I'm currently trying to typeset the ion $\ce{Cr2O7^{2-}}$ with oxidation numbers on. My first thought was to put the oxidation state above the atom, but according to IUPAC, the oxidation state should be in the right superscript. Combined with charge, it looks ugly and wrong:

My current ways of doing this are below

  1. The oxidation number in right superscript. Looks weird with both numbers so close.
  2. The oxidation number above. Looks better, but is against IUPAC.

My question therefore is: Which is the preffered way to typeset this?

The ion typesat in LaTex

Also, I would like to excuse beforehand if this should rather be in tex.stackexchange.


2 Answers 2


My personal preference in this situation would be to put square brackets around the whole ion and put the charge outside.

$$\ce{[Cr^{VI}2O^{-II}7]^{2-}}$$ gives: $$\ce{[Cr^{VI}2O^{-II}7]^{2-}}$$

This is sometimes done with polyatomic species anyway (particularly metal-ligand complexes) to emphasise that the charge is on the whole ion, not on any one particular atom.


Take a look at this answer, which was edited to match IUPAC convention. Oxidation states in formulae are actually written as Arabic numerals, with either a + sign or a - sign before the number (where it is nonzero), on top of the element symbol. Compare with ion charges written as ordinary superscript with the charge following the number:


$\ce{\overset{+6}{Cr}_2\overset{-2}{O}_7^{2-}}$ or $\ce{[\overset{+6}{Cr}_2\overset{-2}{O}_7]^{2-}}$


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