4-Nitrobenzoic acid–2,2′-biimidazole (2/1)

In the title adduct, C7H5NO4·0.5C6H6N4, the complete biimidazole molecule is generated by a crystallographic inversion centre. In the crystal, N—H⋯O and O—H⋯N hydrogen bonds connects the 4-nitrobenzoic acid and 2,2′-biimidazole units, affording multi-dimensional frameworks with graph-set descriptor R 2 2(9).


Related literature
For the potential applications of coordination complexes as functional materials and enzymes, see: Zhang et al. (2003) For hydrogen-bond motifs, see: Bernstein et al. (1995).  Table 1 Hydrogen-bond geometry (Å , ).

Experimental
A mixture of 4-nitrobenzoic acid (1 mmoL, 0.17 g), biimidazole (1 mmoL, 0.14 g), and iron trichloride (1 mmoL, 0.27 g) in 12 ml distilled water sealed in a 25 ml Teflon-lined stainless steel autoclave was kept at 433 K for three days. Colorless crystals suitable for the single X-ray diffraction were obtained.

Refinement
All H atoms were placed in calculated positions with C-H = 0.93Å and refined as riding with U iso (H) = 1.2U eq (carrier).
The lengths of bond H-O were constrained with 0.82 Å .
Figures Fig. 1. The molecular structure of (I), showing the atom-labelling scheme and with displacement ellipsoids at the 30% probability level. Unlabeled atoms are related to labeled atoms by the symmetry code (-x, 2-y, 1-z).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(F 2 ) is used only for calculat-supplementary materials sup-3 ing 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.