In Situ Characterizable High-Spin Nitrosyl–Iron Complexes with Controllable Reactivity in Multiphase Reaction Media

Abstract

The chemistry of non-heme iron centres with the ‘non-innocent’ NO ligand has experienced a renaissance in the last decades because of findings of their biochemical significance. Our work concentrates on high-spin {FeNO}7 complexes which show an S = 3/2 ground state, and their related {Fe(NO)2}9 species. Crystalline complexes were prepared from the reaction of NO with FeII and thoroughly characterized. Bonding, spin situation and oxidation states of the Fe–NO moiety are described. Using quantum-chemical calculations like DFT, CASSCF and EOS, frontier orbitals and spin populations of selected complexes are given. The results are leading to the interpretation of a largely covalent nature of the nitrosyl–iron bond. The investigation of the [Fe(H2O)5(NO)]2+ ion, an enduring issue in Inorganic Chemistry since the nineteenth century, lead to the isolation of a gallate or ferrate salt of the general formula [Fe(H2O)5(NO)][MIII(fpin)2(H2O)]2·xH2O (M = Fe, Ga; x ≈ 8.3). Crystal structure analyses of halogenido-mononitrosyliron compounds (MNICs) and their dinitrosyl analogues (DNICs) are presented. The reaction process is analysed by in situ-UV–vis and in situ-IR measurements. Their application as a competitive-consecutive reaction pattern for engineer partners is introduced. Crystal-structure analyses and the calculation of the electronic properties for nitrosyl-iron compounds with different aminecarboxylato co-ligands like imino- and oxodiacetate as well as ethylenediaminetetraacetate (edta) enable a closer insight towards their structure-properties relationship.