Metal tetrahydridoborates and tetrahydridoborato metalates. 23. Amine solvates of lithium and sodium tetrahydridoborate

A series of amine solvates of LiBH4 and NaBH4 have been prepared and charac terized by LR and NMR spectroscopy as well as by X-ray single-crystal struc ture determinations; LiBH4 crystallizes from pyridine as LiBH4. 3(py), 1, i n which the BH4 anion acts as a bidentate ligand. However, in the structure of LiBH4. 3py*, 2 (py* = p-benzylpyridine), a tridentate BH4 group is obse rved. In contrast, LiBH4. 2(coll), 3 (coll = 2,4,6-trimethylpyridine, colli dine), possesses only a bidentate tetrahydridoborate group, while a trident ate BH4 group is present in monomeric LiBH4. PMDTA, 4 (PMDTA = pentamethyld iethylenetriamine). In contrast, NaBH4. PMDTA, 6, is dimeric in the solid s tate: three of the four H atoms of each BH4 group coordinate to the Na atom s; two form a double bridge to two Na atoms while the third one is bonded o nly to one Na center. LiBH4. TMTA, 5 (TMTA = trimethylhexahydrotriazine), i s also dimeric; however, only two of the nitrogen atoms of the TMTA ligand coordinate to Li. The BH4 groups bridge the two Li centers each with one H atom coordinating to two Li atoms, and two bind to a single Li atom. A tota lly different situation exists for NaBH4. TMTCN, 7 (TMTCN = trimethyltriaza cyclononane), which is tetrameric in the crystal. Only: one hydrogen atom o f the BH4 group functions as a hydride bridge and binds to three Na centers . The molecule contains a Na4B4 heterocubane core. Thus, the different mode s of the interaction of the BH4 groups with the alkali metal atoms are dete rmined by the number of donor atoms from the neutral amine ligand and the s ize of the cation. No definitive conclusion as to the structure of the amin e solvates can be derived from IR and/or B-11 NMR spectra for the solution state. The crystallographic data are as follows. 1: a 10.9939(5) Angstrom, b = 9.9171(4) Angstrom, c = 14.8260(8) Angstrom, beta = 94.721(3)degrees, V = 1611.0(1) Angstrom(3), monoclinic, space group P2(1)/n, Z = 4, R-1 = 0.0 823. 2: a 10.121(1) Angstrom, b = 12.417(2) Angstrom, c = 13.462(3) Angstro m, alpha = 83.189(2)degrees, beta = 86.068(3)degrees gamma = 69.166(4)degre es, V = 1369.3(5) Angstrom(3), triclinic, space group P (1) over bar, Z = 2 , R-1 = 0.0689. 3: a = 28.527(3) Angstrom, b = 10.858(1) Angstrom, c = 11.3 19(1) Angstrom, V = 3505.7(6) Angstrom(3), orthorhombic, space group Fdd2, Z = 8, R-1 = 0.0502. 4: a = 7.591(3) Angstrom, b = 15.325(6) Angstrom, c = 8.719(4) Angstrom, beta = 99.80(2)degrees, V = 999.5(7) Angstrom(3), monocl inic, space group P2(1)/c, Z = 4, R-1 = 0.0416. 5: a 14.68(1) Angstrom, b = 11.830(7) Angstrom, c = 16.960(8) Angstrom, V= 2946(3) Angstrom, orthorhom bic, space group P2(1)2(1)2(1), Z = 8, R-1 = 0.0855. 6: a = 9.993(2) Angstr om, b = 10.008(3) Angstrom, c = 14.472(4) Angstrom, beta = 93.55(2)degrees, V = 1444.6(7) Angstrom(3), monoclinic, space group P2(1)/n, Z = 4, R-1 = 0 .0455. 7: cubic, a = b = c = 13.859(5) Angstrom, V = 2662(2) Angstrom(3), c ubic, space group I(4) over bar 3 m, Z = 8, R-1 = 0.0871.