The low-temperature structure of diethyl ether magnesium oxybromide

Abstract

The crystal structure of the title compound, hexa-μ₂-bromido-μ₄-oxido-tetra­kis­[(diethyl ether)magnesium], [Mg₄Br₆O(C₄H₁₀O)₄], determined from data measured at 173 K, differs from the previously known structure of diethyl ether magnesium oxybromide, which was determined from room-temperature data [Stucky & Rundle (1964 ▶). J. Am. Chem. Soc. 86, 4821–4825]. The title compound crystallizes in the tetra­gonal space group I , whereas the previously known structure crystallizes in a different tetra­gonal space group, namely P 2₁ c. Both molecules have crystallographic symmetry and show almost identical geometric parameters for the Mg, Br and O atoms. The crystal of the title compound turned out to be a merohedral twin emulating a structure with apparent Laue symmetry 4/mmm, whereas the correct Laue group is just 4/m. The fractional contribution of the minor twin component converged to 0.462 (1).

Related literature

For Mg–Br complexes, see: Lerner (2005 ▶); Lerner et al. (2003 ▶); Metzler et al. (1994 ▶). For a polymorph of the title compound, see: Stucky & Rundle (1964 ▶). For the Cambridge Structural Database, see: Allen (2002 ▶).

Experimental

Crystal data

• [Mg₄Br₆O(C₄H₁₀O)₄]

• M _r = 889.18

• Tetragonal,

• a = 10.4630 (13) Å

• c = 15.276 (2) Å

• V = 1672.3 (4) ų

• Z = 2

• Mo Kα radiation

• μ = 7.30 mm⁻¹

• T = 173 K

• 0.25 × 0.22 × 0.18 mm

Data collection

• Stoe IPDS II two-circle diffractometer

• Absorption correction: multi-scan [MULABS (Spek, 2009 ▶; Blessing, 1995 ▶)] T _min = 0.169, T _max = 0.269

• 3746 measured reflections

• 1479 independent reflections

• 1455 reflections with I > 2σ(I)

• R _int = 0.044

Refinement

• R[F ² > 2σ(F ²)] = 0.026

• wR(F ²) = 0.067

• S = 1.08

• 1479 reflections

• 73 parameters

• H-atom parameters constrained

• Δρ_max = 0.62 e Å⁻³

• Δρ_min = −0.56 e Å⁻³

• Absolute structure: Flack (1983 ▶), 689 Friedel pairs

• Flack parameter: −0.02 (2)

Data collection: X-AREA (Stoe & Cie, 2001 ▶); cell refinement: X-AREA; data reduction: X-AREA; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: XP (Sheldrick, 2008 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

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

supplementary crystallographic information

Comment

The solid-state structures of Mg–Br compounds feature coordination numbers of the Mg center from four as in [MgBr(Si^tBu₃)(THF)]₂ (Lerner et al., 2003; Lerner, 2005) to six as in [MgBr₂(THF)₄] (Metzler et al., 1994). Most of the Mg–Br compounds possess an octahedral coordination sphere which surrounds the Mg cation whereas only a few compounds are found in the Cambridge Structural Database (Allen, 2002) with five-coordinated Mg centers as found in the solid-state structure of the title compound. We report here the X-ray crystal structure analysis of [(MgOEt₂)₄Br₆O], which could be isolated from a solution of C₆F₅MgBr in Et₂O.

Data for the crystal structure of the title compound were collected at 173 K. It crystallizes in the tetragonal space group I4 with crystallographic 4 symmetry. The previously known polymorph (Stucky & Rundle, 1964) for which data were collected at room temperature crystallizes in the space group P42₁c and has crystallographic 4 symmetry, too. However, in the latter structure there is severe disorder of the C atoms, whereas in the title compound, no disorder was found. The geometric parameters involving Mg, Br and O atoms agree well in both structures.

Since the structures show striking similarities and were measured at different temperatures, a phase transition between them cannot be excluded.

Experimental

To a suspension of Mg turnings (0.5 g, 20.2 mmol) in 25 ml Et₂O, 2.3 ml C₆F₅Br is added dropwise. The reaction starts when 0.3 ml of C₆F₅Br have been added. The rest of C₆F₅Br is added dropwise at such a rate that the reaction mixture remains at its boiling point and refluxing is continued for 1 h until the magnesium turnings have dissolved completely. During the storing of this solution for 3 weeks, colorless crystals of the title compound were grown at room temperature.

Refinement

H atoms could be located in a difference Fourier map, but they were refined using a riding model with isotropic displacement parameters U_iso(H) set to 1.2U_eq(C_methylene) and C—H = 0.99 Å or U_iso(H) set to 1.5U_eq(C_methyl) and C—H = 0.98 Å. The crystal turned out to be a merohedral twin emulating a structure with Laue symmetry 4/mmm. The twin law (0 1 0/1 0 0/0 0 1) is a twofold rotation about the diagonal between the a and b axis and the fractional contribution of the minor twin component refined to 0.462 (1).

Figures

Fig. 1.

Perspective view of the title compound with displacement ellipsoids at the 50% probability level. H atoms are omitted for clarity. Symmetry operators for generating equivalent atoms: (A): 1 - x, -y z; (B): 1/2 + y, 1/2 - x, 1/2 - z; (C): 1/2 - y, -1/2 + x, 1/2 - z.

Crystal data

[Mg4Br6O(C4H10O)4]	Dx = 1.766 Mg m−3
Mr = 889.18	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4	Cell parameters from 3746 reflections
Hall symbol: I -4	θ = 3.8–25.6°
a = 10.4630 (13) Å	µ = 7.30 mm−1
c = 15.276 (2) Å	T = 173 K
V = 1672.3 (4) Å3	Block, colourless
Z = 2	0.25 × 0.22 × 0.18 mm
F(000) = 868

Data collection

Stoe IPDS II two-circle diffractometer	1479 independent reflections
Radiation source: fine-focus sealed tube	1455 reflections with I > 2σ(I)
graphite	Rint = 0.044
ω scans	θmax = 25.3°, θmin = 3.8°
Absorption correction: multi-scan (MULABS; Spek, 2009; Blessing, 1995)	h = −12→12
Tmin = 0.169, Tmax = 0.269	k = −8→12
3746 measured reflections	l = −13→18

Refinement

Refinement on F2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F2 > 2σ(F2)] = 0.026	w = 1/[σ2(Fo2) + (0.0427P)2 + 0.284P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.067	(Δ/σ)max < 0.001
S = 1.08	Δρmax = 0.62 e Å−3
1479 reflections	Δρmin = −0.56 e Å−3
73 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraints	Extinction coefficient: 0.0036 (4)
0 constraints	Absolute structure: Flack (1983), with 689 Friedel pairs
Primary atom site location: structure-invariant direct methods	Flack parameter: −0.02 (2)
Secondary atom site location: difference Fourier map

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

	x	y	z	Uiso*/Ueq
Mg1	0.40713 (19)	0.12350 (19)	0.32357 (13)	0.0135 (5)
Br1	0.5000	0.0000	0.45892 (4)	0.01815 (19)
Br2	0.19607 (5)	0.04477 (5)	0.24533 (6)	0.02114 (18)
O1	0.5000	0.0000	0.2500	0.0120 (13)
C1	0.2012 (10)	0.4180 (8)	0.3236 (7)	0.044 (2)
H1A	0.1953	0.5113	0.3196	0.065*
H1B	0.1161	0.3823	0.3348	0.065*
H1C	0.2345	0.3836	0.2685	0.065*
C2	0.2906 (8)	0.3818 (7)	0.3982 (6)	0.0286 (17)
H2A	0.3759	0.4195	0.3875	0.034*
H2B	0.2573	0.4174	0.4538	0.034*
O2	0.3026 (5)	0.2433 (5)	0.4064 (3)	0.0210 (10)
C3	0.2032 (8)	0.1864 (7)	0.4613 (5)	0.0289 (16)
H3A	0.1932	0.0953	0.4453	0.035*
H3B	0.1210	0.2299	0.4495	0.035*
C4	0.2326 (9)	0.1958 (10)	0.5579 (5)	0.040 (2)
H4A	0.1629	0.1570	0.5915	0.061*
H4B	0.2413	0.2859	0.5744	0.061*
H4C	0.3126	0.1507	0.5704	0.061*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Mg1	0.0173 (10)	0.0158 (10)	0.0075 (9)	0.0031 (8)	0.0010 (8)	−0.0015 (8)
Br1	0.0265 (7)	0.0226 (6)	0.0054 (3)	0.0057 (6)	0.000	0.000
Br2	0.0149 (3)	0.0285 (3)	0.0200 (3)	0.0026 (2)	−0.0018 (4)	−0.0064 (4)
O1	0.0150 (18)	0.0150 (18)	0.006 (3)	0.000	0.000	0.000
C1	0.056 (5)	0.035 (4)	0.040 (5)	0.020 (4)	−0.001 (5)	0.002 (4)
C2	0.038 (4)	0.015 (3)	0.032 (4)	0.010 (3)	0.004 (3)	−0.008 (3)
O2	0.024 (2)	0.023 (2)	0.015 (2)	0.005 (2)	0.008 (2)	−0.0037 (19)
C3	0.029 (4)	0.027 (4)	0.031 (4)	0.009 (3)	0.013 (3)	0.001 (4)
C4	0.051 (6)	0.056 (6)	0.014 (4)	0.027 (5)	0.009 (3)	−0.004 (4)

Geometric parameters (Å, °)

Mg1—O1	1.969 (2)	C1—H1A	0.9800
Mg1—O2	2.090 (5)	C1—H1B	0.9800
Mg1—Br2i	2.597 (2)	C1—H1C	0.9800
Mg1—Br1	2.625 (2)	C2—O2	1.460 (8)
Mg1—Br2	2.643 (2)	C2—H2A	0.9900
Mg1—Mg1i	3.206 (3)	C2—H2B	0.9900
Mg1—Mg1ii	3.206 (3)	O2—C3	1.463 (9)
Mg1—Mg1iii	3.233 (4)	C3—C4	1.510 (11)
Br1—Mg1iii	2.625 (2)	C3—H3A	0.9900
Br2—Mg1ii	2.597 (2)	C3—H3B	0.9900
O1—Mg1iii	1.9689 (19)	C4—H4A	0.9800
O1—Mg1i	1.969 (2)	C4—H4B	0.9800
O1—Mg1ii	1.969 (2)	C4—H4C	0.9800
C1—C2	1.523 (12)
O1—Mg1—O2	175.84 (18)	Mg1—O1—Mg1i	109.01 (6)
O1—Mg1—Br2i	88.40 (7)	Mg1iii—O1—Mg1ii	109.01 (6)
O2—Mg1—Br2i	95.71 (15)	Mg1—O1—Mg1ii	109.01 (6)
O1—Mg1—Br1	86.78 (7)	Mg1i—O1—Mg1ii	110.39 (12)
O2—Mg1—Br1	90.70 (16)	C2—C1—H1A	109.5
Br2i—Mg1—Br1	118.15 (8)	C2—C1—H1B	109.5
O1—Mg1—Br2	87.12 (7)	H1A—C1—H1B	109.5
O2—Mg1—Br2	91.33 (16)	C2—C1—H1C	109.5
Br2i—Mg1—Br2	120.44 (8)	H1A—C1—H1C	109.5
Br1—Mg1—Br2	120.81 (8)	H1B—C1—H1C	109.5
O1—Mg1—Mg1i	35.49 (3)	O2—C2—C1	111.3 (6)
O2—Mg1—Mg1i	148.63 (17)	O2—C2—H2A	109.4
Br2i—Mg1—Mg1i	52.92 (7)	C1—C2—H2A	109.4
Br1—Mg1—Mg1i	103.98 (7)	O2—C2—H2B	109.4
Br2—Mg1—Mg1i	103.99 (9)	C1—C2—H2B	109.4
O1—Mg1—Mg1ii	35.49 (3)	H2A—C2—H2B	108.0
O2—Mg1—Mg1ii	142.70 (17)	C2—O2—C3	113.0 (6)
Br2i—Mg1—Mg1ii	106.54 (9)	C2—O2—Mg1	126.1 (5)
Br1—Mg1—Mg1ii	103.98 (7)	C3—O2—Mg1	118.4 (4)
Br2—Mg1—Mg1ii	51.63 (7)	O2—C3—C4	112.9 (7)
Mg1i—Mg1—Mg1ii	60.57 (7)	O2—C3—H3A	109.0
O1—Mg1—Mg1iii	34.80 (6)	C4—C3—H3A	109.0
O2—Mg1—Mg1iii	142.56 (16)	O2—C3—H3B	109.0
Br2i—Mg1—Mg1iii	104.34 (9)	C4—C3—H3B	109.0
Br1—Mg1—Mg1iii	51.98 (4)	H3A—C3—H3B	107.8
Br2—Mg1—Mg1iii	104.66 (9)	C3—C4—H4A	109.5
Mg1i—Mg1—Mg1iii	59.72 (4)	C3—C4—H4B	109.5
Mg1ii—Mg1—Mg1iii	59.72 (4)	H4A—C4—H4B	109.5
Mg1iii—Br1—Mg1	76.05 (9)	C3—C4—H4C	109.5
Mg1ii—Br2—Mg1	75.45 (9)	H4A—C4—H4C	109.5
Mg1iii—O1—Mg1	110.39 (12)	H4B—C4—H4C	109.5
Mg1iii—O1—Mg1i	109.01 (6)
O1—Mg1—Br1—Mg1iii	0.0	Br2i—Mg1—O1—Mg1ii	−121.97 (10)
O2—Mg1—Br1—Mg1iii	176.68 (18)	Br1—Mg1—O1—Mg1ii	119.72 (9)
Br2i—Mg1—Br1—Mg1iii	−86.46 (9)	Br2—Mg1—O1—Mg1ii	−1.38 (7)
Br2—Mg1—Br1—Mg1iii	84.71 (9)	Mg1i—Mg1—O1—Mg1ii	−120.57 (8)
Mg1i—Mg1—Br1—Mg1iii	−31.31 (7)	Mg1iii—Mg1—O1—Mg1ii	119.72 (9)
Mg1ii—Mg1—Br1—Mg1iii	31.31 (7)	C1—C2—O2—C3	−86.8 (8)
O1—Mg1—Br2—Mg1ii	1.02 (5)	C1—C2—O2—Mg1	74.9 (8)
O2—Mg1—Br2—Mg1ii	−175.11 (18)	Br2i—Mg1—O2—C2	17.5 (6)
Br2i—Mg1—Br2—Mg1ii	87.47 (9)	Br1—Mg1—O2—C2	135.9 (6)
Br1—Mg1—Br2—Mg1ii	−83.50 (9)	Br2—Mg1—O2—C2	−103.3 (6)
Mg1i—Mg1—Br2—Mg1ii	32.52 (7)	Mg1i—Mg1—O2—C2	16.9 (8)
Mg1iii—Mg1—Br2—Mg1ii	−29.32 (7)	Mg1ii—Mg1—O2—C2	−109.6 (6)
Br2i—Mg1—O1—Mg1iii	118.31 (8)	Mg1iii—Mg1—O2—C2	140.2 (5)
Br1—Mg1—O1—Mg1iii	0.0	Br2i—Mg1—O2—C3	178.3 (5)
Br2—Mg1—O1—Mg1iii	−121.10 (8)	Br1—Mg1—O2—C3	−63.3 (5)
Mg1i—Mg1—O1—Mg1iii	119.72 (9)	Br2—Mg1—O2—C3	57.5 (5)
Mg1ii—Mg1—O1—Mg1iii	−119.72 (9)	Mg1i—Mg1—O2—C3	177.7 (4)
Br2i—Mg1—O1—Mg1i	−1.40 (7)	Mg1ii—Mg1—O2—C3	51.2 (6)
Br1—Mg1—O1—Mg1i	−119.72 (4)	Mg1iii—Mg1—O2—C3	−59.0 (6)
Br2—Mg1—O1—Mg1i	119.19 (10)	C2—O2—C3—C4	−82.1 (8)
Mg1ii—Mg1—O1—Mg1i	120.57 (8)	Mg1—O2—C3—C4	114.7 (6)
Mg1iii—Mg1—O1—Mg1i	−119.72 (9)

Symmetry codes: (i) y+1/2, −x+1/2, −z+1/2; (ii) −y+1/2, x−1/2, −z+1/2; (iii) −x+1, −y, z.