Synthesis, structure and property of manganese(II) complexes with mixed tetradentate imidazole-containing ligand and benzenedicarboxylate

Inorganica Chimica Acta 363 (2010) 3550–3557

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Synthesis, structure and property of manganese(II) complexes with mixed tetradentate imidazole-containing ligand and benzenedicarboxylate Qin Hua a, Zhi Su a, Yue Zhao a, Taka-aki Okamura b, Guan-Cheng Xu a, Wei-Yin Sun a,*, Norikazu Ueyama b a Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructure, Nanjing University, Nanjing 210093, China b Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan

a r t i c l e

i n f o

Article history: Received 30 March 2010 Received in revised form 7 July 2010 Accepted 7 July 2010 Available online 11 July 2010 Keywords: Manganese(II) complex Mixed ligands Crystal structure Magnetic property

a b s t r a c t Three new coordination complexes [Mn(L)(H2O)2](1,4-BDC)2H2O (1), [Mn(L)0.5(1,4-BDC)]CH3OHH2O (2) and [Mn(L)(H2O)2](1,2-HBDC)22H2O (3) were synthesized by solvothermal reactions of 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L) and 1,4-benzenedicarboxylic acid (1,4-H2BDC) or 1,2-benzenedicarboxylic acid (1,2-H2BDC) with Mn(II) salt, and characterized by single crystal X-ray diffraction, IR, thermogravimetric and elemental analyses. In complexes 1 and 3, each ligand L links four Mn(II) atoms to form two-dimensional (2D) cationic network with non-coordinated 1,4-BDC2 and 1,2-HBDC anions lying in the voids between the two adjacent layers, respectively. The 2D layers are further connected together by hydrogen bonds to give three-dimensional (3D) supramolecular structures. However, the 1,4-BDC2 in 2 acts not only as counteranion, but also as bridging ligand leading to the formation of 2fold interpenetrated 3D framework with pcu (primitive cubic unit) topology. The Mn(II) atoms bridged by carboxylate groups in 2 show antiferromagnetic interactions. Ó 2010 Elsevier B.V. All rights reserved.

1. Introduction Over the past decades, the field of coordination polymers has experienced dramatic growth, which is not only due to their interesting framework structures and topologies, but also because of their intriguing properties and potential applications in magnetism, ion exchange, selective guest inclusion, catalysis and gas storage [1–12]. However, the prediction of structure of coordination polymers is still difficult at present because the assembly reaction of coordination polymers is highly affected by factors such as the coordination geometry of metal centers [13], the structure of organic ligands [14], the ligand-to-metal ratio [15], the reaction temperature [16] and solvents [17], as well as the counteranions [18]. In consequence, further investigations are required for understanding the assembly process of coordination polymers as well as for controlling the structure of the coordination frameworks. On the other hand, the coordination compounds with paramagnetic manganese(II) and carboxylate ligands are of great interest driven by their promising applications in the field of molecular magnetism as well as their potential as model compounds of the active sites of the metalloenzymes in the bioinorganic chemistry [19–21]. The multi-carboxylate ligands can adopt varied coordination modes to accomplish the transmission of the magnetic * Corresponding author. Tel.: +86 25 83593485; fax: +86 25 83314502. E-mail address: [email protected] (W.-Y. Sun). 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.07.012

coupling at different degrees [22] and can further act as hydrogen bonding acceptors or donors to assemble into supramolecular structures [23]. In our previous studies, we have reported multidimensional frameworks with varied structures and topologies using multidentate imidazole-containing ligands [24]. As an extension of our work and further study on Mn(II)-carboxylate complexes, we focus our attention on reactions of flexible tetradentate imidazole-containing ligand 1,2,4,5-tetrakis(imidazol-1ylmethyl)benzene (L), 1,4-benzenedicarboxylic acid (1,4-H2BDC) or 1,2-benzenedicarboxylic acid (1,2-H2BDC) (Scheme 1) with Mn(II) salt in this study. Three new coordination complexes [Mn(L)(H2O)2](1,4-BDC)2H2O (1), [Mn(L)0.5(1,4-BDC)]CH3OHH2O (2), and [Mn(L)(H2O)2](1,2-HBDC)22H2O (3) were synthesized and characterized by X-ray crystallography. The impact of the ligand-to-metal ratio on the structure of the complexes was discussed and the magnetic property of 2 was investigated. 2. Experimental 2.1. Materials and measurements All commercially available chemicals and solvents are of reagent grade and were used as received without further purification. Ligand L was prepared according to the literature method [24a,25]. Elemental analysis for C, H and N were performed on a Perkin–Elmer 240C Elemental Analyzer at the analysis center of

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N N

O

OH

2.3. X-ray crystallography

O

N

OH OH N

The crystallographic data for 1 were collected on a Rigaku RAXIS-RAPID imaging plate diffractometer at 200 K, with graphite-monochromated Mo Ka radiation (k = 0.71075 Å). The structure was solved by direct methods using SIR92 [26] and expanded using Fourier techniques [27]. All the non-hydrogen atoms were refined

N

O N

N

O

(a)

OH

(b)

(c)

Table 1 Crystal data and structure refinements for complexes 1–3.

Scheme 1. Schematic representation of Ligand L (a), 1,4-H2BDC (b) and 1,2-H2BDC (c).

Formula Formula weight T (K) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) Volume (Å3) Z Dcalc (g m3) F(0 0 0) h Range (°) Reflections collected Unique reflections Goodness-of-fit (GOF) R1a [I > 2r(I)] wR2b [I > 2r(I)]

Nanjing University. Thermogravimetric analyses (TGA) were performed on a simultaneous SDT 2960 thermal analyzer under nitrogen with a heating rate of 10 °C min1. FT-IR spectra were recorded in the range of 400–4000 cm1 on a Bruker Vector 22 FT-IR spectrophotometer using KBr pellets. Magnetic measurements for complex 2 in the temperature range of 1.8–300 K were performed on a MPMS-SQUID magnetometer at a field of 2000 Oe on crystalline samples in the temperature settle mode. The diamagnetic contributions of the samples were corrected by using Pascal’s constants.

2.2. Synthesis of the complexes 2.2.1. Synthesis of [Mn(L)(H2O)2](1,4-BDC)2H2O (1) A mixture containing Mn(NO3)24H2O (12.6 mg, 0.05 mmol), L (20.0 mg, 0.05 mmol), 1,4-H2BDC (8.3 mg, 0.05 mmol) and NaOH (4.0 mg, 0.1 mmol) in 10 mL of CH3OH and H2O (v/v 1:1) was sealed in a 16 ml Teflon lined stainless steel container and heated at 120 °C for 3 d. After cooling to the room temperature, clear solution was obtained. Block colorless crystals suitable for X-ray diffraction analysis were isolated with a yield of 48% by slow evaporation at room temperature in two weeks. Anal. Calc. for C30H34N8O8Mn (%): C, 52.25; H, 4.97; N, 16.25. Found: C, 52.38; H, 4.94; N, 16.37%. IR (KBr pellet, cm1): 3423 (m, br), 1639 (m), 1583 (m), 1521 (w), 1376 (s), 1237 (w), 1083 (w), 934 (w), 832 (w), 752 (w), 662 (w).

2

3

C30H34MnN8O8 689.59 200 triclinic  P1 8.1528(16) 9.159(2) 11.196(3) 86.776(7) 87.540(7) 64.481(7) 753.1(3) 1 1.521 359 3.01–25.00 5713 2643 1.064 0.0338 0.0764

C20H21MnN4O6 468.35 293(2) triclinic  P1 10.2940(16) 10.7355(17) 10.9828(17) 81.663(3) 77.172(3) 64.806(3) 1069.1(3) 2 1.299 428 1.90–25.50 5427 3884 1.046 0.0596c 0.1319c

C38H40MnN8O12 855.72 293(2) triclinic  P1 8.9824(9) 9.6177(10) 10.7945(11) 90.185(2) 96.399(2) 90.912(2) 926.60(16) 1 1.534 445 1.90–25.00 4638 3212 1.099 0.0310 0.0837

a

R1 = R||Fo|  |Fc||/R|Fo|. wR2 = |Rw(|Fo2|  |Fc2|)|/R|w(Fo2)|1/2, where w = 1/[r2(Fo2) + (aP)2 + bP]. P = (Fo2 + 2Fc2)/3. c The value was obtained using the SQUEEZE program. b

Table 2 Selected bond lengths (Å) and angles (°) for complexes 1–3. [Mn(L)(H2O)2](1,4-BDC)2H2O (1)a Mn1–O1 2.1943(16) Mn1–N2#2 2.2768(17) O1–Mn1–N1 92.65(6) O1–Mn1–N2#3 92.44(6) O1–Mn1–N1#1 87.35(6) N1–Mn1–N2#3 92.77(6) N2#2–Mn1–N2#3 180.0

2.2.2. Synthesis of [Mn(L)0.5(1,4-BDC)]CH3OHH2O (2) A mixture of Mn(NO3)24H2O (25.1 mg, 0.1 mmol), L (20.0 mg, 0.05 mmol), 1,4-H2BDC (16.6 mg, 0.1 mmol) and NaOH (8.0 mg, 0.2 mmol) in 10 mL of CH3OH and H2O (v/v 1:1) was sealed in a 16 ml Teflon lined stainless steel container and heated at 120 °C for 3 d. Block light brown crystals were obtained in 51% yield after cooling to the room temperature. Anal. Calc. for C20H21N4O6Mn (%): C, 51.29; H, 4.52; N, 11.96. Found: C, 51.32; H, 4.43; N, 11.92%. IR (KBr pellet, cm1): 3411 (m, br), 3126 (w), 1606 (s), 1560 (s), 1511 (m), 1394 (s), 1291 (w), 1233 (w), 1085 (m), 935 (w), 831 (w), 750 (m), 658 (w).

2.2.3. Synthesis of [Mn(L)(H2O)2](1,2-HBDC)22H2O (3) The title complex was prepared by similar procedure to that used for preparation of 2 except using 1,2-H2BDC (16.6 mg, 0.1 mmol) instead of 1,4-H2BDC. A clear solution was obtained. Block colorless crystals suitable for X-ray diffraction were isolated with a yield of 38% by slow evaporation at room temperature in ten days. Anal. Calc. for C38H40N8O12Mn (%): C, 53.34; H, 4.71; N, 13.09. Found: C, 53.44; H, 4.62; N, 13.16%. IR (KBr pellet, cm1): 3424 (m, br), 3129 (m), 1691 (m), 1603 (m), 1565 (s), 1514 (m), 1486 (w), 1416 (s), 1234 (m), 1087 (m), 938 (w), 839 (w), 763 (w), 657 (w).

1

[Mn(L)0.5(1,4-BDC)]CH3OH H2O(2)b Mn1–O1 2.126(2) Mn1–O4 2.303(3) Mn1–N4#2 2.223(3) O1–Mn1–O3 150.90(10) O1–Mn1–N1 88.38(11) O1–Mn1–O2#1 118.78(11) O3–Mn1–N1 90.90(11) O2#1–Mn1–O3 90.31(11) O4–Mn1–N4#2 88.10(11) N1–Mn1–N4#2 173.21(11) O2#1–Mn1–N4#2 93.15(13) [Mn(L)(H2O)2](1,2-HBDC)22H2O (3)c Mn1–O5 2.2139(12) Mn1–N4#1 2.2585(14) O5–Mn1–N1 89.35(5) O5–Mn1–O5#3 180.00 O5–Mn1–N4#2 89.98(5) N1–Mn1–N1#3 180.00 N1#3–Mn1–N4#1 91.60(5) a b c

Mn1–N1

2.2601(17)

O1–Mn1–N2#2 O1–Mn1–O1#1 N1–Mn1–N2#2 N1–Mn1–N1#1

87.56(6) 180.0 87.23(6) 180.0

Mn1–O3 Mn1–N1 Mn1–O2#1 O1–Mn1–O4 O1–Mn1–N4#2 O3–Mn1–O4 O3–Mn1–N4#2 O4–Mn1–N1 O2#1–Mn1–O4 O2#1–Mn1–N1

2.362(3) 2.248(3) 2.080(3) 94.94(10) 86.39(11) 55.96(10) 91.55(11) 88.03(11) 146.27(12) 93.17(12)

Mn1–N1

2.2074(13)

O5–Mn1–N4#1 O5–Mn1–N1#3 N1–Mn1–N4#1 N1–Mn1–N4#2 N4#1–Mn1–N4#2

90.02(5) 90.65(5) 88.40(5) 91.60(5) 180.00

Symmetry codes for 1: #1: 2x, 2y, z; #2: x, 1 + y, z; #3: 2  x, 1  y, z. Symmetry codes for 2: #1: 2x, 1y, 1z; #2: x, 1 + y, 1 + z. Symmetry codes for 3: #1: x, 1 + y, z; #2: x, 2y, z; #3: x, 1  y, z.

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anisotropically by full-matrix least-squares method on F2. Hydrogen atoms of L and 1,4-BDC2 in the structure were generated geometrically and the ones of water molecules were located directly. All calculations were carried out on SGI workstation using the TEXSAN crystallographic software package of Molecular Structure Corporation [28]. The crystallographic data collections for 2 and 3 were carried out on a Bruker Smart Apex CCD area-detector diffractometer with graphite-monochromated Mo Ka radiation (k = 0.71073 Å) at 293 K using x-scan technique. The diffraction data were integrated by using the SAINT program [29]. Semi-empirical

absorption corrections were applied using the SADABS program [30]. The structures were solved by direct methods and all the non-hydrogen atoms were refined anisotropically on F2 by the full-matrix least-squares technique using the SHELXL-97 crystallographic software package [31]. For 2, the disorder of solvent molecules causes large R1 and xR2 values, and thus the PLATON SQUEEZE program was applied to treat these disordered solvent molecules, leading to yield better R1 and xR2 values. The presence of CH3OH and H2O molecules in 2 was confirmed by elemental and TG analyses. Hydrogen atoms of ligand L and benzene ring of

Fig. 1. (a) Coordination environment of Mn(II) and 1,4-BDC2 in 1 with ellipsoids drawn at the 30% probability level, hydrogen atoms and free water molecules were omitted for clarity. (b) 2D network linked by Mn(II) and L ligands (left) and the 1,4-BDC2 with space filling mode located between the adjacent 2D layers (right). (c) The 3D structure of 1 linked by O–H  O hydrogen bonds indicated by dashed lines.

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1,4-BDC2/1,2-HBDC in 2, 3 and the H5A of water molecule (O5) in 3 were generated geometrically, the hydrogen atoms (H5B, H6A, H6B) of water molecules (O5, O6) and undeprotonated hydrogen (H44) of 1,2-HBDC in 3 were located directly. Details of the crystal parameters, data collection and refinements for 1–3 are summarized in Table 1. Selected bond lengths and angles for 1–3 are listed in Table 2. 3. Results and discussion 3.1. Description of the crystal structures 3.1.1. [Mn(L)(H2O)2](1,4-BDC)2H2O (1) The results of X-ray crystallographic analysis revealed that  As shown in complex 1 crystallized in triclinic space group P 1. Fig. 1a, each Mn(II) sitting on an inversion center is six-coordinated with slight distorted octahedral coordination geometry by four nitrogen atoms comprised the equatorial plane from four distinct L ligands and two oxygen atoms occupied the apical positions from two water molecules. The Mn–O bond length is 2.1943(16) Å and the Mn–N ones are 2.2601(17) and 2.2768(17) Å, the bond angles around the Mn(II) are in the range of 87.23(6)–180.0° (Table 2). The deprotonation of 1,4-H2BDC to give 1,4-BDC2 in 1 was confirmed by X-ray diffraction analysis as well as the IR spectral data since no IR bands were observed in the range of 1680–1760 cm1 (see Section 2). It is noteworthy that the 1,4-BDC2 did not take part in the coordination with Mn(II), instead, acts as counteranion in 1, although the benzenedicarboxylates link the metal centers with varied coordination modes to generate intriguing frameworks in the previously reported Mn(II)-benzenedicarboxylate complexes [32]. If the two coordinated water molecules are ignored, each Mn(II) atom links four L ligands, and each L ligand in turn connects four Mn(II) atoms. Such coordination mode makes complex 1 a twodimentional (2D) nearly rectangular grid network with (4, 4) topology since the angles formed among the Mn(II) atoms are 87.23(6)° and 92.77(6)°, respectively, and the edge distances are 7.03 and 7.43 Å, and the diagonal lengths are 11.92 and 9.16 Å, respectively. The deprotonated 1,4-BDC2 anions locate between the two adjacent 2D layers (Fig. 1b). In addition, there are O–H  O hydrogen bonds formed between the O–H of coordinated water molecules and the O of the deprotonated carboxylate of 1,4-BDC2 leading to the formation of a three-dimensional (3D) framework as illustrated in Fig. 1c. The hydrogen bonding data of 1 and 3 are summarized in Table 3. 3.1.2. [Mn(L)0.5(1,4-BDC)]CH3OHH2O (2) Considering that the 1,4-BDC2 was uncoordinated with Mn(II) in 1, reactions with different ligand-to-metal ratios were carried out accordingly. When the L:Mn2+:1,4-H2BDC ratio was changed from 1:1:1 used for preparation of 1 to 1:2:2, complex 2 with completely different structure was obtained.

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The polymeric structure of 2 was confirmed by single crystal X-ray structure determination. Complex 2 also crystallized in the  and the 1,4-H2BDC also completely deprotriclinic space group P1 tonated, which are same as those in 1, however, the 1,4-BDC2 in 2 takes part in the coordination with Mn(II). The coordination environment of Mn(II) in 2 is shown in Fig. 2a. It is clear that each Mn(II) with distorted octahedral coordination geometry is coordinated by four oxygen atoms (O1, O2E, O3, O4) from three different 1,4-BDC2 ligands and two nitrogen atoms (N1, N4B) from two distinct L ligands. The Mn–O distances are in the range of 2.080(3)– 2.362(3) Å, and the Mn–N ones are 2.223(3) and 2.248(3) Å, respectively. The coordination angles around Mn(II) vary from 55.96(10)° to 173.21(11)° (Table 2). On the other hand, each L ligand links four Mn(II) atoms to form an infinite one-dimensional (1D) chain (Fig. 2b), which is different from the 2D network in 1. While the 1,4-BDC2 ligands in 2 link the Mn(II) via Mn–O coordination interactions to give a 2D network with Mn2(COO)4 subunits (Fig. 2c). It is noticeable that there are two kinds of 1,4BDC2 with different coordination modes: both carboxylate groups adopt l2-g1:g1-bridging mode in one 1,4-BDC2, while in other one both carboxylate groups adopt l1-g1:g1-chelating mode (Fig. 2c). The 2D networks are further linked together by the L ligands to form the 3D structure (Fig. 2d). If the Mn2(COO)4 subunit is considered as a node, it links four 1,4-BDC2 ligands and two L ligands, and the 1,4-BDC2 and L ligands in turn connect two Mn2(COO)4 subunits, respectively. Therefore, complex 2 can be simplified as a 6-connected net which can be regarded as a pcu (primitive cubic unit) topology with Point (Schläfli) symbol (412, 63). A remarkable feature of 2 is that there are large voids in its single 3D framework (Fig. 2d), as a result, a pair of identical 3D nets interlocks each other leading to the formation of a twofold interpenetrated 3D architecture (Fig. 2e). The frameworks with pcu topology have been demonstrated to show remarkable physical properties such as porous hydrogen storage and magnetic properties of the Prussian blue family [33]. 3.1.3. [Mn(L)(H2O)2](1,2-HBDC)22H2O (3) When 1,2-H2BDC, instead of 1,4-H2BDC, was used in the reaction with the same ligand-to-metal ratio as that used for preparation of 2, complex 3 was obtained. It is unexpected that, in contrast to the complete deprotonation of 1,4-H2BDC and coordination of 1,4-BDC2 ligands with Mn(II) in 2, 1,2-H2BDC is only partial deprotonated to give 1,2-HBDC which was also confirmed by appearance of IR band at 1691 cm1 and the 1,2-HBDC did not take part in the coordination in 3. As revealed by the results of X-ray crystal structural analysis, that the structure of 3 is rather similar to that of 1, namely the Mn(II) in 3 has the same coordination environment (Fig. 3a) with that in 1, similar Mn–L 2D network is also formed in 3 (Fig. 3b) and the anions locate between the two layers and link the 2D layers to give 3D structure via O–H  O hydrogen bonds (Fig. 3c and Table 3). 3.2. Comparison the structure of the complexes

Table 3 Geometry parameters of hydrogen bonds for complexes 1 and 3. D–H  A

d(D  A) (Å)

\D–H  A (°)

1 O1–H1  O11 O1–H2  O12 O2–H4  O12

2.655(2) 2.754(2) 2.736(3)

172(2) 171(2) 177(3)

3 O5–H5A  O2 O5–H5B  O3 O6–H6A  O4 O6–H6B  O3 O1–H44  O6

2.7916(18) 2.7275(18) 2.8043(19) 2.7428(19) 2.6387(19)

168 170 173 171 167

Coordination polymers1–3 were prepared by reactions of Mn(II) salt with the L and the benzenedicarboxylate ligand under different conditions. Notably, the metal-to-ligand ratio plays vital role in the formation of complexes 1 and 2. In 1, the Mn:L:1,4-H2BDC is 1:1:1 and the deprotonated 1,4-BDC2 ligand is uncoordinated, instead acts as counteranion and the hydrogen bonding acceptor to link the 2D sheets to 3D structure. While in 2, the L:Mn:1,4H2BDC was changed to 1:2:2 and the deprotonated 1,4-BDC2 coordinates to Mn(II) with two different coordination modes, as a result the structure of 2 is a twofold interpenetrated 3D framework.

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Fig. 2. (a) Coordination environment of Mn(II) in 2 with ellipsoids drawn at the 30% probability level, hydrogen atoms and free water and methanol molecules were omitted for clarity. (b) 1D double chain linked by Mn(II) and L ligands. (c) 2D network formed by Mn(II) and 1,4-BDC2 ligands. (d) 3D framework of 2. (e) Schematic representation of twofold interpenetrated 3D pcu net of 2.

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Fig. 3. (a) Coordination environment of Mn(II) and 1,2-HBDC in 3 with ellipsoids drawn at the 30% probability level, hydrogen atoms and free water molecules were omitted for clarity. (b) 2D network linked by Mn(II) and L ligands (left) and the 1,2-HBDC with space filling mode located between the adjacent 2D layers (right). (c) The 3D structure of 3 linked by O–H  O hydrogen bonds indicated by dashed lines.

Complexes 2 and 3 were obtained under the same metal-to-ligand ratio, but different dicarboxylate ligands. In 2, we used the 1,4-H2BDC ligand and got a 3D framework, while in complex 3, we chose the 1,2-H2BDC ligand, the carboxylate ligand was partially deprotonated and uncoordinated, thus only yielded a 2D structure. Comparing with the rigid ligands, flexible multidentate ligands can have varied conformation and coordination modes due to their flexibility, thus they can adopt various conformation to meet the different coordination requirement of the metal centers [24a]. In complexes 1–3, L ligands adopt diversiform modes to coordinate the Mn(II) centers (Scheme 2). In 1, the distances between the coordinated N1, N2 and the central benzene ring are 1.194 and 2.423 Å, respectively. The dihedral angles between the imidazole groups and benzene ring plane are 82.47° and 81.10° (Type I, Scheme 2), the L ligands link Mn(II)centers to 2D layer network. In complex 2, ligand L adopts a H-type conformation and coordinates with four Mn(II) atoms. The coordinated N1 and N4 atoms and the central benzene ring are coplanar, the dihedral angles

between the imidazole groups and the benzene ring plane are 82.25° and 84.25°, respectively (Type II, Scheme 2), thus the L ligands connect Mn(II) to infinite 1D chain. In 3, the distance

Scheme 2. The different conformations of the flexible tetradentate ligand L.

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between the coordinated N1 and N4 atoms and the central benzene ring are 2.744 and 1.408 Å, ligand L adopts a up, down, down, up-type conformation and coordinates with four Mn(II) atoms to form 2D layer network (Type III, Scheme 2). 3.3. Thermal stability of complexes 1–3 In order to examine the thermal stability of the coordination polymers, thermogravimetric analyses (TGA) of complexes 1–3 were carried out under a N2 atmosphere and the results are shown in Fig. 4. The TGA data of 1 show a weight loss of 10.97% in the temperature range of 60–115 °C attributed to the loss of two coordinated and two lattice water molecules (Calc. 10.44%), the decomposition of the residue occurs from 260 °C. For 2, the first weight loss of 6.89% was observed in the temperature range of 70–135 °C, corresponding to the release of one methanol molecule (Calc. 6.84%). The second weight loss of 3.81% occurred between 135 and 300 °C, attributed to the elimination of free water molecules (Calc. 3.84%), and the decomposition of the residue began at 425 °C. In the case of 3, there is a weight loss of 8.95% (Calc. 8.43%) in the temperature range of 80–160 °C corresponding to the release of two coordinated and two free water molecules, then the decomposition of the residue occurs in a consecutive step and does not stop until heating to 700 °C.

3.4. Magnetic property of complex 2 The temperature dependence of magnetic susceptibilities of compound 2 was measured in the range of 1.8–300 K, and the vMT versus T and vM versus T curves are shown in Fig. 5. At 300 K, the vMT value is about 8.73 emu K mol1, which is very close to that expected for two uncoupled Mn(II) ions (S1 = S2 = 5/2) [22,34]. As the temperature decreases, the vMT value remains essentially constant and then decreases to 1.21 emu K mol1 at 1.8 K. The decrease in vMT with lowering the temperature suggests the antiferromagnetic interaction between the Mn(II) ions bridged by carboxylate groups. From the crystal structure of 2, the magnetic susceptibility in whole temperature range was fitted by Eq. (1), ^ ¼ 2J~ which is deduced from spin Hamiltonian H S1~ S2 ,

v¼

2Ng 2 b2 e2J=kT þ 5e6J=kT þ 14e12J=kT þ 30e20J=kT þ 55e30J=kT  kT 1 þ 3e2J=kT þ 5e6J=kT þ 7e12J=kT þ 9e20J=kT þ 11e30J=kT ð1Þ

where all symbols have their normal meanings. The best fitting gave J = 0.47 cm1 with reasonable g = 2.06 and R = 5.2  106 P P (R ¼ ½vM T calcd  ðvM TÞobs 2 = ½ðvM TÞobs 2 ). The negative J value suggests the antiferromagnetic interaction within the Mn(II) atoms bridged by the carboxylate groups. 4. Conclusion

100

1 2 3

90 80

Weight (%)

In this study, three new coordination complexes were obtained by the reactions of flexible tetradentate imidazole-containing ligand and benzenedicarboxylic acid with Mn(II) salt. Complexes 1 and 2 were obtained under different metal-to-ligand ratio and show different intriguing framework structure. Complexes 2 and 3 were prepared by using different organic benzenedicarboxylic acid. In 1, Mn(II) atoms and L ligands form 2D sheet framework. In 2, 2-fold interpenetrated 3D pcu net was obtained, while in 3, the partially deprotonated dicarboxylate just acts as counteranion lying between the adjacent 2D layers. The results show that the organic ligand and the metal-to-ligand ratio play an important role in the construction of the coordination frameworks.

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This work was financially supported by the National Natural Science Foundation of China (Grant nos. 20731004 and 20721002) and the National Basic Research Program of China (Grant nos. 2007CB925103 and 2010CB923303).

Temperature (°C) Fig. 4. TG curves of complexes 1–3.

8

0.6

7

0.5

6

0.4

5

0.3

4

-1

9

0.7

0.2

M

3

χ T / emu K mol

χ

M

-1 / emu mol

Appendix A. Supplementary material 0.8

2

0.1

1 0.0 0 0

50

100

150 T/K

200

250

300

Fig. 5. Temperature dependence of the magnetic susceptibility in the form of vM and vMT versus T for 2. The solid lines are the fitted data.

CCDC 770352, 770353 and 770355 contains the supplementary crystallographic data for complexes 1, 2 and 3. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2010.07.012. References [1] S.R. Batten, R. Robson, Angew. Chem., Int. Ed. 37 (1998) 1461. [2] S. Noro, R. Kitaura, M. Kondo, S. Kitagawa, T. Ishii, H. Matsuzaka, M. Yamashita, J. Am. Chem. Soc. 124 (2002) 2568. [3] M. Fujita, M. Tominaga, A. Hori, B. Therrien, Acc. Chem. Res. 38 (2005) 371. [4] Q.-R. Fang, G.-S. Zhu, Z. Jin, Y.-Y. Ji, J.-W. Ye, M. Xue, H. Yang, Y. Wang, S.-L. Qiu, Angew. Chem., Int. Ed. 46 (2007) 6638. [5] S. Kitagawa, S. Noro, T. Nakamura, Chem. Commun. 12 (2006) 701. [6] M. Du, X.-H. Bu, Y.-M. Guo, J. Ribas, Chem. Eur. J. 10 (2004) 1345. [7] X.-Y. Wang, L. Wang, Z.-M. Wang, S. Gao, J. Am. Chem. Soc. 128 (2006) 674. [8] J.-M. Yan, X.-B. Zhang, S. Han, H. Shioyama, Q. Xu, Angew. Chem., Int. Ed. 47 (2008) 2287.

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