Bridging of Thorium by Hydrogen Atoms of Methyltrihydroborate Groups. Crystal Structures of Bis[tetrakis(methyltrihydroborato)thorium(IV)] Etherate and Bis[tetrakis(methyltrihydroborato)thorium(IV) tetrahydrofuranate]

Dimeric complexes of Th(CH3BH3)4 with diethyl ether and tetrahydrofuran have been synthesized and the molecular structures determined by X-ray diffraction. [Th(BH3CH3)4]2O(C2H5)2 is monoclinic, P21/c, a = 20.163 (5) Å, b = 10.353 (3) Å, c = 14.583 (3) Å,β = 104.47 (3)°, Z = 4, dx = 1.73 g cm-3; R = 0.024 (F2 > 2σ). [Th(BH3CH3)4.OC4H8]2 is monoclinic, a = 12.506 (4) Å,b = 11.533 (4) Å, c = 11.662 (4) Å, β = 99.06 (2)°, Z = 4, dx = 1.68 g cm-3; R - 0.019 (F2 > 2σ). The thorium atoms are bridged by two BH3CH3 ligands through one of the hydrogen atoms of each BH3 group; the Th-Th distances are 4.445 (2) and 4.917 (2) Å for the ether and tetrahydrofuran complexes, respectively. The Th-B distances range from 2.48 to 2.63 Å for the terminal BH3CH3 groups and from 2.91 to 3.11 Å for the bridging BH3CH3 groups. The coordination number for Th is 13 for one of the two Th atoms in the ethyl ether complex and 14 for all the others. NMR and IR spectra suggest that the dimeric structure is not maintained in solution.