STABILITY-CONSTANTS OF DIVALENT TRANSITION AND TRIVALENT LANTHANIDE METAL-ION COMPLEXES OF MACROCYCLIC TRIAZATRI(METHYLACETIC ACID)

The azacrown compound, 1,7-dioxa-4,10,13-triazacyclopentadecane-N,N',N ''-tri(methyl-acetic acid)(N3O2-tri(methylacetic acid)) was synthesiz ed by modified procedure of Krespan. Potentiometric method has been us ed to determine the protonation constants of N3O2-tri(methylacetic aci d) and stability constants of complexes on the divalent transition met al ions (Co2-, Ni2-, Cu2-, and Zn2-) and trivalent metal ions (Ce3+, E u3+, Gd3+, and Yb3+) with N3O2-tri(methylacetic acid). The stability c onstants for the complexes of the divalent transition metal ions studi ed in the present work with N3O2-tri(methylacetic acid) were 11.4 for Co2-, 11.63 for Ni2+, 13.51 for Cu2+, and 11.65 for Zn2+, respectively . Thus, the order of the stability constants for complexes on the tran sition metal ions with N3O2-tri(methylacetic acid) was shown Co2-<Ni2- <Cu2->Zn2- as same as the order of Irving-Williams series. The stabili ty constants of Ce3+ Eu3-, Gd3-, and Yb3- trivalent lanthanide metal i on complexes of N3O2-tri(methylacetic acid) were, respectively, 11.26 for Ce3-, 11.56 for Eu3-, 11.49 for Gd3+, and 11.80 for Yb3+. The valu es of the stability constants on trivalent metal ions with the ligand are increasing according to increase atomic number, due to increase ac idity. But the value of stability constant of Gd3- ion is less than th e value of Eu3+ ion. This disordered behavior is also reported by Moel ler.