Synthesis and Molecular Structures of Hydrotris(dimethylpyrazolyl)borate Complexes of the Lanthanides

The reaction of lanthanide triflates with 2 equiv of potassium hydrotris(dimethylpyrazolyl)borate (TpMe2) gives good yields of complexes of composition Ln(TpMe2)2OTf. For La (2), Ce (3), Pr (4), and Nd (5) the complexes are seven-coordinate in the solid state with the triflate group coordinated to the metal in unidentate fashion. Complex 5 crystallizes in the monoclinic space group P21/c with a = 17.629(3) A, b = 12.740(2) A, c = 18.163(3) A, β = 107.35(1)°, V = 3893(1) A3, Z = 4, and Rw = 0.0458. For the complexes of Y (1), Sm (6), Eu (7), Gd (8), Dy (9), Ho (10), and Yb (11), the smaller size of the metal ion leads to ejection of the triflate from the coordination sphere and the complexes are ionic in the solid state with a six-coordinate metal center. Complex 11 crystallizes in the monoclinic space group C2/m with a = 16.593(7) A, b = 13.671(5) A, c = 8.746(2) A, β = 91.66(3)°, V = 1983(1) A3, Z = 2, and Rw = 0.0416. In solution, however, complex 6 adopts a seven-coordinate molecular structure with the...