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

Abstract

The tripodal ligands N[CH₂CH₂N=CHC₆H₃X(OH)-2]₃(X = H, H₃L¹ or Cl-5, H₃L²] afford the mononuclear complexes [Mn^IIIL]. 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 [Mn^III₄O₂L₂]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)Å. 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 Mn^III–Mn^II couples of the MnN₃O₃ spheres. For [MnL] only one such couple is observed. Oxidative responses due to Mn^IV–Mn^III couples are also observed. Some preliminary work on an iron(III) analogue of [Mn₄O₂L₂]²⁺ is also described.