Search for the stannous ion in a chloride/fluoride matrix: cases of Ba_1−x Sn_xCl_1+y F_1−y and of Ba₂SnCl₆

Abstract

With the exception of anhydrous SnCl₂, in divalent tin fluorides and chlorides, tin(II) is always covalent bonded, i.e. its valence orbitals are hybridized and the tin lone pair is located in one of the hybrid orbitals. This lone pair is highly stereoactive and generates a large efg, resulting in a large quadrupole splitting. A doubly disordered Ba_1−x Sn_xCl_1+y F_1−y solid solution has been prepared and found to contain either ionic tin(II) (Sn²⁺ ions) or a mixture of ionic and covalent tin(II), depending on x, y and the method of preparation. The ionic tin(II) spectrum in Ba1−xSn_xCl_1+y F_1−y gives a Mössbauer single line that is broadened by the lattice efg, like in SnCl₂. Now, Sn²⁺ has been found to be present in an undistorted octahedral coordination in a newly isolated compound, Ba₂SnCl₆. It should be the first example of Sn²⁺ that is fully ionic and has a perfectly spherical lone pair.