The Lanthanide Contraction Is a Variable

Abstract

Upon examination of the bond distances of the recently reported series of [Ln(SST) 3 (THF) 2 ] [Ln = lanthanides, SST = tris(trimethylsilyl)siloxide (OSi(SiMe 3 ) 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 Lncontraction 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 Lncontraction, 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 Lncontraction 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.

Reduction chemistry yields stable and soluble divalent lanthanide tris(pyrazolyl)borate complexes

“…The Ln–N( κ 3 -Tp), 6 a , d , f ,10 Eu–( η 5 -Tp), 24 Ln-O(THF), 1 a , b and Ln–O(OPPh 3 ) 21 c ,23 bond distances in 1-Ln , 1-Ln(THF) x and 1-Ln(OPPh 3 ) x (Ln = Eu, x = 2; Yb, x = 1) fall within the expected ranges. All data are consistent with the lanthanide contraction 25 and the increase in ionic radius upon reduction from Ln( iii ) to Ln( ii ). 13 In the absence of coordinating solvents, complex 1-Eu (a) is an unusual example of a dimeric structure, whereas complex 1-Yb (b) is monomeric as expected.…”

Synthesis and Characterization of Solvated Lanthanide Tris(trimethylsilyl)siloxides

“…58−60 A detailed exploration of the literature crystallographic data and successful modeling of this previously unreported behavior is presented elsewhere. 58 (b) Amine adducts. In one reaction series, a new batch of the H-SST reagent was reacted with [Ln(N(TMS) 2 ) 3 ] (Ln = Pr and Ho) in toluene, but instead of isolation of a solvent-free derivative, the mono-NEt 3 derivatives were isolated as [Ln-(SST) 3 (NEt 3 )] (Ln-NEt 3 = Pr-NEt 3 , Ho-NEt 3 ).…”

“…Based on the “hard and soft (Lewis) acid and base” (HSAB) doctrine, − the Ln 3+ ions will increase in hardness as the series is crossed, and it is anticipated that the softer neutral THF ligand interaction with the Ln cations would decrease, resulting in longer bonds; instead, the distance becomes shorter. One explanation of this unusual behavior may be due to the difference in the binding energy curves for the SST ligand versus that for THF, wherein a small covalency of the Ln–O­(SST) bond compared with the ion–dipole attraction of the Ln–O­(THF) bond dictates this behavior. − A detailed exploration of the literature crystallographic data and successful modeling of this previously unreported behavior is presented elsewhere …”

Syntheses and fluorescence properties of lanthanide isostructural complexes derived from aspartic acid

“…1c). On the other hand, for all complexes, the corresponding shortest Ln–O bond distance becomes shorter with the increase in the atomic number of lanthanides, which is also a direct result of the contraction of lanthanides 30 (Fig. S2 and S3†).…”