Successive phase transitions were observed for CsSnBr3 and CH3NH3SnBr3 by means of 81Br NQR and DTA. These compounds are isomorphous with each other and have typical cubic perovskite structures at room temperature. However, with decreasing temperature both compounds showed successive phase transitions and complex 81Br NQR spectra at 77 K. In the case of CH3NH3SnBr3, both 81Br NQR and 119Sn Mössbauer spectra changed markedly with decreasing temperature from those at room temperature. These findings suggested a large distortion of the SnBr6 octahedron from the regular one and were interpreted on the basis of the three-center-four-electron bond model. In relation to these structural changes, a broad-line 1H NMR experiment on CH3NH3SnBr3 was also observed in order to determine the effect of the dynamic properties of the cation.

The structures of the SnBr3− anions in MSnBr3 (M=(CH3)2NH2, (CH3)3NH) and MSnBr3·H2O (M=K, NH4) were deduced by means of 81Br NQR spectroscopy. The former compounds have three 81Br NQR lines in the frequency range 73–80 MHz at 77 K, indicating the presence of pyramidal SnBr3− anions. The anion structure of the latter hydrate, on the other hand, was presumed to be square-pyramid with one terminal and two bridging Br atoms, because two of the 81Br NQR frequencies were considerably low compared with that of the terminal atom. Phase transitions were observed for the latter hydrates. Associated with these, drastic increases of the NQR frequencies were observed only for the bridging atoms, suggesting significant changes in the bridging network.

The title compounds, for which successive structural phase transitions are observed by means of 81Br NQR and DTA are isomorphous and have typical cubic perovskite structure at 20 °C. Especially in the case of MeNH3SnBr3 the 81Br NQR and 119Sn Moessbauer spectra change markedly with decreasing temp. suggesting a change of the tin environment from a regular octahedron at 20 °C to a markedly distorted one at 77 K. These finding are interpreted on the basis of the three‐center‐four‐electron bond model.

Abstractare compared for the compounds ASnBr3 (A: Me2NH2, Me3NH) and ASnBr3·H2O (A: K, NH4).