Infrared spectra of mixtures of water and deuteroacetonitrile containing the Cr3+ cation have been studied as a function of concentration, time and temperature. The CN stretching vibration of CD3CN molecules has been used as a probe of the structural environments. The CN band in the spectra of the solutions is a superposition of four subbands, which may be attributed to CD3CN bound in the first, second, and third solvation shells of the cation and to non-bound CD3CN. The character of changes of the integral intensities of the subbands with time for various H2O:Cr3+ molar ratios are explained by suggesting mechanisms of molecular replacement within the solvation shells of Cr3+.