Synthesis, structure and hydrolytic properties of a family of new Zn complexes containing hexaazamacrocyclic ligands

The synthesis, structure and spectroscopic properties of a family of Zn complexes containing a dinucleating hexaazamacrocyclic ligand (L) and anionic ligands (X) of general formula [Zn2(X)4-n(L)]n+ (1-8; L = H2p, H3p, Me2p, Me2m, Me3p, Me3m; X = Cl, n = 0; X = NO3, n = 2) have been investigated. The solid-state structural characterisation has been performed by means of X-ray diffraction analysis for complexes 3, 5, 7·1/3CH2Cl2 and 8. The Zn complexes 5, 7·1/ 3CH2Cl2 and 8 containing chloride ligands present a distorted N2Cl2 tetrahedral coordination with two non-coordinated N atoms of the macrocyclic ligand. On the other hand, complex 3, which contains nitrate ligands, displays an N3O2 pentacoordination with all the N atoms of the macrocyclic ligand bonded to the metal centres. The different factors governing the relative Zn-Zn disposition are discussed. NMR spectroscopy in solution reveals the presence of fluxional behaviour and a completely different structural arrangement than in the solid state. In particular, evidence for the formation and breaking of Zn-N bonds involving all the macrocyclic ligand aminic N atoms is obtained for the chloride complexes 2 and 4-8. Finally, complexes 1, 3, 5 and 7 hydrolyse p-nitrophenyl acetate (NA) with second-order rate constants ranging from 0.045 to 0.193 M -1S-1, thus manifesting the influence of the ligands over the hydrolytic activity. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.