RESUMEN
The crystal structure of Th(BH4)4 is described. Two of the four BH4- ions are terminal and tridentate (κ3), whereas the other two bridge between neighboring ThIV centers in a κ2,κ2 (i.e., bis-bidentate) fashion. Thus, each thorium center is bound to six BH4- groups by 14 Th-H bonds. The six boron atoms describe a distorted octahedron in which the κ3-BH4- ions are mutually cis; the 14 ligating hydrogen atoms define a highly distorted bicapped hexagonal antiprism. The thorium centers are linked into a polymer consisting of interconnected helical chains wound about 4-fold screw axes. The structures of An(BH4)4 (An = Th, U) were also investigated by DFT. The geometries of [An(BH4)6]2-, [An3(BH4)16]4-, and [An5(BH4)26]6- fragments of the polymeric structures were optimized at the B3LYP and/or PBE levels. Most calculated geometries are 14-coordinate and agree with the experimental structures, but isolated [Th(BH4)6]2- units are predicted to feature 16-coordinate ThIV centers.
RESUMEN
The syntheses and molecular structures of new SmII and TmII N,N-dimethylaminodiboranate (DMADB) complexes are described. Treating SmI2(THF)2 with Na(H3BNMe2BH3) in THF results in the formation of Sm(H3BNMe2BH3)2(THF)3 (1), which can be readily converted to Sm(H3BNMe2BH3)2(DME)2 (DME = 1,2-dimethoxyethane) or Sm(H3BNMe2BH3)2(diglyme) by exchange with the corresponding ether. We also show that Sm(H3BNMe2BH3)2(THF)3 can be prepared by reduction of the SmIII compound Sm(H3BNMe2BH3)3(THF) with KC8 and that addition of 18-crown-6 to this reaction mixture results in the formation of the SmII compound Sm(H3BNMe2BH3)2(18-crown-6). In a similar fashion, two new TmII complexes have been synthesized: treatment of TmI2 in THF with Na(H3BNMe2BH3) results in the formation of Tm(H3BNMe2BH3)2(THF)2 and Tm(H3BNMe2BH3)2(THF)3, which form a cocrystal. IR data and elemental analyses are reported for all the new compounds, as are their crystal structures. 1H and 11B NMR data are provided where available.