Understanding Enemark-Feltham Notation in Iron-Nitrosyl Complexes

Iron-Nitrosyl complexes are redox non-innocent, with NO exhibiting multiple redox states. Enemark-Feltham Notation helps in determining metal-ligand interactions and oxidation states. Detailed information on NO ligands, bonding characteristics, and methods for analyzing iron-NO systems are discussed.

• Chemistry
• Enemark-Feltham
• Iron
• Nitrosyl
• Complexes

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1. 5-ish Slides about Enemark- Feltham Notation Kyle Grice DePaul University November 2018

2. Iron Nitrosyl Complexes NO ligands are redox non-innocent, which means NO has multiple accessible redox states under common conditions In addition, Iron has common several redox and spin-states (Fe2+vs. Fe3+, high spin or low spin).

3. NO (Yes?) As a neutral molecule, NO is a radical with one unpaired electron Bond Order: 2.5 Bond Length: 115 pm NO has been found to be a neurotransmitter and vasodialator There has been significant research in NO-releasing molecules (NORMs) for medical applications.

4. Basics of Enemark-Feltham {M-L}X or {Fe-NO}X where X is the sum of the metal valence and ligand * electrons. NO+ has no * electrons, NO has 1, and NO- has 2. Iron can be high spin or low spin in several oxidation states! Nitroprusside is a blood-pressure lowering compound: Enemark-Feltham Notation: {Fe-NO}6

5. How do we get more detailed info? Often it is hard to determine the exact oxidation state. information can sometimes be obtained from the NO ligand: NO+ ligands have shorter bonds because they have formally triple N-O bonds. They tend to be linear. NO- are bent due to the extra lone pair on the nitrogen. NO is in-between these two extremes in term s of length and angle IR frequencies also help: Linear: 1650 1900 cm-1 Bent: 1520 1690 cm-1 Linear Fe-N-O bonding and a short N-O distance. The molecule is diamagnetic too! This is low spin Fe2+ with a NO+ ligand.

6. Beyond Enemark-Feltham To deconvolute the oxidation state of the iron and the NO, various methods can be used: Evidence from X-ray structures and IR DFT calculations Fe K-edge XAS Fe Mossbauer