A comparison of two Prussian blue models

Selective labeling of compounds containing one element in two or more chemical environments with Mossbauer inactive Fe-56 and with Mossbauer active Fe-57 isotopes has been used to study the nature of the three iron environments in Prussian blue type compounds. The effect of the intersititial ion in Prussian blue upon the nitrogen bonded and carbon bonded irons was studied by exchanging interstitial K+ with cations from Group IA, Group IIA, and including NH4+, H+, and Al+3. For the interstitial Group IA precipitates, the isomer shift values became more positive as the electronegativities decreased and the ionic radii increased. The Cs Prussian blue data were significantly different for both iron environments, giving very broad peaks with a distinct shoulder on the carbon hole active iron peak. This shoulder was found to be due to nitrogen hole iron indicating that the large cesium interstitial iron distorted the lattice in such a way as to permit exchange of the carbon and nitrogen hole irons. This isotope labeling technique is inexpensive and should be widely applicable to Mossbauer studies for atoms in multiple environments in which there is no exchange.