English

• 0.   Introduction

  In coordination chemistry, there are usually cis/trans-configuration isomers in the octahedral complexes, and the cis/trans-complexes often show significantly different structures and properties^[1]. This interesting phenomenon has also been observed in metal-organic frameworks (MOFs)^[2-4]. As a new generation of porous materials, MOFs have been widely applied in various fields such as gas separation, catalysis, sensors, and proton conductivity^[5-9]. Over the past two decades, our group has paid more attention to the substituted 4, 4′-biphenyldicarboxylic acids for constructing MOFs because the judicious selection of substituted groups on the biphenyl ring can finely modulate the topological structures and performances of the resulting MOFs^[10-22]. Among them, 2, 2′-dimethyl-4, 4′-biphenyldicarboxylic acid (H₂L) is one of the most notable ligands. Up to now, we and other groups have reported many novel topological MOFs based on the H₂L ligand^[20-40]. For instance, in 2015 by self-assembling H₂L with the unique 8-connected [Zr₆O₄(OH)₈(H₂O)₄] clusters via a sequential linker installation strategy, Prof. Zhou and coworkers successfully constructed a novel Zr-MOF: [Zr₆O₄(OH)₈(L)₄(H₂O)₄] (PCN-700) with a 3D bcu topological net^[25]. In 2022, by employing H₂L to coordinate with UO₂²⁺ ion, Prof. Farha et al. reported a U-based MOF: (H₃O)_0.9K_0.1[UO₂(L)_1.5] (NU-1303-6) with a six-fold interpenetrated 3D srs topological network^[37]. In 2021, by using H₂L to bind with a cis-[InO₄(μ₂-OH)₂] octahedron, a chiral 3D MOF, [In(μ₂-OH)(L)]·3H₂O·2DMA (DMA=N, N-dimethylacetamide) exhibiting an unprecedented 4-connected umy topology was reported by us^[20]. In 2024, by adopting H₂L to link a rare tetranuclear [In₄(μ₂-OH)₃]⁹⁺ cluster, we successfully constructed a novel trinodal 3, 3, 4-connected 3D MOF: [In₈(μ₂-OH)₆(μ₂-H₂O)₃(L)₆Cl₆]·5DMF·4H₂O (DMF=N, N-dimethylformamide) to show a reversible NH₃ uptake under mild conditions (the regenerated temperature is only 60 ℃)^[22]. As a continuation of our research on the H₂L ligand, herein we report the syntheses of two new MOFs, trans-[Co(L)(μ₂-H₂O)(H₂O)₂]·2H₂O (1) and cis-[Mn(L)(Bipy)] (2) (Bipy=4, 4′-bipyridine). Notably, the trans-[CoO₆] octahedron in 1 induces a 2D sql topological network, while the cis-[MnO₄N₂] octahedron in 2 induces a 3D fsc topological framework. Their thermal stabilities and Hirshfeld surface analyses were also studied.

  1.   Experimental

  1.1   Chemicals and general methods

  Ligand H₂L was prepared according to the reported method^{[20, 25]}. All the other chemicals and solvents used were of analytical grade and used without further purification. Elemental analysis was performed by a Thermo Finnigan Flash 1112A elemental analyzer. IR spectrum (4 000-400 cm^-1) was recorded on a Nicolet 380 FTIR instrument (KBr discs). Thermogravimetric analysis (TGA) was carried out on a NETZSCH STA 449C thermal analyzer under N₂ atmosphere at a scan rate of 10 ℃·min^-1. Powder X-ray diffraction (PXRD) data were collected on a Bruker D8 ADVANCE diffractometer using Cu Kα radiation (λ=0.154 06 nm) at 40 kV and 40 mA in a range of 5°-50°.

  1.2   Syntheses of MOFs 1 and 2

  A mixture of Co(NO₃)₂·6H₂O (0.011 6 g, 0.04 mmol), H₂L (0.010 8 g, 0.04 mmol), DMF (0.25 mL), and H₂O (0.25 mL) was heated in a 25 mL stainless-steel reactor lined with Teflon at 100 ℃ for 48 h. After cooling down to room temperature, the red crystals of 1 were obtained in a yield of 73.7% (0.012 3 g) based on H₂L. FTIR (KBr disc, cm^-1): 3 631(w), 3 384(m), 2 921(m), 1 576(s), 1 530(s), 1 409(vs), 1 372(s), 772(s). Anal. Calcd. for C₁₆H₂₂CoO₉(%): C, 46.05; H, 5.31. Found(%): C, 46.21; H, 5.43.

  A mixture of MnCl₂·4H₂O (0.004 g, 0.02 mmol), Bipy (0.003 2 g, 0.02 mmol), H₂L (0.005 4 g, 0.02 mmol), DMF (0.1 mL) and H₂O (1 mL) was heated in a 25 mL stainless-steel reactor lined with Teflon at 120 ℃ for 48 h. After cooling down to room temperature, the yellow crystals of 2 were obtained in a yield of 75.1% (0.007 2 g) based on H₂L. FTIR (KBr disc, cm^-1): 3 074(w), 2 919(w), 2 854(w), 1 604(s), 1 581(s), 1 542(s), 1 402(vs), 813(s), 628(m). Anal. Calcd. for C₂₆H₂₀MnN₂O₄(%): C, 65.14; H, 4.21; N, 5.84. Found(%): C, 65.32; H, 4.33; N, 5.71.

  1.3   Crystal structure determination

  Suitable single crystals of 1 and 2 were chosen for lattice parameter determination and collection of intensity data on a Rigaku XtaLAB Synergy-R DW diffractometer with a graphite-monochromated Cu Kα (λ=0.154 184 nm) radiation using a ω-2θ scan mode at 298 K. The crystal structures were solved by direct methods with the SHELXT program in the Olex2 software^[41]. All non-hydrogen atoms were refined with anisotropic displacement parameters, and all hydrogen atoms were calculated and refined as riding modes except water molecules. The O5W of 1 was disordered over two positions and refined with an occupancy factor of 0.55(5) for O5W and 0.45(5) for O5WA. The atomic coordinates and anisotropic temperature factors were refined on F ² by the full-matrix least squares method using the SHELXL program^[42]. The crystallographic data of 1 and 2 are listed in Table 1. Selected bond lengths and bond angles are presented in Table 2.

  Table 1

  

  Table 1.  Crystallographic data of MOFs 1 and 2

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  Parameter	1	2
  Empirical formula	C16H22CoO9	C26H20MnN2O4
  Formula weight	417.26	479.38
  Crystal system	Triclinic	Monoclinic
  Space group	P1	C2/c
  a / nm	0.807 1(2)	1.397 5(3)
  b / nm	1.057 8(3)	1.846 4(4)
  c / nm	1.095 7(2)	0.911 4(2)
  α / (°)	85.666(2)
  β / (°)	88.563(2)	98.948(2)
  γ / (°)	83.255(2)
  V / nm3	0.926 2(1)	2.323 1(1)
  Z	2	4
  Dc / (g·cm-3)	1.496	1.371
  μ / mm-1	7.685	4.909
  F(000)	434.0	988.0
  Crystal size / mm	0.19×0.14×0.11	0.25×0.22×0.18
  θ range / (°)	4.047-66.041	3.998-67.953
  Reflection collected	9 334	15 045
  Independent reflection	3 216 (Rint=0.097 7)	2 117 (Rint=0.064 9)
  Reflection observed [I > 2σ(I)]	2 649	2 010
  Data, restraint, number of parameters	3 216, 1, 256	2 117, 0, 152
  Goodness-of-fit on F 2	1.016	1.093
  R1, wR2 [I > 2σ(I)]	0.056 8, 0.146 4	0.034 3, 0.093 8
  R1, wR2 (all data)	0.068 6, 0.153 0	0.035 7, 0.094 5
  (Δρ)max, (Δρ)min / (e·nm-3)	750, -590	340, -460

  Table 2

  

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

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  1
  Co1—O1W	0.205 9(2)	Co1…Co2v	0.403 6(2)	Co2—O4	0.203 5(2)
  Co1—O2	0.204 6(2)	Co2—O2Wii	0.222 6(2)	C1—O1	0.127 2(4)
  Co1—O2W	0.222 8(2)	Co2—O3W	0.207 2(2)
  O1W—Co1—O2Wi	93.91(10)	O2—Co1—O2Wi	93.02(9)	O4—Co2—O2Wii	92.84(9)
  O1W—Co1—O2W	86.09(10)	O2i—Co1—O2	180.00(12)	O4—Co2—O2Wiii	87.16(9)
  1
  O2—Co1—O1Wi	89.21(11)	O3Wiv—Co2—O2Wiii	93.46(9)	O4iv—Co2—O3W	89.31(11)
  O2—Co1—O2W	86.98(9)	O3W—Co2—O2Wiii	86.54(9)	O4iv—Co2—O4	180.00
  2
  Mn1—O1	0.216 3(2)	Mn1—O2ii	0.213 4(2)	Mn1—N1	0.229 3(2)
  Mn1…Mn1ii	0.4889(2)
  O1—Mn1—O1i	165.62(8)	O2ii—Mn1—O1	100.84(5)	N1—Mn1—N1i	89.02(8)
  O1—Mn1—N1	86.11(6)	O2iii—Mn1—N1	175.32(5)	O2ii—Mn1—N1	90.02(6)
  O1—Mn1—N1i	83.65(5)	O2ii—Mn1—O2iii	91.37(8)
  Symmetry codes: i 1-x, -y, 2-z; ii -x, 1-y, 1-z; iii x, 1+y, z-1; iv -x, 2-y, -z; v x, y-1, z+1 for 1; i 1-x, y, 1/2-z; ii 1-x, 1-y, 1-z; iii x, 1-y, z-1/2 for 2.

  2.   Results and discussion

  2.1   Crystal structure analysis

  The X-ray crystallographic study shows that 1 crystallizes in the triclinic P1 space group (Table 1). The asymmetric unit of 1 consists of two crystallographically distinct Co(Ⅱ) ions (the occupancy factors of Co1 and Co2 are 0.5), one L^2- ligand, three coordinated H₂O molecules (O1W, μ₂-O2W, and O3W), and two lattice H₂O molecules (O4W and O5W, Fig.S1, Supporting information). Both Co1 and Co2 ions display trans-[CoO₆] octahedral geometry where two carboxylate oxygen atoms (O2 and O2ⁱ for Co1, and O4 and O4^iv for Co2) from two different L^2- ligands occupy the axial positions, and four coordinated H₂O molecules (O1W, O1Wⁱ, μ₂-O2W, and μ₂-O2Wⁱ for Co1, and μ₂-O2Wⁱⁱ, μ₂-O2Wⁱⁱⁱ, O3W, and O3W^iv for Co2) are in the equatorial positions (Fig. 1a). Their configurations are further confirmed by the SHAPE software with the continuous symmetry measures (CSM) of Co1 and Co2 being calculated as 0.283 and 0.260, respectively^[43]. The bond distances of Co—O [0.203 5(2)-0.222 8(2) nm, Table 2] are comparable to the related Co-based MOFs^{[24, 44]}. Both Co1 and Co2 ions are bridged by a μ₂-O2W to form a 1D chain along the a-axis with a Co1…Co2^v distance of 0.403 6(2) nm (Table 2). These 1D chains are further connected by the L^2- ligands to generate a 2D layer (Fig. 1b). If the trans-[CoO₆] octahedron is regarded as a 4-connected node and the L^2- ligand as a line, the structure of 1 can be simplified as a 2D network with sql topology (Fig. 1c), which shows the same topological net as observed in a related Ni-MOF: [Ni(μ₂-H₂O)(L)(DMF)(H₂O)]·0.5H₂O^[21]. However, there are two obvious structural differences between 1 and the Ni-MOF: (1) 1 belongs to the triclinic P1 space group, whereas the Ni-MOF has the monoclinic P2₁/c space group. (2) Two trans-monocoordinated H₂O molecules exist in 1, while one monocoordinated H₂O and one DMF molecule are found in the Ni-MOF in a trans-configuration. Notably, in 1 there are ten kinds of strong intermolecular OW—H…O hydrogen bonds between the coordinated/lattice H₂O molecules and the uncoordinated/coordinated carboxylic O atoms or the lattice H₂O molecules, two types of C—H…π interactions and a kind of weak intermolecular C—H…O hydrogen bond (Fig.S2 and Table S1). All these interactions further interconnect the adjacent 2D layers to produce a 3D supramolecular network (Fig. 1d).

  Figure 1

  

  Figure 1.  (a) trans-[CoO₆] octahedron in MOF 1; (b) 2D layer consisting of trans-[CoO₆] octahedron and L^2- parallel to the ac plane; (c) 2D sql topological network; (d) 3D hydrogen-bonded supramolecular framework

  Symmetry codes: ⁱ 1-x, -y, 2-z; ⁱⁱ-x, 1-y, 1-z; ⁱⁱⁱ x, 1+y, z-1; ^iv-x, 2-y, -z; ^v 1-x, -y, 1-z; ^vi x, y-1, z+1; ^vii 1-x, 1-y, 2-z; ^viii x, y-1, z; ^ix -x, 1-y, -z; ^x -x, 2-y, -1-z; ^xi x, y, z-1

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  The crystal structure analysis reveals that 2 crystallizes in the monoclinic C2/c space group (Table 1). The asymmetric unit contains one Mn(Ⅱ) ion (the occupancy factor is 0.5), half of the L^2- ligand and half of the Bipy molecule (Fig.S3). The Mn1 ion adopts a cis-[MnO₄N₂] octahedral configuration where two carboxylate O atoms (O1 and O1ⁱ) from two different L^2- ligands occupy the axial positions, and the other two carboxylate O atoms (O2ⁱⁱ and O2ⁱⁱⁱ) and two N atoms (N1 and N1ⁱ) from two different Bipy molecules locate at a cis-position in the equatorial plane (Fig. 2a). The CSM value of Mn1 is 0.506^[43]. The bond distances of Mn—O [0.213 4(2)-0.216 3(2) nm] and Mn—N [0.229 3(2) nm] are in good agreement with the related Mn-based MOFs (Table 2)^[45-46]. Two adjacent Mn1 ions are bridged by two carboxylic groups with a bidentate syn-syn mode to form a 1D [Mn(CO₂)₂]_n chain along the c-axis with a Mn1…Mn1ⁱⁱ distance of 0.488 9(2) nm (Fig. 2b, Table 2). The 1D chains are further linked through the L^2- ligands to form a 2D layer parallel to the ac plane (Fig. 2b). Then the 2D layers are pillared by the Bipy molecules along the b-axis to produce a 3D network (Fig. 2c). If the cis-[MnO₄N₂] octahedron is regarded as a 6-connected node (Fig. 2d) and the L^2- ligand as a 4-connected node (Fig. 2e), the final structure of 2 is a binodal (4, 6)-connected fsc topological framework (Fig. 2f), which is similar to that found in a related 3D Co-MOF: cis-[Co(L)(Bipy)]^[24], a 3D Cu-MOF: [Cu₂(L′)(Bipy)₂]·DMA·3H₂O (H₄L′=2, 2′-disulfonyl-4, 4′-biphenyldicarboxylic acid)^[19] and a multinuclear Cd-MOF: [Cd₁₂(btc)₈(DMF)₁₄(H₂O)₂]·1.5DMF (H₃btc=1, 3, 5-benzenetricarboxylic acid)^[47]. Additionally, two kinds of weak C—H…O hydrogen bonds and two types of weak intermolecular C—H…π interactions are observed in 2 (Fig.S4 and Table S2).

  Figure 2

  

  Figure 2.  (a) cis-[MnO₄N₂] octahedron in MOF 2; (b) 2D layer consisting of Mn(Ⅱ) and L^2- parallel to the ac plane; (c) 2D layers pillared by the Bipy molecules to form a 3D network; (d) cis-[MnO₄N₂] octahedron as a 6-connected node; (e) L^2- as a 4-connected node; (f) binodal (4, 6)-connected fsc topological framework

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

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  2.2   Coordination modes of L^2-

  In MOFs built from the multicarboxylic acids, the ligands often exhibit diverse coordination modes. In 1 and 2, the two carboxylic groups of the H₂L ligand are deprotonated, and there are two types of different coordination modes (Scheme 1). The L^2- ligand in 1 behaves as a bis(unidentate) coordination mode (Scheme 1a), which is also found in our reported [Ni(μ₂-H₂O)(L)(DMF)(H₂O)]·0.5H₂O^[21]. In 2, each L^2- ligand can link four Mn(Ⅱ) ions in a bis(bridging bidentate) syn-syn mode (Scheme 1b), which is similar to that observed in [Mn(L″)(DMF)]_n (H₂L″=2, 2′-dimethoxy-4, 4′-biphenyldicarboxylic acid)^[12]. This obvious difference in the coordination modes of the L^2- ligand can not only induce a trans-[CoO₆] octahedron in 1 and a cis-[MnO₄N₂] octahedron in 2, but also make an important influence on the dihedral angles between the biphenyl rings as well as between the carboxylate group and the phenyl ring. These dihedral angles in 1 and 2 are comparable to the related mononuclear MOFs^{[21, 24, 37]}, as summarized in Table 3.

  Scheme 1

  

  Scheme 1.  Coordination modes of the L^2- ligands in MOFs 1 (a) and 2 (b)

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  Table 3

  

  Table 3.  Comparison of the dihedral angles in the mononuclear MOFs based on H₂L

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  MOF	Coordination mode	SBU	Dihedral angles / (°)		Ref.
  			Ph/Ph rings	Ph/CO2-
  1	bis(unidentate)	trans-[CoO6]	84.72(10)	17.50(19), 14.04(18)	This work
  2	bis(bridging bidentate): syn-syn	cis-[MnO4N2]	66.18(6)	18.66(11)	This work
  [Co(L)(Bipy)]	bis(bridging bidentate): syn-syn	cis-[CoO4N2]	66.07(16)	18.56(21)	[24]
  [Zn(L)(Im)]a	bis(bridging bidentate): syn-anti	[ZnO2N2]	71.05(14)	15.14(28)	[24]
  [Ni(H2O)2(L)(DMF)]·0.5H2O	bis(unidentate)	[NiO6]	83.45(18)	11.30(22)	[21]
  NU-1303-3b	bis(chelating bidentate)	[UO2(CO2)3]	79.15(16)	14.76(29), 6.91(25)	[37]
  			83.96(11)	11.67(18), 3.82(22)
  			76.78(98)	7.63(17), 3.78(18)
  			81.97(12)	10.58(21), 2.75(27)
  			61.53(94)	12.69(14), 8.19(34)
  			86.87(15)	14.78(27), 7.97(22)
  			71.92(20)	14.64(33), 11.20(32)
  			68.36(99)	12.84(65), 4.29(34)
  			89.01(16)	8.39(11), 5.67(17)
  			76.37(46)	6.29(83)
  NU-1303-6b	bis(chelating bidentate)	[UO2(CO2)3]	89.56(10)	19.68(13), 7.43(16)	[37]
  			88.80(88)	8.68(18)
  a Im=imidazole; b NU=Northwestern University.

  2.3   IR spectra, PXRD, and TGA

  In the IR spectra of 1 and 2, the asymmetric or symmetric stretching vibrations of the carboxylate groups were observed around 1 576 or 1 409 cm^-1 for 1 and 1 542 or 1 402 cm^-1 for 2, respectively (Fig.S5). The disappearance of any strong absorption bands around 1 720 cm^-1 proves the complete deprotonation of the carboxyl group of the H₂L ligand during the coordination. The bands at 3 631 and 3 384 cm^-1 are assigned to O—H stretching vibrations of coordinated/lattice H₂O molecules in 1, respectively. The bands at 1 604 and 1 581 cm^-1 can be attributed to C=N stretching vibrations of the pyridyl ring in 2^[1]. The typical stretching vibration peaks of methyl groups were 2 921 cm^-1 for 1 and 2 919 cm^-1 for 2, respectively. These features are in good consistent with the results of their single-crystal X-ray diffraction.

  The PXRD patterns of 1 and 2 and their simulated ones are shown in Fig.S6. The experimental patterns matched well with the simulated ones from single-crystal X-ray diffraction data, verifying the high phase purity of the bulk products.

  TGA curves of 1 and 2 are indicated in Fig. 3. For 1, the weight loss of 21.7% between 25 and 390 ℃ can be assigned to the removal of three coordinated H₂O molecules and two lattice H₂O molecules (Calcd. 21.6%). The framework collapse occurred above 390 ℃. The final residue of 18.2% corresponds well to the theoretical value of CoO (18.0%, Fig. 3a). Due to no solvent molecules in 2, the decomposition of the framework was observed above 370 ℃. The final residue of 14.4% in 2 can be attributed to MnO (Calcd. 14.8%, Fig. 3b). These results indicate that both 1 and 2 have a good thermal stability of the framework.

  Figure 3

  

  Figure 3.  TGA curves of 1 (a) and 2 (b)

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  2.4   Hirshfeld surface analyses

  As a powerful visualization tool, Hirshfeld surface analysis enables a direct observation of various weak intermolecular interactions such as hydrogen bonds and C—H…π within a crystal structure. Therefore, 3D Hirshfeld surface analysis has been performed to understand the intermolecular interactions in 1 and 2, and the corresponding 2D fingerprint plots quantify each type of intermolecular interaction^[48]. Fig. 4 shows the 3D Hirshfeld surfaces of 1 and 2 mapped with d_norm, respectively. The surface is exhibited with a red-white-blue color: the red spots represent close contacts such as O—H…O interactions, while the white and blue regions stand for weak contacts, like C—H…O and C—H…π interactions in 1 and 2^[49]. For 1, there are twelve intense red spots near five water molecules, four carboxyl oxygen atoms, and two Co(Ⅱ) ions. For 2, three strong red dots are observed near the carboxyl oxygen atoms, the pyridine ring, and the Mn(Ⅱ) ion.

  Figure 4

  

  Figure 4.  Three-dimensional Hirshfeld surfaces of 1 and 2 mapped with d_norm along the a-axis

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  Fig. 5 presents the 2D fingerprint plots of 1 and 2, highlighting the contributions of main intermolecular interactions to the Hirshfeld surface. The overall (100%) 2D fingerprint plot for 1 is displayed in Fig. 5a. The maximum contribution is from H…H contacts (39.7%), which appears in the middle of the fingerprint plot (Fig. 5b). The next is O…H/H…O contacts (30.7%) with two sharp symmetric peaks in the plot (Fig. 5c). They have the most significant contribution to the total Hirshfeld surface (70.4%). Additionally, the C…H/H…C contacts (18.0%, Fig.S7a) and Co…O short contacts (7.4%, Fig.S7b) also contribute to the Hirshfeld surface to some extent. The overall (100%) 2D fingerprint plot for 2 is shown in Fig. 5d. The maximum contribution is also from H…H contacts (39.4%) in the middle of the fingerprint plot with one sharp peak at the forefront (Fig. 5e). The next is C…H/H…C contacts (29.8%) in the edges of the fingerprint plot (Fig. 5f). They have the most significant contribution to the total Hirshfeld surface (69.2%). In addition, the O…H/H…O contacts (10.1%, Fig.S8a), Mn…O (7.0%, Fig.S8b), and C…C (6.2%, Fig.S8c) short contacts also make a contribution to the Hirshfeld surface to some extent. The contribution of the weak intermolecular interactions in 1 and 2 to the Hirshfeld surface area is summarized in Table S3. The abundant hydrogen bonding interactions (88.4%) in 1 and (79.3%) in 2 may contribute to their relatively high thermal stabilities of the frameworks, which have been confirmed by the TGA results.

  Figure 5

  

  Figure 5.  Two-dimensional fingerprint plots for 1: (a) all, (b) H…H and (c) O…H/H…O contacts, and 2: (d) all, (e) H…H and (f) C…H/H…C contacts

  Unit: nm.

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  3.   Conclusions

  Two novel MOFs, 1 and 2, based on 2, 2′-dimethyl-4, 4′-biphenyldicarboxylic acid have been synthesized and structurally characterized. X-ray crystallographic analyses reveal that the trans-[CoO₆] octahedral configuration induces a 2D sql topological network in 1, while the cis-[MnO₄N₂] octahedral configuration produces a 3D fsc topological framework in 2. Both 1 and 2 exhibit good thermal stability of the framework.

  
  Supporting information is available at http://www.wjhxxb.cn
  
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  Figure 1  (a) trans-[CoO₆] octahedron in MOF 1; (b) 2D layer consisting of trans-[CoO₆] octahedron and L^2- parallel to the ac plane; (c) 2D sql topological network; (d) 3D hydrogen-bonded supramolecular framework

  Symmetry codes: ⁱ 1-x, -y, 2-z; ⁱⁱ-x, 1-y, 1-z; ⁱⁱⁱ x, 1+y, z-1; ^iv-x, 2-y, -z; ^v 1-x, -y, 1-z; ^vi x, y-1, z+1; ^vii 1-x, 1-y, 2-z; ^viii x, y-1, z; ^ix -x, 1-y, -z; ^x -x, 2-y, -1-z; ^xi x, y, z-1

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  Figure 2  (a) cis-[MnO₄N₂] octahedron in MOF 2; (b) 2D layer consisting of Mn(Ⅱ) and L^2- parallel to the ac plane; (c) 2D layers pillared by the Bipy molecules to form a 3D network; (d) cis-[MnO₄N₂] octahedron as a 6-connected node; (e) L^2- as a 4-connected node; (f) binodal (4, 6)-connected fsc topological framework

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

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  Scheme 1  Coordination modes of the L^2- ligands in MOFs 1 (a) and 2 (b)

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  Figure 3  TGA curves of 1 (a) and 2 (b)

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  Figure 4  Three-dimensional Hirshfeld surfaces of 1 and 2 mapped with d_norm along the a-axis

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  Figure 5  Two-dimensional fingerprint plots for 1: (a) all, (b) H…H and (c) O…H/H…O contacts, and 2: (d) all, (e) H…H and (f) C…H/H…C contacts

  Unit: nm.

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  Table 1.  Crystallographic data of MOFs 1 and 2

  Parameter	1	2
  Empirical formula	C16H22CoO9	C26H20MnN2O4
  Formula weight	417.26	479.38
  Crystal system	Triclinic	Monoclinic
  Space group	P1	C2/c
  a / nm	0.807 1(2)	1.397 5(3)
  b / nm	1.057 8(3)	1.846 4(4)
  c / nm	1.095 7(2)	0.911 4(2)
  α / (°)	85.666(2)
  β / (°)	88.563(2)	98.948(2)
  γ / (°)	83.255(2)
  V / nm3	0.926 2(1)	2.323 1(1)
  Z	2	4
  Dc / (g·cm-3)	1.496	1.371
  μ / mm-1	7.685	4.909
  F(000)	434.0	988.0
  Crystal size / mm	0.19×0.14×0.11	0.25×0.22×0.18
  θ range / (°)	4.047-66.041	3.998-67.953
  Reflection collected	9 334	15 045
  Independent reflection	3 216 (Rint=0.097 7)	2 117 (Rint=0.064 9)
  Reflection observed [I > 2σ(I)]	2 649	2 010
  Data, restraint, number of parameters	3 216, 1, 256	2 117, 0, 152
  Goodness-of-fit on F 2	1.016	1.093
  R1, wR2 [I > 2σ(I)]	0.056 8, 0.146 4	0.034 3, 0.093 8
  R1, wR2 (all data)	0.068 6, 0.153 0	0.035 7, 0.094 5
  (Δρ)max, (Δρ)min / (e·nm-3)	750, -590	340, -460

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

  1
  Co1—O1W	0.205 9(2)	Co1…Co2v	0.403 6(2)	Co2—O4	0.203 5(2)
  Co1—O2	0.204 6(2)	Co2—O2Wii	0.222 6(2)	C1—O1	0.127 2(4)
  Co1—O2W	0.222 8(2)	Co2—O3W	0.207 2(2)
  O1W—Co1—O2Wi	93.91(10)	O2—Co1—O2Wi	93.02(9)	O4—Co2—O2Wii	92.84(9)
  O1W—Co1—O2W	86.09(10)	O2i—Co1—O2	180.00(12)	O4—Co2—O2Wiii	87.16(9)
  1
  O2—Co1—O1Wi	89.21(11)	O3Wiv—Co2—O2Wiii	93.46(9)	O4iv—Co2—O3W	89.31(11)
  O2—Co1—O2W	86.98(9)	O3W—Co2—O2Wiii	86.54(9)	O4iv—Co2—O4	180.00
  2
  Mn1—O1	0.216 3(2)	Mn1—O2ii	0.213 4(2)	Mn1—N1	0.229 3(2)
  Mn1…Mn1ii	0.4889(2)
  O1—Mn1—O1i	165.62(8)	O2ii—Mn1—O1	100.84(5)	N1—Mn1—N1i	89.02(8)
  O1—Mn1—N1	86.11(6)	O2iii—Mn1—N1	175.32(5)	O2ii—Mn1—N1	90.02(6)
  O1—Mn1—N1i	83.65(5)	O2ii—Mn1—O2iii	91.37(8)
  Symmetry codes: i 1-x, -y, 2-z; ii -x, 1-y, 1-z; iii x, 1+y, z-1; iv -x, 2-y, -z; v x, y-1, z+1 for 1; i 1-x, y, 1/2-z; ii 1-x, 1-y, 1-z; iii x, 1-y, z-1/2 for 2.

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  Table 3.  Comparison of the dihedral angles in the mononuclear MOFs based on H₂L

  MOF	Coordination mode	SBU	Dihedral angles / (°)		Ref.
  			Ph/Ph rings	Ph/CO2-
  1	bis(unidentate)	trans-[CoO6]	84.72(10)	17.50(19), 14.04(18)	This work
  2	bis(bridging bidentate): syn-syn	cis-[MnO4N2]	66.18(6)	18.66(11)	This work
  [Co(L)(Bipy)]	bis(bridging bidentate): syn-syn	cis-[CoO4N2]	66.07(16)	18.56(21)	[24]
  [Zn(L)(Im)]a	bis(bridging bidentate): syn-anti	[ZnO2N2]	71.05(14)	15.14(28)	[24]
  [Ni(H2O)2(L)(DMF)]·0.5H2O	bis(unidentate)	[NiO6]	83.45(18)	11.30(22)	[21]
  NU-1303-3b	bis(chelating bidentate)	[UO2(CO2)3]	79.15(16)	14.76(29), 6.91(25)	[37]
  			83.96(11)	11.67(18), 3.82(22)
  			76.78(98)	7.63(17), 3.78(18)
  			81.97(12)	10.58(21), 2.75(27)
  			61.53(94)	12.69(14), 8.19(34)
  			86.87(15)	14.78(27), 7.97(22)
  			71.92(20)	14.64(33), 11.20(32)
  			68.36(99)	12.84(65), 4.29(34)
  			89.01(16)	8.39(11), 5.67(17)
  			76.37(46)	6.29(83)
  NU-1303-6b	bis(chelating bidentate)	[UO2(CO2)3]	89.56(10)	19.68(13), 7.43(16)	[37]
  			88.80(88)	8.68(18)
  a Im=imidazole; b NU=Northwestern University.

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