Copper–halogen stretching frequencies

Abstract
The far-infrared spectra of some halogenocuprates of the types [CuX4]2–(planar and tetrahedral), [Cu2X6]2–, CsCuX3, and M2 ICuCl4,2H2O have been studied. Complexes of the type CuX2L2(X = Cl or Br; L = donor ligand) are also considered. v(Cu–Cl) lies in the range 368—222 cm.–1 and v(Cu–Br) between 278 and 168 cm.–1. The spectra admit of a consistent interpretation without the need to postulate the presence of v(Cu–X) modes in the normal region due to stretching of copper–halogen “long” bonds. Bridging v(Cu–X) frequencies have been assigned but the range is severely overlapped by that of terminal v(Cu–X).
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