The Lanthanide Contraction Is a Variable

Upon examination of the bond distances of the recently reported series of [Ln­(SST)3(THF)2] [Ln = lanthanides, SST = tris­(trimethylsilyl)­siloxide (OSi­(SiMe3)3), and THF = tetrahydrofuran] compounds, it was found that over the Ln-series (La through Lu), the Ln–O­(THF) bond changed by 0.257 Å, wher...

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Published in:Inorganic chemistry 2022-04, Vol.61 (16), p.6120-6127
Main Authors: Cramer, Roger E, Rimsza, Jessica M, Boyle, Timothy J
Format: Article
Language:English
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Summary:Upon examination of the bond distances of the recently reported series of [Ln­(SST)3(THF)2] [Ln = lanthanides, SST = tris­(trimethylsilyl)­siloxide (OSi­(SiMe3)3), and THF = tetrahydrofuran] compounds, it was found that over the Ln-series (La through Lu), the Ln–O­(THF) bond changed by 0.257 Å, whereas the Ln–O­(SST) bond varied by 0.164 Å. Examination of all similarly ligated Ln–O­(THF) (Ln = La vs Lu) structures available in the Cambridge Structural Database (CSD) revealed that this previously unreported, increased Ln-contraction is pervasive. Further evaluations showed that this enhanced Ln-contraction also occurs for pyridine (py) in the [Ln­(SST)3(py)2] family as well as the average Ln–N­(py) (La vs Lu) structure distances recovered from the CSD. Additional ligands, such as halides (Cl and I) were found to display this enhanced Ln-contraction, while other species (i.e., cyclopentadienide, alkoxide, SST, and dimethyl sulfoxide) yielded a “normal” Ln-contraction (La–L vs Lu–L). Gas-phase electronic structure density functional theory calculations were carried out to evaluate the molecular orbital influence on the Ln-contraction between Ln–O­(SST) and Ln–O­(THF). The calculated [Ln­(SST)3(THF)2] structures were found to demonstrate the same capricious Ln-contraction. Based on these studies, one can say that the variability of the Ln-contraction noted in the [Ln­(SST)3(THF)2] experimental data is due to the different bonding types, ion–ion for the Ln–SST bond versus ion–dipole for the Ln–THF bond.
ISSN:0020-1669
1520-510X
DOI:10.1021/acs.inorgchem.2c00261