MOSSBAUER SPECTRA OF TETRAHEDRAL ALKALI DITHIOFERRATES(3)

Mössbauer spectra were taken of a series of compounds with tetrahedrally coordinated (sp2) iron (III) having a general formula AFeS2, where A=Na, K, Rb, Cs, over a temperature range 77°-300° K. The molar susceptibilities were also examined over the same range of temperatures. The almost temperature independence of ΔE Q indicates that level separation is larger or ∼kT. In contrast to the observations in the case of octahedral compounds, the increasing electronegativity of the cation increases the isomeric shift (I.S.) value. This is explained by the fact that the decreasing electronegativity of the cation increases the partial 4s character at iron in the compound. Furthermore, it is pointed out that the Walker, Wertheim, and Jaccarino (WWJ) plot is applicable to the compounds having tetrahedrally bonded (sp3) iron. The internal magnetic field in KFeS2 at -28°C is considered to result not from any magnetic transition, but from relaxation effects, whereas in the case of Na, Rb, and Cs dithioferrates it has been averaged to zero.