1,2-Bis[2-(2-nitro-1H-imidazol-1-yl)ethoxy]ethane

In the crystal structure, the title compound, C12H16N6O6, lies on an inversion centre. The molecule has an antiperiplanar conformation with respect to the C—C bond of the central ethane unit and the two imidazole rings are parallel to each other. The dihedral angle between the imidazole ring and the mean plane of the C and O atoms of the bis(ethoxy)ethane group is 76.04 (6)°. The molecules are stacked along the c axis through a weak C—H⋯O interaction and a π⋯π interaction between the imidazole rings with a centroid–centroid distance of 3.5162 (6) Å. An intramolecular C—H⋯O hydrogen bond is also present.

In the crystal structure, the title compound, C 12 H 16 N 6 O 6 , lies on an inversion centre. The molecule has an antiperiplanar conformation with respect to the C-C bond of the central ethane unit and the two imidazole rings are parallel to each other. The dihedral angle between the imidazole ring and the mean plane of the C and O atoms of the bis(ethoxy)ethane group is 76.04 (6) . The molecules are stacked along the c axis through a weak C-HÁ Á ÁO interaction and a Á Á Á interaction between the imidazole rings with a centroid-centroid distance of 3.5162 (6) Å . An intramolecular C-HÁ Á ÁO hydrogen bond is also present.

Comment
Depending on the availability of oxygen in tissue, nitroimidazoles can undergo different intracellular metabolism. In a normal cell, the molecule undergoes reduction to become a potentially reactive species and can be reoxidized in the presence of normal oxygen levels. In hypoxic tissue, however, the low oxygen concentration is not able to effectively reoxidize the molecule which results in more reactive intermediates that bind with components of hypoxic tissues (Nunn et al., 1995). Thus these compounds can function as hypoxia markers for imaging of hypoxic cells and have received much attention in medicinal and clinic studies (Abdel-Jalil et al., 2006;Kennedy et al., 2006;Nagasawa et al., 2006). In an attempt to develop new hypoxic cell radiosensitizers, we present herein the synthesis and crystal structure of the title nitorimidazole compound, (I).
Bond distances and angles have normal values (Allen et al., 1987).
The crystal packing of (I) in Fig. 2 shows that the molecules are linked by weak C-H···O interactions (Table 1) and stacked into columns along the c axis. The molecules in the adjacent columns are in a face-to-face fashion (Fig. 3). The crystal is stabilized by a weak C-H···O interaction (Table 1). A π···π interaction was also observed in the crystal with the Cg 1 ···Cg 1 ii [symmetry code: (ii) x, 1/2 -y, -1/2 + z] distance of 3.5162 (6) Å; Cg 1 is the centroid of the N1/N2/C1-C3 ring.

Experimental
To a solution of the triethyleneglycol ditosylate (0.458 g, 1.0 mmol) and triethyamine (244 mg, 2.4 mmol) in DMF (10 ml All H atoms were located in a difference map and refined isotropically. Figures Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids and the atomic numbering.

Special details
Experimental. The low-temparture data was collected with the Oxford Cryosystem Cobra low-temperature attachment. 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 Rfactors(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. The highest residual electron density peak is located at 0.76 Å from C6 and the deepest hole is located at 1.04 Å from C1.