Structure–stability relationships of 3-hydroxypyridin-4-one complexes
Abstract
The structural features of the ligand 1-ethyl-3-hydroxy-2-methylpyridin-4-one HL1 and its tris complexes [ML13]·3H2O (M = Fe 1, Ga 2 and Al 3) have been characterized by single-crystal X-ray diffraction. The crystal structures of complexes 1–3 are isomorphous. The comparisons among HL1 and 1–3 indicate that several resonance forms play an important role in determining their structures. It is concluded that the absolute stabilities of the complexes of Al3+ and Ga3+ are similar and both greater than that of the iron(III) complex. A structural comparison between ligand HL1 and the closely related 1-butyl-3-hydroxypyridin-2-one provides an explanation for the higher affinity of 3-hydroxypyridin-4-ones for Fe3+ over 3-hydroxypyridin-2-ones. The complexes of Al3+ and Ga3+ with HL1 can be crystallized both as tri- and dodeca-hydrates. It is shown by comparing the same complex in different environments that neither the interplanar angle nor the twist angle is a reliable structural parameter to characterize a metal complex.