A New Two-dimensional Coordination Polymer Based on Trinuclear Manganese Clusters①

32卷11期 结 构 化 学 （JIEGOU HUAXUE） Vol. 32, No. 11

A New Two-dimensional Coordination Polymer Based on Trinuclear Manganese Clusters①

XU Naa ZHANG Yan-Nanb WANG Xiu-Yanb②

a

(School of Chemical & Environmental Engineering,

China University of Mining & Technology, Beijing 100083, China)

b

(Department of Chemistry, Jilin Normal University, Siping 136000, China)

ABSTRACT A novel two-dimensional Mn(II) coordination polymer, [Mn3(L)2(cis-chdc)2(trans- chdc)]n (L = 2-amino-4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol and chdc = 1,4-cyclo- hexanedicarboxylate), has been hydrothermally synthesized and characterized by elemental analysis, IR, TG, PL and single-crystal X-ray diffraction. Crystallographic data for this compound: monoclinic space group P2/n with a = 11.0058(13), b = 9.0179(11), c = 28.431(3) Å, β = 92.850(2)°, V = 2818.3(6) Å3, Z = 2, C62H56Mn3N10O14, Mr = 1329.99, Dc = 1.567 g/cm3, F(000) = 1370, μ(MoKa) = 0.742 mm-1, R = 0.0553 and wR = 0.1421. The chdc carboxylates bridge the Mn(II) atoms to form a trinuclear Mn(II) cluster. The cis-chdc ligands are held together by the trinuclear Mn(II) clusters to result in a chain structure. Further, the trans-chdc ligands link adjacent chains to furnish a two-dimensional network. The π-π interactions between neighboring layers link the adjacent layers into a three-dimensional supramolecular architecture. Moreover, the N–H···O and O–H···O hydrogen bonds further stabilize the 3D supramolecular architecture. Keywords: coordination polymer, crystal structure, 1,4-cyclohexanedicarboxylate, 2-amino-4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenol

1 INTRODUCTION

The synthesis and characterization of coordination polymers have attracted much attention, owing to their enormous variety of interesting structural topo- logies and potential applications in gas storage, microelectronics, molecular magnet, nonlinear op- tics, chemical separations and heterogeneous cataly- sis[1-5]. Generally, the diverse structures of such materials are always dependent on many factors, such as metal ion, template, metal-ligand ratio, counteranion, pH value, and the number of coor- dination sites provided by organic ligands[6-7]. The aromatic polycarboxylate ligands can serve as

Received 24 March 2013; accepted 5 September 2013 (CCDC 958724)

excellent candidates for building fascinating coor- dination networks due to their versatile bridging fashions. To date, a series of structural motifs, inclu- ding ladder, honeycomb, brick wall, bilayer, her- ringbone, diamondoid, and rectangular grid, have been deliberately designed by employing bridging polycarboxylate ligands[4-8].

Up to now, the typical chelating N,N -based se- condary ligand, such as the traditionally employed 1,10-phenanthroline (phen), has been extensively studied to build novel supramolecular architectures due to its excellent coordinating ability[9-10]. How- ever, coordination polymers based on the new phen derivative L in combination with flexible dicarboxy-

① The project was supported by the Education Office of Jilin Province (No. 2013212)

② Corresponding author. Majoring in coordination chemistry. E-mail: wangxiuyan2004@

XU N. et al.: A New Two-dimensional Coordination

late ligands have not been studied yet. In this paper, we describe the successful synthesis of a new two-dimensional Mn(II) coordination polymer with L and flexible dicarboxylate, namely, [Mn3(L)2(cis- chdc)2(trans-chdc)]n.

2 EXPERIMENTAL

2. 1 Generals

All the materials were of analytical reagent grade and used as received without further purification. Elemental analysis was carried out with a Perkin- Elmer 240C analyzer. IR spectrum was obtained on a Perkin-Elmer 2400LSII spectrometer. Thermal stability experiment was performed on a TG SDT2960 thermal analyzer from room temperature to 900 ℃ under a nitrogen atmosphere at a heating rate of 10 ℃/min. The photoluminescent properties were measured on a Renishaw inVia Raman Microscope at room temperature. 2. 2 Synthesis and crystal growth

A mixture of MnSO4·4H2O (0.112 g, 0.5 mmol), H2chdc (0.086 g, 0.5 mmol) and 4-(1H-imidazo[4,5- f][1,10]phenanthrolin-2-yl)-2-nitrophenol (L ) (0.178 g, 0.5 mmol) was dissolved in 10 mL water. The pH value of the mixture was adjusted to about 6.6 by the addition of triethylamine. The resultant solution was heated at 448 K in a Teflon-lined stainless steel autoclave for five days. Then, the reaction system was cooled to room temperature. Crystals were obtained from the reaction system by filtration. Yield: 31% based on Mn(II). During the hydrothermal reaction, the nitro group of L was reduced to the amino group of L. Anal. Calcd. for C62H56Mn3N10O14 (%): C, 55.99; H, 4.24; N, 10.53. Found (%): C, 55.62; H, 4.36; N, 10.41. IR (KBr, cm-1): 3435w, 1566m, 1488m, 1414m, 1137m, 996w, 809w, 734w, 619w, 540w.

2. 3 X-ray structure determination

A single crystal with dimensions of 0.26mm × 0.14mm × 0.11mm was chosen and mounted on a Bruker-AXS Smart CCD diffractometer equipped with a graphite-monochromatized MoKα (λ =

0.71073 Å) radiation by using an ω-φ scan method at 293(2) K. Out of the 14975 total reflections collected in the 1.95≤θ≤26.02º range, 5536 were independent with Rint = 0.0340, of which 3774 were considered to be observed (I > 2σ(I)) and used in the succeeding refinement. The structure was solved by direct methods with SHELXS-97 program[11] and refined with SHELXL 97[12] by full-matrix least- squares techniques on F2. All non-hydrogen atoms were refined with anisotropic thermal parameters. All H atoms were positioned geometrically (C–H = 0.93 Å) and refined as riding, with Uiso(H) = 1.2Ueq(carrier). The final R = 0.0553 and wR = 0.1421 (w = 1/[σ2(Fo2) + (0.0731P)2 + 3.3155P], where P = (Fo2 + 2Fc2)/3). S = 1.048, (Δρ)max = 0.694, (Δρ)min = –0.435 e/Å3 and (Δ/σ)max = 0.001.

3 RESULTS AND DISCUSSION

3. 1 Description of the crystal structure

Selected bond lengths and bond angles for the compound are given in Table 1. Single-crystal X-ray analysis reveals that the title compound is a two-dimensional network built up by L and cis- and trans-chdc ligands with Mn(II) atoms. As shown in Fig. 1, the asymmetric unit of the compound con- tains one and a half Mn(II) atoms, one and a half chdc anions, and one L ligand. The trans-chdc ligand lies on an inversion centre. The Mn(1) atom is six-coordinated by six carboxylate oxygen atoms from six distinct chdc ligands in a distorted octahedral coordination environment. The Mn(2) atom, however, is seven-coordinated by five car- boxylate oxygen atoms from three different chdc ligands and two nitrogen atoms from one L ligand (Fig. 1). The Mn–O bond lengths range from 2.075(4) to 2.525(7) Å, and the Mn–N distances are 2.266(3) and 2.243(3) Å, which are near the reported ones observed in other analogous structure complex [Mn(L )(1,4-bdc)] (L = 11-fluoro-dipyrido[3,2- a:2 ,3 -c]phenazine and 1,4-bdc = benzene-1,4- dicarboxylate)[8]. Notably, there exist two types of chdc anions: cis- and trans-chdc in the compound.

The chdc carboxylates bridge the Mn(II) atoms to form a trinuclear Mn(II) cluster. The cis-chdc ligands are held together by the trinuclear Mn(II) clusters to result in a chain structure (Fig. 2). Further, the trans-chdc ligands link adjacent chains to furnish a two-dimensional network (Fig. 3). The L ligands are attached on both sides of the layers, and form π-π interactions between the neighboring layers (ca. 3.50 and 3.47 Å). These π-π interactions led the adjacent

layers to generate a three-dimensional supramo- lecular architecture (Fig. 4). Moreover, the N–H···O and O–H···O hydrogen bonds (N(3)–H(3A) = 0.86, H(3A)···O(2)iv = 2.12, N(3)···O(2)iv = 2.882(4) Å, ∠N(3)–H(3A)···O(2)iv = 147.6o (symmetry code: iv –x, –y+1, –z+1) and O(7)–H(7A) = 0.82, H(7A)···O(4)v = 1.93, O(7)···O(4)v = 2.636(5) Å, ∠O(7)–H(7A)···O(4)v = 143.0o (symmetry code: v –x–1, –y+1, –z+1)) further stabilize the structure of 1.

Table 1. Selected Bond Lengths (Å) and Bond Angles (°)

BondMn(1)–O(1) 2.163(8) Mn(2)–N(1) 2.266(3) Mn(2)–O(3) Mn(1)–O(6)iii

2.109(4)

Dist.

Bond

Dist.

Mn(2)–O(1) 2.525(7) Mn(2)–N(2) 2.243(3) Mn(1)–O(3)i 2.155(3)

Mn(2)–O(2)

2.215(3) Mn(1)–O(3) 2.155(3) Mn(1)–O(1)i 2.163(8)

(°)

ii 2.109(4)

Mn(2)–O(5)ii 2.075(4) O(6)ii–Mn(1)–O(6)iii 91.6(3) O(3)i–Mn(1)–O(3) 178.6(2) O(3)i–Mn(1)–O(1) 104.9(2) O(1)–Mn(1)–O(1)i 97.7(4) O(2)–Mn(2)–N(2) 88.81(13) N(2)–Mn(2)–N(1) 73.43(12) N(2)–Mn(2)–O(3) 82.39(12) O(5)–Mn(2)–O(4) 94.69(14) O(5)ii–Mn(2)–O(1) 103.7(2) N(1)–Mn(2)–O(1) 150.7(2)

ii

Angle (°(°O(6)ii–Mn(1)–O(3) 92.35(16) O(6)ii–Mn(1)–O(1) 87.9(3) O(3)–Mn(1)–O(1) 74.2(2) O(5)ii–Mn(2)–O(2) 96.43(14) O(5)ii–Mn(2)–N(1) 92.83(15) O(5)ii–Mn(2)–O(3) 106.75(15) N(1)–Mn(2)–O(3) 133.50(11) O(2)–Mn(2)–O(4) 166.53(12) O(2)–Mn(2)–O(1) 50.8(2) O(3)–Mn(2)–O(1) 64.5(2)

O(6)iii–Mn(1)–O(3) 88.60(16) O(6)iii–Mn(1)–O(1) 162.7(2) O(3)–Mn(2)–O(4) 54.33(12) O(5)ii–Mn(2)–N(2) 166.15(15) O(2)–Mn(2)–N(1) 104.00(12) O(2)–Mn(2)–O(3) 114.75(12) N(2)–Mn(2)–O(4) 82.09(13) N(1)–Mn(2)–O(4) 82.97(11) N(2)–Mn(2)–O(1) 89.6(2) O(4)–Mn(2)–O(1) 118.8(2)

Symmetry transformation: (i): –x+1/2, y, –z+3/2; (ii): x, y–1, z; (iii): –x+1/2, y–1, –z+3/2

Fig. 1. Structure of complex 1 (Symmetric codes: (i) 0.5–x, y, 1,5–z; (ii) x, y–1, z; (iii) 0.5–x, y–1, 1.5–z)

Fig. 2. View of the one-dimensional chain structure constructed by cis-chdc ligands and the trinuclear Mn(II) clusters

XU N. et al.: A New Two-dimensional Coordination

Fig. 3.

View of the two-dimensional layer structure of the title complex

Fig. 4. View of the three-dimensional supramolecular architecture of the title complex constructed by π-π interactions

3. 2 Thermogravimetric analysis

The thermogravimetric experiment of the com- pound was performed under N2 atmosphere with a heating rate of 10 ℃/min in temperature ranging from room temperature to 900 ℃. As illustrated in Fig. 5, the anhydrous compound 1 is thermally stable up to around 170 ℃. The weight loss cor- responding to the release of chdc anion and L ligand occurs in the temperature range of 255～681 ℃. However, it is difficult to determine these weight losses accurately as these processes are overlapped due to the dissociation of organic fractions, such as chdc and L ligand.

3. 3 Photoluminescent property

The luminescent properties of coordination po- lymers have received intense interest[13-14]. Here, the solid-state photoluminescent properties of H2chdc, L and compound 1 were studied in solid state at room temperature. The emission spectra of H2chdc and L ligands show emissions at 421 (λex = 325 nm) and 522 nm (λex = 325 nm), respectively (Fig. 6), which are probably attributable to the π*→n or π*→π transition. The weak emission spectrum for compound 1 shows a main peak at 526 nm (λex = 325 nm), which is close to that of the L ligand. Therefore, the emission of compound 1 can be assigned to the emission of L ligand.

Fig. 5. TG curve of the title complex Fig. 6. Emission spectra of H2chdc, L and the title complex

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