Bis{μ-2,4-di-tert-butyl-6-[3-(1H-imidazol-1-yl)propyliminomethyl]phenolato}bis[acetatocopper(II)]

In the centrosymmetric title compound, [Cu2(C21H30N3O)2(C2H3O2)2], each Cu atom has a distorted tetrahedral coordination geometry defined by N and O atoms in a chelate ring, N of an imidazole ring, and an acetate O atom. The uncoordinated acetate O atom is disordered over two sites with occupancies 0.7:0.3.

In the centrosymmetric title compound, [Cu 2 (C 21 H 30 N 3 O) 2 -(C 2 H 3 O 2 ) 2 ], each Cu atom has a distorted tetrahedral coordination geometry defined by N and O atoms in a chelate ring, N of an imidazole ring, and an acetate O atom. The uncoordinated acetate O atom is disordered over two sites with occupancies 0.7:0.3.

Experimental
Crystal data [Cu 2 (C 21  reactions has been receiving increasing interest due to the aforementioned advantage and its success in many newly discovered processes. Most notable is the asymmetric ring opening of epoxides by a Cr(salen)Cl catalyst which was developed by Jacobsen and co-workers in the mid-1990mid- s (Hansen et al., 1996. A very important reaction in organic synthesis which involves the use of predominantly chromium-based salen complexes is the Diels-Alder reaction. Indeed, there is a report where these catalysts have been employed as part of a lengthy synthetic strategy to afford complex natural products (Huang et al., 2002). In this study, we report the structural characterization of a dinuclear Cu(II) Schiff base complex, which was previously investigated by different techniques (Tas et al., 2004). We envisaged that the free imidazole group of the proposed structure (I) should interact with aliphatic alkyl halides such as n-butyl bromide to give novel copper(II) complexes, leading to ionic liquids. However, all attempts under different and drastic conditions failed.
This led us to reconsider the proposed structure (I). Therefore, for detailed information about the coordination mode of the ligands and for full characterization of the complex, a single-crystal X-ray determination has been carried out.

S3. Refinement
Atom O3 shows disorder and was modelled in two different positions as O3a and O3b with refined occupancy factors of 0.30 (4) and 0.70 (4). All H-atoms were refined using a riding model with C-H = 0.93Å [U iso (H) = 1.2U eq (parent atom)] 1.5U eq (parent atom)] for methyl carbon atoms.

Figure 1
The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. [Symmetry code:

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (