Crystal structure refinement of the electron-transfer-active potassium manganese hexacyanoferrates and isomorphous potassium manganese hexacyanocobaltates

摘要

We report on the crystal structure refinements in the novel electron-transfer-active Prussian Blue analogs (PBA) KMn4II[(Co1-xFexIII)-Fe-III(CN)(6)](3)center dot nH(2)O (n similar or equal to 12). The series of novel PBA with the end members of KMn4[Co(CN)(6)](3)center dot 11.8 H2O and KMn4[Fe(CN)(6)](3)center dot 10.5 H2O have been synthesized for the first time, all showing a number of extra-reflections incompatible with ordinary face-centered cell of the Fm-3m symmetry group. We have analyzed the Rietveld patterns for x = 0, 0.53,1 and found that the extrareflections could be well fitted using several primitive (P) cell symmetries. The best fitting quality was obtained using the noncentrosymmetric space group (S.G.) P (4) over bar 3m (Z=1) with the origin of coordinate system shifted into a zeolitic site. In this structure model, the Co-CN-Mn entities are bent owing to the charge introduced by the K+ insertion that induces also the electron transfer between Mn and Fe. Using Mossbauer spectroscopy the electron transfer activity is identified with the appearance of unsplit resonance at the isomer shift of typically -0.15 mm/s evidencing the low-spin state for Fe3+ and Fe2+ species. In the same P (4) over bar 3m phases doped with Fe-57(2+) into the Mn site, a sequence of discrete values of quadrupole splitting (0 mm/s, 0.9 mm/s, 1.8 mm/s) is observed and attributed to different conformations of the polyhedra, in which the ground states are orbital triplet, doublet and singlet, respectively. (C) 2015 Elsevier Inc. All rights reserved.