μ-Bromido-dibromido-μ-hydroxido-bis[(4S)-2-halo-6-(4-isopropyl-4,5-dihydrooxazol-2-yl)pyridine]dicopper(II) (halo: Cl/Br = 3:1)

The crystal structure of the title complex, [Cu2Br3(OH)(C11H13Br0.5Cl1.5N2O)2], consists of two (2-halo-6-oxazolinyl)pyridine·CuBr units bridged by a Br atom and a hydroxide group. The CuII atoms are five-coordinate with an (N,N)BrCu(Br)(OH) distorted tetragonal–pyramidal core, and relatively short contacts to the bridging atoms (Cu—μ-OH and Cu—μ-Br). There are two symmetry-independent half-molecules in the asymmetric unit, which differ only in the arrangement of the isopropyl group. The molecules are located on a twofold rotation axes.

Therefore, it is of interest to obtain a deeper insight into the structure of different coordination motifs and thus, this could help to enhance our understanding about the coordination behaviour and the scope and limitations of ligands applied in catalysis. Chiral oxazolines and pyridines are regarded as privileged ligands, which have found numerous applications in many asymmetric transformations (Fache et al., 2000;Chelucci & Thummel, 2002). Moreover, N-donor ligands are also found as component parts of enzymatic processes such as the fixation, activation and transport of oxygen (Kaim & Schwederski, 1991;Karlin & Gultneh, 1987), or they are used for studies concerning self-organizing phenomena (Lehn, 1995).
During our work in the field of supramolecular ligands and catalysts, the novel title compound (I) was isolated from a mixture of Cl-and Br-substituted oxazolinyl-pyridine ligands. This mixture was obtained from the oxazoline ring closure reaction of 2-bromo-6-(4-isopropyl-4,5-dihydro-oxazol-2-yl)pyridine under acidic conditions (HCl), and subsequent partial aromatic substitution of the bromine. After complexation with CuBr.SMe 2 , X-ray structure analysis reveales a 3:1 Cl/Br disorder ratio at the 2-halopyridine position, and the complex contains an unprecedented coordination motif of two [(2-halo-6-oxazolinyl)pyridine]Cu II Br units bridged by a Br atom and a hydroxide group. To the best of our knowledge there are various triple bridged dinuclear Cu II complexes bearing different µ 3 -bridging ligands (µ-OH, µ-Br and µpyridazine) (Thompson et al., 1987), but only two double bridged dinuclear Cu II complexes with Cl and OH as µ 2bridging anions have been reported (Walther et al., 1997;Mezei & Raptis, 2004).
In analogy to a previous report, complex (I) was obtained by aerial oxidation of a CDCl 3 solution of a red oxazolinyl pyridine/CuBr complex (Walther et al., 1997). The X-ray structure analysis confirms a distorted tetragonal-pyramidal coordination geometry at the Cu II centers of the dimeric complex. Both chiral oxazolinyl pyridine ligands act as a Noteworthy is the absence of hydrogen bonds for the bridging OH-group. This OH-group is located in a "pocket" constituted by two Br and two Cl atoms of the same molecule. As a consequence no hydrogen-acceptor atom is accessible for hydrogen-bond formation. Although this hydrogen is on a restrained position, it is the only possible location.

S3. Refinement
The two positions of the disordered Cl-versus Br-atoms were determined from the difference map and refined anisotropically with occupancies of 0.75 (Cl) and 0.25 (Br). All H atom bound to C atoms were placed in calculated positions (C -H = 0.95 or 0.98 or 0.99 or 1.00 Å) and refined as riding on their parent atoms with U iso (H) = 1.2 U eq (C) or 1.5 U eq (C). The H atoms bound to the bridging OH groups were found in Fourier difference map, restrained with O-H = 0.85 (2) Å and refined with U iso = 1.2U eq (O) supporting information sup-3 Acta Cryst. (2008). E64, m24-m25

Figure 1
The independent components of (I), showing the atom-labelling scheme. The structure contains a 3:1 Cl/Br disorder at  CPK-plot of the bridging OH-group located in a pocket constituted by two Br (green) and two Cl (orange) atoms, illustrating no possibility for hydrogen bonding.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 0.92 e Å −3 Δρ min = −0.90 e Å −3 Extinction correction: SHELXL, Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.00132 (10) Absolute structure: Flack (1983), 2880 Friedel pairs Absolute structure parameter: −0.002 (7) 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. (