METALLACARBORANE COMPLEXES THAT INCORPORATE THE LANTHANIDES - SYNTHESIS, MOLECULAR-STRUCTURE, AND SPECTROSCOPIC CHARACTERIZATION OF DICARBOLLIDE COMPLEXES OF SAMARIUM AND YTTERBIUM

The interaction of Na2[nido-7,8-C2B9H11] (1) with LnI2 (Ln = Sm, Yb) in THF affords a complex with the composition Ln(C2B9H11)(THF)4 (Ln = Sm (2), Yb (3)). Both these complexes have been fully characterized by spectroscopic techniques, and the molecular structure of the DMF derivative of 3 has been established by a single-crystal X-ray diffraction study. The DMF derivative, Yb(C2B9H11)(DMF)4 (3b), crystallizes in the orthorhombic space group Pbca with a = 10.208 (1) angstrom, b = 17.005 (3) angstrom, c = 31.627 (5) angstrom, V = 5479 angstrom 3, and Z = 8. Data were collected on a modified Picker FACS-1 diffractometer at 25-degrees-C using Mo K-alpha radiation, to a maximum 2-theta = 50-degrees, giving 4841 unique reflections, and the structure was solved by statistical methods. The final discrepancy index was R = 0.082, R(w) = 0.084 for 1424 independent reflections with I > 2-sigma(I). The dicarbollide ligand is eta-5-bound to the Yb ion, and four DMF molecules are coordinated to Yb through the oxygen atoms. Complex 2 is fluxional in solution. The fluxionality of complex 2 in solution has been monitored by variable-temperature B-11 NMR spectroscopy, and a dynamic process involving the Sm2+ ion and the dicarbollide ligand has been proposed. The reaction of closo-1,1,1,1-(THF)4-1,2,3-LnC2B9H11 (Ln = Sm (2), Yb (3)) with [PPN]+[closo-3,1,2-TlC2B9H11]- in THF produces [3,3-(THF)2-commo-3,3'-Ln(3,1,2-LnC2B9H11)2]-[PPN]+ (Ln = Sm (4), Yb (5)), which has been characterized spectroscopically. The molecular structure of 4 has been established by an X-ray diffraction study. The complex 4 crystallizes in the triclinic space group P1BAR with a = 8.9374 (3) angstrom, b = 17.8703 (6) angstrom, c = 18.4989 (7) angstrom, alpha = 107.5402 (9)-degrees, beta = 91.085 (1)-degrees, gamma = 90.705 (1)-degrees, V = 2816 angstrom 3, and Z = 2. Data were collected at 25-degrees-C on a diffractometer equipped with a small Huber circle, using Mo K-alpha radiation, to a maximum of 2-theta = 45-degrees, giving 7358 unique reflections, and the structure was solved by a combination of conventional Patterson, Fourier, and full-matrix least-squares techniques. The final discrepancy index was R = 0.053, R(w) = 0.065 for 5324 independent reflections with I > 3-sigma(I). Both the dicarbollide ligands are eta-5-bound to the Sm ion in a nonparallel or bent fashion, and the coordination sphere about the Sm is completed by two THF molecules. The coordination geometry of 4 can be best described as a distorted tetrahedron. This is the first structurally authenticated example of a bis(dicarbollide)lanthanide complex. The structure of 4 is compared with related bis(cyclopentadienyl)lanthanides.