The Influence of Defects on the Electron-Transfer and Magnetic Properties of Rb_xMn[Fe(CN)₆]_y·zH₂O

Abstract

The synthesis and detailed characterization of a few samples of the compound Rb x Mn[Fe(CN) 6 ] y ‚ zH 2 O are described. The composition of the materials significantly depends on the applied preparative conditions. Analysis of spectroscopic results (FTIR, Raman, 57 Fe Mössbauer, XPS) and X-ray powderdiffraction data yielded a further assessment of the difference in structural features in terms of the amount of Fe(CN) 6 vacancies and the associated number of water molecules. The characteristic individual magnetic behavior, as well as the metal-to-metal charge-transfer capabilities of the various samples, could be related to significant changes within the structures that appear to be associated with the synthetic method used.

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

“…It should be noted that the HT value of the magnetic moment differs significantly from the expected spinonly value of 6.1 µ B . Such differences have been observed previously 19 and can be attributed to the incomplete nature of the phase transition. The temperature dependence of the dc conductivity, σ dc , (measured at 2 and 20 V) is shown in Figure 2, together with the magnetic data.…”

“…17 It is important to note also that the width and the position of the hysteresis loop in this compound depends strongly on the particular x, y, z stoichiometry obtained during the precipitation of the compound, since the extreme insolubility makesfordifficultyinachievingexactlyreproducedcompositions. 18,19 For stoichiometries close to the idealized x ) y ) 1 composition, the phase transition occurs around 230 and 300 K in the heating and cooling cycles, respectively. In most cases, however, the system contains [Fe(CN) 6 ] 3-vacancies ( Figure 1).…”

“…18 If the vacancy concentration exceeds a certain limit (y < ∼0.9), the compound remains in the HT state down to liquid helium temperatures. 19 The dc and ac conductivity measurements have been carried out in the two-probe geometry either on powder samples (diameter 10 mm, thickness ∼0.1 mm) contained in a Teflon sample holder between two stainless steel electrodes or on pellets (diameter 3.3 mm, thickness 0.4 mm) compacted at a pressure of 70 bar for 5 min. There were no significant differences in conductivities or magnetic susceptibilities between the powder samples and pellets, although the latter gave, in general, somewhat better results in terms of standard deviation of the measured conductivity values.…”

Valence‐Tautomeric RbMnFe Prussian Blue Analogues: Composition and Time Stability Investigation

“…The magnetic behavior clearly shows that the sample does not exhibit an electron transfer, which is in agreement with the literature for a Rb x Mn[Fe(CN) 6 ] y ·zH 2 O compound with this stoichiometry. [14,21] The χ M T value at room temperature is 4.75 cm 3 K mol -1 . This value is exactly what would be expected for a paramagnetic {S 1 :S 2 } = {5/2:1/2} spin system.…”

“…If the water content is sufficiently high, the redox potential decreases to such an extent that the Fe III LS -CN-Mn II HS form becomes stable at very-low temperatures. [21] This important role of the incorporated water molecules, which may be coordinated as well as noncoordinated, suggests that the physical properties of these compounds may change with time, but to the best of our knowledge, this occurrence has not been discussed in the literature. It is also important to note that the transition from the HT to LT form is accompanied by a remarkable volume contraction of ca.…”