Bis(2-amino-3-nitropyridinium) dichromate(VI)

The title compound, (C5H6N3O2)2[Cr2O7], consists of 2-amino-3-nitropyridinium cations and discrete dichromate anions linked together by N—H⋯O and C—H⋯O hydrogen bonds, forming thick layers parallel to (101). Layer cohesion is ensured by N—H⋯O hydrogen bonding in addition to electrostatic and van der Waals interactions, forming a three-dimensional framework. The dichromate anion is located on a twofold axis that passes through its bridging O atom.

The title compound, (C 5 H 6 N 3 O 2 ) 2 [Cr 2 O 7 ], consists of 2amino-3-nitropyridinium cations and discrete dichromate anions linked together by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, forming thick layers parallel to (101). Layer cohesion is ensured by N-HÁ Á ÁO hydrogen bonding in addition to electrostatic and van der Waals interactions, forming a threedimensional framework. The dichromate anion is located on a twofold axis that passes through its bridging O atom.

S1. Comment
A new engineering strategy using organic-inorganic hybrid materials have appeared over the past years. The challenge was to combine the advantages of organic crystals and those of the inorganic materials. As a part of our study of crystal packing in amino-nitro "push-pull" system, a new organic-inorganic salt, bis (2-amino-3-nitropyridinium) dichromate (I) have been synthesized.
The dichromate anion has a binary internal symmetry since its bridging oxygen atom is located on a twofold axis, and so is built by only one independent (CrO 4 ) group. This later with one independent (2-NH 2 -3-NO 2 C 5 H 3 NH) + cation constitute the asymmetric unit of (I) (Fig. 1).
The dichromate and organic entities manifest different interactions (electrostatic, H-bonds, Van Der Waals) to keep up the three-dimensionel network cohesion (Fig. 2). The main links are from the N-H···O bonds (Table 1) with H···O bond lengths falling in the range from 1.87-2.59 Å.
It's worth noticing the intracation contact N2-H2B···O6 (see Table 1 for symmetry code) which is always present in nitroaniline in which nitro and amino groups are ortho to one another, as clearly shown in a study of hydrogen patterns of nitroaniline derivatives (Panunto et al., 1987). This situation precludes the rotation of the nitro group with respect to pyridinium ring. The angle between the planes of the NO 2 group and the heterocycle is 7.98° for cation, indicating a coplanar geometry.    Projection of (I) along the b axis.

Bis(2-amino-3-nitropyridinium) dichromate(VI)
Crystal data (C 5  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 > σ(F 2 ) is used only for calculating 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.