Isobaric and isochoric freezing of CH₂BrCl and isostructural relations between CH₂Cl₂, CH₂Br₂ and CH₂BrCl

Bromochloromethane, CH₂BrCl, has been temperature-frozen and in situ pressure-frozen and the structure determined by X-ray diffraction at low temperatures of 170 and 100 K at ambient pressure (0.10 MPa), and at high pressures of 1.04 and 1.72 GPa at room temperature (295 K). CH₂BrCl exhibits a remarkable polymorphism: at low temperature it crystallizes in the monoclinic space group C2/c (phase I), isostructural to the crystals of CH₂Br₂. The pressure-frozen crystal of CH₂BrCl is orthorhombic, space group Pbcn, and is isostructural to the crystal of CH₂Cl₂. In both phases I and II the Br and Cl atoms are substitutionally disordered. The freezing temperatures and pressures of simple dihalomethanes have been correlated to their molecular weight and halogen... halogen distances. Calculated electrostatic potential surfaces have been related to the different crystal packing of dihalomethanes investigated.

Computing details

For all compounds, data collection: CrysAlis CCD (Oxford Diffraction, 2004); cell refinement: CrysAlis RED (Oxford Diffraction, 2004). Data reduction: CrysAlis RED (Oxford Diffraction, 2004) for cbm_170K, cbm_100K; CrysAlis RED (Oxford Diffraction, 2004); REDSHABS (Katrusiak, A. 2003) for cbm_1.04GPa, cbm_1.72GPa. Program(s) used to solve structure: SHELXS97 (Sheldrick, 1990) for cbm_170K, cbm_100K; SHELXS–97 (Sheldrick, 1997) for cbm_1.04GPa, cbm_1.72GPa. Program(s) used to refine structure: SHELXL97 (Sheldrick, 1997) for cbm_170K, cbm_100K; SHELXL–97 (Sheldrick, 1997) for cbm_1.04GPa, cbm_1.72GPa. For all compounds, molecular graphics: X-SEED 2.0; software used to prepare material for publication: SHELXL–97 (Sheldrick, 1997).

Figures

(cbm_170K) bromochloromethane

Crystal data

CH2BrCl	Dx = 2.357 Mg m^−3
Mr = 129.39	Melting point: 185 K
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.959 (2) Å	Cell parameters from 1010 reflections
b = 4.4531 (9) Å	θ = 3.0–29.1°
c = 14.873 (3) Å	µ = 11.73 mm^−1
β = 112.96 (3)°	T = 170 K
V = 729.3 (3) Å^3	Irregular, colourless
Z = 8	0.12 × 0.12 × 0.10 mm
F(000) = 480

Data collection

KM-4 CCD diffractometer	909 independent reflections
Radiation source: fine-focus sealed tube	643 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.109
ω–scans	θmax = 29.1°, θmin = 3.0°
Absorption correction: multi-scan Correction for absorption was made using XEMP (SHELXTL, Sheldrick (1990)).	h = −15→16
Tmin = 0.22, Tmax = 0.32	k = −4→5
2422 measured reflections	l = −20→19

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)] = 0.066	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.172	w = 1/[σ^2(Fo^2) + (0.0777P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.15	(Δ/σ)max = 0.009
909 reflections	Δρmax = 0.83 e Å^−3
36 parameters	Δρmin = −0.66 e Å^−3
6 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.036 (4)

Special details

Experimental. Data were collected at ambient pressure (100 kPa) and 170 K with the crystal obtained by the in situ low-temperature crystallization technique.

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	Occ. (<1)
Br1	0.09023 (3)	0.6643 (2)	0.13228 (7)	0.0531 (5)	0.508 (3)
Cl1	0.09023 (3)	0.6643 (2)	0.13228 (7)	0.0531 (5)	0.492 (3)
Br2	0.34640 (3)	0.6410 (2)	0.13258 (7)	0.0495 (5)	0.492 (3)
Cl2	0.34640 (3)	0.6410 (2)	0.13258 (7)	0.0495 (5)	0.508 (3)
C1	0.2014 (6)	0.43217 (10)	0.1066 (2)	0.057 (2)
H1	0.16979 (17)	0.3694 (12)	0.0388 (4)	0.069*
H2	0.22013 (17)	0.2511 (2)	0.1460 (3)	0.069*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0468 (7)	0.0539 (7)	0.0632 (8)	−0.0041 (4)	0.0265 (5)	−0.0092 (4)
Cl1	0.0468 (7)	0.0539 (7)	0.0632 (8)	−0.0041 (4)	0.0265 (5)	−0.0092 (4)
Br2	0.0369 (6)	0.0517 (7)	0.0577 (8)	0.0020 (4)	0.0159 (5)	0.0027 (4)
Cl2	0.0369 (6)	0.0517 (7)	0.0577 (8)	0.0020 (4)	0.0159 (5)	0.0027 (4)
C1	0.066 (5)	0.026 (3)	0.085 (5)	0.003 (3)	0.034 (4)	−0.007 (3)

Geometric parameters (Å, º)

Br1—C1	1.837 (6)	Br2—C1	1.871 (6)
Cl1—C1	1.837 (6)	Cl2—C1	1.871 (6)
Cl1—C1—Br1	0.00 (5)	Cl1—C1—Br2	111.41 (8)
Cl1—C1—Cl2	111.41 (8)	Br1—C1—Br2	111.41 (8)
Br1—C1—Cl2	111.41 (8)	Cl2—C1—Br2	0.00 (8)

(cbm_100K) bromochloromethane

Crystal data

CH2BrCl	Dx = 2.422 Mg m^−3
Mr = 129.39	Melting point: 185 K
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.874 (2) Å	Cell parameters from 1948 reflections
b = 4.4224 (9) Å	θ = 3.0–29.7°
c = 14.582 (3) Å	µ = 12.05 mm^−1
β = 112.04 (3)°	T = 100 K
V = 709.8 (2) Å^3	Irregular, colourless
Z = 8	0.12 × 0.12 × 0.10 mm
F(000) = 480

Data collection

KM-4 CCD diffractometer	923 independent reflections
Radiation source: fine-focus sealed tube	784 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.078
ω–scans	θmax = 29.7°, θmin = 3.0°
Absorption correction: multi-scan Correction for absorption was made using XEMP (SHELXTL, Sheldrick (1990)).	h = −16→15
Tmin = 0.22, Tmax = 0.32	k = −4→6
3122 measured reflections	l = −19→19

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)] = 0.051	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.128	w = 1/[σ^2(Fo^2) + (0.0553P)^2 + 4.5134P] where P = (Fo^2 + 2Fc^2)/3
S = 1.12	(Δ/σ)max < 0.001
923 reflections	Δρmax = 1.51 e Å^−3
36 parameters	Δρmin = −0.72 e Å^−3
6 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0023 (9)

Special details

Experimental. Data were collected at ambient pressure (100 kPa) and 100 K with the crystal obtained by the in situ low-temperature crystallization technique.

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	Occ. (<1)
Br1	0.08668 (3)	0.67376 (15)	0.13130 (5)	0.0279 (3)	0.475 (3)
Cl1	0.08668 (3)	0.67376 (15)	0.13130 (5)	0.0279 (3)	0.525 (3)
Br2	0.34594 (3)	0.65355 (15)	0.13301 (5)	0.0279 (3)	0.525 (3)
Cl2	0.34594 (3)	0.65355 (15)	0.13301 (5)	0.0279 (3)	0.475 (3)
C1	0.2026 (4)	0.43547 (16)	0.10799 (15)	0.0295 (11)
H1	0.17142 (11)	0.3738 (7)	0.0391 (2)	0.035*
H2	0.22127 (11)	0.26233 (19)	0.1520 (2)	0.035*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0256 (5)	0.0271 (4)	0.0337 (5)	−0.0027 (3)	0.0141 (3)	−0.0051 (3)
Cl1	0.0256 (5)	0.0271 (4)	0.0337 (5)	−0.0027 (3)	0.0141 (3)	−0.0051 (3)
Br2	0.0215 (4)	0.0282 (4)	0.0329 (5)	0.0008 (2)	0.0089 (3)	0.0019 (3)
Cl2	0.0215 (4)	0.0282 (4)	0.0329 (5)	0.0008 (2)	0.0089 (3)	0.0019 (3)
C1	0.030 (3)	0.018 (2)	0.036 (3)	0.0000 (19)	0.007 (2)	−0.005 (2)

Geometric parameters (Å, º)

Br1—C1	1.863 (4)	Br2—C1	1.870 (4)
Cl1—C1	1.863 (4)	Cl2—C1	1.870 (4)
Cl1—C1—Br1	0.00 (4)	Cl1—C1—Br2	110.70 (6)
Cl1—C1—Cl2	110.70 (6)	Br1—C1—Br2	110.70 (6)
Br1—C1—Cl2	110.70 (6)	Cl2—C1—Br2	0.00 (6)

(cbm_1.04GPa) bromochloromethane

Crystal data

CH2BrCl	Dx = 2.655 Mg m^−3
Mr = 129.39	Melting point: 185 K
Orthorhombic, Pbcn	Mo Kα radiation, λ = 0.71073 Å
a = 4.1126 (8) Å	Cell parameters from 1476 reflections
b = 8.0685 (16) Å	θ = 5.1–29.9°
c = 9.755 (2) Å	µ = 13.21 mm^−1
V = 323.69 (11) Å^3	T = 295 K
Z = 4	Cylinder, colourless
F(000) = 240	0.31 × 0.31 × 0.05 mm

Data collection

KM-4 CCD diffractometer	160 independent reflections
Radiation source: fine-focus sealed tube	126 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.083
ϕ– and ω–scans	θmax = 29.9°, θmin = 5.1°
Absorption correction: numerical Correction for absorption of the diamond-anvil cell and the sample were made using program REDSHABS (Katrusiak, A. (2003) REDSHABS. Adam Mickiewicz University Poznań; Katrusiak, A. (2004) Z. Kristallogr. 219, 461-467).	h = −5→5
Tmin = 0.18, Tmax = 0.42	k = −11→10
2144 measured reflections	l = −3→3

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)] = 0.030	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.058	w = 1/[σ^2(Fo^2) + (0.0301P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
160 reflections	Δρmax = 0.18 e Å^−3
25 parameters	Δρmin = −0.23 e Å^−3
2 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.014 (5)

Special details

Experimental. Data were collected at room temperature and pressure of 1.04 (5) GPa with the crystal obtained by the in situ high-pressure crystallization technique. Pressure was determined by monitoring the shift of the ruby R1-fluorescence line.

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.

The DAC imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cl1	0.19106 (12)	0.84807 (8)	0.3854 (2)	0.059 (18)	0.50
Br1	0.19106 (12)	0.84807 (8)	0.3854 (2)	0.052 (7)	0.50
C1	0.0000	0.97434 (8)	0.2500	0.048 (10)
H1	−0.158 (3)	1.0499 (16)	0.2892 (2)	0.057*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.074 (7)	0.033 (3)	0.07 (5)	0.000 (3)	0.008 (12)	−0.005 (12)
Br1	0.053 (2)	0.063 (2)	0.04 (2)	0.0197 (14)	0.008 (4)	0.008 (5)
C1	0.066 (4)	0.028 (3)	0.05 (3)	0.000	−0.006 (8)	0.000

Geometric parameters (Å, º)

Cl1—C1	1.8436 (15)	C1—Cl1^i	1.8436 (15)
Br1—C1	1.8436 (15)	C1—H1	0.9700 (1)
C1—Br1^i	1.8436 (15)
Br1^i—C1—Cl1^i	0.00 (3)	Cl1—C1—Br1	0.00 (9)
Br1^i—C1—Cl1	112.91 (8)	Br1^i—C1—H1	110.1 (9)
Cl1^i—C1—Cl1	112.91 (8)	Cl1^i—C1—H1	110.1 (9)
Br1^i—C1—Br1	112.91 (8)	Cl1—C1—H1	110.52 (11)
Cl1^i—C1—Br1	112.91 (8)	Br1—C1—H1	110.52 (11)

Symmetry code: (i) −x, y, −z+1/2.

(cbm_1.72GPa) bromochloromethane

Crystal data

CH2BrCl	Dx = 2.802 Mg m^−3
Mr = 129.39	Melting point: 185 K
Orthorhombic, Pbcn	Mo Kα radiation, λ = 0.71073 Å
a = 3.9929 (8) Å	Cell parameters from 1548 reflections
b = 7.9351 (16) Å	θ = 5.1–29.6°
c = 9.6808 (19) Å	µ = 13.94 mm^−1
V = 306.73 (11) Å^3	T = 295 K
Z = 4	Cylinder, colourless
F(000) = 240	0.38 × 0.38 × 0.08 mm

Data collection

KM-4 CCD diffractometer	295 independent reflections
Radiation source: fine-focus sealed tube	271 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.057
ϕ– and ω–scans	θmax = 29.6°, θmin = 5.1°
Absorption correction: numerical Correction for absorption of the diamond-anvil cell and the sample were made using program REDSHABS (Katrusiak, A. (2003) REDSHABS. Adam Mickiewicz University Poznań; Katrusiak, A. (2004) Z. Kristallogr. 219, 461-467).	h = −3→3
Tmin = 0.13, Tmax = 0.31	k = −10→10
2283 measured reflections	l = −12→12

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)] = 0.029	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.065	w = 1/[σ^2(Fo^2) + (0.031P)^2 + 0.0922P] where P = (Fo^2 + 2Fc^2)/3
S = 1.20	(Δ/σ)max < 0.001
295 reflections	Δρmax = 0.35 e Å^−3
25 parameters	Δρmin = −0.34 e Å^−3
2 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.005 (2)

Special details

Experimental. Data were collected at room temperature and pressure of 1.72 (5) GPa with the crystal obtained by the in situ high-pressure crystallization technique. Pressure was determined by monitoring the shift of the ruby R1-fluorescence line.

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.

The DAC imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cl1	0.19596 (12)	0.84967 (6)	0.38649 (5)	0.034 (3)	0.50
Br1	0.19596 (12)	0.84967 (6)	0.38649 (5)	0.0377 (17)	0.50
C1	0.0000	0.98034 (8)	0.2500	0.0353 (14)
H1	−0.166 (3)	1.0547 (16)	0.2907 (3)	0.042*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.048 (9)	0.027 (4)	0.027 (4)	0.002 (3)	0.016 (4)	−0.004 (3)
Br1	0.038 (4)	0.044 (2)	0.032 (2)	0.0114 (16)	−0.0010 (17)	0.0061 (13)
C1	0.036 (5)	0.028 (2)	0.042 (2)	0.000	−0.003 (2)	0.000

Geometric parameters (Å, º)

Cl1—C1	1.8529 (6)	C1—Cl1^i	1.8529 (6)
Br1—C1	1.8529 (6)	C1—H1	0.9700 (1)
C1—Br1^i	1.8529 (6)
Br1^i—C1—Cl1^i	0.00 (3)	Cl1—C1—Br1	0.00 (3)
Br1^i—C1—Cl1	111.94 (5)	Br1^i—C1—H1	110.0 (9)
Cl1^i—C1—Cl1	111.94 (5)	Cl1^i—C1—H1	110.0 (9)
Br1^i—C1—Br1	111.94 (5)	Cl1—C1—H1	109.82 (4)
Cl1^i—C1—Br1	111.94 (5)	Br1—C1—H1	109.82 (4)

Symmetry code: (i) −x, y, −z+1/2.