Metal chelates of phosphonate-containing ligands-I Stability of some N,N,N',N'-ethylenediaminetetra(methylenephosphonic) acid metal chelates

A potentiometric investigation of the acid dissociation constants of the octabasic ENTMP [N,N,N',N'-ethylenediaminetetra(methylenephosphonic) acid] is reported. The stability constants of protonated MH(n)L (n = 1, 2, 3 and 4) and unprotonated ML metal chelates of Mg, Ca, Ba and Cd with ENTMP have been measured. The stabilities are in the order Mg < Ca < Ba < Cd.