Dynamic spin-crossover in [FeII(TRIM)2]Cl2 investigated by Mössbauer spectroscopy and magnetic measurements

The magnetic and Mossbauer data of the new coordination complex [Fe II (TRIM) 2 ]CI 2 , where TRIM = 4′-(4-methylimidazole-2′- (2″-methylimidazole)-imidazole) afford evidence for a complete and progressive spin conversion between the 1 A 1 and 5 T 2 spin states. The interstate conversion frequencies measured in the 220–300 K temperature range follow an Arrhenius behavior. The thermal variation of the equilibrium constant over the whole temperature range approximately follows a linear Arrhenius plot, thus indicating a very low degree of cooperativity in this material; a small distortion from the linear plot suggests a vibrational effect.