Tri­bromo­(tetra­hydro­furan)­aluminium(III)

In the title compound, [AlBr₃(C₄H₈O)], (I), the Al atom, the O atom and one of the Br atoms are located on a crystallographic mirror plane; as a result, there is one half mol­ecule in the asymmetric unit. Tetra­hydro­furan shows a disorder due to puckering of the five-membered ring. (I) is isomorphous with [AlCl₃(C₄H₈O)] and [GaCl₃(C₄H₈O)].

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](O-C) = 0.011 Å
• R factor = 0.058
• wR factor = 0.110
• Data-to-parameter ratio = 16.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Recently, we have reported the X-ray crystal structure analysis of [GaCl₃(C₄H₈O)] (C₄H₈O = thf; Scholz et al., 2002). Halides of group 13 elements have found widespread use as starting material in inorganic chemistry. The synthesis of group 13 element clusters depends on the oxidation state of elements in the halides on the one hand and the solvent used on the other hand. AlBr₃ feature a cyclic, dimeric arrangement in non-donor solvents like alkenes or benzene. In contrast to that, monomeric adducts from AlBr₃ are formed in the presence of Lewis bases. We were interested in the syntheses of aluminium cluster compounds with bulky substituents, such as the supersilyl (tri-tert-butylsilyl) group. Therefore, we have prepared a solution of AlBr₃(thf) in pentane. Colourless crystals of the title compound, (I), were grown from this solution at ambient temperature.

The molecule of (I) is located on a crystallographic mirror plane, passing through the Al1, O1 and Br1 atoms (Fig. 1 and Table 1). All other atoms occupy general positions. As a result of that, there is just half a molecule in the asymmetric unit. The crystal structure of (I) is isomorphous with those of [AlCl₃(C₄H₈O)] (Engelhardt et al., 1996) and [GaCl₃(C₄H₈O)] (Scholz et al., 2002).

S2. Experimental

Colourless crystals of the title compound, (I), were obtained from a solution of 0.168 g (0.63 mmol) AlBr₃ and 0.5 ml tetrahydrofuran in 5 ml pentane at ambient temperature.

S3. Refinement

All H atoms were refined with fixed individual displacement parameters [U_iso(H) = 1.2U_eq(C)] using a riding model with C—H = 0.99 Å. Atom C2 is disordered, therefore it was refined employing a split model. It was assumed that the probabilities of the two conformations, C1—C2—C2'ⁱ-C1ⁱ and C1—C2'-C2ⁱ—C1ⁱ are 50% each [symmetry code: (i) x, 1/2 − y, z]. Furthermore, the two C1—C2 and C1—C2' distances as well as the distances C2—C2'ⁱ and C2'-C2ⁱ were restrained to the same length. However, the anisotropic displacement parameter of C2 has a max/min ratio of 18.8.

Computing details

Data collection: X-AREA (Stoe & Cie, 2001); cell refinement: X-AREA; data reduction: X-AREA; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 1991).

Figures

Fig. 1. A perspective view of the title compound, (I), with the atom-numbering scheme. Displacement ellipsoids are at the 50% probability level. Only one of the two disordered conformation of tetrahydrofuran is shown. [Symmetry code: (i) x, 1/2 − y, z.]

(I)

Crystal data

[AlBr3(C4H8O)]	F(000) = 316
Mr = 338.81	Dx = 2.313 Mg m^−3
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yb	Cell parameters from 4175 reflections
a = 6.3475 (11) Å	θ = 2.1–25.2°
b = 10.779 (2) Å	µ = 12.46 mm^−1
c = 7.4326 (12) Å	T = 100 K
β = 106.971 (13)°	Plate, colourless
V = 486.39 (15) Å^3	0.12 × 0.08 × 0.05 mm
Z = 2

Data collection

Stoe IPDS-II two-circle diffractometer	918 independent reflections
Radiation source: fine-focus sealed tube	714 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.082
ω scans	θmax = 25.1°, θmin = 2.9°
Absorption correction: multi-scan (MULABS; Spek, 1990; Blessing, 1995)	h = −7→7
Tmin = 0.302, Tmax = 0.546	k = −12→12
4060 measured reflections	l = −8→8

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.058	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.110	H-atom parameters constrained
S = 1.11	w = 1/[σ^2(Fo^2) + (0.0137P)^2 + 5.177P] where P = (Fo^2 + 2Fc^2)/3
918 reflections	(Δ/σ)max < 0.001
55 parameters	Δρmax = 1.07 e Å^−3
2 restraints	Δρmin = −1.82 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Al1	0.5779 (6)	0.2500	0.3861 (5)	0.0241 (8)
Br1	0.2463 (2)	0.2500	0.4424 (2)	0.0523 (5)
Br2	0.63120 (18)	0.07473 (13)	0.23733 (18)	0.0650 (5)
O1	0.7882 (12)	0.2500	0.6136 (11)	0.0265 (19)
C1	0.8720 (17)	0.1368 (9)	0.7279 (14)	0.041 (2)
H1A	0.7532	0.0949	0.7664	0.049*
H1B	0.9371	0.0774	0.6575	0.049*
C2	1.043 (6)	0.188 (5)	0.894 (4)	0.068 (17)	0.50
H2A	1.1881	0.1897	0.8691	0.082*	0.50
H2B	1.0539	0.1372	1.0069	0.082*	0.50
C2'	0.980 (7)	0.179 (4)	0.923 (4)	0.058 (13)	0.50
H2'A	1.1091	0.1275	0.9870	0.070*	0.50
H2'B	0.8732	0.1783	0.9972	0.070*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Al1	0.0196 (16)	0.0272 (19)	0.0226 (18)	0.000	0.0018 (14)	0.000
Br1	0.0198 (6)	0.1072 (15)	0.0310 (8)	0.000	0.0088 (5)	0.000
Br2	0.0412 (6)	0.0687 (8)	0.0655 (8)	0.0231 (6)	−0.0152 (5)	−0.0438 (7)
O1	0.020 (4)	0.027 (5)	0.028 (5)	0.000	0.000 (3)	0.000
C1	0.045 (6)	0.039 (6)	0.037 (6)	0.010 (5)	0.010 (5)	0.011 (5)
C2	0.07 (2)	0.11 (3)	0.004 (10)	0.05 (2)	−0.014 (15)	−0.003 (13)
C2'	0.08 (2)	0.044 (18)	0.05 (2)	0.029 (16)	0.021 (16)	−0.004 (15)

Geometric parameters (Å, º)

Al1—O1	1.823 (8)	C1—H1A	0.9900
Al1—Br1	2.262 (4)	C1—H1B	0.9900
Al1—Br2^i	2.264 (2)	C2—C2'^i	1.51 (4)
Al1—Br2	2.264 (2)	C2—H2A	0.9900
O1—C1	1.494 (10)	C2—H2B	0.9900
O1—C1^i	1.494 (10)	C2'—C2^i	1.51 (4)
C1—C2'	1.49 (2)	C2'—H2'A	0.9900
C1—C2	1.49 (2)	C2'—H2'B	0.9900
O1—Al1—Br1	107.3 (3)	O1—C1—H1B	111.2
O1—Al1—Br2^i	106.24 (17)	H1A—C1—H1B	109.2
Br1—Al1—Br2^i	111.72 (10)	C1—C2—C2'^i	108 (3)
O1—Al1—Br2	106.24 (17)	C1—C2—H2A	110.1
Br1—Al1—Br2	111.72 (10)	C2'^i—C2—H2A	108.1
Br2^i—Al1—Br2	113.13 (18)	C1—C2—H2B	110.3
C1—O1—C1^i	109.6 (9)	C2'^i—C2—H2B	110.9
C1—O1—Al1	124.8 (5)	H2A—C2—H2B	109.2
C1^i—O1—Al1	124.8 (5)	C1—C2—H2'A	113.7
C2'—C1—O1	106.8 (19)	C2'^i—C2—H2'A	128.2
C2—C1—O1	103 (2)	C1—C2'—C2^i	102 (3)
C2'—C1—H1A	91.8	C1—C2'—H2'A	111.9
C2—C1—H1A	111.2	C2^i—C2'—H2'A	112.7
O1—C1—H1A	111.2	C1—C2'—H2'B	110.0
C2'—C1—H1B	124.8	C2^i—C2'—H2'B	110.1
C2—C1—H1B	111.2	H2'A—C2'—H2'B	109.5
Br1—Al1—O1—C1	84.2 (8)	C1^i—O1—C1—C2	−12 (2)
Br2^i—Al1—O1—C1	−156.1 (7)	Al1—O1—C1—C2	178 (2)
Br2—Al1—O1—C1	−35.4 (9)	C2'—C1—C2—C2'^i	−77 (10)
Br1—Al1—O1—C1^i	−84.2 (8)	O1—C1—C2—C2'^i	28 (4)
Br2^i—Al1—O1—C1^i	35.4 (9)	C2—C1—C2'—C2^i	56 (10)
Br2—Al1—O1—C1^i	156.1 (7)	O1—C1—C2'—C2^i	−25 (4)
C1^i—O1—C1—C2'	9 (2)	C1—C2—C2'^i—C1^i	−33 (5)
Al1—O1—C1—C2'	−161 (2)	C1—C2'—C2^i—C1^i	33 (5)

Symmetry code: (i) x, −y+1/2, z.