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 d_π–p_π bonding in inorganic heterocycles is discussed.