1,4-Bis(2-nitrophenoxy)butane

The asymmetric unit of the title compound, C16H16N2O6, contains one-half molecule, the mid-point of the central C—C bond being located on a crystallographic inversion center. The crystal structure shows weak interactions between the O atoms of the nitro groups and two different C—H groups of the benzene rings. The extended weak hydrogen-bond formation, involving the NO2 groups, generates an infinite three-dimensional network.

The asymmetric unit of the title compound, C 16 H 16 N 2 O 6 , contains one-half molecule, the mid-point of the central C-C bond being located on a crystallographic inversion center. The crystal structure shows weak interactions between the O atoms of the nitro groups and two different C-H groups of the benzene rings. The extended weak hydrogen-bond formation, involving the NO 2 groups, generates an infinite three-dimensional network.   Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x þ 1; y; z; (ii) Àx þ 1; y À 1 2 ; Àz þ 3 2 ; (iii) Àx; Ày; Àz þ 1.

Related literature
Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: SHELXTL-Plus (Sheldrick, 2008); program(s) used to solve structure: SHELXTL-Plus; program(s) used to refine structure: SHELXTL-Plus; molecular graphics: SHELXTL-Plus and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXTL-Plus.  The title compound (I) has been synthesized as a chemical precursor of a variety of acyclic and macrocyclic multidentate ligands and metal complexes.
Compound (I) crystallizes with the molecule being situated on a crystallographic inversion center that is localized at the midpoint of the C8-C8 i bond [symmetry code: (i) -x, -y, -z + 1] (Fig. 1). As a consequence of the centrosymmetric nature of the molecule a dihedral angle of 0° is observed between the benzene rings in (I). The torsion angle between a benzene ring and the corresponding nitro group is 38.5 (1)°. The conformation of the central chain is described by torsion angles, C6-O3-C7-C8, -178.2 (1)°, O3-C7-C8-C8 i , 62.6 (2)° and C7-C8-C8 i -C7 i , constrained by symmetry to 180.0°. This trans-gauche-trans conformation stabilized in the solid state for (I) is less common than the all-trans conformation that is generally found in aliphatic systems. This molecular conformation is stabilized by weak intramolecular hydrogen bonds involving O3 and a symmetry related C-H group (O3···H8B 2.900 (2) Å). Nevertheless, O atoms in (I) may coordinate to a metal center as a chelating ligand after changing the conformation of this potential ligand. These observations suggest that (I) is a highly flexible molecule, with an almost free rotation about all σ bonds.
In addition, the crystal structure shows weak interactions between oxygen atoms of the nitro groups and two different C-H groups of benzene rings (O1···H3A 2.627 and O2···H5A 2.577 Å) as shown in Fig 2. The extended weak H bond formation, using the NO 2 groups, produces an infinite three-dimensional network of the title compound.
The solution was gently boiled and 1,4-dibromobutane (8.40 ml) was added during 30 min. Gentle reflux was mantained for another 2 h. Then solvent (15.0 ml) was destilled from the mixture and the remaining mixture was poured into water (250 ml). The granular yellow solid was filtered off, washed with dilute aqueous sodium hydroxide solution and water, then dried (23.8 g). M.p. 442-443 K, yield 81%.
Suitable crystals were obtained as colorless blocks from acetonitrile solution by slow evaporation of the solvent at 298 K. The solid was characterized by IR (KBr disc), 1 H-NMR and elemental analysis, which are in agreement with the X-ray structure.
supplementary materials sup-2 Refinement Hydrogen atoms bonded to C atoms were included in calculated positions and refined using the riding method, with C-H distances constrained to 0.93 (aromatic CH) and 0.97 Å (methylene CH 2 ) and U iso (H) = 1.2U eq (carrier C). Fig. 1. Molecular structure of (I). Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. Atoms not labelled are related to the asymmetric unit by symmetry code -x, -y, -z + 1.

Special details
Experimental. Experimental absorption correction were not applied because the molecule is purely organic, and no better structure refinement was obtained.
Geometry. All e.s. 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.