Synthesis and Characterization of Two Cu(II) Nitronyl Nitroxide Complexes

Two new nitronyl nitroxide Cu(II) complexes {[Cu(hfac) 2 ] 2 (NIT-4PyPh)} 2 (1) and [Cu(hfac) 2 ][(NIT-3PyPh) 2 ](2)(NIT-4PyPh=2-[4-(4-pyridinylmethoxy) phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide,NIT-3PyPh=2-[4-(3-p yridinylmethoxy)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide,hfac =hexafluoroacetylacetone), have been synthesized and characterized. The X-ray crystal structure analyses show that structures of the two complexes are different. Complex 1 crystallizes in cyclic metal-radical dimer consisting of four Cu(hfac) 2 and two NIT-4PyPh ligands; four Cu(II) atoms adopt two coordinated modes. In the ring, each Cu(II) ion is hexa-coordinated by four oxygen atoms of two hfac ligands and one oxygen atom (ONCNO) and one nitrogen atom of the pyridinyl group from two different radicals. Outside the ring, each Cu(II) is penta-coordinated by four oxygen atoms of two hfac ligands and one oxygen atom (ONCNO) from the radical ligand. Complex 2 crystallizes in discrete molecule, while the Cu(II) atom is hexa-coordinated by four oxygen atoms of two hfac molecules and two nitrogen atoms of the pyridinyl group from two radical ligands.


Materials and Measurements
All chemicals and solvents used for the syntheses were of reagent grade and were used without further purification. The radical ligands [11] [12] and Cu(hfac) 2 •H 2 O have been performed according to the literature methods. All reactions were conducted in aerobic conditions. Elemental analyses for carbon, hydrogen, and nitrogen were carried out on a Model 240 Perkin-Elmer elemental analyzer. Infrared spectra were taken on a Bruker Tensor 27 Fourier transform infrared spectroscopy in the region 4000 -400 cm −1 , using KBr pellets. Ultraviolet-visible spectra were recorded on a Cary 50 UV-Vis spectrophotometer in stated solvent.

X-Ray Crystallography
The diffraction data were collected at 150 K with Mo-Kα (λ = 0.71073 Å) radiation using a Bruker CCD APEX-Ⅱ diffractometer. The structures were solved by direct methods and refined by full-matrix least-squares methods on F 2 by using the SHELXL-97 program package [13]. Empirical absorption corrections from φ and ω scan were applied. All non-hydrogen atoms were refined anisotropically, and all hydrogen atoms were added theoretically. Crystal parameters, data collection procedure, and refinement results for complexes 1-2 are summarized in detail in Table 1. Selected bond lengths and angles for the two complexes are listed in Table 2.

The Complex {[Cu(hfac)2]2(NIT-4PyPh)}2(1)
The perspective view of the molecular structure of the complex 1 is illustrated in Figure 1. The important bond lengths and angles are displayed in Table 2 (7). Here, we could consider ONCNO as a bidentate bridged two different Cu(hfac) 2 units.

The Complex [Cu(hfac)2(NIT-3PyPh)2](2)
A view of the molecular structure of complex 2 is shown in Figure 2. The important bond lengths and angles are displayed in Table 2. Single-crystal X-ray analysis reveals that complex 2 crystallizes in the monoclinic space group P2 1 /n.

Conclusion
Two new Cu-Radial complexes have been synthesized, and characterized by X-ray single crystal diffraction, elemental analysis, infrared spectroscopy and Uv-Vis spectroscopy. The analysis results indicated that complex 1 display an interesting cyclic dimers, whereas, the complex 2 exhibit a discrete molecule and two N atoms (-pyridyl group) of two radical ligands. The magnetic properties of the two complexes 1-2 are under researching.