Effective Ionic Radii in Nitrides

A set of 102 empirical effective ionic radii applicable to nitrides has been derived from over 500 experimental interatomic distances observed in 324 crystal structure determinations of nitrides, amides, ammines, cyanides, azides, imides, nitrosyls, nitryls and of organometallic compounds. The radii take into account the oxidation numbers and electronic spin states of the cations, and the coordination numbers of both the cations and nitride ions. Cation-nitride interatomic distances can be estimated from the sums of the appropriate radii, on average within less than 0.02 A of the observed experimental distances. These radii are empirically useful, but no physical significance should be attached to them. The dependence of the nitride ion radius on coordination number is greater than that of the oxide ion. Individual cation radii can assume rather different values, depending on whether they are bonded to oxide, sulfide or nitride ions. Effective ionic radii are useful, among other things, for checking that the results of crystal structure determinations are reasonable, and for predicting cation-anion distances to be used as observations in the computer simulation of crystal structures.