[ainoko_hikaru]

Hi! I was wondering if anyone can help explain to me why certain ligands tend to have their masses change in direction when in a magnetic field, such as K₄Fe(CN)₆ and K₂Fe(CN)₆?

I have tried to research how and so far, I can only come up with things such as the masses tend to change in an NMR spectrum on changes in temperature, or the potassium hexacyanofurrate has anisotropic properties (which I still can't understand yet). There are also sites and articles saying that it is due to paramagnetism or diamagnetism. However, nothing tells of how the masses of the aforementioned ligands change direction of their masses whenever in a magnetic field. Does it also have something to do with what they say as the crystal field theory? (I'm not sure what that means exactly, though). I've done as thorough a research as I could but I could not find a definite answer. Please help. Thank you.

[Borek]

Are you sure they are changing MASS? and not some other property?

[ainoko_hikaru]

yes, or atleast that was what the professor asked. The exact question was: K₄Fe(CN)₆ and K₂Fe(CN)₆ masses change in opposite direction in a magnetic field. explain why.

[BluePill]

I believe this is because of the magnetic susceptibility due to the presence of a lone pair. Paramagnetism and diamagnetism is a factor here. Stong-field effects and the concept of hyperligation (and hypoligation) can be of help to you here.

[Borek]

It still doesn't mean MASS change. That's Physics101.

[BluePill]

Weight change.

[ainoko_hikaru]

Then I believe the professor may be wrong in his terms. Regardless, if that may be the condition as how BluePill said, then which of the two is paramagnetic and diamagnetic? I was able to find out more about the question. It would seem that only one of the compounds given would decrease in weight and the other increase. I am confused about the question myself but I would only like to understand how the principle of changing a weight of a compound in a magnetic field works.

If we take K₄Fe(CN)₆, taking the oxidation state of iron it would be +2 since CN₆ would be -6 and the four K⁺ would be equal to +4. Taking iron, its configuration would have a [Ar]3d⁶. Is it correct to say that this is diamagnetic, following crystal field theory? It is diamagnetic since cyanide is a strong-field ligand and would tend to have the electron spins at the low-spin complex. I'm not sure at my explanation though. How could I then explain how the weights change?

If it is diamagnetic, then what can I assume about its weight?

I may have gotten this wrong, please tell me if I followed correctly. Thank you.

[BluePill]

Maybe hyperligation won't work here. Try using crystal field splitting. Using an octahedral field on K₄Fe(CN)₆, Fe would have a [Ar]3d⁶ configuration, yes? We know that cyanide is a strong-field ligand. Therefore, splitting energy is greater. So you place the 6 electrons into the t_2g orbitals first and you will get a diamagnetic molecule which is not susceptible to magnetism.

Let's look at K₂Fe(CN)₆. The Fe would have 3d⁴ configuration, yes? Again, using what we know about cyanide and invoking crystal field splitting. We place 4 electrons into the t_2g orbitals first. Following Hund's rule of maximum multiplicity (ignoring the other rules), there would be 2 unpaired electrons at the t_2g orbitals. Making it paramagnetic and susceptible to magnetism.

Let's also hope experts would also jump in. I'm not so sure about change in weight in magnetism. But I do believe there is a concept of apparent weightlessness.

[ainoko_hikaru]

Ah, i see. I understand how crystal field splitting was applied. However, what I do not understand now is how diamagnetism and paramagnetism would be applied here. Would the magnetic field have no effect on K₄Fe(CN)₆ since it is diamagnetic and K₂Fe(CN)₆ would then have its weight to "change in direction"? I'm beginning to think that only one of the compounds I have mentioned will have their weights to "change in direction" in a magnetic field. The other might have an increase in weight (?) or have no change at all. 

[BluePill]

Paramagnetic materials are attracted to magnetic fields due to sudden change in spin orientation. Diagmagnetic materials are opposite of paramagnetic materials, they are repelled by magnetic fields.

Weightlessness could be attributed to diamagnetic materials. It's like they are "levitating" (I'm putting quotations because these are extremely weak and should be measured by very sensitive instruments). Increase in weight could be attributed to paramagnetic materials because they get attracted by the magnetic field.

Word of warning though, this is a part that I am not very sure.

[ainoko_hikaru]

Then I have misunderstood in my previous statement. If that is truly the case, then K₄Fe(CN)₆ would be the one to 'decrease' in weight or have its weight 'change in direction' and K₂Fe(CN)₆ would be the one to 'increase' in weight.

Let us hope someone may be able to verify if this is true.

[BluePill]

I'm pretty sure about chemistry. I'm just not sure with the physics of my answer. 

[ainoko_hikaru]

Ah, I see. I thank you for your time of helping me find the answer to my question, BluePill. I am not good in physics so I really cannot be of any help here. I understand crystal field splitting a little as I am currently studying coordination chemistry. I am only aware now that the question given to me may be about the magnetic susceptibility of ligands. I just cannot find any source that may explain how this change of weight takes place.

[BluePill]

I think I'm right. I found a source:
http://chemwiki.ucdavis.edu/index.php?title=Inorganic_Chemistry/Crystal_Field_Theory/Crystal_Field_Theory/Magnetic_Properties_of_Coordination_Complexes_%28CFT%29&bc=0#Filling_of_d-orbitals_in_a_complex.

I used the Google terms: magnetism, weight change, ligands

How can we measure magnetism in a compound?

The Gouy balance is used to measure paramagnetism by suspending the complex in question against an equivalent weight with access to a magnetic field. We first weigh the complex without a magnetic field in its presence, and then again in the presence of a magnetic field. If the compound is paramagnetic it will visibly be pulled towards the electromagnet, the distance proportional to the magnitude of the compound's  paramagnetism. If the compound, however, is diamagnetic, it will not be pulled towards the electromagnet, and instead might even be slightly repelled by it. This will be proven by the decreased weight or the no change in weight. The change in weight directly corresponds to the amount of unpaired electrons in the compound.

[ainoko_hikaru]

I see. Then what I said earlier,

Then I have misunderstood in my previous statement. If that is truly the case, then K₄Fe(CN)₆ would be the one to 'decrease' in weight or have its weight 'change in direction' and K₂Fe(CN)₆ would be the one to 'increase' in weight.

Let us hope someone may be able to verify if this is true.

may be considered as correct?