Liu He, Liu Chunhe, Zhong Bohua
(No.7 Department, Beijing Institute of Pharmacology and Toxicology, Beijing 100850)

Abstract The title complex [Cu(II)(bipy)₂Cl]·NO₃·3H₂O(bipy = 2,2'-bipyridine) has been synthesized and characterized by X-ray diffraction analysis. The Cu(II) center is five-coordinated and in a distorted trigonal bipyramidal geometry. The complexes form a quasi-one-dimensional structure through neighboring p-p interactions.
Keywords crystal stucture, 2,2'-bipyridine, p-p interaction

Received May 8, 2004; Supported by the National Natural Science Foundation of China (No. 20302015).

2.EXPERIMENTAL
2.1 Materials and Instruments
All the reagents for syntheses were commercially available and used without further purification or purified by standard methods prior to use. Elemental analyses were performed on a Perkin-Elmer 240C analyzer.
2.2 Preparation of the title complex
A homogenized mixture of CuCl₂·2H₂O(0.1mmol) and bipy(0.2mmol) accurately weighed were added into water solution. After stirring for 30 min, a solution of AgNO₃ (0.1mmol)in water was added and stirring for another1h. The AgCl depositions were filtered. The blue cube crystals suitable for structure determination were obtained by slow evaporation of the solvent. Yield: 45%. Anal. Calcd for C₂₀H₂₂CuN₅O₆: C, 45.55; H, 4.20; N, 13.28. Found: C, 45.61; H, 4.26; N, 2.31.
2.3 Single crystal X-ray diffraction
The blue cube crystal was mounted on a BRUKER SMART 1000 CCD diffractometer equipped with a graphite monochromator for data collection. The determination of unit cell parameters and data collections were performed with MoKa radiation (l = 0.71073 Å). A total of 9340 reflections with 3976 independent ones with R_int = 0.0223 and 3315 observed reflections with I > 2s (I) were collected in the range of 1.84 < q < 25.03o by an w /q scan mode at 298(2) K. All data were corrected by using SADABS method.The structure was solved by direct methods with SHELXL-97 program⁵. The final refinement was performed by full-matrix least-squares methods with anisotropic thermal parameters for non-hydrogen atoms on F². Cu(II) atom in the complex was located from E-maps. The hydrogen atoms were added theoretically, riding on the concerned atoms and being refined with fixed thermal factors. The weighting scheme was w = 1/[s ²(F_o²) + (0.0710P)²+ 1.1220P], where P = (F_o² + 2F_c²)/3. The refinement converged to the final R = 0.0393 and wR = 0.1125. S = 1.026. Molecular graphics were drawn with the program package XP. Crystallographic data and experimental details for structural analyses are summarized in Table 1. Positional parameters and atomic coordinates are given in Table 2, whereas the selected bond distances and angles are listed in Table 3, respectively. Full crystallographic details have been deposited with the Cambridge Crystallographic Data Center and allocated the deposition number CCDC-227251.

Table 1 Crystal and experimental data

Table 2 Atomic Coordinates (×10⁴) and Equivalent Isotropic Displacement Parameters (10³×Ų)

Table 3 Select bond distance (Å) and bond angles (°)

3. RESULTS AND DISCUSSION
The ORTEP view of title complex with atom labeling is shown in Fig. 1(a). It consists of a discrete [Cu(II)(bipy)Cl]⁺ cation and the uncoordinated NO₃^- anion and H₂O molecules. The Cu(II) center is coordinated by four nitrogen atoms of the two bipyridine which thus binds metal center in a bidentate fashion, and a Cl^- anion. The four Cu-N bonds are appreciably different of the two ligands: with the longer bonds being 2.087(2) and 2.110(2) Å, and the other two shorter bonds being 1.983(2) and 1.987(2)Å, respectively. The Cu-Cl distances are 2.3007(9) Å. The coordination geometry around Cu(II) can be described as a distorted trigonal bipyramidal geometry with N(4)-Cu(1)-N(2) angle of 175.05(10)° occupying the axial positions. The Cu(II) center deviates by 0.007 Å from the plane defined by Cl(1), N(1) and N(3). The sum of the bond angles [Cl(1)-Cu(1)-N(1) = 128.17(7)°, N(1)-Cu(1)-N(3) = 108.65(9)° and N(3)-Cu(1)-Cl(1) = 123.18(7)°] is 360°. In this complex, the Cu(II) center is coordinated by the N-atoms of two pyridine rings forming a seven-membered chelate ring. As shown in Fig.1(b), there are the O-H···O and O-H···Cl hydrogen bonds, in which the coordinated Cl^- and dissociate NO₃^- anions link the uncoordinated water molecules, whereas the O···O distances are in the range of 2.704-2.782 Å and O···Cl is 3.241 Å. The neighboring aromatic rings of 2,2'-bipyridine moiety between the adjacent complex are parallel to each other and separated by approximately 3.40 and 3.55Å, indicating the presence of significant face-to-face p-p stacking interactions. The p-p interactions link the complex into a quasi-one-dimensional structure.

                                   (a)                                                                                  (b)

REFERENCES
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Sheldrick G M. SHELXL-97, Program for X-ray Crystal Structure Refinement; Göttingen University: Germany, 1997.

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