Insight into chalcogenolate-bound {Fe(NO)₂}⁹ dinitrosyl iron complexes (DNICs): covalent character versus ionic...

Area of Science:

• Coordination Chemistry
• Inorganic Chemistry
• Materials Science

Background:

• Dinitrosyl iron complexes (DNICs) are crucial in various biological and chemical processes.
• The thermal instability of certain DNICs, like {Fe(NO)2}9 complexes, presents synthetic and characterization challenges.
• Understanding the electronic structure and ligand interactions of DNICs is key to controlling their reactivity.

Purpose of the Study:

• To synthesize and characterize the thermally unstable {Fe(NO)2}9 dinitrosyl iron complex [(OMe)2Fe(NO)2]- (2).
• To investigate the factors governing the binding affinity of chalcogenolate ligands to the {Fe(NO)2}9 motif.
• To elucidate the electronic structure of DNIC 2 and compare it with related complexes.

Main Methods:

• Single-crystal X-ray diffraction for structural determination.
• X-ray Absorption Spectroscopy (XAS) for electronic structure analysis.
• Time-Dependent Density Functional Theory (TD-DFT) computations.
• Solid-state UV-vis spectroscopy.

Main Results:

• DNIC 2 is stabilized by intermolecular [Fe(OMe)2(K+)] interactions.
• Ligand binding affinity follows the order [SEt]- > [SPh]- > [OPh]- > [OMe]-.
• DNIC 2 exhibits a distinct XAS Fe K-edge pre-edge energy (7114.2 eV), suggesting a predominantly ionic {FeIII(NO-)2}9 electronic structure.
• TD-DFT and UV-vis spectra indicate lower charge transfer energy for DNIC 2 compared to complexes with dominant metal-ligand covalency.

Conclusions:

• The electronic structure of DNIC 2 is characterized by dominant ionic Fe-OMe bonds, differing from the covalent character in related DNICs.
• The observed ligand binding affinities are influenced by both electron-donating ability and soft-hard interactions.
• This study provides valuable insights into the structure-property relationships of thermally unstable dinitrosyl iron complexes.