English

• 0.   Introduction

  In recent years, coordination polymers (CPs) designed and synthesized by metal ions and organic ligands have attracted extensive attention, because they are not only structurally diverse, but also display potential applications as functional materials in adsorption separation^[1], magnetism^[2], proton conduction^[3], catalysis^[4], and chemical sensing^[5]. At present, there have been many studies on the structures and related properties of CPs. The results show that the preparation of CPs can be affected by many factors, including the coordination properties of metal ions^[6], the structure of ligands^[7], solvents^[8], pH^[9], temperature^[10], and so on. Among them, the reasonable selection of the ligand is very important for the construction of target CPs. Especially in the design and synthesis of magnetic CPs, the selection of suitable bridging ligands can deliver magnetic interactions more efficiently. Semi-rigid polycarboxylate ligands combine the advantages of rigid and flexible ligands and have various coordination modes such as syn-syn, syn-anti, anti-anti, and μ-oxo, which can exhibit various ways of transferring magnetic interactions^[11]. Besides, Mn(Ⅱ) ion with five unpaired electrons is often used to construct novel magnetic CPs. Several carboxylate-bridged Mn(Ⅱ) complexes with interesting magnetic properties have been reported^[12-14].

  To synthesize new magnetic materials formed by manganese metal ions and semi-rigid polycarboxylic acid ligands, a semi-rigid polycarboxylic acid ligand, 6-(3′, 4′-dicarboxylphenoxy)-1, 2, 4-benzenetricarboxylic acid (H₅L), was chosen for the following reasons: (1) two benzene rings can rotate freely by —O— group, which exhibit conformational flexibility; (2) five carboxyl groups of the ligand can be partially or completely deprotonated to form diverse coordination modes; (3) benzene rings can function as a mediator for transmitting exchange interaction between paramagnetic metal centers^[15]. Furthermore, the mixed-ligands strategy is an effective method for assembling different types of CPs^[16-17]. N-donor ligands are electroneutral and have simple coordination modes, which can satisfy the coordination geometry requirements of the metal ions in the assembly process by cooperative coordination with carboxylic acid groups^[18-19].

  Hence, in this work, we employed H₅L as polycarboxylate ligand, terminal ligand 1, 10-phenanthroline (phen) and bridging ligand 1, 4-bis(1H-imidazol-1-yl)benzene (1, 4-bib) as the auxiliary ligands to assemble two new Mn(Ⅱ) CPs, namely {[Mn₂(HL)(phen)₃(H₂O)₂]·7.5H₂O}_n (1) and [Mn₄(HL)₂(1, 4-bib)₃(H₂O)₂]_n (2) (Scheme 1). Complexes 1 and 2 exhibit different molecular structures and dimensionalities. The synthesis, structures, and magnetic properties of 1 and 2 are discussed in detail.

  Scheme 1

  

  Scheme 1.  Synthesis strategy for complexes 1 and 2

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  1.   Experimental

  1.1   Materials and methods

  H₅L was obtained from Jinan Henghua Sci. & Tec. Co., Ltd. of China and used as received. All other solvents and materials used in the experiments were purchased commercially without any further purification. The FTIR spectra with KBr pellets were recorded in a range of 4 000-400 cm^-1 on a Bruker TENSOR27 spectrometer. Elemental analyses (C, H, and N) were performed on an Elementar UNICUBE organic elemental analyzer. The powder X-ray diffraction (PXRD) patterns were measured on a Bruker D8 Advance instrument equipped with Cu Kα radiation (λ=0.154 18 nm) at room temperature and collected from 5° to 50° with a scanning speed of 5 (°)·min^-1. The operating voltage and current were 40 kV and 100 mA, respectively. Thermal stability analyses were performed on an SDT 650 thermal gravimetric analyzer from room temperature to 800 ℃ with a heating rate of 10 ℃·min^-1 under N₂ atmosphere. Magnetic susceptibility measurement data were obtained with a SQUID magnetometer (Quantum MPMS) in a temperature range of 2-300 K by using an applied field of 1 000 Oe.

  1.2   Preparation of complexes 1 and 2

  A mixture of Mn(CH₃COO)₂·4H₂O (24.51 mg, 0.10 mmol), H₅L (39.00 mg, 0.10 mmol), phen (18.02 mg, 0.10 mmol), and H₂O (10 mL) was placed in a 15 mL Teflon-lined stainless steel vessel, and the pH of the reaction suspension was adjusted to 4 with HNO₃ (1 mol·L^-1). The mixture was heated to 120 ℃ and kept constant for 72 h. After cooling to room temperature, yellow bulk crystals of 1 were obtained, then washed with distilled water and dried in air. Yield: 35% (based on H₅L). Elemental analysis Calcd. for C₅₃H₄₉Mn₂ N₆O_20.50(%): C, 52.70; N, 6.96; H, 4.10; Found(%): C, 52.01; N, 6.75; H, 4.38. FTIR (KBr, cm^-1): 3 418(s), 2 920(w), 1 599(s), 1 517(w), 1 425(w), 1 381(m), 1 261(w), 1 219(w), 1 102(w), 846(m), 782(w), 728(m) (Fig.S1, Supporting information).

  The preparation of complex 2 was similar to the preparation of 1, except that phen (18.02 mg, 0.10 mmol) was replaced by 1, 4-bib (21.00 mg, 0.10 mmol). Finally, colorless block crystals of 2 were collected by filtration and washed with distilled water. The yield of the product was 45% (based on H₅L). Elemental analysis Calcd. for C₃₅H₂₃Mn₂N₆O₁₂(%): C, 50.68; N, 10.13; H, 2.80; Found(%): C, 50.47; N, 9.93; H, 2.89. FT-IR (KBr, cm^-1): 3 415(s), 2 921(w), 1 617(s), 1 563(w), 1 382(m), 1 312(w), 1 260(w), 1 225(w), 1 112(w), 780(w), 710(w), 622(w), 483(w) (Fig.S1).

  1.3   X-ray crystallography

  Single crystal X-ray data of complexes 1 and 2 were collected on a D8-Quest diffractometer equipped with Mo Kα radiation (λ=0.071 073 nm), and the absorption correction of crystal diffraction data was carried out by using the SADABS program. The crystal skeletons of 1 and 2 were analyzed by the direct method using the Olex2 and SHELXL-2014. All non-hydrogen atoms and anisotropic parameters were refined by full-matrix least-squares on F ². The H atoms were refined as follows: the H atoms attached to C atoms were positioned geometrically, while the hydrogen atoms of lattice water molecules were located in the difference Fourier maps, and the distances of the O—H bond were limited to 0.082 nm. For complex 1, some guest solvent molecules were found to be highly disordered, so they were removed by using the SQUEEZE option of PLATON. The detailed crystallographic data and structure refinement parameters of 1 and 2 are collected in Table 1, and selected bond lengths and angles of the complexes are given in Tables S1 and S2.

  Table 1

  

  Table 1.  Crystal data and structure refinement parameters for complexes 1 and 2

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  Parameter	1	2
  Empirical formula	C53H38Mn2N6O15·5.5H2O	C35H23Mn2N6O12
  Formula weight	1207.86	829.47
  T / K	294	295
  Crystal system	Monoclinic	Triclinic
  Space group	C2/c	P1
  a / nm	2.735 98(9)	1.117 3(3)
  b / nm	1.448 58(2)	1.120 2(3)
  c / nm	2.743 88(9)	1.448 7(4)
  α / (°)		91.511(9)
  β / (°)	97.155(2)	93.75(1)
  γ / (°)		117.544(9)
  V / nm3	10.790 1(3)	1.600 9(8)
  Z	8	2
  F(000)	4 984	842
  Dc / (g·cm-3)	1.487	1.721
  μ / mm-1	0.55	0.87
  θ range / (°)	2.8-25.5	2.8-25.0
  Goodness-of-fit on F 2	1.01	1.04
  Reflection collected	46 843	13 908
  Independent reflection	10 019 (Rint=0.044)	5 553 (Rint=0.040)
  Reflection observed [I > 2σ(I)]	7 348	4 076
  R1 [I > 2σ(I)]	0.041	0.042
  wR2 [I > 2σ(I)]	0.102	0.103

  2.   Results and discussion

  2.1   Description of crystal structures

  The single-crystal diffraction analysis shows that complex 1 crystallizes in monoclinic P1 space group, and its asymmetric unit consists of two Mn(Ⅱ) ions, one HL^4- ligand, three phen ligands, two coordination water molecules, and solvent molecules. As shown in Fig.1a, the Mn1 and Mn2 ions both adopt six-coordination to form the twisted octahedron configuration, and the metal ion is located in the center of the octahedron. Mn1 is coordinated with two carboxyl oxygen atoms (O2 and O3^ⅰ) from two HL^4- ligands and four nitrogen atoms (N1, N2, N3, and N4) from two phen ligands. Mn2 is surrounded by two carboxyl oxygen atoms (O4 and O7^ⅱ) from two different HL^4- ligands, two nitrogen atoms (N5 and N6) from phen ligand, and two coordination water molecules (O12 and O13). The Mn—O and Mn—N bond distances vary from 0.210 2(2) to 0.223 7(2) nm, and 0.225 1(2) to 0.233 4(2) nm, respectively.

  Figure 1

  

  Figure 1.  (a) Coordination environment of Mn(Ⅱ) ion in complex 1 with the thermal ellipsoids at 30% probability level; (b) 1D chain structure formed by HL^4- ligands linking to Mn(Ⅱ) ions; (c) 2D layered structure formed by π…π stacking interactions between the benzene rings of phen

  Symmetry codes: ^ⅰ-x+1/2, -y+1/2, -z; ^ⅱ -x+1, -y, -z.

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  In the assembly of complex 1, the H₅L ligands are partially deprotonated and adopt the coordination mode of μ₄-(κ¹-κ¹)-(κ⁰-κ¹)-(κ⁰-κ¹)-(κ⁰-κ⁰)-(κ⁰-κ⁰). To accommodate the formation of coordination bonds, the two benzene rings of the ligand are twisted with a dihedral angle of 84.80(1)°. Mn1 and Mn1^ⅰ are bridged by two carboxyl groups from two different HL^4- ligands to form an eight-membered ring, and the Mn…Mn distance is 0.471 6(2) nm. Mn2 and Mn2^ⅱ are connected by two different HL^4- ligands to form a sixteen-membered ring with Mn…Mn distance of 0.913 4(2) nm. Eight- membered and sixteen-membered rings appear alternately along the a-axis direction, forming a 1D chain structure (Fig.1b). Moreover, the phen ligands are located at two apices of each 1D chain. 1D chains are further build into a 2D layer lying in the ab plane organized by weak π…π interactions between the pyridine rings of phen. The distance between the centroids is 0.362 9(2) nm (Fig 1c).

  Complex 2 crystallizes in monoclinic crystal system, space group C2/c, and its asymmetric unit includes two Mn(Ⅱ) ions, one HL^4- ligand, one half 1, 4-bib ligands, and one coordinated water molecule. As shown in Fig.2a, the Mn1 ion adopts the six-coordination with five carboxylated oxygen atoms (O1, O3, O4^ⅲ, O6^ⅰ, and O11^ⅱ) from the four HL^4- ligands and one nitrogen atom (N3) from the 1, 4-bib ligand to form an octahedral configuration in which Mn1 is located at the center of the octahedron, while O1, O3, O11^ⅱ and N3 are located on the equatorial plane, and O4^ⅲ and O6^ⅰ are located on the axis perpendicular to the equatorial plane. The Mn2 ion adopts five-coordination to form a deformed triangular bipyramid configuration, and the five vertices of the triangular bipyramid are occupied by three carboxyl oxygen atoms (O1, O3^ⅲ, and O10^ⅳ), a nitrogen atom (N1) from the 1, 4-bib ligand and a coordination water molecule (O12). The corresponding Mn—O bond lengths around Mn1 and Mn2 range from 0.211 0(2) to 0.228 2(2) nm, and Mn—N bond lengths are 0.216 6(3) and 0.219 3(3) nm.

  Figure 2

  

  Figure 2.  (a) Displacement ellipsoid plot (30% probability) of the coordination environments of Mn(Ⅱ) ions in complex 2; (b) Mn(Ⅱ) tetranuclear unit in 2; (c) 3D polyhedral structure of 2 (the polyhedron of Mn1 and Mn2 are represented with green and orange colors, respectively); (d) 3D topology net of 2

  Symmetry codes: ^ⅰ-x, -y, -z; ^ⅱ x, y+1, z; ^ⅲ -x+1, -y+1, -z.

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  Different from that in complex 1, HL^4- connects Mn(Ⅱ) ions in the coordination mode of μ₇-(κ¹-κ²)-(κ⁰-κ²)-(κ¹-κ⁰)-(κ¹-κ¹)-(κ⁰-κ⁰), with the dihedral angle being 89.79(8)°. Four Mn(Ⅱ) ions are connected via carboxylic groups to form a tetranuclear manganese unit, in which four coplanar Mn(Ⅱ) ions are connected by two equivalent μ₃-η¹∶η² carboxylic acid bridges, forming an Mn₄ parallelogram (Fig.2b). There are two different bridging motifs between non-equivalent Mn(Ⅱ) ions, which define the edges of Mn₄ parallelogram. The one is a μ₂-η¹∶η¹ carboxylic bridge with a distance between Mn and Mn of 0.354 6(2) nm. The other is μ₂-η² carboxylic bridge with a longer Mn…Mn distance of 0.385 9(2) nm. Tetranuclear units are connected by HL^4- establishing a 2D layered structure parallel to the ab plane. Adjacent 2D layers are further connected by 1, 4-bib to form a 3D framework (Fig.2c).

  From the topological point of view, the HL^4- ligand could be viewed as a 3-connected node, and the tetranuclear manganese unit could be regarded as an 8-connected linker, so the overall structure of 2 can be viewed as a (3, 8)-connected 3D network structure with the topological symbol of {4³}₂{4⁶.6¹⁸.8⁴} (Fig.2d).

  2.2   Structural comparison

  Generally, the structures of CPs are influenced by many factors, including synthesis conditions (solvent, pH, temperature, molar ratio of reactants), anion types, metal ions, ligands, etc. Herein, complexes 1 and 2 were both obtained by the reaction of polycarboxylic acid ligand H₅L, N-auxiliary ligand, and manganese salt under hydrothermal conditions. The conditions for the synthesis of 1 and 2 are similar, with the difference being the N-auxiliary ligand. Due to the large steric hindrance and single coordination mode of auxiliary ligand phen, it is easy to chelate with metal ions, which ultimately leads to the formation of the 1D chain structure of 1. In 2, due to the addition of auxiliary ligand 1, 4-bib, the partial coordination sites of metal ions are occupied by nitrogen atoms in 1, 4-bib which plays the role of bridging ligand, and finally, 2 forms a 3D framework structure.

  Analyzing and comparing the synthesis and structure of complexes 1 and 2, it is found that the structural differences between complexes 1 and 2 are due to the different coordination modes of the ligand HL^4-. Fig.3 shows the coordination pattern of HL^4- in the manganese complexes, μ₄-(κ¹-κ¹)-(κ⁰-κ¹)-(κ⁰-κ¹)-(κ⁰-κ⁰)-(κ⁰-κ⁰) for 1 in the presence of phen coligand and μ₇-(κ¹-κ²)-(κ⁰-κ²)-(κ¹-κ⁰)-(κ¹-κ¹)-(κ⁰-κ⁰) for 2 in the presence of 1, 4-bib coligand, indicating that the N-donor coligands have a significant effect on the coordination mode of the ligand HL^4-, resulting in the structures differences between 1 and 2.

  Figure 3

  

  Figure 3.  Various coordination modes of HL^4- observed in complexes 1 (left) and 2 (right)

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  2.3   PXRD analysis

  The phase purity of complexes 1 and 2 were characterized by PXRD. The experimental and simulated PXRD patterns are shown in Fig.S2. The positions of the experimental diffraction peaks were consistent with those of the simulated diffraction peaks based on the result of the single-crystal diffraction experiments, indicating the high phase purity of 1 and 2. The difference of peak intensities may be attributed to the different crystallographic orientations of the crystals.

  2.4   Thermal stability analysis

  To evaluate the stability of complexes 1 and 2, thermogravimetric analysis (TGA) was performed (Fig.S3). In the TGA curve of 1, there was a weight loss of 14.29% from 30 to 140 ℃, corresponding to the liberation of free and coordinated water molecules (Calcd. 14.16%), and further weight loss was observed at about 250 ℃, owing to the collapse of the framework of 1. For 2, a weight loss of 2.35% was observed in a temperature range of 85-120 ℃, which corresponds to the release of the coordinated water molecule (Calcd. 2.17%). A continuous weight loss starting at 315 ℃ was accompanied by the subsequent decomposition of the framework.

  2.5   Magnetic properties

  To gain insight into magnetic changes of complexes 1 and 2, the variable-temperature magnetization of finely ground single-crystal samples was measured in a temperature range of 2-300 K with an applied magnetic field of 1 000 Oe.

  The magnetic susceptibility of 1 is shown as χ_M^-1 and χ_MT vs T plots in Fig.4a. At 300 K, the experimental χ_MT value of 1 was 8.68 cm³·mol^-1·K, which is slightly lower than the expected value (8.75 cm³·mol^-1·K) of two uncorrelated spins of Mn(Ⅱ) ions (g=2.0, S= 5/2). With the decrease in temperature, the χ_MT value decreased first slowly and then rapidly, reaching the minimum value of 4.83 cm³·mol^-1·K at 2.0 K, suggesting the existence of antiferromagnetic behavior. The χ_M value increased monotonously with the decrease in temperature indicating antiferromagnetic ordering. In the 2-300 K range, the magnetic susceptibility could be well fitted to the Curie-Weiss law, χ=C/(T-θ), yielding a Curie constant C=8.80 cm³·mol^-1·K and a negative Weiss constant θ of -1.62 K (Fig.4b). The negative θ value further confirms a dominant antiferromagnetic interaction between the Mn(Ⅱ) ions.

  Figure 4

  

  Figure 4.  (a) χ_M and χ_MT vs T plots and (b) χ_M^-1 vs T plots for complex 1

  The solid line represents the best fit.

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  To quantitatively evaluate the magnetic interactions in complex 1, it is necessary to determine the main magnetic interaction pathways in CPs. As mentioned above, the structure of 1 is considered to be a 1D chain formed by two different Mn(Ⅱ) dimers alternately connected along the a-axis. The Mn…Mn distance of binuclear Mn(Ⅱ) linked by a pair of carboxyl groups is 0.471 6(2) nm, while the Mn…Mn distance of binuclear Mn(Ⅱ) connected by ligands is 0.913 4(2) nm. Therefore, the magnetic interaction between the binuclear manganese linked by ligands can be ignored. We speculated that the main magnetic interaction of 1 may be limited to the Mn₂(μ-COO)₂ dimer. Taking into account the dinuclear Mn(Ⅱ) model, the magnetic susceptibility data were analyzed using the Bleaney- Bowers expression based on a Heisenberg Hamiltonian Ĥ=-JŜ₁Ŝ₂^[20]. Here, J is the exchange coupling parameter between Mn(Ⅱ) ions for 1. The corresponding equation is given as follows:

  $ {\chi }_{\mathrm{d}\mathrm{i}\mathrm{m}\mathrm{e}\mathrm{r}}=\frac{{N}_{\mathrm{A}}{g}^{2}{\beta }^{2}}{kT}·\frac{A}{B} $

  (1)

  where A=exp(2x)+5exp(6x)+14exp(12x)+30exp(20x)+55exp(30x), B=1+3exp(2x)+5exp(6x)+exp(21x)+9exp(2x)+11exp(30x), x=J/(kT), and N_A, g, β, and k have their usual meanings.

  Further, the inter-dimer interaction (zj′) through intermolecular interaction is treated by the molecular field approximation. Thus, the total magnetic susceptibility is:

  $ {\chi }_{\mathrm{M}}=\frac{{\chi }_{\mathrm{d}\mathrm{i}\mathrm{m}\mathrm{e}\mathrm{r}}}{1-\left(\frac{2zj\text{'}}{{N}_{\mathrm{A}}{g}^{2}{\beta }^{2}}\right){\chi }_{\mathrm{d}\mathrm{i}\mathrm{m}\mathrm{e}\mathrm{r}}} $

  (2)

  Based on Eq.2, the optimization gave the following parameters: J=-0.60 cm^-1, zj′=-0.40 cm^-1, and g=1.92 with the agreement factor R=4.66×10^-3. The g value was in accord with the expectation for a dinuclear Mn(Ⅱ) complex^[21]. The small negative J value further suggests weak antiferromagnetic interaction within the Mn₂(μ-COO)₂ dimer in 1.

  For 2, the observed χ_MT value at 300 K was about 8.76 cm³·mol^-1·K, being close to the spin-only value of 8.75 cm³·mol^-1·K expected for two high-spin Mn(Ⅱ) ions (g=2.0 and S=5/2) (Fig.5a). As the temperature was lowered, the χ_MT value continued to decrease slowly until about 60 K. Below this temperature, the value of the χ_MT decreased sharply, reaching a minimum value of 4.47 cm³·mol^-1·K at 2.0 K, indicating the antiferromagnetic behavior. The χ_M value of 2 increased with temperature decreasing, and a round peak appeared near 13 K. The increase of the χ_M value below 8 K is due to the presence of paramagnetic impurities. Above 13 K, a typical paramagnetic Curie-Weiss behavior was observed, with a negative Weiss constant θ= -26.05 K and Curie constant C=9.70 cm³·mol^-1·K (Fig.5b). The negative θ value is indicative of antiferromagnetic interactions in 2.

  Figure 5

  

  Figure 5.  (a) χ_M and χ_MT vs T plots and (b) χ_M^-1 vs T plot for 2

  The solid line represents the best fit.

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  Based on the structure analysis of complex 2, the main magnetic interactions may be considered to occur within the discrete tetranuclear manganese units linked by carboxylate groups, whereas the exchange interactions between Mn(Ⅱ) ions from adjacent tetranuclear units can be ignored because these units are well separated. The Mn…Mn interactions within tetranuclear unit are 0.354 6(2) and 0.385 9(2) nm, and the exchange angles are 78.402(9)° and 101.598(9)°, respectively. Considering the 3D characteristics of 2, the system can be magnetically treated as a square Mn₄ unit model. The magnetic susceptibility for such a system can be expressed as^[22]:

  $ {\chi }_{\mathrm{t}\mathrm{e}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{m}\mathrm{e}\mathrm{r}}=\frac{{N}_{\mathrm{A}}{g}^{2}{\beta }^{2}}{3kT}·\frac{A}{B} $

  (3)

  $ {\chi }_{\mathrm{M}}=\frac{{\chi }_{\mathrm{t}\mathrm{e}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{m}\mathrm{e}\mathrm{r}}(1-\rho )}{1-\left(\frac{zj\text{'}}{{N}_{\mathrm{A}}{g}^{2}{\beta }^{2}}\right){\chi }_{\mathrm{t}\mathrm{e}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{m}\mathrm{e}\mathrm{r}}}+\frac{4NA{g}^{2}{\beta }^{2}\rho }{3kT} $

  (4)

  where A=90exp(2x)+630exp(6x)+2 016exp(12x)+4 320 exp(20x) + 6 390exp(30x) + 8 190exp(42x) + 8 400exp(56x)+7 344exp(72x)+5 310exp(90x)+2 310exp(110x), B=6 + 45exp(2x) + 105exp(6x) + 168exp(12x) + 216exp(20x)+231exp(30x)+195exp(42x)+150exp(56x)+102exp(72x)+57exp(90x)+21exp(110x), and x=J/(kT). Molecular field approximation (zJ′) and paramagnetic impurities (ρ) are added in Eq.4 to explain the actual magnetic property of 2.

  Here χ_tetramer is the susceptibility of the square Mn₄ unit, deduced from the exchange Hamiltonian Ĥ=-2J(Ŝ₁Ŝ₂+Ŝ₁Ŝ_2′+Ŝ_1′Ŝ₂+Ŝ_1′Ŝ_2′+Ŝ₂Ŝ_2′). The best-fit parameters were found as J=-3.16 cm^-1, g=1.97, zj′=4.90 cm^-1, ρ=0.48, and R=7.91×10^-4. The negative value of J further corroborates the presence of antiferromagnetic interactions between Mn(Ⅱ) ions through the carboxylic bridging. Moreover, compared to 1, the stronger antiferromagnetic exchange coupling may be attributed to complete coplanar Mn₄ subunits in which the shorter Mn…Mn distances facilitate electron interactions.

  3.   Conclusions

  In summary, we have successfully constructed two Mn(Ⅱ) coordination polymers (1 and 2) through a similar synthesis process. Structure and properties modulation has been achieved by using N-auxiliary ligands with different linkages. Structural analyses reveal that two kinds of binuclear manganese units are alternately connected and extended along the a-axis to form a 1D chain in complex 1, and the Mn(Ⅱ)-carboxylate tetranuclear are cooperatively extended by HL^4- and 1, 4-bib coligand to generate a (3, 8)-connected 3D network with a new topological symbol {4³}₂{4⁶.6¹⁸.8⁴} in complex 2. Magnetic studies indicate the presence of antiferromagnetic exchanges in 1 and 2. 1 presents an Mn₂ dinuclear model with a coupling value of J=-0.60 cm^-1, and 2 represents a square Mn₄ tetranuclear model with a coupling value of J=-3.16 cm^-1. Subsequent works will be focused on the construction of novel coordination polymers based on other polynuclear metal units by using similar organic ligands.

  Supporting information is available at http://www.wjhxxb.cn

  
  
• 1. [1]

     JIANG C H, WANG X K, OUYANG Y G, LU K B, JIANG W F. Recent advances in metal-organic frameworks for gas adsorption/separation[J]. Nanoscale Adv., 2022, 4(9): 2077-2089 doi: 10.1039/D2NA00061J

  2. [2]

     WAN Q, WAKIZAKA M, YAMASHITA M. Single-ion magnetism behaviors in lanthanide(Ⅲ) based coordination frameworks[J]. Inorg. Chem. Front., 2023, 10(18): 5212-5224 doi: 10.1039/D3QI00925D

  3. [3]

     YE Y X, GONG L S, XIANG S C, ZHANG Z J, CHEN B L. Metal- organic frameworks as a versatile platform for proton conductors[J]. Adv. Mater., 2020, 32(21): 1907090 doi: 10.1002/adma.201907090

  4. [4]

     DUAN W L, LI Y X, FENG Y, LI W Z, LUAN J. Controllable synthesis of copper-organic frameworks via ligand adjustment for enhanced photo-Fenton-like catalysis[J]. J. Colloid Interface Sci., 2023, 646(15): 107-117

  5. [5]

     王思璐, 张凤凤, 张成, 王潇, 唐龙, 岳二林, 王记江, 侯向阳. 用于痕量监测Zr⁴⁺、Cr₂O₇^2-、Fe³⁺、HPO₄^2-和指纹识别的功能化Eu³⁺/Tb³⁺配位聚合物荧光探针的构筑[J]. 无机化学学报, 2024, 40(2): 441-450WANG S L, ZHANG F F, ZHANG C, WANG X, TANG L, YUE E L, WANG J J, HOU X Y, Design and synthesis of Eu³⁺/Tb³⁺-functionalized coordination polymers as visible fluorescent probes for trace monitoring Zr⁴⁺, Fe³⁺, Cr₂O₇^2-, HPO₄^2- and identifying fingerprints[J]. Chinese J. Inorg. Chem., 2024, 40(2): 441-450

  6. [6]

     YANG D D, LU L P, ZHU M L. Structural diversity, magnetic properties and luminescence of Ni(Ⅱ), Co(Ⅱ) and Zn(Ⅱ) coordination polymers derived from 3, 3′-[(5-carboxy-1, 3-phenylene)bis(oxy)]dibenzoic acid and 1, 10-phenanthroline[J]. Acta Crystallogr. Sect. C, 2019, C75(12): 1580-1592

  7. [7]

     LEE K, VIKNESHVARAN S, LEE H, LEE S. Ligand-mediated electrocatalytic activity of Cu-imidazolate coordination polymers for OER in water electrolysis[J]. Int. J. Hydrog. Energy, 2024, 51(2): 1184-1196

  8. [8]

     NOTASH B, KHEIRKHAH B R, KHORSHIDI G. Topological control through the solvent effect in two-dimensional cadmium coordination polymers[J]. J. Mol. Struct., 2023, 1294(15): 136324

  9. [9]

     SU F, LI S D, HAN C, WU L T, WANG Z J. Tuning three coordination polymers with dinuclear metal units via pH control: Syntheses, structures, and magnetic properties[J]. J. Solid State Chem., 2022, 311: 123121 doi: 10.1016/j.jssc.2022.123121

  10. [10]

      TANG S S, HE X M, XUAN H, ZHANG K H, KONG W L, ZHANG J. Structural tuning of coordination polymers with photoluminescent properties via temperature control[J]. J. Coord. Chem., 2024, 77(3): 244-253

  11. [11]

      LI S, LU L, FENG S, ZHU M. Syntheses, structures, magnetic properties and luminescence of four coordination polymers based on an asymmetric semirigid tricarboxylate ligand[J]. J. Solid State Chem., 2019, 269: 56-64 doi: 10.1016/j.jssc.2018.09.007

  12. [12]

      WANG A, YANG B, WANG Y, HU Z, WEI Z, ZHU M, ENGLERT U. Structure, magnetic properties and spin density of two alternative Mn(Ⅱ) coordination polymers based on 1, 4-bis(2′-carboxyphenoxy)benzene[J]. Dalton Trans., 2022, 51(12): 4869-4877 doi: 10.1039/D1DT04240H

  13. [13]

      HAN X H, LIU B, WANG Z H, CRAZE A R, SUN H X, KHAN M R, LIU J, LIU Z Y, LI J P. Structure diversity and magnetic properties of manganese and cobalt coordination polymers with multiple carboxyl bridges[J]. Inorg. Chim. Acta, 2022, 533(1): 120788

  14. [14]

      黎彧, 赵振宇, 邹训重, 冯安生, 顾金忠. 由醚氧桥连四羧酸配体构筑的锰(Ⅱ)和锌(Ⅱ)配位聚合物的合成、晶体结构、荧光及磁性质[J]. 无机化学学报, 2020, 36(2): 377-384LI Y, ZHAO Z Y, ZOU X Z, FENG A S, GU J Z. Syntheses, crystal structures, luminescent and magnetic properties of 2D manganese(Ⅱ) and zinc(Ⅱ) coordination polymers based on an ether-bridged tetracarboxylic acid[J]. Chinese J. Inorg. Chem., 2020, 36(2): 377-384

  15. [15]

      LOU Y, WANG J, TAO Y, CHEN J, MISHIMA A, OHBA M. Structure modulation of manganese coordination polymers consisting of 1, 4-naphthalene dicarboxylate and 1, 10-phenanthroline[J]. Dalton Trans., 2014, 43(22): 8508-8514

  16. [16]

      CHEN S H, WANG H Q. Synthesis, structures, and characterizations of four uranyl coordination polymers constructed by mixed- ligand strategy[J]. J. Radioanal. Nucl. Chem., 2023, 332(4): 1367-1376

  17. [17]

      MENG L, LIANG Y Y, MEI L, GENG J S, HU K Q, YU J P, WANG X P, FUJITA T, CHAI Z F, SHI W Q. Mixed-ligand uranyl squarate coordination polymers: Structure regulation and redox activity[J]. Inorg. Chem., 2022, 61(1): 302-316

  18. [18]

      AGUIRRE-DIAZ L M, ECHEVERRI M, PAREDES-GIL K, SNEJKO N, GOMEZ-LOR B, GUTIERREZ-PUEBLA E, MONGE M A. The effect of auxiliary nitrogenated linkers on the design of new Cadmium-based coordination polymers as sensors for the detection of explosive materials[J]. Chem. ‒Eur. J., 2021, 27(16): 5298-5306

  19. [19]

      QIAN J F, TIAN W J, YANG S, SUN Z H, CHEN L, WEI M J, WU Z, HE M Y, ZHANG Z H, MEI L. Auxiliary ligand-dependent adaptive regulation of uranyl coordination in mixed-ligand uranyl compounds of flexible biphenyltetracarboxylic acid[J]. Inorg. Chem., 2020, 59(23): 17659-17670

  20. [20]

      LI S, LU L, ZHU M, FENG S, SU F, ZHAO X. Exploring the syntheses, structures, topologies, luminescence sensing and magnetism of Zn(Ⅱ) and Mn(Ⅱ) coordination polymers based on a semirigid tricarboxylate ligand[J]. CrystEngComm, 2018, 20(36): 5442-5456

  21. [21]

      GOMEZ V, CORBELLA M, FONT-BARDIA M, CALVET T. A μ_{1, 1}- or μ_{1, 3}-carboxylate bridge makes the difference in the magnetic properties of dinuclear Mn(Ⅱ) compounds[J]. Dalton Trans., 2010, 39(48): 11664-11674

  22. [22]

      LI X L, LIU G Z, XIN L Y, WANG L Y. Binuclear and tetranuclear Mn(Ⅱ) clusters in coordination polymers derived from semirigid tetracarboxylate and N-donor ligands: Syntheses, new topology structures and magnetism[J]. J. Solid State Chem., 2017, 246: 252-257

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  Scheme 1  Synthesis strategy for complexes 1 and 2

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  Figure 1  (a) Coordination environment of Mn(Ⅱ) ion in complex 1 with the thermal ellipsoids at 30% probability level; (b) 1D chain structure formed by HL^4- ligands linking to Mn(Ⅱ) ions; (c) 2D layered structure formed by π…π stacking interactions between the benzene rings of phen

  Symmetry codes: ^ⅰ-x+1/2, -y+1/2, -z; ^ⅱ -x+1, -y, -z.

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  Figure 2  (a) Displacement ellipsoid plot (30% probability) of the coordination environments of Mn(Ⅱ) ions in complex 2; (b) Mn(Ⅱ) tetranuclear unit in 2; (c) 3D polyhedral structure of 2 (the polyhedron of Mn1 and Mn2 are represented with green and orange colors, respectively); (d) 3D topology net of 2

  Symmetry codes: ^ⅰ-x, -y, -z; ^ⅱ x, y+1, z; ^ⅲ -x+1, -y+1, -z.

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  Figure 3  Various coordination modes of HL^4- observed in complexes 1 (left) and 2 (right)

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  Figure 4  (a) χ_M and χ_MT vs T plots and (b) χ_M^-1 vs T plots for complex 1

  The solid line represents the best fit.

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  Figure 5  (a) χ_M and χ_MT vs T plots and (b) χ_M^-1 vs T plot for 2

  The solid line represents the best fit.

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  Table 1.  Crystal data and structure refinement parameters for complexes 1 and 2

  Parameter	1	2
  Empirical formula	C53H38Mn2N6O15·5.5H2O	C35H23Mn2N6O12
  Formula weight	1207.86	829.47
  T / K	294	295
  Crystal system	Monoclinic	Triclinic
  Space group	C2/c	P1
  a / nm	2.735 98(9)	1.117 3(3)
  b / nm	1.448 58(2)	1.120 2(3)
  c / nm	2.743 88(9)	1.448 7(4)
  α / (°)		91.511(9)
  β / (°)	97.155(2)	93.75(1)
  γ / (°)		117.544(9)
  V / nm3	10.790 1(3)	1.600 9(8)
  Z	8	2
  F(000)	4 984	842
  Dc / (g·cm-3)	1.487	1.721
  μ / mm-1	0.55	0.87
  θ range / (°)	2.8-25.5	2.8-25.0
  Goodness-of-fit on F 2	1.01	1.04
  Reflection collected	46 843	13 908
  Independent reflection	10 019 (Rint=0.044)	5 553 (Rint=0.040)
  Reflection observed [I > 2σ(I)]	7 348	4 076
  R1 [I > 2σ(I)]	0.041	0.042
  wR2 [I > 2σ(I)]	0.102	0.103

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