I wrote this mini-example:

\documentclass[12pt,fleqn,A4,danish]{article}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage[text={14cm,20cm},centering]{geometry}
\begin{document}
\title{Amsmath problem}
\author{}
\date{}
\maketitle
Bla bla $\mathrm{AuCl_4^−}$ and $\mathrm{TOA^+}$

\end{document}

and get this result:

....
! Missing { inserted.
<to be read again>
\begingroup
l.10 bla bla $\mathrm{AuCl_4^−}
$ and $\mathrm{TOA^+}$
?

On a suggestion of a friend I tried ${\mathrm{AuCl_4^−}}$

with the same result. I also tried his suggestion
to use mhchem, i.e.

\ce{[AuCl4]^-}

and this didn't work either (yes, I did add
\usepackage{mhchem} )

This is supposed to work, and does on my
friend's machine. Could this be a defective
texlive, or am I really doing something
wrong?

--
db

Hi!

If I compile your example I get the same error message too.

> Bla bla $\mathrm{AuCl_4^−}$ and $\mathrm{TOA^+}$

Whilst disassembling your lines, I get an error code for the -:
Unicode character − (U+2212) not set up for use with LaTeX.

Does this help you?

Cheers
Marckus

Am 23.06.2024 um 16:49 schrieb db:
> I wrote this mini-example:
>
> \documentclass[12pt,fleqn,A4,danish]{article}
> \usepackage{amsmath}
> \usepackage{graphicx}
> \usepackage[text={14cm,20cm},centering]{geometry}
> \begin{document}
> \title{Amsmath problem}
> \author{}
> \date{}
> \maketitle
> Bla bla $\mathrm{AuCl_4^−}$ and $\mathrm{TOA^+}$
>
> \end{document}
>
> and get this result:
>
> ...
> ! Missing { inserted.
> <to be read again>
> \begingroup
> l.10 bla bla $\mathrm{AuCl_4^−}
> $ and $\mathrm{TOA^+}$
> ?
>
> On a suggestion of a friend I tried ${\mathrm{AuCl_4^−}}$
>
> with the same result. I also tried his suggestion
> to use mhchem, i.e.
>
> \ce{[AuCl4]^-}
>
> and this didn't work either (yes, I did add
> \usepackage{mhchem} )
>
> This is supposed to work, and does on my
> friend's machine. Could this be a defective
> texlive, or am I really doing something
> wrong?
>

Le 23/06/24 à 14h49, db a écrit :

> I wrote this mini-example:
>
> \documentclass[12pt,fleqn,A4,danish]{article}
> \usepackage{amsmath}
> \usepackage{graphicx}
> \usepackage[text={14cm,20cm},centering]{geometry}
> \begin{document}
> \title{Amsmath problem}
> \author{}
> \date{}
> \maketitle
> Bla bla $\mathrm{AuCl_4^−}$ and $\mathrm{TOA^+}$
>
> \end{document}

The following, relying on `chemformula`, works nicely with an up to
date TeX Live 2024:

--8<---------------cut here---------------start------------->8---
\documentclass{article}
\usepackage{chemformula}
\begin{document}
Bla bla \ch{AuCl4^−} and \ch{TOA^+}.
\end{document}
--8<---------------cut here---------------end--------------->8---
--
Denis

Il Sun, 23 Jun 2024 14:49:17 -0000 (UTC), db ha scritto:

> \maketitle Bla bla $\mathrm{AuCl_4^−}$ and $\mathrm{TOA^+}$

The problems comes from the minus sign on the first chemical formula. You
did not use the keyboard minus sign but the slash symbol.

Your minus sign: −
Keyboard minus sign: -

If you substitute it, then it will work.

Ciao, Mauro