FORMATION EQUILIBRIUM OF A COPPER(II)-BINUCLEAR COMPLEX OF A NEW PYRIDYL-CONTAINING TETRAOXO OCTAAZA MACROCYCLIC LIGAND AND ITS POLAROGRAPHIC-REDUCTION BEHAVIOR

We have studied the complexation reaction of a newly synthesized 26-membered octaaza macrocycle, 3, 6, 9, 17, 20, 23, 29, 30-octaazatricyclo[23.3.1.1.(11,15)]triaconta-1(29), 11, 13, 15(30), 25, 27-hexaene-2, 10, 16, 24-tetraone (TOBP, L), with a Cu(II) ion by pH-metric titration. It accomodates two copper(II) ions in its macrocyclic cavity with a simultaneous dissociation of the four amide protons to yield a binuclear complex designated as [Cu(2)H(-4)L]degrees. The formation constant of [Cu(2)H(-4)L]degrees, K-Cu2H-4L (=[Cu(2)H(-4)L degrees][H+](4)/[Cu2+](2)[L]), was found to be (3.5+/-0.2)x10(-12) mol(2) dm(-6). At the dropping mercury electrode the Cu(II) binuclear complex gave two reduction steps of equal height in a berate buffer solution, corresponding to the following reduction scheme: [GRAPHICS] ICS]