四氧化三铁

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\usepackage{chemfig}
\begin{document}
\chemfig{
Fe
	(-[3.3,1]O
		-[2,1]Fe
			(-[0.7,1]O)
			(-[7.3,1]O)
	)
	(-[0.7,1]O
		-[2,1]Fe
			(-[3.3,0.8])
			(-[4.7,0.8])
	)
}
\end{document}