1-Nitro-4-(4-nitrophenoxy)benzene: a second monoclinic polymorph

In the title compound, C12H8N2O5, the aromatic rings are inclined to one another by 56.14 (7)°. The nitro groups are inclined by to the benzene rings to which they are attached by 3.86 (17) and 9.65 (15)°. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming a three-dimensional structure. The title compound is a new monoclinic polymorph, crystallizing in space group P21/c. The first polymorph crystallized in space group C2/c and the molecule possesses twofold rotation symmetry. Two low-temperature structures of this polymorph (150 K and 100 K, respectively) have been reported [Meciarova et al. (2004). Private Communication (refcode IXOGAD). CCDC, Cambridge, England, and Dey & Desiraju (2005). Chem. Commun. pp. 2486–2488].

In the title compound, C 12 H 8 N 2 O 5 , the aromatic rings are inclined to one another by 56.14 (7) . The nitro groups are inclined by to the benzene rings to which they are attached by 3.86 (17) and 9.65 (15) . In the crystal, molecules are linked by C-HÁ Á ÁO hydrogen bonds, forming a three-dimensional structure. The title compound is a new monoclinic polymorph, crystallizing in space group P2 1 /c. The first polymorph crystallized in space group C2/c and the molecule possesses twofold rotation symmetry. Two low-temperature structures of this polymorph (150 K and 100 K, respectively) have been reported [Meciarova et al. (2004). Private Communication (refcode IXOGAD). CCDC, Cambridge, England, and Dey & Desiraju (2005). Chem. Commun. pp. 2486Commun. pp. -2488.

Comment
The molecular structure of the title molecule is illustrated in Fig. 1. The molecule has a a twisted V-shape with the two nitrophenyl rings being inclined to one another by 56.14 (7) °. The nitro group N11/O11/O12 is inclined to the benzene ring C11-C16, to which it is attached, by 3.86 (17) °, while the nitro group N21/O21/O22 is inclined to benzene ring C21-C26 by 9.65 (15) °.
In the crystal, molecules are linked by C-H···O hydrogen bonds forming a three-dimensional structure (Table 1 and Fig. 2).
The title compound is a new monoclinic polymorph, crystallizing in space group P2 1 /c. The first polymorph crystallized in space group C2/c and the the molecule possesses two-fold rotation symmetry with the ether O atom lying on the twofold rotation axis. The 150 K structure was reported on by (Meciarova et al., 2004), while the 100 K structure was reported on by (Dey & Desiraju, 2005). Taking the 100 K structure as reference it can be seen that the molecular structure is slightly different to that of the present polymorph with the two nitrophenyl rings being inclined to one another by 66.75 (6) ° and the nitro group being inclined to the benzene ring by 12.97 (13) °. In the crystal, molecules are also linked by C-H···O hydrogen bonds forming a three-dimensional structure.

Experimental
A mixture of 4-nitrochlorobenzene (38.2 mmol), 1,6-hexan-diol (19.1 mmol) and anhydrous potassium carbonate (38.2 mmol) in 50 ml of THF was placed in a three necked prebaked round bottom flask fitted with a reflux condenser, a nitrogen inlet and a magnetic stirrer. After refluxing for 18 h in an inert atmosphere, the mixture was cooled to room temperature and poured into 400 ml of water, yielding a yellow solid. The product was filtered, dried and recrystallized from ethanol. The title compound was obtained as a by-product in the form of block-like yellow crystals [yield 10%; M.p. = 416 K].

Refinement
C-bound H atoms were included in calculated positions and refined as riding atoms: C-H = 0.95 Å with U iso (H) = 1.2U eq (C).