答案1
以下是一个想法:
\documentclass{article}
\usepackage{chemfig}
\begin{document}
%\schemedebug{true}
\schemestart
\subscheme{
\chemleft[
\chemfig{P^{+}(-[:120]HOH_2C)(-[:-120]HOH_2C)(-[:-60]CH_2OH)-[:60]CH_2OH}
\chemright]
}
\chemfig{SO_4^{2-}}
\schemestop
\chemmove{\node at (c2.south east) {$\scriptstyle2$};}
\end{document}