Structure cristalline de (NH4)2PO3H,H2O: Stereochimie de l'Ion PO3H2− et ses relations avec PO3F2− et SO32−

(NH₄)₂PO₃H, H₂O crystallizes in the monoclinic system, space group P2₁/c, with a = 6.322(1) Å, b = 8.323(1) Å, c = 12.676(1) Å, β = 98.84(1) and Z = 4. The structure was refined to R = 0.022 based on 853 independent X-Rays intensities. Improved dimensions of the tetrahedral PO₃H^2? ion have been obtained: P?H = 1.34(2) and P?O = 1.514(2) Å. The geometry of this ion is compared with that of PO₃F^2? and SO₃^2? ions and we find a decrease of the volume: V_F? > V_H+ > V_{lone pair}.