Chemistry - Superscript and subscript together after the same atom

Solution 1:

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.

References:

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.

Solution 2:

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: $\mathrm{PO_4{}^{3-}}$