Dynamics of Lanthanide(III) complexes from crystallographic data and computational studies

The analysis of the X-ray structures of rare-earth polyaminopolycarboxylate complexes provides information on the potential energy surfaces associated with N-C-C-X of five-membered chelate rings, as demonstrated with DFT studies. This combined analysis of experimental and computational data provides important information on the dynamics of rare-earth complexes leading to isomer interconversion. • Puckering of five-membered chelate rings differs significantly depending on donor type. • N-C-C-X dihedrals display Gaussian distributions in the solid state. • DFT provides potential energy surfaces that afford force constants for the dihedral angles. • Widths of the Gaussian distributions correlate with quadratic force constants. • Cubic and quartic force constants are affected by environmental effects. In this study we take advantage of the large body of X-ray data reported for lanthanide complexes, as well as their similar coordination chemistry properties, to gain insight on the dynamic processes involving λ ↔ δ configurational changes leading to isomer interconversion. The analysis of X-ray data reveals that different donor groups are characterized by Gaussian distributions of the dihedral N–C–X–Y angles ϕ. In the case of ethylenediamine groups (X = C; Y = N) Gaussian distributions are very narrow, while acetates (X = C; Y = O) provide very broad distributions. The analysis of the potential energy surfaces (PESs) using DFT reveals that ethylenediamine groups are characterised by well-defined deep energy minima, while those of acetate groups are rather swallow. Other donor groups like acetamide, pyridine or phosphinate show intermediate Gaussian distributions with respect to ethylenediamine and acetates. The PESs were fitted to a potential incorporating quadratic, cubic and quartic terms. The quadratic force constants k 11 obtained for the different donor types follow the trend of the full width at half maxima (FWHM) of Gaussian distributions obtained from X-ray data. The k 11 values are very similar for a given donor group, while the anharmonic cubic ( k 111 ) and quartic ( k 1111 ) force constants vary significantly depending on the environment of the donor group. Overall, this work demonstrates that the analysis of X-ray crystallographic data in lanthanide complexes can provide very useful information on their coordination chemistry preferences and dynamic processes.