LI Wei LI Yu-Lin LI Chng-Hong TAN Xiong-Wen

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Synthesis, Crystal Structure andProperties of a New Binuclear Copper(II) Complex with 5-Oxo-4-oxa-tricyclo[4.2.1.0]nonane-9-carboxylic Acid (TNCA)①

LI Weia, cLI Yu-Lina②LI Chang-Hongb②TAN Xiong-Wena

a(421008)b(421002)c(421008)

binuclear copper(II) complex, thermal stability, electrochemical and magnetic properties;

1 INTRODUCTION

The aromatic carboxylic acids with a variety of coordinating modes are often used as ligands to construct metal-organic complexes because their complexes can exhibit high thermal, good physical and chemical properties in practical use[1-4]. Bicycle[2.2.1]hept-2-en-5,6-dicarboxylic acidand its derivatives are important flexiblearomatic carboxy- lic acids, which can be used as ligands to form coordination polymers, but researches based on this ligand are extremely rare[5-9]. Triazoles and its derivatives show diverse unique magnetic properties such as magneto-structural correlations and novel molecular magnetic materials. The derivatives of 1,2,4-triazole can adopt monodentate terminal or biden-tate N,N?-bridging coordination mode, which makes them easily link two adjacent metal ions to yield dinuclear, linear trinuclear, or linear polymeric metal compounds with double or triple triazole bri-dges[10-13]. However, the coordination chemistry of 3-(pyridin-2-yl)-1,2,4-triazole mixed with organic carboxylic acid has been less investigated[14-16]. Here, we designed and synthesized a new binuclear copper complex with the 3-(pyridin-2-yl)-1,2,4-triazole(Hpt) and5-oxo-4-oxa-tricyclo[4.2.1.0]nonane-9-carboxy-lic acid (TNCA). Thermal stability, electrochemical and magnetic properties of 1 is also reported.

2 EXPERIMENTAL

2. 1 Materials and instruments

All reagents were of analytical grade and used as obtained from commercial sources without further purification, 5-oxo-4-oxa-tricyclo[4.2.1.0]nonane-9-carboxylic acid[5]and 3-(pyridin-2-yl)-1,2,4-tria-zole[17]were prepared previously.Crystal structure determination was carried out on aBruker SMART APEX CCDsingle-crystal diffractometer. Elemental analyses were performed on a Perkin-Elmer 2400 elemental analyzer. IR spectra were recorded on a Bruker Vector22 FT-IR spectrophotometer using KBr discs. Magnetic measurements in the range of 3.0～300 K were performed on a MPMS-SQUID magne- tometer at a field of 2 kOe on a crystalline sample in the temperature settle mode. The electrochemical properties were measured on an EC550 electroche- mical workstation from Wuhan. Thermogravimetric analyses were performed on a simultaneous SPRT-2 pyris1 thermal analyzer at a heating rate of 10 K/min.

2. 2 Synthesis of 1

A mixture of TNCA (72.8 mg, 0.4 mmol), Hpt (58.4 mg, 0.4 mmol), and Cu(Ac)2·H2O (79.8 mg, 0.4 mmol) was dissolved in 25 mL of mixed solvent (the volume ratio of ethanol and water: 3:1). The pH value of the resultant mixture was adjusted to 6.0 by adding sodium hydroxide solution. The reaction was kept stirring at 60℃ for 15 h. Afterwards, the resultant solution was filtrated, and the filtrate was kept untouched and evaporated slowly at room temperature. Blue block-shaped single crystals suitable for X-ray diffraction analysis were obtained about two weeks later. Yield: 48% (based on TNCA). m.p.: 582.0～584.0 K. Anal. Calcd. (%) for C32H40Cu2N8O14: C, 43.12; H, 4.56; N, 12.58. Found (%): C, 43.29; H, 4.54; N, 12.62. Main IR (KBr, cm-1): IR (/cm-1): 3425(w), 3054(w), 1658(m), 1604(vs), 1556(s), 1480(vs), 1387(s), 1364(m), 1275(m), 1006(m), 879(m), 790(m), 718(m).

2. 3 Determination of the crystal structure

A single crystal with dimensions of 0.20 mm ×0.18 mm ×0.12 mm was put on aBruker SMART APEX CCDdiffractometer equipped with a graphite- monochromatic Moradiation (= 0.71073 ?) using a-scan mode at 113(2) K. A total of 13301 reflections were collected in the range of 2.39≤≤25.02°, of which 6284 were independent (int= 0.0485) and 4783 were observed(> 2()). All data were corrected byfactors and empirical absorp- tion. The crystal structure was solved directly by program SHELXS-97, and refined by program SHELXL-97[18]. The hydrogen and non-hydrogen atoms were corrected by isotropic and anisotropic temperature factors respectively through full-matrix least-squares method. The final=0.0556,= 0.1388 (= 1/[2(F2) + (0.0738)2+ 0.0000], where= (F2+ 2F2)/3), (?/)max= 0.002,= 1.051, (?)max= 2.263 and (?)min= –0.700 e·?-3.

3 RESULTS AND DISCUSSION

3. 1 Crystal structure of 1

Fig. 1. ORTEP-drawing of 1 with 30% thermal ellipsoids. Lattice water molecules and hydrogenatoms are omitted for clarity

Fig. 2. View of the packing structure of 1 formed by hydrogen bonds

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

Table 2. Hydrogen Bond Lengths (?) and Bond Angles (°) of Complex 1

Symmetry codes:(a) –+ 1, –+ 2, –+ 1; (b)+ 1,,; (c)–+ 1, –+ 1, –+ 2; (d)– 1,,

There are hydrogen bonding interactions with D···A separations in the 2.664(3)～2.916(3) ? region and the D–H–A angels range from 116.3(1)° to 173.5(3)°. Such different kinds of hydrogen bon- ding interactions (O–H···O and O–H···N) extend the mononuclear compound into a 3supramolecular network (Fig. 2). The results suggest that the reaction conditions have remarkable influence on the structure of the complexes.

3. 2 Magnetic properties of 1

The temperature dependence of magnetic suscep- tibility of the title complex was investigated from 300to 3.0 K with an applied magnetic field of 2 kOe. TheM.and 1/M.curves are shown in Fig. 3. The product ofXTdecreases gradually from 0.8905 cm3·K·mol-1at 300 K to 0.010995 cm3·K·mol-1at 3.0 K. As can be seen from Fig. 3, the short-range order phenomenon occurred at the time of 1/Xin 26 K, which is the characteristic of anti-ferromagnetic compounds. In addition, accor- ding to the Curie-Weiss law,M=/(–), the Curieconstant (= 1.167 cm3·K·mol–1) and Weiss constant (= –92.73 K) are obtained from a linear fit of the 1/X.(see Fig. 4) data in the temperature range of 104～300 K, and the linear regression equation is 1/X= 0.8569T + 79.457, with correla- tion coefficient of 0.999. Such magnetic behavior indicates that copper complexis aparamagneticsystem, which showsa weakanti-ferromagnetic. TheMdropped suddenly at low temperature can be attributed to theanti-ferromagnetic interaction between the chains[20].

Fig. 3. Temperature dependence of the magnetic susceptibility of 1 in the form ofXT.and 1/m.

Fig. 4. Temperature dependence of the magnetic susceptibility of 1 in the form of 1/X

3. 3 Electrochemical properties of 1

We employed a conventional three-electrode system for the cyclic voltammetric measurement (CV), where a Ag/AgCl electrode, a glassy carbon electrode and a platinum electrode as the reference electrode, working electrode and counter electrode, respectively were chosen. 1 was dissolved in DMF, with the resulting solution having a concentration of 3 × 10-5mol×L-1. A NaClO4solution in 1 × 10-3mol×L-1is used as the supporting electrolyte. The cyclic voltammogram of 1in the scan range of –0.50～0.50 V at a scan rate of 0.05 V×s-1is shown in Fig. 5. There is an oxidation peak with the oxidation potential of 0.161 V, corresponding to the CuI/CuIIoxidation process[21, 22].

Under the same conditions, we also measured the electrochemical properties of 1 by linear sweep stripping voltammetry. In the potential scan rate range of 0.05～0.70 V×s?1, the influence of the potential scan rate () on the oxidation peak current (pa) and the oxidation peak potential (pa) was studied.pais proportional to, and the linear regression equation ispa= 70.94+ 6.779 (pa/μA,/V×s-1) with a correlation coefficient of 0.9968 (Fig. 6), which indicates that the electrode reaction process of 1 was controlled by adsorption. In addition,pashifts to a more positive value with increasing, and it is proportional to ln. The linear regression equation ispa= –0.042ln– 0.4689 (pa/V,/V×s-1) with a correlation coefficient of 0.9913.

Fig. 5. Cyclic voltammogram of 1 inwater-methamol (scan rate: 0.10 V·s-1)

Fig. 6. Effect of the potential scan rate () on the oxidation peak current (pa) and the oxidation peak potential (pa) of 1

3. 4 Thermal stability of 1

The thermogravimetric analysis (Fig. 7) of 1 demonstrated that the weight loss of the complex in the air from room temperature to 870 K occurred mainly in 4 stages. The first stage takes place from 440 to 470 K with the weight loss of 8.10%, cor- responding to the release of four free water mole- cules (calcd: 8.12%). The second stage occurs at 470～510 K with the weight loss of 4.02% due to the departure of two coordinated water molecules (calcd: 4.06%). The third stage is observed from 510 to 610 K with the weight loss of 32.66%, resulting from the loss of two Hpt molecules (calcd: 32.70%). A strong endothermic peak near 580 K can be attributed to the endothermic melting of the complex, which confirms to the melting point of the compound. The fourth stage is found from 610 to 770 K with the weight loss of 37.14% owning to the release of two TNCA-anions (calc: 37.20%). In air, the final product is copper oxide with the final residue residual rate to be about 17.98% (calcd.: 17.92%).

Fig. 7. TG and DTG curves of 1

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23 November 2017;

8 January 2018 (CCDC 741931)

the Scientific Research Found of Hunan Provincial Education Department of China (17A049, 17C0226), Industry and Research Key Project of Hengyang City (2017KJ155, 2017KJ193) and Doctoral Scientific Research Foundation of Hengyang Normal University (17D01)

E-mail: li_weihnxy@163.com or lichanghong4444@126.com

10.14102/j.cnki.0254-5861.2011-1897