Synthesis and Crystal Structure of a 4 , 4 ’-bipyridine Linked Dinuclear Copper ( II ) Complex Derived from 2-{ [ 2-( 2-hydroxyethylamino ) ethylimino ] methyl }-6-methylphenol

A novel 4,4’-bipyridine linked dinuclear copper(II) complex, [Cu2L2(bipy)](NO3)2·bipy (L = 2-{[2-(2-hydroxyethylamino)ethylimino]methyl}-6-methylphenol; bipy = 4,4’-bipyridine), was prepared and characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction. The Cu···Cu distance is 11.129(2) Å. The Cu atom is coordinated by one phenolate O, one imine N, and one amine N atoms of a Schiff base ligand, and one N atom of the bridging 4,4’-bipyridine ligand, forming a square planar geometry. In the crystal structure of the complex, the dinuclear copper complex cations are linked by 4,4’-bipyridine molecules through intermolecular O–H···N hydrogen bonds, to form 1D chains running in the [2 0 –1] direction.


Introduction
3][4][5][6][7] Among the complexes, those with polynuclear structures have been widely studied for their interesting magnetic properties. 8,9he building block method, because of its directive function of the target structures as well as the expected physical properties, has become one of the most important synthetic strategies for the preparation of polynuclear complexes.The prime method for designing polynuclear complexes is to use suitable bridging ligands, such as carboxylate anions, pseudohalide anions, etc. [10][11][12] 4,4'-Bipyridine and its analogs have proved especially useful as bridging ligands, resulting in a large number of polynuclear structures.4][15][16][17][18] As a continuation of such work, we report here a new 4,4'-bipyridine bridged dinuclear copper(II) complex,

1. Materials and Measurements
Commercially available 3-methylsalicylaldehyde, 2-(2-aminoethylamino)ethanol, and 4,4'-dipyridyl were purchased from Aldrich.Other solvents and reagents were made in China.All of the chemicals were used as received.C, H and N elemental analyses were performed with a Perkin-Elmer 240 elemental analyser.Infrared spectra were recorded on a Nicolet AVATAR 360 spectrometer as Zhang et al.: Synthesis and Crystal Structure of a 4,4'-bipyridine ... KBr pellets in the 4000-400 cm -1 region.Thermal stability analysis was performed on a Perkin-Elmer Pyris Diamond TG-DTA thermal analyses system.

3. X-ray Crystallography
Diffraction intensities for the complex were collected at 298(2) K using a Bruker D8 VENTURE PHOTON diffractometer with Mo K α radiation (λ = 0.71073 Å).The collected data were reduced using SAINT program, 19 and multi-scan absorption corrections were performed using SADABS program. 20Structure of the complex was solved by direct methods and refined against F 2 by full-matrix least-squares methods using SHELXTL. 21All of the nonhydrogen atoms were refined anisotropically.Hydrogen atoms were placed in idealized positions and constrained to ride on their parent atoms.Crystallographic data for the complex are summarized in Table 1.Selected bond lengths and angles are given in Table 2.

2. Crystal Structure Description of the Complex
Molecular structure of the complex is shown in Figure 1 together with the atom numbering scheme.X-ray crystallography indicates that the asymmetric unit of the complex contains a 4,4'-bipyridine bridged centrosymmetric dinuclear copper(II) complex cation, a hydrogen bonded 4,4'-bipyridine molecule, and two nitrate anions.The inversion center of the dinuclear complex cation is located at the midpoint of the 4,4'-bipyridine ligand.The Cu•••Cu distance is 11.129(2) Å.The Cu II atom is coordinated by one phenolate O, one imine N, and one amine N atoms of a Schiff base ligand, and one N atom of the bridging 4,4'bipyridine ligand, forming a square planar geometry.The significant distortion of the square planar coordination is mainly revealed by the bond angles.The bond angle

4. Thermal Property
Thermal gravimetric analysis (TG) were conducted from 25 to 1000 °C under air atmosphere at a heating rate of 10 °C/min to examine the stability of the complex (Figure 3).The first step started at 202 °C and completed at 326 °C, probably corresponding to the loss of the coordinated and uncoordinated bipy ligands and methylbenzylidene moiety of the Schiff base ligands.The observed weight loss of 51.5% is close to the calculated value (52.3%).The second step, from 326 °C to 473 °C, probable corresponds to the loss of the remaining moieties of the Schiff base ligands and the nitrate anions, and the formation of the final product CuO.The total observed weight loss of 85.0% agrees well with the calculated value (84.1%).

Conclusions
A novel dinuclear copper(II) complex has been prepared and characterized by elemental analyses, IR spectroscopy, and single crystal X-ray diffraction.The Cu II atom is coordinated by one phenolate O, one imine N, and one amine N atoms of a Schiff base ligand, and one N atom of the bridging 4,4'-bipyridine ligand, forming a square planar geometry.Crystal structure of the complex are stabilized by intermolecular O-H•••N hydrogen bonds.Thermal analysis indicates that the complex is stable up to 202 °C.

Figure 1 .
Figure 1.The structure of the complex, showing the atom-numbering scheme.Displacement ellipsoids are drawn at the 30% probability level.Unlabelled atoms are at the symmetry position (2 -x, 1 -y, -z).

Figure 2 .
Figure 2. The crystal packing of the complex, viewed along the b axis.Hydrogen bonds are shown as dashed lines.

Figure 3 .
Figure 3. TG curve of the complex.

Table 1 .
Crystallographic data and refinement parameters for the complex