Universal 'bond valence versus bond length' correlation curve for manganese-oxygen bonds

The oxidation-state independent `bond valence (s) versus bond length (r)' correlation curve for manganese-oxygen bonds has been closely approximated using the modified two-parameter Trömel s = f(r) function [Trömel (1983). Acta Cryst. B39, 664-669], s = [(r0 - l)/(r - l)](2), where r0 = 1.763 (2) Å and l = 1.148 (9) Å. The r0 and l refinable parameters of the above function can be regarded as the alternative bond-valence parameters intended for use in the modern bond-valence model [Brown (2009). Chem. Rev. 109, 6858-6919] in cases where the traditional bond-valence parameters (r0; n) and (r0; b) fail.