2,7-Bis(bromo­meth­yl)-9,9′-diethyl­fluorene

The asymmetric unit of the title compound, C₁₉H₂₀Br₂, contains one half-mol­ecule, with the other half generated by a crystallographic twofold rotation axis passing through the Csp³ ring atom and the mid-point of the Csp²—Csp² single bond of the five-membered ring. The fluorene ring system is essentially planar. The non-H atoms of the two symmetry-related ethyl groups are coplanar. This plane and the plane of the fluorene ring system are perpendicular to one another, with a dihedral angle of 89.8 (1)°. The mol­ecules are linked into zigzag layers parallel to the ab plane by C—H...Br hydrogen bonds. The adjacent layers are cross-linked by C—H...π inter­actions and Br...Br short contacts [3.3774 (3) Å] into a three-dimensional framework.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.042
• wR factor = 0.140
• Data-to-parameter ratio = 58.4

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT431_ALERT_2_B Short Inter HL..A Contact  Br1    ..  Br1     ..       3.38 Ang.

Alert level C
PLAT061_ALERT_3_C Tmax/Tmin Range Test RR' too Large .............       0.82
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.59

Alert level G
ABSTM02_ALERT_3_G  When printed, the submitted absorption T values will be
            replaced by the scaled T values. Since the ratio of scaled T's
            is identical to the ratio of reported T values, the scaling
            does not imply a change to the absorption corrections used in
            the study.
            Ratio of Tmax expected/reported      0.590
            Tmax scaled      0.145 Tmin scaled      0.063

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

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 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
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Fluorene and its polymeric derivatives have been used as laser-generating (Bazyl, 1986) or photo-active fluorescent materials (Johansson et al., 2001). Homopolymers and copolymers of fluorene derivatives have emerged as the most attractive blue-emitting materials due to their high effiency and excellent thermal stability (Lee & Tsuysui, 2000). Fluorene derivatives can also be used as potential anti-HIV and anticancer drugs (Abdel-Rahman et al., 1994). In view of this wide range of activities associated with fluorene derivatives, the X-ray crystal structure determination of 2,7-bis(bromomethyl)-9,9-diethylfluorene was undertaken.

The asymmetric unit of the title compound contains one half-molecule (Fig.1). The other half is generated by a crystallographic twofold axis of symmetry; this axis passes through the atom C8 and the mid-point of the C6—C6A bond [symmetry code: (A) -x, y, 1/2 - z] and is parallel to the b axis of the unit cell.

The C—C distances in the benzene ring lie in the range 1.388 (2)–1.403 (2) Å. The C6—C6A distance of 1.459 (3) Å is longer than the normal Csp²—Csp² bond distance, but comparable to that observed in similar structures (McFarlane et al., 2005, 2006; Leclerc et al., 1998; Hu et al., 2005, 2006). The angles subtended at C8 lie in the range 100.9 (2)–112.46 (8)°, deviating significantly from the ideal tetrahedral angle of ca 109.5°.

The three fused rings are essentially coplanar, the dihedral angles formed by the five-membered ring with the two benzene rings being 0.46 (7)°. The non-hydrogen atoms of the two symmetry-related ethyl groups are coplanar, and this plane is perpendicular to the plane of the fused-ring system [dihedral angle 89.8 (1)°].

In the crystal structure the molecules are linked by C4—H4···Br1ⁱ [symmetry code: (i) 1/2 - x, 1/2 + y, z] hydrogen bonds into zigzag layers parallel to the ab plane. Such a layer, viewed approximately along the c axis, is shown in Fig.2. The adjacent layers are cross-linked by C—H···π hydrogen bonds (Table 1) involving the C1—C6 benzene ring (centroid Cg1) and Br1···Br1(1 - x, 1 - y, 1 - z) short contacts [3.3774 (3) Å] into a three-dimensional framework (Fig.3).

Related literature

For general background, see: Abdel-Rahman et al. (1994); Bazyl (1986); Johansson et al. (2001); Lee & Tsuysui (2000). For related structures, see: Hu et al. (2005, 2006); Leclerc et al. (1998); McFarlane et al. (2005, 2006). Cg1 is the centroid of the C1–C6 benzene ring.

S2. Experimental

To prepare the title compound, a mixture of 9,9-diethylfluorene (1.11 g, 5 mmol), paraformaldehyde (0.33 g, 11.0 mmol) and 33% HBr solution in acetic acid (10 ml) was heated at 333–343 K for 20 h. The precipitate obtained after cooling the reaction mixture was collected by filtration and washed with water and dried in vacuo. The crude product was recrystallized from hexane.

S3. Refinement

H atoms were positioned geometrically and allowed to ride on their parent atoms, with C—H = 0.95–0.99 Å and U_iso(H) = xU_eq(carrier atom), where x = 1.5 for methyl C and 1.2 for all other C atoms. The highest residual electron density peak is located 0.70 Å from atom Br1 and the deepest hole is located 0.17 Å from atom Br1.

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 1998); program(s) used to refine structure: SHELXTL (Sheldrick, 1998); molecular graphics: SHELXTL (Sheldrick, 1998); software used to prepare material for publication: SHELXTL (Sheldrick, 1998) and PLATON (Spek, 2003).

Figures

	Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atomic numbering. Atoms labelled with the suffix A are generated by the symmetry operation (-x, y, 1/2 - z).
	Fig. 2. A C—H···Br hydrogen-bonded (dashed lines) layer, viewed approximately along the c axis. H atoms not involved in hydrogen bonding have been omitted.
	Fig. 3. The crystal packing of the title compound, viewed approximately along the b axis. Dashed lines indicate C—H···Br and Br···Br interactions while the dotted lines denote C—H···π interactions. H atoms not involved in hydrogen bonding have been omitted.

2,7-Bis(bromomethyl)-9,9'-diethylfluorene

Crystal data

C19H20Br2	F(000) = 816
Mr = 408.17	Dx = 1.617 Mg m^−3
Orthorhombic, Pbcn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2n 2ab	Cell parameters from 6378 reflections
a = 10.9244 (2) Å	θ = 2.3–35.8°
b = 8.8066 (2) Å	µ = 4.83 mm^−1
c = 17.4316 (4) Å	T = 100 K
V = 1677.04 (6) Å^3	Block, yellow
Z = 4	0.58 × 0.49 × 0.40 mm

Data collection

Bruker SMART APEX II CCD area-detector diffractometer	5609 independent reflections
Radiation source: fine-focus sealed tube	3854 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.045
Detector resolution: 8.33 pixels mm^-1	θmax = 41.3°, θmin = 3.0°
ω scans	h = −20→20
Absorption correction: multi-scan (SADABS; Bruker, 2005)	k = −15→16
Tmin = 0.106, Tmax = 0.246	l = −32→32
69232 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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.140	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0752P)^2 + 0.7685P] where P = (Fo^2 + 2Fc^2)/3
5609 reflections	(Δ/σ)max = 0.001
96 parameters	Δρmax = 1.23 e Å^−3
0 restraints	Δρmin = −1.42 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	0.348167 (16)	0.49225 (2)	0.517755 (10)	0.02468 (6)
C1	0.04152 (13)	0.38455 (16)	0.31212 (8)	0.0172 (2)
C2	0.09122 (14)	0.35223 (17)	0.38370 (8)	0.0189 (2)
H2	0.1030	0.2499	0.3993	0.023*
C3	0.12362 (15)	0.47126 (18)	0.43244 (9)	0.0196 (2)
C4	0.10699 (15)	0.62203 (18)	0.40870 (9)	0.0220 (3)
H4	0.1294	0.7025	0.4422	0.026*
C5	0.05831 (15)	0.65573 (17)	0.33714 (9)	0.0218 (3)
H5	0.0474	0.7581	0.3214	0.026*
C6	0.02571 (13)	0.53575 (17)	0.28861 (9)	0.0180 (2)
C7	0.17355 (15)	0.4393 (2)	0.51043 (9)	0.0224 (3)
H7A	0.1629	0.3302	0.5223	0.027*
H7B	0.1269	0.4983	0.5489	0.027*
C8	0.0000	0.2745 (2)	0.2500	0.0177 (3)
C9	0.10677 (16)	0.17259 (18)	0.22344 (9)	0.0219 (3)
H9A	0.1343	0.1105	0.2675	0.026*
H9B	0.0759	0.1021	0.1837	0.026*
C10	0.21637 (17)	0.2570 (2)	0.19130 (10)	0.0278 (3)
H10A	0.2821	0.1845	0.1800	0.042*
H10B	0.2453	0.3312	0.2290	0.042*
H10C	0.1926	0.3096	0.1441	0.042*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.02126 (9)	0.02858 (10)	0.02421 (9)	0.00002 (5)	−0.00302 (5)	−0.00119 (5)
C1	0.0166 (5)	0.0190 (5)	0.0158 (5)	0.0002 (4)	−0.0003 (4)	0.0001 (4)
C2	0.0199 (6)	0.0211 (6)	0.0159 (5)	0.0000 (4)	−0.0009 (4)	0.0002 (4)
C3	0.0177 (5)	0.0247 (6)	0.0165 (5)	−0.0014 (5)	−0.0005 (4)	−0.0021 (4)
C4	0.0223 (6)	0.0223 (6)	0.0214 (6)	−0.0019 (5)	−0.0023 (5)	−0.0039 (5)
C5	0.0231 (6)	0.0189 (5)	0.0234 (6)	−0.0014 (5)	−0.0028 (5)	−0.0015 (5)
C6	0.0175 (5)	0.0184 (5)	0.0180 (5)	0.0000 (4)	−0.0011 (4)	−0.0010 (4)
C7	0.0205 (6)	0.0288 (7)	0.0179 (6)	−0.0027 (5)	−0.0012 (5)	−0.0016 (5)
C8	0.0204 (8)	0.0184 (7)	0.0144 (7)	0.000	0.0005 (6)	0.000
C9	0.0266 (7)	0.0224 (6)	0.0167 (6)	0.0056 (5)	0.0014 (5)	0.0006 (4)
C10	0.0223 (6)	0.0363 (9)	0.0247 (7)	0.0069 (6)	0.0028 (6)	0.0037 (6)

Geometric parameters (Å, º)

Br1—C7	1.9679 (17)	C6—C6^i	1.459 (3)
C1—C2	1.390 (2)	C7—H7A	0.99
C1—C6	1.404 (2)	C7—H7B	0.99
C1—C8	1.5226 (19)	C8—C1^i	1.5226 (19)
C2—C3	1.395 (2)	C8—C9^i	1.5426 (19)
C2—H2	0.95	C8—C9	1.5426 (19)
C3—C4	1.403 (2)	C9—C10	1.516 (3)
C3—C7	1.492 (2)	C9—H9A	0.99
C4—C5	1.388 (2)	C9—H9B	0.99
C4—H4	0.95	C10—H10A	0.98
C5—C6	1.400 (2)	C10—H10B	0.98
C5—H5	0.95	C10—H10C	0.98
C2—C1—C6	120.28 (13)	C3—C7—H7B	109.3
C2—C1—C8	128.63 (13)	Br1—C7—H7B	109.3
C6—C1—C8	111.08 (12)	H7A—C7—H7B	108.0
C1—C2—C3	119.47 (14)	C1—C8—C1^i	100.90 (16)
C1—C2—H2	120.3	C1—C8—C9^i	112.46 (8)
C3—C2—H2	120.3	C1^i—C8—C9^i	111.01 (8)
C2—C3—C4	119.92 (14)	C1—C8—C9	111.01 (8)
C2—C3—C7	120.41 (15)	C1^i—C8—C9	112.46 (8)
C4—C3—C7	119.66 (14)	C9^i—C8—C9	108.88 (17)
C5—C4—C3	121.14 (14)	C10—C9—C8	115.02 (14)
C5—C4—H4	119.4	C10—C9—H9A	108.5
C3—C4—H4	119.4	C8—C9—H9A	108.5
C4—C5—C6	118.63 (14)	C10—C9—H9B	108.5
C4—C5—H5	120.7	C8—C9—H9B	108.5
C6—C5—H5	120.7	H9A—C9—H9B	107.5
C5—C6—C1	120.55 (14)	C9—C10—H10A	109.5
C5—C6—C6^i	130.98 (9)	C9—C10—H10B	109.5
C1—C6—C6^i	108.47 (8)	H10A—C10—H10B	109.5
C3—C7—Br1	111.64 (11)	C9—C10—H10C	109.5
C3—C7—H7A	109.3	H10A—C10—H10C	109.5
Br1—C7—H7A	109.3	H10B—C10—H10C	109.5
C6—C1—C2—C3	0.9 (2)	C8—C1—C6—C6^i	−0.10 (19)
C8—C1—C2—C3	179.90 (12)	C2—C3—C7—Br1	110.20 (15)
C1—C2—C3—C4	−0.6 (2)	C4—C3—C7—Br1	−71.06 (18)
C1—C2—C3—C7	178.13 (14)	C2—C1—C8—C1^i	−179.00 (18)
C2—C3—C4—C5	0.1 (2)	C6—C1—C8—C1^i	0.04 (7)
C7—C3—C4—C5	−178.62 (15)	C2—C1—C8—C9^i	62.65 (18)
C3—C4—C5—C6	0.0 (2)	C6—C1—C8—C9^i	−118.31 (14)
C4—C5—C6—C1	0.3 (2)	C2—C1—C8—C9	−59.61 (18)
C4—C5—C6—C6^i	−179.5 (2)	C6—C1—C8—C9	119.43 (14)
C2—C1—C6—C5	−0.8 (2)	C1—C8—C9—C10	−58.97 (16)
C8—C1—C6—C5	−179.91 (12)	C1^i—C8—C9—C10	53.24 (17)
C2—C1—C6—C6^i	179.03 (15)	C9^i—C8—C9—C10	176.71 (16)

Symmetry code: (i) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4···Br1^ii	0.95	2.88	3.8058 (16)	164
C7—H7B···Cg1^iii	0.99	2.71	3.5589 (17)	144

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