Structure and 119Sn Mossbauer-spectroscopic characterization of BaRhSn2

The stannide BaRhSn2 was synthesized by induction melting of an arc-melted RhSn2 precursor compound with barium in a sealed tantalum ampoule. The structure of BaRhSn2 was refined from single-crystal X-ray diffractometer data: MgCuAl2 type, Cmcm, a = 437.56(4), b = 1242.35(10), c = 767.30(6) pm, wR2 = 0.0845, 469 F-2 values and 16 variables. The rhodium and tin atoms form a two-dimensional [RhSn2](delta-) polyanionic network with short Rh-Sn (273-274 pm) and Sn-Sn (303-312 pm) distances. The large barium atoms lead to a substantial orthorhombic distortion of the (lonsdaleite-related) tin substructure, forcing a break of the Sn-Sn bond in b direction. This change in the tin substructure is reflected in the Sn-119 Mossbauer spectrum. The tin atoms exhibit a higher s electron density which is expressed in an increased isomer shift of delta = 2.08(1) mm s(-1) as compared to the previously reported stannide CaRhSn2 with a three-dimensional [RhSn2](delta-) polyanionic network and delta = 1.96(4) mm s(-1).