Probing Lewis acidity of Y(BH4)(3) via its reactions with MBH4 (M = Li, Na, K, NMe4)

作者：Jaron Tomasz^*; Grochala Wojciech

来源：Dalton Transactions, 2011, 40(48): 12808-12817.

DOI：10.1039/c1dt10955c

High-energy milling of Y(BH4)(3) (containing LiCl as a by-product, which has not been removed) with MBH4 (M = Li, Na, K, (CH3)(4)N) leads to the first two examples of quasi-ternary yttrium borohydrides: KY(BH4)(4) and (CH3)(4)NY(BH4)(4), while no chemical reaction is observed for LiBH4 and NaBH4. KY(BH4)(4) is isostructural to NaSc(BH4)(4) (Cmcm, a = 8.5157(4) angstrom, b = 12.4979(6) angstrom, c = 9.6368(5) angstrom, V = 1025.62(9) angstrom(3), Z = 4), while (CH3)(4)NY(BH4)(4) crystallises in primitive orthorhombic cell, similarly to KSc(BH4)(4) (Pnma, a = 15.0290(10) angstrom, b = 8.5164(6) angstrom, c = 12.0811(7) angstrom, V = 1546.29(17) angstrom(3), Z = 4). The thermal decomposition of hydrogen-rich KY(BH4)(4) (8.6 wt.% H) involves the formation of an unidentified intermediate at 200. degrees C and recovery of KBH4 at higher temperatures; at 410 degrees C, KCl and YH2 are observed. The thermal decomposition of (CH3)(4)NY(BH4)(4) occurs via two partly overlapping endothermic steps with concomitant emission of H-2 and organic compounds. Heating of a NaBH4/Y(BH4)(3) mixture above 165 degrees C results in a mixed-cation mixed-anion borohydride, NaY(BH4)(2)Cl-2, but not NaY(BH4)(4). The reduced reactivity of Y(BH4)(3) towards borohydride Lewis bases when compared to hypothetical scandium borohydride can be explained by the lower Lewis acidity of Y(BH4)(3) than Sc(BH4)(3).

• 出版日期2011