On the effective ionic radii for ammonium

A set of effective ionic radii corresponding to different coordination numbers (CNs) and compatible with the radii system by Shannon [Acta Cryst. (1976), A32, 751-767] has been derived for ammonium: 1.40 Å (CN = IV), 1.48 Å (CN = VI), 1.54 Å (CN = VIII) and 1.67 Å (CN = XII). The bond-valence parameters r0 = 2.3433 Å and B = 0.262 Å have been determined for ammonium-fluorine bonds.