Hello Nabila,

I am not really an expert in organometallic chemistry, but I hope this can help. First of all, I think we need to know what kind of compounds you are talking about, and the lattice symmetry. For instance, in Prussian blue derivatives the lattice has octahedral symmetry, so that the Fe 3d levels are split in two eg orbitals lying at higher energy and three t2g states at lower energy. Fe(III) has 5 electrons in the 3d shell, so the high-spin configuration puts 1 electron with spin up in each of the 5 3d orbitals, for a total spin moment S = 5/2. In the low spin configuration (when the splitting between the eg and the t2g sub-bands is very large), all five electrons are in the 3 t2g states at low energy, so 4 of them must have paired spins and the total spin moment is S=1/2. I don't think that the magnetic moments that you find in your measurement match these values, but of course this might be different if the Fe ions are placed in an environment with a different symmetry. A spin crossover transition consists in a transformation between those two configurations, usually driven by some external perturbation (application of pressure, temperature, etc) that somehow affects the lattice and therefore changes the eg-t2g splitting. However, I seem to understand that you find those two moments present simultaneously in your sample. Is this correct? If this is the case, I would rather think of some sort of ferrimagnetic material, but again more information would be needed.

Regards,

Hello Juan

I have synthesized  mixed complexes with iron(III).The primary ligand is an oxime and the second one is an amino acid . These complexes were characterized by spectroscopic methods especially EPR and magnetism. There are two complexes of iron(III). So i found two magnetic moments : 2.6 BM and 3.3 BM. These values are two small for high spin (S=5/2) complexes (μ =5.91BM) or too large for low spin (S = 1/2) iron(III) complexes ( μ=2.00 BM).

The magnetic moments I found are not for the same sample but for two complexes.

Can we talk about spin-admixed system ?

Furthermore, on the EPR spectra two bands were observed for each  iron(III) complex with effective g values of 4.24 and 2.07. 

So what is the correlation between the magnetic moments and the RPE results?

Regards,

Hello Nabila,

I am not an expert in EPR, but in general in magnetometry measurements you must consider whether the magnetic field that you apply is sufficient to saturate the sample. If you get a magnetic moment that is too large for low-spin then you can rule out this option, but it is still possible that you haven't reached the saturation magnetization of the high-spin state.

Now I understand that the two values of magnetic moment that you mention were obtained on different samples, which means that they must be rather inhomogeneous. If you have access to other techniques, such as SQUID magnetometry, it might be useful to measure magnetization curves as a function of temperature, to see how the samples magnetization approaches saturation.

Regards,

Juan