(E)-1,2-Bis(4-fluoro­phen­yl)ethane-1,2-dione

Fun, H.-K.; Kia, R.

doi:10.1107/S1600536808023350

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 64| Part 8| August 2008| Pages o1617-o1618

doi:10.1107/S1600536808023350

Open

access

(E)-1,2-Bis(4-fluorophenyl)ethane-1,2-dione

Hoong-Kun Fun ^a ^* and Reza Kia ^a ‡

^aX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
^*Correspondence e-mail: hkfun@usm.my

(Received 22 July 2008; accepted 24 July 2008; online 31 July 2008)

The title compound, C₁₄H₈F₂O₂, is a substituted benzil with an s-trans conformation of the dicarbonyl unit. This conformation is also shown by the O—C—C—O torsion angle of −110.65 (12)°. An unusual feature of the structure is the length, 1.536 (2) Å, of the central C—C bond connecting the carbonyl units, which is significantly longer than a normal Csp²—Csp² single bond. This is probably the result of decreasing the unfavourable vicinal dipole–dipole interactions by increasing the distance between the two electronegative O atoms [O⋯O = 3.1867 (12) Å] and allowing orbital overlap of the dione with the π system of the benzene rings. The dihedral angle between the aromatic rings is 64.74 (5)°. In the crystal structure, neighbouring molecules are linked together by weak intermolecular C—H⋯O (× 2) hydrogen bonds. In addition, the crystal structure is further stabilized by intermolecular π–π interactions with centroid–centroid distances in the range 3.6416 (6)–3.7150 (7) Å.

Related literature

For bond-length data, see Allen et al. (1987 ). For carbonyl–carbonyl interaction, see Allen et al. (1998 ). For related structures and applications see, for example: Kaftory & Rubin (1983 ); Frey et al. (1995 ); Crowley et al. (1983 ); More et al. (1987 ); Brown et al. (1965 ); Gabe et al. (1981 ); Kimura et al. (1979 ); Stevens & Dubois (1962 ); Shimizu & Bartlett (1976 ); Rubin (1978 ).

Experimental

Crystal data

C₁₄H₈F₂O₂
M_r = 246.20
Monoclinic, P 2₁ /c
a = 12.1351 (2) Å
b = 7.3500 (1) Å
c = 13.1572 (2) Å
β = 110.507 (1)°
V = 1099.16 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.12 mm⁻¹
T = 100.0 (1) K
0.39 × 0.30 × 0.28 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2005 ) T_min = 0.903, T_max = 0.967
14891 measured reflections
3489 independent reflections
2846 reflections with I > 2σ(I)
R_int = 0.022

Refinement

R[F² > 2σ(F²)] = 0.042
wR(F²) = 0.107
S = 1.06
3489 reflections
163 parameters
H-atom parameters constrained
Δρ_max = 0.39 e Å⁻³
Δρ_min = −0.21 e Å⁻³

Table 1
Selected centroid⋯centroid distances (Å)

Cg1⋯Cg1ⁱ	3.6416 (6)
Cg2⋯Cg2ⁱⁱ	3.7150 (7)
Symmetry codes: (i) -x+1, -y+2, -z; (ii) -x+2, -y+2, -z+1. Cg1 and Cg2 are the centroids of the C1–C6 and C9–C14 benzene rings, respectively.

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H2A⋯O1ⁱⁱⁱ	0.93	2.40	3.2648 (15)	155
C11—H11A⋯O2^iv	0.93	2.51	3.3098 (16)	145
Symmetry codes: (iii) x, y-1, z; (iv) $[x, -y+{\script{5\over 2}}, z+{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2; data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2003 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808023350/zl2128sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808023350/zl2128Isup2.hkl

checkCIF report

Comment top

Investigation of photophysical properties of α-dicarbonyls has focused on the intramolecular carbonyl group electronic interaction as a function of their geometrical relationship. In previous extensive studies of the photochemistry of these compounds (Stevens & Dubois, 1962; Shimizu & Bartlett, 1976), biacetyl and benzil were the exclusive experimental vehicles for photophysical study. The structure of vicinal di- and polycarbonyl compounds have been of interest for many years (Rubin, 1978; Crowley et al., 1983; Kaftory et al., 1983; Frey et al., 1995; Kimura et al., 1979). Only a limited amount of data has been gathered from solid-state configurations such as in single crystals or as inclusion dopants in host crystals.

In the title compound (I, Fig.1), bond lengths, bond angles, and torsion angles of the dicarbonyl unit deviate significantly from normal values (Allen et al., 1987) in order to minimize the repulsive interactions resulting from juxtaposition of dipolar carbonyl groups (Allen et al., 1987). The C7–C8 bond distance connecting the carbonyl units is longer than those in normal sp²–sp² single bonds, such as in butadiene. This is probably the result of decreasing the unfavourable vicinal dipole-dipole interactions. The dicarbonyl unit has an s-trans conformation as indicated by the torsion angle of O1–C7–C6–C5, and O2–C8–C9–C10 being -174.32 (11) and 174.49 (11)°, respectively. This conformation is substantiated by the torsion angle of O–C–C–O, being -110.65 (12)°. The overal effect is to maximize the distance between the two electronegative oxygen atoms [O1···O2 = 3.1867 (12) Å] and to allow orbital overlap of the dione with the π system of the benzene rings. The dihedral angle between two phenyl rings is 64.74 (5)°. In the crystal structure, neighbouring molecules are linked together by weak intermolecular C—H···O (2 ×) hydrogen bonds. The packing mode (Fig. 2) tends to be dominated by van der Waals close packing interactions and the preference for aligning the substituted phenyl rings parallel to each other along the c axis with centroid to centroid distances of the π rings of 3.6416 (6) to 3.7150 (7) Å.

Related literature top

For bond-length data, see Allen et al. (1987, 1998). For related structures and applications see, for example: Kaftory & Rubin, (1983); Frey et al. (1995); Crowley et al. (1983); More et al. (1987); Brown et al. (1965); Gabe et al. (1981); Kimura et al. (1979); Stevens & Dubois (1962); Shimizu & Bartlett (1976); Rubin (1978).

Experimental top

The synthetic method has been described earlier (Frey et al., 1995). Single crystals suitable for X-ray diffraction were obtained by evaporation of a methanol solution at room temperature.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2003).

Figures top

	Fig. 1. The molecular structure of (I) with atom labels and 50% probability ellipsoids for non-H atoms.
	Fig. 2. The crystal packing, showing parallel aligning of the benzene rings along the c axis. Intermolecular C—H···O interactions are shown as dashed lines.

(E)-1,2-Bis(4-fluorophenyl)ethane-1,2-dione top

Crystal data top

C₁₄H₈F₂O₂	F(000) = 504
M_r = 246.20	D_x = 1.488 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 6651 reflections
a = 12.1351 (2) Å	θ = 3.2–30.8°
b = 7.3500 (1) Å	µ = 0.12 mm⁻¹
c = 13.1572 (2) Å	T = 100 K
β = 110.507 (1)°	Block, pale-yellow
V = 1099.16 (3) Å³	0.39 × 0.30 × 0.28 mm
Z = 4

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	3489 independent reflections
Radiation source: fine-focus sealed tube	2846 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.022
ϕ and ω scans	θ_max = 31.0°, θ_min = 3.2°
Absorption correction: multi-scan (SADABS; Bruker, 2005)	h = −15→17
T_min = 0.903, T_max = 0.967	k = −8→10
14891 measured reflections	l = −18→18

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.107	H-atom parameters constrained
S = 1.06	w = 1/[σ²(F_o²) + (0.0458P)² + 0.3386P] where P = (F_o² + 2F_c²)/3
3489 reflections	(Δ/σ)_max = 0.001
163 parameters	Δρ_max = 0.39 e Å⁻³
0 restraints	Δρ_min = −0.21 e Å⁻³

Crystal data top

C₁₄H₈F₂O₂	V = 1099.16 (3) Å³
M_r = 246.20	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 12.1351 (2) Å	µ = 0.12 mm⁻¹
b = 7.3500 (1) Å	T = 100 K
c = 13.1572 (2) Å	0.39 × 0.30 × 0.28 mm
β = 110.507 (1)°

Data collection top

Bruker SMART APEXII CCD area-detector diffractometer	3489 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2005)	2846 reflections with I > 2σ(I)
T_min = 0.903, T_max = 0.967	R_int = 0.022
14891 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.042	0 restraints
wR(F²) = 0.107	H-atom parameters constrained
S = 1.06	Δρ_max = 0.39 e Å⁻³
3489 reflections	Δρ_min = −0.21 e Å⁻³
163 parameters

Special details top

Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment.

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 (Å²) top

	x	y	z	U_iso*/U_eq
F1	0.35237 (6)	0.66325 (10)	0.08245 (6)	0.03021 (18)
F2	1.21050 (6)	1.20663 (11)	0.59266 (6)	0.03299 (19)
O1	0.69635 (7)	1.33900 (11)	0.19570 (7)	0.0273 (2)
O2	0.85192 (7)	1.05531 (12)	0.12153 (7)	0.02583 (19)
C1	0.64396 (10)	0.85311 (15)	0.16653 (9)	0.0200 (2)
H1A	0.7218	0.8152	0.1869	0.024*
C2	0.55476 (10)	0.72510 (16)	0.14036 (9)	0.0217 (2)
H2A	0.5712	0.6012	0.1434	0.026*
C3	0.44035 (10)	0.78766 (16)	0.10962 (9)	0.0215 (2)
C4	0.41085 (10)	0.96950 (17)	0.10511 (9)	0.0223 (2)
H4A	0.3327	1.0060	0.0844	0.027*
C5	0.50092 (10)	1.09585 (16)	0.13226 (8)	0.0202 (2)
H5A	0.4836	1.2193	0.1304	0.024*
C6	0.61811 (9)	1.03855 (15)	0.16255 (8)	0.0183 (2)
C7	0.71259 (9)	1.17601 (15)	0.18983 (9)	0.0201 (2)
C8	0.83778 (9)	1.11508 (14)	0.20254 (9)	0.0195 (2)
C9	0.93465 (9)	1.14174 (14)	0.30709 (9)	0.0186 (2)
C10	0.91694 (10)	1.22467 (15)	0.39561 (9)	0.0206 (2)
H10A	0.8422	1.2644	0.3896	0.025*
C11	1.01017 (11)	1.24806 (15)	0.49231 (10)	0.0231 (2)
H11A	0.9995	1.3047	0.5514	0.028*
C12	1.11907 (10)	1.18496 (16)	0.49832 (9)	0.0230 (2)
C13	1.14030 (10)	1.09925 (16)	0.41347 (10)	0.0228 (2)
H13A	1.2149	1.0563	0.4212	0.027*
C14	1.04700 (9)	1.07948 (15)	0.31680 (9)	0.0204 (2)
H14A	1.0589	1.0245	0.2578	0.025*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
F1	0.0221 (3)	0.0307 (4)	0.0367 (4)	−0.0068 (3)	0.0089 (3)	−0.0029 (3)
F2	0.0255 (4)	0.0401 (5)	0.0272 (4)	−0.0061 (3)	0.0014 (3)	0.0002 (3)
O1	0.0255 (4)	0.0194 (4)	0.0371 (5)	0.0035 (3)	0.0110 (4)	0.0006 (3)
O2	0.0237 (4)	0.0296 (4)	0.0263 (4)	−0.0006 (3)	0.0114 (3)	−0.0042 (3)
C1	0.0174 (5)	0.0227 (5)	0.0199 (5)	0.0039 (4)	0.0064 (4)	0.0032 (4)
C2	0.0225 (5)	0.0202 (5)	0.0227 (5)	0.0026 (4)	0.0082 (4)	0.0026 (4)
C3	0.0189 (5)	0.0256 (6)	0.0200 (5)	−0.0022 (4)	0.0068 (4)	−0.0002 (4)
C4	0.0169 (5)	0.0291 (6)	0.0207 (5)	0.0041 (4)	0.0062 (4)	0.0011 (4)
C5	0.0199 (5)	0.0220 (5)	0.0190 (5)	0.0051 (4)	0.0070 (4)	0.0014 (4)
C6	0.0179 (5)	0.0207 (5)	0.0166 (4)	0.0024 (4)	0.0065 (4)	0.0016 (4)
C7	0.0192 (5)	0.0216 (5)	0.0200 (5)	0.0023 (4)	0.0075 (4)	0.0014 (4)
C8	0.0189 (5)	0.0162 (5)	0.0251 (5)	0.0003 (4)	0.0097 (4)	0.0009 (4)
C9	0.0184 (5)	0.0148 (5)	0.0238 (5)	−0.0002 (4)	0.0089 (4)	0.0014 (4)
C10	0.0199 (5)	0.0183 (5)	0.0264 (5)	0.0001 (4)	0.0118 (4)	0.0011 (4)
C11	0.0272 (6)	0.0203 (5)	0.0243 (5)	−0.0031 (4)	0.0121 (4)	−0.0010 (4)
C12	0.0215 (5)	0.0212 (5)	0.0240 (5)	−0.0046 (4)	0.0050 (4)	0.0033 (4)
C13	0.0177 (5)	0.0213 (5)	0.0302 (6)	0.0005 (4)	0.0093 (4)	0.0045 (4)
C14	0.0207 (5)	0.0172 (5)	0.0263 (5)	0.0013 (4)	0.0118 (4)	0.0020 (4)

Geometric parameters (Å, º) top

F1—C3	1.3551 (13)	C6—C7	1.4751 (15)
F2—C12	1.3536 (14)	C7—C8	1.5358 (15)
O1—C7	1.2209 (14)	C8—C9	1.4764 (15)
O2—C8	1.2193 (13)	C9—C10	1.3962 (15)
C1—C2	1.3836 (16)	C9—C14	1.4009 (14)
C1—C6	1.3955 (15)	C10—C11	1.3854 (17)
C1—H1A	0.9300	C10—H10A	0.9300
C2—C3	1.3818 (15)	C11—C12	1.3764 (17)
C2—H2A	0.9300	C11—H11A	0.9300
C3—C4	1.3795 (17)	C12—C13	1.3824 (17)
C4—C5	1.3825 (16)	C13—C14	1.3826 (16)
C4—H4A	0.9300	C13—H13A	0.9300
C5—C6	1.4005 (14)	C14—H14A	0.9300
C5—H5A	0.9300

Cg1···Cg1ⁱ	3.6416 (6)	Cg2···Cg2ⁱⁱ	3.7150 (7)

C2—C1—C6	120.58 (10)	O2—C8—C9	123.53 (10)
C2—C1—H1A	119.7	O2—C8—C7	116.53 (10)
C6—C1—H1A	119.7	C9—C8—C7	119.81 (9)
C3—C2—C1	117.70 (11)	C10—C9—C14	119.72 (10)
C3—C2—H2A	121.1	C10—C9—C8	122.02 (9)
C1—C2—H2A	121.1	C14—C9—C8	118.26 (9)
F1—C3—C4	118.28 (10)	C11—C10—C9	120.35 (10)
F1—C3—C2	118.08 (10)	C11—C10—H10A	119.8
C4—C3—C2	123.64 (11)	C9—C10—H10A	119.8
C3—C4—C5	118.03 (10)	C12—C11—C10	118.01 (10)
C3—C4—H4A	121.0	C12—C11—H11A	121.0
C5—C4—H4A	121.0	C10—C11—H11A	121.0
C4—C5—C6	120.24 (10)	F2—C12—C11	118.37 (11)
C4—C5—H5A	119.9	F2—C12—C13	118.00 (10)
C6—C5—H5A	119.9	C11—C12—C13	123.63 (11)
C1—C6—C5	119.80 (10)	C12—C13—C14	117.81 (10)
C1—C6—C7	120.96 (10)	C12—C13—H13A	121.1
C5—C6—C7	119.24 (10)	C14—C13—H13A	121.1
O1—C7—C6	123.95 (10)	C13—C14—C9	120.44 (10)
O1—C7—C8	117.05 (10)	C13—C14—H14A	119.8
C6—C7—C8	118.80 (9)	C9—C14—H14A	119.8

C6—C1—C2—C3	0.53 (16)	O1—C7—C8—C9	65.39 (14)
C1—C2—C3—F1	179.13 (9)	C6—C7—C8—C9	−119.59 (11)
C1—C2—C3—C4	−0.89 (17)	O2—C8—C9—C10	174.49 (11)
F1—C3—C4—C5	−179.60 (9)	C7—C8—C9—C10	−1.26 (15)
C2—C3—C4—C5	0.41 (17)	O2—C8—C9—C14	−6.17 (16)
C3—C4—C5—C6	0.42 (15)	C7—C8—C9—C14	178.08 (9)
C2—C1—C6—C5	0.26 (16)	C14—C9—C10—C11	0.97 (16)
C2—C1—C6—C7	−179.72 (10)	C8—C9—C10—C11	−179.71 (10)
C4—C5—C6—C1	−0.75 (15)	C9—C10—C11—C12	−0.93 (16)
C4—C5—C6—C7	179.23 (10)	C10—C11—C12—F2	−179.73 (10)
C1—C6—C7—O1	−174.32 (10)	C10—C11—C12—C13	−0.22 (17)
C5—C6—C7—O1	5.70 (16)	F2—C12—C13—C14	−179.18 (10)
C1—C6—C7—C8	11.03 (15)	C11—C12—C13—C14	1.31 (17)
C5—C6—C7—C8	−168.95 (9)	C12—C13—C14—C9	−1.24 (16)
O1—C7—C8—O2	−110.65 (12)	C10—C9—C14—C13	0.15 (16)
C6—C7—C8—O2	64.37 (13)	C8—C9—C14—C13	−179.20 (10)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2A···O1ⁱⁱⁱ	0.93	2.40	3.2648 (15)	155
C11—H11A···O2^iv	0.93	2.51	3.3098 (16)	145

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

Experimental details

Crystal data
Chemical formula	C₁₄H₈F₂O₂
M_r	246.20
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	12.1351 (2), 7.3500 (1), 13.1572 (2)
β (°)	110.507 (1)
V (Å³)	1099.16 (3)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.12
Crystal size (mm)	0.39 × 0.30 × 0.28

Data collection
Diffractometer	Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2005)
T_min, T_max	0.903, 0.967
No. of measured, independent and observed [I > 2σ(I)] reflections	14891, 3489, 2846
R_int	0.022
(sin θ/λ)_max (Å⁻¹)	0.724

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.042, 0.107, 1.06
No. of reflections	3489
No. of parameters	163
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.39, −0.21

Computer programs: APEX2 (Bruker, 2005), SAINT (Bruker, 2005), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2003).

Selected interatomic distances (Å) top

Cg1···Cg1ⁱ

3.6416 (6)

Cg2···Cg2ⁱⁱ

3.7150 (7)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2A···O1ⁱⁱⁱ	0.9300	2.4000	3.2648 (15)	155.00
C11—H11A···O2^iv	0.9300	2.5100	3.3098 (16)	145.00

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

Footnotes

‡Additional correspondance author, e-mail: zsrkk@yahoo.com.

Acknowledgements

HKF and RK thank the Malaysian Government and Universiti Sains Malaysia for the Science Fund grant No. 305/PFIZIK/613312. RK thanks Universiti Sains Malaysia for the award of a post-doctoral research fellowship.

References

Allen, F. H., Baalham, C. A., Lommerse, J. P. M. & Raithby, P. R. (1998). Acta Cryst. B54, 320–329. Web of Science CrossRef CAS IUCr Journals Google Scholar
Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1–S19. CrossRef Web of Science Google Scholar
Brown, C. J. & Sadanaga, R. (1965). Acta Cryst. 18, 158–164. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Bruker (2005). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Crowley, J. I., Balanson, R. D. & Mayerle, J. J. (1983). J. Am. Chem. Soc. 105, 6416–6422. CSD CrossRef CAS Web of Science Google Scholar
Frey, J., Faraggi, E., Rappoport, Z. & Kaftory, M. (1995). J. Chem. Soc. Perkin Trans. 2, pp. 1745–1748. CrossRef Google Scholar
Gabe, E. J., Le Page, Y., Lee, F. L. & Barclay, L. R. C. (1981). Acta Cryst. B37, 197–200. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Kaftory, M. & Rubin, M. B. (1983). J. Chem. Soc. Perkin Trans. 2, pp. 149–154. CrossRef Google Scholar
Kimura, M., McCluney, R. E. & Watson, W. H. (1979). Acta Cryst. B35, 483–484. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
More, M., Odou, G. & Lefebvre, J. (1987). Acta Cryst. B43, 398–405. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Rubin, M. B. (1978). Chem. Rev. 78, 1121–1164. CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Shimizu, N. & Bartlett, P. D. (1976). J. Am. Chem. Soc. 98, 4193–4200. CrossRef CAS Web of Science Google Scholar
Spek, A. L. (2003). J. Appl. Cryst. 36, 7–13. Web of Science CrossRef CAS IUCr Journals Google Scholar
Stevens, B. & Dubois, J. T. (1962). J. Chem. Soc. pp. 2813–2815. CrossRef Web of Science Google Scholar