Brown Ring Test

Profile & Magnetic State:

$$[\text{Fe}(\text{H}_2\text{O})_5(\text{NO})]^{2+} \implies \text{Iron Oxidation State } = +1 \quad (d^7 \text{ system}) \qquad \mu \approx 3.87 \text{ BM} \quad (n = 3)$$

Concept: Identifies the highly testable qualitative coordination crossover complex where charge transfer occurs as neutral nitric oxide converts internally into a coordinated nitrosonium ($$\text{NO}^+$$) ligand by donating an electron to reduce the iron center.

Notation:

• $$[\text{Fe}(\text{H}_2\text{O})_5(\text{NO})]^{2+}$$ = Pentaaquanitrosyliron(II) sulfate derivative complex;
• $$n$$ = Number of unpaired electrons;
• $$\mu$$ = Spin-only magnetic moment in Bohr Magnetons.