METAL-COMPLEXES WITH MACROCYCLIC LIGANDS .39. MONONUCLEAR AND BINUCLEAR COPPER(II) COMPLEXES OF A BRIDGING BIS[1,4,7-TRIAZACYCLONONANE]

The new bis-macrocycle 1,1'-[(1H-pyrazol-3,5-diyl)bis(methylene)]bis[1,4,7-triazacyclononane] (1) was synthesized and its complexation with Cu2+ studied. Potentiometric and spectrophotometric titrations indicate that, in addition to the mononuclear species [Cu(LH(2))](4+), [Cu(LH)](3+), [CuL](2+), and [Cu(LH(-1))](+), binuclear complexes such as [Cu(2)L](4+), [Cu-2(LH(-1))](3+), and [Cu-2(LH(-2))](2+) are also formed in solution. The stability constants and spectral properties of these are reported. The binuclear species [Cu-2(LH(-1))](3+) specifically reacts with an azide ion to give a ternary complex [Cu-2(LH(-1))(N-3)](2+), the stability and structure of which were determined spectrophotometrically and by X-ray diffraction, respectively. The two Cu2+ ions are in a square-pyramidal coordination geometry. The axial ligand is one of the N-atoms of the 1,4,7-triazacyclononane ring, whereas at the base of the square pyramid, one finds the other two N-atoms of the macrocycle, one N-atom of the pyrazolide and one of the azide, both of which are bridging the two metal centres. In [Cu-2(LB(-1))(N-3)](2+), a strong antiferromagnetic coupling is present, thus resulting in a species with a low magnetic moment of 1.36 B.M. at room temperature.