Hydroxonium 1-ammonioethylidene-1,1-bisphosphonate

The title compound, H3O+·C2H8NO6P2 −, contains a disordered H3O+ cation and an NH3C(CH3)(PO3H)2 anion. The three H atoms of the H3O+ cation are statistically distributed over four positions with occupancies of 0.75, resulting in a pseudo tetrahedron. Multiple N—H⋯O and O—H⋯O hydrogen bonds generate an intricate three-dimensional network.

The title compound, H 3 O + ÁC 2 H 8 NO 6 P 2 À , contains a disordered H 3 O + cation and an NH 3 C(CH 3 )(PO 3 H) 2 anion. The three H atoms of the H 3 O + cation are statistically distributed over four positions with occupancies of 0.75, resulting in a pseudo tetrahedron. Multiple N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds generate an intricate three-dimensional network.

Comment
Phosphonic acids are interesting ligands. They can complex various metal ions and a series of organic-inorganic hydrid materials containing phosphonic acids have been prepared and characterized. Such materials have potential applications in catalysts, sensors, sorbents, magnetic and luminescent materials (Finn et al., 2003). In addition, introduction of some functional groups to phosphonic acids, such as crown ether, -COOH, -OH, -NR 2 or mixed group will modify their complexing ability (Clearfield, 2002). 1-Aminoethylidene-1,1-diphosphonic acid (AEDPH 4 ) exists as a zwitterion and is inclined to transfer one proton to the amino group (Bollinger & Roundhill, 1993;Fernández et al., 2003;Li et al., 2008 ). Its deprotonation would result in predictable hydrogen aggregates from stronger P-O-H···O-P to weaker C-H···O hydrogen bonds.
However, its crystal structure is still unknown (Yin et al., 2005). Herein, we report the structure of the title compound, (I).
The asymetric unit of (I) is built up from one deprotonated AEDPH 4 anion and a disordered H 3 O + cation which are linked through OW-H···O hydrogen bonds ( Fig. 1, Table 1 Table 1).

Experimental
The title compound was synthesized according to the US Patent 4239695 (Chai et al., 1980). It was crystallized unexpectedly when 4,4 ' -bipyridine was adding into the AEDPH 4 H 2 O solution to synthesize the complex. However, the 4,4 ' -bipyridine was not present in the final product. Hydroxonium 1-ammonioethylidene-1,1-bisphosphonate

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.