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(NR)] (R = SiMe) with three equivalents of tris(trimethylsilyl)silanol (H-OSi(SiMe)) or H-SST) in tetrahydrofuran (THF) were undertaken. The products were crystallographically characterized as [Ln(SST)(THF)] (where = , , , , , , , , , , , , , and ). In general, these compounds are similar to the previously reported [Gd(SST)(THF)] 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 (-4) bound [Ln(SST)(NEt)] ( = , ; NEt = 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)] with the final products identified as [Tm(SST)(NEt)] () or [Tm(SST)(NHPr)] (NHPr = di-iso-propylamine; ). The products isolated from reactions undertaken in pyridine (py) were identified as [Ln(SST)(py)] ( = , , and ). The 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-tol)Tm(SST)] (). Multinuclear NMR (H and Si) data support the retention of the solid-state structures of all of these compounds in solution. Photoluminescent measurements of , , , and were found to display emission and lifetime profiles in the visible range due to - transitions, consistent with trivalent lanthanide metal centers.