Solvated CrBr₂(thf)₂, a linear chain in the solid state

In the title compound, di­bromo­bis­(tetra­hydro­furan-O)chromium(II), [CrBr₂(C₄H₈O)₂], CrBr₂ is solvated by two tetra­hydro­furan (thf) mol­ecules, with a Cr—O distance of 2.072 (3) Å and a Cr—Br distance of 2.5825 (5) Å. The Cr atom lies on the center of inversion. The Cr atom is octahedrally coordinated, with the thf Cr—O bond orthogonal to the Cr—Br bond, and the vacant sites are occupied with a Cr...Br intermolecular interaction of 2.9874 (5) Å. The latter interaction is almost orthogonal to the Cr—O vector. This extends the system into a linear chain along the [100] direction.

Key indicators

• Single-crystal X-ray study
• T = 203 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.027
• wR factor = 0.071
• Data-to-parameter ratio = 15.8

checkCIF results

No syntax errors found



ADDSYM reports no extra symmetry


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.184     0.293
          Tmin and Tmax expected:      0.154     0.293
          RR =      1.195
          Please check that your absorption correction is appropriate.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

(THF)₂CrBr₂, (I), bears a close resemblance to the parent compound CrBr₂ (Tracy et al., 1962). Both show slightly distorted octahedral coordination and both have similar in-plane Cr—Br bond distances, 2.5825 (5) Å in (I) and 2.545 (1) Å in CrBr₂. The solvent molecule, THF in this case, occupies an in-plane coordination site with a Cr—O distance of 2.072 (3) Å. The solvent molecule is coordinated orthogonally to the Cr—Br vector with an angle of 90.009 (8)°. The THF molecule is in a half-chair conformation with a total puckering amplitude of Q_T = 0.363 Å (Cremer & Pople, 1975). The orientation of the THF molecule is influenced by the intramolecular interactions C4—H4a···Br1 and C1—H1a···Br1ⁱ (see Table 1) which tilt the ring towards each Br atom. The out-of-plane coordination site is occupied with an intermolecular Cr1···Br1ⁱⁱ interaction of 2.9874 (5) Å [symmetry code: (ii) 1 + x, y, z]. The corresponding interaction in CrBr₂ has a Cr···Br distance of 2.998 (1) Å. The distortion from ideal octahedral geometry is also reflected in the Br1—Cr1—Br1ⁱⁱ angle of 94.65 (2)°. With the THF molecules occupying the other coordination sites, (I) can only form a staggered chain instead of the planar sheets found in CrBr₂. In this case, the direction of propagation is along [100] (Fig. 1). Other solvent coordinated Cr^IIBr₂ species that are octahedrally coordinated show a wide range of Cr—Br distances. The complex CrBr₂(CH₃CN)₂ (Halepoto et al., 1990), which also forms linear chains, has an in-plane Cr—Br distance of 2.545 Å and an out-of-plane distance of 2.976 (1) Å. However, the molecular species trans-CrBr₂(pyridine)₄ (Holah et al., 1998) has a Cr—Br bond distance of 2.998 (1) Å which indicates a very weakly associated Br atom.

S2. Experimental

(THF)₂CrBr₂ was synthesized as a side product during the attempted synthesis of a chromocene bromide. Tetramethylethylenediyl(η⁵-biscyclopentadienyl)chromocene^II carbonyl (331 mg, 1.1 mmol) was reacted with 1-bromo-2-methylpropane (155 mg, 1.1 mmol) in THF for 20 h at 378 K, with no color change. Dibromomethane (excess) was then added to increase the bromide concentration. Excess solvent and reagents were removed under reduced pressure and the green residue redissolved in THF (20 ml) and filtered. The resulting solution was concentrated to promote crystallization and cooled in a 278 K refrigerator overnight. The supernatant was decanted yielding a green crystalline product. The supernatant was concentrated under reduced pressure to yield a fine pale green powder. Combined yield 68 mg, 19.1%, m.p. > 573 K.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT-Plus (Bruker, 1999); program(s) used to solve structure: SHELXTL (Sheldrick, 1998); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. Packing diagram of (I) showing the staggered propagation along the [100] direction. H atoms have been omitted for clarity.

dibromobis(tetrahydrofuran-O)chromium(II)

Crystal data

[CrBr2(C4H8O)2]	Z = 1
Mr = 356.03	F(000) = 174
Triclinic, P1	Dx = 2.126 Mg m^−3
a = 4.1043 (7) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.4530 (13) Å	Cell parameters from 839 reflections
c = 9.2875 (16) Å	θ = 2.2–27.4°
α = 87.777 (3)°	µ = 8.18 mm^−1
β = 78.619 (3)°	T = 203 K
γ = 87.281 (3)°	Plate, pale yellow
V = 278.07 (8) Å^3	0.25 × 0.20 × 0.15 mm

Data collection

Siemens SMART 1000 diffractometer	962 independent reflections
Radiation source: normal-focus sealed tube	897 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
Detector resolution: 8.3 pixels mm^-1	θmax = 25.0°, θmin = 2.2°
ω scans	h = −4→4
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1999)	k = −8→8
Tmin = 0.184, Tmax = 0.293	l = −11→11
2917 measured reflections

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)] = 0.027	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.071	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0436P)^2 + 0.1523P] where P = (Fo^2 + 2Fc^2)/3
962 reflections	(Δ/σ)max = 0.001
61 parameters	Δρmax = 0.58 e Å^−3
0 restraints	Δρmin = −0.70 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
Br1	0.10559 (9)	0.70378 (5)	0.37413 (4)	0.02022 (17)
Cr1	0.5000	0.5000	0.5000	0.0180 (2)
O1	0.4032 (7)	0.6622 (3)	0.6810 (3)	0.0245 (6)
C1	0.2743 (10)	0.5980 (5)	0.8298 (4)	0.0242 (9)
H1A	0.3974	0.4886	0.8536	0.029*
H1B	0.0382	0.5724	0.8425	0.029*
C3	0.2812 (11)	0.9167 (5)	0.8283 (4)	0.0244 (9)
H3A	0.0454	0.9507	0.8342	0.029*
H3B	0.3948	1.0190	0.8558	0.029*
C2	0.3237 (10)	0.7515 (5)	0.9266 (4)	0.0240 (9)
H2A	0.5459	0.7433	0.9508	0.029*
H2B	0.1558	0.7528	1.0177	0.029*
C4	0.4399 (10)	0.8560 (5)	0.6761 (4)	0.0232 (9)
H4A	0.3266	0.9144	0.6022	0.028*
H4B	0.6753	0.8848	0.6524	0.028*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0210 (2)	0.0198 (2)	0.0199 (3)	0.00074 (15)	−0.00461 (16)	0.00071 (15)
Cr1	0.0230 (5)	0.0167 (4)	0.0144 (5)	0.0034 (3)	−0.0046 (4)	−0.0026 (3)
O1	0.0390 (16)	0.0173 (13)	0.0152 (14)	−0.0007 (12)	−0.0004 (12)	−0.0019 (11)
C1	0.029 (2)	0.022 (2)	0.018 (2)	0.0006 (16)	0.0015 (17)	−0.0007 (16)
C3	0.027 (2)	0.024 (2)	0.021 (2)	0.0004 (16)	−0.0020 (17)	−0.0058 (16)
C2	0.028 (2)	0.027 (2)	0.017 (2)	0.0021 (17)	−0.0026 (17)	−0.0052 (17)
C4	0.032 (2)	0.0162 (19)	0.021 (2)	−0.0041 (16)	−0.0036 (17)	−0.0010 (15)

Geometric parameters (Å, º)

Br1—Cr1	2.5825 (5)	O1—C4	1.458 (4)
Cr1—O1^i	2.072 (3)	C1—C2	1.527 (6)
Cr1—O1	2.072 (3)	C3—C4	1.512 (5)
Cr1—Br1^i	2.5825 (5)	C3—C2	1.528 (6)
O1—C1	1.450 (5)
O1^i—Cr1—O1	180.00 (9)	C1—O1—Cr1	124.1 (2)
O1^i—Cr1—Br1^i	90.09 (8)	C4—O1—Cr1	125.1 (2)
O1—Cr1—Br1^i	89.91 (8)	O1—C1—C2	104.7 (3)
O1^i—Cr1—Br1	89.91 (8)	C4—C3—C2	103.6 (3)
O1—Cr1—Br1	90.09 (8)	C1—C2—C3	102.1 (3)
Br1^i—Cr1—Br1	180.0	O1—C4—C3	105.2 (3)
C1—O1—C4	110.7 (3)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4A···Br1	0.98	2.99	3.599 (4)	122
C1—H1A···Br1^i	0.98	2.99	3.607 (4)	122

Symmetry code: (i) −x+1, −y+1, −z+1.