Chemistry of C-Trimethylsilyl-Substituted Heterocarboranes. 30. Synthetic and Structural Studies on Oxide Ion Encapsulating Tetralanthanide Tetrahedra Surrounded by “Carbons Apart” C<sub>2</sub>B<sub>4</sub>-Carborane Ligands (Ln(III) = La, Nd, Gd, Tb, Ho, Lu)

The reactions of <i>closo-exo</i>-5,6-Na(THF)<sub>2</sub>-1-Na(THF)<sub>2</sub>-2,4-(SiMe<sub>3</sub>)<sub>2</sub>-2,4-C<sub>2</sub>B<sub>4</sub>H<sub>4</sub> (<b>1</b>) with anhydrous LnCl<sub>3</sub> (Ln = La, Nd, Gd, Tb, Ho, Lu) and freshly distilled H<sub>2</sub>O in molar ratios of 5:4:1 gave crystalline solids, identified as the new oxolanthanacarboranes {[η<sup>5</sup>-1-Ln(THF)<i><sub>n</sub></i>-2,4-(SiMe<sub>3</sub>)<sub>2</sub>-2,4-C<sub>2</sub>B<sub>4</sub>H<sub>4</sub>]<sub>4</sub>(μ-Cl)<sub>2</sub>(μ<sub>4</sub>-O)}·<i>y</i>THF (Ln = La (<b>2</b>), <i>n</i> = 0, <i>y</i> = 1; Ln = Nd (<b>3</b>), <i>n</i> = 1, <i>y</i> = 0; Ln = Gd (<b>4</b>), <i>n</i> = 0, <i>y</i> = 1; Ln = Tb (<b>5</b>), <i>n</i> = 1, <i>y</i> = 0; Ln = Ho (<b>6</b>), <i>n</i> = 0, <i>y</i> = 1; Ln = Lu (<b>7</b>), <i>n</i> = 1, <i>y</i> = 0), in 73−86% yields. All new compounds were characterized by IR spectroscopy and elemental analyses. While the diamagnetic compounds <b>2</b> and <b>7</b> were also studied by <sup>1</sup>H, <sup>13</sup>C, and <sup>11</sup>B NMR spectroscopy, the lanthanacarboranes <b>3</b> and <b>5</b>−<b>7</b> were further characterized by single-crystal X-ray diffraction analyses. The species <b>3</b>, <b>5</b>, and <b>7</b> were found to be isostructural, all containing oxide ion encapsulating tetralanthanide cores, Ln(μ<sub>4</sub>-O), that are stabilized by coordinating two carborane ligands:  one in an η<sup>5</sup> fashion via the C<sub>2</sub>B<sub>3</sub>-bonding face and the other via two Ln−H−B bridges to a neighboring cage. Complexes <b>3</b> and <b>5</b>−<b>7 </b>crystallized in the monoclinic space group <i>C</i>2/<i>c</i> with <i>a = </i>23.748(5), 23.577(5), 28.403(5), and 23.544(5) Å, <i>b = </i>18.632(5), 18.513(5), 12.835(2), and 18.440(5) Å, <i>c </i><i>= </i>22.798(5), 22.602(5), 27.879(5), and 22.480(5) Å, β<i> = </i>104.338(5), 104.092(5), 117.820(3), and 104.153(5)°, and <i>V = </i>9774(64), 9568(4), 8989(13), and 9464(4) Å<sup>3</sup>, respectively (<i>Z = </i>4). The final refinements of <b>3</b> and <b>5</b>−<b>7 </b>converged at R1<i> = </i>0.0795, 0.0703, 0.0367, and 0.0904; <i>w</i>R2<i> =</i>0.1793, 0.1686, 0.794, and 0.1844, and GOF = 1.401, 1.305, 1.446, and 1.498, respectively. The room-temperature magnetic susceptibility of the holmium compound <b>6 </b>was found to be 10.3 μ<sub>B</sub> per lanthanide metal.