Oxonium ammonio(cyclopropyl)methylenebis(hydrogenphosphonate) monohydrate

The title compound, H3O+·C4H10NO6P2 −·H2O, was obtained from the reaction of cyclopropanecarbonitrile with PCl3, followed by dropwise addition of water. The asymmetric unit comprises an oxonium cation, a zwitterionic monoanion containing a positively charged ammonium group and two negatively charged phosphonic acid residues and a water molecule of crystallization. The hydroxonium cation and water molecule are hydrogen bonded to the anion and further N—H⋯O and O—H⋯O bonds create a three-dimensional network.

The title compound, H 3 O + ÁC 4 H 10 NO 6 P 2 À ÁH 2 O, was obtained from the reaction of cyclopropanecarbonitrile with PCl 3 , followed by dropwise addition of water. The asymmetric unit comprises an oxonium cation, a zwitterionic monoanion containing a positively charged ammonium group and two negatively charged phosphonic acid residues and a water molecule of crystallization. The hydroxonium cation and water molecule are hydrogen bonded to the anion and further N-HÁ Á ÁO and O-HÁ Á ÁO bonds create a three-dimensional network.

Comment
The organic diphosphonic acids are potentially very powerful chelating agents used in metal extractions and are tested by the pharmaceutical industry for use as efficient drugs preventing calcification and inhibiting bone resorption (Tromelin et al., 1986, Matczak-Jon & Videnova-Adrabinska, 2005. Diphosphonic acids are used in the treatment of Paget disease, osteoporosis and tumoral osteolysis (Szabo et al., 2002). The asymmetric unit of titled compound ( Fig. 1) contains one molecule which exists as zwitterions with the proton transferred from one of the phosphonic group to the nitrogen atom. In the crystal structure of the compound the phosphorus atom displays a slightly distorted tetrahedral geometry provided by three oxygen atoms and one carbon atom. Bond lengths and angles have normal values (Allen et al., 1987). The asymmetric unit contains one hydroxonium ion and one water molecule. The structure is stabilized by three-dimensional intramolecular O-H···O and N-H···O hydrogen bonds network (Table 1).
Dry hydrogen chloride at about 278 K was brought into contact with the surface of a mixture of cyclopropanecarbonitrile (73.7 ml, 1 mol) and PCl 3 (87.4 ml, 1 mol) while stirring the mixture drop-wise addition of water (54 ml, 3 mol) was made in the molar ratio 1:1:3. After an a hour the solution becomes cloudy and sets. After cooling the product it was dissolved in water and separated by addition of acetone. The saturated solution was left at room temperature. Colourless crystals of the title compound were obtained after 1 week.

Refinement
H atoms bonded to O and N atoms were located in a difference map. Other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.99 Å for CH 2 [U iso (H) = 1.2Ueq(N)] and C-H = 1.00 Å for CH [U iso (H) = 1.2Ueq(C)]. The strong H-bond between O5 and O7 was treated as an equilibrium between hydroxonium ion and water molecule. The position of the H atom was freely refined. Fig. 1. The asymmetric unit of title compound showing 50% probability displacement ellipsoids for the non-hydrogen atoms.

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 mat- 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 Rfactors(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.