Visualising the carboxylate shift at a bioinspired diiron(ii) site in the solid state

Abstract

A novel pyrazolate-based diiron(II) complex shows five different binding modes of exogenous carboxylate ligands in a single crystal structure. Temperature dependent X-ray data reveal thermally induced disorder due to carboxylate dynamics that resemble the carboxylate shift, as it is known from various diiron enzyme active sites.

Modelling Binuclear Metallobiosites: Insights from Pyrazole‐Supported Biomimetic and Bioinspired Complexes

“…The carboxylate shift has thus received significant attention in the literature, and has been experimentally observed in the gas phase86 and in solution87 in the case of zinc complexes. Iron model complexes have reproduced aspects of the carboxylate shift,6,77,88–90 but not until recently was it visualized directly in the solid state 91. This was achieved by combining a dinucleating pyrazolato‐based scaffold with iron(II) acetate, leading to a pair of binuclear iron complexes containing exogenous acetato ligands which display five distinct coordination modes in a single crystal.…”

Spin State Variations and Spin‐Crossover in Diiron(II) Complexes of Bis(pentadentate) Pyrazolate‐Based Ligands

“…Pyrazolate ligands with multidentate chelate arms, offering two tri‐ or tetradentate binding compartments, often form diiron(II) complexes of the type [LFe 2 X n ] m + with a single pyrazolato bridge and exogenous co‐ligands X ( X being an anionic or neutral ligands that can be involved in dynamic processes or ligand exchange equilibria.) , . For example, the diiron(II) complex of a unique pyrazolate‐based ligand providing two pincer‐type {PNN} binding pockets was shown to undergo rapid multistep triflate/MeCN ligand exchange equilibria in MeCN solution, giving rise to a reversible and complete temperature dependent low‐spin/high‐spin transition…”

19F NMR study of ligand dynamics in carboxylate-bridged diiron(ii) complexes supported by a macrocyclic ligand

“…In the solid state structure of [LFe 2 (OAc 3 )]·2MeCN, where L is a bis-tetradentate pyrazolate, all carboxylate binding modes in a dinuclear system were observed within two molecules in the asymmetric unit in the crystals. 14 Moreover, the solution structures of these complexes may differ from those in the solid or may switch between multiple conformations. For example, 19 F NMR spectroscopic studies of [Fe 2 (Ar 4F-Ph CO 2 ) 4 (THF) 2 ] (Ar 4F-Ph = 2,6-bis-4-fluorophenylphenyl) revealed an equilibrium between doubly and quadruply bridged forms, with conversion to the quadruply bridged form below −60 °C.…”