Laser Raman study of phase transitions in [N(CH3)4]2COCl4 single crystals

Abstract Temperature‐dependent Raman spectra of oriented single crystals of [N(CH 3 ) 4 ] 2 CoCl 4 are reported. An assignment of the observed Raman bands has been made and it was found that the N(CH 3 ) 4 + and CoCl 4 2− groups occupy sites of C s symmetry in the lattice at room temperature. However, because of rapid reorientation, the CoCl 4 2− groups retain an effective tetrahedral symmetry. The prototypic to incommensurate to commensurate phase transitions are associated with the orientational dynamics of the CoCl 4 tetrahedra. The monoclinic to orthorhombic super lattice phase transition at 122 K in [N(CH 3 ) 4 ] 2 CoCl 4 is triggered by the distortion of the N(CH 3 ) 4 + groups in the lattice.