High Quality Content by WIKIPEDIA articles! Phosphonates or phosphonic acids are organic compounds containing C-PO(OH)2 or C-PO(OR)2 groups (where R=alkyl, aryl). Bisphosphonates were first synthesized in 1897 by Von Baeyer and Hofmann. An example of such a bisphosphonate is HEDP (Etidronic acid or Didronel). Since the work of Schwarzenbach in 1949, phosphonic acids are known as effective chelating agents. The introduction of an amine group into the molecule to obtain -NH2-C-PO(OH)2 increases the metal binding abilities of the phosphonate. Examples for such compounds are NTMP, EDTMP and DTPMP. These common phosphonates are the structure analogues to the well-known aminopolycarboxylates NTA, EDTA, and DTPA. The stability of the metal complexes increases with increasing number of phosphonic acid groups. Phosphonates are highly water-soluble while the phosphonic acids are only sparingly soluble. Phosphonates are not volatile and are poorly soluble in organic solvents.