Low-temperature far-infrared spectra of some tetrachloropalladate(II) and tetrachloroplatinate(II) salts

Abstract

Far-i.r. spectra of A₂[PdCl₄] and A₂[PtCl₄](A = K, NH₄, or ND₄) have been investigated at temperatures below 100 K for the first time. Several new bands occur in the 200–360 cm^–1 region on cooling to ca. 20 K. These and other features are discussed with the aid of single-crystal polarised-transmission measurements on [NH₄]₂[MCl₄](M = Pd or Pt) in the range 60–180 cm^–1, which yield evidence for the positions of the translatory modes. A theoretical analysis is given of the space groups to which these solids might transform at low temperatures. Among the structural possibilities considered are out-of-plane distortions of the anions.