Synthesis, characterization and crystal structure of a new binuclear copper(II) complex with indole-3-propionic acid

Abstract A binuclear copper(II) complex, Cu₂(IPA)₄(CH₃OH)₂ (1) (HIPA = indole-3-propionic acid), was synthesized and characterized by IR, elemental analysis and X-ray diffraction. The crystal of 1 belongs to Triclinic system, space group P. Two Cu(II) ions in 1 are bridged by four IPA anions to form a binuclear complex. Each central Cu(II) ion is coordinated by four carboxylate O atoms from four bridging IPA anions and one O atom from a methanol molecule in distorted square pyramidal geometry.
Keywords indole-3-propionic acid, crystal structures, binuclear copper complex

2. EXPERIMENTAL
2.1 Instruments and chemicals
IR spectrum was recorded on a Perkin-Elmer Spectrum one FT-IR Spectrometer in the 4000 -400 cm^-1 region by using KBr pellets. Elemental analysis for C, H and N atoms were carried out on a Model 2400 II Perkin-Elmer elemental analyzer. All reagents were of analytical grade from commercial sources and were used without any further purification.
2.2 Synthesis of Cu₂(IPA)₄(CH₃OH)₂ (1)
HIPA was dissolved in 5 mL of methanol and the pH value was adjust to about 7 with 1 mol·L^-1 NaOH solution. Then the solution of Cu(NO₃)₂·3H₂O (0.5 mmol) in 10 mL of methanol was added. The mixture was stirred at 60ºC for 4 h. and then filtered. The filtrate was allowed to stand in air at room temperature for several days, yielding green platelike single crystals suitable for analysis.
    IR (KBr) n:_. 3411.64(vs), 1606.18(s), 1423.69(vs), 1384.79(ms), 1358.64(w), 1226.90(w), 1094.85(m), 1010.66(m), 740.23(s), 613.77(m), 493.85(m)cm^-1.
    Anal. calcd for C₄₆H₄₈Cu₂N₄O₁₀: C, 58.48; H, 5.13; N, 5.93%. found: C, 57.62; H, 5.52; N, 5.86%.
2.3 X-ray crystallography of 1

Table 1 Crystal data and structure refinement for complex 1

A single crystal of 1 with dimensions of 0.21 mm × 0.17 mm × 0.07 mm was selected and mounted on a Bruker Smart 1000 diffractometer with Mo Ka radiation (l = 0.071073 nm) by using an w-scan technique at 298(2) K. 10895 reflections were collected in the rang of 1.41 to 25.01, of which 7338 (R_int = 0.0863) unique reflections and 2858 observed ones with I >2s (I) were used in the succeeding refinements. The coordinates of the hydrogen atoms were obtained from difference Fourier maps and refined with a common isotropic thermal parameter. All calculations were carried out using SHELXS-97^[12] and refined by full-matrix least-squares, based on F², using SHELXL-97^[13] programs. Details of data collection and processing are given in Table 1.

    The selected bond lengths and bond angles are listed in Table 2, and Figure 1 shows the molecular structure of 1. In the complex, four IPA anions adopt bidentate bridging coordination mode using two oxygen atoms of the carboxylate groups. The Cu···Cu separation is 0.26221(17) nm which is comparable well to that in the reported dinuclear caboxylate-bridged complexes^[14-18]. Each Cu(II) atom is coordinated by five oxygen atoms from four bridging ligands and one methanol molecule. The Reejijk distortion index t value^[19] is 0.00183 nm for Cu1 and 0.00267 nm for Cu2, respectively, indicating slightly distorted square pyramidal (sp) configuration for the copper(II) atoms. The equatorial plane of each copper(II) contains of four oxygen atoms from four ligands with the average Cu-O bond lengths of 0.19744 and 0.19817 nm for Cu1 and Cu2, respectively. Cu1 and Cu2 are displaced by 0.02006 and 0.01854 nm out of the basal plane towards the axial methanol ligand, respectively. The methanol O atom occupies the apical position of the coordination sphere. The molecular architecture is stabilized by an extensive 1-D band (Fig.2, Table 3) of hydrogen bonds (N-H···O) and (O-H···O) involving the IPA ions and methanol molecules.

Fig. 2 the 1D band diagram of the title compound along a-axis
(Some atoms have been omitted for carily)

Table 2　Selected bond lengths (nm) and bond angles (^o)

Table 3 Hydrogen-bonding geometry (nm, °) for the title complex

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一个新型的吲哚-3-丙酸双核铜配合物的合成和晶体结构表征
邓秀君 边贺东 于青 梁宏
(广西师范大学化学化工学院,桂林 541004,中国)
摘要 本文合成了一个新型的双核配合物Cu₂(IPA)₄(CH₃OH)₂（HIPA=吲哚-3-丙酸），并用红外、元素分析、X射线衍射等方法对其结构进行表征。该单晶属三斜晶系，空间群为P，晶体结构表明，两个铜原子通过四个配体桥联形成一个双核配合物中。每个Cu²⁺处于一个畸变的四方锥配位环境中，配位原子分别来自四个配体羧基上的氧原子、以及一个甲醇氧原子。
关键词 吲哚-3-丙酸，晶体结构，双核铜配合物

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