Synthesis and Characterization of Solvated Lanthanide Tris(trimethylsilyl)siloxides

In an effort to develop precursors for the production of lanthanide silicate (LnSiO) materials, the reactions of [Ln(NR₂)₃] (R = SiMe₃) with three equivalents of tris(trimethylsilyl)silanol (H-OSi(SiMe₃)₃) or H-SST) in tetrahydrofuran (THF) were undertaken. The products were crystallographically characterized as [Ln(SST)₃(THF)₂] (where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). In general, these compounds are similar to the previously reported [Gd(SST)₃(THF)₂] complex, where each metal center of the monomeric species is found to adopt a trigonal bipyramidal (TBP; τ = av 0.95) geometry; however, the crystallographic structure solutions for these crystals invoke a much larger unit cell that reveals the complex disorder of the axial THF ligands. Using incompletely washed H-SST, the tetrahedrally (T-4) bound [Ln(SST)₃(NEt₃)] (Ln-NEt = Pr-NEt, Ho-NEt; NEt₃ = triethylamine) compounds were isolated from the same reaction run in toluene. Rational syntheses of amine derivatives were realized by performing the same reaction with pure H-SST in toluene containing the appropriate amine and [Ln(NR₂)₃] with the final products identified as [Tm(SST)₃(NEt₃)] (Tm-NEt) or [Tm(SST)₃(NHPr₂)] (NHPr₂ = di-iso-propylamine; Tm-NHPr). The products isolated from reactions undertaken in pyridine (py) were identified as [Ln(SST)₃(py)₂] (Ln-py = Ce-py, Eu-py, and Tm-py). The Ln-py structures exhibit the larger unit cell noted for the THF derivatives with each Ln adopting a TBP (τ = av 0.98) metal center possessing equatorial SST and axial py ligands. The same reaction run in toluene led to the isolation of [(η⁶-tol)Tm(SST)₃] (Tm-tol). Multinuclear NMR (¹H and ²⁹Si) data support the retention of the solid-state structures of all of these compounds in solution. Photoluminescent measurements of Tb, Sm, Dy, and Eu were found to display emission and lifetime profiles in the visible range due to f-f transitions, consistent with trivalent lanthanide metal centers.