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Acta Crystallogr Sect E Struct Rep Online. 2010 May 1; 66(Pt 5): m575.
Published online 2010 April 28. doi:  10.1107/S1600536810014200
PMCID: PMC2979026

Redetermination of di-μ-hydrido-hexa­hydridotetra­kis(tetra­hydro­furan)dialuminium(III)magnesium(II)

Abstract

The structure of the title compound, [Mg(AlH4)2(C4H8O)4], has been redetermined at 150 K. The MgII ion is hexa­coordinated to four tetra­hydro­furan (THF) ligands, and two AlH4 anions through bridging H atoms. The Al—H distances are more precise compared to those previously determined [Nöth et al. (1995 [triangle]). Chem. Ber. 128, 999–1006; Fichtner & Fuhr (2002 [triangle]). J. Alloys Compd, 345, 386–396]. The mol­ecule has twofold rotation symmetry.

Related literature

For the synthesis of Mg(AlH4)2·4THF, see: Ashby et al. (1970 [triangle]); Shen & Che (1991 [triangle]); Nöth et al. (1995 [triangle]). For the synthesis of AlH4MgBH4, see: Ashby & Goel (1977 [triangle]). For previous determinations of the crystal structure of Mg(AlH4)2·4THF, see: Noth et al. (1995 [triangle]); Fichtner & Fuhr (2002 [triangle]). For the thermal decomposition properties of Mg(AlH4)2·4THF, see: Dilts & Ashby (1972 [triangle]). For other alanate structures, see: Sklar & Post (1967 [triangle]); Lauher et al. (1979 [triangle]); Fichtner & Fuhr (2002 [triangle]); Fichtner et al. (2004 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-66-0m575-scheme1.jpg

Experimental

Crystal data

  • [Al2MgH8(C4H8O)4]
  • M r = 374.75
  • Orthorhombic, An external file that holds a picture, illustration, etc.
Object name is e-66-0m575-efi1.jpg
  • a = 10.161 (2) Å
  • b = 14.027 (3) Å
  • c = 16.429 (3) Å
  • V = 2341.6 (8) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.16 mm−1
  • T = 150 K
  • 0.38 × 0.31 × 0.19 mm

Data collection

  • Nonius Kappa CCD diffractometer
  • Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997 [triangle]) T min = 0.940, T max = 0.969
  • 5018 measured reflections
  • 2687 independent reflections
  • 1973 reflections with I > 2σ(I)
  • R int = 0.017

Refinement

  • R[F 2 > 2σ(F 2)] = 0.041
  • wR(F 2) = 0.119
  • S = 1.07
  • 2687 reflections
  • 122 parameters
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.30 e Å−3
  • Δρmin = −0.30 e Å−3

Data collection: COLLECT (Nonius, 1998 [triangle]); cell refinement: SCALEPACK (Otwinowski & Minor, 1997 [triangle]); data reduction: DENZO (Otwinowski & Minor 1997 [triangle]) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: SHELXTL (Sheldrick, 2008 [triangle]); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810014200/ci5044sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810014200/ci5044Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

This work was funded by the US Department of Energy, the Office of Energy Efficiency and Renewable Energy (EERE) under Contract No. DE-FC3605GO15062 as part of the DOE Metal Hydride Center of Excellence.

supplementary crystallographic information

Comment

Mg(AlH4)2.4THF, (I), is a starting material for the synthesis of Mg(AlH4)2 which is an interesting candidate for hydrogen storage applications because of its high theoretical hydrogen storage capacity. Ashby et al. (1970) reported the synthesis of (I) by the metathesis reaction between NaAlH4 and MgCl2. Noth et al. (1995) and recently Fichtner & Fuhr (2002) reported the crystal structure of (I), but neither of the groups obtained high quality single crystal X-ray diffraction data. In the present work good quality single crystals were obtained from reaction between NaAlH4 and ClMgBH4 where the product, AlH4MgBH4.THF disproportionated to form (I). The crystal structure was determined using single crystal X-ray diffraction and compared with the previously reported data.

In general, the present crystal structure determination confirms the previous results. As previously described by Noth et al. (1995) and Fichtner & Fuhr (2002), the structure of (I) consists of discrete octahedral building blocks where four THF molecules and two tetrahedral AlH4 units are connected to a Mg central atom. Fichtner & Fuhr (2002) reported only lattice parameters without coordinates of the atoms. Noth et al. (1995) reported the Al—H(t) and Al—H(b) bond lengths as 1.214 and 1.528 Å, respectively, which are shorter than expected. Moreover, the structure was only refined to a final R value of 0.065. We have redetermined this crystal structure at 150 K, with a final R value of 0.040 to obtain more precise data. In the present work, the Al—H(t) and Al—H(b) bond lengths were found to be 1.524 and 1.573 Å, respectively, which are close to the Al—H bond distance in other alanates. Al—H distances reported in other alanates with AlH4 tetrahedral are 1.547 Å (at 8 K) for LiAlH4 (Sklar & Post, 1967), 1.532 Å (at 296 K) for NaAlH4 (Lauher et al., 1979), 1.55 Å (at 200 K) for Mg(AlH4)2.Et2O (Fichtner & Fuhr, 2002) and 1.65 Å (at 230 K) for Ca(AlH4)2.4THF (Fichtner et al., 2004).

Experimental

All the manipulations were carried out in high vacuum lines and an Ar filled glove box to avoid the compounds reacting with oxygen and moisture. Solvents were dried by vacuum distillation from sodium benzophenone ketyl. Precursor ClMgBH4 was synthesized by ball milling MgCl2 and Mg(BH4)2 in 1:1 mole ratio in a high energy ball mill for 1 h. AlH4MgBH4 was prepared by the procedure reported by Ashby & Goel (1977). In a typical procedure, a clear solution of NaAlH4 in THF was added to a solution of ClMgBH4 in THF with rapid stirring for 60 min at room temperature. After completion of reaction, NaCl was filtered out from the solution and the solvent was removed from the filtrate under dynamic vacuum. The obtained AlH4MgBH4.THF powder was dissolved in benzene, filtered, concentrated, and aged for 2 days. AlH4MgBH4.THF slowly disproportionated to give colourless crystals of (I).

Refinement

H atoms bonded to aluminium atoms were located and refined isotropically. The range of refined Al–H distances is 1.50 (2)–1.573 (18) Å. The remaining H atoms were placed in calculated positions [C–H = 0.99 Å] and refined using a rigid model with Uiso(H) = 1.2Ueq(C).

Figures

Fig. 1.
The molecular structure of [Mg(AlH4)2(C4H8O)4], showing 50% probability displacement ellipsoids and the atomic numbering scheme. Atoms labelled with the suffix A are generated by the symmetry operation (-x, 1/2-y, z).

Crystal data

[Al2MgH8(C4H8O)4]F(000) = 824
Mr = 374.75Dx = 1.063 Mg m3
Orthorhombic, PcnbMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2b 2acCell parameters from 2687 reflections
a = 10.161 (2) Åθ = 2.4–27.5°
b = 14.027 (3) ŵ = 0.16 mm1
c = 16.429 (3) ÅT = 150 K
V = 2341.6 (8) Å3Cube, colourless
Z = 40.38 × 0.31 × 0.19 mm

Data collection

Nonius Kappa CCD diffractometer2687 independent reflections
Radiation source: fine-focus sealed tube1973 reflections with I > 2σ(I)
graphiteRint = 0.017
[var phi] and ω scansθmax = 27.5°, θmin = 2.4°
Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997)h = −13→13
Tmin = 0.940, Tmax = 0.969k = −18→18
5018 measured reflectionsl = −21→21

Refinement

Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.041Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.119H atoms treated by a mixture of independent and constrained refinement
S = 1.07w = 1/[σ2(Fo2) + (0.0615P)2 + 0.6568P] where P = (Fo2 + 2Fc2)/3
2687 reflections(Δ/σ)max = 0.001
122 parametersΔρmax = 0.30 e Å3
0 restraintsΔρmin = −0.30 e Å3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/Ueq
Al10.22387 (5)0.44321 (4)0.13620 (3)0.03294 (17)
Mg10.00000.25000.13728 (4)0.02116 (19)
O10.16625 (10)0.16699 (8)0.13767 (6)0.0298 (3)
O30.00000.25000.01068 (8)0.0269 (3)
O20.00000.25000.26391 (8)0.0270 (3)
C8−0.06993 (19)0.23112 (14)−0.12525 (9)0.0429 (5)
H8A−0.13410.2828−0.13560.052*
H8B−0.08150.1806−0.16670.052*
C40.27768 (17)0.17950 (14)0.19205 (12)0.0439 (5)
H4A0.25880.15150.24610.053*
H4B0.29820.24800.19910.053*
C50.02463 (19)0.33286 (12)0.31515 (9)0.0370 (4)
H5A−0.02850.38800.29670.044*
H5B0.11890.35070.31360.044*
C7−0.08466 (18)0.19178 (13)−0.04047 (9)0.0382 (4)
H7A−0.17730.1962−0.02220.046*
H7B−0.05700.1242−0.03860.046*
C6−0.0151 (2)0.30305 (13)0.39968 (10)0.0445 (5)
H6A−0.10980.31510.40940.053*
H6B0.03730.33700.44150.053*
C20.3257 (2)0.05289 (16)0.10336 (13)0.0573 (6)
H2A0.37810.03960.05380.069*
H2B0.3177−0.00660.13540.069*
C30.3878 (2)0.1296 (2)0.15261 (16)0.0763 (8)
H3A0.44800.10220.19380.092*
H3B0.43820.17370.11740.092*
C10.1945 (2)0.09039 (16)0.08170 (14)0.0587 (6)
H1A0.19450.11430.02500.070*
H1B0.12720.03960.08650.070*
H10.1142 (17)0.3641 (12)0.1382 (9)0.034 (5)*
H20.2892 (19)0.4426 (13)0.2215 (13)0.055 (6)*
H30.3167 (19)0.4126 (16)0.0687 (13)0.063 (6)*
H40.156 (2)0.5361 (18)0.1206 (14)0.076 (7)*

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
Al10.0350 (3)0.0315 (3)0.0323 (3)−0.0085 (2)−0.0024 (2)0.0047 (2)
Mg10.0227 (4)0.0223 (4)0.0184 (3)0.0009 (3)0.0000.000
O10.0284 (6)0.0313 (6)0.0297 (6)0.0073 (5)−0.0075 (4)−0.0111 (4)
O30.0292 (8)0.0336 (8)0.0178 (7)−0.0037 (6)0.0000.000
O20.0401 (9)0.0208 (7)0.0200 (7)−0.0038 (7)0.0000.000
C80.0587 (12)0.0459 (11)0.0243 (8)0.0041 (9)−0.0085 (8)−0.0006 (7)
C40.0391 (10)0.0438 (10)0.0488 (11)0.0098 (8)−0.0215 (8)−0.0096 (9)
C50.0550 (11)0.0294 (9)0.0268 (8)−0.0089 (8)0.0003 (7)−0.0075 (7)
C70.0442 (10)0.0455 (10)0.0249 (8)−0.0094 (8)−0.0090 (7)−0.0014 (7)
C60.0556 (12)0.0522 (12)0.0257 (8)−0.0139 (9)0.0049 (8)−0.0098 (8)
C20.0657 (14)0.0601 (14)0.0462 (11)0.0366 (11)−0.0033 (10)−0.0097 (10)
C30.0344 (12)0.107 (2)0.0876 (17)0.0248 (12)−0.0139 (11)−0.0386 (16)
C10.0526 (12)0.0554 (13)0.0681 (14)0.0211 (10)−0.0125 (10)−0.0379 (11)

Geometric parameters (Å, °)

Al1—H11.573 (18)C4—C31.471 (3)
Al1—H21.55 (2)C4—H4A0.99
Al1—H31.52 (2)C4—H4B0.99
Al1—H41.50 (2)C5—C61.505 (2)
Mg1—O1i2.0517 (11)C5—H5A0.99
Mg1—O12.0518 (11)C5—H5B0.99
Mg1—O32.0800 (15)C7—H7A0.99
Mg1—O22.0804 (15)C7—H7B0.99
Mg1—H11.977 (18)C6—C6i1.519 (4)
O1—C11.443 (2)C6—H6A0.99
O1—C41.4529 (19)C6—H6B0.99
O3—C7i1.4537 (17)C2—C11.477 (3)
O3—C71.4537 (17)C2—C31.487 (3)
O2—C51.4567 (17)C2—H2A0.99
O2—C5i1.4567 (17)C2—H2B0.99
C8—C71.506 (2)C3—H3A0.99
C8—C8i1.517 (4)C3—H3B0.99
C8—H8A0.99C1—H1A0.99
C8—H8B0.99C1—H1B0.99
H1—Al1—H2106.3 (9)O2—C5—C6105.40 (13)
H1—Al1—H3104.8 (10)O2—C5—H5A110.7
H2—Al1—H3113.1 (11)C6—C5—H5A110.7
H1—Al1—H4107.0 (11)O2—C5—H5B110.7
H2—Al1—H4110.9 (11)C6—C5—H5B110.7
H3—Al1—H4114.0 (12)H5A—C5—H5B108.8
O1i—Mg1—O1179.65 (6)O3—C7—C8105.66 (13)
O1i—Mg1—O390.18 (3)O3—C7—H7A110.6
O1—Mg1—O390.18 (3)C8—C7—H7A110.6
O1i—Mg1—O289.82 (3)O3—C7—H7B110.6
O1—Mg1—O289.82 (3)C8—C7—H7B110.6
O3—Mg1—O2180.0H7A—C7—H7B108.7
O1i—Mg1—H191.4 (5)C5—C6—C6i102.59 (11)
O1—Mg1—H188.6 (5)C5—C6—H6A111.2
O3—Mg1—H190.4 (4)C6i—C6—H6A111.2
O2—Mg1—H189.6 (4)C5—C6—H6B111.2
C1—O1—C4109.08 (13)C6i—C6—H6B111.2
C1—O1—Mg1125.75 (10)H6A—C6—H6B109.2
C4—O1—Mg1125.10 (10)C1—C2—C3104.88 (16)
C7i—O3—C7109.37 (16)C1—C2—H2A110.8
C7i—O3—Mg1125.32 (8)C3—C2—H2A110.8
C7—O3—Mg1125.32 (8)C1—C2—H2B110.8
C5—O2—C5i109.39 (16)C3—C2—H2B110.8
C5—O2—Mg1125.30 (8)H2A—C2—H2B108.8
C5i—O2—Mg1125.30 (8)C4—C3—C2105.13 (18)
C7—C8—C8i102.78 (11)C4—C3—H3A110.7
C7—C8—H8A111.2C2—C3—H3A110.7
C8i—C8—H8A111.2C4—C3—H3B110.7
C7—C8—H8B111.2C2—C3—H3B110.7
C8i—C8—H8B111.2H3A—C3—H3B108.8
H8A—C8—H8B109.1O1—C1—C2106.93 (15)
O1—C4—C3105.34 (15)O1—C1—H1A110.3
O1—C4—H4A110.7C2—C1—H1A110.3
C3—C4—H4A110.7O1—C1—H1B110.3
O1—C4—H4B110.7C2—C1—H1B110.3
C3—C4—H4B110.7H1A—C1—H1B108.6
H4A—C4—H4B108.8

Symmetry codes: (i) −x, −y+1/2, z.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CI5044).

References

  • Ashby, E. C. & Goel, A. B. (1977). Inorg. Chem.16, 2082–2085.
  • Ashby, E. C., Schwartz, R. D. & James, B. D. (1970). Inorg. Chem.9, 325–332.
  • Dilts, J. A. & Ashby, E. C. (1972). Inorg. Chem.11, 1230–1236.
  • Fichtner, M., Frommen, C. & Fuhr, O. (2004). Inorg. Chem 44, 3479–3484. [PubMed]
  • Fichtner, M. & Fuhr, O. (2002). J. Alloys Compd, 345, 286–296.
  • Lauher, J. W., Dougherty, D. & Herley, P. J. (1979). Acta Cryst. B35, 1454–1456.
  • Nonius (1998). COLLECT Nonius BV, Delft, The Netherlands.
  • Nöth, H., Schmidt, M. & Treitl, A. (1995). Chem. Ber.128, 999–1006.
  • Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press.
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
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  • Sklar, N. & Post, B. (1967). Inorg. Chem 6, 669–671.

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