The Synthesis and Characterisation of Manganese Amine Complexes

Abstract

The synthesis of a series of new manganese amine complexes is described. The reactions involve both macrocyclic and linear amines, together with acetato and benzoato ligands, Complexes ranging in nuclearity from one to possibly eighteen, and oxidation states II to IV, including mixed valent states, resulted. The characterisation of the products using infrared, ultraviolet-visible, and e.s.r spectral methods, as well as X -ray structural analysis and preliminary electrochemical studies are reported. In many cases, difficulty was encountered in obtaining crystals which were suitable for single crystal X- -ray studies, and the structural analysis of only four complexes is discussed. Further X -ray investigations are continuing. Complex 6, [Mn3(dien)3(CH3COO)2O3]I3 CH3OH.H2O is an oxo-centred Mn(III) trimer with an interesting feature, a µ2-peroxide bridge between two of the manganese atoms. The implications. of this structure upon. the current state of the inorganic model approach to the water oxidising centre of PS II is discussed. The structural description of a novel heptanuclear mixed-valence Mn(II, III) complex, 16, [Mn7(trien)2(dien)2(CH3COO)8O4](PF6)4.2H2O is reported. The core of this complex incorporates two Mn4(µ2-O)2 units, one inverted with respect to the other, and sharing a common manganese atom. Hence the core has been coined a 'siamese-twin butterfly'. In the reaction resulting in this oxidative deamination reaction were identified using n.m.r., gas chromatography and mass spectrometry. The structure of a valence-trapped hexameric complex, 25, [Mn6(3,2,3-tet)4(CH3COO)3)6]I5 4THF 2H2O is also discussed. The core of this complex is composed of a central Mn(III4)(µ3-O)2 unit with two peripheral di-µ2-oxo bridged Mn(IV) atoms. The formulation of this complex is also shared with several of the other 2,3,2 -tet and 3,2,3 -tet complexes investigated. The only monomeric complex to be synthesised, 28, Mn(3,2,3-tet)(IOBz)2]ClO4, was also. structurally investigated. Here, 3-iodobenzoate was used and in the resulting complex, the benzoate ligands are coordinated in a unidentate fashion, which was not observed in the other complexes. The amine occupies four planar sites around the central Mn(III) atom.