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I'm trying to find an easy experiment involving a chemical reaction in which two paramagnetic reactants A and B react to give a product which is diamagnetic (or the reverse). The idea is to show that A is paramagnetic, B is paramagnetic, but A+B --> C is diamagnetic.

Or, another experiment: an experiment in which a change in temperature changes paramagnetic to diamagnetic (or the reverse). I've seen such an experiment but cannot remember the details. All I can say is that there was a color change and, at the same moment, a paramagnetic/diamagnetic shift

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  • $\begingroup$ Thermal decomposition reactions which produce oxygen would satisfy your requirement since oxygen is diamagnetic, right. $\endgroup$ – DHMO Jan 21 '17 at 4:33
  • $\begingroup$ Oxygen in its ground state is famously paramagnetic! For OP: for the second part of your question, you may be interested in complexes which can undergo spin transitions, in particular the $\mathrm{d^6}$ Fe(II) complexes. High-spin Fe(II) is paramagnetic, but low-spin Fe(II) is diamagnetic. en.wikipedia.org/wiki/Spin_transition Also how about Ni(II) complexes $\ce{Ni(PPh3)2X2}$ which can flip between square planar (diamagnetic) and tetrahedral (paramagnetic) geometry? I don't know much about those so just putting them out there. $\endgroup$ – orthocresol Jan 22 '17 at 15:45
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Seems to me any reaction involving the recombination of two radicals leads to a closed-shell diamagnetic species (which oxygen is definitely not!). I can't think of any other examples immediately. You could make singlet oxygen, which is diamagnetic, from paramagnetic triplet oxygen by irradiation, but then there is only one reactant.

If you heat a paramagnetic substance enough so that the thermal energy can overcome the energy that is gained by the alignment of your magnetic moments, I believe the substance will not exhibit paramagnetism in a magnetic field above that temperature. So that seems doable.

Edit: Actually, I found an example: ozone is diamagnetic and can be made from paramagnetic oxygen and an oxygen radical. So that could be a possible reaction where you have two paramagnetic reagents combining into a diamagnetic product.

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