Reinvestigation of the crystal structure of ammoniumtetrametaphosphate, (NH4)4P4O12

Abstract
The crystal structure of (NH4)4P4O12 has been reinvestigated in order to obtain accurate values for the bond lengths and angles in the P4O12 4– ion. Three-dimensional intensity data were recorded on an automatic three-circle diffractometer, using Mo radiation. The structure was refined by anisotropic block-diagonal least-squares methods to R 5·5% for 1431 observed independent reflexions. The P4O12 4– ion has a chair-shaped eight-membered ring structure. The bond lengths and angles are: P–O(endo) 1·613(4), 1·600(4); P–O(exo) 1·472(4), 1·481(4), 1·483(4)Å; P–O–P 131·2(0·2); O(endo)–P–O(endo) 98·7 (0·2), 104·5(0·2); O(exo)–P–O(exo) 122·2(0·2), 118·7(0·2)°. The significance of these results in connection with current theories on dπpπ bonding in inorganic heterocycles is discussed.

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