Tri-methyl-phosphine oxide dihydrate.

The title hydrate, Me 3 PO·2H 2 O, crystallizes in the ortho-rhom-bic space group Pbca with eight formula units per unit cell. The extended structure displays O-H⋯O hydrogen bonding, with Me 3 PO mol-ecules as acceptors and water mol-ecules acting as donors and acceptors of hydrogen bonds, forming hydrogen-bonded layers, which propagate in the ac plane.