Molecular interactions in crystalline dibromomethane and diiodomethane, and the stabilities of their high-pressure and low-temperature phases

Dibromomethane, CH₂Br₂, and diiodomethane, CH₂I₂, have been in situ pressure-crystallized in a diamond–anvil cell and their structures determined by single-crystal X-ray diffraction at 0.61 and 0.16 GPa, respectively. The pressure-frozen CH₂Br₂ crystal is isostructural with its C2/c phase obtained by cooling. CH₂I₂ is known to form several phases at low temperature, one of which is isostructural with CH₂Br₂. However, pressure freezing leads to the polar Fmm2 phase. The formation of the polar CH₂I₂ structure at 0.16 GPa has been rationalized by the electrostatic and anisotropic van der Waals interactions of the I atoms. No ferroelectric behaviour of the Fmm2 polar phase II of CH₂I₂ has been determined. The diffraction, calorimetric and dielectric constant studies reveal considerable temperature hysteresis of transformations between the CH₂I₂ phases, as well as metastable regions strongly dependent on the sample shape and history.

Computing details

For all compounds, data collection: CrysAlis (Oxford Diffraction, 2004); cell refinement: CrysAlis (Oxford Diffraction, 2004); data reduction: CrysAlis (Oxford Diffraction, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1990); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

(1dbm) Dibromomethane

Crystal data

CH2Br2	Dx = 3.173 Mg m^−3
Mr = 173.85	Melting point: 221 K
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 12.031 (2) Å	Cell parameters from 1495 reflections
b = 4.3385 (9) Å	θ = 5.1–30.1°
c = 14.795 (3) Å	µ = 22.00 mm^−1
β = 109.51 (3)°	T = 293 K
V = 727.9 (3) Å^3	Cylinder, colourless
Z = 8	0.47 × 0.47 × 0.10 mm
F(000) = 624

Data collection

Kuma KM4CCD κ geometry diffractometer	330 independent reflections
Radiation source: fine-focus sealed tube	170 reflections with > 4σ(I)
Graphite monochromator	Rint = 0.178
ω scans	θmax = 30.1°, θmin = 5.1°
Absorption correction: analytical Katrusiak, A. (2003). REDSHADE - Program for correcting reflections intensities for DAC absorption, gasket shadowing and sample crystal absorption. Adam Mickiewicz University, Poznań. Katrusiak, A. (2004). Z. Kristallogr. 219, 461-467	h = −15→16
Tmin = 0.03, Tmax = 0.09	k = −6→5
2222 measured reflections	l = −14→13

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)] = 0.068	H-atom parameters constrained
wR(F^2) = 0.149	w = 1/[σ^2(Fo^2) + (0.065P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.89	(Δ/σ)max < 0.001
330 reflections	Δρmax = 0.58 e Å^−3
25 parameters	Δρmin = −0.57 e Å^−3
0 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: 0.0017 (9)

Special details

Experimental. High-pressure measurement at 0.61 GPa.

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	0.0797 (3)	0.6831 (5)	0.1273 (4)	0.062 (4)
Br2	0.3469 (3)	0.6580 (5)	0.1305 (4)	0.067 (4)
C1	0.206 (2)	0.425 (3)	0.127 (3)	0.019 (4)*
H1	0.1812	0.2970	0.0701	0.023*
H2	0.2255	0.2894	0.1825	0.023*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.048 (4)	0.0584 (15)	0.085 (11)	−0.0030 (14)	0.030 (6)	−0.003 (2)
Br2	0.052 (4)	0.0551 (15)	0.105 (12)	0.0050 (14)	0.038 (7)	0.005 (2)

Geometric parameters (Å, º)

Br1—C1	1.888 (15)	C1—H1	0.9700
Br2—C1	1.961 (16)	C1—H2	0.9700
Br1—C1—Br2	112.5 (7)	Br1—C1—H2	109.1
Br1—C1—H1	109.1	Br2—C1—H2	109.1
Br2—C1—H1	109.1	H1—C1—H2	107.8

(1djm) Diiodomethane

Crystal data

CH2I2	Dx = 3.920 Mg m^−3
Mr = 267.83	Melting point: 279 K
Orthorhombic, Fmm2	Mo Kα radiation, λ = 0.71073 Å
a = 7.3128 (15) Å	Cell parameters from 1073 reflections
b = 13.074 (3) Å	θ = 3.1–29.2°
c = 4.7465 (9) Å	µ = 13.64 mm^−1
V = 453.82 (16) Å^3	T = 293 K
Z = 4	Cylinder, colourless
F(000) = 456	0.43 × 0.43 × 0.09 mm

Data collection

Kuma KM4CCD κ geometry diffractometer	170 independent reflections
Radiation source: fine-focus sealed tube	162 reflections with > 4σ(I)
Graphite monochromator	Rint = 0.075
ω scans	θmax = 29.2°, θmin = 3.1°
Absorption correction: analytical Katrusiak, A. (2003). REDSHADE - Program for correcting reflections intensities for DAC absorption, gasket shadowing and sample crystal absorption. Adam Mickiewicz University, Poznań. Katrusiak, A. (2004). Z. Kristallogr. 219, 461-467	h = −3→3
Tmin = 0.11, Tmax = 0.26	k = −17→17
1030 measured reflections	l = −6→6

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.026	w = 1/[σ^2(Fo^2) + (0.P)^2 + 16.8177P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.076	(Δ/σ)max = 0.015
S = 1.33	Δρmax = 0.44 e Å^−3
170 reflections	Δρmin = −0.54 e Å^−3
14 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
3 restraints	Extinction coefficient: 0.0123 (14)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.2 (7)

Special details

Experimental. High-pressure measurement at 0.16 GPa.

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
I1	0.0000	0.13600 (4)	0.24295 (9)	0.0475 (11)
C1	0.0000	0.0000	−0.00375 (10)	0.04 (3)
H1	0.11283 (15)	0.0000	−0.1265 (2)	0.056*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.054 (3)	0.0376 (7)	0.0504 (8)	0.000	0.000	0.0018 (18)
C1	0.06 (9)	0.034 (11)	0.029 (10)	0.000	0.000	0.000

Geometric parameters (Å, º)

I1—C1	2.1290 (7)	C1—H1	1.0100 (2)
I1—C1—I1^i	113.27 (4)	I1—C1—H1	108.49 (4)
I1—C1—I1^i	113.27 (4)	I1^i—C1—H1	108.49 (4)
I1^i—C1—I1^i	0.000 (14)	I1^i—C1—H1	108.49 (4)

Symmetry code: (i) x, −y, z.

(1djm_nis) Diiodomethane

Crystal data

CH2I2	Dx = 3.812 Mg m^−3
Mr = 267.83	Melting point: 279 K
Orthorhombic, Fmm2	Mo Kα radiation, λ = 0.71073 Å
a = 7.411 (3) Å	Cell parameters from 596 reflections
b = 13.137 (4) Å	θ = 3.1–29.1°
c = 4.7942 (15) Å	µ = 13.26 mm^−1
V = 466.8 (3) Å^3	T = 2702 K
Z = 4	Cylinder, colourless
F(000) = 456	0.12 × 0.12 × 0.12 mm

Data collection

Kuma KM-4-CCD diffractometer	265 reflections with > 4σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.148
Graphite monochromator	θmax = 29.1°, θmin = 3.1°
ω scans	h = −10→9
530 measured reflections	k = −10→17
298 independent reflections	l = −6→6

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.063	w = 1/[σ^2(Fo^2) + (0.1205P)^2 + 2.0615P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.177	(Δ/σ)max = 0.006
S = 1.14	Δρmax = 1.72 e Å^−3
298 reflections	Δρmin = −2.10 e Å^−3
14 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
3 restraints	Extinction coefficient: 0.015 (3)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.6 (10)

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
I1	0.0000	0.13523 (4)	0.24218 (8)	0.0509 (8)
C1	0.0000	0.0000	−0.00326 (10)	0.054 (8)
H1	0.11192 (14)	0.0000	−0.1235 (2)	0.070*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.0736 (11)	0.0307 (9)	0.0483 (10)	0.000	0.000	0.0009 (15)
C1	0.11 (2)	0.031 (14)	0.025 (10)	0.000	0.000	0.000

Geometric parameters (Å, º)

I1—C1	2.1308 (8)	C1—H1	1.0100 (3)
I1—C1—I1^i	112.96 (5)	I1—C1—H1	108.37 (4)
I1—C1—I1^i	112.96 (5)	I1^i—C1—H1	108.37 (4)
I1^i—C1—I1^i	0.000 (14)	I1^i—C1—H1	108.37 (4)

Symmetry code: (i) x, −y, z.