Structural Chemistry of 1-Hydroxyethylidenediphosphonic Acid Complexes

The structural features of complexes of 1-hydroxyethylidenediphosphonic acid (HEDP) with different metals (geometric isomerism, dentate numbers and the mode of coordination of organophosphorus ligand, the structural type and degree of oligomerization, regular distortions of the coordination polyhedron, and the mutual influence of the ligands) are considered. The dependences of the complex structures and of the degree of deprotonation of the HEDP ligands on the synthesis conditions (solution pH and metal : HEDP ratio), on the nature of the metal and the outer-sphere cation, on the composition of the hydrate sphere, and on the availability of the accompanying ligands are also established.