Mössbauer Studies on Spin Transition in Zinc Dilution Complexes Fe_1-xZn_x(dpp)₂(NCS)₂.py (x = 0.05-0.40)

A series of spin transition complexes Fe_1-xZn_x(dpp)₂(NCS)₂py (x = 0.05, 0.10, 0.15. 0.20, 0.25, and 0.40; py=pyridine) has been synthesized and studied by Mössbauer spectroscopy. The high spin structure is frozen at room temperature, and the induced meta-stable high-spin phase by the so-called rapid cooling method is monitored by temperature and time dependent Mössbauer spectra. The investigation on dynamic relaxation of the high-spin state to the low spin state at 80 K reveals sigmoid behaviour and existence of cooperative effect for low diluted complexes. This cooperative effect is wrecked by the dilution of Zn(II) ions in Fe(II) ion sites, and relaxation curves gradually become to obey the first-order kinetics as the ratio of the dilution increases.