Potassium Bromide Disk Method for the Infrared Studies of Coördination Compounds

The infrared absorption of tetrakis(ethylenethiocarbamide)copper(I) nitrate, ethylenethiocarbamide, and potassium nitrate have been measured by the potassium bromide disk method. The assignment of the frequencies of ethylenethiocarbamide explains that part of the spectrum (the wavelength region between 7 and 13 microns) in which various CH2 deformation frequencies are expected to appear. Generally speaking the infrared spectrum of tetrakis(ethylenethiocarbamide)copper(I) nitrate can be regarded as the superposition of the spectra of ethylenethiocarbamide and potassium nitrate, except for the absorption peaks at 9.6 and 14 microns, which do not appear in the infrared spectra of ethylenethiocarbamide and potassium nitrate. It is interesting to note that these wavelengths correspond to the Raman frequencies (1050 cm—1 and 720 cm—1) of potassium nitrate, which should be infrared-inactive. The appearance of these frequencies in the absorption spectrum is explained by the distortion of the nitrate ion in tetrakis(ethylenethiocarbamide)copper(I) nitrate.