Vibrational spectra and pseudo-exact force constants of [Ni(NH3)6]2+, [Zn(NH3)4]2+, and [Zn(CN)4]2− with 58Ni/62Ni, 64Zn/68Zn and H/D isotopic substitution

Abstract

Abstract The vibrational spectra of [Ni(NH3)6]Cl2, [Ni(ND3)6]Cl2, [58Ni(NH3)6]Cl2, [62Ni(NH3)6]Cl2, [Zn(NH3)4]I2, K2[Zn(CN)4], K2[64Zn(CN)4], K2[(68Zn(CN)4] are reported. Two different methods have been developed which allow to calculate pseudo-exact force constants. It is shown for [Ni(NH3)6]]2+ and [Zn(NH3)4]2+ that reasonable force constants for the skeletons of hexammine and tetrammine metal complexes can be calculated from Raman and infrared data of the isotopically substituted ions using the point mass model, if the isotope shifts can be measured accurately. These force constants are more reliable than previously reported values. In complexes such as [Zn(CN)4]2−, where the ligand and skeletal vibrations are relatively strongly coupled, reliable force constants for part of the force field may under certain conditions be obtained from the “High Low Frequency Separation Method” employing isotopic data.