Li Dan, Li Rongzhen, Qi Zhiyu, Shi Xuhua, Feng Xiaolong^#, Cai Jiwen^#
(Department of Chemistry, Shantou University, Shantou, Guangdong 515063; ^#Instrumentation Analysis & Research Center, Zhongshan University, Guangzhou, 510275, China)

Received Mar.2, 2001; Supported by the National Natural Science Foundation of China (No.29901004),  Natural Science Foundation of Guangdong Province of China(No. 000779) and project 211 of Shantou University.

Abstract Reaction of [Cu(CH₃CN)₂(PPh₃)₂](BF₄) with 2,2'-dipyridylamine (dpa) afforded the mononuclear copper(I) mixed-ligand complex, [Cu(dpa)(PPh₃)₂](BF₄)· CH₃CN ·CHCl₃. The complex was characterized with elemental analysis, infrared spectrometry and X-ray crystallography. The complex cation consisted of a distorted tetrahedral N2P2 core, contributed by triphenylphosphine and 2,2'-dipyridylamine, respectively.
Keywords copper(I) complex, triphenylphosphine, 2,2'-dipyridylamine, crystal structure

Heterocyclic nitrogen compounds play important roles in biological system and have attracted increasing attention. Currently there is considerable interest in the coordination chemistry of copper(I) with biological or medicinal activities. Syntheses of copper(I) complexes with heterocyclic nitrogen ligands such as imidazole, pyridine and pyrazole derivatives are of great interest to bioinorganic chemists since such kind of complexes can be used to mimic the reduced state of certain active sites of proteins like haemocyanin and tyrosinase.^[1-2] These complexes can serve as model complexes for exploring the function of copper in biologic system. The molecular design and structural determination of the complexes are intriguing aspects of bioinorganic chemistry, inorganic syntheses and metal-based drugs.^[3]
    In the previous papers, the copper(I)-phosphine coordination chemistry have been reported^[4-6]. As an extension of these studies we now introduce a bidentate heterocyclic nitrogen ligand, 2,2'-dipyridylamine (dpa) to form a copper(I) mixed-ligand complex. The synthesis and crystal structure of [Cu(dpa)(PPh₃)₂](BF₄)· CH₃CN · CHCl₃ are presented.

1 EXPERIMENTAL
1.1 Instruments and materials
CHN elemental analyses were performed by using a Perkin-Elmer 240C analyser. Infrared absorption spectra were recorded on a Nicolet Magna 750 FT-IR spectrometer with KBr tablets. Triphenylphosphine (Merk), 2,2'-dipyridylamine (Aldrich) and other reagents for synthesis are commercially available without further purification.
1.2 Preparation
To a chloroform solution (10 ml) of [Cu(CH₃CN)₂(PPh₃)₂](BF₄) ^[7] (0.76g, 1 mmol) was added 2,2'-dipyridylamine (0.17g, 1 mmol). The light yellow solution was stirred 4 hours and turn to light green. Keep stirring for another 7 hours, the resulting solution was then filtered and concentrated to ca. 5 ml. The solid product was obtained by addition of absolute diethyl ether to the solution. Recrystallization of the crude product from a chloroform-n-hexane solution afforded a colorless crystal that is suitable for X-ray crystallographic determination. The crystals were identified as [Cu(dpa)(PPh₃)₂](BF₄)· CH₃CN ·CHCl₃ (Elemental analysis for the crystal sample: Found C, 58.41; H, 4.21; N, 5.65%. Calc. for C₄₉H₄₃BCl₃CuF₄N₄P₂: C, 58.47; H, 4.31; N, 5.57%).
1.3 Crystallography   
A single crystal with dimensions of 0.24mm×0.12mm×0.11mm was selected to collect the diffraction intensity data on a Brucker SMART CCD diffractometer fitted with graphite-monochromated Mo Ka radiation, l= 0.071073 nm. The measurement was carried out at room temperature. All of the calculations were performed by using the SHELXTL package. The structure was solved by direct methods and refined by full matrix least squares. The total of 23702 reflections were collected in the range of 4.03°<q<24.71°. The unique reflections are 8296 with R_int = 0.0357. Goodness of fit on F² is 1.055. Final R indices [I>2s (I)] R₁ = 0.0722, wR₂ = 0.2172. Largest diff. Peak and hole are 1.174 and 0.743 e·Å^-3, respectively.

2 RESULTS AND DISCUSSION
2.1 Synthesis and infrared spectrum
Title complex was obtained from the ligand substitution reaction of [Cu(CH₃CN)₂(PPh₃)₂](BF₄). Two CH₃CN ligands were replaced by dpa, containing two pyridine nitrogen atoms which coordinated to copper. Although most copper(I) compounds may be oxidized easily in air, the title complex is stable. This may be due to the coordination of copper with the reducing ligand triphenylphosphine.
    The IR spectrum of the title complex shows a serial of strong peaks at 492, 504, 517, 695, 744, 1027, 1434, 1479 cm^-1 from PPh₃. The broad band at around 3450 cm^-1 and very strong peaks at 1579, 1631 cm^-1 are due to N-H and C=N stretching vibration of dpa, respectively, and several weak bands at 2852, 2922 and 3053 cm^-1 can be assigned to the aliphatic C-H stretching vibration. A strong broad band at 1084 cm^-1 indicates the existence of BF₄^- ion.
2.2 Crystal structure   
The empirical formula of the title complex is C₄₉H₄₃BC_l3CuF₄N₄P₂, formula weight 1006.51. The crystal is monoclinic space group P2₁/n with a = 14.530(4) Å, b = 18.954(5) Å, c = 18.244(5) Å, a= 90° , b = 102.960(4)° ,  g = 90° , V = 4896(2) ų, Z = 4 and Dc = 1.365 mg/m³, m = 0.728 mm^-1, F(000) = 2064. Non-hydrogen coordinates and thermal parameters are listed in Table 1. Selected bond lengths and angles are given in Table 2. Figure 1 and 2 show the structure and unit-cell of the title complex, respectively.

Table 1 Non-Hydrogen Atomic Coordinates (×10⁴) and Thermal Parameters (Ų×10³)

Table 2 Selected bond lengths and angles of the title complex

Figure 1 Molecular structure of [Cu(dpa)(PPh₃)₂](BF₄)· CH₃CN ·CHCl₃ with atom numbering schemes

Table 3 Selected bond lengths and angles of related copper(I) complexes

   As shown in Figure 1, title complex is mononuclear Cu(I) complex. The structure consists of discrete [Cu(dpa)(PPh₃)₂]⁺ and BF₄^- ions, with CH₃CN and CHCl₃ solvent molecules. There is no special reciprocity between two adjacent molecules (Figure 2). In [Cu(dpa)(PPh₃)₂]⁺ cation, the coordination geometry about Cu(I) can be described as distorted tetrahedral with a N2P2 donor set, contributed by PPh₃ and dpa. For comparison, Table 3 summarized selected bond lengths and angles of several similar Cu(I) complexes with CuN₂P₂ core. In [Cu(dpa)(PPh₃)₂]⁺, the Cu-N distances of 2.070(4) and 2.087(4) Å are comparable to those of complexes listed in Table 3, but are much longer than those in Cu(II) complex [Cu(dpa)(PPr)₂] 2H₂O (HPPr = phenylpropanoic acid) with the values of 1.979(3) and 1.975(3) Å. ^[10] The Cu(I) complexes in Table 3 have similar Cu-P distances. The P-Cu-P and N-Cu-N angles of 124.99(5) and 91.18(18)° are quite different from those in [Cu(py)₂(PPh₃)₂]⁺ (115.85(9) and 101.5(2)°), indicating the angle distortions are much greater in [Cu(dpa)(PPh₃)₂]⁺ than in pseudotetrahedral [Cu(py)₂(PPh₃)₂]⁺. Obviously, this is due to that two coordination sites are occupied by a bidentate ligand dpa.
    The crystal structure of title complex has been deposited at the Cambridge Crystallographic Data Centre with the deposition number of CCDC 165706.

Figure 2 Unit-cell contents of [Cu(dpa)(PPh₃)₂](BF₄)· CH₃CN ·CHCl₃

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[3] Karlin K D, Tyeklar Z (eds.). Bioinorganic Chemistry of Copper, New York: Chapman & Hall, 1993.
[4] Li Dan, Yip H K, Che C M et al. J. Chem. Soc., Dalton Trans, 1992, 2445.
[5] Li Dan, Che C M, Wong W T et al. J. Chem. Soc., Dalton Trans, 1993, 653.
[6] Li Dan, Yang K E, Huang S W, Jiang Q Z. Spectroscopy and Spectral Analysis, 1996, 16: 10.
[7] Diez J, Falagan S, Gamasa P et al. Polyhedron, 1988, 7 (1): 37.
[8] Kirchhoff J R, McMillin D R, Robinson W R et al. Inorg. Chem., 1985, 24 (23): 3928.
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[10] Feng X W, Gong Y Q, Jiang Y T et al. Chinese J. Inorg. Chem., 1999, 15 (2): 243.

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