Deuterium isotope effect in the two-step spin-state transition of [FeII(5-NO2-sal-N(1,4,7,10))] investigated by Mِssbauer spectroscopy and magnetic susceptibility

Deuteration of the secondary amine functions of [FeII(5-NO2-sal-N(1,4,7,10))] has been performed in order to investigate the H/D isotope effect on the intermolecular hydrogen bond network responsible for the propagation of the two-step spin-state transition along the linear chains of this unique material. Mِssbauer spectroscopy and magnetic susceptibility studies show that the two-step spin-state crossover is retained upon deuteration. However, the critical temperatures experience a different increase upon deuteration (140.5 to 150.3 K (Tc1), 176.8 to 183 K (Tc2)) while there is no noticeable variation in the cooperativeness of the two transitions upon deuteration. The proposed interpretation for the different H/D isotope effect on the two steps of this spin-state transition is based upon the changes in hydrogen bond lengths resulting from the two structural phase transitions of [FeII(5-NO2-sal-N(1,4,7,10))] reported in the literature.