Chemistry of C-Trimethylsilyl-Substituted Heterocarboranes. 30. Synthetic and Structural Studies on Oxide Ion Encapsulating Tetralanthanide Tetrahedra Surrounded by “Carbons Apart” C₂B₄-Carborane Ligands (Ln(III) = La, Nd, Gd, Tb, Ho, Lu)

The reactions of closo-exo-5,6-Na(THF)₂-1-Na(THF)₂-2,4-(SiMe₃)₂-2,4-C₂B₄H₄ (1) with anhydrous LnCl₃ (Ln = La, Nd, Gd, Tb, Ho, Lu) and freshly distilled H₂O in molar ratios of 5:4:1 gave crystalline solids, identified as the new oxolanthanacarboranes {[η⁵-1-Ln(THF)_n-2,4-(SiMe₃)₂-2,4-C₂B₄H₄]₄(μ-Cl)₂(μ₄-O)}·yTHF (Ln = La (2), n = 0, y = 1; Ln = Nd (3), n = 1, y = 0; Ln = Gd (4), n = 0, y = 1; Ln = Tb (5), n = 1, y = 0; Ln = Ho (6), n = 0, y = 1; Ln = Lu (7), n = 1, y = 0), in 73−86% yields. All new compounds were characterized by IR spectroscopy and elemental analyses. While the diamagnetic compounds 2 and 7 were also studied by ¹H, ¹³C, and ¹¹B NMR spectroscopy, the lanthanacarboranes 3 and 5−7 were further characterized by single-crystal X-ray diffraction analyses. The species 3, 5, and 7 were found to be isostructural, all containing oxide ion encapsulating tetralanthanide cores, Ln(μ₄-O), that are stabilized by coordinating two carborane ligands:  one in an η⁵ fashion via the C₂B₃-bonding face and the other via two Ln−H−B bridges to a neighboring cage. Complexes 3 and 5−7 crystallized in the monoclinic space group C2/c with a = 23.748(5), 23.577(5), 28.403(5), and 23.544(5) Å, b = 18.632(5), 18.513(5), 12.835(2), and 18.440(5) Å, c = 22.798(5), 22.602(5), 27.879(5), and 22.480(5) Å, β = 104.338(5), 104.092(5), 117.820(3), and 104.153(5)°, and V = 9774(64), 9568(4), 8989(13), and 9464(4) ų, respectively (Z = 4). The final refinements of 3 and 5−7 converged at R1 = 0.0795, 0.0703, 0.0367, and 0.0904; wR2 =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 6 was found to be 10.3 μ_B per lanthanide metal.