5 ish Slides about Enemark Feltham Notation Kyle

5 -ish Slides about Enemark. Feltham Notation Kyle Grice De. Paul University November 2018

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 (Fe 2+ vs. Fe 3+, high spin or low spin).

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.

Basics of Enemark-Feltham • {M-L}X or {Fe-NO}X where X is the sum of the metal valence and ligand π* electrons. • NO+ has no π* 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

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 Fe 2+ with a NO+ ligand.

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