Electronic Absorption Spectrum and Structure of CuCl4=

Abstract

Polarized crystal‐absorption spectra in the near‐infrared, visible, and ultraviolet regions are reported for Cs₂CuCl₄. The near‐infrared bands are analyzed on the basis of the known structure of the CuCl₄⁼ ion with D_2d symmetry. The positions and polarizations of the bands are accounted for and the minor effcets of spin—orbit coupling and the true‐site symmetry (C_s) are discussed. The observations agree very well with the theoretical calculations of Lohr and Lipscomb and differ from the pure electrostatic crystal‐field theory. An analysis of the electron‐transfer bands has been made. It is concluded that the CuCl₄⁼ ion in solution has a structure which is close to that found in the crystal of Cs₂CuCl₄.