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Six Co(II) coordination polymers based on two isomeric semi-rigid ether-linked aromatic tetracarboxylate acid: syntheses, structural comparison, and magnetic properties Zheng Zhu, Cun-gang Xu, Mei Wang, Xia Zhang, Hu Wang, Qing-dan Luo, Shuang-yu Bi, and Yu-hua Fan Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01070 • Publication Date (Web): 07 Sep 2017 Downloaded from http://pubs.acs.org on September 9, 2017

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Crystal Growth & Design

Six Co(II) coordination polymers based on two isomeric semi-rigid ether-linked aromatic tetracarboxylate acid: syntheses, structural comparison, and magnetic properties Zheng Zhu †, Cun-gang Xu†, Mei Wang†, Xia Zhang†, Hu Wang†, Qing-dan Luo†, Shuang-yu Bi‡* and Yu-hua Fan†* †

Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong 266100, P. R. China

‡

Max Planck Institute for Terrestrial Microbiology LOEWE Center for Synthetic Microbiology (SYNMIKRO), Marburg 35043, Germany

Abstract Six Co(II) coordination polymers including {[Co5(L1)2(bibp)2]·bibp}n (1), {[Co2(L1)(bibp)2·2H2O}n (2), {[Co2(L1)(bimmb)2]·DMF}n (3), [Co2(L1)(bimb)·3H2O]n (4), [Co(L2)(bibp)(H2O)]n (5), and [Co2(L2)(bimb)]n (6) (H4L1/H4L2= 5,5′-(1,4/1,3-phenylenebis(methoxy))diisophthalic acid, bibp= 4,4'-bis(imidazolyl)biphenyl, bimmb= 1,4-bis(imidazol-1-ylmethyl)benzene, and bimb= 1,4-bis(lmidazol)butane) were synthesized under solvothermal conditions and structurally characterized. Complex 1 and 2 are co-crystallized in a one-pot reaction with significant differences in the structures. Complex 1 exhibits a three-dimensional (3D) metal-organic framework composed of an interesting pentanuclear [Co5(µ3-O)2N4(COO)8]2- cluster. Complex 2 shows a 3D four-fold interpenetrated bbf topological framework. Complex 3 has a 2D zigzag network, three of which further interpenetrate each other, reconstructing a 2D + 2D → 2D network with new-topology. Complex 4 shows a novel topological 3D framework with a [Co2(COO)3(H2O)3N2] cluster. Complex 5 exhibits a new topological framework with the point symbol [44. 62] [4]2. And complex 6 displays [Co2(COO)2(bimb)] binuclear SBUs based on sq1 framework with the point symbol [44. 62]. Variable-temperature magnetic studies indicate that complexes 1, 4, and 6 exhibit antiferromagnetic couplings between carboxyl-bridging Co(II) ions.

Introduction As functional materials for different applications, such as in gas adsorption

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magnetic [3- 5], catalysis [6, 7], optics [8, 9], and molecular recognition [10, 11], the study of coordination polymers (CPs) or metal-organic frameworks (MOFs) have drawn considerable attentions since the strategies were launched in the 1990s. How to rational design and synthesis the new coordination polymers with certain characters is still a challenge for crystal engineers. This is because, the crystallization is a complicated process and depending on many experimental factors, such as the original structure of the ligands, the ratios of the raw materials, synthesis temperature, solvent, and so on. [12- 15] To choose the right liangds with certain function and functional metal ions could be the most rational way to obtain predictable frameworks and properties. [16-19] The semi-rigid tetracarboxylate ligands, such as methylene-linked or ether-linked aromatic tetracarboxylate ligands [20- 23], have attracted much attention in constructing CPs since the freely rotating methylene or ether bounds in the ligand can adopt various conformations via bending, stretching, or twisting depending on the coordination environment of the metal center and the competition and cooperation of different coligands. Magnetic CPs constructed with the first row transition metal ions and organic homo-/heterobridges have currently been a focus of research due to their variant oxidation states and attractive magnetic properties. [24- 27] As molecular spin valves and transistors, magnetic CPs has complicated magnetostructrual correlation. It is undoubtedly that both the center metal ions and the organic ligands in CPs are highly important for the structural controls and magnetic responses. [28] Cobalt(II) based magnetic CPs are fascinating to study which is because the cobalt(II) ions can adopt various stable coordination polyhedral and exhibiting SBUstantial spin-orbit coupling contributions to the magnetic moments, and further have make an influence on the overall magnetic behavior. [29- 32] In these spirits, we chose two semi-rigid ether-linked aromatic tetracarboxylate ligands, and three different N-donor coligands (a rigid one, a semi-rigid one and a flexible one), and successfully synthesized six Co-based CPs with different features, {[Co5(L1)2(bibp)2]·bibp}n (1), {[Co2(L1)(bibp)2·2H2O}n (2), {[Co2(L1)(bimmb)2]·DMF}n (3), [Co2(L1)(bimb)·3H2O]n (4), [Co(L2)(bibp)(H2O)]n (5), and [Co2(L2)(bimb)]n (6) (H4L1/H4L2 = 5,5′-(1,4/1,3-phenylenebis(methoxy))diisophthalic acid, bibp = 4,4'-bis(imidazolyl)biphenyl, bimmb = 1,4-bis(imidazol-1-ylmethyl)benzene, and bimb = 1, 4- bis(lmidazol)butane). The effects of the conformations of H4L ligands and coligands, and the coordination geometry of Co ions on the assembly of frameworks are unraveled in detail. Furthermore, the thermal stability and magnetic properties of complexes 1, 4, 6 are also investigated. And the magnetostructural relationships are also discussed and compared in detail.

Experimental section Materials and physical measurements All reagents and solvents were purchased from Jinan Henghua Sci. Tec. Co. Ltd., and


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used without further purification. Infrared spectra were recorded on the Nicolet 170SX spectrometer in the 4000-400 cm-1 region by using KBr pellets. Elemental analysis of C, H, N were performed in a model 2400 PerkinElmer analyzer. Thermogravimetric (TG) analyses were measured on a Perkin-Elmer TGA-7 thermogravimetric analyzer under air conditions from room temperature to 800 ℃ with a heating rate of 10 ℃ min-1. The X-ray powder diffractions (XRPD) were collected on an Enraf-Nonius CAD-4 X-ray single-crystal diffractometer with Cu-Kα radiation. Topological analysis were performed and confirmed by the Topos program and the Systre software. [33- 35] The variable temperature magnetic susceptibilities were measured on polycrystalline samples with a Quantum Design MPMS SQUID susceptometer. We have reported the syntheses routes and the structural descriptions of complexes 5 and 6 recently. [23] So, there is no involvement about these two parts in this report. Synthesis of {[Co5(L1)2(bibp)2]·bibp}n (1) and {[Co2(L1)(bibp)2·2H2O}n (2) A mixture of Co(NO3)2·6H2O (0.064 g, 0.2 mmol), bibp (0.046 g, 0.1 mmol), H4L1 (0.045 g, 0.1 mmol), H2O (4.5 mL), DMF (4.5 mL) were stirred for 0.5 hour in air. And then the solution was transformed into the Teflon-lined stainless steel vessel (15 mL), sealed, and heated to 160 ℃ for 3 days. SBUsequently, the vessel was cooled to the room temperature at the degree of 5 ℃ h-1. Purple flakey crystals (1) (yield 45.46%) and violet bluck crystals (2) (yield 38.36%) were collected (based on H4L). The two crystals were manually separated. Anal. Calcd for C102H72N12O22Co5 (1) and C60H46N8O12Co2 (2): C, 57.99; H, 3.44; N, 7.90% for 1; C, 60.61; H, 3.90; N, 9.42% for 2. Found: C, 57.94; H, 3.41; N, 7.95; O, 16.66% for 1; C, 60.45; H, 4.01; N, 9.23; O, 16.33% for 2. IR (KBr disk, cm−1): 3421.46 (w), 3122.59 (w), 1652.50 (m), 1636.50 (s), 1609.08 (m), 1580.46 (s), 1515.89 (s), 1455.94 (m), 1373.61 (s), 1262.14 (w), 1058.93 (m), 821.92 (m), 777.44 (m), 659.36 (w), 517.37 (w) for 1; 3408.22 (m), 3121.84 (w), 1651.00 (w), 1620.22 (m), 1561.42 (s), 1519.21 (s), 1452.86 (m), 1396.35 (s), 1366.85 (s), 1308.36 (m), 1256.84 (m), 1056.13 (m), 820.95 (m), 777.63 (m), 730.55 (m), 654.59 (w) for 2. Synthesis of {[Co2(L1)(bimmb)2]·DMF}n (3) A mixture of Co(NO3)2·6H2O (0.064 g, 0.2 mmol), bimmb (0.024 g, 0.1 mmol), H4L1 (0.046 g, 0.1 mmol), H2O (6.0 mL), DMF (3.0 mL) were stirred for 0.5 hour in air. And then the solution was transformed into the Teflon-lined stainless steel vessel (15 mL), sealed, and heated to 130 ℃ for 3 days. SBUsequently, the vessel was cooled to the room temperature at the degree of 5 ℃ h-1. Red flake crystals were collected in 85.41% yield (based on H4L). Anal. Calcd for C55H49Co2N9O11: C, 60.61; H, 3.90; N, 9.42%. Found: C, 60.23; H, 4.21; N, 9.33; O, 16.55%. IR (KBr disk, cm−1): 3411.72 (w), 3141.38 (w), 1666.36 (m), 1653.30 (w), 1624.75 (m), 1576.95 (s), 1558.99 (s), 1455.87 (w), 1397.95 (m), 1370.01 (s), 1318.22 (m), 1254.34 (m), 1107.63 (w), 1086.90 (m), 1039.06 (m), 803.17 (m), 780.30 (m), 730.11 (m), 656.38 (w). Synthesis of [Co2(L1)(bimb)·3H2O]n (4) A mixture of Co(NO3)2·6H2O (0.064 g, 0.2 mmol), bimb (0.019 g, 0.1 mmol), H4L1 (0.046 g, 0.1 mmol), H2O (4.5 mL), DMF (4.5



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mL) were stirred for 0.5 hour in air. And then the solution was transformed into the Teflon-lined stainless steel vessel (15 mL), sealed, and heated to 130 ℃ for 3 days. SBUsequently, the vessel was cooled to the room temperature at the degree of 5 ℃ h-1. Purple block crystals were collected in 82.36% yield (based on H4L). Anal. Calcd for C17H17CoN2O6.5: C, 49.53; H, 4.16; N, 6.80%. Found: C, 49.40; H, 4.36, N, 6.64; O, 25.38%. IR (KBr disk, cm-1): 3364.78 (w), 3115.26 (m), 1637.12 (m), 1585.71 (s), 1548.83 (s), 1455.59 (m), 1378.73 (s), 1319.00 (w), 1269.05 (m), 1234.27 (w), 1098.99 (m), 1039.80 (m), 851.22 (w), 779.80 (m), 709.34 (m), 662.81 (w). Tab. 1 Summary of crystal data and structure refinement parameters for 1- 4 Complex 1 2 3 4 Empirical formula C102H72Co5N12O22 C60H46Co2N8O12 C55H49Co2N9O11 C17H17CoN2O6.5 formula weight 2112.37 1188.91 1129.89 412.26 Crystal system monoclinic monoclinic triclinic monoclinic Space group P21/c P21/n Cc P1 a (Å) 20.8956(19) 6.9056(5) 13.023(3) 15.5554(15) b (Å) 12.7991(12) 22.8131(15) 13.738(4) 15.3824(15) c (Å) 17.7796(16) 16.3836(11) 16.403(4) 15.6622(15) α (°) 90 90 108.646(3) 90 β (°) 105.029(2) 91.377(2) 103.208(3) 110.576(2) γ(°) 90 90 97.095(3) 90 3 V (Å ) 4592.4(7) 2580.3(3) 2644.9(12) 3508.6（ 6） Z 2 2 2 8 −3 1.528 1.53 1.419 1.561 Dcalcd(Mg m ) −1 µ (mm ) 0.968 0.72 0.697 1.018 Reflections collected 8081 19549 18538 8868 Data/parameters 8081/712 5738/373 9307/696 3105/248 F(000) 2158 1224 1168 1696 T (K) 296(2) 170 296(2) 293（ 2） Rint 0 0.0494 0.0407 0.0333 Final R indices R1 = 0.0824 R1 = 0.0405 R1 = 0.0706 R1 = 0.0327 [I > 2σ(I)] wR2 = 0.2050 wR2 = 0.0988 wR2 = 0.2135 wR2 = 0.0796 R1 = 0.134 R1 = 0.0607 R1 = 0.1121, R1 = 0.0446 R indices (all data) wR2 = 0.2276 wR2 = 0.2509 wR2 = 0.0898 wR2 = 0.1085 Gof 1.069 1.045 1.1 1.062 a

R1 = Σ‖Fo| − |Fc‖/Σ|Fo|, wR2 = [Σw(Fo2− Fc2)2]/[Σw(Fo2)2]1/2

X-ray crystal structure determination The suitable crystals of complexes 1- 4 were collected single-crystal X-ray diffraction. The data were collected on a Bruker Apex Smart CCDC diffractometer, using graphite-monochromated Mo-kα radiation (λ = 0.71073 Å) by using the ω-2ө scan


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mode at room temperature (298(2) K) or lower. The structure was solved by direct methods using SHELXS-97. [36] The non-hydrogen atoms were defined by the Fourier synthesis method. Positional and thermal parameters were refined by the full matrix least-squares method (on F2) to convergence. [37] Crystallographic data for complexes 1 - 4 are given in Table 1. Selected bond lengths and angles for 1- 4 are listed in Table S1a~e†. CCDC numbers for complexes of 1- 4 are: 1448271, 1514522, 1455398 and 1505305, respectively.

Results and discussion Structure of complex {[Co5(L1)2(bibp)2]·bibp}n (1) Singal-crystal X-ray structural analysis reveals that 1 crystallizes in the monoclinic space group P2(1)/c featuring a deh1 topological framework. Its asymmetric unit consists of two-and-a-half Co(II) cations, one L14- and one bibp ligand (Fig.1a). The complex consists of a centro-symmetric pentanuclear metallic cluster [Co5(µ3-O)2N4(COO)8]2-. The central cation (Co1) lies on an inversion center in an almost regular octahedral coordination sphere made of four oxygen from four L4- and two µ3-O atoms. The other four peripheral cobalt cations are in two independent coordination shapes. Each shape contains two cobalt cations (Co2 and Co2b, Co3 and Co3b), and the two cobalt cations of each shape are in the opposite directions with Co1 as the symmetrical center, respectively. The Co2/Co2b cation is in an octahedral surrounding with slightly distorted made of four oxygen atoms from four L14-, one µ3-O atom, and one nitrogen atom from bibp. Co3/Co3b cation is in the four-coordinated triangular pyramid geometry constructed by two oxygen atoms from two independent L14-, one µ3-O atom and one nitrogen atom from bibp. All the cobalt cations in the cluster are perfectly coplanar, with the distances are 3.2002(17) Å (Co2-Co3), 3.5394(9) Å (Co2-Co1) and 3.6007(13) Å (Co1-Co3), respectively. The Co…O distances are in the range of 1.930(6) - 2.109(5) Å, the Co…N distances are 2.014(6) Å and 2.144(6) Å, the corresponding angles are in the range of 81.2(2) - 98.8(2)°(O-Co-O) and 84.5(2) 177.8(2)° (N-Co-O). All the bond lengths are quite similar to the cluster [Co5(µ3-OH)2N4(COO)8] from the report of Ju’s group. [38] Each cluster is connected to eight L4- ligands and four bibp ligands, and each L14- is connected to four independent clusters (Fig. 1b). In addition, in the crystal stacks, there are two different types of channels (A and B) along the a axis direction (Fig. 1c), and each of the A channel is occupied by one protonated [bibp]2+ counterion. If we consider the clusters and L14- ligands as the 10- and 4-connected notes, respectively, the complexes will be simplified as a 2-nodal 4, 10-c network, with the net point symbol (3.45)2(34.412.510.614.73.82) (Fig. 1d), determined by TOPOS program. From the simplified topos framework, it is clearly found that each cluster is surrounded with twelve neighboring clusters connecting by eight L14- ligands and two bibp ligands (Fig. S1†). To our best knowledge, this is the first report for M5 clusters (M=Co(II), Zn(II), Fe(II)) which has this highest numbers of the similar cluster surroundings. [39- 41]



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Fig. 1 a) Coordination environment of Co(II) in 1 and the [Co5(µ3-O)2N4(COO)8]2cluster (All the H atoms are omitted for clarity, except that on the proton carboxylic acid groups). Symmetry codes: #1 –x + 1, -y + 1, -z + 1 #2 x, -y + 3/2, z + 1/2 #3 x, -y + 3/2, z - 1/2 #4 x, -y + 1/2, z + 1/2 #5 x, -y + 1/2, z - 1/2 #6 –x + 2, -y + 1, -z + 1 #7 x + 1, y, z #8 x - 1, y, z #9 –x + 1, -y + 1, -z + 2; b) Four [Co5(µ3-O)2N4(COO)8]2- clusters are connected together with one L4- ligand; c) The 3D frameworks of 1 with two different types of channels (A and B) along the a axis direction; and d) 3D topology 2-nodal 4, 10-c network with the net point symbol (3.45)2(34.412.510.614.73.82). Structure of {[Co2(L1)(bibp)2·2H2O}n (2) Singal-crystal X-ray structural analysis reveals that 2 crystallizes in the monoclinic space group P2(1)/n, featuring a four-fold interpenetrated bbf topological framework. The asymmetry unit of complex 2 consists of one Co(II) cation, a half L14-, one bibp ligand and one lattice water molecule (Fig. 2a). The Co(II) center exhibits tetrahedral coordination sphere which is arranged by two O atoms from two different L14- ligands and two N atoms from two different bibp ligands. The distances of Co-O and Co-N are 1.9552(16) -1.9875(16) Å and 2.029(2) 2.0262(19) Å, respectively. The L14- ligands are connected by two Co(II) cations to form a 2D zigzag fold ([Co-L]n) in bc plane (Fig. 2b). And the bibp ligands are joined by two Co(II) cations to construct a 1D zigzag line ([Co-bibp]n) alone b axis (Fig. 2c). The adjacent [Co-L]n folds are further sewed up with two identical [Co-bibp]n lines to constructing a 3D framework (Fig. 2d). The empty space of such frameworks is filled by other three identical frameworks, leading to a four-fold interpenetrated network, and resulting in a 3D framework (Fig. 2e). From the view of topological point, the Co center and the L14- ligand could be simplified as two kinds of 4-connected nodes. Thus, the overall 3D framework of 2 is a 2-nodal 4, 4-c network, and the point symbol of it is (64.82)(66)2, determined by TOPOS program.



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Fig. 2 a) Coordination environment of Co(II) in 2 (All the H atoms are omitted for clarity, except that on the proton carboxylic acid groups). Symmetry codes: #1 -1/2 + x, 1/2 - y, -1/2 + z #2 5/2 - x, - 1/2 + y, 3/2 - z #3 -1/2 + x, 1/2 - y, -1/2 + z #4 5/2 - x, 1/2 + y, 3/2 – z #5 -2 - x,-y,1-z; b) The 2D zigzag fold of [Co-bibp]n (left) and its topology structure (right); c) The two different [Co-bibp]n lines (left) and their topology structure (right); d) View of the single 3D framework of 2 along the c axis direction (left) and it’s topology structure (right); and e) The 3D topology view of four-fold interpenetrated frameworks of 2. Structure of {[Co2(L1)(bimmb)2]·DMF}n (3) Singal-crystal X-ray structural analysis reveals that 3 crystallizes in the monoclinic space group P1. The asymmetric unit of complex 3 consists of one L14- ligand, two bimmb ligands, two Co cations and one lattice DMF (Fig. 3a). Co1 and Co2 are both tetra-coordinated and surrounded with two oxygen atoms from two different L4-, and two nitrogen atoms from two different bimmb ligands, forming highly distorted tetrahedrons. The bond distances of Co-O and Co-N are in the range of 1.975(4) - 2.023(4) Å and 2.009(5) - 2.029(5) Å. All the correlative bond distances and angels are in normal range. The L14- ligands parallel-aligned with Co cation as the connection points, and the syn-bimmb ligands


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connected two neighboring Co1 and Co2 as “hats” at both side of L14- ligands in intervals, form an infinitely 1D linear structure. Then, the liners are connected by anti-bimmb ligands to form a zigzag 2D fold (Fig. 3b). Three of the folds further interpenetrate each other to form a 2D structure. And finally, the 2D structures are connected with adjoining others forming a 3D framework (Fig. 3c). Topological analysis using TOPOS program identifies the propagated single 2D net as a 3-nodal net 4, 4, 4-c network, build a new topological framework with the point symbol (3.4.53.6)4(32.42.52)(42.52.72).



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Fig. 3 a) Coordination environment of Co(II) in 3 (All the H atoms are omitted for clarity, except that on the proton carboxylic acid groups). Symmetry codes: #1 –x + 2, -y + 2, -z + 1 #2 –x + 3,-y + 1,-z + 1 #3 –x + 1, -y, -z + 1 #4 –x + 2, -y - 1, -z + 1 #5 x + 1, y - 1, z #6 x - 1, y + 1, z; b) View of zigzag 2D fold of 2 along with (1, 1, 0) plane (middle), the coordinated modes of L4- and bimb ligands (left), and view of the fold alone with (1, 1, 1) plane; and c) the 2D three-interpenetrated fold of 2 (left) with its topology structure (right). Structure of [Co2(L1)(bimb)(H2O)3]n (4) Singal-crystal X-ray structural analysis reveals that 4 crystallizes in the monoclinic space group Cc. The asymmetry unit of complex 4 consists half L14- ligand, half bimb ligand, one Co(II) cation and one and a half coordinated H2O molecules (Fig. 4a). The center Co(II) cation is in the hexa-coordinated with slightly distorted octahedron geometry, constructed by five O atoms from three different L14- ligands and two water molecules, and one N atom from one bimb ligand. The bond distances of Co-O and Co-N are in the range of 2.031(5) 2.166(4) Å and 2.098(5) Å. Two neighboring Co(II) connected with two carboxylic groups from two different L14- ligand and one water molecule, are surrounded by other two water molecules, two deprotonated carboxylic groups and two nitrogen atoms, constructing a SBU, say [Co2(COO)3(H2O)3N2] cluster. In this aspect, one bimb ligand connected two SBUs to build a 1D straight line alone c axis direction, one L14ligand connected four SBUs, and one SBU is surrounded with 12 other SBUs via four L14- ligands and two bimb ligands (Fig. 4b). If we define the SBU and L14- ligand as 6-connected and 4-connected node, respectively, the 3D framework of 4 could be simplified as an 2-nodal 4, 6-c network, building a new topological framework with the point symbol (42.64)(42.68.85) (Fig. 4c), determined by TOPOS program.


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Fig. 4 a) Coordination environment of Co(II) in 4 (All the H atoms are omitted for clarity, except that on the proton carboxylic acid groups). Symmetry codes: #1 x - 1/2, y + 1/2, z #2 –x + 1, y, -z + 1/2 #3 x + 1/2, y - 1/2, z #4 –x + 1/2, -y - 1/2, -z #5 –x +1, y, -z -1/2; b) The [Co2(COO)3(H2O)3N2] cluster (red one) is surrounded with 12 other same clusters (blue ones) via four L14- ligands and two bimb ligands; and c) The 3D framework of 4 with the clusters (left) and its topological framework (right).


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Fig. 5 Coordination environment of Co(II) in 5 (a), 6 (b) and the [Co2(COO)2(bimb)] SBU in 6 (b) (Some of the H atoms are omitted for clarity). •

Comparison of Coordination modes and Structural Diversity As described above, complexes 1 - 6 possess quite different polydimensional architectures. These differences have been found deeply influenced by the central metal ions, ligands, and the reaction environment. As illustrated in Scheme 1. H4L1 is fully deprotonated in 1, 2, 3, and 4 (a, b, c, and d respectively), while H4L2 is fully deprotonated in 6 (e) or partly deprotonated as H2L22- in 5 (f). Two tetracarboxylate ligands adopted synconformation (1, 2, and 5) or anticonformation (3, 4, and 6). The asymmetric units contain only one tetracarboxylic acid, and each H4L1 or H4L2 ligand connects two Co(II) cations in 5, four in 2 and 4 six in 3 and 6 and eight in 1. The H4L1and H4L2 adopt six coordination modes, acting as bi-, tetra-, hexa- or octa-dentate ligands in 1- 6. In coordination mode of a (1), four carboxylic groups are all bis-monodentated. The coordination mode of b (2), c (3), d (4) and e (5) all consist of four or two monodentate carboxylic groups. While, the modes of b and c are similar, only with slightly differences in conformation. Coordination mode of d (4), consists of two bis-monodentate and two monodentate carboxylic groups. Coordination f (6) consists of two bis-monodentate and two chelating carboxylic groups. Due to the flexibility of ether linkage in H4L, two terminal phenyl groups could be freely rotate around the central phenyl ring to display various dihedral angles.



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Scheme. 1 Coordination modes of H4L1/ H4L2 in complexes 1 - 6.

Scheme. 2 Coordination modes of three N-donor ligands in complexes 1 - 6. Meanwhile, three of the auxiliary ligand: bibp, bimmb, and bimb act as bidentate spacers in these complexes, but with different conformation (Scheme. 2). Two imidazol terminals of bibp in 1 and 5 display synconformation (a), while anticonformation in 2

(b); both two conformations (synconformation and

anticonformation) of bimmb exist in 3 (c and d); as the most flexible auxiliary ligand, bimb just displays synconformation in 4 (e) and 6 (f), but with different crook degrees. Two kinds of coordination geometries around Co(II) centers are observed. The Co(II) center in 2 and 3 adopt tetrahedral geometry, in 4, 5, and 6 are in hexahedral geometry, while two of the above geometries are exist in 1. The two kinds of coordination geometries have significantly differences in different complexes, respectively.


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As concerned above, the structures of the complexes are deeply influenced by the coordination modes of the ligands and the central metal ions. Thermogravimetric Analyses (TGA) The thermostabilities of the frameworks were characterized by TGA (Fig. S2†). complex 1 show no obviously decrease before 400 ℃ ， indicated the well thermalstabilities of it. Complex 2 could be seen a slightly decrease of 5% (calcd.: 3.03%) around 100 ℃, this decrease due to the loss of one latticed water molecular; and the framework began decomposed after 400 ℃. For complex 3, an obviously decomposing at the range of 7% (calcd.: 6.15%) occurred because of the decomposing of a latticed DMF molecular; the framework then began decomposed after 410 ℃. The first staple weight loss of complex 4 occurred at the range of 100- 240 ℃ with 13% (calcd.: 13.11%) due to the loss of three coordinating water molecular, the framework then continuously decomposed following the first staple. In all, complexes 1- 4 show good thermostabilities under 200 ℃. Magnetic Properties of 1, 4, and 6 Variable-temperature magnetic studies of 1, 4, and 6 were taken in the temperature range of 2- 300 K under an applied field of 1KOe. The bulk purity of 1 - 4 were sustained through comparing the PXRD of experimental results and the simulated ones of single crystal structure (Fig. S3- 6†).

Tab. 2 Curie and Weiss Constants of Complexes 1, 4, and 6 Complex constants 1 (15- 300K) 4 (2- 300K) 6 (2- 300K) Curie constants (cm3 K mol-1) 20.37 1.94 2.48 Weiss constants (K) -44.40 -5.05 -4.71 For complex 1, as shown in Fig. 6, the χMT value is 18.08 cm3 K mol-1 at 300 K, almost twice higher than the expected value of 9.375 cm3 K mol-1 for five Co(II) ions independent (g = 2.0, S = 3/2), or the value for the reported ones with the similar Co(II) cluster.

[38, 39]

This indicates the importance of orbital contribution generated

from the high-spin octahedral Co(II) ions. [42, 43] As the sample was cooling down, the χMT value decreased gradually and reached the value of 1.66 emu K mol-1 at 2 K. While, the χM value increases smoothly along with the decrease of temperature. These reasults clearly manifest that the presence of dominant antiferromagnetic coupling interactions between the Co(II) ions, and the structure of the carboxylate and hydroxyl groups in the [Co5(µ3-O)2N4(COO)8]2- pentanuclear cluster may be responsible for this phenomenon. [44- 46] To further estimate the intramolecular exchange constant, the



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χM-1- T was plotted and it well obeys the Curie-Weiss law above 15 K, with C = 20.37 cm3 K mol-1 and θ = -44.40 K, this was also reveals the dominant antiferromagnetic interactions between the Co(II) ions and the presence of spin-orbit coupling. [47] To our disappointed, we could not find an exact magnetic solution to fit the magnetic value for such complicated pentanuclear cluster.

Fig. 6 Temperature dependence of χMT and χM for complex 1 under 1KOe field (left) and the temperature dependence of χM-1 (the red line present the best fit of the CurieWeiss law χM = C/ (T- θ)) (right). Complexes 4 and 6 both contain binuclear clusters and their magnetic characters are very similar (Fig. 7 for 4 and Fig. 8 for 6). The χMT value of 4 and 6 are 1.97 cm3 K mol-1 and 2.48 cm3 K mol-1 at 300 K, respectively, which are all larger than the expected spin-only value of 1.875 cm3 K mol-1 for a unit composed of two noninteracting Co(II) cations (g = 2, S = 3/2). Upon cooling, the χMT values decreased gradually from 300 K to 25 K, and then abrupt decreased to 1.11 cm3 K mol-1 and 1.30 cm3 K mol-1 at 2 K. For the values of χM, two of them increase smoothly along with the cooling process. Both magnetic behaviors indicate the presence of antiferromagnetic coupling interactions between the binuclear Co(II) ions in complexes 4 and 6. Although the two complexes exhibit similar magnetic capabilities, the structural influences are largely different. Based on the structural analysis, the antiferromagnetic interaction for 4 is mainly arise from the significant orbital angular momentum contributions from the local 4T1g ground term of the distorted octahedral Co(II) ions. [48, 49] While for 6, due to the binuclear clusters are interconnect by large L ligand, it should be mainly arise from the magnetic exchange coupling within the binuclear Co(II) cluster.

[50]

The χM-1- T plots are well followed the Curie-Weiss law

with C = 1.94 cm3 K mol-1 and θ = -5.05 K for 4, and C = 2.48 cm3 K mol-1 and θ = -4.71 K for 6. The negative values of θ for 4 and 6 also mean the antiferromagnetic coupling interactions between the binuclear Co(II) cluster.


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Fig. 7 Temperature dependence of χMT and χM for complex 4 under 1KOe field (the red line is the best fit of data) (left) and the temperature dependence of χM-1 (the red line present the best fit of the Curie- Weiss law χM = C/ (T- θ)) (right).

Fig. 8 Temperature dependence of χMT and χM for complex 6 under 1KOe field (the red line is the best fit of data) (left) and the temperature dependence of χM-1 (the red line present the best fit of the Curie- Weiss law χM = C/ (T- θ)) (right). To further understand the behavior of magnetic for 4 and 6 quantitatively, the empirical expression for the strength of the antiferromagnetic exchange interaction of Co(II) in 4 and 6 was employed. The following list equation 1

[51, 52]

is based on the

general isotropic exchange Hamiltonian, Ĥ = -2JŜ1Ŝ2, with J is the magnetic exchange coupling constant and S1 = S2 = 3/2. χ

/ / / / /

(1)

The best fit parameters for the experimental data over 2- 300 K was calculates and gives g = 1.99, J = -0.26 with R = 1.90 × 10-6 for complex 4, and g = 2.04, J = - 1.37 with R = 2.1× 10-6. The negative value of J in the two complexes is in agreement with



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the negative values of θ, and further manifest that the coupling between Co(II) centers is antiferromagnetic.

Conclusion In summary, utilizing two semi-rigid ether-linked aromatic tetracarboxylate ligands and three different types of N-donor ligands, six cobalt(II) complexes were successfully synthesized. Complex 1 and 2 are co-crystallized and 1 featuring a deh1 topological framework with an interestingly pentanuclear [Co5(µ3-O)2N4(COO)8]2cluster, while 2 is a four-fold interpenetrated 3D structure with bbf topological framework. Complex 3 exhibits a 2D + 2D → 2D network with new topological network. And complex 4 is an 3D framework with a [Co2(COO)3(H2O)3N2] cluster, and build a new topological framework with the point symbol (42.64)(42.68.85). Complexes 5 and 6 are both 2D planar construction, and 6 displays [Co2(COO)2(bimb)] binuclear SBUs. The antiferromagnetic interaction of complex 1 could be mediated through the carboxylate and hydroxyl groups in the [Co5(µ3-O)2N4(COO)8]2- pentanuclear cluster. The antiferromagnetic interaction of complexes 4 and 6 are similar but with different structural influences due to the difference of the coordination environment around Co(II) ions in two complexes. This study show that some Co-based coordination polymers could be used in the area of molecular based magnetic materials. The related studies are still under way.

Supporting Information Selected bond lengths and angles for complex 1- 4, the central SBU surrounding environment of complex 1, the thermogravimetric curves for complexes 1- 4, and the experimental crystals’ PXRD patterns of complex 1- 4 compared with the simulated pattern. *

Corresponding authors

Fax: +86 532 66781932 E-mail address: [email protected] (Yu-hua Fan), [email protected] (Shuang-yu Bi)


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Acknowledgement This work was supported by National Natural Science Foundation of China (Nos. 21371161 and 21601171), the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20120132110015).



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For Table of Contents use only

Six Co(II) coordination polymers based on two isomeric semi-rigid ether-linked aromatic tetracarboxylate acid: syntheses, structural comparison, and magnetic properties Zheng Zhu †, Cun-gang Xu†, Mei Wang†, Xia Zhang†, Hu Wang†, Qing-dan Luo†, Shuang-yu Bi‡* and Yu-hua Fan†*

Six Co(II) coordination polymers based on two isomeric semi-rigid ether-linked aromatic tetracarboxylate acid have been successfully solvothermally synthesized and characterized magnetically and structurally. Magnetization data for complex 1with the Co5 unit and for complex 4 and 6 with the Co2 units show the antiferromagnetic coupling in the units themselves own.


Coordination Polymers Based on Two Isomeric ... - ACS Publications

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