2,2,4,4-Tetra­bromo-1,1,3,3-tetra­methyl­cyclo­diborazane

The title compound, C₄H₁₂B₂Br₄N₂, contains an almost square four-membered ring that results from the head-to-tail dimerization of the dimethyl­amino­dibromo­borane. The dimer has almost mmm symmetry and does have 2/m crystallographic symmetry. The crystal structure involves C—H...Br hydrogen bonds.

Key indicators

• Single-crystal X-ray study
• T = 173 K
• Mean [sigma](N-B) = 0.005 Å
• R factor = 0.032
• wR factor = 0.085
• Data-to-parameter ratio = 22.6

checkCIF/PLATON results

No syntax errors found



Alert level B
ABSTM02_ALERT_3_B  The ratio of expected to reported Tmax/Tmin(RR') is < 0.75
            Tmin and Tmax reported:      0.210     0.662
            Tmin(prime) and Tmax expected:      0.318     0.662
            RR(prime) =      0.660
            Please check that your absorption correction is appropriate.

Author Response: The faces of the crystal were not clearly defined to allow indexation.

PLAT061_ALERT_3_B Tmax/Tmin Range Test RR' too Large .............       0.61

Alert level C
PLAT480_ALERT_4_C Long H...A H-Bond Reported H1A    ..  BR1     ..       3.02 Ang.
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.17 Ratio

   0 ALERT level A = In general: serious problem
   2 ALERT level B = Potentially serious problem
   2 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

The structure of the title compound is shown in Fig. 1. Head-to-tail dimerization of dimethylaminodibromoborane results in a NBNB four-membered ring only slightly deviating from square geometry. The shortest intermolecular contact between hydrogen and bromine from adjacent molecules is of 3.022 Å.

Related literature

For related structures featuring an aminodibromoborane skeleton, see: Abu Ali et al. (2001); Klebe et al. (1984); Nie et al. (2005); Nöth et al. (1983). Aminohalogenoboranes are direct precursors for diboranes, see: Ishimaya et al. (2002).

S2. Experimental

The title compound was prepared by substituent redistribution from tris(dimethylamino)borane and tribromoborane. Suitable crystals were obtained upon allowing the crude reaction mixture to stand at 293 K.

S3. Refinement

All H atoms attached to C atoms were fixed geometrically and treated as riding with C—H = 0.97 Å and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2006); software used to prepare material for publication: SHELXTL (Bruker, 2006).

Figures

Fig. 1. The molecular structure of dimethylaminodibromoborane dimer, with the atom-labeling scheme. The B and Br atoms lie in the crystallographic mirror plane and the N atoms lie on the twofold axis. Displacement ellipsoids are drawn at the 50% probability level. H atoms omitted for clarity. Symmetry codes: (i) -x + 2, y, -z + 1; (ii) -x + 2, -y, -z + 1; (iii) x, -y, z.

2,2,4,4-Tetrabromo-1,1,3,3-tetramethylcyclodiborazane

Crystal data

C4H12B2Br4N2	F(000) = 400
Mr = 429.42	Dx = 2.445 Mg m^−3
Monoclinic, C2/m	Melting point: 340 K
Hall symbol: -C 2y	Mo Kα radiation, λ = 0.71073 Å
a = 11.1089 (13) Å	Cell parameters from 1609 reflections
b = 8.7842 (10) Å	θ = 3.1–28.2°
c = 6.9077 (8) Å	µ = 13.75 mm^−1
β = 120.074 (2)°	T = 173 K
V = 583.33 (12) Å^3	Plate, colourless
Z = 2	0.08 × 0.08 × 0.03 mm

Data collection

Bruker APEXII CCD area-detector diffractometer	769 independent reflections
Radiation source: fine-focus sealed tube	683 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.048
φ and ω scans	θmax = 28.2°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Bruker, 2006)	h = −14→14
Tmin = 0.210, Tmax = 0.662	k = −10→11
2689 measured reflections	l = −9→9

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)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.085	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0389P)^2 + 1.911P] where P = (Fo^2 + 2Fc^2)/3
769 reflections	(Δ/σ)max < 0.001
34 parameters	Δρmax = 0.74 e Å^−3
0 restraints	Δρmin = −1.42 e Å^−3

Special details

Experimental. The crystal was made of many different layers so it was twinned. To solve this problem, we had to cut a very small plate (we couldn't even see it with the camera). This is why we measured a crystal that we were unable to index correctly for the absorption correction.

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	1.17185 (5)	0.0000	0.31107 (9)	0.03261 (19)
Br2	1.28193 (6)	0.0000	0.83699 (9)	0.0429 (2)
N1	1.0000	0.1319 (4)	0.5000	0.0230 (8)
B1	1.1096 (5)	0.0000	0.5364 (8)	0.0205 (9)
C1	1.0398 (4)	0.2347 (5)	0.6963 (9)	0.0449 (10)
H1A	1.1199	0.2969	0.7227	0.067*
H1C	1.0644	0.1731	0.8293	0.067*
H1B	0.9613	0.3012	0.6651	0.067*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0359 (3)	0.0390 (3)	0.0348 (3)	0.000	0.0266 (2)	0.000
Br2	0.0411 (3)	0.0391 (4)	0.0231 (3)	0.000	−0.0028 (2)	0.000
N1	0.0233 (18)	0.0197 (18)	0.0300 (19)	0.000	0.0164 (16)	0.000
B1	0.018 (2)	0.023 (2)	0.022 (2)	0.000	0.0107 (18)	0.000
C1	0.042 (2)	0.037 (2)	0.069 (3)	−0.0175 (17)	0.037 (2)	−0.032 (2)

Geometric parameters (Å, º)

Br1—B1	1.995 (5)	N1—B1	1.606 (4)
Br2—B1	1.998 (5)	B1—N1^ii	1.606 (4)
N1—C1	1.499 (4)	C1—H1A	0.9800
N1—C1^i	1.499 (4)	C1—H1C	0.9800
N1—B1^ii	1.606 (4)	C1—H1B	0.9800
C1—N1—C1^i	106.0 (5)	N1^ii—B1—Br2	114.8 (2)
C1—N1—B1^ii	115.7 (2)	N1—B1—Br2	114.8 (2)
C1^i—N1—B1^ii	115.8 (3)	Br1—B1—Br2	106.5 (2)
C1—N1—B1	115.8 (3)	N1—C1—H1A	109.5
C1^i—N1—B1	115.7 (2)	N1—C1—H1C	109.5
B1^ii—N1—B1	87.7 (3)	H1A—C1—H1C	109.5
N1^ii—B1—N1	92.3 (3)	N1—C1—H1B	109.5
N1^ii—B1—Br1	114.2 (2)	H1A—C1—H1B	109.5
N1—B1—Br1	114.2 (2)	H1C—C1—H1B	109.5

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1A···Br1^iii	0.98	3.02	3.982 (4)	167

Symmetry code: (iii) −x+5/2, −y+1/2, −z+1.