Crystal structure and cation lone electron pair activity of Bi2S3 between 0 and 10 GPa

Crystal structure of Bi2S3 was refined at eight distinct hydrostatic pressures in the range 0-10 GPa using a CCD equipped 4-circle diffractometer and a diamond-anvil cell. Coefficients of the BM3 equation of state are as follows: zero-pressure volume 498.4(7) angstrom(3), bulk modulus K-0 36.6(15) GPa and its pressure derivative 6.4(5). The bulk of compression takes place in the structural space between Bi4S6 ribbons, where lone-electron pairs are accommodated. Eccentricity of Bi in its coordination polyhedra decreases in the process, with long Bi-S distances decreasing, whereas the opposing short Bi-S distances stay constant or even increase in length. All these phenomena are compatible with the movement of lone-electron pairs of Bi closer to the parent atom at increasing pressure.