CUI Hong-Xia WANG Yan-Chao (Department of Chemistry and Chemical Engineering,Shengli College China University of Petroleum, Dongying 257097, China) (Department of Basic, Liaoning Institute of Science and Technology, Benxi 117004, China)

1 INTRODUCTION

Design and construction of coordination polymers are interesting fields in supramolecular chemistry and crystal engineering. Several synthetic strategies, such as pH-dependent assembly[1], solvent-mediated assembly[2], template-mediated selfassembly[3], temperature-dependent assembly[4]and metal ion-mediated self-assembly[5], have been developed. Such approaches have been recognized as excellent strategies to build up molecular architectures not only for their aesthetical structures[6]but also for the discovery of interesting properties such as single-molecule magnets (SMMs) behavior especially in polynuclear clusters[7]. These complexes can be used as hydrogen adsorption and storage materials[8], catalysts[9], molecular sieves[10]and charge-transfer complexes[11]. Cyanido-bridged metal complexes have also been developed in the area[12]. Diamagnetic [Ni(CN)4]2-is an excellent model for magnetic studies which bridge paramagnetic ions. Otherwise, the [Ni(CN)4]2-, as a bridging ligand, can be constructed into 1D, 2D and 3D structures[13].

In this paper, we report two copper-nickel complexes, in which [Ni(CN)4]2-as bridging ligand and the macrocyclic with different sizes form two difference structures.

2 EXPERIMENTAL

2.1 Generals

All reagents were commercially available and used as received, and i-Pr3TACN and DACH were synthesized according to literature methods[14-15]. C,H and N elemental analyses were carried out using a Perkin-Elmer analyzer model 240. IR analyses were carried out using Bruker Tensor 27 FTIR Spectrometer (KBr pellets). The magnetic susceptibility data were obtained using a Quantum Design PPMS 6000 magnetometer in the temperature range of 75–300 K at an applied magnetic field of 2 kG.

2.2 Syntheses of complexes 1 and 2

A water solution (20 mL) of K2Ni(CN)4(0.111 g,0.4 mmol) and CuCl2(0.08 g, 0.4 mmol) was layered with an acetonitrile solution (20 mL) of(i-Pr3TACN) (0.07 g, 0.4 mmol). After about 4 weeks, block-shaped blue crystals of 1 formed from the solution. The crystals were collected, washed with water and methanol, and dried in the air. Yield:51% (based on tetracyanonickelate salts). Anal.Calcd. (%) for C19H37CuN7NiO2: C, 44.07; H, 7.20;N, 18.94. Found (%): C, 44.05; H, 7.22; N, 21.93%.IR (KBr): CN 2162 (coordinated) and 2126 cm-1(uncoordinated).

Complex 2 was synthesized by following the same procedure as 1, while using DACH instead of i-Pr3TACN. Yield: 26% (based on tetracyanonickelate salts). Anal. Calcd. (%) for C9H10CuN6Ni: C,33.32; H, 3.11; N, 25.90. Found (%): C, 33.31; H,3.13; N, 25.90. IR (KBr): 2175 (coordinated) and 2139 cm-1(uncoordinated).

2.3 Crystallographic data collection and refinement

Diffraction data for complexes 1 and 2 were collected at 293 K with a Bruker SMART 1000 CCD diffractometer using a Mo-Kα radiation (λ = 0.71073 ?) with an ω-2θ scan mode. An empirical absorption correction (SADABS) was applied to the raw intensities[16]. These structures were solved by direct methods (SHELXS-97) and refined by full-matrix least-squares procedures on F2using SHELXL-97[17-18]. Hydrogen atoms were added theoretically and refined with riding model position parameters and fixed isotropic thermal parameters. Crystallographic data and refinement details are given in Table 1.The crystal data file is listed in the supplemental material. The selected bond lengths and bond angles of 1 and 2 are listed in Tables 1 and 2, respectively.

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

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

Crystal data for 1: C19H37CuN7NiO2, Mr= 517.81,monoclinic system, space group P21/c, a =8.5896(17), b = 18.092(4), c = 15.615(3) ?, β =95.61(3)o, V = 2415.1(8) ?3, Z = 4, Dc= 1.424 g/cm3,μ = 1.688 mm-1, F(000) = 1092, φ and ω scans,1.73＜θ＜27.88°. Total reflections: 18582, unique reflections: 5622. Final R = 0.0475, wR = 0.0747,goodness of fit = 1.030.

Crystal data for 2: C9H10CuN6Ni, Mr= 324.48,monoclinic system, space group P21/c, a = 8.666(4),b = 13.800(6), c = 10.845(5) ?, β = 93.237(7)o, V =1294.9(10) ?3, Z = 4, Dc= 1.664 g/cm3, μ = 3.082 mm-1, F(000) = 652, φ and ω scans, 2.39＜θ＜23.25°.Total reflections: 4326, unique reflections: 1854.Final R = 0.0289, wR = 0.0703, goodness of fit =1.026.

3 RESULTS AND DISCUSSION

3.1 Structures of complexes 1 and 2

The structure of complex 1 is shown in Fig. 1.The symmetric unit in this crystal contains two[Ni(CN)4]2-bridging two cis-[Cu(i-pr3TACN)]2+in cis-positions to form a [2+2] type of discrete molecular square. The distances of Cu–Ni and Cu–Cu are 4.937 and 7.337 ?, respectively, and the Cu–N(macrocycle) distances (2.068–2.215 ?) are close to the Cu–N(cyano) distances (1.993 and 1.978 ?)but longer than the Ni(2)–C(cyano) distances(1.849(5)–1.881(5) ?). Furthermore, the C–N(coordinated) distances of the cyano groups are close to the C–N(uncoordinated) distances (Tables 1 and 2).Interestingly, a cyclic water tetramer is located in complex 1. Within the cluster, the four water molecules are fully coplanar and each water monomer acts as both single hydrogen bond donor and acceptor (The hydrogen bond is as shown in Table 3).The average hydrogen bond distance within the water tetramer is 2.76 ?, which is shorter than 2.78 ? estimated in the udud water tetramer of (D2O)4[19].The most remarkable feature in 1 is that the cyclic water tetramer connects the [2+2] molecular square through hydrogen bond to form a 3D structure (Fig. 2).

Fig. 1. Coordination environment for Cu(II) in complex 1

Fig. 2. 3D structure through hydrogen bonding connects of 1 and the cyclic water tetramer in 1

Table 3. Hydrogen Bonds in Water Cluster in Complex 1

The symmetric unit in complex 2 contains a[Ni(CN)4]2-bridge and a cis-[Cu(DACH)]2+in cis-positions to form a [2+2] type of molecular square. According to Table 2, the metal-ligand bond distances of 2, the Cu–N and Ni–N distances, are in the ranges of 1.965(4)–2.120(4) ? and 1.866(4)–2.144(5) ?, respectively. The zigzag chains of the composition (-Ni–C(l)–N(l)–Cu–N(2)–C(2)-) which propagate along the a axis and the remaining bridging cyano groups (-C(3)–N(3)-) link another cis-[Cu(DACH)]2+unit giving rise to a 2D β-pucker structure (Fig. 3). The terminal cyano groups(-C(4)–N(4)-) are not coordinated with the[Cu(DACH)]2+unit.

Fig. 3. 2D pucker network of 2 and the coordination environment for Cu(II)

3.2 Magnetic properties

The magnetic susceptibilities of 1 and 2 have been measured in the temperature range of 75–300 K (Fig. 4). With the temperature decrease, χMT slowly decreases, indicating a weak antiferromagnetic interaction between Cu(II) ions, which is normal for the Cu(II) complexes bridged by diamagnetic [Ni(CN)4]2-[20]. We have fitted the two complexes as binuclear entities (Equation 1),yielding g = 2.01, J = –22.11 cm-1and g = 2.01, J =–32.50 cm-1for 1 and 2, respectively.

Fig. 4. Temperature dependence of χMT vs. T for 1 and 2

4 CONCLUSION

In summary, we have successfully constructed two different structures by changing the size of macrocyclic ligand, a cyanide bridged [2+2] type of molecular square (1) and a 2D β-pucker structure (2).The result may provide useful information for the construction of crystal structure. The complexes exhibit a weak antiferromagnetic interaction between copper ions and the J values of –22.11 and–32.50 cm-1for 1 and 2, respectively.

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