Poly[1H-imidazol-3-ium [di-μ-nitrato-sodium]]

In the title compound {(C3H5N2)[Na(NO3)2]}n, the NaI ion is coordinated by eight O atoms from three bidentate nitrate anions and two O atoms from two monodentate nitrate anions, displaying a bicapped trigonal–prismatic geometry. The imidazolium cation is essentially planar (r.m.s. deviation for all non-H atoms = 0.0018 Å). In the crystal, the NaI ions are connected by bridging nitrate ligands, forming layers parallel to (010). The imidazolium cations are sandwiched between these layers. Weak C—H⋯O hydrogen bonds link the layers into a three-dimensional network. In addtion, π–π interactions between the imidazolium rings [centroid–centroid distance = 3.588 (3) Å] are observed.


compound.
The asymmetric unit of the title compound (I) (Fig. 1) contains one Na I ion, one protonated imidazole molecule and two coordinated nitrate anions. The Na centre is coordinated by eight O atoms from three bidentate nitrate anions and two O atoms from two monodentate nitrate anions, displaying a bicapped trigonal-prismatic geometry (Fig. 2). The Na-O bond distances range from 2.4321 (16) to 2.6239 (17) Å. The C-N distances lie in the range 1.328 (2)-1.376 (2) A°. The imidazolium cation is essentially planar giving an r.m.s. deviation for all non-H atoms of 0.0018 A°, with a maximum deviation from the mean plane of -0.0028 (1)Å for the C4 atom. The crystal packing can be described by alterning twodimensional polymecric layers and double layers of imidazolium ions. A two-dimensional layer structure is thus constructed parallel to (010) (Fig. 3). Weak hydrogen bonds are formed between imidazolium cation and the nitrate O atoms of adjacent layers ( Fig. 3) further connect the two-dimensional layers into a three-dimensional network. In addition, π···π contacts between the imidazolium rings, [centroid-centroid distance = 3.588 (3) Å with ca 1.382 Å slippage] are also observed.

Experimental
All chemicals used (reagent grade) were commercially available. The compound was obtained by using hydrothermal method in Teflon-lined autoclave. The mixture of barium nitrate, imidazole, sodium hydroxide and deionized water in the molar ratio 1:1:3:264 was stirred for half an hour, and transferred in a Teflon-lined autoclave, then treated at 423 K for 4 d. After the mixture was slowly cooled to room temperature, colorless needles suitable for X-ray diffraction analysis were collected from the final reaction system by filtration, washed several times with distilled water and dried in air at ambient temperature.

Refinement
Approximate positions for all the H atoms were first obtained from the difference electron density map. However, the H atoms were situated into idealized positions and the H-atoms have been refined with the riding-model approximation. The applied constraints were as follow: C aryl -H aryl = 0.95 Å; N aryl -H aryl = 0.88 Å and U iso (H aryl ) = 1.2 U eq (C aryl ).

Figure 1
The asymetric unit of (I), with displacement ellipsoids drawn at the 50% probability level.  The coordination of the unieque Na I ion.  A partial packing diagram of (I), showing alterning layers with hydrogen bond shown as dashed lines.

Poly[1H-imidazol-3-ium [di-µ-nitrato-sodium]]
Crystal data (C 3  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.19 e Å −3 Δρ min = −0.29 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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.