Template-Assisted Synthesis of Co,Mn-MOFs with Magnetic ... - NSFC

Article pubs.acs.org/crystal

Template-Assisted Synthesis of Co,Mn-MOFs with Magnetic Properties Based on Pyridinedicarboxylic Acid Yanyan Liu, Huijun Li, Yi Han, Xiaofeng Lv, Hongwei Hou,* and Yaoting Fan Department of Chemistry, Zhengzhou University, Zhengzhou 450052, P. R. China S Supporting Information *

ABSTRACT: To investigate the influence of organic molecules with reactive functional groups as templates on the structures of the resulting MOFs, four novel complexes based on the pyridyl carboxylic acid ligand 5-(pyridin-4-yl)isophthalic acid (H2pyip), namely, [Mn3(pyip)2(HCOO)2(H2O)2]n (1), {[Co(pyip)(H2O)]· H2O}n (2), {[Mn2(pyip)2(H2O)4]·5H2O}n (3), and [Co(pyip)(EtOH)(H2O)]n (4), have been synthesized under solvothermal conditions. In the presence of 4,4′-bipyridyl as the template, 3D coordination framework 1 with the Schläfli symbol of (4·6·7) (42·5·65·73·82·9·11) was obtained. Using cyanoacetic acid as the template, we obtained 2D double-layered structure 2 with the Schläfli symbol of (43) (46·66·83). 3 and 4 are prepared in the absence of a templating agent. 3 features an infinite 2D network with a 1D water chain penetrating the 1D channel and further results in a 3D supramolecule through hydrogen-bond interactions. 4 contains two independent 2D networks that are further connected to a 2D double-layered supramolecular framework by hydrogen bonds. The template-assisted method is a potential approach for obtaining specific intriguing complexes that might be difficult to access by routine synthetic methods. Magnetic investigations revealed that both 1 and 2 exhibit weak antiferromagnetic interactions mediated by pyip2−.

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INTRODUCTION The design and construction of novel metal−organic frameworks (MOFs) is considered as one of the most important issues in coordination chemistry, because MOFs have intriguing aesthetic structures and topological features1 with wide potential applications, such as molecular magnetism,2 heterogeneous catalysis,3 gas storage,4 and photoluminescent materials.5 Generally, MOFs are constructed through the coordination of metal ions and organic linkers.6 To obtain novel MOFs, much effort has been devoted to the design and modification of secondary building units (SBUs) favoring organic linkers. The well-known materials M2(O2C)4, Zn4O, and M3(μ3-O) have been widely utilized as paddle-wheel, octahedral, and triangularshaped SBUs to construct intriguing frameworks in particular solvent systems.7 Recently, template-assisted synthesis has attracted much attention as a promising approach owing to the preparation of tunable structures or structures that might be difficult to access by routine synthetic methods.8 Although a large number of MOFs have been produced by this method, such MOFs have been formed with inert organic molecules or inorganic ions as templating agents.9 MOFs generated using organic molecules with reactive functional groups as templates have been less documented. The main reason is that reactive functional groups of the organic templating agents are probably coordinated with metal ions before target ligands during the assembly process. However, employing such organic molecules as templates is beneficial for the preparation of MOFs with adjustable structures and properties; thus, the corresponding © 2012 American Chemical Society

research has attracted much attention. As has been reported, pyrazine and 4,4′-bipyridine have been used as templates to realize structural conversions from nonporous to porous MOFs,10 whereas the use of butanoic acid as a template for the synthesis of an MOF was found to improve the performance of a poorly adsorbing porous material.11 Inspired by these ideas, in this work, we employed organic molecules with reactive functional groups (4,4′-bipyridyl and cyanoacetic acid) as templating agents and chose 5-(pyridin-4-yl)isophthalic acid (H2pyip) as the target ligand to prepare two novel complexes, namely, [Mn3(pyip)2(HCOO)2(H2O)2]n (1) and {[Co(pyip)(H2O)]·H2O}n (2). In addition, the two new complexes {[Mn2(pyip)2(H2O)4]·5H2O}n (3) and [Co(pyip)(EtOH)(H2O)]n (4) were also isolated without a templating agent. Magnetic studies revealed that 1 exhibits weak antiferromagnetic interactions and that an efficient magnetic superexchange pathway mainly results from the trinuclear units. 2 also displays weak antiferromagnetic exchange, in which the main pathway of magnetic transmission is associated with the two Co ions in dinuclear units.

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EXPERIMENTAL SECTION

Materials and Physical Measurements. All starting materials were purchased commercially and used without purification. Elemental Received: February 17, 2012 Revised: May 22, 2012 Published: May 24, 2012 3505

dx.doi.org/10.1021/cg300237e | Cryst. Growth Des. 2012, 12, 3505−3513

Crystal Growth & Design

Article

Table 1. Crystallographic Data for Complexes 1−4

a

parameter

1

2

3

4

empirical formula formula weight crystal system space group T (K) a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (Mg/m3) F(000) R(int) data/restraints/parameters goodness-of-fit on F2 final Ra indices [I > 2σ(I)] R indices (all data)

C28H18Mn3N2O14 773.28 monoclinic P2(1)/c 293(2) 11.140(2) 17.579(4) 7.8365(16) 90 106.23(3) 90 1473.4(5) 2 1.743 778 0.0493 2744/4/220 1.094 R1 = 0.0545, wR2 = 0.1407 R1 = 0.0707, wR2 = 0.1527

C13H8CoNO6 335.15 triclinic P1̅ 293(2) 7.2133(14) 10.076(2) 10.213(2) 113.83(3) 99.51(3) 104.30(3) 627.9(2) 2 1.773 340 0.0359 2949/7/202 1.066 R1 = 0.0613, wR2 = 0.1916 R1 = 0.0898, wR2 = 0.2859

C26H32Mn2N2O17 754.42 triclinic P1̅ 293(2) 11.023(2) 11.495(2) 13.324(3) 104.17(3) 96.75(3) 108.01(3) 1522.1(5) 2 1.646 776 0.0519 7213/58/478 1.135 R1 = 0.0763, wR2 = 0.1791 R1 = 0.0914, wR2 = 0.1904

C15H14CoNO6 364.21 triclinic P1̅ 293(2) 10.096(2) 10.992(2) 15.649(3) 86.29(3) 73.19(3) 65.78(3) 1513.2(5) 4 1.599 748 0.0313 7187/10/428 1.107 R1 = 0.0653, wR2 = 0.1529 R1 = 0.0797 wR2 = 0.1634

R1 = ∑||Fo| − |Fc||/∑|Fo|; wR2 = [∑(||Fo| − |Fc||)2/∑w|Fo|2]1/2. EtOH (3 mL), and H2O (2 mL) in a Teflon-lined stainless steel vessel (12 mL). The vessel was heated to 80 °C for 72 h and then cooled to room temperature at a rate of 5 °C h−1. Colorless crystals of 3 were isolated by washing with DMF and were then dried in vacuo. The yield was 39.4% based on H2pyip. Anal. Calcd for C26H32Mn2N2O17 (%): C, 41.36; H, 4.24; N, 3.71. Found: C, 41.42; H, 4.32; N, 3.85. IR (KBr, cm−1): 3385 (m), 1617 (s), 1560 (m), 1506 (m), 1445 (m), 1416 (w), 1374 (m), 1302 (w), 1226 (w), 1104 (w), 1086 (m), 1016 (m), 840 (m), 777 (s), 735 (s), 688 (w), 640 (s), 565 (w), 509 (w), 443 (w). Preparation of [Co(pyip)(EtOH)(H2O)]n (4). The same synthetic procedure as used for 3 was performed with Co(NO3)2·6H2O (0.0437 g, 0.15 mmol) instead of MnCl2·4H2O. The resulting pink prism-like crystals of 4 were washed with DMF and dried in vacuo. The yield was 40.2% based on H2pyip. Anal. Calcd for C15H14CoNO6 (%): C, 49.56; H, 3.85; N, 3.85. Found: C, 49.64; H, 3.94; N, 3.91. IR (KBr, cm−1): 3448 (m), 2973 (w), 2360 (w), 1890 (w), 1615 (s), 1578 (w), 1506 (m), 1453 (m), 1364 (m), 1228 (w), 1226 (w), 1081 (m), 1045 (m), 837 (s), 775 (s), 730 (s), 648 (s), 566 (m), 508 (m), 441 (m). Crystal Data Collection and Refinement. Crystal data for 1−4 were collected on a Rigaku Saturn 724 charge-coupled device (CCD) diffractomer (Mo Kα, λ = 0.71073 Å) at temperature of 20 ± 1 °C. The structures were solved by direct methods and refined with a fullmatrix least-squares technique based on F2 with the SHELXL-97 crystallographic software package.12 All non-hydrogen atoms were refined anisotropically, whereas hydrogen atoms were located and refined geometrically. Table 1 lists the crystallographic crystal data and structure processing parameters of the polymers. Selected bond lengths and bond angles are also reported in Table 2.

analyses (C, H, and N) were performed on a FLASH EA 1112 elemental analyzer. IR spectra were recorded in the range of 400− 4000 cm−1 on a Bruker Tensor 27 spectrophotometer using KBr pellets. Thermogravimetric/differential scanning calorimetry (TG/ DSC) measurements were performed by heating the sample on a Netzsch STA 409PC differential thermal analyzer. Powder X-ray diffraction (XRD) patterns were recorded on a Bruker D8 advance scanning electron microscope with Cu Kα radiation (λ = 1.54 Å) and a scan rate of 4°/min. Variable-temperature magnetic susceptibilities were measured with an MPMS XL-7 superconducting quantum interference device (SQUID) magnetometer. Diamagnetic corrections were made with Pascal’s constants for all constituent atoms. Syntheses. Preparation of [Mn3(pyip)2(HCOO)2(H2O)2]n (1). A solid mixture of 5-(pyridin-4-yl) isophthalic acid (H2pyip, 0.0122 g, 0.05 mmol), 4,4′-bipyridyl (4,4′-bpy, 0.0078 g, 0.05 mmol), and MnCl2·4H2O (0.0297 g, 0.15 mmol) was dissolved in dimethylformamide (DMF, 3 mL), EtOH (3 mL), and H2O (2 mL) in a Teflon-lined stainless steel vessel (12 mL). The vessel was heated to 120 °C for 72 h and then cooled to room temperature at a rate of 5 °C h−1. The resulting colorless prism-like crystals of 1 were washed with DMF and dried in vacuo. The yield was 30.2% based on H2pyip. Anal. Calcd for C28H18Mn3N2O14 (%): C, 43.57; H, 2.33; N, 3.63. Found: C, 43.40; H, 2.21; N, 3.47. IR (KBr, cm−1): 3363 (m), 1614 (s), 1557 (s), 1505 (m), 1442 (m), 1415 (w), 1386 (m), 1302 (m), 1257 (w), 1103 (w), 1081 (w), 1048 (w), 937 (w), 881 (m), 837 (m), 734 (s), 643 (s), 572 (w), 443 (w). Preparation of {[Co(pyip)(H2O)]·H2O}n (2). A solid mixture of 5-(pyridin-4-yl) isophthalic acid (H2pyip, 0.0122 g, 0.05 mmol), cyanoacetic acid (0.0043 g, 0.05 mmol), and Co(NO3)2·6H2O (0.0437 g, 0.15 mmol) was dissolved in DMF (3 mL), EtOH (3 mL), and H2O (2 mL) in a Teflon-lined stainless steel vessel (12 mL). The vessel was heated to 130 °C for 72 h and then cooled to room temperature at a rate of 5 °C h−1. The resulting pink prism-like crystals of 2 were washed with DMF and dried in vacuo. The yield was 34.5% based on H2pyip. Anal. Calcd for C13H8CoNO6 (%): C, 46.83; H, 2.40; N, 4.20. Found: C, 46.70; H, 2.24; N, 4.14. IR (KBr, cm−1): 3386 (m), 1605 (w), 1507 (w), 1458 (m), 1407 (m), 1339 (m), 1278 (m), 1229 (w), 1154 (m), 1025 (m), 841 (m), 775 (s), 646 (s), 544 (w), 505 (m), 464 (m), 409 (w). Preparation of {[Mn2(pyip)2(H2O)4]·5H2O}n (3). A solid mixture of 5-(pyridin-4-yl)isophthalic acid (H2pyip, 0.0122 g, 0.05 mmol) and MnCl2·4H2O (0.0297 g, 0.15 mmol) was dissolved in DMF (3 mL),

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RESULTS AND DISCUSSION Design and Synthesis. As an excellent ligand for building MOFs with interesting structures and promising properties, H2pyip has carboxylate O atoms and a pyridine N atom, which result in varied coordination modes and strong coordination abilities with respect to metal ions.13−15 It is worth emphasizing that template-assisted synthesis has been demonstrated to be a powerful method for the construction of novel MOFs. The use of MnCl2·4H2O and 4,4′-bipyridyl as a template led to 1 at 120 °C. 2 was obtained using Co(NO3)2·6H2O and employing cyanoacetic acid as a template at 130 °C. When the reactions were carried out in the absence of templating agent, no crystals 3506



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Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes 1−4a Complex 1 Mn(1)−O(3) Mn(1)−O(7) Mn(1)−O(2) Mn(2)−O(6)#1 Mn(2)−O(1)#4 Mn(2)−O(4) O(3)−Mn(1)−O(5) #1 O(5)#1−Mn(1)−O (7) O(5)#1−Mn(1)−N (1)#2 O(6)#3−Mn(2)−O (1)#4 O(6)#3−Mn(2)−O (4) Mn(2)−O(1)−Mn(1)

2.130(4) 2.190(4) 2.266(3) 2.130(3) 2.184(3) 2.192(4) 94.94(15) 85.20(16)

O(3)−Mn(1)−N(1) #2 93.54(13) O(7)−Mn(1)−N(1) #2 82.17(13) O(1)#4−Mn(2)−O (1) 88.29(15) O(1)#4−Mn(2)−O (4) 102.95(12) O(1)−Mn(2)−O(4) Complex 2

N(1)−Co(1)#1 O(3)−Co(1)#3 Co(1)−O(1) Co(1)−O(3)#3 Co(1)#2−O(3)−Co (1)#3 O(3)#4−Co(1)−O (1) O(3)#4−Co(1)−O (5) O(1)−Co(1)−O(5)

2.073(4) 2.242(4) 2.095(4) 2.242(4) 102.91(15)

O(5)−Co(1)−O(3) #3 N(1)#5−Co(1)−O (2) O(5)−Co(1)−O(2)

170.27(15)

Mn(1)−O(1) Mn(1)−O(6)#1 Mn(1)−O(8)#2 Mn(1)−O(5)#1

Mn(1)−O(5)#1 Mn(1)−N(1)#2 Mn(1)−O(1) Mn(2)−O(6)#3 Mn(2)−O(1) Mn(2)−O(4)#4 O(3)−Mn(1)−O(7)

162.96(16) 95.74(17) 87.96(17)

152.29(14)

O(3)−Co(1)#2 Co(1)−N(1)#5 Co(1)−O(5) Co(1)−O(2) O(3)#4−Co(1)−N (1)#5 N(1)#5−Co(1)−O (1) N(1)#5−Co(1)−O (5) O(3)#4−Co(1)−O (3)#3 O(3)#4−Co(1)−O (2) O(1)−Co(1)−O(2)

89.00(16)

O(3)#3−Co(1)−O (2) Complex 3

2.146(4) 2.226(3) 2.316(3) 2.496(3)

Mn(1)−O(2) Mn(1)−N(1) Mn(1)−O(7)#2 Mn(2)−O(3)

Complex 3 2.168(3) 2.220(4) 2.325(3) 2.130(3) 2.184(3) 2.192(4) 176.71(13) 93.28(13)

Mn(2)−O(4) Mn(2)−N(2)#1 Mn(2)−O(10) O(1)−Mn(1)−O(2)

2.181(4) 2.300(3) 2.349(3) 175.30(15)

O(2)−Mn(1)−O(6) #1 O(2)−Mn(1)−N(1)

91.68(16)

180.00(19) 88.68(13) 91.32(13)

Co(1)−O(4)#1 Co(1)−N(1)#2 Co(1)−O(9) Co(2)−O(8)#3 Co(2)−O(12) Co(2)−O(6) O(4)#1−Co(1)−O (11) O(11)−Co(1)−N(1) #2 O(11)−Co(1)−O(1)

2.044(2) 2.099(3) 2.161(3) 2.029(3) 2.120(3) 2.188(3) 92.54(13)

2.095(3) 2.150(3) 2.218(3) 2.091(3) 2.160(3) 2.218(3) 115.37(12)

O(4)#1−Co(1)−O (9) O(8)#3−Co(2)−N (2)#4 N(2)#4−Co(2)−O (12) N(2)#4−Co(2)−O (10) N(2)#4−Co(2)−O (6)

85.06(12)

Co(1)−O(11) Co(1)−O(1) Co(1)−O(2) Co(2)−N(2)#4 Co(2)−O(10) Co(2)−O(5) O(4)#1−Co(1)−N (1)#2 O(4)#1−Co(1)−O (1) N(1)#2−Co(1)−O (1) O(11)−Co(1)−O(9) O(8)#3−Co(2)−O (12) O(8)#3−Co(2)−O (10) O(12)−Co(2)−O (10) O(12)−Co(2)−O(6)

90.18(12)

O(4)−Mn(2)−N(2) #1 O(3)−Mn(2)−O(9)

2.033(3) 2.073(4) 2.123(4) 2.261(4) 104.32(16) 92.09(15) 92.64(16) 77.09(15) 103.03(14)

90.88(13) 91.12(13)

60.31(13) 86.30(13)

2.202(4) 2.281(3) 2.362(3) 2.168(4)

85.81(14) 135.76(12)

O(4)−Mn(2)−O(11)

89.76(14)

2.216(3) 2.314(3) 2.526(3) 90.40(13)

O(6)#1−Mn(1)−N (1) 90.65(14) O(2)−Mn(1)−O(8) #2 136.47(11) N(1)−Mn(1)−O(8) #2 176.67(13) O(3)−Mn(2)−O (11) 92.30(14) O(3)−Mn(2)−N(2) #1 88.43(14) O(11)−Mn(2)−N (2)#1 92.32(14) O(4)−Mn(2)−O(9) Complex 4

O(1)−Mn(1)−O(8) #2 O(6)#1−Mn(1)−O (8)#2 O(3)−Mn(2)−O(4)

90.00(14)

Mn(2)−O(11) Mn(2)−O(9) Mn(2)−O(12) O(1)−Mn(1)−O(6) #1 O(1)−Mn(1)−N(1)

117.99(12) 91.40(13) 89.81(12) 149.26(11)

90.74(15) 87.70(11) 90.82(13) 88.54(14) 135.35(12) 89.19(12)

153.26(10) 91.05(12) 177.35(11)

88.24(11) 178.34(11) 93.04(13)

Symmetry transformations used to generate equivalent atoms: For 1, #1 −x + 2, y − 1/2, −z + 3/2; #2 x + 1, y, z + 1; #3 x, −y + 1/2, z − 1/2; #4 −x + 2, −y, −z + 1. For 2, #1 x + 1, y, z + 1; #2 x, y − 1, z; #3 −x, −y + 1, −z + 1; #4 x, y + 1, z; #5 x − 1, y, z − 1. For 3, #1 x, y + 1, z; #2 x − 1, y + 1, z + 1. For 4, #1 x + 1, y, z; #2 x + 1, y − 1, z; #3 x − 1, y, z; #4 x − 1, y + 1, z.

a

Crystal Structure. [Mn3(pyip)2(HCOO)2(H2O)2]n (1). Crystal structure determination revealed that 1 crystallizes in the monoclinic crystal system of the P2(1)/n space group. 1 displays a (3,6)-connected three-dimensional (3D) noninterpenetrating framework built from linear trinuclear manganese clusters and pyip2− ligands (Figure 1a). The asymmetric unit contains two independent Mn atoms that adopt different coordination environments (Figure 1b). Mn1 is in a distorted octahedral geometry, coordinated by three carboxylate O atoms, one O atom of water, one O atom of a formate ions, and one pendant pyridyl N atom from pyip2−; Mn2 is also six-coordinated but by four carboxylate O atoms and two O atoms of two formate ions. The Mn−O bond lengths vary from 2.130(3) to 2.325(3) Å, and the Mn−N bond length is 2.220(4) Å, which are in the normal ranges in both cases. It is noticeable that the formate ions were generated from the in situ hydrolysis of DMF. This phenomenon is always found under solvothermal conditions.17−19 The carboxylate groups

or precipitates were produced. This fact indicates that the templating agents were crucial for the formation of these MOFs. Interestingly, when we reduced the temperature to 80 °C, the two aforementioned reaction systems, in the absence of templating agents, gave rise to the two new coordination polymers 3 and 4, respectively. This means that regulating the temperature is necessary for the preparation of these new complexes. Generally, the solvents used are limited to water or mixtures of water with other common organic solvents (MeOH, EtOH, MeCN, DMF) to facilitate the crystallization of the products in the process of preparing MOFs. In this contribution, all of the complexes were prepared under solvothermal conditions (DMF/EtOH/H2O = 3:3:2). DMF was employed as a weak base to deprotonate H2pyip and provide automatic control of the acid/base balance of the solution.16 In addition, DMF can provide formate ions at high temperature to coordinate with metal ions.17−19 The formate ions of 1 were generated from the in situ hydrolysis of DMF. 3507



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Figure 1. (a) Two-dimensional (2D) layer built from trinuclear linear Mn(II) units and pyip2− ligands. (b) Coordination environment around trinuclear linear Mn(II) units in 1. (c) Three-dimensional (3D) stacking supramolecular network with one-dimensional (1D) lozenge-shaped channels. The polyhedral presentation indicates the coordination environments for trinuclear linear Mn(II) units. (d) 3D topology (3,6)-connected net with the Schläfli symbol of (4·6·7) (42·5·65·73·82·9·11).

Chart 1. Coordination Modes of the Carboxylate Group in H2pyip

in each pyip2− ligand adopt μ2-η2:η1 and syn−syn-μ2-η1:η1 coordination modes. Meanwhile, the formate ions link Mn1 and Mn2 in the syn−syn-μ2-η1:η1 coordination mode (type I, Chart 1). The most striking feature of 1 is that two formate ions and four sharing carboxylate groups ligate two Mn1 and one Mn2 atoms to form a linear Mn(II) trimer with an intratrimer Mn···Mn separation of 3.5288(12) Å. The Mn1−O−Mn2 angle is 102.95(12)° for the μ2-η2:η1-carboxylate oxygen bridges. In 1, each Mn(II) trimer is ligated by two pyridyl and four carboxylate ends from six pyip groups, and each pyip group links

three trimers to yield a 3D framework (Figure 1c), arranged along an axis to form one-dimensional (1D) lozenge-shaped channels with a diameter of ∼11 Å. To the best of our knowledge, 3D coordination polymers with linear Mn(II) trimers have rarely been reported until now.24,26 The overall framework of 1 can be described as a (3,6)-connected rtl net with a Schläfli symbol of (4·6·7) (42·5·65·73·82·9·11), considering pyip2− and the Mn(II) trimer as 3- and 6-connected nodes, respectively (Figure 1d). {[Co(pyip)(H2O)]·H2O}n (2). Crystal structure determination revealed that 2 forms a two-dimensional (2D) double-layered 3508



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structure in the triclinic crystal system of space group P1.̅ In 2, there is only one independent metal Co(II) center, which is sixcoordinated and linked by four carboxylate O atoms from three pyip2− ligands, one pyridyl N atom from another pyip2− ligand, and one O atom from one aqua ligand (Figure 2a). The lengths

102.91(15)°. Each Co(II) dinuclear unit is ligated by two pyridyl N atoms and four carboxylate group ends from six pyip2− ligands, and each pyip2− ligand links three Co(II) dinuclear units to form a 2D double-layer network through bridging coordination of carboxylate O atoms (Figure 2b). The overall structure of 2 can be described as an infinite 2D topology (3,6)-connected framework with Schläfli symbol (43) (46·66·83) (Figure 2c) by simplifying Co(II) dinuclear units as six-connected nodes and pyip2− ligands as three-connected nodes. {[Mn2(pyip)2(H2O)4]·5H2O}n (3). 3 crystallizes in a triclinic system with space group P1̅ and exhibits an infinite 2D network. As shown in Figure 3a, the asymmetric unit contains two crystallographically independent Mn(II) centers that adopt similar coordination environments, being surrounded by two pyip2− ligands and five guest H2O molecules. The coordination geometry around Mn1 or Mn2 can be best described as a distorted octahedron defined by three carboxylate O atoms, two O atoms of aqua ligands, and one pyridyl N atom from pyip2−. The Mn−O bond lengths vary in the range of 2.146(4)−2.526(3) Å, and the Mn−N distances are 2.281(3) and 2.300(3) Å, both falling into normal ranges. Each pyip2− ligand takes μ1-η1:η0 and μ1-η1:η1 coordination modes (type III, Chart 1) and links three Mn2+ atoms, giving rise to an extended 2D layer. The neighboring 2D layers with 1D channels are further assembled into a 3D supramolecular architecture (Figure 3d), through hydrogen bonds [O1···O9, 2.782(4) Å; O2···O6, 2.771(5) Å; O3···O8, 2.775(4) Å] between the aqua ligands and the carboxylate oxygen atoms. It is noticeable that five lattice water molecules are connected to furnish a 1D water chain, that runs through the 1D channels (Figure 3d). In addition, the 3D supramolecular network can be consolidated through the strong hydrogen bonding among the 1D water chains, aqua ligands, and carboxylate oxygen atoms, in which five lattice water molecules show three- (O13, O14) or four(O15, O16, O17) coordinate hydrogen-bonding configurations (Figure 3b). Moreover, the 1D water chains interconnect the adjacent polymeric chains through hydrogen bonds between lattice water molecules and aqua ligands to form circle-like channels, and the pyridyl groups of pyip2− ligands reside in the channels (Figure 3c). A particularly interesting feature of this framework is the presence of water chains formed by strong hydrogen-bonding between water molecules and aqua ligands or carboxylate oxygen atoms. In addition, water chains play important roles in the formation or reinforcement of high-dimensional supramolecular architectures. Recently, 1D water chains penetrating channels have been found in some examples of such architectures, which is the enrichment of crystal engineering.22,23 [Co(pyip)(EtOH)(H2O)]n (4). Single-crystal X-ray diffraction analysis revealed that 4 is an infinite 2D network that crystallizes in the triclinic space system in space group P1̅. In 4, two independent 2D networks containing Co1 or Co2 and pyip2− ligands exist. It is worth noting that the two Co atoms (Co1 or Co2) have similar coordination environments, being octahedrally coordinated and bonded to three carboxylate O atoms from two different pyip2− ligands, one O atom of one aqua ligand, one O atom from EtOH, and one N atom from pyip2− (Figure 4a). The lengths of Co−O bonds vary from 2.029(3) to 2.218(3) Å, and the Co−N distances are 2.091(3) and 2.099(3) Å, which are in the normal ranges in both cases. The carboxylate groups in each pyip2− ligand connect Co1 or Co2, adopting μ1-η1:η0 and μ1-η1:η1 coordination

Figure 2. (a) Coordination environment around dinuclear Co(II) units in 2. (b) 2D double-layered structure. (c) 2D topology (3,6)connected framework with the Schläfli symbol (43) (46·66·83).

of the Co−O bonds fall in the range 2.033(3)−2.261(4) Å, and the Co−N distance is 2.073(4) Å, both of which are similar to those reported for cobalt carboxylate complexes.20,21 The carboxylate groups in each pyip2− ligand adopt a μ2-η2:η0 coordination mode (type II, Chart 1) to connect the two Co(II) ions and generate a rectangle-shaped dinuclear unit with a Co···Co distance of 3.3458(15) Å and a Co−O−Co angle of 3509



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Figure 3. (a) Asymmetric unit and atom labeling scheme of 3. (b) Hydrogen bonds between the aqua ligands and carboxylate oxygen atoms. (c) 2D supramolecular layer of 3 with circle-like channels. (d) 3D stacking supramolecular network constructed from the hydrogen bonds. The polyhedral presentation indicates a 1D water chain formed by five lattice water molecules.

modes (type III, Chart 1). Each pyip2− ligand links three Co2+ atoms, and each Co2+ atom connects three pyip2− ligands. Thus, a 2D framework with a (3,3) topology can be formed. It should be noted that the hydrogen bonds between aqua ligands and coordinated O atoms [O6···O9, 2.778(4) Å; O2···O10, 2.802(4) Å] further connect adjacent 2D networks to generate a 2D double-layered framework (Figure 4b), which suggests that the hydrogen bonds have a positive effect on the final structure of the complex. XRD Patterns and Thermal Analyses. To confirm the phase purity of these complexes, powder XRD patterns were recorded for complexes 1−4, and they were found to be comparable to corresponding simulated patterns calculated

from the single-crystal diffraction data (Figure S1 of the Supporting Information), indicating the phase purity of each bulk sample. The thermogravimetric analysis (TGA) curve of 1 shows weight losses of 4.27% and 12.37% from 110 to 305 °C, corresponding to the losses of coordinated water (calculated, 4.65%) and formate ions (calculated, 12.67%); above this temperature, the framework begins to decompose, and the remaining weight is ascribed to the formation of MnO (observed, 27.92%; calculated, 27.54%). The TGA curve of 2 reveals a weight loss of 11.11% in the range of 172−375 °C, consistent with the loss of guest and coordinated water (calculated, 10.81%); the further weight loss represents the decomposition of organic components, and then the remaining 3510



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Figure 5. Temperature dependence of the magnetic susceptibility of 1 in the form of χM and χM−1 versus T in the temperature range 2−300 K.

syn−syn-μ2-η1:η1 coordination mode and one carboxyl group in μ2-η1:η2 coordination mode with a Mn1−O−Mn2 angle of 102.95(12)°. (c) The Mn1···Mn2 separation is 3.5288(12) Å in the trinuclear unit, and the shortest Mn···Mn distance between adjacent units linked by pyip2− is 7.9427(15) Å. Taking these characteristics into consideration, we speculate that the efficient magnetic superexchange pathway mainly results from the trinuclear Mn units. The χM and χM−1 versus T plots of 2 are presented in Figure 6. As the temperature decreases, χM increases gradually until it Figure 4. (a) Coordination environment around Co1 and Co2. (b) 2D double-layered structure of hydrogen bonds between aqua ligands and coordinated O atoms in 4.

weight corresponds to the formation of CoO (observed, 22.28%; calculated, 22.51%). For 3, an initial weight loss of 21.38% occurs between 100 and 205 °C due to the loss of guest water and coordinated water (calculated, 21.47%); the second step of weight loss begins at 415 °C, from which the organic groups of 3 were decomposed, and then the remaining weight corresponds to the formation of MnO (observed, 19.04%; calculated, 18.82%). For 4, the weight losses of 5.23% and 12.74% in the range of 110−380 °C are attributed to the release of water (calculated, 4.96%) and EtOH (calculated, 12.67%), respectively; then the framework begins to collapse in the next stage, and the remaining weight corresponds to the formation of CoO (observed, 20.88%; calculated, 20.65%) (Figure S2 of the Supporting Information). Magnetic Studies. The magnetic properties of complexes 1 and 2 were investigated over the temperature range of 2−300 K at an applied field of 2000 Oe. Plots of χM and χM−1 versus T for 1 are shown in Figure 5. Upon cooling, the χM value increased continuously, reaching a maximum of 2.78 cm3 mol−1. This phenomenon is typical for antiferromagnetic interactions. The inverse susceptibility plot is linear and follows the Curie−Weiss law, χM = C/(T − θ), with the Curie constant C = 9.64 cm3 K mol−1 and the Weiss temperature θ = −3.29 K. The small negative θ value indicates that the overall magnetic interactions among the Mn(II) atoms are weakly antiferromagnetic. From the viewpoint of magnetism, it is important to point out some structural features: (a) 1 is a 3D noninterpenetrating framework containing linear trinuclear Mn units (Mn1···Mn2···Mn1). (b) Mn1 and Mn2 in each trinuclear unit are triply bridged by two carboxyl groups in

Figure 6. Temperature dependence of the magnetic susceptibility of 2 in the form of χM and χM−1 versus T in the temperature range 2−300 K.

reaches a value of 0.11 cm3 mol−1 at 29 K; then, it rapidly rises to a maximum value of 1.37 cm3 mol−1 at 2 K. This phenomenon is typical for antiferromagnetic couplings. The magnetic susceptibility obeys the Curie−Weiss law, χM = C/(T − θ), with the Curie constant C = 3.29 cm3 K mol−1 and the Weiss constant θ = −0.39 K in the range of 2−300 K. The small negative Weiss constant suggests overall weak antiferromagnetic interactions in the system. Some structural features should be emphasized for the investigation of the magnetic properties of 2: (a) 2 has a 2D double-layered network that is made up of dinuclear Co units. (b) The two Co atoms in the dinuclear Co unit are bridged by two carboxyl groups in μ2-η2:η0 coordination mode (μ-oxo) with a Co−O−Co angle of 102.91(15)°. (c) The Co···Co distance is 3.3458(15) Å in the dinuclear unit, whereas the shortest distance between the Co ions of adjacent dinuclear 3511



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units is 8.3759(13) Å, so the magnetic interaction of the latter can be neglected. Based on these structural traits, we infer that the main pathway of magnetic transmission for 2 is associated with the two Co ions in the dinuclear unit. Carboxylate ligands display versatile coordination modes, such as syn−syn, syn−anti, anti−anti, and μ-oxo(μ2-η2:η0) coordination modes, so they have been widely used to construct MOFs with interesting magnetic properties.24−26 Studies of the magnetic interactions of complexes have revealed that syn−syn carboxylate conformations can cause antiferromagnetic couplings, whereas weak ferromagnetic or antiferromagnetic interactions are observed in syn−anti and anti−anti conformations.27−29 On the other hand, when the carboxylate coordination mode is μ-oxo(μ2η2:η0), the M−O−M angle has a significant effect on the magnetic exchange.30−32 Weak antiferromagnetic interactions should be observed in μ-oxo(μ2-η2:η0) bridge modes with Cu−O−Cu angles larger than 97.5°, whereas the magnetic coupling should be ferromagnetic for smaller values of this angle.31 When it comes to Ni(II) complexes, antiferromagnetic exchange is observed for Ni− O−Ni angles larger than 93.5°.31 To the best of our knowledge, research on the magneto−structural correlation of Co(II) complexes is insufficiently reliable because of the complication of the large spin−orbit coupling in hexacoordinated Co(II). However, a Co−O−Co angle of 96−99° leads to weak ferromagnetic coupling.30 Considering these features, it is reasonable that the magnetic interaction of 1 is weakly antiferromagnetic because the main magnetic exchange pathway is from trimeric Mn(II) ions through two carboxylate groups in syn−syn-μ2-η1:η1 coordination modes and one carboxylate group in μ2-η2:η1 coordination mode with a larger Mn−O−Mn angle of 102.95(12)°. It is reasonable that the θ value is −0.39 K for 2, which has a Co−O−Co angle of 102.91(15)°, which indicates that there are overall weak antiferromagnetic interactions in this complex.

CONCLUSIONS To study the influence of organic molecules with reactive functional groups as templates on the structures of resulting MOFs, four complexes based on pyridyl carboxylic acid (H2pyip) have been prepared. 1 and 2 exhibit infinite 3D and 2D structures, respectively, with polynuclear metal units and antiferromagnetic properties, whereas 3 and 4 display 2D network structures. Template-assisted synthesis is a potential method for the design and synthesis of interesting MOFs with attractive structures and properties. ASSOCIATED CONTENT

S Supporting Information *

XRD spectra and TGA curves of complexes 1−4. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*Fax: (86) 0371-67761744. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was funded by the National Natural Science Foundation (Nos. 20971110 and 91022013) and the Outstanding Talented Persons Foundation of Henan Province. 3512



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