Q36 · CSIR-NET Chemistry, June 2014
Paper: CSIR-NET June 2014 · Subject: Inorganic Chemistry · Chapter: Inorganic Spectroscopy · Topic: Electronic Spectra Tanabe Sugano · Marks: 2 · Difficulty: Hard
The correct order of the isomeric shift in Mössbauer spectra ($^{57}\mathrm{Fe}$ source) of iron compounds is
(a)Fe (II) $>\mathrm{Fe}$ (III) $>\mathrm{Fe}$ (IV)
(b)Fe (III) $>\mathrm{Fe}$ (II) $>\mathrm{Fe}$ (IV)
(c)Fe(IV) > Fe(III) Fe(II)
(d)$\operatorname{Fe}($ IV $)>\operatorname{Fe}($ II $)>\operatorname{Fe}($ III $)$
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
Isomer shift decreases as s-electron density at the nucleus rises with oxidation state (less d shielding): Fe(II) > Fe(III) > Fe(IV).
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