Synthesis and Magnetic Characterization of Mononuclear Co(Ⅱ) Complex Based on Pyrazine-Containing Hydrazone Schiff Base Ligand

Yu CHEN Zhao-Dong WANG

Citation:  Yu CHEN, Zhao-Dong WANG. Synthesis and Magnetic Characterization of Mononuclear Co(Ⅱ) Complex Based on Pyrazine-Containing Hydrazone Schiff Base Ligand[J]. Chinese Journal of Inorganic Chemistry, 2021, 37(3): 525-530. doi: 10.11862/CJIC.2021.050 shu

吡嗪酰腙席夫碱单核Co(Ⅱ)配合物的合成与磁性

    通讯作者: 王召东, ouwzdong@qq.com
  • 基金项目:

    重庆文理学院重大科研项目培育基金 P2017CH10

    重庆市永川区科技局自然科学基金计划 2020nb0224

摘要: 合成了一个基于吡嗪酰腙席夫碱配体H2L的单核Co(Ⅱ)配合物(NHEt3)[Co(HL)2]·3H2O(1),并通过红外光谱、热重分析、X射线单晶衍射分析及变温磁化率测定等对配合物进行了表征。X射线单晶衍射分析表明,该配合物包含1个Co(Ⅱ)、2个去质子化的HL-配体以及未参与配位的3个水分子和1个质子化三乙胺,中心Co(Ⅱ)与N2O4六配位形成扭曲的八面体构型。配合物1以及去除水分子后的1的磁性测试表明二者均具有缓慢的高低自旋转换,其不同之处归属为氢键对磁性的影响。

English

  • Spin-crossover (SCO) complexes have attracted much attention due to their promising applications in molecule-based memory devices, sensors and switches[1-2]. Most of the work has focused on Fe(Ⅱ)[3-4] and Fe(Ⅲ)[5-6] complexes, there are still some mononuclear Co(Ⅱ)complexes with abrupt or gradual SCO properties based on derivatives of terpyridine(terpy) [7] and Schiff base ligands[8]. The central Co(Ⅱ)ion is coordinated by N6[9-10] and N4O2 donor sets[11]. To the best of our knowledge, there are no reported Co(Ⅱ)SCO complexes with N2O4 donor sets. The hydrazone Schiff base ligands have been well studied due to their ease of synthesis, modularity and various coordination modes with keto-enol tautomerism[12]. Pyrazine-based hydrazone ligand H2L as shown in Scheme 1 has been used to construct single-molecule magnets (SMMs) with rare earth metals[13-17]. As a complementary work to this ligand system, herein, we synthesized a mononuclear Co(Ⅱ)complex (NHEt3)[Co(HL)2]·3H2O (1) and characterized it with IR, thermogravimetric analysis (TGA), X-Ray single diffraction and magnetic susceptibility.

    Scheme1

    Scheme1.  Structure of H2L

    All chemical reagents were commercially available and used without further purification. H2L was synthesized according to the reported method[13]. FT-IR spectra were recorded in a range of 4 000~400 cm-1 on a PerkinElmer FT-IR spectrometer Frontier. Powder X-Ray diffraction (PXRD) patterns were recorded on a Rigaku Smartlab X-Ray diffractometer with Cu radiation (λ =0.154 178 nm, U=40 kV, I=26 mA) in a range of 5°~50° (2θ). Elemental analyses for C, H and N were measured on an Elementar Vario MICRO analyzer. TGA curves were measured in a Al2O3 crucible using a PerkinElmer TGA instrument in a temperature range of 25~800 ℃ under a N2 flow at a heating rate of 20 ℃·min-1. Magnetic susceptibility measurements for the samples were performed on the Quantum Design MPMS-XL instrument operating under a field of 1 000 Oe in a temperature range of 2~300 K.

    The methanol solution of CoC2O4·2H2O(0.035 5 g, 0.20 mmol) was added dropwise to the mixed solution of H2L (0.054 5 g, 0.20 mmol) in CH3OH and CH2Cl2 with the addition of NEt3 (5 drops) as a deprotonation reagent. The color of the mixture changed from yellow to brown slurring. After stirring for 6 h and the filtration, reddish brown filtrate was obtained. After slow evaporation of the filtrate for two weeks, needle like brown crystals were obtained for X-ray diffraction analysis. Yield: 52% (based on CoC2O4·2H2O). Anal. Calcd. for C32H43CoN9O9(%): C, 50.79; H, 5.73; N, 16.66. Found(%): C, 51.36; H, 5.28; N, 17.27. IR (KBr, cm-1): 3 431 (s), 2 934 (w), 2 831(w), 2 681 (w), 1 623(s), 1 600(s), 1 534(s), 1 475(s), 1 437(s), 1 345 (m), 1 243(w), 1 219(s), 1153(s), 1 083(m), 1 019(m), 976(m), 934(m), 858(w), 744(m), 643(w), 581(w), 453(w).

    Single-crystal diffraction data were recorded on a Bruker SMART APEX Ⅱ CCD diffractometer with Mo (λ=0.071 073 nm) radiation at 298 K. The crystal structure was solved by direct methods and refined by full-matrix least-squares method on F2 using the SHELXTL 2014/7 program and OLEX2[18-19]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms on water molecules were generated by the Q peaks. A water solvent molecule was severely disordered without adding hydrogen atoms and was modeled using the squeeze program. The details of singlecrystal diffraction data and selected bond lengths and bond angles are listed in Table 1 and 2, respectively.

    Table 1

    Table 1.  Crystal data and structure refinement for complex 1
    下载: 导出CSV
    Complex 1 (298 K) 1 (100 K)
    Empirical formula C32H43CoN9O9 C32H43CoN9O9
    Fourmula weight 756.67 756.67
    Crystal system Monoclinic Monoclinic
    Space group P21/c P21/c
    a / nm 1.582 17(15) 1.576 9(6)
    b / nm 1.015 77(10) 1.011 1(4)
    c / nm 2.194 6(2) 2.171 7(8)
    β/(°) 92.364(2) 92.914(7)
    V / nm3 3.524 0(6) 3.458(2)
    Z 4 4
    Dc / (g·cm-3) 1.426 1.454
    μ/ mm-1 0.549 0.564
    F(000) 1 548 1 580
    θ range / (°) 2.217~25.027 2.223~23.828
    Reflection collected, unique 17 474, 6 225 (Rint=0.051) 17 008, 6 077
    Data, restraint, parameter 6 225, 39, 469 6 077, 12, 474
    Final R indices [I > 2σ(I)] R1=0.066 3, wR2=0.163 4 R1=0.073 6, wR2=0.176 6
    R indices (all data) R1=0.106 1, wR2=0.186 7 R1=0.119 8, wR2=0.199 8
    Goodness of fit on F2 1.024 1.043

    Table 2

    Table 2.  Selected bond lengths (nm) and angles (°) for complex 1
    下载: 导出CSV
    1 (298 K)
    Co(1)—O(1) 0.190 8(3) Co(1)—O(2) 0.188 4(3) Co(1)—O(4) 0.189 7(3)
    Co(1)—O(5) 0.188 1(3) Co(1)—N(2) 0.186 4(3) Co(1)—N(4) 0.185 7(4)
    O(2)—Co(1)—O(1) 177.32(14) O(2)—Co(1)—O(4) 89.71(14) O(4)—Co(1)—O(1) 87.82(14)
    O(5)—Co(1)—O(1) 90.91(13) O(5)—Co(1)—O(2) 91.58(13) O(5)—Co(1)—O(4) 178.60(13)
    N(2)—Co(1)—O(1) 83.24(14) N(2)—Co(1)—O(2) 95.80(14) N(2)—Co(1)—O(4) 91.20(15)
    N(2)—Co(1)—O(5) 89.22(14) N(4)—Co(1)—O(1) 92.39(14) N(4)—Co(1)—O(2) 88.34(14)
    N(4)—Co(1)—O(4) 83.70(16) N(4)—Co(1)—O(5) 95.78(15) N(4)—Co(1)—N(2) 173.43(17)
    1 (100 K)
    Co(1)—O(1) 0.188 7(3) Co(1)—O(2) 0.188 5(3) Co(1)—O(3) 0.190 7(3)
    Co(1)—O(5) 0.189 9(4) Co(1)—N(1) 0.186 6(4) Co(1)—N(2) 0.186 7(4)
    O(1)—Co(1)—O(3) 91.16(15) O(1)—Co(1)—O(4) 179.14(16) O(2)—Co(1)—O(1) 91.39(15)
    O(2)—Co(1)—O(3) 177.26(15) O(2)—Co(1)—O(5) 89.46(15) O(5)—Co(1)—O(3) 87.99(15)
    N(1)—Co(1)—O(1) 88.80(16) N(1)—Co(1)—O(2) 95.52(16) N(1)—Co(1)—O(3) 83.52(16)
    N(1)—Co(1)—O(5) 91.21(17) N(1)—Co(1)—N(2) 173.35(19) N(2)—Co(1)—O(1) 96.40(17)
    N(2)—Co(1)—O(2) 88.51(16) N(2)—Co(1)—O(3) 92.21(17) N(2)—Co(1)—O(5) 83.53(18)

    CCDC: 1973542, 1(298 K); 20274281, 1(100 K).

    Single-crystal X-Ray diffraction analysis reveals that 1 crystallizes in monoclinic system, space group P21/c. The coordination environment of Co(Ⅱ)in 1 is shown in Fig. 1. It consists of a Co(Ⅱ)ion, two deprotonated HL-, one protonated NEt3 and three free H 2O molecules. The central Co(Ⅱ)is coordinated by two nitrogen atoms and four oxygen atoms from HL-. There could be amido-enol tautomerism in one HL-ligand and the enol was deprotonated in order to balance the charge of the complex. The Co(Ⅱ)ion has a distorted octahedral coordination geometry where four oxygen donors form the basal plane, and the two nitrogen donors occupy the apical position. The distortion parameter, , is defined as the sum of the deviation from the 12 cis-O— Co—O, N—Co—O, N—Co—N angels[1]. The smaller value of 35.63° for 1 shows a slightly distorted octahedral geometry. The Co—N bond lengths (Co1—N2 0.186 4(3) nm, Co1—N4 0.185 7(4) nm) are slightly shorter than the reported Co complex with N2O4 donor sets. While the Co—O bond lengths (Co1—O1 0.190 8(3) nm, Co1—O2 0.188 4(3) nm, Co1—O4 0.189 7(4) nm, Co1— O5 0.188 1(3) nm) are comparable to the reported Co complex[20]. We also determined the crystal structure of 1 at 100 K as shown in Fig. 1, it reveals the same structure composition and coordination environment of the central Co ion. The bond lengths of Co—O and Co—N are slightly different with 1 at 298 K. The value of 37.29° also shows a slightly distorted octahedral geometry. The free water molecules form O—H…O hydrogen bonds with O from phenol and methoxy group as shown in Fig. 2. There are also O —H…N hydrogen bonds with N from pyrazine N and N atom from the protonated triethylamine.

    Figure 1

    Figure 1.  Coordination environment of Co(Ⅱ) ion in complex 1 (left: 298 K, right: 100 K) with 50% probability thermal ellipsoids

    Solvent molecules and all hydrogen atoms have been omitted except NH group for clarity

    Figure 2

    Figure 2.  Packing structure of complex 1 (298 K) with hydrogen bonding

    PXRD pattern of the complex was determined at room temperature to check the phase purity as shown in Fig. 3. The peak positions of the experimental PXRD match well with the simulated one, indicating the purity of the complex.

    Figure 3

    Figure 3.  PXRD patterns for 1

    TGA of 1 was carried out in a range of 25~800 ℃ under nitrogen atmosphere. As shown in Fig. 4, the first weight loss of 6.9% from 95 to 185 ℃ is attributed to the loss of free H2O molecules (Calcd. 6.89%). The second weight loss of 13.1% from 195 to 260 ℃ is attributed to the loss of one protonated NEt3 (Calcd. 13.7%). After that, the complex began to decompose.

    Figure 4

    Figure 4.  TGA curve of 1

    The magnetic susceptibilities χm of 1 and dehydrated 1 were measured in the 2~300 K temperature range. The χmT versus T plots for both in cooling and heating mode are shown in Fig. 5. The χmT value of 1.40 cm3·mol-1·K was lower than the theoretical value of 1.88 cm3·mol-1·K of the high-spin mononuclear Co(Ⅱ), indicating a mixture of high-spin and low-spin state. The χmT decreased gradually as the temperature lowered. It reached 0.848 cm3·mol-1·K at about 168 K, then it began to increase slowly to 0.935 cm3·mol-1·K at 147 K, indicating a slightly reverse spin transition due to possible phase changes during this period of temperature range[21-23]. This was confirmed by the slightly different bond lengths and the value for complex 1 at 298 K and 100 K. The χmT was 0.44 cm3·mol-1·K at 59 K corresponding to the mononuclear Co(Ⅱ)low -spin state, and it decreased with decreasing temperature until it reached about 0.02 cm3·mol-1·K at 2 K, there was a small hysteresis loop in the cooling and heating mode as shown in Fig. 5. In order to check the solvent effects on the magnetic properties, the dehydrated complex 1 was obtained by annealing 1 at 115 ℃ for 6 h in vacuo. The χmT value of 0.89 cm3· mol-1·K for dehydrated 1 was significantly lower than the theoretical value of 1.88 cm3·mol-1·K of the high-spin mononuclear Co(Ⅱ), indicating a majority of lowspin state. The χmT decreased gradually as the temperature lowered. It reached 0.43 cm3·mol-1·K at about 78 K corresponding to the mononuclear Co(Ⅱ)low-spin state. It also kept decreasing to ca. 0.02 cm3·mol-1·K at 2 K, and no hysteresis loop was observed in the cooling and heating mode. The difference of 1 and the dehydrated 1 can be assigned as the hydrogen bonding effects on the magnetic properties[24].

    Figure 5

    Figure 5.  χmT vs T plots for complex 1 (cooling: black, heating: red) and dehydrated 1 (cooling: blue, heating: pink) in cooling and heating mode

    Inset: "reverse"fragment of the curve around 150 K

    In summary, we have successfully synthesized and characterized a new mononuclear Co(Ⅱ)complex based on a pyrazine-containing hydrazone Schiff base ligand with rare N2O4 donor sets. The complex 1 exhibited a gradual spin transition with an unusual reverse spin state transition due to possible phase changes. The dehydrated 1 also showed a gradual spin transition, and the differences can be assigned as the hydrogen bonding effects on the magnetic properties.


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  • Scheme1  Structure of H2L

    Figure 1  Coordination environment of Co(Ⅱ) ion in complex 1 (left: 298 K, right: 100 K) with 50% probability thermal ellipsoids

    Solvent molecules and all hydrogen atoms have been omitted except NH group for clarity

    Figure 2  Packing structure of complex 1 (298 K) with hydrogen bonding

    Figure 3  PXRD patterns for 1

    Figure 4  TGA curve of 1

    Figure 5  χmT vs T plots for complex 1 (cooling: black, heating: red) and dehydrated 1 (cooling: blue, heating: pink) in cooling and heating mode

    Inset: "reverse"fragment of the curve around 150 K

    Table 1.  Crystal data and structure refinement for complex 1

    Complex 1 (298 K) 1 (100 K)
    Empirical formula C32H43CoN9O9 C32H43CoN9O9
    Fourmula weight 756.67 756.67
    Crystal system Monoclinic Monoclinic
    Space group P21/c P21/c
    a / nm 1.582 17(15) 1.576 9(6)
    b / nm 1.015 77(10) 1.011 1(4)
    c / nm 2.194 6(2) 2.171 7(8)
    β/(°) 92.364(2) 92.914(7)
    V / nm3 3.524 0(6) 3.458(2)
    Z 4 4
    Dc / (g·cm-3) 1.426 1.454
    μ/ mm-1 0.549 0.564
    F(000) 1 548 1 580
    θ range / (°) 2.217~25.027 2.223~23.828
    Reflection collected, unique 17 474, 6 225 (Rint=0.051) 17 008, 6 077
    Data, restraint, parameter 6 225, 39, 469 6 077, 12, 474
    Final R indices [I > 2σ(I)] R1=0.066 3, wR2=0.163 4 R1=0.073 6, wR2=0.176 6
    R indices (all data) R1=0.106 1, wR2=0.186 7 R1=0.119 8, wR2=0.199 8
    Goodness of fit on F2 1.024 1.043
    下载: 导出CSV

    Table 2.  Selected bond lengths (nm) and angles (°) for complex 1

    1 (298 K)
    Co(1)—O(1) 0.190 8(3) Co(1)—O(2) 0.188 4(3) Co(1)—O(4) 0.189 7(3)
    Co(1)—O(5) 0.188 1(3) Co(1)—N(2) 0.186 4(3) Co(1)—N(4) 0.185 7(4)
    O(2)—Co(1)—O(1) 177.32(14) O(2)—Co(1)—O(4) 89.71(14) O(4)—Co(1)—O(1) 87.82(14)
    O(5)—Co(1)—O(1) 90.91(13) O(5)—Co(1)—O(2) 91.58(13) O(5)—Co(1)—O(4) 178.60(13)
    N(2)—Co(1)—O(1) 83.24(14) N(2)—Co(1)—O(2) 95.80(14) N(2)—Co(1)—O(4) 91.20(15)
    N(2)—Co(1)—O(5) 89.22(14) N(4)—Co(1)—O(1) 92.39(14) N(4)—Co(1)—O(2) 88.34(14)
    N(4)—Co(1)—O(4) 83.70(16) N(4)—Co(1)—O(5) 95.78(15) N(4)—Co(1)—N(2) 173.43(17)
    1 (100 K)
    Co(1)—O(1) 0.188 7(3) Co(1)—O(2) 0.188 5(3) Co(1)—O(3) 0.190 7(3)
    Co(1)—O(5) 0.189 9(4) Co(1)—N(1) 0.186 6(4) Co(1)—N(2) 0.186 7(4)
    O(1)—Co(1)—O(3) 91.16(15) O(1)—Co(1)—O(4) 179.14(16) O(2)—Co(1)—O(1) 91.39(15)
    O(2)—Co(1)—O(3) 177.26(15) O(2)—Co(1)—O(5) 89.46(15) O(5)—Co(1)—O(3) 87.99(15)
    N(1)—Co(1)—O(1) 88.80(16) N(1)—Co(1)—O(2) 95.52(16) N(1)—Co(1)—O(3) 83.52(16)
    N(1)—Co(1)—O(5) 91.21(17) N(1)—Co(1)—N(2) 173.35(19) N(2)—Co(1)—O(1) 96.40(17)
    N(2)—Co(1)—O(2) 88.51(16) N(2)—Co(1)—O(3) 92.21(17) N(2)—Co(1)—O(5) 83.53(18)
    下载: 导出CSV
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  • 发布日期:  2021-03-10
  • 收稿日期:  2020-08-10
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