Chemmacros: Redox reaction within align environment

Question

I am currently writing an experimental protocol with overleaf and want to include a redox reaction and both half equations. They should be numbered as 1.1, 1.2 and 1.3, so I am using {align} within {subequations}. I want the half equations to have arrows and oxidation numbers above them to highlight the oxidation and reduction reactions, but I just cannot get it to work.

To make it more clear, I have only included the arrow on the oxidation half equation at this point. The arrow does show up in the lower left corner of the page and not above the oxidation half equation where it should.

Another problem is that the first square bracket in the complex ion [Mn(C_2O_4)_3]^3- within the reduction half equation causes the whole ion and the equilibrium arrows to disappear, which does not happen in the oxidation half equation as there is a stoichiometric coefficient following after the equilibrium arrows.

Here is my code:

\documentclass[titlepage,a4paper,12pt]{article}
\usepackage[]{geometry}
\geometry{a4paper,inner=28mm,outer=18mm,top=20mm,bottom=20mm,footskip=10mm,headsep=5mm,headheight=15mm}
\usepackage{amsmath}
\usepackage{chemmacros}
\usechemmodule{all}
\chemsetup[redox]{explicit-sign = true}
\chemsetup[redox]{pos=top}
\begin{document}
\section{Theorie}
\begin{subequations}
\renewcommand{\theequation}{\theparentequation.\arabic{equation}}
\begin{align}
        %
        % Full reaction
        \ch{KMnO4 + 4 MnSO4 + 15 H2C2O4 &<=> 5 [Mn(C2O4)3]^3- + 22 H^+ + 4 H2O + SO4^2- + K^+}\
        %
        % oxidation half equation
        \ch{4 "\OX{MnOx1,\ox{+2,Mn}}" SO4 + 12 H2C2O4 &<=> 4 [ "\OX{MnOx2,\ox{+3,Mn}}" (C2O4)3]^3- + 24 H^+ + 4 SO4^2- + 4 \el}
        \redox(MnOx1,MnOx2)[->,red]{Oxidation}\
        %
        % reduction half equation
        \ch{K "\ox{+7,Mn}" O4 + 3 H2CO4 + 4 $\el$ + 2 H^+ &<=> [ "\ox{+3,Mn}" (C2O4)3]^3- + K^+ + 4 H2O}
\end{align}
\end{subequations}
\end{document}

Answer 1

Not exactly what you seem to have had in mind, but probably nevertheless useful/interesting:

\documentclass[titlepage,a4paper,12pt]{article}
\usepackage[]{geometry}
\geometry{a4paper,inner=28mm,outer=18mm,top=20mm,bottom=20mm,footskip=10mm,headsep=5mm,headheight=15mm}
\usepackage{amsmath}
\usepackage{chemmacros}
\usechemmodule{all}
\chemsetup[redox]{explicit-sign = true}
\chemsetup[redox]{pos=top}
% Definition of subreactions environment from: https://tex.stackexchange.com/a/356406/134144
\makeatletter
@ifundefined{ignorespacesafterend}{\def\ignorespacesafterend{\global@ignoretrue}}{}
\newenvironment{subreactions}{%
  \refstepcounter{reaction}%
  \protected@edef\theparentequation{\thereaction}%
  \setcounter{parentequation}{\value{reaction}}%
  \setcounter{reaction}{0}%
  \def\thereaction{\theparentequation\alph{reaction}}%
  \ignorespaces
}{%
  \setcounter{reaction}{\value{parentequation}}%
  \ignorespacesafterend
}
\makeatother
\begin{document}
\section{Theorie}
{\small
\vspace{7mm}
\ch{K "\OX{MnOx7,\ox{+7,Mn}}" O4 + 4 "\OX{MnOx2,\ox{+2,Mn}}" SO4 + 15 H2C2O4 <=> 5 [ "\OX{MnOx3,\ox{+3,Mn}}" (C2O4)3]^3- + 22 H^+ + 4 H2O + SO4^2- + K^+}
\redox(MnOx2,MnOx3)[->,red]{Oxidation}
\redox(MnOx7,MnOx3)[->,blue][-1]{Reduktion}
\vspace{7mm}
\begin{subreactions}
  \begin{reactions}
  &\color{red}Ox:&  4 "\ox{+2,Mn}" SO4 + 12 H2C2O4 &<=> 4 [ "\ox*{+3,Mn}" (C2O4)3]^3- + 24 H^+ + 4 SO4^2- + 4 \el\
  &\color{blue}Red:&   K "\ox{+7,Mn}" O4 + 3 H2CO4 + 4 \el + 2 H^+ &<=> \relax [ "\ox{+3,Mn}" (C2O4)3]^3- + K^+ + 4 H2O
  \end{reactions}
\end{subreactions}
}
\end{document}