Theoretical Vibrational Analysis of Bidentate and Unidentate Coordination of Carbonate, Nitrate, Sulfate, and Perchlorate Ions to a Metal

In this study, firstly, the vibrational analysis of the bidentate coordination of the title ions to metal was theoretically performed as combined with group-theoretical analysis. In the calculation, the DFT method with B3LYP functional was used at the DEF2-TZVP level set and, cobalt, nickel, and copper were chosen as metal. As expected, the coordination of the ions to the metal atom lowered the symmetry and so, the splitting of degenerate modes occurred together with the appearance of IR inactive modes. The calculated frequencies for all the modes were given together with their symmetry species in tables. These results showed that all the splitting bands of the degenerate modes are nearly center-out, and if the intensity of degenerate mode is high the intensities of its splitting bands are also high or vice versa. Then, to compare, some metal complexes with bidentate and unidentate ligands were optimized and, their calculated frequencies were given together with their corresponding experimental data in tables. From these results it was concluded that the vibrational frequency value of the M-O stretching mode is lower in the unidentate than in the bidentate complexes due to the decreasing of the force constant, and the splitting bands of degenerate modes are larger in the bidentate than in the unidentate complexes.