Infrared Spectroscopic Studies of Hexammine- and Pentammine-chromium(III) Complexes

Twenty-nine samples of hexammine and pentammine complexes of chromium (III) and cobalt (III) have been prepared, and their infrared spectra have been measured in the region of 2∼25μ. The absorption peaks of these complexes have been found to shift to higher frequencies in the N-H stretching vibrations, and to lower frequencies in the N-H deformation and the Cr-N stretching vibrations in the order of the chlorides, the bromides and the iodides. In a potassium bromide prism region, three absorption bands due to the Cr-N stretching vibrations have been observed in hexammine- and halopentamminechromium(III) halides, but only one in the aquopentamminechromium(III) complexes. The shifts of the absorption bands observed have been discussed from the standpoint of the hydrogen bond formation.