Ethyl [1-(4-bromophenyl)-1-hydroxy-3-oxobutyl](phenyl)phosphinate monohydrate

In the title hydrate, C18H20BrO4P·H2O, a staggered conformation is found when the organic molecule is viewed down the central P—C bond, with the oxo and hydroxyl groups being diagonally opposite; each of the central P and C atoms has an S-configuration. The crystal structure features supramolecular double chains along the b axis mediated by Ohydroxyl–H⋯Ooxo, Owater–H⋯Ooxo, and Owater–H⋯Owater hydrogen bonds.

In the title hydrate, C 18 H 20 BrO 4 PÁH 2 O, a staggered conformation is found when the organic molecule is viewed down the central P-C bond, with the oxo and hydroxyl groups being diagonally opposite; each of the central P and C atoms has an S-configuration. The crystal structure features supramolecular double chains along the b axis mediated by O hydroxyl -HÁ Á ÁO oxo , O water -HÁ Á ÁO oxo , and O water -HÁ Á ÁO water hydrogen bonds.

Comment
The title hydrate, (I), was investigated as a part of on-going studies on the enantioselective synthesis of the biologically significant R-hydroxyphosphinates (Samanta et al., 2010). The crystal structure analysis of diastereoisomer in (I), Fig.   1, confirms the stereochemistry of the C1 atom to be S and that of the P2 atom to be likewise S. There are significant hydrogen bonding interactions in the structure and the solvent water molecules play a pivotal role in the supramolecular aggregation. Direct links between molecules are found through the agency of O1 hydroxyl -H1o···O2 oxo hydrogen bonds, Fig. 2 Fig. 3.

Experimental
The title compound was prepared as described in the literature (Samanta et al., 2010). Crystals were obtained by dissolving the diastereomeric products obtained in the cross aldol reaction in a minimum amount of ethyl acetate and then diluting with hexane. The solution was kept in the open to allow solvent slow evaporation, and colourless blocks of (I) were obtained after 24 h.
The methyl H-atoms were rotated to fit the electron density. The O-H H atoms were located from a difference map and refined with O-H = 0.840±0.001 Å, and with U iso (H) = 1.5U eq (O).

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