Fig. 1: Crystal structures of (MV)BiBr5 viewed along the [100] direction.

a Phase α at 0.1 MPa/243 K34. b Phase β at 0.1 MPa/296 K. c Phase γ at 0.29 GPa/296 K. d Phase γ’ at 3.45 GPa/296 K. The 1D BiBr5 chains of four phases are displayed for comparison. The CH···Br hydrogen bonds are shown as red dashed lines in all phases.