A 119Sn Mössbauer-spectroscopic characterization of the diamagnetic birefringence material Sn2B5O9Cl

The crystal structure of diamagnetic borate chloride Sn 2 B 5 O 9 Cl exhibits two crystallographically independent tin sites which both show pronounced lone-pair activity of the tin atoms. This is reflected in substantial quadrupole splitting in the 119 Sn Mössbauer spectrum. The isomer shifts of 3.887(8) and 4.137(7) mm s −1 clearly indicate divalent tin. In agreement with bond valence calculations, the Sn1 atoms have a lower charge and the higher isomer shift, compatible with a higher electron density at the tin nuclei.