One-dimensional iron(II) compounds exhibiting spin crossover and liquid crystalline properties in the room temperature region.

A novel series of 1D Fe(II) metallomesogens have been synthesized using the ligand 5-bis(alkoxy)- N-(4 H-1,2,4-triazol-4-yl)benzamide (C n -tba) and the Fe(X) 2. sH 2O salts. The polymers obey the general formula [Fe(C n -tba) 3](X) 2. sH 2O [X = CF 3SO 3 (-), BF 4 (-); n = 4, 6, 8, 10, 12]. The derivatives with n = 4, 6 exhibit spin transition behavior like in crystalline compounds, whereas those with n = 8, 10, 12 present a spin transition coexisting with the mesomorphic behavior in the room-temperature region. A columnar mesophase has been found for the majority of the metallomesogens, but also a columnar lamellar mesophase was observed for other derivatives. [Fe(C 12-tba) 3](CF 3SO 3) 2 represents a new example of a system where the phase transition directly influences the spin transition of the Fe(II) ions but is not the driving energy of the spin crossover phenomenon. The compounds display drastic changes of color from violet (low-spin state, LS) to white (high-spin state, HS). The compounds are fluid, and it is possible to prepare thin films from them.