Effect of the nature of lanthanide on intramolecular C-F→Ln dative interactions in hexafluoroisopropoxide complexes

Electronic structures of a series oflanthanide complexes with hexafluoroisopropoxide ligands [Ln(OCH(CF))(μ-OCH(CF))(DME)] (Ln = Ce, Sm, Tm, Yb; DME is dimethoxyethane) were studied by quantum chemical calculations at the density functional theory (DFT) level. Intramolecular C-F→Ln interactions are present in all these compounds. A decrease in the ionic radius of lanthanide in the series from Ce to Yb leads to an increase in the degree of filling of the coordination sphere from 92.9(2) to 97.3(2)%, resulting in a systematic decrease in the delocalization index between lanthanide and fluorine atoms. An experimental-theoretical study of the complexes using a molecular invariom provided an estimate of the energy of Ln⋯F interactions, which also decreases for the complexes of the late lanthanides (Tm, Yb) compared with the complexes of the early lanthanides (Ce, Sm). Geometry optimization of the isolated molecule leads to an increase in the number of non-covalent interactions involving fluorine atoms (F⋯F, F⋯H, and F⋯O) and in their energy compared to the molecular invariom. The topological characteristics of electron density in the coordination sphere of lanthanide atoms determined by quantum chemical calculations are in good agreement with those estimated using the molecular invariom.