The betainic form of (imidazol-2-yl)phenylphosphinic acid hydrate

Single crystals of the title compound, (imidazolium-2-yl)phenylphosphinate monohydrate, C9H9N2O2·H2O, were obtained from methanol/water after deprotection and oxidation of bis(1-diethoxymethylimidazol-2-yl)phenylphosphane. In the structure, several N–H⋯O and P—O⋯H–O hydrogen bonds are found. π–π interactions between the protonated imidazolyl rings [centroid–centroid distance = 3.977 (2) Å] help to establish the crystal packing. The hydrate water molecule builds hydrogen bridges to three molecules of the phosphinic acid by the O and both H atoms.

The molecular structure of the title compound is shown in Figure 1 Table 1). These chains are further connected by N-H···O and O-H···O hydrogen bonding to the water molecules. Each two water molecules and two symmetry related molecules of the title compounds forms 8-membered hydrogen bonded rings that are located on centres of inversion. Additionally to the hydrogen bonding network, in the solid state packing a pairwise π-π stacking of imidazolyl rings with a centroid distance of 3.977 Å is observed ( Figure 3).

Experimental
To a solution of 1-diethoxy-2-isopropylimidazole (Kunz et al., 2003) in diethyl ether a solution of tert.-BuLi in hexane (1.5 M, 1.1 equivalents) is added dropwise at -78 °C. After the solution was stirred for 30 min at -78 °C and 30 min at room temperature the temperature is lowered again to -78 °C and half an equivalent of dichlorophenylphosphane in diethyl ether (20 ml) is added drop-wise. After the mixture was stirred over night conc. ammonia was added, the phases were separated and the organic layer washed with bidest. water (3 x 100 ml). The organic layer was dried over anhydrous Na 2 SO 4 . After filtration and removal of the volatiles in vacuo the protected (imidazolyl)phosphane was obtained. After deprotection in an acetone-water mixture (10:1) perhydrol was added. The product precipitated as white solid which was collected by filtration,

Refinement
Appropriate positions of all H atoms were found in difference map. The C-H atoms and the H atom of N1 were positioned with idealized geometry and refined using a riding model with U iso (H) = 1.2 U eq (C,N). For the O-H H atoms and the H atom at N2 positional and isotropic displacement parameters were refined. Fig. 1. The components of the title compound with their hydrogen bond enviroment. Hydrogen atoms are drawn with an arbitrary radius and displacement ellipsoids at the 30% probability level. Dashed lines indicate hydrogen bonding establishing a three dimensional network. Fig. 2. Diagram showing the supramolecular association of the betainic acid and water molecules of I in layers perpendicular to [-1 0 1]; symmetry codes: (A) x +1/2, y -1/2, z -3/2; (B) x + 1/2, -y + 3/2, z + 1/2 (C) -x + 1, -y + 1, -z + 2; (D) x + 1, y, z + 1; (E) -x + 3/2, y -1/2, -z + 5/2; the atoms of the unlabeled left part of the figure are generated by translation along [0 0 -1].

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.
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq P1 0.21068 (