MANGANESE COMPLEXES OF 1.3-BIS(3-NITROSALICYLIDENEAMINO)PROPAN-2-OL - STRUCTURE AND MAGNETIC AND ELECTROCHEMICAL PROPERTIES

Four complexes [Mn-II(3NO(2)-Hsalpro)] 1, [Mn-2(II)(3NO(2)-salpro)(O(2)CMe)].4MeOH 2, [Mn-2(III)(3NO(2)- salpro)(2)(H2O)].H2O 3 and [{Mn-III(3NO(2)-salpro)}(2)].2dmf 4, [3NO(2)-H(3)salpro = 1,3-bis(3-nitrosalicyliaeneamino) propan-2-ol, dmf = dimethylformamide] have been synthesized and studied. The structure of 4 was solved by direct methods and refined to conventional agreement indices R = R' = 0.041. The molecular structure consists of discrete [{Mn-III(3NO(2)-salpro)}(2)] units and lattice-held dmf molecules. The co-ordination octahedron around each Mn-III includes three donors from each of the two pentadentate trianionic ligands. Both ligands asymmetrically bridge the Mn atoms affording an intra-dinuclear Mn...Mn' separation of 3.223(1) Angstrom. The symmetry-related manganese centres are in a distorted-octahedral environment. Infrared, ESR spectroscopic, magnetic susceptibility and electrochemical studies of 1-4 evidence a variety of structural types and nuclearities. Complex 1, resulting from the reaction of manganese(II) acetate with 3NO(2)-H(3)salpro, is characterized by the MnL stoichiometry while 2, resulting from the reaction of manganese(II) acetate with Na-3(3NO(2)-salpro), is characterized by the Mn(2)L stoichiometry. Two structurally different dinuclear manganese(III) complexes characterized by the same overall formulation [{Mn-III(3NO(2)-salpro)(solvent)}(2)] were obtained from the reaction of 1 with O-2. In non-dehydrated methanol, the asymmetric dinuclear species 3 is formed. When this complex is dissolved in dry dmf the water molecule is driven out of the manganese co-ordination sphere and a subsequent ligand environment reorganization affords 4. Variable-temperature magnetic susceptibility studies established the presence of isotropic magnetic exchange interactions between the manganese(III) centres of the dimeric species 3 and 4 (J = -1.9 and -1.6 cm(-1), respectively) and crystalline field anisotropy of Mn-III (D = -2.6 and -2.5 cm(-1), respectively). Electrochemical studies indicated that the Mn-2(II), (MnMnIII)-Mn-II, Mn-2(III) and Mn-III Mn-IV oxidation states are accessible for 4 in dmf-water.