Hello Jahan,
since you are new to the forum, you perhaps don't know yet why a
minimal working example (MWE) is important and how to make one. Please follow the link and Thorsten's link to learn why and how.
Here I made an MWE which uses your code snippet but doesn't show the behavior:
Code: Select all
\RequirePackage{filecontents}
\begin{filecontents}{\jobname.bib}
@article{crabtreeReview,
title = "Organometallic alkane CH activation",
author={R. Crabtree},
journal = "Journal of Organometallic Chemistry",
volume = "689",
number = "24",
pages = "4083 - 4091",
year = "2004",
}
\end{filecontents}
\documentclass{article}
\begin{document}
\section{Main text}
See \cite{crabtreeReview}.
\bibliography{\jobname}
\bibliographystyle{plain}
\end{document}
I took the time for this, to show how
filecontents can be used for creating a MWE with a bibliography. Of course one can post a normal document and the bibliography as a separate file.

- bibliography.png (15.96 KiB) Viewed 2084 times
As you can see, the problem doesn't appear. That's why further information is required to fix it, since we don't know what's in your code, besides the bib snippet.
Stefan