How can you tell from a magnetic moment? 3d7 and 3d5 are both paramagnetic, so wouldn't they give you the same result?

How can you tell from a magnetic moment? 3d7 and 3d5 are both paramagnetic, so wouldn't they give you the same result?

They are both paramagnetic, but

Eff. Mag. Moment = 2[S(S+1)]

^{1/2} (spin only approx)

But, d5 low spin and d7 low spin give the same result (S=1/2 for both), however the Eff. Mag. Moment of d5 low spin will be temperature dependant, but d7 low spin will not be (first order orbital effects).

d5 high spin will have a slighty higher eff mag moment than high spin d7 (but this could be masked by orbital effects). The Eff. Mag. Moment of d7 high spin will be temperature dependant, but d5 high spin will not be (first order orbital effects).

Also high spin d5 gives only very very weak d-d spectra, since all d-d transitions in d5 high spin are spin forbidden, but the d-d spectra for d7 (high or low spin) is quite a bit stronger.

Guess who's been revising spectra and magnetism today...