Département de chimie moléculaire

Prussian blue analogs, RbxMn[Fe(CN)6]y·zH2O with different stoichiometries were synthesized. Elemental analyses reveal a quasilinear decrease in x and y when z increases. Some of these samples present a 1st-order phase transition between the MnII-FeIII and MnIII-FeII electronic states with large thermal hysteresis loops observed in the magnetic susceptibility. The phase-transition temperatures correlate with the stoichiometry, but quant. predictions cannot be made because of the disordered nature of the compounds Contrary to previous literature reports, calorimetric and Raman spectroscopic measurements reveal that the charge-transfer phase transition is accompanied by a significant entropy change, $Δ$S = 48-59 JK-1 mol-1, of mainly vibrational origin. In addition to the thermal phase transition, Raman spectra also show that ≲120 K a photoinduced MnIII-FeII to MnII-FeIII conversion occurs in certain stoichiometries.