Solvates of Lithium Tetrahydridoborates with Various Amines: From Molecular to Extended Structures of Lithium Tetrahydridoborate

Abstract

Several solvates of LiBH4 with amines have been prepared and characterized by X-ray structure determinations. LiBH4·3H2NPh (1) is monomeric with a triply bridging BH4 group. LiBH4·2en (3) is shown to be an ionic compound containing chains of cationic [Li(en)2)]+ units. In contrast, the BH4 group of LiBH4·triene (4) forms triple hydride bridges to the Li centers of a Li(triene) chain, making the Li atoms hexacoordinated by 3 × N and 3 × H atoms. Reaction of LiBH4 with tert-butylamine generates the compound 3LiBH4·4H2NtBu (2). The structure of 2 consists of an infinite chain of LiBH4 units having three different kinds of Li centers, two of which have an environment of 2 × N and 4 × H atoms, whereas the third type is surrounded by five hydrogen atoms. Pyrrolidine reacts with LiBH4 to give LiBH4·HNC4H8 (5), the structure of which in the solid state shows an infinite chain with heptacoordinated Li centers (N and 6 × H). In contrast, dibenzylamine gives the compound LiBH4·2HN(CH2Ph)2 (6), which is dimeric with hexacoordinated Li centers (2 × N and 4 × H) in the crystal, and a similar structure was found for LiBH4·(iPrNCH2)3 (7) but with heptacoordinated Li ions (3 × N and 4 × H). Addition of (MeNCH2)3 to LiBH4 in toluene leads to 4LiBH4·2(MeNCH2)3 (8), in which the two amine ligands bind to two Li ions, Li1 being hexacoordinated by (4 + 2) N atoms, Li2 by 2 × N atoms and 4 × H atoms from two different BH4 groups. Li2 is part of a layer structure composed of Li3(BH4)4− units. In contrast, a chain structure is evident in 3LiBH4·2(PhCH2NCH2)3 (9), as shown by the presence of separate Li[(PhCH2NCH2)3]2 cations and Li2(BH4)3 anionic building blocks.