Study of homo- and heteronuclear complex formation in 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP)—erbium(iii) and HEDP—erbium(iii)—calcium(ii) systems in an aqueous solution

Erbium( iii )—HEDP and erbium( iii )—calcium( ii )—HEDP systems (HEDP is 1-hydroxyethylidene-1,1-diphosphonic acid) have been studied using potentiometry method in association with mathematical modelling. In the erbium( iii )—HEDP system the formation of compexes having various degree of deprotonation of a ligand, 1 : 1 and 2 : 1 monoand dinuclear complexes, as well as mononuclear bis-complexes has been shown. It was found, that heteronuclear complexes generated in erbium( iii )—calcium( ii )—HEDP system, do not coincide neither with calcium nor with erbium forms in composition.