Experimental and theoretical vibrational study of tetraaquatris(succinate)diholmium(III) hexahydrate, a bidimensional hybrid coordination polymer

The hybrid network existing in the lattice of tetraaquatris(succinate)diholmium(III) hexahydrate is developed by two succinate ligands adopting trans and gauche conformational forms. The presence of both rotamers is evidenced in the vibrational spectra of the title compound. Theoretical and experimental spectroscopic methods that include the study of the deuterated compound, are applied in order to perform a correct identification of the normal modes of vibration of each conformer. DFT (B3LYP) calculations using the 6-311G∗ basis set are used to predict the optimized ligand structure and vibrational spectra. Carboxylate bending modes and Ho-O stretching vibrations are also estimated by using the CEP-121G triple-split pseudopotential basis, at the same level of theory. Water modes are assigned with the assistance of the spectra of partial and totally dehydrated compound. A good agreement between the theoretical and experimental vibrational spectra and the structural data is found. These spectroscopic results constitute a valuable contribution to structural elucidation in those cases in which single-crystal DRX data is not available.