Dichloridobis[4,4,5,5-tetramethyl-2-(5-methyl-1H-imidazol-4-yl-κN 3)-2-imidazoline-1-oxyl 3-oxide-κO]copper(II)

In the title complex, [CuCl2(C11H17N4O2)2], the CuII ion, lying on an inversion center, is six-coordinated in a distorted octahedral [Cu(N2O2Cl2)] environment by two N,O-bidentate nitronyl nitroxide radical ligands and two trans-chloride anions. In the imidazoline-1-oxyl-3-oxide unit of the ligand, the four methyl groups and the C atoms to which they are bonded are disordered over two sets of sites, with a refined occupancy ratio of 0.737 (5):0.263 (5).

In the title complex, [CuCl 2 (C 11 H 17 N 4 O 2 ) 2 ], the Cu II ion, lying on an inversion center, is six-coordinated in a distorted octahedral [Cu(N 2 O 2 Cl 2 )] environment by two N,O-bidentate nitronyl nitroxide radical ligands and two trans-chloride anions. In the imidazoline-1-oxyl-3-oxide unit of the ligand, the four methyl groups and the C atoms to which they are bonded are disordered over two sets of sites, with a refined occupancy ratio of 0.737 (5):0.263 (5).

Comment
The design and synthesis of molecule-based magnetic materials is one of the major subjects of material sciences (Stroh et al., 2003;Kahn et al., 2000;Fursova et al., 2003). In this field, nitronyl nitroxides acting as useful paramagnetic building blocks have been extensively used to assemble molecular magnetic materials due to their donor atoms and their ability to assemble extended arrangement with changing magnetic coupling (Muppidi et al., 2006;Wang et al., 2005;Gao et al., 2010). In this article, we report the synthesis and crystal structure of a novel Cu II complex with nitronyl nitroxide radical.
The crystal structure of the title complex is shown in Figures 1 and 2. The copper(II) ion is six-coordinated in a slightly distorted octahedral CuN 2 O 2 Cl 2 environment. Two nitronyl nitroxide radicals, acting as bidentate chelating ligands, coordinate the Cu II ion leading to two six-membered chelate rings, and the copper coordination is completed by two trans-arranged chloride anions.

Experimental
The nitronyl nitroxide radical 4,4,5,5-tetramethyl-2-(5-methylimidazol-4-yl)-2-imidazoline-1-oxyl-3-oxide was prepared according to the literature method (Ullman et al., 1970(Ullman et al., , 1972. The complex was synthesized by mixing 3 ml of an ethanol solution of the radical ligand (0.6 mmol) and 5 ml of an ethanol solution of CuCl 2 .2H 2 O (0.3 mmol). After stirring for two hours at room temperature, the mixture solution was filtered. The clear deep purple filtrate was diffused with diethyl ether vapor at room temperature. Deep purple crystals suitable for X-ray analysis were obtained after a week.

Refinement
All H atoms attached to C atoms were geometrically fixed and allowed to ride on the corresponding parent atom with C-H = 0.96 Å and U iso (H) = 1.5U eq (C) for methyl groups or U iso (H) = 1.2U eq (C) for other H atoms. Two C atoms in one cycle and the four methyl groups bonded to these atoms (C5, C6, C7, C8, C9, C10) are disordered over two sites. Site occupancies were refined and converged to 0.737 (5) and 0.263 (5). The pair of C-C, C-N 1,2-distances and corresponding 1,3-distances were restrained to be equal within 0.01 Å of each other. The displacement parameters for C5 and C5', C6 and C6', C7 and C7', C8 and C8', C9 and C9', C10 and C10', were constrained to be the same using the EADP constraint (Sheldrick, 2008 Fig. 1.