature to 800 °C, with an empty Al2O3 crucible as reference. The simultaneous differential scanning calorimetric and thermogravimetric (DSC-TG) analysis were performed on a NETZSCH STA 449F3 instrument in the N2 flow with a heating rate of 5 K/min from the temperature of 25 to 250 °C, with an empty Al2O3 crucible as reference. The variable-temperature PXRD for 1 was recorded on a Bruker D8 Advance Diffractometer (Cu Kα, λ = 1.54056 Å) with a scanning rate of 1.2°/min, and an additional pump was used for keeping a vacuum environment. The solid UV−visible absorption data were acquired on a Shimadzu UV-3600Plus UV/vis/ NIR spectrometer with an additional equipment of a temperature control chamber. The ambient humidity is measured with a hygrometer. The magnetic measurements were performed on the polycrystalline samples using the Quantum Design PPMS magnetometer and Quantum Design MPMS XL-7 SQUID magnetometer with experimental diamagnetic correction. The sample of 1 was sealed in a capsule with a drop of water to ensure the humid atmosphere. As revealed by VT-PXRD measurement (Figure S7) for complex 1 at vacuum environment, the bulk samples of 2 and 3 for magnetic measurements were obtained by warming the bulk samples of 1 to 5 °C and to 30 °C under vacuum for 30 min, respectively. Synthesis of [Co3(pimda)2(H2O)5] (1). A mixture of CoCl2·6H2O (71.4 mg, 0.3 mmol), H3pimda (39.6 mg, 0.2 mmol), and Et3N (60.6 mg, 0.6 mmol) in 10 mL of aqueous solution was sealed in a 25 mL Teflon lined stainless steel container and heated at 170 °C for 4 days. The container was then cooled to room temperature at a rate of 7 °C/ h. The pink crystalline product of 1 was separated by filtration and washed with water. Yield: 84% based on H3pimda. Anal. Calcd (%): N, 8.52; C, 29.24; H, 3.68. Found (%): N, 8.58; C, 29.33; H, 3.59. X-ray Crystallography. A suitable single crystal of 1 was mounted on a thin glass fiber, and X-ray single crystal structural data of that crystal with the direct blowing of dry N2 flow were collected on a Bruker D8 QUEST diffractometer with Mo Kα radiation (λ = 0.71073 Å) at 120 K, 278 K, 288 K, and 313 K for 1, 1_Int, 2, and 3, respectively. The crystal of 1_Re was obtained through immersing the single crystal of 3 in water for about 1 min, and the crystal data was collected at 120 K. Another suitable single crystal of 1 was sealed in a capillary and used for indexing and intensity data collection on the same diffractometer at 278 K, 313 K, and 388 K for 1_seal, 2_seal, and 3_seal, respectively.
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RESULTS AND DISCUSSION The hydrothermal treatment of CoCl2·6H2O, H3pimda, and Et 3 N led to the formation of pink crystals of [Co3(pimda)2(H2O)5] (1). Single-crystal X-ray diffraction (SCXRD) analysis at 120 K revealed that 1 crystallizes in the tetragonal chiral space group P43212 with the Flack parameter of 0.082(13), indicating enantiomeric purity of the single crystal. The attempt to obtain the crystal structure of the opposite enantiomer failed. Moreover, solid-state CD spectral measurements (Figure S1) for 10 randomly selected single crystals of 1 all displayed positive and negative Cotton effects at 282 and 215 nm, respectively, which is in accordance with the CD spectra of the bulk sample, indicating the enantiomeric excess of 1. Considering the starting materials are achiral, such an unusual symmetry breaking phenomenon of 1 should be attributed to spontaneous asymmetrical crystallization.26−29 In the structure of 1, there are two crystallographically independent Co(II) centers, Co1 and Co2, involved in an asymmetric unit (Figure 1a). Co1 ion is chelated by two N−O bidentate sites (N1 and O2) from two pimda3− ligands and one H2O molecule (O1W), resulting in the distorted trigonal bipyramid (D3h) coordination geometry, while octahedral (Oh) coordination geometry is found for Co2, which is coordinated by one N−O bidentate site (O4 and N2), one O−O bidentate site (O1 and O3), and two H2O molecules (O2W and O3W). Each H3pimda ligand is completely deprotonated, giving the trivalent pimda3− anion and chelating one Co1 and two Co2 ions, forming a {Co3(pimda)} unit. Along the c axis, the triangular {Co3(pimda)} units connect with each other through the sharing Co2 ions in a Δ-type chain,30 displaying a 1D lefthanded helical chain along the 43 screw axis (Figure 2a). It is B
DOI: 10.1021/acs.inorgchem.8b00235 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 2. 1D Δ-type chains along the c axis of the unit cell and the corresponding polyhedral representations of the crystal structures for 1 (a), 2 (b), and 3 (c) which could be reversibly transformed through a two-step dehydration/rehydration process. Due to the releasing of the coordinated water molecules around Co2 ions for 1 in two-steps, the helicity conversion with left-handed 43 (1) ↔ 21 (2) ↔ 43 (3) for a 1D Δ-type chain in the three complexes and the space group variation of P43212 (1) ↔ P212121 (2) ↔ P43212 (3) are observed. The hydrogen atoms and propyl groups of pimda3− ligands are omitted for clarity. Color code: (a) Co1, cyan; Co2, yellow; (b) Co1, cyan; Co2, yellow; Co3, purple; (c) Co1, cyan; Co2, purple.
Figure 3. Color changes of the powder samples at 5 °C, 30 °C, and 125 °C in the air are shown on (a), (b), and (c) respectively. (d) A comparison of the VT-PXRD in the air with the simulated PXRD patterns of 1, 2, and 3. Some peaks are marked with their hkl Miller indices. Evolution of the unit cell parameters of the a (blue), b (red) and c (green) axes from a single crystal of 1 under dry N2 flow (e) or sealed in a capillary (f) at various temperatures. The pale green, gray, and dark cyan areas correspond to the structural stabilization temperature range for 1, 2, and 3, respectively.
further connected with other four Δ-type chains by the shared Co1 ions along the ab plane, leading to a 3D structure (Figure 1d) which is similar to a reported coordination polymer, [Co3(eimda)2(H2O)5] (H3eimda = 2-ethyl-1H-imidazole-4,5dicarboxylic acid).31 With the Co(II) ions as nodes, the topologic analysis of the framework for 1 by software TOPOS 5.132,33 gave a 4-connected uninodal net with the point symbol of {32·104} (Figure 1e), which is the same with the hyperkagomé topology constructed by Ir(IV)3 triangles in Na4Ir3O8.34 Hydrogen bonds are clearly observed between the neighboring coordinated water or between the coordinated water and the carboxylates from pimda3−, affording abundant supramolecular interactions and playing an important role on stabilizing the 3D framework (Figure S2 and Table S4). No solvent guests were found in the frameworks. Thermogravimetric analysis (TGA) (Figure S3) displays two steps of weight loss under 25−45 °C (2.8%) and 100−120 °C
(2.6%), corresponding to one coordinated H2O molecule (calcd. 2.7%) for each step. Simultaneous DSC-TG analysis (DTA) (Figure S4) also shows two endothermic peaks at 30.5 and 110.2 °C from the DSC curve, which correspond to the first and second dehydration behaviors as revealed by TG curve. Additionally, these two dehydrated products were respectively confirmed by the X-ray crystallography: [Co3(pimda)2(H2O)4] (2) and [Co3(pimda)2(H2O)3] (3). In order to deeply investigate the dehydration behavior, we successfully collected the single-crystal structures of 2 and 3 upon heating 1 under a dry N2 flow at 15 and 40 °C, respectively. It is well to be reminded that the measuring temperatures of collecting single-crystal data for 2 (15 °C) and 3 (40 °C) are much lower than the corresponding dehydration temperature from TGA, 25 and 100 °C for 2 and 3, respectively, which would be explained below. Additionally, the dehydrated single crystals of 3 can rapidly recover to 1 if C
DOI: 10.1021/acs.inorgchem.8b00235 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry immersed in water in less than a minute, indicating the reversible SCSC transformation (Table S1). As revealed by the crystal structural refinements, interestingly, although complexes 2 and 3 possess the same hyperkagomé topology with 1, complex 2 crystallizes in a lower-symmetry orthorhombic P212121 while 1 and 3 both crystallize in tetragonal P43212 (Table S1). For 2, three crystallographically independent Co(II) centers were found in the asymmetric unit (Figure 1b) while only two crystallographically independent Co(II) centers are in 1 and 3 (Figure 1a, c). By comparing the structures of 1 and 2, we found that during the dehydration transformation from 1 to 2, the coordination environment of Co1 is virtually similar (Table S3). But for the Co2 ions, surprisingly, only half of Co2 ions in 1 undergo dehydration at the first dehydration step, leading to an additional crystallographically independent Co3 center (Figure 1b) with a distorted trigonal bipyramid (D3h) coordination geometry in 2. The 4-fold helicity in 1 (Figure 2a) thus converts to the 2fold helicity of the Δ-type chain in 2 (Figure 2b). At the second dehydration process, the remaining hydrated Co2 ions in 2 continue to release the coordinated water molecule. As a result, the 43 screw axis restores and the space group transforms from P212121 for 2 back to P43212 for 3 (Figure 2c), giving the structures containing two crystallographically independent Co(II) centers for 3. The variable-temperature powder X-ray diffraction (VTPXRD) in the air further confirms the crystallographic change during the dehydration process. For instance, the (102) and (103) reflections for 1 and 3, which are in the tetragonal crystal system, could split into the (102)/(012) reflections and (103)/ (013) reflections, respectively, for 2. The splitting of reflections for 2 is due to the inequality of the a and b axes in the orthorhombic phase (Figure 3d and Figure S6). Moreover, an obvious color deepening from pink to dark violet (Figure 3a−c, Figure S5) for the powder samples was observed upon heating from 5 to 30 °C and 125 °C. Such a phenomenon is in accordance with the change of coordination environment of Co2 ions from 6-coordinated octahedral (Oh) to 5-coordinated trigonal bipyramid (D3h). Similar color changes driven by coordination number diversifications have also been reported in some Co(II) based complexes.8 Moreover, when the samples are cooled to low temperature (5 °C) again, the color returns to pink in several minutes and the PXRD pattern recovers to that of the hydrated phase 1, indicating the reversible adsorption of water molecules from the atmosphere (see Figure S6 and the Supporting video for more details). To probe the affiliation of the two water molecules (O3W and O4W) in the first dehydration process, we deliberately conducted a single-crystal X-ray diffraction on an intermediate phase, 1_Int ([Co3(pimda)2(H2O)5−x], 0 < x < 1) (Table S1) at 278 K under dry N2 flow. As revealed by the structural comparison between 1 and 1_Int, the O3W is speculated to be released in light of the enlargement of the bond length between Co2 and O3W from 2.151 Å in 1 to 2.359 Å in 1_Int (Figure 4). As far as we know, though dehydration induced structural transformation was widely reported in coordination polymers, it is rare that the water molecules binding to the crystallographically identical Co(II) release in two steps, which leads to the conversion of crystallographic symmetry. Such structural transformation should give rise to the changes of the coordination spheres of Co(II) as well as the hydrogen bonding in the frameworks. It should be noted that the
Figure 4. Comparison of the bond length between the coordinated water molecules and Co(II) atoms for the structure of 1 (a), the intermediate phase (1_Int) (b), and the first dehydration phase 2 (c) in the ORTEP views (60% thermal ellipsoids) during the first dehydration process, respectively. The hydrogen atoms are omitted for clarity.
deviation of the hexacoordinate Co2 ions from ideal Oh symmetry in 2 (CShM value = 1.08) is smaller than that in 1 (CShM value = 1.39) (Table 1), suggesting the slight Table 1. CShM Values Calculated by SHAPE 2.137,38 for the Co(II) Ions in 1−3 Coordination geometry 1 2
3
Co1 Co2 Co1 Co2 Co3 Co1 Co2
Trigonal bipyramid Octahedron (Oh) Trigonal bipyramid Octahedron (Oh) Trigonal bipyramid Trigonal bipyramid Trigonal bipyramid
(D3h) (D3h) (D3h) (D3h) (D3h)
CShM value 1.43 1.39 1.55 1.08 1.50 1.67 1.88
movement of the coordinated atoms around Co2 during the structural transformation from 1 to 2. Additionally, the O3W− H3WB···O1WA hydrogen bond is obviously shortened from 3.492 Å for 1 to 3.288 Å for 2 (Figure 5 and Table S4), as well as the Co2−O3W bond (1: Co2−O3W = 2.151 Å; 2: Co2− O3W = 2.137 Å) (Table S3). Such shortening (Δd = 0.20 Å) of the O3W−H3WB···O1WA hydrogen bond from 1 to 2 is more obvious than the changes (|Δd| = 0.04−0.07 Å) of other hydrogen bonds (Figure 5), indicating the coordinated O3W becomes more stable in 2 and thus higher temperature is
Figure 5. View of the hydrogen bonds (purple dashed line) connection types for the coordinated water molecules around the different coordination spheres of Co2 and Co3 ions along the c axis of the unit cell in 1 (a), 2 (b, c), and 3 (d). For clarity, the hydrogen atoms and propyl groups of pimda3− ligands are omitted. D
DOI: 10.1021/acs.inorgchem.8b00235 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry necessary to remove the remaining O3W, whilst 3 has the trend of transformation to 2 due to the unsaturated coordination numbers (n = 5) of Co2 ions, which are more distorted from D3h coordination geometry (CShM value = 1.88) in comparison to the Co3 center in 2 (CShM value = 1.50) (Table 1). As a result, it is beneficial for trapping the thermally stable product of 2 at the intermediate temperatures. As mentioned above, the temperatures for collecting single crystal data of 2 (15 °C) and 3 (40 °C) under a dry N2 flow are much lower than the dehydration temperature obtained from TG analysis. We speculated that though the powder samples for TG measurement are also performed in N2 flow as purge gas (15 L/min), the N2 flow is from the crucible bottom to the top outlet, preventing direct blowing of N2 gas over the bulk samples of 1, thus leading to the higher humidity environment in comparison to that of the SCXRD measurement under running N2 flow (20 L/min). In order to probe the humidity sensitivity, variable-temperature unit-cell determinations for a single crystal of 1 under dry N2 flow (low humidity in Figure 3e) and sealed in a capillary (high humidity) (Figure 3f) were both performed. The sealing operation for the single crystal of 1 was performed in the air with a relative humidity (RH) of 45% at room temperature. Considering this point, we have reason to believe that the atmosphere humidity for 1 in a capillary should be higher than that in dry N2 flow. The derived evolutions of a, b, and c axis at various temperatures are shown in Figure 3e, f. Upon heating, the cell parameters transform from 1 (tetragonal phase, a = b) to 2 (symmetry-breaking orthorhombic phase, a ≠ b) to 3 (tetragonal phase, a = b). Under dry N2 flow (Figure 3e), the two-step dehydration temperatures are located at T1 = 255 K (−18 °C) and T2 = 307 K (34 °C), which are significantly lower than those sealed in the capillary, T1 = 297 K (24 °C) and T2 = 383 K (110 °C) (Figure 3f). These results reveal that the dehydration temperature could be highly dependent on the humidity. It should be noted that the structural transformation temperatures (T1 = 297 K, T2 = 383 K) for the single crystal in a capillary roughly fall in the temperature ranges (T1 = 293−303 K, T2 = 383−398 K) for the powder sample as revealed by the VTPXRD in the air (Figure S6). Besides the study of the structural dynamics of 1, the magnetic behaviors for 1−3 are also explored in light of the following points: (i) in terms of antiferromagnetic coupling, the hyperkagomé topological lattice is under active investigation recently due to the intrinsic strong spin frustration;34−36 (ii) the magnetic anisotropy of the Co2 ions can be responsible to temperature and humidity due to the change of coordination geometry, which may lead to interesting magnetic behaviors. As shown in Figure 6a, the χMT values for 1−3 in the high temperature region are all obviously larger than the spin-only value (5.62 cm3 K mol−1) for three Co(II) ions with S = 3/2 due to the unquenched orbital contribution.39 Upon cooling, the χMT values for 1 and 2 continuously decrease to the minimum of 0.91 cm3 K mol−1 and 0.89 cm3 K mol−1 at 2 K, suggesting the presence of spin−orbit coupling and/or antiferromagnetic coupling in the systems. Above 50 K, the χM−1 vs T data is well fitted by the Curie−Weiss law (χM = C/ (T − θ)), giving C = 8.75 cm3 K mol−1, θ = −42.8 K for 1 and C = 8.77 cm3 mol−1 K, θ = −43.0 K for 2 (Figure S8a, b). The negative Weiss constants further reveal the moderate antiferromagnetic interaction and the contribution of spin− orbit coupling from Co(II) ions. Zero-field-cooled/field-cooled (ZFC/FC) curves (Figure S8e, f) under 100 Oe are almost
Figure 6. (a) χMT vs T plot for 1−3 in an applied dc field of 1000 Oe. Inset: χM vs T plot for 3 at variable fields (100−5000 Oe). (b) Zerofield-cooled (ZFC) and field-cooled (FC) molar magnetic susceptibilities of 3 obtained in a dc applied field of 100 Oe. (c) The χM′ and χM″ vs T plots under Hdc = 0, Hac = 5 Oe for 3. (d) The magnetic hysteresis at 2 K for 3. Inset: The enlargement of the hysteresis loop for 3 in the field range of ±5 kOe at 2 K.
superimposed down to 1.8 K, which indicates the absence of magnetic phase transition for both complexes arising from the occurrence of spin-competing interaction. An empirical parameter provided by Ramirez for evaluating the strength of frustration40 is calculated with using the equation, f = |θ/TC|, giving the value of f > 26 for both complexes, suggesting the presence of strong spin competition. Complex 3 displayed distinct magnetic behavior in comparison to 1 and 2. The Curie−Weiss fitting of χM−1 vs T data gives C = 8.33 cm3 K mol−1 and θ = −47.1 K for 3 (Figure S9a). Upon cooling, the χMT value decreases to a minimum at ca. 4.8 K and then abruptly increases to reach a maximum at ca. 4 K. The magnetic susceptibilities are highly dependent on the applied fields, that is, decreasing upon the increasing field (Figure 6a inset), suggesting a canted antiferromagnetic longrange ordering. Such spin canted behavior for 3 is rather different from 1 and 2, which likely owes to the existence of Dzyaloshinsky Moriya (DM) interaction41 originating from the change of coordination geometry of Co2 ions from a distorted Oh to D3h.42 A “λ” type divergence of the FC/ZFC curves at TC = 4.4 K is observed. Alternating-current (ac) magnetic susceptibilities at a zero dc field show the shape peaks at ca. 4.5 K for both real and imaginary components, confirming the presence of magnetic ordering of 3 (Figure 6b, c). The fast increasing of field-dependent magnetization at low magnetic field (
