Syntheses for 2-(pyridyl N-oxide) methylphosphonic acid, 1-H, and 2-(pyridyl N-oxide) hydroxymethylphosphonic acid, 4-H, are described, and the crystal structures of both ligands are presented, Combination of these ligands with freshly prepared erbium hydroxide results in the formation of the isostructural complexes Er(L-)(3)(LH).8H(2)O. The crystal structure determinations of the complexes show that extensive hydrogen bonding links the individual eight coordinate Er(L-)(3)(LH) molecular units into a 3-D structure.