No abstract

3-[(((2′-pyridyl)methyl)imino)methyl]benzene-1,2-diol, H 2 L 2 ) 3-[((2-(2′-pyridyl)ethyl)imino)methyl]benzene-1,2-diol, and H 3 L 3 ) 3-[((2-(4′-imidazolyl)ethyl)imino)methyl]benzene-1,2-diol, have been synthesized and studied. 1 crystallizes in the monoclinic system, space group P2 1 /c, Z ) 2, a ) 11.396(1) Å, b ) 18.583(2) Å, c ) 9.888(1) Å, and ) 103.51(1)°. The structure was solved by direct methods and refined to conventional agreement indices R ) 0.028 and R w ) 0.029. The molecular structure of 1 consists of discrete [Mn II 2 L 1 (CH 3 CO 2 ) 2 (CH 3 OH)] 2 molecules. 1 is a chainlike bis-dinuclear Mn(II) complex involving an unprecedented arrangement of pentacoordinated (N 2 O 3 ) and hexacoordinated (O 6 ) manganese ions as the outer and inner pairs of metal centers, respectively. The different Mn‚‚‚Mn distances result from significant differences in bridging moieties, two catecholato bridges for the shortest distance between inner manganese ions, and one catecholato and two acetato bridges for the longer distances between inner and outer manganese ions. The symmetry of the N 2 O 3 donor set around the outer Mn(1) is close to a trigonal bipyramid while the O 6 ligand environment of the inner Mn(2) can be described as a rhombically distorted octahedron. The synthesis, IR, EPR, and magnetic susceptibility of 1-3 suggest a similar bis-dinuclear structure for all three complexes. Variabletemperature magnetic susceptibility studies establish the presence of antiferromagnetic exchange interactions between Mn(II) centers of 1-3 with predominence of the interactions between inner and outer metal ions (-3.4 to -5 cm -1 ) over the interaction between inner manganese ions (-0.5 to 0.5 cm -1 ). EPR spectroscopy indicates that the bis-dinuclear arrangement of complexes 1-3 is retained in aprotic solvents. As shown by EPR, O 2 oxidation leads to the release of the constitutive Mn(II) dinuclear units, prior to formation of mononuclear Mn(II) and finally Mn(III) species. Observation of two irreversible two-electron oxidation waves in the CV profiles of 1-3 is consistent with a similar splitting of the bis-dinuclear complex molecules induced by electrochemical oxidation. These studies suggest that complexes resulting from the reaction of manganese with the fully oxidized form of such electroactive ligands may afford interesting new higher oxidation-state polynuclear Mn species.