Crystal structure of NbSe 2 I 2 Single crystal XRD was performed to unveil the crystallographic information of NbSe 2 I 2 , and the detailed information is listed in Table 1 in Supporting Information. NbSe 2 I 2 is triclinic at room temperature. It has a space group P 1 (No. 2), iso-structural to NbSe 2 Br 2 , and this matches the previously published low temperature (<199 • C) structure for NbSe 2 I 2 . Above the transition temperature at around 199 • C, a higher-symmetry monoclinic phase with a space group of C2/m (No. 12) is more stable for NbSe 2 I 2 , and it can be inferred that the C2/m phase formed first during CVT growth and then transformed into the P 1 phase as the sample cooled naturally. The transformation from the C2/m phase to the P 1 phase can be understood as a sliding of abplane sheets as well as a twist of atoms in the ab-plane.