On the structure of the NH+4 ion in aqueous solution

X-ray diffraction data from a 3.5 M solution of (NH₄)₂SO₄ and a 1.5 M solution of NH₄ClO₄ were examined. A model, in which NH⁺₄ ions are eight-coordinated with the N-H₂O distance 3.00–3.05 A, is consistent with experimental data, but there are insufficient reasons to prefer such a model to another in which NH⁺₄ ions simply replace H₂O molecules in the unchanged solvent structure.