Mono- and tetra-nuclear manganese(III) complexes of tripodal tris[2-(salicylideneamino)ethyl]amines

Abstract

The tripodal ligands N[CH2CH2NCHC6H3X(OH)-2]3(X = H, H3L1 or Cl-5, H3L2] afford the mononuclear complexes [MnIIIL]. Structural work has shown that the symmetry of the facial MnN3O3 co-ordination sphere in the two solvates [MnL2]·3H2O and [MnL2]·MeOH varies considerably as the former has C3 and the latter C1 symmetry. The implications of these differences are discussed. Reaction of [MnL] with manganese(III) acetate dihydrate in alkaline media affords the antiferromagnetic tetranuclear cations [MnIII4O2L2]2+ in high yields. X-Ray studies on [Mn4O2L12][PF6]2·4MeCN have revealed a centrosymmetric Mn4(µ3-O)28+ core, with the shortest Mn ⋯ Mn contact being 2.906(3)A. The metal co-ordination spheres are of two types: facial-MnN3O3 and MnNO5. The cyclic voltammograms of [Mn4O2L2]2+ display two successive waves due to the MnIII–MnII couples of the MnN3O3 spheres. For [MnL] only one such couple is observed. Oxidative responses due to MnIV–MnIII couples are also observed. Some preliminary work on an iron(III) analogue of [Mn4O2L2]2+ is also described.