DEUTERIUM-ISOTOPE EFFECT IN THE 2-STEP SPIN-STATE TRANSITION OF [FE-II(5-NO2-SAL-N(1,4,7,10))] INVESTIGATED BY MOSSBAUER-SPECTROSCOPY AND MAGNETIC-SUSCEPTIBILITY

Deuteration of the secondary amine functions of [Fe-II(5-NO2-sal-N(1,4 ,7,10))] has been performed in order to investigate the H/D isotope ef fect on the intermolecular hydrogen bond network responsible for the p ropagation of the two-step spin-state transition along the linear chai ns of this unique material. Mossbauer spectroscopy and magnetic suscep tibility studies show that the two-step spin-state crossover is retain ed upon deuteration. However, the critical temperatures experience a d ifferent increase upon deuteration (140.5 to 150.3 K (T-c1), 176.8 to 183 K (T-c2)) while there is no noticeable variation in the cooperativ eness of the two transitions upon deuteration. The proposed interpreta tion for the different H/D isotope effect on the two steps of this spi n-state transition is based upon the changes in hydrogen bond lengths resulting from the two structural phase transitions of [Fe-II(5-NO2-sa l-N(1,4,7,10))] reported in the literature.