In the chemical formula of some ion compounds, there is the necessity to write the charge in the superscript and the numbers of atoms in the subscript, but together at the right of the same symbol like in the PO43− ion:

stacked vs. staggered notation for the phosphate anion

Does IUPAC provide universal guidelines saying that I have to typewrite the two numbers in a stacked or staggered way?


From IUPAC Green Book [1, p. 51]:

In writing the formula for a complex ion, spacing for charge number can be added (staggered arrangement), as well as parentheses: $\ce{SO4^2-}$, $\ce{(SO4)^2-}$. The staggered arrangement is now recommended.

Also, as you are apparently a $\mathrm{\LaTeX}$-user, the same convention is used by default in chemformula package. From the manual:

If a compound does not start with a sub- or superscript and there is both a sub- and a superscript, the superscript is shifted additionally by a length determined from the option charge-hshift = {❬dim❭}, also see page 13f.

The second point follows IUPAC’s recommendations.


  1. IUPAC “Green Book” Quantities, Units, and Symbols in Physical Chemistry, 3rd ed.; Cohen, R. E., Mills, I., Eds.; IUPAC Recommendations; RSC Pub: Cambridge, UK, 2007. ISBN 978-0-85404-433-7.

International and various national standards (e.g. ISO 80000, DIN 1338) do not agree with the typographic disaster of the staggered notation that was introduced in Nomenclature of Inorganic Chemistry – IUPAC Recommendations 2005 (Red Book). The standardized notation still is aligned: $\mathrm{PO_4^{3-}}$ or $\mathrm{(PO_4)^{3-}}$.

Nevertheless, the current IUPAC recommendations as well as the ACS Style Guide stagger the subscript and superscript: $\mathrm{PO_4{}^{3-}}$


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