G. Del Piero

The chemistry and the stereochemistry of poly(n-alkyliminoalanes) : X. The crystal and molecular structure of the tetramers HAlN-i-Pr)4 and (MeAlN-i-Pr)4

The crystal and molecular structures of the tetramer(HAlN-i-Pr) 4 (I) and its methylated derivative (MeAlN-i-Pr) 4 (II) have been determined from single-crystal, three-dimensional X-ray diffraction data obtained on a diffractometer. A block matrix least-squares refinement converged to a conventional R factor of 8.4% for I and 7.0% for II. Both molecular structures are built up of a cubic cage (AlN) 4 . Main average bond lengths are: AlN 1.913(2) in I and 1.923(1) in II; NC 1.509(6) in I and 1.485(9) in II; AlH 1.50(5) and AlC 1.946(11) A. Crystal data: I, orthorhombic, space group Pccn , cell constants a 21.965(7), b 20.006(9), c 19.833(12) A, Z = 16; II, triclinic, space group P1, cell constants a 16.924(11), b 8.864(5), c 9.471(7) A, α 109.5(1), β 110.9(1), γ 90.2(1)°, Z = 2.

The chemistry and the stereochemistry of poly (N-alkyliminoalanes) : XI. The crystal and molecular structure of the hexamer (HAlN-n-Pr)6 and the octamer (Haln-n-Pr)8

Abstract The crystal and molecular structures of the hexamer, (HAlN-n-Pr)6 (I) and octamer (HAlN-n-Pr)8 (II) have been determined by the Patterson procedure and by direct methods, respectively, using tridimensional X-ray diffraction data collected by counter methods. The block-matrix least-squares refinement led to a final R value of 5.7% for I and 5.8% for II. The molecular framework of I, (AlN)6, is shaped as a hexagonal prism, while that of II, (AlN)8, may be derived from a combination of such a hexameric cage with a square ring of a dimer. The main average bond lengths A are: AlN, 1.913(11) for I and 1.916(2) for II; NC, 1.508(5) and 1.516(4); AlH, 1.53(2) and 1.50(2), respectively. Crystal data: I, trigonal space group P3; a 16.801(2), c 9.647(2) A; Z - 3; II, triclinic space group P1, a 21.99(1), b 10.58(1), c 9.75(1)A, α 97.7(5), β 91.9(5), γ 100.3(5)°; Z = 2.

The chemistry and the stereochemistry of poly(N-alkyliminoalanes) : XV. The crystal and molecular structure of the compounds [((THF)Mg)(HA1N-t-Bu)3] and [((THF)3Ca)(HA1N-t-Bu)3] · THF

Abstract The compounds [((THF)Mg)(HA1N-t-Bu)3] (I) and [((THF)3Ca)(HA1N-t-Bu)3] · THF (II) have been structurally characterized from single-crystal diffraction data. The molecular structures are based on an (A1N)4 “cubane” type framework in which an aluminum is replaced by an alkaline earth metal. According to the size and the coordination of the “foreign” atom (four for Mg, six for Ca) the cubic geometry of the cage is increasingly distorted. Coordination is completed by one molecule of THF to the Mg atom and three molecules to the Ca atom; in II a molecule of THF crystallizes with a cage molecule. Mean MgN and CaN bond distances are 2.090(4) and 2.490(2) A. Crystal data: I, orthorombic, space group Pbca, a 17.107(2), b 17.305(4) and c 20.220(5) A, Z = 8, calculated density 1.031 g/cm3; II, orthorombic, space group Pbca, a 20.48(1), b 20.38(1), c 20.51(1), Z = 8, calculated density 1.081 g/cm3.

The chemistry and the sterechemistry of Poly(N-Alkyliminoalanes ☆: XIII. The crystal and molecular structure of the hexamers (ClAlN-i-Pr)6 and (Me0.83H0.17AlN-i-Pr)6MeAlN-i-Pr)6

Abstract The crystall and molecular structures of (ClAlN-i-Pr) 6 (I), and of (Me 0.83 H 0.17 AlN-i-Pr) 6 (MeAlN-i-Pr) 6 have been determined by single crystal three-dimensional X-ray analysis. Block-matrix least-squares refinements led to conventional R factor of 0.039 for I and 0.037 for II. The compounds are isostructural, as the cage molecules consist of a prismatic hexagonal framework, (AlN) 6 , similar to that observed for the parent hydrogenated analogue (HAlN-i-Pr) 6 .Some differences in bond distances and angles are discussed, in connection with the different Al-bonded substituents. Crystal data: I, trigonal space group R 3 ; a = 17.083(2), c = 9.652(1); Z = 3; D c 1.46 g cm −3 ; II, trigonal space group R 3 , a = 17.378(3), c = 9.706(3) »; Z = 3; D c 1.15 g cm −3 .

The chemistry and the stereochemistry of poly(n-alkyliminoalanes)

Abstract The crystal and molecular structure of the adduct (HAlN-i-Pr)6AlH3 has been determined from single-crystal and three dimensional X-ray diffraction data collected by counter methods. The cage-type molecular structure consists of two six-membered rings, (AlN)3, joined together by four adjacent transverse AlN bonds; the loss of two of these bonds allows the complexation of one alane molecule, with five-coordination of the aluminum (trigonal bipyramidal geometry), through two AlN bonds and two AlHAl bridge bonds. The AlN bond lengths range from 1.873 to 1.959 A; the average AlH bond length is 1.50(1) A for the four-coordinated aluminum atoms; the average distance of the two apical hydrogens from the five-coordinated aluminum atom is 1.92(5) A. Colourless prismatic crystals of the compound have the following crystal data: triclinic space group P 1 ; a = 17.13(2); b = 10.78(2); c = 10.20(2) A; α = 124.3(4), β = 92.0(4), γ = 92.1(5); Z = 2; calculated density 1.157 g/cm3. The structure has been refined by block-matrix, least-squares methods using 4358 independent reflections to a standard unweighted R factor of 4.9%.

The chemistry and the stereochemistry of poly(N-alkyliminoalanes) ☆: IV. The preparation and crystal structure of [H(HAlN-i-Pr)5AlH2]·LiH/Et2O

Abstract The compound [H(HAlN-i-Pr) 5 AlH 2 ]·LiH/Et 2 O has been prepared, and its crystal and molecular structure has been determined from single-crystal, three-dimensional X-ray diffractometer data. The molecular structure is a pseudohexameric cage, consisting of a five-membered fragment, AlNAlNAl, crosslinked to a six-membered cyclohexane type ring, (AlN) 3 . The hydrogen atom of LiH is indistinguishable from the other hydridic hydrogens, so that the N -isopropyliminoalane part of the molecule may be considered as an anion with a formal charge of −1. The lithium cation is linked to two adjacent molecules through three LiHAl bridges, the fourth position of its tetrahedral coordination being occupied by the oxygen of diethyl ether. Large distortions of the tetrahedral valence angles occur, both on the aluminum atoms and on the nitrogen atoms, together with a noticeable spread of the AlN bond lengths, averaging 1.919(4) A. Colourless crystals of the compound have the following crystal data: orthorhombic space group Pna 2 1 ; a = 19.76(2), b = 10.38(1), c = 16.60(2) A; Z = 4; calculated density 1.048 g/cm 3 . The structure has been refined by block-matrix least-squares methods, using 2487 independent reflections, to an usual R factor of 5.9%.

The direct synthesis of magnesium amides and the crystal structure of an unusual magnesium tert-butylamide

Abstract The magnesium amides Mg(NHi-C3H7)2; Mg(N(C2H5)2)2 and Mg(NC5H10)2 have been prepared by direct synthesis from magnesium and i-C3H7NH2, (C2H5)2NH or C5H10NH, respectively, at high temperature and under a pressure of hydrogen. When an excess of Mg was used MgH2 was isolated, suggesting that magnesium hydride is an intermediate in this reaction. t-C4H9NH2 gave two crystalline products, NMg6(NHt-C4H9)9 (I) and an insoluble material, probably (MgNR)x. The structure of I was determined by X-ray crystallography.

The chemistry and the stereochemistry of poly(N-alkyliminoalanes) ☆: V. The preparation and crystal structure of the pentamer [(HalN-i-Pr)2(H2AlNH-i-Pr)3]

Abstract The compound [(HAlN-i-Pr) 2 (H 2 AlNH-i-Pr) 3 ] has been prepared and the crystal and molecular structure determined by an X-ray analysis, carried out with three-dimensional data collected on a diffractometer. The molecule is made up of a cyclohexane-type ring, [(HAlN-i-Pr) 2 (H 2 AlNH-i-Pr)], in skewboat conformation, on each side of which is bonded an -H 2 AlNH-i-Pr- bridging unit between a nitrogen atom and an aluminum atom of the ring. The molecule lies on a binary axis of the crystal, but this symmetry is fulfilled only by a statistical orientation of the asymmetric molecular units (the statistical model is not however completely defined). The AlN bond lengths range from 1.901 to 1.985 A; the average NC bond length is 1.527(9) A. Main crystal data are: monoclinic space group C 2/ c ; a = 10.15(2), b = 21.64(3), c = 12.84(2) A, β = 111.9(5)°; Z = 4; calculated density 1.095 g/cm 3 . The structure was solved by direct methods and block-matrix least-squares converged to an R value of 5.6%.

The preparation and crystal structure of bis(μ-N,N′-diethylethylenediamido)bis(dihydridoaluminum)hydridoaluminum, HAl[(EtN(CH2)2NEt)AlH2]2, and its chlorinated derivative, (H0.85Cl0.15)Al[(EtN(CH2)2NEt)AlH(H0.7Cl0.3)]2

Abstract The compounds HAl[(EtN(CH 2 ) 2 NEt)AlH 2 ] 2 (I) and (H 0.85 Cl 0.15 )Al[(EtN(CH 2 ) 2 NEt)AlH(H 0.7 Cl 0.3 )] 2 (II) have been prepared and their crystal structures determined by X-ray analysis. Block-matrix least-squares refinement led to a final R values of 0.050 and 0.095 for I and II, respectively. The molecular structure of I is built up of two AlH 2 groups and one AlH group, connected to each other through two diethylethylenediamine bridging groups. In II, a similar molecular conformation contains hydrogenated and chlorinated molecules randomly co-crystallized. Two different types of AlH bond distances (1.66(4)–1.70(4) and 1.48(6)–1.51(6) A) are observed for AlH 2 groups in I; the longer bonds are probably higher in ionic character. The AlN bond distances range from 1.918(3) to 2.068(3) A in I and from 1.914(5) to 2.078(5) A in II. Crystal data. I: triclinic, space group P 1 , a 7.433(2), b 7.436(2), c 18.810(7) A, α 95.8(1), β 109.9(1), γ 82.6(1)°, Z = 2; II: triclinic, space group P 1 , a 7.645(3), b 7.574(3), c 19.069(9) A, α 95.6(1), β 111.3(1), γ 81.1(1)°, Z = 2.

Calcium alkoxyalanates : I. Synthesis and physicochemical characterization

Soluble calcium alkoxyalanates, Ca[AlH4−n(OR)n]2, in which n ranges from 1 to 3, generally complexed with tetrahydrofuran, have been obtained by partial alcoholysis of calcium alanate with various branched aliphatic alcohols and with 2-methoxyethanol in toluene. With a few exceptions X-ray powder diffraction patterns and infrared AlH absorptions indicate that the calcium alkoxyalanates are individual molecular species.