Self‐Assembly of Dimeric MnIII–Schiff‐Base Complexes Tuned by Perchlorate Anions

Abstract

AbstractThe synthesis and structural and spectroscopic characterisation of 12 manganese(III)–Schiff‐base complexes of the formula [MnLn(H2O/CH3OH)2](ClO4)(mH2O) (m = 0, 1) are described. The multidentate H2Ln and H4Ln Schiff‐base ligands were obtained by condensation of different diamines (1,2‐diaminoethane, 1,2‐diamino‐2‐methylethane, 1,2‐diamino‐2,2‐dimethylethane, 1,3‐diamino‐2,2‐dimethylpropane) and 2,3‐dihydroxybenzaldehyde, 3‐methoxy‐2‐hydroxybenzaldehyde or 3‐ethoxy‐2‐hydroxybenzaldehyde. The crystal structures of H2L3 and H4L10 ligands were solved by X‐ray crystallography, revealing their ability to bind metal centres. Recrystallisation of complexes 2 and 8 from methanol yielded single crystals of [MnL2(H2O)2](ClO4) and [MnL8(H2O)2](ClO4). Their X‐ray characterisation shows a tetragonally elongated octahedral geometry for the manganese coordination sphere, formed by the chelation of the N2O2 donor set of the inner compartment of the Schiff base to the equatorial plane of the octahedron and by the binding of two water molecules in the axial positions. The octahedron entities are linked in pairs by μ‐aquo bridges between neighbouring axial water molecules and also by π–π stacking interactions, establishing dimeric structures. Perchlorate anions are accommodated in the cavities of the framework and form hydrogen bonds with the aqua ligands, leading to infinite spirals of the complexes generated by a screw axis along a. Moreover, the peroxidase activity of the crystallographically solved complexes 2 and 8, studied in the presence of the water‐soluble trap ABTS, agrees with the predicted rate according to the activity/rhombicity correlation.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)