Pressure-frozen benzene I revisited

The crystal structure of benzene, C₆H₆, in situ pressure-frozen in phase I, has been determined by X-ray diffraction at 0.30, 0.70 and 1.10 GPa, and 296 K. The molecular aggregation within phase I is consistent with van der Waals contacts and electrostatic attraction of the positive net atomic charges at the H atoms with the negative net charges of the C atoms. The C—H...aromatic ring centre contacts are the most prominent feature of the two experimentaly determined benzene crystal structures in phases I and III, whereas no stacking of the molecules has been observed. This specific crystal packing is a likely reason for the exceptionally high polymerization pressure of benzene. The changes of molecular arrangement within phase I on elevating the pressure and lowering the temperature are analogous.

Computing details

For all compounds, data collection: CrysAlis CCD 1.171.23 beta (Oxford Diffraction Poland, 2004); cell refinement: CrysAlis RED 1.171.24 beta (Oxford Diffraction Poland, 2004); data reduction: CrysAlis RED 1.171.24 beta (Oxford Diffraction Poland, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).

Figures

(I) benzene

Crystal data

C6H6	The unit-cell dimensions corrected for the effect of the gasket-shadowing: Katrusiak Andrzej - being prepared for publication
Mr = 78.11	Dx = 1.139 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
a = 7.243 (3) Å	Cell parameters from 249 reflections
b = 9.310 (17) Å	θ = 4.7–23.1°
c = 6.756 (3) Å	µ = 0.06 mm^−1
V = 455.6 (9) Å^3	T = 296 K
Z = 4	, colourless
F(000) = 168	0.1 mm (radius)

Data collection

KM4-CCD diffractometer	48 independent reflections
Radiation source: fine-focus sealed tube	48 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.145
Detector resolution: 16.4 pixels mm^-1	θmax = 23.1°, θmin = 4.7°
HP ω scans – for more details see: A. Budzianowski, A. Katrusiak in High–Pressure Crystallography (Eds.: A. Katrusiak, P. F. McMillan), Dordrecht: Kluwer Acad. Publ., 2004 pp.157–168	h = −7→6
Absorption correction: integration Crystal absorption, DAC absorption and gasket shadowing absorption has been applied A. Katrusiak, Z. Kristallogr. 2004, 219, 461-467	k = −5→6
Tmin = 0.481, Tmax = 0.919	l = −6→5
293 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.132	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.295	w = 1/[σ^2(Fo^2) + (0.0508P)^2 + 19.4433P] where P = (Fo^2 + 2Fc^2)/3
S = 1.30	(Δ/σ)max < 0.001
48 reflections	Δρmax = 0.17 e Å^−3
13 parameters	Δρmin = −0.20 e Å^−3
0 restraints	Extinction correction: SHELXL
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.02 (7)

Special details

Experimental. high-pressure measurement at 0.30 (5) GPa - the high pressure benzene I

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
C1	−0.052 (4)	0.146 (7)	0.019 (5)	0.030 (11)*
H1	−0.0831	0.2424	0.0322	0.036*
C2	0.087 (4)	0.083 (7)	0.135 (6)	0.026 (11)*
H2	0.1456	0.1398	0.2295	0.032*
C3	0.141 (5)	−0.058 (7)	0.115 (6)	0.037 (12)*
H3	0.2377	−0.0940	0.1911	0.045*

Geometric parameters (Å, º)

C1—C3^i	1.38 (5)	C2—H2	0.9300
C1—C2	1.40 (4)	C3—C1^i	1.38 (5)
C1—H1	0.9300	C3—H3	0.9300
C2—C3	1.38 (8)
C3^i—C1—C2	117 (5)	C3—C2—H2	118.4
C3^i—C1—H1	121.4	C1^i—C3—C2	120 (4)
C2—C1—H1	121.4	C1^i—C3—H3	120.1
C1—C2—C3	123 (4)	C2—C3—H3	120.1
C1—C2—H2	118.4
C3^i—C1—C2—C3	2 (7)	C1—C2—C3—C1^i	−2 (7)

Symmetry code: (i) −x, −y, −z.

(II) benzene

Crystal data

C6H6	The unit-cell dimensions corrected for the effect of the gasket-shadowing: Katrusiak Andrzej - being prepared for publication
Mr = 78.11	Dx = 1.157 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
a = 7.287 (6) Å	Cell parameters from 376 reflections
b = 9.20 (2) Å	θ = 4.7–29.6°
c = 6.688 (9) Å	µ = 0.07 mm^−1
V = 448.4 (12) Å^3	T = 296 K
Z = 4	, colourless
F(000) = 168	0.1 mm (radius)

Data collection

KM4-CCD diffractometer	179 independent reflections
Radiation source: fine-focus sealed tube	94 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.132
Detector resolution: 16.4 pixels mm^-1	θmax = 29.6°, θmin = 4.7°
HP ω scans – for more details see: A. Budzianowski, A. Katrusiak in High–Pressure Crystallography (Eds.: A. Katrusiak, P. F. McMillan), Dordrecht: Kluwer Acad. Publ., 2004 pp.157–168	h = −9→9
Absorption correction: integration Crystal absorption, DAC absorption and gasket shadowing absorption has been applied A. Katrusiak, Z. Kristallogr. 2004, 219, 461-467	k = −9→8
Tmin = 0.477, Tmax = 0.865	l = −7→7
1167 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)] = 0.053	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.136	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ^2(Fo^2) + (0.060P)^2 + 0.030P] where P = (Fo^2 + 2Fc^2)/3
179 reflections	(Δ/σ)max < 0.001
37 parameters	Δρmax = 0.11 e Å^−3
0 restraints	Δρmin = −0.09 e Å^−3

Special details

Experimental. high-pressure measurement at 0.70 (5) GPa - the high pressure of benzene I

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
C1	−0.0537 (8)	0.1425 (9)	0.0097 (12)	0.037 (2)
H1	−0.085 (6)	0.246 (7)	0.034 (8)	0.044*
C2	0.0840 (7)	0.0924 (10)	0.1373 (10)	0.040 (2)
H2	0.140 (6)	0.156 (6)	0.219 (8)	0.048*
C3	0.1343 (7)	−0.0521 (9)	0.1235 (12)	0.044 (2)
H3	0.220 (6)	−0.080 (6)	0.204 (9)	0.052*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.039 (3)	0.028 (8)	0.043 (6)	0.005 (4)	0.002 (4)	0.002 (5)
C2	0.034 (4)	0.060 (7)	0.025 (6)	0.005 (4)	−0.005 (3)	−0.001 (4)
C3	0.043 (4)	0.048 (7)	0.039 (6)	0.002 (5)	−0.007 (4)	0.006 (5)

Geometric parameters (Å, º)

C1—C3^i	1.353 (10)	C2—H2	0.90 (5)
C1—C2	1.396 (8)	C3—C1^i	1.353 (10)
C1—H1	0.99 (6)	C3—H3	0.86 (5)
C2—C3	1.382 (10)
C3^i—C1—C2	120.8 (8)	C1—C2—H2	119 (4)
C3^i—C1—H1	127 (3)	C1^i—C3—C2	121.4 (7)
C2—C1—H1	113 (3)	C1^i—C3—H3	123 (4)
C3—C2—C1	117.9 (7)	C2—C3—H3	116 (4)
C3—C2—H2	123 (4)
C3^i—C1—C2—C3	−0.2 (10)	C1—C2—C3—C1^i	0.2 (10)

Symmetry code: (i) −x, −y, −z.

(III) benzene

Crystal data

C6H6	The unit-cell dimensions corrected for the effect of the gasket-shadowing: Katrusiak Andrzej - being prepared for publication
Mr = 78.11	Dx = 1.205 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
a = 7.221 (4) Å	Cell parameters from 530 reflections
b = 9.05 (2) Å	θ = 4.8–29.4°
c = 6.590 (5) Å	µ = 0.07 mm^−1
V = 430.65 (10) Å^3	T = 296 K
Z = 4	, colourless
F(000) = 168	0.1 mm (radius)

Data collection

KM4-CCD diffractometer	126 independent reflections
Radiation source: fine-focus sealed tube	108 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.151
Detector resolution: 16.4 pixels mm^-1	θmax = 29.4°, θmin = 4.8°
HP ω scans – for more details see: A. Budzianowski, A. Katrusiak in High–Pressure Crystallography (Eds.: A. Katrusiak, P. F. McMillan), Dordrecht: Kluwer Acad. Publ., 2004 pp.157–168	h = −9→9
Absorption correction: integration Crystal absorption, DAC absorption and gasket shadowing absorption has been applied A. Katrusiak, Z. Kristallogr. 2004, 219, 461-467	k = −5→5
Tmin = 0.479, Tmax = 0.850	l = −8→8
1400 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)] = 0.142	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.248	H atoms treated by a mixture of independent and constrained refinement
S = 1.01	w = 1/[σ^2(Fo^2) + (0.P)^2 + 7.984P] where P = (Fo^2 + 2Fc^2)/3
126 reflections	(Δ/σ)max < 0.001
13 parameters	Δρmax = 0.13 e Å^−3
0 restraints	Δρmin = −0.12 e Å^−3

Special details

Experimental. high-pressure measurement at 1.10 (5) GPa - the high pressure of benzene I

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
C1	−0.0565 (15)	0.145 (3)	0.0049 (19)	0.040 (4)*
H1	−0.0920	0.2438	0.0067	0.048*
C2	0.0835 (13)	0.096 (2)	0.1399 (15)	0.021 (3)*
H2	0.1369	0.1585	0.2348	0.025*
C3	0.1374 (18)	−0.053 (3)	0.123 (2)	0.048 (5)*
H3	0.2329	−0.0880	0.2049	0.057*

Geometric parameters (Å, º)

C1—C3^i	1.32 (2)	C2—H2	0.9300
C1—C2	1.419 (16)	C3—C1^i	1.32 (2)
C1—H1	0.9300	C3—H3	0.9300
C2—C3	1.41 (3)
C3^i—C1—C2	121 (2)	C3—C2—H2	121.6
C3^i—C1—H1	119.4	C1^i—C3—C2	122.0 (16)
C2—C1—H1	119.4	C1^i—C3—H3	119.0
C1—C2—C3	116.8 (14)	C2—C3—H3	119.0
C1—C2—H2	121.6
C3^i—C1—C2—C3	3 (2)	C1—C2—C3—C1^i	−3 (2)

Symmetry code: (i) −x, −y, −z.