Patent ID: 8709599

Claim:
A spin transition material composed of at least one compound corresponding to the formula Fe 1-m M m (R-Trz) 3 X b Y c (I) in which: M is a metal, other than Fe, having a 3d 4 , 3d 5 , 3d 6 or 3d 7 configuration; 0≦m<1; R-Trz represents a 1,2,4-triazole ligand carrying an R substituent on the nitrogen in the 4 position; R is an alkyl group or an R 1 R 2 N— group in which R 1 and R 2 represent, each independently of the other, H or an alkyl radical; X represents at least one noncoloring monovalent or divalent anion selected from the group consisting of BF 4 − , PF 6 − , ClO 4 − , Br − , Cl − , NO 3 − , CF 3 SO 3 − , CH 3 SO 3 − , SO 4 2− and CO 3 2− ; Y represents at least one coloring anion which has at least two aromatic rings and at least one SO 3 − group; b>0 and c>0, b and c being chosen so that the electrical neutrality of the compound (I) is adhered to and b and c are such that 10 −5 ≦c/b≦0.1 (in moles), so as to provide a spin transition associated with a change in color being other than pink or white.