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The Carboxylate Twist: Hysteretic Bistability of a High-Spin Diiron(II) Complex Identified by Mössbauer Spectroscopy


  • Financial support by the DFG (International Research Training Group 1422 “Metal Sites in Biomolecules: Structures, Regulation and Mechanisms”; see and the Evonik Foundation (PhD fellowship for B.B.) is gratefully acknowledged.


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In a twist: The carboxylate ligand in the clamp of a highly preorganized diferrous site shows temperature-dependent dynamic behavior, coined the “carboxylate twist”. It leads to a fluctuation of the electric field gradient and thus averaged Mössbauer resonances at higher temperatures, resulting in magnetic and spectroscopic hysteresis even without any spin-crossover or valence tautomerism.