Crystallographic detection of the spin state in FeIII complexes

Conor T. Kelly, Michael Griffin, Kane Esien, Solveig Felton, Helge Müller-Bunz, Grace G. Morgan

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5 Citations (Scopus)
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We report a single example of thermal spin crossover in a series of FeIII complexes, [FeIII(R-sal2323)]+, which typically stabilize the low-spin (S = 1/2) state. Single-crystal X-ray diffraction analysis of 53 such complexes with varying “R” groups, charge-balancing anions, and/or lattice solvation confirms bond lengths in line with an S = 1/2 ground state, with only the [FeIII(4-OMe-sal2323)]NO3 complex (1a) exhibiting longer bond lengths associated with a percentage of the spin sextet form at room temperature. Structural distortion parameters are investigated for the series. A magnetic susceptibility measurement of 1a reveals a gradual, incomplete transition, with T1/2 = 265 K in the solid state, while Evans method NMR reveals that the sample persists in the low-spin form in solution at room temperature. Computational analysis of the spin state preferences for the cations [FeIII(4-OMe-sal2323)]+ and [FeIII(sal2323)]+ confirmed the energetic preference for the spin doublet form in both, and the thermal spin crossover in complex 1a is therefore attributed to perturbation of the crystal packing on warming.

Original languageEnglish
Pages (from-to)6429-6439
JournalCrystal Growth and Design
Issue number11
Early online date17 Oct 2022
Publication statusPublished - 02 Nov 2022


  • Condensed Matter Physics
  • General Materials Science
  • General Chemistry


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