Study of double ionic disorder (cationic and anionic) and disorder of two kinds of tin(II) (ionic and covalent) within the same material: the incredibly complex Ba_(1-x)Sn_xCl_(1+y)F_(1-y) solid solution and its study by Mossbauer spectroscopy

摘要

A doubly disordered Ba_(1-x)Sn_xCl_(1+y)F_(1-y) solid solution has been prepared. X-ray diffraction shows that Ba and Sn are fully disordered on the Ba site of the BaClF structure. In addition, while the two anionic sites remain ordered, for y>0 the y Cl in excess are disordered with the remaining (1-y) F on the F site, whereas for y<0, the (-y) excess F are disordered with the remaining (1+y) Cl on the Cl site. ~(119)Sn Mossbauer spectroscopy showed the Ba_(1-x)Sn_xCl_(1+y)F_(1-y) solid solution is a truly unique material. Indeed, in addition to the rarity of being a doubly disordered solid solution over a wide range of chemical composition, it also exhibits a variable mixture of ionic tin(II) (Sn~(2+) stannous ions, with a non-stereoactive lone pair) and covalently bonded tin(II) (with a stereoactive lone pair). A new material, Ba_2SnCl_6, has been prepared and its crystal structure solved. It contains octahedrally coordinated Sn~(2+), with a perfectly non-stereoactive lone pair, for the first time in a chloride. This makes the lone pair a potential charge carrier.