A theoretical study of divalent lanthanide (Sm and Yb) complexes with a triazacyclononane-functiionalized tetramethylcyclopentadienyl ligand

A density functional theory (DFT) study of the divalent lanthanide complexes [C5Me4SiMe2(iPr(2)-tacn)]LnI (Ln = Sm, Yb; tacn = 1,4-diisopropyl-1,4,7-triazacyclononane) is presented. A methodological study was done with various density functionals that employ large-core ECPs for the lanthanide atoms. The DFT results were compared with recent experimental X-ray structures for the compounds investigated here. The B3PW91 functional was found to give the best description of the complexes at an affordable level of computational effort. The geometry of the [C5Me4SiMe2(Pr-i(2)-tacn)]LnI complexes was found to be a distorted trigonal bipyramidal and the essential structural features are correctly reproduced from the DFT calculations. Further model studies show that the computations can be simplified by replacing the methyl groups (which do not interact with the lanthanide center directly) with hydrogen atoms to still provide reasonable predictions for the structure of the complex.