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According to me, $\ce{MnO4^2-}$ is paramagnetic and $\ce{MnO4^-}$ is diamagnetic. On the basis of this, the corresponding potassium salts inherit these magnetic properties, i.e. $\ce{K2MnO4}$ is paramagnetic and $\ce{KMnO4}$ is diamagnetic.

However, according to my class teacher $\ce{KMnO4}$ is paramagnetic.

Is potassium manganate(VII) dia- or paramagnetic?

andselisk
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Tips
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  • Unanswered duplicate: https://chemistry.stackexchange.com/questions/140123/why-is-potassium-permanganate-paramagnetic?r=SearchResults – Nilay Ghosh Feb 17 '21 at 04:07
  • @Nilay_Ghosh Both are different questions – Tips Feb 17 '21 at 04:11
  • See this paper, it is a complex story "Magnetic Studies on Potassium Permanganate" https://iopscience.iop.org/article/10.1088/0370-1328/79/2/318 – AChem Feb 17 '21 at 04:21
  • In this article It's say that Potassium permanganate is Dimagnetic https://www.chemedx.org/video/paramagnetism-oxidation-states-manganese-potassium-permanganate#:~:text=Manganese%20-%20Potassium%20Permanganate-,Paramagnetism%3A%20Oxidation%20States%20of%20Manganese%20-%20Potassium%20Permanganate,unpaired%20electrons%20per%20Mn%20atom. – Tips Feb 17 '21 at 04:45
  • In the relatively authentic paper I showed you, it says the same thing. KMnO4 crystal is diamagnetic but there are finer details of feeble paramagnetism. Your teacher is not right. – AChem Feb 17 '21 at 05:43
  • @saketkumar It is diamagnetic, not dimagnetic. – Poutnik Feb 17 '21 at 05:47
  • For eventual writing and formatting of chemical formulas or equations, see how to use MathJax with mhchem extension . Note the preferred plain text text for titles. – Poutnik Feb 17 '21 at 05:55
  • Paramagnetism in KMnO4 is normally attributed to the Van Vleck Mechanism - see https://iopscience.iop.org/article/10.1088/0370-1328/79/2/318 (as mentioned above) and https://en.wikipedia.org/wiki/Van_Vleck_paramagnetism – Ian Bush Feb 17 '21 at 09:58

1 Answers1

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Actually it is diamagnetic but due to a phenomenon called charge transfer spectrum (CTS), oxygen transfers one electron to manganese and $\ce{KMnO4}$ as a whole becomes paramagnetic. This is also the reason why it shows a characteristic colour while diamagnetic complexes are colourless due to absence of d-d transitions.

Tyberius
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Saahas Sharma
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    What would be the percentage of the excited state from charge transfer, in let's say a solution of KMnO4 ? Because a significant number of the molecules have to be in excited state before the bulk material gains paramagnetic properties. – S R Maiti Apr 26 '21 at 20:37