A molecular helix wrapped around a rigid rod can unwind and move between binding sites.

The first single crystal-based description of a spin transition compound from the patented [Fe(Rtrz)₃]X₂·nH₂O family is reported, properly the compound with Rtrz = 4-amino-1,2,4-triazole, X = NO₃ and n = 2. This study definitively proves the 1-D polymeric nature of the crystal structure and allows a description of the [Fe(Rtrz)₃] chains, as well as of the anions and water implementation within the crystal lattice opening the possibility of subsequent investigations of the structure-property correlation within this peculiar family of spin transition compounds.