Synthesis and Characterization of Solvated Lanthanide Tris(trimethylsilyl)siloxides.

In an effort to develop precursors for the production of lanthanide silicate (LnSiO x ) materials, the reactions of [Ln(NR 2 ) 3 ] (R = SiMe 3 ) with three equivalents of tris(trimethylsilyl)silanol (H-OSi(SiMe 3 ) 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 (NEt 3 )] ( Ln-NEt 3 = Pr-NEt 3 , Ho-NEt 3 ; NEt 3 = 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(NR 2 ) 3 ] with the final products identified as [Tm(SST) 3 (NEt 3 )] ( Tm-NEt 3 ) or [Tm(SST) 3 (NHPr 2 i )] (NHPr 2 i = di-iso-propylamine; Tm-NHPr 2 i ). 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 [(η 6 -tol)Tm(SST) 3 ] ( Tm-tol ). Multinuclear NMR ( 1 H and 29 Si) 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.