Ferromagnetic exchange in a twisted, oxime-bridged [Mn-2(III)] dimer

The dimeric complex [Mn-2(III)(Naphth-sao)(2)(Naphth-saoH)(2)(MeOH)(2)]center dot 4MeOH (1.4MeOH), acts as a simple model complex with which to examine the magneto-structural relationship in polymetallic, oxime-bridged Mn-III complexes. Dc magnetic susceptibility studies reveal that ferromagnetic exchange is mediated through the heavily twisted Mn-O-N-Mn moiety (J = + 1.24 cm(-1)) with magnetisation measurements at low temperatures and high fields suggesting significant anisotropy. Simulations of high field, high frequency EPR data reveal a single ion anisotropy, D-(MnIII) = -3.94 cm(-1). Theoretical studies on simplified model complexes of 1 reveal that calculated values of the exchange coupling and the anisotropy are in excellent agreement with experiment, with the weak ferromagnetism resulting from an accidental orthogonality between the Mn-N-O plane of the first MnIII ion and the Jahn-Teller axis of the second Mn-III ion.