Trimethylphosphine oxide dihydrate

Trimethylphosphine oxide and water molecules form 16-membered hydrogen-bonded rings interconnected into layers.

The trimethylphosphine oxide molecule is an acceptor of two OÁ Á ÁH-O hydrogen bonds, whereas both water molecules are donors of hydrogen bonds to Me 3 PO and H 2 O, and acceptors of hydrogen bonds from adjacent water molecules (Table 1, Fig. 2). Two Me 3 PO and six H 2 O molecules form a hydrogen-bonded 16-membered ring ( Fig. 2) with an R 6 8 (16) graph-set motif (Etter, 1990). Each water molecule participates in three rings, whereas the trimethylphosphine molecule participates in two rings. These rings are interconnected into layers that extend parallel to the ac plane, whereby each ring is surrounded by six other rings (Figs. 2, 3). Hydrogen-bonded layers and layers of Me 3 P groups are stacked along the b-axis direction (Fig. 3). Table 1 Hydrogen-bond geometry (Å , ).  (11) 172.0 (14)

Figure 2
Hydrogen-bonded rings (depicted by blue dashed lines) are conjoined into layers parallel to the ac-plane.

Figure 3
Crystal packing and the unit cell of Me 3 POÁ2H 2 O viewed along the crystallographic b-axis (top) and c-axis (bottom). Hydrogen bonds are indicated by blue dashed lines.

Figure 1
The asymmetric unit and the atom-labelling scheme of the Me 3 POÁ2H 2 O crystal structure. Displacement ellipsoids are depicted at the 50% probability level, hydrogen atoms are shown as spheres of arbitrary radius, and hydrogen bonds are indicated by blue dashed lines.

Synthesis and crystallization
Trimethylphosphine oxide (2.3 mg) was dissolved in a mixture of acetone-d 6 (0.6 ml) and diethyl ether-d 10 (0.3 ml) in an NMR tube that was capped and cooled to À20 C in an ethanol cooling bath. The Dewar flask containing the bath and sample was sealed and placed in a freezer at À80 C. Crystals of Me 3 POÁ2H 2 O grew within 3 days. The single crystals were examined, selected, and transferred to the diffractometer employing a previously described low-temperature crystalmounting procedure (Lozinšek et al., 2021). The crystals melt at room temperature.

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.