Structure of triphenylphosphine oxide hemihydrate.

C18H15OP.1/2H2O, Mr = 287.30, orthorhombic, Fdd2, a = 19.794 (18), b = 32.540 (12), c = 9.459 (6) A, V = 6092.5 (22) A3, Z = 16, Dx = 1.253 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 1.76 cm-1, F(000) = 2416, T = 294 K, R = 0.037 for 1677 reflections with I greater than 3 sigma(I). The water O atoms sit on a crystallographic twofold axis and are linked by hydrogen bonds to two of the oxide molecules with O...OW distances of 2.856 (3) A. Considerable conformational flexibility is conferred on the molecule by the long P--C bonds (around 1.8 A each).