Crystal-structural role of 1-hydroxyethane-1,1-diphosphonate ions

The crystal-chemical role of the 1-hydroxyethane-1,1-diphosphonic acid (HED P) anions in the crystal structures of compounds studied up until now is an alyzed. The HEDP anions can function as bi-, tri-, tetra-, penta-, or hexad entate ligands and exhibit fourteen different types of coordination. One li gand forms no more than eight O...A bonds with neighboring complex-forming ions A. The HEDP ligands can be at most tridentate chelating ligands with r espect to one A atom; the oxygen atom of the alpha-hydroxy group of HEDP is always involved in the coordination with such A atoms.