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I am a theoretical physicist, so I am not very familiar with chemical names. The material I am interested in is $\ce{\alpha-NaMnO2}$. Would that be pronounced alpha sodium manganese dioxide? Is it important to say the $\alpha$?

If it's relevant, I'm talking about Phys. Rev. Lett. 2020, 124 (19), No. 197203.

Apologies if this is a trivial question, I tried looking up the answer, it may just be that I am not using the correct search terms.

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The anions of the form $\ce{MnO_x^y-}$ are referred to as manganates (see Wikipedia). I'm not sure if there might be a "special" name for $\ce{MnO2^-}$ specifically (that's the species you have here) because I never encountered this anion in my lab times, but given that $\ce{MnO4^2-}$ are the "normal" manganates and $\ce{MnO4^-}$ the permanganates, I think manganate would be the term used here as well.

Now to distinguish the ambiguity in $x$ and $y$ you usually add the oxidation state of the central metal (in this case manganese) in the form of roman numbers. Since actually the same stoichiometric formula ($\ce{NaMnO2}$) could give rise to different stable crystal structures (depending on external conditions) one uses the greek letter to distinguish between these different structures. So, yes, to be precise the $\alpha$ is needed and I would call the compound $\alpha$-Sodium-manganate(III) pronounced "alpha sodium manganate three".

But in day to day conversations one would rarely use the full thing if it is clear from context. First thing usually the $\alpha$ is dropped and next the (III). So taking to a lab colleague, where it is clear you can just say Sodium manganate.

Update: I just saw that the materialsproject has something on your compound under ID mp-18957, where they tagged it as Sodium manganese(III) oxide.

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    $\begingroup$ I think the best best way to talk about it depends on the context. The more familiar someone is with you/the project, the more informal. $\endgroup$ May 20 '20 at 15:52
  • $\begingroup$ @kskinnerx16 Agreed. In the right circumstances it might be referred to as simply "NMO". $\endgroup$
    – Anyon
    Jul 14 at 22:12
  • $\begingroup$ It is not manganate. Sodium manganese(III) oxide; or sodium manganese dioxide is the correct name. $\endgroup$
    – Binh Thien
    Jul 15 at 2:43
  • $\begingroup$ To back up the other comment with manganese in a comparatively low oxidation state it is probably best viewed as a mixed memtal oxide - I doubt there are discrete MnO2- ions in the lattice. $\endgroup$
    – Ian Bush
    Jul 15 at 14:34

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