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 angstrom (CN = IV), 1.48 angstrom (CN = VI), 1.54 angstrom (CN = VIII) and 1.67 angstrom (CN = XII). The bond-valence parameters r(0) = 2.3433 angstrom and B = 0.262 angstrom have been determined for ammonium-fluorine bonds.