Correlation between the Stoichiometry and the Bistability of Electronic States in Valence‐Tautomeric Rb_xMn[Fe(CN)₆]_y·zH₂O Complexes

Abstract

A series of Prussian blue analogues, RbxMn[Fe(CN)6]y·zH2O with different stoichiometries have been synthesized. Elemental analyses reveal a quasilinear decrease in x and y when z increases. Some of these samples present a first‐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 quantitative 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, ΔS = 48–59 J K–1 mol–1, of mainly vibrational origin. In addition to the thermal phase transition, Raman spectra also show that below ca. 120 K a photoinduced MnIII–FeII to MnII–FeIII conversion occurs in certain stoichiometries.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Interplay between the Charge Transport Phenomena and the Charge-Transfer Phase Transition in RbxMn[Fe(CN)6]y·zH2O

“…In our case, this phonon frequency ω ph can be calculated as 5.8 × 10 13 s -1 (∼310 cm ), which falls in the range of typical frequencies of breathing modes of the metal-coordination polyhedra in Prussian blue analogues. 29 As mentioned before, the conduction due to a process of siteto-site charge transfer must involve a dielectric relaxation. This is because a hop to a new site can lead to successful charge transport only if the polarization cloud follows.…”

Metal-to-ligand and ligand-to-metal charge transfer in thin films of Prussian blue analogues investigated by X-ray absorption spectroscopy

“…They consist of a 3D coordination network containing Fe(II)-CN-M(III) (M = Mn, Co) entities in their low-temperature (LT) phase and Fe(III)-CN-M(II) entities in their high-temperature (HT) phase. A number of Fe(CN) 6 sites are however vacant 5,11 and filled by water molecules that bond to M ions through their O atoms. 12 Noncoordinated water molecules are often observed as well.…”

“…Raman spectrum exhibits two bands at 2159 and 2169 cm À1 which have been assigned to the HT pairs Mn(II)-NC-Fe(III) (RbMnFe3). 11 Another sample similarly obtained was let in an oven at 125 1C during 1 week. The composition moved from a pure HT form to a mixture of both the HT, the LT Mn(III)-NC-Fe(II) and the reduced Mn(II)-NC-Fe(II) forms (RbMnFe2) as suggested by the appearance of two broad bands centred at 2090 and 2133 cm À1 in Raman spectra.…”

“…The composition moved from a pure HT form to a mixture of both the HT, the LT Mn(III)-NC-Fe(II) and the reduced Mn(II)-NC-Fe(II) forms (RbMnFe2) as suggested by the appearance of two broad bands centred at 2090 and 2133 cm À1 in Raman spectra. 11 w We can note that this time evolution is influenced by the water content which cannot be really controlled during the synthesis but varies also depending on the experimental conditions (vacuum, nitrogen atmosphere or air).…”

Growth Dynamics of Photoinduced Phase Domain in Cyano-Complex Studied by Boundary Sensitive Raman Spectroscopy

“…The peaks at 2099 and 2117 cm −1 in Fig. 2b can be assigned to LTP, since a previous report by Cobo et al [12] clearly assigned two sharp peaks at 2096 and 2114 cm −1 to LTP. Furthermore, Vertelman et al [10] and Lummen et al [11] have observed several broadened peaks at 2086-2130 cm −1 in the Raman spectra and assigned them to LTP.…”