Manganese complexes with planar or tridimensional acyclic or cyclic Schiff base ligands

The coordination properties toward manganese(II) salts of a variety of [1 + 2], [2 + 1], [2 + 2] and [3 + 1] acyclic and cyclic ligands with different shapes and coordinating moieties have been studied. These ligands, obtained by condensation of suitable formyl- and primary amine precursors, give rise to mono- or dinuclear manganese(II) or manganese(III) complexes, characterized by elemental analyses, IR spectroscopy, ESI-MS spectrometry together with X-ray structural determinations. In particular, in the structure of [Mn(H 3-L C2)(H 2O) 2](Cl)(H 2O), where the planar, potentially dinucleating ligand H 5-L C2 forms by the [2 + 1] condensation of pyridoxal hydrochloride and 1,3-diamino-2-propanol, the central octahedral manganese(III) ion resides into the N 2O 2 Schiff base moiety of [H 3-L C2] 2-, which does not behave as a compartmental system as the central alcoholic group does not take part in the coordination. In [Mn(H 3-L A5)]·0.25H 2O·CH 3OH, where the potentially dinucleating ligand H 6-L A5 forms by the [3 + 1] condensation of 3-formylsalicylic acid and tris(aminoethyl)amine, the central octahedral manganese(III) ion resides into the external O 3O 3 site while the inner N 4O 3 site does not participate in the coordination because of the protonation of the imine groups. Although the formulation and properties in the solid state of the prepared manganese complexes can be recognized, also with the aid of the related zinc(II) analogs, by usual physico-chemical measurements, their solubility and stability in organic solvents or in water is not predictable in advance, because of the occurrence of demetalation-metalation reactions, mainly detected by ESI-MS experiments. These metal encapsulation-release processes, however, represent a necessary prerequisite for further investigations aimed at the use of these complexes in medicine, based on metal ion release in consequence of specific external stimuli.