Mossbauer spectroscopy cubic symmetry

Magnetic nanoparticles in the sol-gel silica glass were obtained by heat treatment at 1000°C in air during 6 h and identified by X-ray and Mossbauer spectroscopy as y-Fe203 (maghemite) [11], The magnetic parameters of maghemite used in computer simulations of the SPR spectra, are Ms = 370 kA m 1 and = —4.64 kJ m"3 (cubic symmetry) [35],... 

We are now faced with a dramatic contradiction X-ray diffraction shows that tin and the other metal are disordered on the unique metal site of the fluorite structure. The symmetry of this site is cubic, therefore, since tin(ll) has one lone pair, and a stereoactive lone pair would be duplicated six or eight times by the symmetry of the site, and in addition, it would repel away the fluoride ions, the lone pair cannot be stereoactive and tin has to be present in the form of the Sn stannous ion. However, in contradiction with the symmetry requirements, Mossbauer spectroscopy shows unquestionably that the tin lone pair is stereoactive and Sn—F bonding is covalent. 

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