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

Abstract

The dimeric complex [MnIII2(Naphth-sao)2(Naphth-saoH)2(MeOH)2][middle dot]4MeOH (1[middle dot]4MeOH), acts as a simple model complex with which to examine the magneto-structural relationship in polymetallic, oxime-bridged MnIII 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 MnIII ion.