Metal Complexes with Macrocyclic Ligands. Part XXXIX. Mono‐ and binuclear copper(II) complexes of a bridging bis[1, 4, 7‐triazacyclononane]

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Abstract
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(LH2)]4+, [Cu(LH)]3+, [CuL]2+, and [Cu(LH−1)]+, binuclear complexes such as [Cu2L]4+, [Cu2(LH−1)]3+, and [Cu2(LH‐2)]2+ are also formed in solution. The stability constants and spectral properties of these are reported. The binuclear species [Cu2(LH−1)]3+ specifically reacts with an azide ion to give a ternary complex [Cu2(LH−1)(N3)]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 [Cu2(LH−1)(N3)]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.

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