2-Nitrophenylacetic acid: hydrogen-bonded sheets of R 22 (8) and R 44 (18) rings

Mol­ecules of the title compound, C8H7NO4, are linked into centrosymmetric R22(8) dimers by paired O—H⋯O hydrogen bonds, and these dimers are linked by two C—H⋯O hydrogen bonds into sheets of R22(8) and R44(18) rings.

The plane of atoms C1/C11/C12 is almost orthogonal to the plane of the aryl ring ( Fig. 1, Table 1), while the C-NO 2 plane makes a dihedral angle of 30.1 (2) with the ring.
The molecules of (I) are linked into sheets by a combination of N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds (Table 2). Paired O-HÁ Á ÁO hydrogen bonds link the molecules into centrosymmetric R 2 2 (8) (Bernstein et al., 1995) dimers (Fig. 2). Two C-HÁ Á ÁO hydrogen bonds link the dimers, so forming a (100) sheet built from R 2 2 (8) and R 4 4 (18) rings. The resulting net is of type (4,4) (Batten & Robson, 1998). There are no direction-specific interactions between adjacent sheets. In particular, C-HÁ Á Á(arene) hydrogen bonds and aromaticstacking interactions are both absent. The structure of the isomeric 4-nitrophenylacetic acid, (II), was reported some years ago [Cambridge Structural Database (Version of November 2005;Allen, 2002) refcode SEMTAF; Grabowski et al., 1990]. The authors reported the formation of a centrosymmetric hydrogen-bonded dimer, but further aggregation of the dimers was not reported. In the event, the dimers are linked into sheets by a single aromaticstacking interaction (Fig. 4).

Experimental
A commercial sample of (I) (Acros) was crystallized from ethanol (m.p. 412-413 K).  The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
Part of the crystal structure of (I), showing the formation of a centrosymmetric R 2 2 (8) dimer. For the sake of clarity, H atoms bonded to C atoms have been omitted. Atoms marked with an asterisk (*) are at the symmetry position (1 À x, 1 À y, 1 À z).

Figure 3
A stereoview of part of the crystal structure of (I), showing the formation of a (100) sheet of R 2 2 (8) and R 4 4 (18) rings. For the sake of clarity, H atoms bonded to aromatic C atoms have been omitted.

Figure 4
A stereoview of part of the crystal structure of (II), showing the formation of a sheet of -stacked hydrogen-bonded dimers. The original atomic coordinates (Grabowski et al., 1990) have been used. For the sake of clarity, H atoms bonded to C atoms have been omitted. Table 1 Selected torsion angles ( ).