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I have the structure of the nitrate ion written down in chemfig and I'd like to add its charge as an apex outside the square brackets (see below). Is there a correct way to do it or do I just \raisebox a minus sign?

It should look like this:
enter image description here


\documentclass{article}
\usepackage{chemfig}
\usetikzlibrary{calc}
\begin{document}
\[\schemestart\chemleft[
\chemfig{\lewis{246,O}-[:30]N(-[@{leg}:90]@{Oss}\lewis{024,O})-[:-30]\lewis{026,O}}\chemright]
\chemmove{\draw[->]($(Oss)+(0:2.5mm)$).. controls +(-10:2mm) and +(10:3mm).. ($(leg)+(0:.5mm)$);}
\schemestop\]
\end{document}
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1 Answer 1

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Compounds inside \schemestart and \schemestop are tikz nodes with names you can refer to. chemfig names them c1, c2, … but you can also give them own names. You can use this in \chemdraw to place the minus:

\documentclass{article}
\usepackage{chemfig}
\usetikzlibrary{calc}
\begin{document}
\begin{center}
  \schemestart
    \chemleft[
      \chemfig{\lewis{246,O}-[:30]N(-[@{leg}:90]@{Oss}\lewis{024,O})-[:-30]\lewis{026,O}}
    \chemright]
  \schemestop
  \chemmove{
    \draw[->]
      ($(Oss)+(0:2.5mm)$)
      .. controls +(-10:2mm) and +(10:3mm)..
      ($(leg)+(0:.5mm)$);
    \node[xshift=5pt] at (c1.north east) {$-$} ;
  }
\end{center}
\end{document}

enter image description here

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