Fig. (b) shows the room-temperature 119 Sn Mössbauer spectrum for our c-BaSnF 4 sample. The spectrum features an asymmetric quadrupole doublet with an isomer shift of around 3 mm s -1 , characteristic of covalently bonded Sn (II), and a large quadrupole splitting parameter (∆ > 1.5 mm s -1 ), indicating that Sn exhibits a stereoactive lone pair . The experimental spectrum can be reconstructed using two quadrupole doublets with distinct isomer-shift and quadrupole-splitting parameters (see the Supporting Information for details), indicating some degree of variation in Sn-F bonding interactions and in the coordination geometry around individual tin cations.