# Missing-\endcsname-error in citing the references

Preamble

\usepackage{graphicx}
\usepackage{hyperref}
\usepackage{movie15}
\usepackage{cite}


Document body

Laboratory reflectance spectra of differentiated meteorites can be used
to identify indicate the rock-forming materials of asteroids at small
scales \cite{Gaffey} and \cite{Trigo-Rodríguez1}.
properties of asteroids and their reflective behavior were obtained
by much sensitive and precise spectrometers \cite{Dotto} and  \cite{Trigo-Rodríguez2}. \\


error:

! Missing \endcsname inserted.
\IeC
l.120 ...cite{Gaffey} and \cite{Trigo-Rodríguez1}

• Welcome to TeX.SX! Please help us (and also you) and add a minimal working example (MWE), that illustrates your problem. Reproducing the problem and finding out what the issue is will be much easier when we see compilable code, starting with \documentclass and ending with \end{document}. Oct 25, 2018 at 11:02
• \usepackage{graphicx} \usepackage{hyperref} \usepackage{movie15} \usepackage{cite} Oct 25, 2018 at 11:54
• At the moment my best guess is that the non-ASCII char í in \cite{Trigo-Rodríguez1} is problematic. Entry keys are mean to be internal names and must be reasonably safe. With a non-Unicode engine í is not reasonably safe. Change the key of Trigo-Rodríguez1 to Trigo-Rodriguez1 (with i instead of í) in both the .bib and .tex file and compile again. Oct 25, 2018 at 11:54
• Since you have some responses below that seem to answer your question, please consider marking one of them as ‘Accepted’ by clicking on the tickmark below their vote count (see How do you accept an answer?). This shows which answer helped you most, and it assigns reputation points to the author of the answer (and to you!). It's part of this site's idea to identify good questions and answers through upvotes and acceptance of answers. Feb 15, 2019 at 22:04

The citation/entry keys in your .bib file should not contain non-ASCII chars such as í if you use a non-Unicode engine. The reason for that is that the keys are used as internal identifiers and so LaTeX must be able to handle them without them breaking easily.

Change Trigo-Rodríguez1 and Trigo-Rodríguez2 to

Trigo-Rodriguez1


and

Trigo-Rodriguez2


repectively, i.e. replace the í with i in the key in both your .bib and .tex file.

Related: What characters are allowed to use as delimiters for BibTeX keys? and linked questions.