MONONUCLEAR AND TETRA-NUCLEAR MANGANESE(III) COMPLEXES OF TRIPODAL TRIS[2-(SALICYLIDENEAMINO)ETHYL]AMINES

The tripodal ligands N[CH2CH2N=CHC6H3X(OH)-2]3 (X = H, H-3L1 or Cl-5, H-3L2] afford the mononuclear complexes [Mn(III)L]. 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(mu3-O)28+ core, with the shortest Mn...Mn contact being 2.906(3) angstrom. 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.