PREPARATION AND CRYSTAL-STRUCTURE OF URANIUM(IV) BOROHYDRIDE-BIS(TETRAHYDROFURAN), U(BH4)4.2OC4H8

Uranium(IV) borohydride reacts quantitatively with tetrahydrofuran to form U(BH4)4·2OC4H8, a pale green solid which has been characterized by single-crystal x-ray diffractometry. This air- and moisture-sensitive compound can be sublimed at 50-60°C and 10-5 mm. U(BH4)4·2OC4H8 is orthorhombic with a=7.134 (4) A, b=11.311 (6) Å, c=10.442 (7) Å, and Z=2, (dx=1.74 g cm-3). The space group is Pnc2 or Pncm. For 789 data, where I>2σ, the structure refined to R=0.027 and=0.032 in space group Pncm, with disorder in both the THF and boron positions. The complex is a monomer with a distorted-octahedral arrangement about the uranium of four borohydride groups and two THF molecules. The U-O distance is 2.47 (1) Å. The U-B distance of 2.56 (4) Å is characteristic of the triple-hydrogen-bridge bonds found in uranium(IV) borohydride. A configuration is assigned to the hydrogen atoms which places 12 of them at the corners of an hexagonal antiprism, capped by the two oxygen atoms of THF, giving the uranium atom 14 nearest neighbors. This compound is the only known uranium borohydride complex which is monomeric in the solid state. © 1978, American Chemical Society. All rights reserved.