Abstract
Symmetry-breaking spin-state transitions in two of three isostructural salts of MnIII spin-crossover cations, [MnIII(3-OMe-5-NO2-sal2323)]+, with heavy anions are reported. The ReO4- salt undergoes two-step spin crossover which is coupled with a re-entrant symmetry-breaking structural phase transition between a high temperature phase (S = 2, C2/c), an intermediate ordered phase (S = 1/S = 2, P21/c), and a low temperature phase (S = 1, C2/c). The AsF6- complex undergoes an abrupt transition between a high temperature phase (S = 2, C2/c) and a low temperature ordered phase (S = 1/S = 2, P-1). The SbF6- complex undergoes a gradual transition between a high temperature phase (S = 2, P-1) and a low temperature spin-state ordered phase (S = 1/S = 2, P-1). Correlation of the volume of the anion andT1/2in these complexes and three analogous complexes with similar anions, BF4-, ClO4-, PF6-, reveals an increase in T1/2 upon increasing the anion volume. We rationalise that the volume of the anionsmodulates the elastic interactions between the MnIII sites, with increasing elastic frustration with the larger anions resulting in a two-stepped transition for [MnIII(3-OMe-5-NO2-sal2323)]ReO4and the stabilisation of the mixed (HS:LS) state to low temperature for [MnIII(3-OMe-5-NO2-sal2323)]AsF6 and [MnIII(3-OMe-5-NO2-sal2323)]SbF6.
Published Version
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