Electronic structure and spectra of rhodium(II) tetracarboxylate complexes

The DFT B3LYP geometry optimization was carried out and the IR spectra were calculated for rhodium(II) tetracarboxylate complexes Rh₂(O₂CR)₄ (R = H, CH₃, CF₃, C₆H₅) and for the compound Rh₂(O₂CH)₄(H₂O)₂ with two axially coordinated water molecules. A minor influence of the substituent R on the electronic structure and geometric and spectral characteristics of the cage was noted. From the calculation results, it was concluded that the Rh(II)-Rh(II) stretching vibrations should be attributed to about 300 cm^?1. The results obtained for rhodium(II) dimers were compared with analogous data for Mo₂(O₂CH)₄. Analysis of the electronic structure including consideration of the natural bond orbitals indicates the presence of a strong Rh(II)-Rh(II) single bond and a quadruple Mo(IV)-Mo(IV) bond. The electronic spectra of Rh₂(O₂CR)₄ (R = H, C₆H₅) and Rh₂(O₂CH)₄(H₂O)₂ were simulated by the TDDFT technique.