Crystal structure of the phosphinyl-stabilised ylide Me3NNP(=O)Ph-2 centerdot H2O

Crystals of trimethylammonio-P,P-diphenylphosphinamidate hydrate, Me3NNP(=O )Ph-2. H2O, are held together by hydrogen bonds which link two Me3NNP(=O)Ph 2 and two water molecules to form a centrosymmetric O4H4 ring belonging to graph set R-4(2)(8). Each P=O oxygen atom can thereby act as acceptor to tw o hydrogen bonds, rather than to only one, as in the two-fold symmetric P=O ...H-O-H...O=P motif commonly found in phosphine oxide hemihydrates. The un usual P-N bond in Me3NNP(=O)Ph-2 is short enough [1.614(3) Angstrom] to ind icate some multiple character.