HUANG Qiu-Ping LI Gui ZHANG Shu-Hua ZHANG Hai-Yang

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A New Tetranuclear Cobalt Cluster with (1-Benzimidazol-2-yl)-methanol Synthesis and Crystal Structure①

HUANG Qiu-Ping LI Gui ZHANG Shu-Hua②ZHANG Hai-Yang

(C541004)

A new tetranuclear cluster [Co4(bm)6Cl2]·(H2O)2·(CH3OH) (1,Hbm is (1-benzi- midazol-2-yl)-methanol) has been synthesized by solvothermal method and structurally determined by IR, elemental analysis, and single-crystal X-ray diffraction. Complex1 belongs to monoclinicspace group21/with= 21.1713(5),= 12.7948(3),= 24.0195(9) ?,= 95.309(3)°,= 6478.6(3) ?3,= 4,(000) = 2568,D= 1.289 g·cm–3,M= 1257.63,= 9.096 mm–1,= 1.000, the final= 0.0861 and= 0.2552 for 4956 observed reflections with> 2(). Two connected face-sharing cubes are observed in the framework of 1, each with one vertex missing. Complex 1 forms a 2-D network through N–H···O hydrogen bonds. The apparent holes can be observed.

(1-Benzimidazol-2-yl)-methanol, tetranuclear cluster, crystal structure

1 INTRODUCTION

The rational design and synthesis of polynuclear complexes, aiming at understanding the structural and chemical factors that govern the exchange coupling between paramagnetic centers, are of con- tinuing interest in biology, chemistry and physics[1-3].Particular interest has focused on the develop- ment of single molecule magnets (SMM)[4-16]. An effective and facile approach for the synthesis of such complexes is still the appropriate choice of well-designed organic ligands as bridges or terminal groups with metal ions or metal clusters as nodes.Hbm possessing one oxygen atom of the methanol group and two nitrogen atoms of the benzimidazol group may provide the potential to construct unpre- dictable and interesting polymetallic clusters. Pre- vious investigations implied that [Co7(bm)12]·(ClO4)2·-13H2O and [Co4(bm)4Cl4(C3H7OH)4] favor the ferro- magnetic coupling through3--bridges[17]. In the reference, we reported anion induced diversification from heptanuclear to tetranuclear clusters. Herein,Hbm reacted with cobalt salts in the presence of different anions (ClO4–, Cl–, HCOO–) in propan-1-ol solvent[17].

In order to further examine the effect of different solvents on the structural assembly, direct reactions of (1-benzimidazol-2-yl)-methanol with CoCl2·4H2O in methanolsolvent under the same hydrothermal conditions were carried out. The complex[Co4-(bm)6Cl2]·(H2O)2·(CH3OH) (1) can be obtained. It is different from the previously reported tetranuclear or heptanuclear clusters, which indicates that the solvents have an important influence on the struc- tures of the bm-bridged cobalt(II) assemblies.

2 EXPERIMENTAL

2.1 Materials and instruments

All solvents and chemicals were commercial reagents and used without further purification. The elemental analysis was performed on a PE 1700 CHN auto elemental analyzer. The crystal structure was determined by Bruker CCD area-detector and SHELXL crystallographic software of molecular structure. The FT-IR spectra were recorded from KBr pellets in the range of 4000～400 cm–1on a Bio-Rad FTS-7 spectrometer.

2.2 Syntheses of [Co4(bm)6Cl2]·(H2O)2·(CH3OH) (1)

A mixture of CoCl2·4H2O (0.238 g, 1 mmol), Hbm (0.148 g, 1 mmol) and methanol (10 mL) with a pH adjusted to 7 by the addition of triethylamine was poured into a Teflon-lined autoclave (15 mL) and then heated at 120 ℃ for 4 days. Red crystals of 1 were collected by ?ltration, washed with methanol and dried in air. Phase pure crystals of 1 were obtained by manual separation (yield: 144.6 mg,. 69% based on Hbm ligans). Anal. Calcd. for 1: C49H50N12Cl2Co4O9(M= 1257.63). calcd.: C, 46.79; H, 4.02; N, 13.37%. Found: C, 46.78; H, 4.09; N, 13.43%. IR data for 1 (KBr, cm–1, Fig. S1): 3425 s, 1626 m, 1458 s, 1274 m, 1069 m, 738 m, 607 m, 520 w.

2.3 Crystal structure determination

A red crystal of complex 1 having approximate dimensions of 0.38mm × 0.32mm × 0.25mm was selected and mounted on a glass fibre. All mea- surements were made on a Bruker SMART APEX CCD diffractometer with a graphite-monochroma- tized Curadiation (= 1.54178 ?) by using the-scan mode in the range of 3.92≤≤63.26° at 298(2) K. Raw frame data were integrated with the SAINT program[18]. The structure was solved by direct methods with SHELXS-97 and refined by full-matrix least-squares on2using SHELXL-97[18]. The empirical absorption correction was applied with the program SADABS[18]. All non-hydrogen atoms were refined anisotropically, while all hydro- gen atoms were set in the calculated positions and refined by a riding model. The methanol molecule is disordered over two sets of sites in a 0.608(1): 0.392(1) ratio.The selected bond distances and bond angles are listed in Table 1.

Table 1. Selected Bond Lengths (?) and Bond Angles (°) for 1

Symmetry codes: (i) ?+2, ?, ?+1; (ii) ?+1, ?+2, ?+1

3 RESULTS AND DISCUSSION

3.1 Crystal structure description

Single-crystal X-ray crystallographic analysis re- veals that complex 1crystallizes in a monoclinic space group21/. Complex1 belongs to mono- clinicspace group21/with= 21.1713(5),= 12.7948(3),= 24.0195(9) ?,= 95.309(3)°,= 6478.6(3) ?3,= 4,(000) = 2568,D= 1.289 g·cm-3,M= 1257.63,= 9.096 mm–1,= 1.000, the final= 0.0861 and= 0.2552 for 4956 observed reflections with> 2(). This structure contains two identical but independent molecular units. As shown in Fig. 1, complex 1 is a cen- trosymmetric tetranuclear cobalt cluster. The mole- cule consists of four Co(II), two Cl–anions, sixligands, one methanol molecule and two water molecules. The framework of tetranuclear Co4O6cluster, which is bridged by2-O and3-O alkoxide groups, exhibits two connected face-sharing cubes, each with one vertex missing. All four Co(II) ions are in the +2 oxidation state, as evidenced by the bond valence summation calculations, charge balance considerations and the presence of typical bond lengths for Co(II) ions[19-20]. It is different from the coordination environment between Co(1) and Co(2) and the coordination polyhedron for CoIIion shown as Fig. 2. Co(1) is five-coordinated by two2-alkoxide oxygen atoms, one3-alkoxide oxygen atom, one benzimidazol N atom and one Cl–anion to form a distorted trigonal bipyramidal geometry with O(3) and Cl(1) located at the apical positions and the–Co(1)–(= O, N) angles of equator position falling in the range of 108.5(4)～116.4(3)° andtheO(3)–Co(1)–Cl(1) angle of the apical position to be 171.7(4)°. The Co(2) ion is six-coordinated by two N and two O atoms (O(1), O(2), N(1), N(3)) from twoligands of3:1:2coordination mode (Scheme 1a) and two3-O atoms (O(3), O(3A), symmetry code: (i) ?+2, ?, ?+1) from twoligands of4:1:3coor-dination mode (Scheme 1b), forming a distorted octahedral geometry with-angles–Co(2)–(X = O, N) ranging from 76.0(2) to 100.4(3)° and Co(2)–X (X = O, N) bonds of 1.970(8)～2.072 (8) ?. In intraclusters, the Co–O–Co angles fall in the 101.8(3)～111.4(3)° range, and the adjacent Co···Co distances locate in a narrow range of 3.177～3.252 ?. The two coor- dination modes of theligand in 1 were observed in the heptanuclear cluster [Co7(bm)12]·(ClO4)2·13H2O[17].

Scheme 1. Coordination modes of the bm ligand

Fig. 1. Structure of 1 with all water and methanol molecules and all H atoms omitted

Fig. 2. Coordination polyhedron for CoII

Fig. 3. Packing drawing of 1. The water and methanol molecules are omitted

Table 2. Hydrogen Bond Parameters of Complex 1

Symmetry codes: (iii) ?+2, ?+3, ?+1; (iv) ?+2, ?+4, ?+1; (v)?1,?3,; (vi)?1/2, ?+7/2,+1/2

3.2 IR spectrum properties

IR spectral data of the Hbm ligand and complex 1 are shown in Fig. S1. Comparison of the IR spectra of complex 1 with those of the free ligand reveals that the medium strong band at 3258 cm–1can be assigned to the N–H of the ligand[22], and that at 3425 cm–1to the uncoordinated water molecules associated with complex 1[23]. The C=N of the free ligand at 1620 cm–1was shifted to higher fre- quencies (1626 cm–1) in complex 1, suggesting its participation in chelation[24]. The strong bands at 1440 and 1458 cm–1are assigned to C=C benzene ring in the free ligand and complex 1, respectively[25]. The C–O of free ligand at 1270, 1208 and 1049 cm–1were shifted to higher frequencies (1274, 1215, 1069 cm–1) in complex 1, suggesting its participation in chelation[26-27]. The bands at 744 and 738 cm–1of the free ligand and complex 1 can be owned to the aromatic C–H out-of-plane bending vibration[25].

4 CONCLUSION

A new tetranuclear cobalt cluster based on the (1-nenzimidazol-2-yl)-methanol has been success- fully synthesized from a conventional solvothermal synthesis method. The framework of tetranuclear {Co4O6} clusterexhibits two connected face-sharing cubes, each with one vertex missing.The apparent holes can be observed along thedirection. The elemental analysis and IR data are consistent with the X-ray analysis results.

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10 December 2013;

24 January 2014 (CCDC 974609)

① This work was financially supported by the National Natural Science Foundation of China (No. 21161006), Program for Excellent Talents in Guangxi Higher Education Institutions (Gui Jiao Ren [2012]41) and Program of the first session backbone teacher of Guangxi of China

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