Ammonium imidazolium dichromate

In the crystal structure of the title compound, (C3H5N2)(NH4)[Cr2O7], the anions and cations are linked through N—H⋯O hydrogen bonds, resulting in a three-dimensional structure which contains three kinds of layers parallel to (001). One layer contains imidazole cations, the other two layers the ammonium cations and dichromate anions. The dichromate anion has an eclipsed conformation with a dihedral angle of 14.65 (18)° between the mean planes of the O—P—O—P—O backbone.

In the crystal structure of the title compound, (C 3 H 5 N 2 )-(NH 4 )[Cr 2 O 7 ], the anions and cations are linked through N-HÁ Á ÁO hydrogen bonds, resulting in a three-dimensional structure which contains three kinds of layers parallel to (001). One layer contains imidazole cations, the other two layers the ammonium cations and dichromate anions. The dichromate anion has an eclipsed conformation with a dihedral angle of 14.65 (18) between the mean planes of the O-P-O-P-O backbone.

Related literature
The title compound was synthesized as part of a search for ferroelectric materials. For general background to ferroelectric compounds with metal-organic framework structures, see: Fu et al. (2009); Ye et al. (2006); Zhang et al. (2008Zhang et al. ( , 2010. For graph-set motifs, see: Bernstein et al. (1995).

Run-Qiang Zhu Comment
We synthesized the title compound to find ferroelectric material by dielectric measurements of compound as a function of temperature (Fu et al., 2009;Ye et al., 2006;Zhang et al., 2008;Zhang et al., 2010). In the range from 190 K to near its melting point (m.p. >370 K), no dielectric anomaly was observed.
A view of the title compound is shown in Fig.1. The structure is consolidated by multiple intermolecular and intramolecular hydrogen bonds between N and O. This hydrogen bondings (table 1, Fig.2) produces a three-dimensional net work. The N···O distances of the hydrogen bonding are in the range of 2.827 (4) -3.011 (4) for table 1. Hydrogen bonding is the most reliable desigen element in the non-covalent assembly of molecules with donor and accept functionalities, and as such it is the most important interaction in crystal engineering (Bernstein et al., 1995).

Experimental
A mixture of imidazole (0.68 g, 10 mmol), ammonium dichromate (2.5 g, 10 mmol) in water was stirred for several days at ambient temperature, red sheet crystals were obtained.

Refinement
Hydrogen atom positions were calculated and allowed to ride on their parent atoms with aromtic C-H = 0.93 Å and N-H = 0.86 Å, and with Uĩso(H) =1.2Ueq(C or N).The H atoms on N1 were freely refined.

Figure 2
Packing diagram of the title compound, showing the structure along the a axis. Hydrogen bonds are shown as dashed lines.

Ammonium imidazolium dichromate
Crystal data 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.