Isomerization effect of counter anion on the spin crossover transition in [Fe(4-NH₂trz)₃](CH₃C₆H₄SO₃)₂·nH₂O

We have investigated the spin crossover transition of the triazole bridged one dimensional Fe^II complexes, [Fe(4-NH₂trz)₃](o-, m-, p-tos)₂·nH₂O (tosH = toluenesulfonic acid), in order to study the isomerization effect of counter anion on the spin crossover phenomenon by means of ⁵⁷Fe Mössbauer spectroscopy and magnetic susceptibility measurement. In the heating process, the spin transition of the all salts occurs around room temperatures, i.e. those of o-, m-, p-tos salts are 330 K, 319 K and 320 & 350 K, respectively. In the cooling process, the structural isomerization effect of counter anion on the spin crossover phenomenon is more remarkable than that in the heating process. In the case of o-tos salt, the spin transition occurs at 250 K with thermal hysteresis of 80 K. On the other hand, in the case of the m-tos salt, the spin transition occurs abruptly at 319 K with negligible small hysteresis. In the case of the p-tos salt, the spin transition occurs abruptly at 295 K in the cooling process in spite of stepwise spin transitions in the heating process.