Bis(3,5-diamino-4H-1,2,4-triazol-1-ium) 3,4-dioxocyclobutane-1,2-diolate

The asymmetric unit of the title compound, 2C2H6N5 +·C4O4 2−, contains two 3,5-diamino-4H-1,2,4-triazolium cations and one squarate dianion. The squaric acid molecule donated one H atom to each of the two 3,5-diamino-1,2,4-triazole molecules at their N atoms. The squaric acid dianion has four C—O bonds which are shorter than a normal single C—O bond (1.426 Å) and are slightly longer than a normal C=O bond (1.23 Å), which indicates the degree of electron delocalization in the dianion. In the crystal, the cations and dianions are linked by N—H⋯N and N—H⋯O hydrogen bonds into a three-dimensional network.

The asymmetric unit of the title compound, 2C 2 H 6 N 5 + ÁC 4 O 4 2À , contains two 3,5-diamino-4H-1,2,4-triazolium cations and one squarate dianion. The squaric acid molecule donated one H atom to each of the two 3,5-diamino-1,2,4-triazole molecules at their N atoms. The squaric acid dianion has four C-O bonds which are shorter than a normal single C-O bond (1.426 Å ) and are slightly longer than a normal C O bond (1.23 Å ), which indicates the degree of electron delocalization in the dianion. In the crystal, the cations and dianions are linked by N-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds into a three-dimensional network.
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009  Hydrogen-bonded systems generated from organic cations and anions are of special interest since they are likely to show stronger hydrogen bonds than neutral molecules thus enabling the simple acid-base chemistry to tune the donor and acceptor properties of the counter ions (Mathew et al., 2002). Squaric acid (H 2 C 4 O 4 , 3,4-dihydroxy-3-cyclobutene-1,2dione) has been of much interests because of its cyclic structure and possible aromaticity (Frankenbach et al., 1992;Yeşilel et al., 2008). The molecule possesses a certain degree of electron delocalization, but it is most pronounced in the dianion (Mathew et al. 2002). This property is important in crystal packing (Bertolasi et al., 2001). The squarate dianion does not act like a chelating ligand but rather like a bridge between two or more metal atoms as a mono-or polydentate ligand. The 1,3-bis (monodentate) bridging coordination mode is very useful in generating one dimensional polymeric structures and the dimensionality can be expanded to two-dimensional or three-dimensional arrays using multidentate spacer ligands (Correa et al., 2007). We have been interested in the preparation of metal complexes by organic amines and carboxylic acids. In line with our interests, it was our design to synthesize a squarato-bridged zinc(II) complex.
However, our proposed structure was not obtained; instead a new polymeric supramolecular triazolium squarate structure was formed. Herein we present the crystal structure of the new compound.
In the crystal packing (Fig. 2), the structure of the compound is stabilized by intermolecular N-H···N and N-H···O hydrogen bonds (Table 1) into a three dimensional network.

Experimental
Zinc chloride (1 mmol, 0.136 g) and 3,5-diamino-1,2,4-triazole (1 mmol, 0.099 g) were dissolved in 10 ml of distilled water. The solution was heated gently for 5 minutes, followed by drop-wise addition of an aqueous solution of squaric acid (0.057 g, 0.5 mmol) dissolved in 5 ml of hot water. The mixture was heated on a steam bath for 15 minutes and filtered while hot. The filtrate was allowed to crystallize at ambient temperature.

Refinement
All the H atoms were located in a difference Fourier map and were refined freely [N-H = 0.867 (13) to 1.001 (15) Å].

Figure 1
The molecular structure of the title compound, showing 50% probability displacement ellipsoids.  The crystal packing of the title compound, approximately viewed along the b axis, showing the three dimensional network.  (Cosier & Glazer, 1986) operating at 100.0 (1) K. 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.