Synthesis, Crystal Structure and Properties of a Copper Complex with the Bicycle[2.2.1]-2-heptene-5,6-dicarboxylic Acid①

LI Wei LI Chng-Hong LI Heng-Feng TAN Xiong-Wen

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Synthesis, Crystal Structure and Properties of a Copper Complex with the Bicycle[2.2.1]-2-heptene-5,6-dicarboxylic Acid①

LI Weia, bLI Chang-HongcLI Heng-Fenga②TAN Xiong-Wena, b

a(,410083)b(421008)c(421002)

copper(II) complex, crystal structure, properties analysis

1 INTRODUCTION

Copper is one of the important elements of life, and its complexes with organic acids widely exist in the life system, which has special biological activities and catalysis[1]. Simulation synthesis of the life system of copper(II) complexes with organic acid formation and the studies on the relation of structures and properties of the complexes are of great significance to reveal the structure of metal enzyme and understand the life phenomena[2]. Despite the fact that a great number of copper com- plexes with aromatic carboxylic acids and second ligands have recently been reported[3], copper com- plexes with flexible carboxylic acid, especially flexible various unsaturated carboxylic acids and second ligand complexes, have been scarcely explo- red[4]. In order to research the structures and pro- perties of copper complexes with various unsatura- ted organic carboxylic acids and further enrich the model copper complexes, a new copper(II) complex 2{Cu(C10H8N2)[C8H11O2(COO)](H2O)3}·(H2O)5with bicycle[2.2.1]hept-2-en-5,6-dicarboxylic acid (H2L) and 2,2?-bipyridine has been synthesized, and its structure was characterized by X-ray diffraction analysis. The thermal stability and electrochemical properties of the complex were also studied. The result shows that the electron transfer in the elec- trolysis is quasi-reversible. In addition, the complex is stable under 80 ℃.

2 EXPERIMENTAL

2.1 Reagents and instruments

H2L was prepared by ourselves[5], the other ma- terials were of analytical grade and used without further purification. Crystal structure was determi- ned on a Bruker SMART APEX CCD diffractometer. Thermal stability (TG) study was executed on a PRT-2 Pyris1 instrument in air. Electrochemical experiment was carried out using an EC550 (Wuhan Gaoshi Ruilian Company).

2.2 Synthesis of the complex

2 mmol H2L (0.364 g) and 2 mmol of basic copper carbonate (0.478 g) were added into 20 mL of methanol and water (v:v = 5:1) and stirred at 55～60 ℃ for about 4.0. Then 2 mmol 2,2?-bipyridine(about 0.312 g) was added and mixed with the pH value being adjusted to 6.0～6.5 by adding dilute triethylamine, and then stirredat 50～60 ℃ for about 20 h. Afterwards, the resultant solution was filtrated, and thefiltrate was kept untouched and evaporated slowly at room temperature. Blue block-shaped single crystals suitablefor X-ray diffraction analysis were obtained after twoweeks.Yield: 36.4%. IR (/cm-1): 3483(w), 3445(w), 3082(w), 1594(vs), 1578(vs), 1547(m), 1457(vs), 1292(vs), 1271(m), 1182(m), 1148(m), 876(m), 761(vs), 742(s), 700(w), 474(w).

2.3 Structure determination

A single crystal with dimensions of 0.18mm × 0.17mm× 0.15mm was put on adiffractometer equipped with a graphi- te-monochromatic Moradiation (= 0.71073 ?) by using a-scan mode at 296(2) K. Corrections forfactors and empirical adsorption correction were applied. Out of 6288 total reflections collected in the 1.69≤≤25.01o range, 3785 were inde- pendent withint= 0.0205, of which 3423 were considered to be observed (> 2()) and used in the succeeding refinement. All calculations were performed using SHELXS-97 and SHELXL-97[6]. The final refinement including hydrogen atoms was converged to= 0.0360,= 0.0950 (= 1/[2(F2) + (0.0422)2+ 1.7713], where= (F2+ 2F2)/3),(?/)max= 0.001,= 1.065, (?)max= 409 and (?)min= –502 e·nm-3.

3 RESULTS AND DISCUSSION

3.1 Crystal structure of the complex

Selected bond lengths and bond angles are shown in Table 1. Hydrogen bond lengths and bond angles are listed in Table 2. The crystal structure of the title complex is revealed in Fig. 1, and its packing diagram in Fig. 2. As shown in Fig. 1, the whole unit consists of one copper ion, H2L and 2,2′- bipyridine together with coordinated and free water molecules. The central copper ion is coordinated with two nitrogen atoms from 2,2?-bipyridine, one oxygen atom from the H2L molecule and three oxygen atoms from water molecules, giving an octahedral coordination geometry. In the CuN2O4octahedron, the bond angles of N(1)–Cu(1)–N(2), N(2)–Cu(1)–O(2), O(2)–Cu(1)–O(6) and O(6)–Cu(1)– N(1) are 79.87(9), 98.71(8), 84.92(7) and 96.46(8)o, respectively, with the total to be 359.96o, indicating that N(1), N(2), O(2), O(4) and Cu(I) are almost coplanar, while O(5) and O(7) occupy the axial positions. The Cu–N bond lengths range from 2.054to 2.070 ?, and the mean distance is 2.062 ? which is close to that in[CuI(2,2?-bipy)2]{[CuII(2,2?-bipy)2]2(BW12O40)}·4H2O,[Cu2(-ox)(L)2(CH3COCH3)2-(ClO4)2], Cu(-methylbenzoic acid)2(2,2?-bipy)·(H2O), Cu2(-C6H5COC6H5COO)4(C10H8N2)2(H2O)2and {[Cu(2,2?-bipy)-(HPDA)](HPDA)(H2O)}(Cu–N = 1.980～2.070 ?)[7]. It suggests that the complex coordinated with 2,2′-bipyridine is stable. The Cu–O bond lengths range from 2.0620to 2.0760 ?, avera- ged by 2.0696 ?.In carboxyl group participating in coordination, the bond O(1)–C(18) in 1.264(5) ? is different from O(2)–C(18) in 1.258(5) ?, indicating a monodentate coordination mode of H2L after dissociating the hydroxyl hydrogen atom.

Fig. 2 and Table 2 show another noticeable cha- racteristic of the title complex, several hydrogen bonding interactions existing between oxygen in water connected with H2L via its coordinated oxy- gen atoms: O(5)–H(5A)×××O(4) (2.690(3) ?, 171°) and O(8)–H(8A)×××O(1) (2.667(3) ?, 161°). The oxygen atoms in free water molecules are linked by hydrogen bonds: O(9)–H(9A)×××O(8) (2.802(3) ?, 166°) and O(9)–H(9B)×××O(10) (2.767(7) ?, 152°). Hydrogen bonds contribute to the stability of the compound[8].

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

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

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

Fig. 1. Molecular structure of the title complex

Fig. 2. Hydrogen bond linking of the neighboring molecules

3.2 Infrared spectrum of the complex

The wide adsorption peaks at about 3483 and 3445 cm-1are the characteristic peaks of OH group in H2O. Two strong peaks at 1578 and 1292 cm-1could be assigned to theas(coo-)ands(coo-)stretching vibration of H2L ligand. In addition, Δcoo-(Δcoo-=as(coo-)–s(coo-)) of the complex, 286 cm-1, was greater than 200 cm-1, which indicates that car- boxylic radicals in the ligand of H2L coordinate with copper ions in a monodentate manner. The charac- teristic absorption peaks of 2,2?-bipyridine in the complex shift to 1566, 1493 and 772 cm-1from 1580, 1463 and 760 cm-1, respectively. This reveals that the nitrogen atom in 2,2?-bipyridine also coordinates with Cu(II)[9]. The above analysis conforms to our experimental results.

3.3 Thermal stability property

Thermal stability property (TG) of the title com- pound was executed on a PRT-2 pyris1 instrument in air atmosphere (Fig. 3). There are three weight-loss stages from room temperature to 600 ℃. The first stage occurs at 80～200 ℃with weightloss of 19.88%, corresponding to the removal of three water molecules (theoretical value is 19.86%). The second stage takes place from 200～300 ℃with weightloss of 31.40% due to the departure of one 2,2?-bipy- ridine molecule (theoretical value is 31.40%). The third stage is observed at 300～420 ℃with weight loss of 48.21% resulting from the release of one H2L molecule (theoretical value is 48.32%), confirming to the crystal structure. Under the air atmosphere, the final product is copper oxide with the rate of about 15.66% (the theoretical value is 15.94%).

Fig. 3. TG curve of the title complex

Fig. 4. Cyclic voltammogram of the title complex

Based on the above analysis, the pyrolytic process of the complex may be divided into the following stages:

3.4 Cyclic voltammogram (CV) of the complex

Fig. 4 is the cyclic voltammogram of the title complex. Cyclic voltammograms of ligand 2,2?- bipyridine, H2L and the complex were determined using a three-electrode system, with the glassy carbon electrode as the working electrode, platinum electrode as the auxiliary electrode, SCE as the reference electrode, DMF as solvent, and HAc- NaAc as the buffer solution. The experimental result demonstrated no redox peak in the two liagnds by the cyclic scanning at room temperature and at 0.100 V/s within –0.200～1.400 V, and only a pair of redox peaks occurred in the title complex (concen- tration = 3.0 × 10-6mol/L). The potentials of its anodic and cathodic peaks are as below: Epa= 0.680, Epc= 0.449 V, ΔE = 0.231 V, suggesting that the electron transfer in the electrolysis was quasi-rever- sible[10].

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20 December 2013;

17 July 2014 (CCDC 976858)

theNatural Science Foundation of Hunan Province (No.11JJ9006),Key Project of Science and Technology Plan of Hunan Province (2012FJ2002) and the Construct Program of the Key Discipline in Hunan Province

. E-mail: lihengfeng@gmail.com