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Article Cite This: Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Coordination Frameworks Containing Magnetic Single Chain of Imidazoledicarboxylate-Bridged Cobalt(II)/Nickel(II): Syntheses, Structures, and Magnetic Properties Wenbo Wang,† Ruiying Wang,‡ Lina Liu,† and Benlai Wu*,† †

College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China School of Chemical Engineering, Henan Vocational College of Applied Technology, Zhengzhou 450042, P. R. China

‡

S Supporting Information *

ABSTRACT: Five new magnetic coordination frameworks with formulas of {[Co2(HL)2(H2O)4]·4H2O}n (1), {[Ni2(HL)2(H2O)4]·4H2O}n (2), [Co(HL)(bpy)]n (3), [Co(HL)(pbim)]n (4), and [Ni(HL)(pbim)]n (5) [H3L = 2-(5-bromo-pyridin-3-yl)1H-imidazole-4,5-dicarboxylic acid, bpy = 4,4′-bipyridine, and pbim = 1,1′-(5-methyl-1,3phenylene)bis(1H-imidazole)] have been synthesized and structurally characterized by elemental, thermogravimetric, and X-ray diffraction analyses. In all compounds, the doubly deprotonated (HL)2− ligands adopt the same μ-kN,O:kN′,O′ coordination mode, showing very interesting coordination orientation in the construction of those coordination polymers. Complexes 1 and 2 feature (HL)2−-bridged linear chain structures. Complex 3 is a 2D network with (4,4) grids built up from the (HL)2−bridged linear chains observed in 1 being further linked by rod-like bpy bridges replacing the coordination of water molecules. Those almost or completely linear chains formed by the bis-N,O-chelation of the imidazoledicarboxylate of (HL)2− in 1−3 are rarely observed in the complexes of 4,5-imidazoledicarboxylic acid and its derivatives, giving a typical structure model to investigate the magnetic exchange-coupling mediated by imidazoledicarboxylate. Isostructural complexes 4 and 5 are 2D helicates where (HL)2−-bridged left- and right-handed helixes are doubly linked into the mesolayer structures with 63 topology through the further coordination of angular spacers pbim. Remarkably, the formation of (HL)2−-bridged linear chains or helical chains is mainly dependent on the trans- or cis-chelation of two (HL)2− ligands around the same metal center, which could be finely tuned by the structural features of auxiliary ligands used. Magnetostructural analyses disclose that the bisN,O-chelating imidazoledicarboxylates of (HL)2− transmit antiferromagnetic interactions along the (HL)2−-bridged metal− organic chains with the spin-coupling constants of −4.89, −17.8,−6.55, −7.35, and −19.6 cm−1 for 1−5, respectively. Notably, the μ-kN,O:kN′,O′ coordination mode of (HL)2− ligand dominates the assembly of metal−organic frameworks as well as the magnetic exchange between the paramagnetic ions in those magnetic chains, but the magnetic exchange-coupling depends strongly on the nature of the metal center.

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INTRODUCTION During the past decades, the studies of metal−organic frameworks (MOFs) have greatly attracted current interest owing to their unique structures and diverse topologies as well as intriguing potential applications in multiple fields.1−11 Among the many attributes of MOFs, molecular magnetism related to basic and applied sciences has been extensively investigated since the 1980s, and constantly renewed by the discovery of new systems such as long-range-ordered molecular magnets, single-molecule magnets, and single-chain magnets presenting new magnetic phenomena and magnetostructural correlations.12−24 In general, the construction of magnetic MOFs is based on paramagnetic transition metal ions and short organic ligands.12−24 Undoubtedly, both the paramagnetic metal centers and short organic ligands in MOFs are highly important for the structural control and magnetic properties. On the one hand, paramagnetic transition metal elements that have variable oxidation states, which allow the variation of spin © XXXX American Chemical Society

quantum number and magnetic anisotropy, two important parameters in magnetism. On the other hand, the bridging ligands play significant and cooperative roles in constructing magnetic MOFs due to that they can mediate magnetic and structural diversities. To obtain magnetic MOFs, azide and carboxylate, which have variable bridge modes and particular efficiency in transmitting magnetic couplings, have been frequently used to synthesize magnetic materials.25−28 The N-heterocyclic ligands such as polypyridine,29 imidazole,30 and triazole31 are another type of the most appealing bridges for the construction of magnetic metal clusters and magnetic MOFs where the Nheterocyclic ligands use their multiple N-donors to bridge metal ions and their rigid conjugated structures to transmit magnetic Received: February 1, 2018 Revised: April 14, 2018

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DOI: 10.1021/acs.cgd.8b00174 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Scheme 1. Schematic Representation of Main Ligand H3L and Auxiliary Organic Bridges bpy and pbim and the Existing Forms and Coordination Mode of Ligand H3L in Complexes 1−5

temperature-dependent magnetic measurements were determined on a Quantum Design SQUID-XL7 magnetometer. Synthesis of {[Co2(HL)2(H2O)4]·4H2O}n (1). A mixture of Co(NO3)2· 6H2O (0.0146 g, 0.05 mmol), H3L (0.0156 g, 0.05 mmol), acetonitrile (1 mL), and H2O (6 mL) was sealed into a 25 mL Teflon-lined stainless autoclave and heated to 150 °C for 72 h under autogenous pressure. After cooling to room temperature at a rate of 5 °C h−1, brown rod-like crystals of 1 were collected, washed with distilled water, and dried in air, resulting in 57% yield (based on Co). Anal. Calcd for C20H24Br2Co2N6O15 (%): C, 27.23; H, 2.74; N, 9.53. Found: C, 27.55; H, 2.71; N, 9.60. IR (KBr, cm−1): 3440 (br), 1616 (m), 1558 (vs), 1457 (m), 1384 (m), 1013 (m), 890 (m), 779 (w), 744 (w), 709 (w), 618 (s), 543 (w). Synthesis of {[Ni2(HL)2(H2O)4]·4H2O}n (2). A mixture of NiSO4· 6H2O (0.0131 g, 0.05 mmol), H3L (0.0156 g, 0.05 mmol), NaOH (0.0040 g, 0.1 mmol), and deionized H2O (7 mL) was sealed in a 25 mL Teflon-lined stainless autoclave and heated at 160 °C for 96 h. After cooling to room temperature at a rate of 5 °C h−1, pale blue block crystals of 2 were obtained, washed with distilled water, and dried in air, resulting in 53% yield (based on Ni). Anal. Calcd for C20H24Br2Ni2N6O15 (%): C, 27.25; H, 2.74; N, 9.53. Found: C, 27.40; H, 2.73; N, 9.56. IR (KBr, cm−1): 3445 (br), 1558 (m), 1540 (s), 1473 (s), 1406 (m), 1278 (m), 1131 (m), 1105 (w), 890 (w), 743 (w), 699 (w), 625 (m), 570 (w), 509 (w). Synthesis of [Co(HL)(bpy)]n (3). A mixture of Co(NO3)2·6H2O (0.0146 g, 0.05 mmol), H3L (0.0156 g, 0.05 mmol), bpy (0.0078 g, 0.05 mmol), NaOH (0.0040 g, 0.1 mmol), and deionized H2O (7 mL) was sealed in a 25 mL Teflon-lined stainless autoclave and heated at 150 °C for 72 h. After cooling to room temperature at a rate of 5 °C h−1, brown block crystals of 3 were obtained, washed with methanol, and dried in air, resulting in 59% yield (based on Co). Anal. Calcd for C20H12BrCoN5O4 (%): C, 45.74; H, 2.30; N, 13.34. Found: C, 45.90; H, 2.27; N, 13.40. IR (KBr, cm−1): 3423 (br), 3079 (m), 1608 (m), 1580 (s), 1478 (m), 1278 (m), 1129 (s), 1075 (m), 821 (w), 791 (w), 743 (w), 633 (s), 550 (w). Synthesis of [Co(HL)(pbim)]n (4) and [Ni(HL)(pbim)]n (5). A mixture of Co(NO3)2·6H2O (0.0146 g, 0.05 mmol), H3L (0.0156 g, 0.05 mmol), pbim (0.0112 g, 0.05 mmol), NaOH (0.0040 g, 0.1 mmol), methanol (1 mL), and deionized H2O (6 mL) was sealed in a 25 mL Teflon-lined stainless autoclave and heated at 150 °C for 72 h. After cooling to room temperature at a rate of 5 °C h−1, red rod-like crystals of 4 were obtained, washed with methanol, and dried in air, resulting in 61% yield (based on Co). Anal. Calcd for C23H16BrCoN7O4 (%): C, 46.56; H, 2.72; N, 16.53. Found: C, 46.67; H, 2.68; N, 16.61. IR (KBr, cm−1): 3422 (br), 1606 (m), 1569 (vs), 1505 (s), 1471 (m), 1277 (m), 1124 (s), 1064 (w), 790 (w), 743 (w), 654 (s), 575 (w). Following the same synthetic procedure of 4 except that Co(NO3)2·6H2O (0.0146 g, 0.05 mmol) was replaced by Ni(NO3)2·6H2O (0.0145 g, 0.05 mmol), blue rod-like crystals of 5 were obtained in 67% yield (based on Ni). Anal. Calcd for C23H16BrNiN7O4 (%): C, 46.58; H, 2.72; N, 16.53. Found: C, 46.47; H, 2.76; N, 16.50. IR (KBr, cm−1): 3422 (br), 1603 (m), 1574 (vs), 1503 (s), 1481 (m), 1403 (s), 1322 (s), 1279 (s), 1126 (m), 1064 (w),935 (w), 790 (w), 742 (w), 654 (s), 577 (w). X-ray Structure Determination and Structure Refinement. On an Oxford diffractometer equipped with a CCD detector, singlecrystal X-ray data were collected at 293(2) K using graphite-

coupling. Additionally, 4,5-imidazoledicarboxylic acid and its derivatives, which are honored with versatile coordination modes and intriguing coordination orientation due to the ingenious combination of two carboxyl groups with an imidazole ring, are ideal multifunctional connectors in the exploration for MOFs, and especially for magnetic MOFs.32−36 However, the magnetic MOFs in a large number of the MOF materials based on this type of ligands are relatively few. In particular, the multiple connections of this type of ligand with metal centers have limited the formation of magnetic singlechain structures largely. Thus, the construction of the magnetic single-chain structures based on this type of ligand is still challenging. Very recently, we have successfully constructed a series of interesting cadmium(II) coordination polymers based on another new derivative of 4,5-imidazoledicarboxylic acid, namely, 2-(5-bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylic acid (H3L), and N-heterocyclic ancillary ligands.37 In those CdII complexes, the strongly bis-chelating coordination mode μ-kN,O:kN′,O′ of the imidazoledicarboxylate of (HL)2− absolutely dominated the resulting architectures, which were further modulated by the coordination and configuration of the additional ligands. As a continuation of our work, we intend to use H3L ligands as bridges and the selected transition metal ions CoII and NiII, which possess special magnetic anisotropy and spin quantum number,28,38−44 as magnetic moment carriers to establish newfangled magnetic MOFs. Moreover, Nheterocyclic ancillary ligands such as rod-like bridge 4,4′bipyridine (bpy) and V-shaped bridge 1,1′-(5-methyl-1,3phenylene)bis(1H-imidazole) [pbim] are further used to modulate the architectures of CoII/NiII and H3L (Scheme 1). Finally, five new magnetic MOFs, namely, {[Co 2 (HL) 2 (H 2 O) 4 ]·4H 2 O} n (1), {[Ni 2 (HL) 2 (H 2 O) 4 ]· 4H2O}n (2), [Co(HL)(bpy)]n (3), [Co(HL)(pbim)]n (4), and [Ni(HL)(pbim)]n (5), have been obtained. It is important to note that these 1−2D coordination polymers all consist of the magnetic single chains built up from the bis-chelation of the imidazoledicarboxylate of (HL)2− with magnetic moment carriers CoII/NiII. In this contribution, we report their synthesis, crystal structures, thermal stabilities, and magnetic properties.

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EXPERIMENTAL SECTION

Materials and General Procedures. All chemicals purchased were of analytical grade and used without further purification. Ligand H3L was prepared according to our reported procedure.37 Element analyses for C, H, and N were performed on a Carlo-Erba 1106 elemental analyzer. IR spectra (KBr pellets) were recorded on a Nicolet NEXUS 470 FT-IR spectrophotometer from 400 to 4000 cm−1. Thermal analysis curves were scanned from 30 to 800 °C under air on a STA 409 PC thermal analyzer. The powder X-ray diffraction (PXRD) patterns of the samples were recorded by a RIGAKUDMAX2500 X-ray diffractometer with Cu−Kα radiation. The B



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Table 1. Crystal Data and Structure Refinement for 1−5 compounds

1

2

3

4

5

formula temp (K) formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z, ρcalcd (g/cm3) GOF R1, wR2 (I > 2σ(I)) largest diff. peak and hole

C20H24Br2Co2N6O15 293(2) 882.13 triclinic P1̅ 9.0400(7) 9.1914(8) 9.6102(6) 100.665(6) 114.682(7) 91.457(7) 708.30(10) 1, 2.068 1.052 0.0510 0.1291 1.081 −0.614

C20H24Br2N6Ni2O15 293(2) 881.69 monoclinic P21/n 9.0703(3) 9.0796(3) 17.0881(7) 90 91.818(4) 90 1406.58(9) 2, 2.082 1.038 0.0528 0.1425 1.701 −0.562

C20H12BrCoN5O4 293(2) 525.19 orthorhombic Pbcm 11.4001(7) 14.0531(9) 13.0286(8) 90 90 90 2087.3(2) 4, 1.671 1.044 0.0693 0.1862 2.485 −1.851

C23H16BrCoN7O4 293(2) 593.27 monoclinic C2/c 25.981(2) 8.4748(5) 22.620(2) 90 104.353(10) 90 4825.0(7) 8, 1.633 0.941 0.0928 0.2290 1.030 −0.784

C23H16BrN7NiO4 293(2) 593.05 monoclinic C2/c 25.81(14) 8.46(2) 22.43(6) 90 104.3(5) 90 4744(32) 8, 1.661 1.049 0.0670 0.1908 0.914 −0.930

Figure 1. View of the typically linear chain structure in 1 formed by the imidazoledicarboxylates of (HL)2− ligands bis-chelating two independent CoII, showing the coordination environments of Co1 and Co2. Symmetry codes: (A) 2 − x, −y, 1 − z; (B) 1 − x, 1 − y, 1 − z. monochromated Cu Kα radiation (λ = 1.5418 Å) for 1−5. Absorption corrections were applied by using the multiscan program SADABS.45 Structural solutions and full-matrix least-squares refinements based on F2 were performed with the SHELXS-9746 and SHELXL-9747 program packages, respectively. All the non-hydrogen atoms were refined with anisotropic displacement parameters during the final cycles. The H atoms attached to C were generated geometrically, while the H atoms attached to O were located from different Fourier maps and treated as idealized contributions. The nitrogen atom and its meta-carbon atom in the pyridyl of (HL)2− ligand in isomorphous 4 and 5 are statistically distributed, and thus, the bromine atom is also statistically attached at two positions. The R1 value of 4 is slightly high, which perhaps results from the weak diffraction owing to the thinner single crystal as well as the above-mentioned statistical distributions of some atoms in ligand (HL)2−. Though the single crystal structure of 5 was solved, the data completeness is only 0.776 due to the weak X-ray diffraction signals at higher theta values. Further attempts to get suitable single crystals 5 by different methods as well as the recollecting crystal data at a lower temperature were of fail. Nevertheless, the isostructural nature of 4 and 5 was further confirmed by the powder X-ray diffraction patterns. The crystal and refinement data are collected in Table 1, and the selected bond distances and angles are given in Table S1. It should be mentioned that the crystal and refinement data as well as the selected bond distances and angles of 5 are not too accurate owing to the relatively low data completeness.

satisfactory elemental analysis and X-ray diffraction. In 1−5, every H3L ligand removes two protons and acts as a divalent anion (HL)2−. In combination with the following structural analysis, it can be observed that the proton dissociation from the H3L ligand in 1, 2, 4, and 5 occurred in the imidazole group and one carboxyl. However, for (HL)2− ligand in 3, the protons of its imidazole and two carboxyls were removed, and meanwhile, its pyridyl was protonated. The phase purities of the as-synthesized crystalline products 1−5 were determined by powder X-ray diffraction (PXRD) measurements. As shown in Figures S1−S5, the calculated PXRD patterns from the single-crystal X-ray diffraction data are in conformity to the observed ones, indicating the phase purities of those polycrystalline samples. Comparatively, the slight peak shifts may be due to the baseline drift of the PXRD diffractometer and the different measuring temperatures for single-crystal diffraction and powered X-ray diffraction. The differences in intensity perhaps originate in the preferred orientation of the powder samples. Thermal stability of those compounds was investigated by the TGA technique. As shown in Figure S6, the dehydration processes of compounds 1 and 2 began from 50 °C. With heating, they suffered slow continuous weight losses until complete decomposition. Compounds 3−5 are stable up to 305, 360, and 377 °C, respectively. As overtaken by their heat-resistant temperatures, the samples of 3−5 suffered continuous decomposition processes. Structural Analysis and Discussion. {[Co2(HL)2(H2O)4]· 4H2O}n (1) and {[Ni2(HL)2(H2O)4]·4H2O}n (2). Compound 1 crystallizes in the triclinic space group P1̅, and its asymmetric unit comprises two crystallographically independent one-half CoII, one (HL)2−, two coordinated H2O, and two lattice H2O.

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RESULTS AND DISCUSSION Synthesis and General Characterization of Compounds 1−5. Compounds 1−5 were hydro/solvothermally synthesized, and their reaction conditions were fine-tuned to obtain appropriate crystals. In the preparation of 3−5, the auxiliary ligands bpy and pbim were used, respectively. The chemical formulas of those compounds have been confirmed by C



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As shown in Figure 1, every doubly deprotonated (HL)2− ligand adopts a μ-kN,O:kN′,O′ coordination mode with its imidazoledicarboxylate bis-chelating two independent CoII and thus bridges Co1 and Co2 to form a 1D chain structure where the neighboring CoII centers are separated by 6.5274(6) Å. The independent Co1 and Co2 atoms are located at the inversion centers of their N2O4 coordination octahedra ligated by two trans-chelating imidazoledicarboxylates from two symmetryrelated (HL)2− ligands and two water molecules (Figure 1). The bond lengths and cis-bond angles for Co1 and Co2 cover the ranges of 2.062(4)−2.149(4) Å and 78.7(1)−101.3(1)°, indicating a slight distortion of their coordination geometries from an ideal octahedron. Notably, the polymeric chain of 1 is a typically linear chain structure where the dihedral angle between the two chelating rings formed by each (HL)2− ligand bis-chelating two CoII centers is 2.4(2)°, indicating that all the chelating rings along the same chain are almost coplanar. Additionally, the linear feature of the imidazoledicarboxylatebridged chain in 1 is also reflected by the specially small dihedral angles between the imidazole ring and the chelating rings (being in a range of 1.7(2)−3.9(2)°). In 1, the polymeric chains are further assembled through interchain O−H···N hydrogen-bond interactions occurring from the coordinated water molecules to the uncoordinated Npyridyl atoms (O5···N3C = 2.729(6) Å, C = 1 − x, −y, 1 − z), resulting in a 2D supramolecular framework (Figure 2) that stacks up along the c axis (Figure S7).

Similarly to that in 1, those polymeric chains of 2 are further linked through interchain O−H···N and O−H···O hydrogenbond interactions occurring from the coordinated water molecules to the uncoordinated Npyridyl and Ocarboxyl atoms (O5···N3C = 2.724(4) Å, O5···O3D = 2.981(4) Å; C = −1 + x, y, z; D = −x, 1 − y, 1 − z), forming a 2D supramolecular framework (Figure S9) that also stacks up along the c axis (Figure S10). [Co(HL)(bpy)]n (3). Compound 3 crystallizes in the orthorhombic Pbcm space group and its asymmetrical unit includes one-half CoII, one-half (HL)2−, and one-half bpy molecule. As shown in Figure 3, every CoII center in 3 is transchelated by two imidazoledicarboxylates from two symmetryrelated (HL)2− ligands and two pyridyls from two symmetryrelated bpy ligands, with a C2 axis passing through the resulting N4O2 coordination octahedron along the CoII ion and the two bpy ligands. The coordination octahedron of CoII in 3 is also slightly deviated from an ideal octahedron, being very similar to that observed in 1. The dihedral angle between the two chelating rings around the same metal center in 3 is 4.6(2)°, unlike those cases observed in 1 and 2 where the two chelating rings around the same metal center are absolutely coplanar. Ligands (HL)2− in 3 also adopt the μ-kN,O:kN′,O′ coordination mode and bridge CoII centers into a typically linear chain structure as observed in 1 and 2 (Figure 4). The dihedral angle between the protonated pyridy and imidazoledicarboxylate of ligand (HL)2− is definitely 90°, and the two chelating rings formed by each (HL)2− ligand bis-chelating two CoII centers are coplanar. In the chain of 3, all the coordinated CoII and N atoms are located at the same line. Very interestingly, those c axially extended linear chains are further joined by the rigid rod-like ancillary ligands bpy along the a axis, forming a 2D structure with (4,4) grids (Figure 4). In a sense, the formation of 3 can be regarded as the in situ replacement of the terminal ligand water in 1 by the bridge bpy. In the 2D structure of 3, the distances of two CoII centers separated by each (HL)2− or bpy are 6.5143(4) and 11.400(2) Å, respectively. Finally, those 2D frameworks interdigitate together along the b axis through interlayered Br···π interactions originating from the Br atoms of (HL)2− ligands in one layer to the imidazole rings of (HL)2− ligands in the adjacent layers (Figure S11, Br-to-centroid distance being 3.797(3) Å). [Co(HL)(pbim)]n (4) and [Ni(HL)(pbim)]n (5). Isostructural compounds 4 and 5 crystallize in the monoclinic space group C2/c, and thus, only the crystal structure of 4 is described in detail as a representative case. The asymmetric unit of 4 contains one CoII, one (HL)2−, and one pbim. Each CoII center in 4 is six-coordinated and located in a distorted N4O2 coordination octahedron ligated by two cis-chelating imidazoledicarboxylates from two symmetry-related (HL)2− ligands and two imidazole groups from two symmetry-related pbim ligands (Figure 5). Notably, the dihedral angle between the two chelating rings around the same CoII center is 79.8(2)°, which is close to a right angle. Ligands (HL)2− in 4 also adopt the μ-kN,O:kN′,O′ coordination mode and connect CoII ions to form b axially extended left- and right-handed helixes with the 21 helical pitches being 8.4748(5) Å (Figure 6), and those adjacent leftand right-handed helixes are doubly bridged by the further coordination of the auxiliary bridges pbim to fabricate a 2D mesolayer structure with 63-topology (Figure S12). In the 2D structure of 4, the distances of two CoII centers separated by

Figure 2. View of the 2D supramolecular framework of 1 formed by interchain hydrogen-bonding interactions.

Compound 2 crystallizes in the monoclinic space group P21/ n, and its asymmetric unit consists of two crystallographically independent one-half NiII, one (HL)2−, two coordinated H2O, and two lattice H2O. Though 1 and 2 crystallize in different space groups, they are very similar in structure. First, the coordination modes of (HL)2− and metal centers in 1 and 2 are completely the same. Second, the two independent metal atoms in both complexes are located at the inversion centers of their N2O4 coordination octahedra. In the end, they feature the same linear chain structure (Figure S8). In 2, the dihedral angle between the two chelating rings formed by each (HL)2− ligand bis-chelating two NiII centers is 2.8(1)°, and the distances of two NiII centers separated by each (HL)2− is 6.4170(3) Å. In the same chain of 2, the dihedral angles between the imidazole ring and the chelating rings range from 1.1(2) to 3.8(2)°, being very close to those values describing the linear feature of the imidazoledicarboxylate-bridged chain in 1. D



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Figure 3. View of the coordination environment of the CoII in 3. Symmetry code: (A) x, 1/2 − y, 1 − z; (B) − 1 + x, y, z; (D) x, y, 3/2 − z; (E) x, 1/2 − y, −1/2 + z.

Figure 4. View of the 2D polymeric framework with (4,4) grids in 3.

could be finely tuned by the structural features of auxiliary ligands used. In the complex family of 4,5-imidazoledicarboxylic acid and its derivatives, various architectures including discrete clusters, 1D chains, 2D layers, and 3D frameworks have been reported,32−37 but those almost or completely linear chains formed by the bis-N,O-chelation of the imidazoledicarboxylate of (HL)2− in 1−3 are indeed rare, giving a typical structure model to investigate the magnetic coupling mediated by imidazoledicarboxylate. Magnetic Properties Studies. Based on the above structural analyses, MOFs 1−5 consist of linear or helical metal−organic polymer chains formed by the bis-N,O-chelation of the imidazoledicarboxylates of (HL)2− ligands with paramagnetic ions CoII/NiII. In those chain structures, the separation distances between two adjacent CoII or between two adjacent NiII are 6.5274(6) Å for 1, 6.4170(3) Å for 2, 6.5143(4) Å for 3, 6.469(2) Å for 4, and 6.39(3) Å for 5, respectively, and the two chelating rings formed by each (HL)2− ligand bis-N,O-chelating two CoII or NiII centers for 1− 3 are almost or completely coplanar, whereas the dihedral

each (HL)2− or pbim are 6.469(2) and 10.615(2) Å, respectively. The distance of two CoII centers separated by each (HL)2− in 4 is slightly shorter than those observed in 1 and 3. Remarkably, the dihedral angle between the two chelating rings formed by each (HL)2− ligand bis-chelating two CoII centers in 4 is 15.5(2)°, indicating not exactly the same as those observed in 1−4 where the two chelating rings formed by each (HL)2− ligand bis-chelating two metal centers are almost or completely coplanar. Finally, those 2D frameworks interdigitate together through the interlayered Br···π interactions originating from the Br atoms of (HL)2− ligands in one layer to the imidazole rings of pbim ligands in the adjacent layers (Br-to-centroid distance being 3.853(4) Å), resulting in a 3D crystal structure of 4 (Figure S13). In 1−5, (HL)2− ligands all adopt the μ-kN,O:kN′,O′ coordination mode, and bis-chelate with six-coordinated metal ions CoII/NiII to direct the structural assemblies. Very intriguingly, the formation of (HL)2−-bridged linear chains or helical chains is mainly dependent on the trans- or cis-chelation of two (HL)2− ligands around the same metal center, which E



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The corresponding graphs of χM versus T and χMT versus T are presented in Figures 7−11.

Figure 7. χM vs T plot and χMT vs T plot with the theoretical fit (−) for 1.

Figure 5. View of the coordination environment of the CoII in 4. Symmetry code: (A) 1 − x, 1 − y, 1 − z; (B) 3/2 − x, −1/2 + y, 3/2 − z.


Cobalt(II) Compounds 1, 3, and 4. The χMT values at 300 K are about 2.78, 3.29, and 3.01 cm3 mol−1 K for 1, 3, and 4, respectively, which are obviously larger than the spin-only value (1.875 cm3 mol−1 K) for a magnetically isolated high-spin CoII ion in an octahedral environment, indicating the significant orbital contribution typical for the 4T1g ground state of an octahedral high-spin CoII ion.28,44,48 The magnetic behaviors of 1 and 3 are very similar (Figures 7 and 9). Upon cooling from 300 K, the χMT values of 1 and 3 decrease gradually down to 0.35 cm3 mol−1 K at 4 K and 0.46 cm3 mol−1 K at 5 K, respectively, and then abruptly increase, reaching a peak value of 0.99 cm3 mol−1 K at 2.5 K for 1 and 0.73 cm3 mol−1 K at 3.4 K for 3. After further cooling, their χMT values drop sharply to

Figure 6. View of b axially extended left- and right-handed helixes constructed by the imidazoledicarboxylates of (HL)2− ligands bischelating CoII ions in the 2D mesolayer of 4 (5-bromo-pyridin-3-yl groups were omitted for clarity).

angles of those for 4 and 5 are 15.5(2)° and 16.3(2)°, respectively. Those structural parameters indicate that perhaps there is meaningful magnetic coupling exchanged by the conjugated imidazole bridges of (HL)2− ligands along the chains. Thus, the temperature-dependent magnetic susceptibilities (χM) of polycrystalline samples 1−5 were measured at a field of 1 kOe in a temperature range of 2−300 K, respectively.

Figure 9. χM vs T plot and χMT vs T plot with the theoretical fit (−) for 3. F



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0.94 and 0.58 cm3 mol−1 K at 2 K, respectively. As temperature lowers, their χM values begin to increase slowly and then suddenly increase below 6 K. Best-fitting their susceptibility data at 25−300 K with the Curie−Weiss law yields C = 3.00 cm3 mol−1 K and θ = −28.27 K for 1, and C = 3.64 cm3 mol−1 K and θ = −39.51 K for 3 (Figures S14 and S15). The initial reductions of their χMT values and the negative θ values indicate the presence of possible antiferromagnetic interactions between CoII ions. The decays in the values of their χMT may also be attributed to the spin−orbit coupling and zero-field splitting of CoII ions in an octahedral ligand field.26,34 As for the peak values of χMT around 2.5 K for 1 and 3.4 K for 3, it maybe indicates the occurrence of weak ferromagnetism in their systems.44,49 Upon cooling for 4, the χMT value decreases monotonically, while the χM value reaches a maximum value around 12 K with an increase below 4 K (Figure 10). Its χM−1

given in the whole temperature range. Since their magnetic behaviors at the lower temperature range display complexity, which perhaps involve intrachain antiferromagnetic interactions, the spin-canting effect, and/or the saturation effect,34,44,49 and they could not be fitted by eq 1. Nickel(II) Compounds 2 and 5. The χMT values at 300 K are about 1.29 and 1.19 cm3 mol−1 K for 2 and 5, respectively, which are larger than the spin-only value (1.00 cm3 mol−1 K) expected for a magnetically isolated NiII ion, revealing a certain orbital contribution.34 Upon cooling, the χMT values of 2 and 5 decrease monotonically, while their χM values reach a maximum value around 25 and 29 K, respectively (Figures 8 and 11). The



magnetic behaviors of 2 and 5 suggest typical antiferromagnetic interactions between NiII ions. As for the Curie tails observed below 6 K for 2, it is maybe attributed to a small amount of paramagnetic impurity. Structurally, nickel(II) compounds 2 and 5 can magnetically be handled as infinite uniform chains as above cobalt(II) compounds 1, 3, and 4. In this context, the magnetic data of 2 and 5 in the whole temperature range can be fitted by eq 1 as well as considering the effect of a magnetically dilute impurity for 2. The results of the best fit are J = −17.8 cm−1, g = 2.37, ρ = 0.002, and R = 1.25 × 10−4 for 2, and J = −19.6 cm−1, g = 2.30, and R = 8.90 × 10−5 for 5. For clear comparison, the structural and magnetic parameters of complexes 1−5 are collected in Table 2.

vs T plot above 25 K follows the Curie−Weiss law with C = 3.46 cm3 mol−1 K and θ = −43.12 K (Figures S16). The magnetic behaviors of 4 are typical of antiferromagnetic interactions between CoII ions. The increase of χM value below 4 K could be attributed to the presence of a paramagnetic impurity and weak ferromagnetism.34 According to the structural data, compounds 1, 3, and 4 can magnetically be handled as infinite uniform chains in which magnetic coupling is exchanged through the bis-chelating imidazoledicarboxylate bridges. The interchain magnetic interactions in 2D polymers 3 and 4 should be negligible because the long CoII··· CoII separations across the long bpy and pbim linkers exclude efficient magnetic couplings. For 1, 3, and 4, their intrachain magnetic interaction (J) can be evaluated using the classical spin expression derived by Fisher for isotropic Heisenberg chains (H = −J∑SiSi+1):28,50,51 χ chain = [Ng 2β 2S(S + 1)/3kT ][(1 + u)/(1 − u)]

Table 2. Interchain and Intrachain Distances between Two Adjacent CoII or between Two Adjacent NiII and the Fitting Values of the Intrachain Magnetic Interaction of Complexes 1−5a

compounds

interchain distance between two adjacent metal centers (Å)

intrachain distance between two adjacent metal centers (Å)

fitting value of the intrachain magnetic interaction (cm−1)

1 2 3 4 5

6.372(4) 6.417(3) 11.400(2) 10.615(2) 10.60(6)

6.5274(6) 6.4170(3) 6.5143(4) 6.469(2) 6.39(3)

−4.89 −17.8 −6.55 −7.35 −19.6

(1)

where u is the well-known Langevin function defined as u = coth[JS(S + 1)/kT] − kT/[JS(S + 1)] with S = 3/2. The best fit of the experimental data of 1 and 3 above 25 K to eq 1 gives the following parameters: J = −4.89 cm−1, g = 2.46, and R = 1.48 × 10−2 for 1; J = −6.55 cm−1, g = 2.67, and R = 2.37 × 10−2 for 3 (the agreement factor, R = ∑[(χMT)obsd − (χMT)calc]2/ ∑[(χMT)obsd]2). For 4, further introducing the ρ parameter, denoting the molar fraction of a magnetically dilute impurity to reproduce the experimental data above 25 K, the best fitting parameters are J = −7.35 cm−1, g = 2.66, ρ = 0.08, and R = 2.71 × 10−3. It should be mentioned that the fitting of χMT for cobalt(II) compounds 1, 3, and 4 is done above 25 K and is not

a

The interchain distance between two adjacent metal centers for 1D polymers 1 and 2 means the interchain shortest distance between two adjacent metal centers, and that for 2D polymers 3−5 means the distance of two metal centers separated by the ancillary bridge bpy or pbim. G



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(2) Noh, T. H.; Jung, O. S. Recent Advances in Various Metal− Organic Channels for Photochemistry beyond Confined Spaces. Acc. Chem. Res. 2016, 49, 1835−1843. (3) Kuang, X.; Wang, Z. L.; Sun, X.; Zhang, Y.; Wei, Q. Metal Oxideand N-Codoped Carbon Nanosheets: Facile Synthesis Derived from MOF Nanofibers and Their Application in Oxygen Evolution. Chem. Commun. 2018, 54, 264−267. (4) Liu, J. L.; Zhu, D. D.; Guo, C. X.; Vasileff, A.; Qiao, S. Z. Design Strategies toward Advanced MOF-Derived Electrocatalysts for EnergyConversion Reactions. Adv. Energy Mater. 2017, 7, 1700518. (5) Lee, K. J.; Lee, J. H.; Jeoung, S.; Moon, H. R. Transformation of Metal−Organic Frameworks/Coordination Polymers into Functional Nanostructured Materials: Experimental Approaches Based on Mechanistic Insights. Acc. Chem. Res. 2017, 50, 2684−2692. (6) Wang, M.; Guo, L.; Cao, D. Metal−Organic Framework as Luminescence Turn-on Sensor for Selective Detection of Metal Ions: Absorbance Caused Enhancement Mechanism. Sens. Actuators, B 2018, 256, 839−845. (7) Pang, J.; Yuan, S.; Qin, J.; Liu, C.; Lollar, C.; Wu, M.; Yuan, D.; Zhou, H.-K.; Hong, M. Control the Structure of Zr-Tetracarboxylate Frameworks through Steric Tuning. J. Am. Chem. Soc. 2017, 139, 16939−16945. (8) Li, L.; Zhang, S.; Xu, L.; Wang, J.; Shi, L.-X.; Chen, Z.-N.; Hong, M.; Luo, J. Effective Visible-Light Driven CO2 Photoreduction via a Promising Bifunctional Iridium Coordination Polymer. Chem. Sci. 2014, 5, 3808−3813. (9) Li, Y.-P.; Wang, X.-X.; Li, S.-N.; Sun, H.-M.; Jiang, Y.-C.; Hu, M.C.; Zhai, Q.-G. The Power of Heterometalation through Lithium for Helix Chain-Based Noncentrosymmetric Metal−Organic Frameworks with Tunable Second-Harmonic Generation Effects. Cryst. Growth Des. 2017, 17, 5634−5639. (10) Dong, X.-Y.; Li, B.; Ma, B.-B.; Li, S.-J.; Dong, M.-M.; Zhu, Y.-Y.; Zang, S.-Q.; Song, Y.; Hou, H.-W.; Mak, T. C. W. Ferroelectric Switchable Behavior through Fast Reversible De/adsorption of Water Spirals in a Chiral 3D Metal−Organic Framework. J. Am. Chem. Soc. 2013, 135, 10214−10217. (11) Huang, R.-W.; Wei, Y.-S.; Dong, X.-Y.; Wu, X.-H.; Du, C.-X.; Zang, S.-Q.; Mak, T. C. W. Hypersensitive Dual-Function Luminescence Switching of a Silver-Chalcogenolate Cluster-Based Metal−Organic Framework. Nat. Chem. 2017, 9, 689−697. (12) Kahn, O. Molecular Magnetism; VCH: New York, 1993. (13) Miller, J. S.; Drillon, M. Magnetism: Molecules to Materials; Wiley-VCH: Weinheim, Germany, 2002−2005; Vols. I−V. (14) Liu, K.; Zhang, X.; Meng, X.; Shi, W.; Cheng, P.; Powell, A. K. Constraining the Coordination Geometries of Lanthanide Centers and Magnetic Building Blocks in Frameworks: A New Strategy for Molecular Nanomagnets. Chem. Soc. Rev. 2016, 45, 2423−2439. (15) Deng, Y.-K.; Su, H.-F.; Xu, J.-H.; Wang, W.-G.; Kurmoo, M.; Lin, S.-C.; Tan, Y.-Z.; Jia, J.; Sun, D.; Zheng, L.-S. Hierarchical Assembly of a {MnII15MnIII4} Brucite Disc: Step-by-Step Formation and Ferrimagnetism. J. Am. Chem. Soc. 2016, 138, 1328−1334. (16) Guo, L.-Y.; Su, H.-F.; Kurmoo, M.; Tung, C.-H.; Sun, D.; Zheng, L.-S. Core−Shell {Mn7⊂(Mn,Cd)12} Assembled from Core {Mn7} Disc. J. Am. Chem. Soc. 2017, 139, 14033−14036. (17) Kurmoo, M. Magnetic Metal−Organic Frameworks. Chem. Soc. Rev. 2009, 38, 1353−1379. (18) Weng, D. F.; Wang, Z. M.; Gao, S. Framework-Structured Weak Ferromagnets. Chem. Soc. Rev. 2011, 40, 3157−3181. (19) Arnold, P. L. Single-Molecule Magnets Uranyl Steps in the Ring. Nat. Chem. 2012, 4, 967−969. (20) Habib, F.; Murugesu, M. Lessons Learned from Dinuclear Lanthanide Nano-Magnets. Chem. Soc. Rev. 2013, 42, 3278−3288. (21) Zhang, P.; Guo, Y.-N.; Tang, J. Recent Advances in DysprosiumBased Single Molecule Magnets: Structural Overview and Synthetic Strategies. Coord. Chem. Rev. 2013, 257, 1728−1763. (22) Zhao, L.; Wu, J.; Ke, H.; Tang, J. Family of Defect-Dicubane Ni4Ln2 (Ln = Gd, Tb, Dy, Ho) and Ni4Y2 Complexes: Rare Tb(III) and Ho(III) Examples Showing SMM Behavior. Inorg. Chem. 2014, 53, 3519−3525.

CONCLUSION In summary, five new one- and two-dimensional coordination frameworks based on the magnetic single chains of imidazoledicarboxylate-bridged cobalt(II)/nickel(II) have been successfully synthesized from H3L ligand and Nheterocyclic ancillary ligands bpy and pbim. First, the doubly deprotonated (HL)2− ligands in all compounds adopt the same μ-kN,O:kN′,O′ coordination mode, showing very interesting coordination orientation in the construction of those coordination polymers. Second, the formation of (HL)2−bridged linear chains or helical chains is mainly dependent on the trans- or cis-chelation of two (HL)2− ligands around the same metal center, which could be finely tuned by the structural features of auxiliary ligands used. Magnetostructural analyses have been disclosed that the bis-N,O-chelating imidazoledicarboxylates of (HL)2− bridges transmit antiferromagnetic interactions along the (HL)2−-bridged metal−organic polymer chains with the spin-coupling constants of −4.89, −17.8, −6.55, −7.35, and −19.6 cm−1 for 1−5, respectively. Notably, the μkN,O:kN′,O′ coordination mode of (HL)2− ligand dominates the assembly of metal−organic frameworks as well as the magnetic exchange between the paramagnetic ions in those magnetic chains, but the magnetic-exchange coupling depends strongly on the nature of the metal centers.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.8b00174. Additional structural figures for the related compounds, the TGA curves and PXRD patterns, IR spectra, selected bond lengths and angles (PDF) Accession Codes

CCDC 1821191−1821194 and 1823900 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +86 0371 67783126. ORCID

Benlai Wu: 0000-0003-1354-3365 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the National Natural Science Foundation of China (21271157) and the Foundation and Research in Cutting-Edge Technologies in the Project of Henan Province (122300410092).

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