English

• 0.   Introduction

  In recent years, the rational design and assembly of coordination polymers has been of considerable interest due to their potential applications, archite-ctures, and topologies^[1-5]. Many factors, such as the coordination geometry of the metal centers, type and connectivity of organic ligands, stoichiometry, reaction conditions, template effect, presence of auxiliary ligands, and pH values can play the key role in the construction of the coordination networks^[6-10]. The design and selection of the special ligands is very important in the construction of these coordination polymers.

  Multi-carboxylate biphenyl ligands have been certified to be of great significance as constructors due to their strong coordination abilities in various modes, which could satisfy different geometric require-ments of metal centers^{[7-9, 11-16]}. In order to extend our research in this field, we chose two biphenyl tricar-boxylic acid ligands, biphenyl-2, 5, 3′-tricarboxylate acid (H₃bptc) and 2-(4-carboxypyridin-3-yl)terephalic acid (H₃cptc) to construct novel coordination comp-ounds. Both ligands possesses the following features: (1) they have three carboxyl groups that may be completely or partially deprotonated, inducing rich coordination modes and allowing interesting structures with higher dimensionalities; (2) they can act as hydrogen-bond acceptor as well as donor, depending upon the degree of deprotonation; (3) the free rotation of C-C single bonds between two the aromatic rings could form numbers of coordination geometries of metal centers; thus, it may ligate metal centers in different orientation.

  Taking into account these factors, we herein report the syntheses, crystal structures, and magnetic properties of two Ni(Ⅱ) and Mn(Ⅱ) coordination compounds constructed from biphenyl tricarboxylic acid ligands.

  1.   Experimental

  1.1   Reagents and physical measurements

  All chemicals and solvents were of AR grade and used without further purification. Carbon, hydrogen and nitrogen were determined using an Elementar Vario EL elemental analyzer. IR spectra were recorded using KBr pellets and a Bruker EQUINOX 55 spectrometer. Thermogravimetric analysis (TGA) data were collected on a LINSEIS STA PT1600 thermal analyzer with a heating rate of 10 ℃·min^-1. Magnetic susceptibility data were collected in the 2~300 K temperature range with a Quantum Design SQUID Magnetometer MPMS XL-7 with a field of 0.1 T. A correction was made for the diamagnetic contribution prior to data analysis.

  1.2   Synthesis of [Ni₂(μ₃-Hbptc)(Hbptc)(phen)₃ (H₂O)]₂·4H₂O (1)

  A mixture of NiCl₂·6H₂O (0.047 g, 0.20 mmol), H₃bptc (0.057 g, 0.2 mmol), phen (0.040 g, 0.2 mmol), NaOH (0.016 g, 0.40 mmol), and H₂O (10 mL) was stirred at room temperature for 15 min, and then sealed in a 25 mL Teflon-lined stainless steel vessel, and heated at 160 ℃ for 3 days, followed by cooling to room temperature at a rate of 10 ℃·h^-1. Green block-shaped crystals of 1 were isolated manually, and washed with distilled water. Yield: 45% (based on H₃bptc). Anal. Calcd. for C₆₆H₄₆Ni₂N₆O₁₅(%): C 61.91, H 3.62, N 6.56; Found(%): C 61.75, H 3.60, N 6.61. IR (KBr, cm^-1): 3 318w, 2 924m, 1 714w, 1 587s, 1 564s, 1 517m, 1 471w, 1 424m, 1 407w, 1 373w, 1 216w, 1 147w, 1 100w, 1 042w, 985w, 927w, 852w, 805w, 776w, 724m, 643w, 516w.

  1.3   Synthesis of {[Mn₃(μ₄-cptc)₂(2, 2′-bipy)₂(H₂O)₄]·2H₂O}_n (2)

  A mixture of MnCl₂·4H₂O (0.059 g, 0.30 mmol), H₃cptc (0.057 g, 0.2 mmol), 2, 2′-bipy (0.047 g, 0.3 mmol), NaOH (0.024 g, 0.60 mmol), and H₂O (10 mL) was stirred at room temperature for 15 min, and then sealed in a 25 mL Teflon-lined stainless steel vessel, and heated at 160 ℃ for 3 days, followed by cooling to room temperature at a rate of 10 ℃·h^-1. Yellow block-shaped crystals of 2 were isolated manually, and washed with distilled water. Yield: 62% (based on H₃cptc). Anal. Calcd. for C₄₈H₄₀Mn₃N₆O₁₈(%): C 49.97, H 3.49, N 7.28; Found(%): C 50.14, H 3.51, N 7.23. IR (KBr, cm^-1): 3 057w, 1 598m, 1 569s, 1 471w, 1 430w, 1 373s, 1 262w, 1 170w, 1 153w, 1 048w, 1 031w, 1 014w, 933w, 904w, 868w, 852w, 810w, 765m, 730w, 707w, 649w, 551w. The compounds are insoluble in water and common organic solvents, such as methanol, ethanol, acetone, and DMF.

  1.4   Structure determinations

  Two single crystals with dimensions of 0.25 mm×0.22 mm×0.21 mm (1) and 0.26 mm×0.24 mm×0.23 mm (2) were analyzed at 293(2) K on a Bruker SMART APEX Ⅱ CCD diffractometer with Mo Kα radiation (λ=0.071 073 nm). The structures were solved by direct methods and refined by full matrix least-square on F² using the SHELXTL-2014 program^[17]. All non-hydrogen atoms were refined anisotropically. All the hydrogen atoms were positioned geometrically and refined using a riding model. A summary of the crystallography data and structure refinements for 1 and 2 is given in Table 1. The selected bond lengths and angles for compounds 1 and 2 are listed in Table 2. Hydrogen bond parameters of compounds 1 and 2 are given in Table 3 and 4.

  表 1

  

  表 1  Crystal data for compounds 1 and 2

  Table 1.  Crystal data for compounds 1 and 2

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  Compound	1	2
  Chemical formula	C66H46Ni2N6O15	C48H40Mn3N6O18
  Molecular weight	1 280.51	1 153.68
  Crystal system	Triclinic	Triclinic
  Space group	P1	P1
  a/nm	1.243 18(6)	0.719 34(4)
  b/nm	1.422 15(10)	1.023 41(5)
  c/nm	1.662 89(11)	1.739 84(11)
  α/(°)	95.289(6)	96.993(5)
  β/(°)	96.231(5)	101.237(5)
  γ/(°)	108.755(5)	106.819(5)
  V/nm3	2.742 1(3)	1.180 71(13)
  Z	2	1
  F(000)	1 320	589
  θ range for data collection/(°)	3.244-25.049	3.409-25.050
  Limiting indices	-14 ≤ h ≤ 14, -16 ≤ k ≤ 16, -19 ≤ l ≤ 15	-8 ≤ h ≤ 8, -12 ≤ k ≤ 12, -18 ≤ l ≤ 20
  Reflection collected, unique (Rint)	17 820, 9 694 (0.061 9)	7 235, 4 178 (0.031 6)
  Dc/(g·cm-3)	1.551	1.623
  μ/mm-1	0.768	0.876
  Data, restraint, parameter	9 694, 0, 804	4 178, 0, 340
  Goodness-of-fit on F2	1.039	1.060
  Final R indices [I≥2σ(I)]R1, wR2	0.074 3, 0.153 2	0.043 8, 0.081 8
  R indices (all data)R1, wR2	0.134 7, 0.196 3	0.061 6, 0.091 5
  Largest diff. peak and hole/(e·nm-3)	1 173 and -461	426 and -560

  表 2

  

  表 2  Selected bond lengths (nm) and bond angles (°) for compounds 1 and 2

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

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  1
  Ni(1)-O(1)	0.207 9(3)	Ni(1)-O(2)A	0.207 O(4)	Ni(1)-N(1)	0.212 2(4)
  Ni(1)-N(2)	0.207 9(5)	Ni(1)-N(3)	0.207 3(5)	Ni(1)-N(4)	0.211 8(5)
  Ni(2)-O(6)	0.204 9(4)	Ni(2)-O(7)	0.221 2(4)	Ni(2)-O(8)	0.211 7(4)
  Ni(2)-O(13)	0.202 8(4)	Ni(2)-N(5)	0.206 9(5)	Ni(2)-N(6)	0.205 9(5)
  O(2)A-Ni(1)-N(3)	98.3O(17)	O(2)A-Ni(1)-N(2)	88.22(18)	N(3)-Ni(1)-N(2)	170.67(18)
  O(2)A-Ni(1)-O(1)	88.08(14)	N(3)-Ni(1)-O(1)	96.01(15)	N(2)-Ni(1)-O(1)	90.84(16)
  O(2)A-Ni(1)-N(4)	174.09(17)	N(3)-Ni(1)-N(4)	78.83(19)	N(2)-Ni(1)-N(4)	94.05(19)
  O(1)-Ni(1)-N(4)	97.32(16)	O(2)A-Ni(1)-N(1)	87.61(16)	N(3)-Ni(1)-N(1)	94.15(19)
  N(2)-Ni(1)-N(1)	79.39(19)	O(1)-Ni(1)-N(1)	169.44(18)	N(4)-Ni(1)-N(1)	87.46(17)
  O(13)-Ni(2)-O(6)	91.43(18)	O(13)-Ni(2)-N(6)	103.13(18)	O(6)-Ni(2)-N(6)	95.08(19)
  O(13)-Ni(2)-N(5)	91.4O(19)	O(6)-Ni(2)-N(5)	174.41(19)	N(6)-Ni(2)-N(5)	79.58(19)
  O(13)-Ni(2)-O(8)	156.13(17)	O(6)-Ni(2)-O(8)	83.04(17)	N(6)-Ni(2)-O(8)	100.49(18)
  N(5)-Ni(2)-O(8)	96.23(18)	O(13)-Ni(2)-O(7)	95.71(17)	O(6)-Ni(2)-O(7)	89.44(17)
  N(6)-Ni(2)-O(7)	160.49(19)	N(5)-Ni(2)-O(7)	95.08(18)	O(8)-Ni(2)-O(7)	61.17(16)
  2
  Mn(1)-O(1)	0.210 2(2)	Mn(1)-O(5)A	0.214 6(2)	Mn(1)-O(7)	0.213 2(2)
  Mn(1)-N(1)A	0.226 7(3)	Mn(1)-N(2)	0.230 1(3)	Mn(1)-N(3)	0.232 3(3)
  Mn(1)-O(2)	0.220 2(2)	Mn(1)-O(2)B	0.220 2(2)	Mn(1)-O(4)A	0.213 4(2)
  Mn(1)-O(4)C	0.213 4(2)	Mn(1)-O(8)	0.223 1(3)	Mn(1)-O(8)B	0.223 1(3)
  O(1)-Mn(1)-O(7)	99.47(10)	O(1)-Mn(1)-O(5)A	90.87(10)	O(7)-Mn(1)-O(5)A	163.79(9)
  O(1)-Mn(1)-N(1)A	103.66(9)	O(7)-Mn(1)-N(1)A	91.28(9)	O(5)A-Mn(1)-N(1)A	74.06(9)
  O(1)-Mn(1)-N(2)	86.36(10)	O(7)-Mn(1)-N(2)	93.64(10)	O(5)A-Mn(1)-N(2)	99.48(10)
  N(1)A-Mn(1)-N(2)	167.97(11)	O(1)-Mn(1)-N(3)	156.17(10)	O(7)-Mn(1)-N(3)	88.7O(10)
  O(5)A-Mn(1)-N(3)	86.72(10)	N(1)A-Mn(1)-N(3)	98.46(10)	N(2)-Mn(1)-N(3)	70.71(10)
  O(4)C-Mn(2)-O(2)	87.09(9)	O(4)A-Mn(2)-O(2)	92.91(9)	O(4)C-Mn(1)-O(8)B	93.19(9)
  O(4)A-Mn(1)-O(8)B	86.81(9)	O(2)-Mn(1)-O(8)B	89.65(9)	O(2)-Mn(1)-O(8)	90.35(9)
  Symmetry codes: A:-x+1, -y, -z+1 for 1; A: x, y+1, z; B: -x, -y+1, -z; C: -x, -y, -z for 2.

  表 3

  

  表 3  Hydrogen bond parameters of compound 1

  Table 3.  Hydrogen bond parameters of compound 1

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  D-H…A	d(D-H)/nm	d(H…A)/nm	d(D…A)/nm	∠DHA/(°)
  O(4)-H(4)…O(9)A	0.082	0.168	0.248 2	163.0
  O(12)-H(12)…O(8)B	0.082	0.180	0.254 7	151.1
  O(13)-H(1W)…O(9)C	0.085	0.175	0.259 7	179.8
  O(13)-H(2W)…O(5)	0.085	0.177	0.262 2	179.7
  O(14)-H(3W)…O(3)D	0.085	0.195	0.280 5	179.3
  Symmetry codes: A:-x-1, y-1, z; B: -x+1, -y+1, -z; C: x-1, y, z; D: x+1, y+1, z.

  表 4

  

  表 4  Hydrogen bond parameters of compound 2

  Table 4.  Hydrogen bond parameters of compound 2

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  D-H…A	d(D-H)/nm	d(H…A)/nm	d(D…A)/nm	∠DHA/(°)
  O(7)-H(1W)…O(6)A	0.086	0.198	0.276 4	151.5
  O(7)-H(2W)…O(9)B	0.085	0.184	0.268 8	179.2
  O(8)-H(3W)…O(3)C	0.090	0.209	0.286 5	143.5
  Symmetry codes: A: x-1, y+1, z; B: x-1, y, z; C: x+1, y+1, z.

  CCDC: 1588394, 1; 1588395, 2.

  2.   Results and discussion

  2.1   Description of the structure

  2.1.1   [Ni₂(μ₃-Hbptc)(Hbptc)(phen)₃(H₂O)]₂·4H₂O (1)

  Single-crystal X-ray diffraction analysis reveals that compound 1 crystallizes in the triclinic space group P1. Its asymmetric unit contains two crystallo-graphically unique Ni(Ⅱ) atoms, two Hbptc^2- blocks, three phen moieties, one H₂O ligand and two lattice water molecules. As depicted in Fig. 1, the six-coordinated Ni1 atom displays a distorted octahedral {NiN₄O₂} geometry filled by two carboxylate O atoms from two different μ₃-Hbptc^2- blocks and four N atoms from two phen ligands. The Ni2 center is coordinated by one carboxylate O atom from one μ₃-Hbptc^2- block, two carboxylate O atoms from one terminal Hbptc^2- block, one O atom from the H₂O ligand, and two N atoms from one phen moiety, thus composing distorted octahedral {NiN2O₄} geometry. The lengths of the Ni-O bonds range from 0.202 8(4) to 0.221 2(4) nm, whereas the Ni-N distances vary from 0.205 9(5) to 0.212 2(4) nm; these bonding parameters are comparable to those found in other reported Ni(Ⅱ) compounds^{[7, 9, 11]}. In 1, the Hbptc^2- ligands adopt two different coordination modes (modes Ⅰ and Ⅱ, Scheme 1), in which the deproto-nated carboxylate groups show the monodentate, bidentate or uncoordinated modes. The dihedral angles between two phenyl rings in the Hbptc^2- are 52.52° and 39.91°, respectively. Two μ₃-Hbptc^2- ligands bridge alternately neighboring Ni(Ⅱ)ions to form a discrete tetranuclear nickel(Ⅱ) structure (Fig. 2). These Ni4 units are assembled to a 3D supramolecular framework through O-H…O hydrogen bond (Fig. 3 and Table 3).

  图 Scheme 1

  

  图 Scheme 1  Coordination modes of Hbptc^2-/cptc^3- ligands in compounds 1 and 2

  Figure Scheme 1.  Coordination modes of Hbptc^2-/cptc^3- ligands in compounds 1 and 2

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  图 1

  

  图 1  Drawing of the asymmetric unit of compound 1 with 30% probability thermal ellipsoids

  Figure 1.  Drawing of the asymmetric unit of compound 1 with 30% probability thermal ellipsoids

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  图 2

  

  图 2  Tetranuclear nickel(Ⅱ) unit

  Figure 2.  Tetranuclear nickel(Ⅱ) unit

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  图 3

  

  图 3  Perspective of 3D supramolecular framework viewed from b axis in 1

  Figure 3.  Perspective of 3D supramolecular framework viewed from b axis in 1

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  2.1.2   {[Mn₃(μ₄-cptc)₂(2, 2′-bipy)₂(H₂O)₄]·2H₂O}_n (2)

  The asymmetric unit of 2 consists of two crystallographically distinct Mn(Ⅱ) atoms (Mn1 with full occupancy; Mn2 is positioned on a twofold rotation axis), one μ₄-cptc^3- block, one 2, 2′-bipy ligand, two coordinated and one lattice water molecule. As shown in Fig. 4, six-coordinate Mn1 atom reveals distorted octahedral {MnN₃O₃} environment, filled by one N and two O atoms from three individual μ₄-cptc^3- blocks, one O atom from the H₂O ligand, and two N atoms from the 2, 2′-bipy moiety. The Mn2 center is coordinated by four carboxylate O atoms from four distinct cptc^3- moieties and two O atoms from two H₂O ligands, thus forming octahedral {MnO₆} geometry. The Mn-O distances range from 0.210 2(2) to 0.223 1(3) nm, whereas the Mn-N distances vary from 0.226 7(3) to 0.232 3(3) nm; these bonding parameters are compar-able to those observed in other Mn(Ⅱ) compounds^{[7-9, 11]}. In 2, the cptc^3- block acts as a μ₄-N, O₄-spacer and its COO^- groups take a monodentate or bidentate mode (mode Ⅲ, Scheme 1). In cptc^3-, a dihedral angle (between pyridyl and benzene rings) is 52.30°. Three neighboring Mn(Ⅱ) ions are bridged by four different μ₄-cptc^3- ligands, giving rise to a centrosymmetric trinuclear Mn(Ⅱ) subunit with the Mn…Mn distance of 0.508 4(6) nm (Fig. 5). The adjacent Mn3 subunits are further linked by the cptc^3- blocks into a 1D chain (Fig. 6), having the shortest distance of 1.023 4(5) nm between the neighboring trimanganese(Ⅱ) subunits.

  图 4

  

  图 4  Drawing of the asymmetric unit of compound 2 with 30% probability thermal ellipsoids

  Figure 4.  Drawing of the asymmetric unit of compound 2 with 30% probability thermal ellipsoids

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  图 5

  

  图 5  Trinuclear Mn(Ⅱ) unit in compound 2

  Figure 5.  Trinuclear Mn(Ⅱ) unit in compound 2

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  图 6

  

  图 6  One dimensional chain along a axis in compound 2

  Figure 6.  One dimensional chain along a axis in compound 2

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  2.2   TGA analysis

  To determine the thermal stability of compounds 1 and 2, their thermal behaviors were investigated under nitrogen atmosphere by thermogravimetric analysis (TGA). As shown in Fig. 7, compound 1 loses its four lattice and two coordinated water molecules in the range of 152~241 ℃ (Obsd. 3.9%, Calcd. 4.2%), followed by the decomposition at 325 ℃. The TGA curve of 2 reveals that two lattice and four coor-dinated water molecules are released between 98~238 ℃ (Obsd. 9.6%, Calcd. 9.4%), and the dehydrated solid begins to decompose at 382 ℃.

  图 7

  

  图 7  TGA curves of compounds 1 and 2

  Figure 7.  TGA curves of compounds 1 and 2

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  2.3   Magnetic properties

  Variable-temperature magnetic susceptibility studies were carried out on powder samples of 1 and 2 in the 2~300 K temperature range. For 1, the χ_MT value at 300 K is 4.08 cm³·mol^-1·K, which is close to the value of 4.00 cm³·mol^-1·K for four magnetically isolated Ni(Ⅱ) center (S_Ni=1, g=2.0). Upon cooling, the χ_MT value drops down very slowly from 4.08 cm³·mol^-1 ·K at 300 K to 3.64 cm³·mol^-1·K at 60 K, and then decreases steeply to 1.40 cm³·mol^-1·K at 2 K (Fig. 8). In the 8~300 K interval, the χ_M^-1 vs T plot for 1 obeys the Curie-Weiss law with a Weiss constant θ of -6.52 K and a Curie constant C of 4.15 cm³·mol^-1·K, sugg-esting a weak antiferromagnetic interaction between the Ni(Ⅱ) ions.

  图 8

  

  图 8  Temperature dependence of χ_MT (○) and 1/χ_M(□) vs T for compound 1

  Figure 8.  Temperature dependence of χ_MT (○) and 1/χ_M(□) vs T for compound 1

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  We tried to fit the magnetic data of 1 using the following expression^[18] for a dinuclear Ni(Ⅱ) unit:

  $ H = - J{S_1}{S_2} \\ {\chi _{{\rm{M}}'}} = \frac{{N{\beta ^2}{g^2}}}{{3k(T-\theta )}}\frac{{\sum {S'(S' + 1)(2S' + 1){{\rm{e}}^{-E(S')/(kT)}}} }}{{\sum {(2S' + 1){{\rm{e}}^{-E(S')/(kT)}}} }} $

  $ {\chi _{\rm{M}}}{\rm{ = }}{\chi _{{\rm{M}}'}}(1-\rho ) + \frac{{4S(S + 1)N{\beta ^2}{g^2}\rho }}{{3kT}} + {\rm{TIP}} $

  where ρ is a paramagnetic impurity fraction and TIP is temperature independent paramagnetism. Using this model, the susceptibility for 1 above 60 K was simul-ated, leading to the values of J=-2.25 cm^-1, g=2.10, ρ=0.010, and TIP=4.58×10^-6 cm³·mol^-1, with the agreement factor R=∑(T_obs-T_calc)²/∑(T_obs)²=6.14×10^-4. The negative J parameter confirms that a weak anti-ferromagnetic exchange coupling exists between the adjacent Ni(Ⅱ) centers, which is in agreement with a negative θ value.

  For 2, the χ_MT value at 300 K is 13.41 cm³·mol^-1 ·K, which is close to the value of 13.12 cm³·mol^-1·K expected for three magnetically isolated high-spin Mn(Ⅱ) centers (S_Mn=5/2, g=2.0). Upon cooling, the χ_MT value drops down very slowly from 13.41 cm³·mol^-1·K at 300 K to 12.60 cm³·mol^-1·K at 70 K and then decreases steeply to 2.81 cm³·mol^-1·K at 2 K (Fig. 9). The χ_M^-1 vs T plot for 2 in the 2~300 K interval obeys the Curie-Weiss law with a Weiss constant θ of -4.34 K and a Curie constant C of 13.59 cm³·mol^-1·K. The negative value of θ and the decrease of the χ_MT should be attributed to the overall antiferromagnetic coupling between the Mn(Ⅱ) centers within the Mn₃ unit. According to the structure of compound 2, there is one set of magnetic exchange pathway within the trinuclear cluster via carboxylate bridge (Fig. 5). We tried to fit the magnetic data of 2 using the following expression^[19-20] for the linear trinuclear Mn(Ⅱ) motif:

  图 9

  

  图 9  Temperature dependence of χ_MT (○) and 1/χ_M(□) vs T for compound 2

  Figure 9.  Temperature dependence of χ_MT (○) and 1/χ_M(□) vs T for compound 2

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  $ \begin{array}{l} \hat H =-2\sum\limits_{i = 1}^n {\sum\limits_{j > 1}^n {{J_{ij}}{{\vec S}_i}{{\vec S}_j}} } \\ \hat H =-2{J_{12}}{{\vec S}_1}{{\vec S}_2}-2{J_{23}}{{\vec S}_2}{{\vec S}_3} - 2{J_{13}}{{\vec S}_1}{{\vec S}_3}\\ \chi = \frac{{N{\beta ^2}{g^2}}}{{3kT}}\frac{{\sum\limits_{{S_{\rm{T}}}} {{S_{\rm{T}}}({S_{\rm{T}}} + 1)(2{S_{\rm{T}}} + 1){{\rm{e}}^{ - E({S_{\rm{T}}})/(kT)}}} }}{{\sum\limits_{{S_{\rm{T}}}} {(2{S_{\rm{T}}} + 1){{\rm{e}}^{ - E({S_{\rm{T}}})/(kT)}}} }} \end{array} $

  $ {\chi _{\rm{m}}} = \frac{\chi }{{1- [2zJ'/(N{g^2}{\beta ^2})]\chi }} $

  where S_T is tolal spin of the linear trinuclear Mn(Ⅱ) motif; J₁₂=J₂₃=J₁, J₁₃=J₂ (J₁₂ and J₂₃ are the exchange interactions between the "central" Mn(Ⅱ) and two "outer" Mn(Ⅱ) atoms; J₂ is the exchange interaction between the "outer" Mn(Ⅱ) ions within a Mn₃ unit), zJ′ refers to the intercluster coupling constant in the 1D chain. This model gives satisfactory results with the superexchange parameters: J₁/k_B=-1.32 K, J₂/k_B=-0.41 K, zJ′/k_B=-0.20 K, and g=2.02. The agreement factor defined by R=∑(χ_mT_exp-χ_mT_calc)²/∑(χ_mT_exp)² is 7.54× 10^-4. These values confirm the presence of antiferro-magnetic interaction between the Mn(Ⅱ) ions within a trinuclear subunit. The inercluster magnetic interaction (zJ′) is rather small, indicating that the exchange interactions between two magnetic clusters are very weak, which is probably due to a long separation (1.023 4(5) nm) of the adjacent magnetic subunits. In compounds 1 and 2, there is one type of the magnetic exchange pathway within the Ni₄ and Mn₃ units, namely via double μ₂-η¹:η¹-carboxylate (syn-syn) bridges (Fig. 2 and 5).

  3.   Conclusions

  In summary, two new coordination compounds, namely [Ni₂(μ₃-Hbptc)(Hbptc)(phen)₃(H₂O)]₂·4H₂O (1) and {[Mn₃(μ₄-cptc)₂(2, 2′-bipy)₂(H₂O)₄]·2H₂O}_n (2), have been synthesized under hydrothermal conditions. The compounds feature the 0D tetranuclear and 1D chain structures, respectively. Magnetic studies show an antiferromagnetic coupling between the adjacent metal centers.

• 1. [1]

     Huang Y B, Liang J, Wang X S, et al. Chem. Soc. Rev., 2017, 46:126-157 doi: 10.1039/C6CS00250A

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  Scheme 1  Coordination modes of Hbptc^2-/cptc^3- ligands in compounds 1 and 2

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  Figure 1  Drawing of the asymmetric unit of compound 1 with 30% probability thermal ellipsoids

  H atoms and lattice water molecules were omitted for clarity except those of COOH groups; Symmetry codes: A: -x+1, -y, -z+1

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  Figure 2  Tetranuclear nickel(Ⅱ) unit

  Phen ligands are omitted for clarity; Symmetry codes: A: -x+1, -y, -z+1

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  Figure 3  Perspective of 3D supramolecular framework viewed from b axis in 1

  Phen ligands are omitted for clarity; Dotted lines represent the H-bonds; Symmetry codes: A: x-1, y-1, z; B: -x+1, -y+1, -z

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  Figure 4  Drawing of the asymmetric unit of compound 2 with 30% probability thermal ellipsoids

  H atoms were omitted for clarity; Symmetry codes: A: x, y+1, z; B: -x, -y+1, -z; C: -x, -y, -z

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  Figure 5  Trinuclear Mn(Ⅱ) unit in compound 2

  Symmetry codes: A: -x, -y+1, -z

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  Figure 6  One dimensional chain along a axis in compound 2

  2, 2′-bipy ligands are omitted for clarity; Symmetry codes: A: -x, -y+1, -z; B: x, y+1, z; C: -x, -y+2, -z; D: x, y-1, z; E: -x, -y, -z

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  Figure 7  TGA curves of compounds 1 and 2

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  Figure 8  Temperature dependence of χ_MT (○) and 1/χ_M(□) vs T for compound 1

  Red curve represents the best fit to the equations in the text; Blue line shows the Curie-Weiss fitting

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  Figure 9  Temperature dependence of χ_MT (○) and 1/χ_M(□) vs T for compound 2

  Red curve represents the best fit to the equations in the text; Blue line shows the Curie-Weiss fitting

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  Table 1.  Crystal data for compounds 1 and 2

  Compound	1	2
  Chemical formula	C66H46Ni2N6O15	C48H40Mn3N6O18
  Molecular weight	1 280.51	1 153.68
  Crystal system	Triclinic	Triclinic
  Space group	P1	P1
  a/nm	1.243 18(6)	0.719 34(4)
  b/nm	1.422 15(10)	1.023 41(5)
  c/nm	1.662 89(11)	1.739 84(11)
  α/(°)	95.289(6)	96.993(5)
  β/(°)	96.231(5)	101.237(5)
  γ/(°)	108.755(5)	106.819(5)
  V/nm3	2.742 1(3)	1.180 71(13)
  Z	2	1
  F(000)	1 320	589
  θ range for data collection/(°)	3.244-25.049	3.409-25.050
  Limiting indices	-14 ≤ h ≤ 14, -16 ≤ k ≤ 16, -19 ≤ l ≤ 15	-8 ≤ h ≤ 8, -12 ≤ k ≤ 12, -18 ≤ l ≤ 20
  Reflection collected, unique (Rint)	17 820, 9 694 (0.061 9)	7 235, 4 178 (0.031 6)
  Dc/(g·cm-3)	1.551	1.623
  μ/mm-1	0.768	0.876
  Data, restraint, parameter	9 694, 0, 804	4 178, 0, 340
  Goodness-of-fit on F2	1.039	1.060
  Final R indices [I≥2σ(I)]R1, wR2	0.074 3, 0.153 2	0.043 8, 0.081 8
  R indices (all data)R1, wR2	0.134 7, 0.196 3	0.061 6, 0.091 5
  Largest diff. peak and hole/(e·nm-3)	1 173 and -461	426 and -560

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

  1
  Ni(1)-O(1)	0.207 9(3)	Ni(1)-O(2)A	0.207 O(4)	Ni(1)-N(1)	0.212 2(4)
  Ni(1)-N(2)	0.207 9(5)	Ni(1)-N(3)	0.207 3(5)	Ni(1)-N(4)	0.211 8(5)
  Ni(2)-O(6)	0.204 9(4)	Ni(2)-O(7)	0.221 2(4)	Ni(2)-O(8)	0.211 7(4)
  Ni(2)-O(13)	0.202 8(4)	Ni(2)-N(5)	0.206 9(5)	Ni(2)-N(6)	0.205 9(5)
  O(2)A-Ni(1)-N(3)	98.3O(17)	O(2)A-Ni(1)-N(2)	88.22(18)	N(3)-Ni(1)-N(2)	170.67(18)
  O(2)A-Ni(1)-O(1)	88.08(14)	N(3)-Ni(1)-O(1)	96.01(15)	N(2)-Ni(1)-O(1)	90.84(16)
  O(2)A-Ni(1)-N(4)	174.09(17)	N(3)-Ni(1)-N(4)	78.83(19)	N(2)-Ni(1)-N(4)	94.05(19)
  O(1)-Ni(1)-N(4)	97.32(16)	O(2)A-Ni(1)-N(1)	87.61(16)	N(3)-Ni(1)-N(1)	94.15(19)
  N(2)-Ni(1)-N(1)	79.39(19)	O(1)-Ni(1)-N(1)	169.44(18)	N(4)-Ni(1)-N(1)	87.46(17)
  O(13)-Ni(2)-O(6)	91.43(18)	O(13)-Ni(2)-N(6)	103.13(18)	O(6)-Ni(2)-N(6)	95.08(19)
  O(13)-Ni(2)-N(5)	91.4O(19)	O(6)-Ni(2)-N(5)	174.41(19)	N(6)-Ni(2)-N(5)	79.58(19)
  O(13)-Ni(2)-O(8)	156.13(17)	O(6)-Ni(2)-O(8)	83.04(17)	N(6)-Ni(2)-O(8)	100.49(18)
  N(5)-Ni(2)-O(8)	96.23(18)	O(13)-Ni(2)-O(7)	95.71(17)	O(6)-Ni(2)-O(7)	89.44(17)
  N(6)-Ni(2)-O(7)	160.49(19)	N(5)-Ni(2)-O(7)	95.08(18)	O(8)-Ni(2)-O(7)	61.17(16)
  2
  Mn(1)-O(1)	0.210 2(2)	Mn(1)-O(5)A	0.214 6(2)	Mn(1)-O(7)	0.213 2(2)
  Mn(1)-N(1)A	0.226 7(3)	Mn(1)-N(2)	0.230 1(3)	Mn(1)-N(3)	0.232 3(3)
  Mn(1)-O(2)	0.220 2(2)	Mn(1)-O(2)B	0.220 2(2)	Mn(1)-O(4)A	0.213 4(2)
  Mn(1)-O(4)C	0.213 4(2)	Mn(1)-O(8)	0.223 1(3)	Mn(1)-O(8)B	0.223 1(3)
  O(1)-Mn(1)-O(7)	99.47(10)	O(1)-Mn(1)-O(5)A	90.87(10)	O(7)-Mn(1)-O(5)A	163.79(9)
  O(1)-Mn(1)-N(1)A	103.66(9)	O(7)-Mn(1)-N(1)A	91.28(9)	O(5)A-Mn(1)-N(1)A	74.06(9)
  O(1)-Mn(1)-N(2)	86.36(10)	O(7)-Mn(1)-N(2)	93.64(10)	O(5)A-Mn(1)-N(2)	99.48(10)
  N(1)A-Mn(1)-N(2)	167.97(11)	O(1)-Mn(1)-N(3)	156.17(10)	O(7)-Mn(1)-N(3)	88.7O(10)
  O(5)A-Mn(1)-N(3)	86.72(10)	N(1)A-Mn(1)-N(3)	98.46(10)	N(2)-Mn(1)-N(3)	70.71(10)
  O(4)C-Mn(2)-O(2)	87.09(9)	O(4)A-Mn(2)-O(2)	92.91(9)	O(4)C-Mn(1)-O(8)B	93.19(9)
  O(4)A-Mn(1)-O(8)B	86.81(9)	O(2)-Mn(1)-O(8)B	89.65(9)	O(2)-Mn(1)-O(8)	90.35(9)
  Symmetry codes: A:-x+1, -y, -z+1 for 1; A: x, y+1, z; B: -x, -y+1, -z; C: -x, -y, -z for 2.

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  Table 3.  Hydrogen bond parameters of compound 1

  D-H…A	d(D-H)/nm	d(H…A)/nm	d(D…A)/nm	∠DHA/(°)
  O(4)-H(4)…O(9)A	0.082	0.168	0.248 2	163.0
  O(12)-H(12)…O(8)B	0.082	0.180	0.254 7	151.1
  O(13)-H(1W)…O(9)C	0.085	0.175	0.259 7	179.8
  O(13)-H(2W)…O(5)	0.085	0.177	0.262 2	179.7
  O(14)-H(3W)…O(3)D	0.085	0.195	0.280 5	179.3
  Symmetry codes: A:-x-1, y-1, z; B: -x+1, -y+1, -z; C: x-1, y, z; D: x+1, y+1, z.

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  Table 4.  Hydrogen bond parameters of compound 2

  D-H…A	d(D-H)/nm	d(H…A)/nm	d(D…A)/nm	∠DHA/(°)
  O(7)-H(1W)…O(6)A	0.086	0.198	0.276 4	151.5
  O(7)-H(2W)…O(9)B	0.085	0.184	0.268 8	179.2
  O(8)-H(3W)…O(3)C	0.090	0.209	0.286 5	143.5
  Symmetry codes: A: x-1, y+1, z; B: x-1, y, z; C: x+1, y+1, z.

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