Far-infrared single crystal reflectance spectra of some tetra-alkylammonium tetrachlorometallates; influence of crystal field effects and distortion on the vibrations of the ‘tetrahedral’ anions

Abstract

The far-i.r. polarised reflectance spectra (40–400 cm^–1) of single crystals of (NMe₄)₂MCl₄(M = Co, Cu, or Zn) and (NEt₄)₂MCl₄(M = Co or Ni) at room temperature and 105 K are reported. The spectra show evidence for disorder in the structures of the complexes examined. Factor group splittings in the tetramethylammonium complexes at low temperature indicate removal of the diffraction symmetry at the MCl₄^2–, sites due to variations in the orientation of the anions. The effects of the crystal field on the internal vibrations of the approximately tetrahedral MCl₄^2– ions is examined, and the relationship between the magnitude of the splitting of the T_d modes and the tetragonal distortion of the anions is discussed.