In a one-dimensional phthalocyanine molecular conductor $\text{TPP}{\left[\text{Fe}\left(\text{Pc}\right){\left(\text{CN}\right)}_2\right]}_2$, giant negative magnetoresistance was observed at low temperatures, where the resistivity increases. To clarify the origin of this magnetoresistance, we investigated the low-temperature insulating state, revealing a diffuse x-ray streak midway between the Bragg peaks. This suggests charge order driven by Coulomb repulsion among $\pi$-conduction electrons. The intensity increases below the temperature where the short-range antiferromagnetic order of $d$ local moments develops, which stabilizes the charge order via a Hund-like intramolecular $\pi \text{−}d$ interaction.

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• Charge order
• Giant magnetoresistance
• Molecular solids
• X-ray diffraction